Publications of The University of Texas COMMITTEE ON PUBLICATIONS W. P. Stewart P. T.Flawn L. F. Anderson L.Lebowitz G. H.Ayres H.T.Odum W. A.Cunningham J. R. Stockton J. R. D.Eddy F. H. Wardlaw ADMINISTRATIVEPUBLICATIONS ANDGENERAL RULES W. B.Shipp C. H.Eads J. G. ASHBURNE L.G. Kennamer R. Levy The University publishes bulletins twice a month, so numbered that the first two digits of the number show the year of issue and the last two the position in the yearly series. (For example, No. 6101 is the first publication of the year 1961.) These bulletins comprise the official publications of the University, publications on humanistic and scientific subjects, and bulletins issued from time to time by various divisions of the University. The following bureaus and divisions distribute publications issued by them; communications concerning publications in these fields should be addressed to The University of Texas, Austin, Texas, care of the bureau or division issuing the publication:Bureau of Business Research, Bureau of Economic Geology, Bureau of Engineering Research, Bureau of Industrial Chemistry, Bureau of Public School Service, and Division of Extension. Communications concerning all other publications of the University should be addressed to University Publications, The University of Texas, Austin. Additionalcopiesofthispublicationmaybesecured fromthe Bureau ofEconomic Geology, The University of Texas, Austin 12, Texas The benefits of education and of useful knowledge, generally a community, are essential to the preserva diffused through tion of a free government. Sam Houston Cultivated mind is the guardian genius of Democracy, and while guided and controlled by virtue, the noblest attribute of man. It is the only dictator that freemen acknowledge, and the only security which freemen desire. MIRABEAUB.LAMAR PUBLISHED BY THE UNIVERSITY TWICE A MONTH. SECOND-CLASS POSTAGE PAID AT AUSTIN, TEXAS. Contents Page ABSTRACT, by Peter T. Flawn 1 INTRODUCTION, by Peter T. Flawn 5 General statement 5 Purpose and scope of the report 7 Cooperation with industry 7 Previous work 8 Acknowledgments 9 Method of study -11 Nature of the problem . 11 Petrographic methods 11 X-ray methods 12 Collection of data -12 Nomenclature --13 Structural and stratigraphic nomenclature 13 Petrographic nomenclature -14 Recognition of Stanley, Jackfork, and Atoka sandstones insubsurface 18 The surface of Paleozoic and metamorphic rocks 19 General remarks 19 Configuration of the pre-Cretaceous surface 19 Fossils in Ouachita facies rocks 20 THE OUACHITA MOUNTAINS OF OKLAHOMA AND ARKANSAS, by August Goldstein, Jr 21 21 General statement Cambrian(?), Ordovician, and Silurian stratigraphy ....1 25 Stratigraphic synopses 25 Lukfata sandstone 25 --25 Collier shale Crystal Mountain sandstone 26 Mazarn shale 26 Blakely sandstone 26 Womble shale 27 Bigfork chert 27 28 Polk Creek shale Blaylock sandstone 28 Missouri Mountain shale 29 - Stratigraphic analysis 30 Devonian, Mississippian, and Pennsylvanian stratigraphy 33 Stratigraphic synopses 33 Pinetop chert and limestone 33 Woodford chert 33 Arkansas novaculite 33 Caney shale and Sycamore(?) limestone 34 Hot Springs sandstone 34 Stanley shale 35 - Jackfork sandstone 36 Johns Valley shale 37 Springer formation 38 Wapanucka limestone 38 Chickachoc chert 39 Atoka formation 40 Stratigraphic analysis 42 Structure of the Ouachita Mountains 46 Central anticlinorium 46 Potato Hills anticlinorium -47 Frontal belt 47 THE MARATHON AREA, by Peter T. Flawn 49 General statement 49 Cambrian, Ordovician, and Devonian stratigraphy 49 Stratigraphic synopses 49 Stratigraphic analysis 51 Mississippian, Pennsylvanian, and Lower Permian stratigraphy 53 Stratigraphic synopses 53 Stratigraphic analysis 54 Deformation of the Ouachita structural belt in the Marathon area 56 OTHEREXPOSURES OFTHEOUACHITABELT,byPeter T.Flawn 59 Central Texas 59 Solitario area 59 General statement 59 Stratigraphic synopses 60 Stratigraphic and structural analysis 60 Persimmon Gap and Dog Canyon areas 62 General statement 62 Stratigraphic synopses 62 Stratigraphic and structural analysis 63 THESUBSURFACE OUACHITASTRUCTURAL BELTINTEXAS AND SOUTHEAST OKLAHOMA, by Peter T. Flawn 65 General statement 65 — Cambrian(?) Lower Mississippian rocks of Ouachita facies 65 Lithologic descriptions 65 Chert-siliceous shale 66 Limestone-dolomite 66 Shale 66 Siltstone and sandstone 66 Stratigraphy and distribution 67 - Mississippian-Pennsylvanian rocks of Ouachita facies 72 Stanley shale, Tesnus formation, and Mississippian-Pennsylvanian rocks undivided (Tesnus? ) 72 Shale 72 Sandstone 72 Jackfork sandstone 73 Atoka formation 73 Dimple and Haymond formations 74 Stratigraphy and distribution ofMississippian-Pennsylvanian rocks 74 Dark clastic rocks of unknown age 77 Lithologic description 77 Stratigraphy and distribution 77 Age and correlation 78 Phyllite, slate, metaquartzite, marble, and schist of unknown age 79 Lithologic description 79 Stratigraphy and distribution 80 Age and correlation 80 THE SUBSURFACE OUACHITA STRUCTURAL BELT EAST OF THE OUACHITAMOUNTAINS,byPhilipB.King 83 Introduction 83 Regional geology 85 Tectonic provinces 85 Triassic(?) _ 86 Permian(?) 86 Pennsylvanian 87 Mississippian 88 Devonian to Cambrian 89 Appalachian system 89 Subcrop extensions of Appalachian system 89 Ouachita system 90 Suwanee basin 90 Weakly metamorphosed rocks 91Appalachian system 91 Ouachita system 92 Metamorphic and plutonic rocks 93 Geophysical data 94 Relations between Ouachita and Applachian systems 97 _ THEOUACHITASTRUCTURAL BELTINMEXICO,byPeter T.Flawn 99 General remarks 99 Exposures of pre-Mesozoic rocks innorthern Mexico 99 Sierra del Carmen 99 Sierra del Cuervo 99 Page Placer de Guadalupe area 101 — Las Delicias Acatita area 101 Caopas-Rodeo area 101 Galeana area 102 Sierra de Catorce _ 102 Cd. Victoriaarea 102 Potrero de La Mulaarea 102 Wells penetrating pre-Mesozoic rocks innorthern Mexico 103 Analysis of outcrop and well data 104 Summary 106 IGNEOUS ROCKS ANDVEINROCKS INTHEOUACHITABELT,by Peter T.Flawn 107 Theoretical considerations 107 Paleozoic igneous activity inthe Ouachita belt 107 Areas of outcrop 107 Evidence from subsurface 109 Paleozoic or Precambrian igneous rocks encountered in wells 109 Post-Paleozoic igneous activity in the Ouachita belt 11l General remarks 11l Post-Paleozoic igneous rocks encountered in wells penetrating the Ouachita belt 115 Igneous rocks intrudedinMesozoic andTertiary rocks overlyingoradjacent to the Ouachita belt '. 115 Veins inOuachita facies rocks 117 General remarks 117 Veins in the Ouachita Mountains 117 Veins in the Marathon Basin 117 Veins inthe Sierra del Carmen 118 Veins inthe subsurface Ouachita structural belt 118 Conclusions 118 METAMORPHISMINTHEOUACHITABELT,byPeter T.Flawn 121 General statement 121 Zone of incipient to very weak metamorphism 122 Zone of low-grade, high-shearing metamorphism 123Metamorphism east of the Ouachita Mountains 123 Age of the metamorphism 124 POST-OROGENIC PALEOZOIC ROCKS LYINGONTHEOUACHITABELT, by Peter T. Flawn 125 General remarks 125 Discussion of wellspenetrating undeformed and unmetamorphosed late Paleozoic rocks 125 Interpretation of wellspenetrating undeformed and unmetamorphosed late Paleozoic rocks ... 126 TheproblemofHumbleOil&Refining CompanyNo.1Marberry 127 FORELANDBASINANDSHELFROCKSNORTHANDWEST OFTHEOUACHITA STRUCTURAL BELT, by Peter T.Flawn 129 General statement 129 The frontal basins 129 Black Warrior basin 129 McAlester basin, by August Goldstein, Jr 130 Grayson County area 132 Fort Worth basin 133 Paleozoic trough east and south of the Llano uplift 135 Kerr and Val Verde basins 136 Basins east and south of the known course of the Ouachita belt 138 Summary 139 Uplifts north and west of the Ouachita belt 140 Ozark uplift 140 Arbuckle uplift 141 Muenster arch 142 Llano uplift 142 Fort Stockton high (Pecos arch) 143 Devils River uplift 144 Diablo Platform 145 Summary 145 CLAYMINERALSOFTHEOUACHITASTRUCTURAL BELTANDADJACENT FORELAND, by Charles E. Weaver 147 Introduction 147 Page Explanation of symbols and ratios 149 Acknowledgments 149 Sharpness ratio 149 General remarks on mineralogy 149 Distribution of clay minerals inthe Ouachita belt 152 Oklahoma 152 Trans-Pecos Texas 154 Buried Ouachita beltinTexas 157 Southern Appalachians, Black Warrior basin, and buried eastern segmentof the Ouachita belt 157 Metamorphism 159 Regional trends 160 TECTONICS, by Peter T.Flawn 163 General statement 163 Basis for subdivision 163 Theoretical considerations 163 Rocks of the Ouachita belt 164 The frontal zone 165 General remarks 165 Major structures of the salients , 165 Concealed frontal zone of the Ouachita belt between the salients 166 Frontal zone east of the Ouachita Mountains 167 Frontal zone in Mexico 167 Differences between the salients and the concealed Texas segment 168 Development of the salients 168 Interior zone of the Ouachita belt 169 General remarks 169 Extent and nature of the interior zone 169 Boundary between the interior and frontal zones 169 Gravity anomalies of the Ouachita belt 170 Problem areas 171 Ouachita-Arbuckle junction 171 Position of the Ouachita front inGrayson and Collin counties, Texas 172 Uvalde and Kinney counties, Texas .' 172 HISTORY OF THE OUACHITA SYSTEM, by Philip B. King 175 Precambrian framework 175 r Early geosynclinal phase (Cambrian to Devonian) 177 Late geosynclinal phase (Mississippian and Early Pennsylvanian) 182 Orogenic phase (mainly Pennsylvanian) 186 Post-orogenic phase (Permian and later) 189 ECONOMIC POSSIBILITIES, by August Goldstein, Jr., and Peter T.Flawn 191 General statement 191 — Possibilities of petroleum production in rocks of Ouachita facies 191 Possibilitiesofpetroleumproductioninrocksofforelandfaciesunderlying or adjacent to the Ouachita structural belt 193 Conclusions 195 BIBLIOGRAPHY 197 APPENDIX 211 Part 1. Summary reports on wellspenetrating rocks of the Ouachita belt and immediately adjacent foreland inTexas, by Peter T. Flawn 211 Part 2. Summary reports on selected wellspenetrating rocks of the Ouachita belt and adjacent foreland in Oklahoma and Mexico,by August Goldstein, Jr., and Peter T.Flawn... 339 Part3.Summary reports onselected wellspenetrating Paleozoic rocksinthe southeastern states, by PhilipB.King 347 Unit penetrated 347 Triassic ( ? ) 347 Permian ( ? ) 348 Pennsylvanian 348 Mississippian and Pennsylvanian (?) 354 Devonian to Cambrian of Appalachian system 354 Devonian to Cambrian of Ouachita system 356 Devonian to Cambrian of Suwanee basin 356 Weakly metamorphosed rocks . 358 Metamorphic and plutonic rocks 359 INDEX 387 Illustrations — Figures Page 1. Ouachita Mountains inOklahoma and Arkansas 24 2. Devils River uplift, Kinney and Val Verde counties, Texas Inpocket 3. Development of the Trans-Pecos segment of the structural Ouachita belt Inpocket 4. Gravity map showing Bouguer anomaly of part of southeastern United States 96 5. Geologic index map for northern Mexico 100 6 Distribution of sharpness ratio and kaolinite along the Ouachita belt inTexas and Oklahoma 147 7. Distribution of sharpness ratio and kaolinite along the Ouachita belt in Mississippi and Alabama 148 8. Method of measuring sharpness ratio 150 9. Distribution of clay facies in Upper Mississippian and Lower Pennsylvanian rocks 151 10. Generalized cross section showing distribution of clay facies inthe Upper Mississippian and Lower Pennsylvanian of southern Oklahoma 153 11. Generalized cross section showing distribution of clay facies inthe Upper Mississippian and Lower Pennsylvanian of central Texas 156 12. Generalized correlation chart for clay-mineral zones 161 13. Position ofthe Ouachita frontin Grayson and Collincounties, Texas 173 — Plates Page 1. Regional structural map of the Ouachita system Inpocket 2. Geologic map and cross sections of the Ouachita structural belt in Texas and Oklahoma Inpocket 4. Structure contours on top of the Ouachita belt inTexas and Oklahoma Inpocket 5. Photomicrographs oflower Paleozoic Ouachita facies rocks from the frontal zone of the Ouachita belt 364 6. Photomicrographs of sandstone from the Stanley shale inthe frontal zone of the Ouachita belt 366 7. Photomicrographs of Mississippian-Pennsylvanian sandstone (including sandstone from the Tesnus formation) from the frontal zone of the Ouachita belt 368 8. Photomicrographs of rocks from the frontal zone of the Ouachita belt 370 9. Photomicrographs of rocks from the frontal and interior zones of the Ouachita belt close to the Luling front 371 10. Photomicrographs of low-grade metamorphic rocks from the interior zone of the Ouachita belt 374 11. Photomicrographs of metamorphosed rocks from the Ouachita belt 376 12. Photomicrographs of igneous rocks from the interior zone of the Ouachita belt 378 13, 14. Cores ofstrongly deformed black slate from the interior zone of the Ouachita belt immediately south of the Luling front 380, 383 15. Core of chloritic sericite phyllite from the interior zone of the Ouachita belt 384 **c|C* ' ' •yULS of P«^W.V ' tn />«.ktf- Tables Tables— Page 1. Classification of metamorphoed argillaceous and arenaceous rocks 16 22 2. Paleozoic formations of the Ouachita Mountains 55 3. Paleozoic formations of the Marathon region 4. Wellsinwhichpre-Stanley (pre-Tesnus) Ouachita facies formationshave been identified.... 70 5. Paleozoic orPrecambrian igneous rocks encountered inwellsin the Ouachita structural belt 112 6. Post-Paleozoic igneous rocks encountered in wellsin the Ouachita structural belt 114 7. Average sharpness ratios in rocks of the subsurface Ouachita belt in Texas 159 System The Ouachita Peter T. Flawn,1 August Goldstein, Jr.,2 Philip B. King,3 and Charles E. Weaver 4 Abstract Peter T. Flawn This publication analyzes available surface and subsurface data on the largely concealed Ouachita system and interprets the stratigraphy, tectonics, and history of the geosyncline and deformed belt. Itis a joint undertaking by four authors on various parts of the system and aspects of its development. The publication is introduced by a general statement of the problem, an explanation of the method of attack and the nature and extent of industry cooperation, a discussion of petrographic, stratigraphic, and structural nomenclature, a discussion of the present surface of Paleozoic and metamorphic rocks, and a summary of the fossil record. The terms incipient, very weak, weak, and low-grade metamorphism are defined by mineralogical parameters. The name Ouachita system is applied to a belt of deformed Paleozoic rocks which borders the southern edge of the Central Stable Region of North America in the same way that the Appalachian system borders the eastern edge. The deformed rocks of the Ouachita belt are known to extend from a point ineast-central Mississippi westward and southward along a sinuous course into Mexico, but in the more than 1,300 miles of known length of the system a strike length of only about 275 miles is exposed. Except in Mexico, the interior parts of the system have subsided deeply beneath younger sedimentary rocks of the Gulf Coastal Plain, and outcrop and borehole data are available only for a relatively narrow strip of the belt adjoining the 1Bureau of Economic Geology, The University of Texas, Austin. 2 Bell Oil and Gas Company, Tulsa, Oklahoma. 3 U.S. Geological Survey, Menlo Park, California. * Continental OilCompany, Ponca City, Oklahoma. foreland (maximum widthabout 80miles), but detailed studies of the stratigraphy and tectonics permit inferences concerning the parts of the system beyond the down-dip limitof wellcontrol. The Ouachita Mountains, from which the system derives its name, are in a major structural salient of the deformed belt and are composed of a thick folded and faulted sedimentary sequence of distinctive facies — Ouachita facies. This includes relatively thin lower Paleozoic dark graptolitic and siliceous shales, cherts, sandstones, and limestones, and a relatively thick upper Paleozoic dominantly clastic sequence which includes deep-water turbidite deposits. The important change in stratigraphic character of the sequence occurs between Arkansas novaculite and Stanley shale and took place in Early or Middle Mississippian time. Ouachita Mountain rocks are strongly folded, broken by reverse faults, and thrust northward ornorthwestward along a series of low-angle faults. Strike-slip movement of the mass took place along transverse faults bordering the Arbuckle buttress. Along the northern front of the Ouachita Mountains, fore- land (Arbuckle) facies rocks as well as rocks of transitional facies occur within the deformed belt, so that the facies boundary and the tectonic boundary are not coincident. Incipient to low-grade metamorphism occurs along the axis of the Broken Bow- Benton uplift, an anticlinorium that forms the central part of the range, and in other areas along loci of strong deformation. Inthe Marathon Basin, similarly located within a structural salient of the Ouachita Bureau ofEconomic Geology, The University of Texas system, rocks and structures are exposed that are remarkably similar to those of the Ouachita Mountains, differing only in structural scale and lack of metamorphism. Both areas are characterized by a pronounced negative gravity anomaly. Likewise, in both areas stratigraphic studies indicate that clastic rocks are more abundant southward and that clastic rock units thicken in the same direction. In the Ouachita Mountains, Marathon Basin, and in other exposures of the belt in Persimmon Gap and the Solitario in Trans-Pecos Texas, the lower Paleozoic rocks are raised along thrust faults and incomplexly faulted anticlinoria. Rocks of similar facies and with the same kind of deformation are recognizable in well cores and samples taken from the concealed Texas segment of the belt between the Ouachita Mountains and the Marathon Basin. Lower Paleozoic rocks of Ouachita facies form the subcrop in disconnected areas along the front of the belt and within it. These probably indicate structurally high areas along faults and anticlinal axes similar to those observed in the areas of outcrop. Ouachita Mountains lithologic units and structures can be traced in the subsurface as far south as central Texas; Marathon Basin lithologic units and structures can be traced eastward and westward in subsurface for some tens of miles. Belts of rocks with no outcrop equivalents have been penetrated by wells within the concealed Texas segment ;these include dark clastic rocks, metasedimentaryrocks, metavolcanic rocks, and partly mylonitized granitic rocks. Zones of metamorphism of different character and intensity cross lithologic boundaries. Rocks and structures of the Ouachita Mountains pass eastward beneath coastal plain deposits and follow a southeasterly course into Mississippi. Data on this segment of the system are scanty, and lithologicunits and metamorphic zones have not been mapped in as much detail as in the Texas segment. Here gross lithologictectonic units include a frontal belt of deformed upper Paleozoic rocks and the extension of the Broken Bow—Benton uplift. The junction with the Appalachian system in Alabama is complex. Deformed lower Paleozoic carbonate rocks in the Valley and Ridge province of the Appalachian system bend sharply northwestward and constitute a northwest-trending sub crop belt in Alabama and Mississippi. Interior zones probably cross each other complexly without either system clearly overriding or being overridden by the other. In northern Mexico scattered outcrops of pre-Mesozoic rocks and a few boreholes indicate a Paleozoic tectonic land, now largely concealed, where deformed and metamorphosed belts of sedimentary rocks are intruded by granitic material. In this area, the interior part of the Ouachita system did not subside so deeply as in Texas and the southeastern states, perhaps because of more extensive introduction of granitic material into the crust. Metamorphism inthe Ouachita system is of two types: (1) incipient to weak metamorphism, largely dynamic, distributed irregularly within the frontal zone of the belt, for the most part along the axes of major structures and along loci of strong deformation, and (2) low-to medium- grade regional metamorphism with a strong shearing component forming a broad band in the interior zone. Several periods of metamorphism are indicated: (1) an older regional metamorphism entirely within the interior part of the system and accompanied by emplacement of numerous quartz veins; (2) a later (pre- Atoka) low-grade high-shear metamorphism which accompanied dislocation and thrusting of the interior zone toward the craton ;this metamorphism locally effected retrograde metamorphism, mylonitization, and phyllonitization, breaking the earlier formed quartz veins and converting them into augen; (3) post-Atoka metamorphism, mostly along deformation axes in the frontal zone of the system. Several wells have penetrated postorogenic rocks of late Paleozoic age, The Ouachita System mainly red beds, lying in structurally low areas within the deformed and metamorphosed terrane. The Ouachita system is bordered on the north by various positive and negative structural elements lying within or along the edge of the craton. These include (1) older positive elements that influenced the location of the geosyncline and the course of the subsequent deformed belt and include such elements as the Ozark, Llano, and Devils River uplifts, and (2) subsequently formed late Paleozoic uplifts and basins which resulted from the general mobility of the craton during the late Paleozoic orogeny; these include the frontal basins which border the Ouachita belt from Mississippi to Mexico and features such as the Muenster uplift and Fort Stockton high orPecos arch. The Arbuckle element, which formed a buttress against the thrust of the Ouachita system, is not a — simple epeirogenic uplift its rocks were deformed and raised during an independent intra-cratonic orogeny. X-ray studies of shales within and adjacent to the Ouachita belt support petrographic observations as to the degree of alteration. A new measurement, sharpness ratio (SR),appears tobe avalidtoolfor determining degree of metamorphism in slates and shales. Two tectonic provinces are recognized within the Ouachita system:(1) a frontal zone bordering the craton where deformation was by flexure, analogous to the Valley and Ridge tectonic province of the Appalachian system, and (2) an interior zone where deformation was mainly by shear, analogous to the Blue Ridge tectonic province of the Appalachian system. The boundary between these twoprovinces, the Luling front, is marked by very highly sheared rocks, locally mylonitized, and probably is a zone of complex thrust faulting. The frontal zone is broadly developed in the Ouachita and Marathon salients, which do not appear to be typical of the system as a whole. Within the salients the frontal zone of the belt is much wider than in the concealed segments and contains younger rocks. Probably the areas of the salients remained actively negative and received sediments through Atoka time while other parts of the belt were emerged. The subcrop pattern of rock units suggests that the entire area of the Ouachita Mountains is a complexly deformed synclinorium, a concept which is supported by gravity data. In the area of the Devils River uplift, the rocks of the interior zone have overridden an attenuated or telescoped frontal zone, and rocks of foreland facies mantling the uplift are strongly deformed and slightly metamorphosed. Frontal overthrusts with a minimum displacement of 8 to 10 miles occur along the course of the Ouachita bek. They have been mapped on the surface in some areas, proved by drilling in others, and inferred from subcrop geology in others. Gravity data show a pronounced minimum along the course of the frontal zone, suggesting itisathickbodyofsedimentary rocks. Gravity patterns in the interior zone are more complex, withdisconnected maxi- ma which may represent bodies of differing lithologies, possibly intrusive bodies. The early history of the belt is difficult toreconstruct because littleisknown about the southern margin of the craton inPrecambrian time. Extensive late Precambrian volcanic activity north of the developing Ouachita belt is indicated by rhyolitic lavas and pyroclastic rocks extending from New Mexico to Oklahoma. Resistant massifs, such as the Llano and Devils River uplifts, probably influenced the zone of subsidence of the early phase of the Ouachita geosyncline. The oldest rocks exposed in the salients are Late Cambrian but the nature of the deformation suggests that they are underlain by a thick body of sedimentary rocks which may include late Precambrian sedimentary rocks in the lower part. Early Paleozoic rocks are thin widespread argilla ceous and siliceous rocks with a few clastic wedges and are characterized by a pelagic fauna. Rock and faunal facies are remarkably persistent, and thin units represent Bureau of Economic Geology, The University of Texas long time intervals. These deposits are not clearly miogeosynclinal or eugeosynclinal but have more of the attributes of a "starved" eugeosynclinal deposit; they are in many ways similar to the leptogeosynclinal deposits in some Alpine basins which are starved orogenic basins. However, they also show many of the features of shallow- water deposition. The abundant silica may have been derived from volcanic ash emanating from more mobile parts of the belt to the south. Sandstone wedges which thicken to the south suggest that there were early Paleozoic orogenic movements. A drastic change in sedimentation occurred in Early Mississippian time when the mobile part of the belt moved toward the craton. Thick deposits of Late Mississippian and Early Pennsylvanian clastic rocks were dumped into long narrow restricted basins. These are mainly sandstone and shale but also include tuff, siliceous shale, and remarkable boulder beds. Inpart, these sediments were deposited in deep water, being transported by turbidity currents from rapidly rising tectonic lands within the system. The orogenic phase overlapped the geosynclinal phase. In the eastern part of the belt the deformation was mainly Pennsylvanian, but to the west it began later and continued into Early Permian time, or even later inMexico. With the orogenic movements came a rearrangement of depositional patterns and a creation of new basins along the front of the belt bordering the foreland. No rocks younger than Atoka occur in the Ouachita Mountains, and the mountains were probably an area of active deformation and erosion during Dcs Moines time; the detritus was deposited in the new basin created through the northward shift of depositional axes. Depositional environments changed from deep water to shallow as the new basin filled and downwarping ceased. In the eastern part of the Ouachita system the final orogenic phase began in Atoka and continued at least through Dcs Moines time as rocks of that age in the basin north of the system are thrown into linear folds parallel to those in the Ouachita belt. The final movement culminated in frontal overthrusting and lateral movements along the flanks of the Arbuckle buttress. In the western segment the last orogenic phase is dated by conglomerates in the middle of the Gaptank formation as beginning inMissouri time. Frontal overthrusts occurred inEarly Permian timebut before deposition of the type Wolfcamp sequence. Lower Paleozoic Ouachita facies rocks moved over foreland basin rocks along the frontal overthrust. Southwestward in Mexico deformed Permian sequences contain tectonic sediments and lavas and are in truded by granitic rocks. Orogeny in this area continued into late Permian time or possibly later. In the post-orogenic phase the salients were raised by epeirogenic movements while the rest of the system continued to subside beneath younger sedimentary rocks. Post-orogenic sedimentary rocks, mostly red beds, are preserved in structurally low areas in local basins within the interior part of the belt. Possibilities for oil and gas production are summed up as follows: (1) Ouachita — facies rocks poor, except for possible accumulations in fractured rocks where they have been juxtaposed with possible source beds; (2) late Paleozoic foreland facies rocks inbasins along the front of the Ouachita belt—fair;although most sandstones are argillaceous and quartzitic, Atoka sandstones inthe McAlester basin contain commercial gas accumulations; there are also possibilities in areas favorable for reef development; (3) early Paleozoic foreland facies rocks adjacent to the Ouachita belt orbeneath allochthonous plates of Ouachita — facies rocks good, where rocks are platform facies rather than trough or deep- basin facies. Introduction Peter T. Flawn General Statement The name Ouachita system is applied to a belt of deformed Paleozoic rocks which borders the southern edge of the Central Stable Region of North America in the same way that the Appalachian system delimits the eastern margin of the stable area. Rocks and structures of the Ouachita system, however, are not as well exposed as those of its eastern analog. The largest area of exposure of the deformed belt is the Ouachita Mountains of eastern Oklahoma and western and central Arkansas where folded and faulted rocks ranging in age from Cambrian(?) to Middle Pennsylvanian (Atokan) form a series of parallel ridges and valleys over a strike distance of 220 miles. The total area of the Ouachita Mountains exceeds 12,000 square miles. The only other major exposure of the Ouachita system is in Trans-Pecos Texas where the Marathon uplift provides excellent exposures of highly deformed thrust- faulted Paleozoic rocks over a strike distance of nearly 50 miles; orogenic movements in this area involved rocks ranging from Cambrian through Pennsylvanian and probably Early Permian (Wolfcamp) age. There are other smaller exposures of the deformed belt west and south of the Marathon area in the Solitario uplift and near Persimmon Gap in Brewster County, Texas, and at the base of the Sierra del Carmen southeast of the town of Boquillas in Coahuila, Mexico. In Burnet County in central Texas, a glimpse of steeply dipping rocks of the belt can be seen in Cypress Creek and the Turkey Bend area during periods of low water inLake Travis. Thus the total length of exposed parts of the belt is not more than 275 miles. Between the widely separated exposures in Oklahoma-Arkansas and Texas and eastward from the outcrops in Arkansas, the course of the Ouachita system has been outlined by boreholes and by geophysical observations. Itis now known that rocks and structures of the Ouachita system extend nearly 1,300 miles from the Rio Grande inTexas toapoint inwestern Alabama only 60 miles from where the Appalachian folds disappear beneath the coastal plain (P. B. King, 1950, fig. 1; 1951, p. 149; this report, pp. 83-98). It is much more difficult to trace the Ouachita system southward into Mexico because exposures of Paleozoic rocks are widely separated, only a few wells penetrate the thick cover of Mesozoic rocks, and this area was strongly deformed during Laramide orogeny. Although data are insufficient to determine the nature and trend of the structures of the belt in Mexico, north- central and northeastern Mexico was probably a Paleozoic tectonic land and the Paleozoic orogenic belt probably extended at least 300 miles south of the Rio Grande, and perhaps farther (Flawn and Diaz G., 1959).The eastward extension of the Ouachita system in the subsurface poses one of the major problems in North American structural geology. The trends of the Ouachita and Appalachian systems, as projected and defined by drilling,meet in the subsurface at an acute angle. A number of possible interpretations of this junction have been outlined by P. B. King (1950, pp. 666-669; this report, pp. 97-98). Several geologists have discussed in a general way the possibility that the Ouachita system crosses the Appalachian system and continues southeastward into Florida (P. B. King, 1950, pp. 666-667; Woods, 1956, p. 7; Applin, 1956, personal communication toP.B.King);there issome geophysical evidence to support this concept (Woollard, 1955, p. 1638; Woods, Bureau of Economic Geology, The University of Texas 1956, p.7;E.R.King,1959, p.2853).In a previous paper, Flawn (1959b, p. 24) gested that the Ouachita system was deflected around the end of the southwest- plunging Appalachian structures ina sharp structural recess and continues southeastward into Florida. P. B. King (this report, p. 97) believes that the two systems are parts of an originally continuous belt of deformation and suggests that their junction may be comparable to the extremely complex junctions observed within island arc systems where trends cross each other but do not continue very far beyond the intersection. The Ouachita system is concealed for 80 percent of its proved length, and those parts that are exposed are structural salients along the frontal margin of the belt; information from wells is likewise largely restricted to that part of the belt bordering the foreland. The interior parts of the Ouachita system have been depressed beneath the great thicknesses of sedimentary rocks in the Gulf Coastal Plain and the Mississippi embayment. Those wells which have encountered the more deeply buried parts of the deformed belt south and east of the front penetrated highly sheared metasedimentary rocks, mostly phyllite and phyllitic metaquartzite. Several of the more southerly wells found fine-grained mica schist, locally garnetiferous, and at the western end of the belt phyllitic marbles are common. Insouthwest Texas, inBexar and Medina counties, partly mylonitized granitic rock and altered volcanic rock have been penetrated. These wells provide tantalizing glimpses of an orogenic belt that is the foundation of at least the inner part of the Gulf Coastal Plain and which is probably much more extensive. The linear extent of the Ouachita system and what littlecan beseen ofitsrocks and structures suggest that it is a major orogenic belt, most of which is completely buried. From the structural front of the belt to the down- dip limit of well control is about 50 miles. This includes an outer zone approximately 35miles wide where unmetamorphosed and very weakly metamorphosed rocks are folded, faulted, and thrust against and over the foreland, and part of another tectonic unit composed of highly sheared low-grade metamorphic rocks characterized by well- developed foliation, slaty cleavage, and fracture cleavage. In the classic picture of an alpine-type deformed belt,three major zones have been recognized (Bucher, 1955, pp. 348-362) : (1) an outer belt of folded and thrust- faulted rocks where the deformation is surficial; (2) a marginal belt of "peel" thrusts and piled up nappes wherein the basement is involved in the deformation; and (3) an inner belt characterized by deep crustal folds and metasomatism. Inthe southern Appalachians (P. B.King,1950, pp. 638-656; Bucher, 1955, pp. 360-361), the Valley and Ridge province corresponds to zone (1), the Blue Ridge province is analogous to zone (2), and the metamorphic and plutonic Piedmont belt (including the eastern part of the Blue Ridge province) represents zone (3). The distance from the Allegheny front of the Valley and Ridge province to the Blue Ridge front is approximately 40 miles; the Blue Ridge thrust belt has similar width. To the south east the core of metamorphic and plutonic rocks is at least 120 miles wide to where it is concealed by overlapping Coastal Plain deposits. If the Appalachian system is bilaterally symmetrical (P. B.King,1950, p.655),itmust be considerably more than 200 miles wide with concealed marginal and outer zones south and east of the metamorphic and plutonic belt. If the Ouachita and Appalachian systems are compared (and itseems advisable to compare the two great Paleozoic orogenic systems of the North American continent), the Ouachita system shows, in outcrop and borehole, an outer or frontal zone of unmetamorphosed to very weakly metamorphosed folded and thrust-faulted rocks similar structurally to that of the Appalachian Valley and Ridge province, and the edge of an interior zone wherein phyllite, slate, and metaquartzite show The Ouachita System well-developed foliation, slaty cleavage, and fracture cleavage very similar to rocks of the Blue Ridge province. The boundary between the frontal and interior zones of the Ouachita belt is herein named the Luling front. Nowhere, however, has there been found a well-defined core of metamorphic and plutonic rocks comparable tothe Appalachian Piedmont. A few of the most southerly wells encountered metamorphic rocks of medium grade containing garnet and amphibole that suggest the presence of a morehighlymetamorphosed terrane inthis direction, but well control is inadequate to fix boundaries. Ifthe Ouachita system is a first-rank orogenic belt, its core must lie south and east of the known part beneath the thick prism of Coastal Plain sedimentary rocks; if the Ouachita system is symmetrical the hidden core is flanked by marginal and outer zones stillfarther south. Within the known part of the structural belt is a large body of rocks of distinctive — facies Ouachita facies —as well as rocks of foreland facies, rocks of transitional facies, metamorphic rocks, and igneous rocks. Rocks of Ouachita facies include thick upper Paleozoic geosynclinal and post-orogenic deposits and a lower Paleozoic sequence of siliceous rocks and dark fine-grained clastic rocks that is not particularly thick where exposed orpenetrated by wells. Purpose and Scope of the Report This report on the Ouachita system is an outgrowth of studies of the Texas and southeast New Mexico basement which began in 1950. During these studies the writer examined many cores and cuttings from wells that penetrated the metamorphosed part of the Ouachita structural belt. Obviously the Ouachita structural belt posed so many important tectonic problems that itranked as a major problem in its own right and deserved more than a chapter in a publication on the Precambrian basement. Consequently, when results of the Precambrian basement study were ready for publication, a new project on the Ouachita structural belt was formu lated. As the study depended largely on information from wells, the major oil com panies operating in Texas were consulted to determine the extent of their interest. Without industry cooperation a regional subsurface study would not have been pos sible. The companies concerned with oil exploration in Texas proved to be very much interested in encouraging a project on the Ouachita structural belt and coop erated by furnishing well samples and stratigraphic information. The main objectives of the project were (1) to develop the broad tectonic pattern within the deformed belt, (2) to evaluate the economic potential of its frontal structures, and (3) to assess its role in the structural development of the North American continent. Early inthe course of the work itbecame apparent that itwould be desirable to study the whole of the Ouachita belt rather than merely the Texas segment and to include the results of X-ray studies of the shales of the Ouachita system. Invitations to co- authorship were extended to August Goldstein, Jr.,PhilipB.King,and Charles E. Weaver. Their participation inthe project has made itpossible to present a unified picture of the Ouachita system. Authorship of the various chapters of the report is shown on pages iii-vi. Cooperation withIndustry The first step insecuring the cooperation of operating oil companies inthe Ouachita structural belt project was a letter from the Director of the Bureau of Economic Geology, the late John T. Lonsdale, addressed to company geologists and executives, which outlined the proposed project and invited suggestions. Following unanimous expression of interest, the project was officially started. Implementation of cooperation was left to the companies ;some appointed a contact man for the project, generally a staff or research geologist; others left the mechanics of cooperation to district or division geologists. Both methods Bureau ofEconomic Geology, The University of Texas were successful, inasmuch as both provided a free interchange of information between the Bureau of Economic Geology and the company. Throughout the course of the project, preliminary results were made available to all. Geologists from many companies visited the Bureau of Economic Geology to discuss the work and the general problems. This research project is thus an illustration of successful voluntary cooperation between industry and a State agency. Previous Work Development of geological thinking about the Ouachita structural belt records the work of distinguished geologists of two generations. From about 1800 to 1887, reports on the Ouachita Mountains in the Arkansas Territory, later the State of Arkansas, and the Indian Territory, later the State of Oklahoma, were limited to the observations of explorers who made geological reconnaissances and mineral surveys (Honess, 1923, pp. 27-31). In 1887 and thereafter, geologic mapping was undertaken in Arkansas by T. B. Comstock (1888), L. S. Griswold (1892), R. A.F. Penrose (1892), J. C. Branner (1896, 1897), G. H. Ashley (1897), N.F. Drake (1897), A. H. Purdue (1909a, 1909b, 1910), and Purdue and Miser (1923). J. A.Taff (1901a, 1901b, 1902, 1903) made the first geological map of the western and northern Ouachitas of Oklahoma following an earlier reconnaissance by R. T. Hill (1891) .Abibliography of earlier geological publications on Arkansas geology is givenbyJ.C.Branner (1909). Modern study of the geology of the Ouachita Mountains began with the work ofH.D.Miser who,inhis earlier studies, was guided by A.H.Purdue (Purdue and Miser, 1923; Miser and Purdue, 1918, 1929; Miser, 1921, 1929, 1931, 1934a, 1934b, 1934c, 1943; Miser and Honess, 1927) ;Miser's research laid a broad foun dation for allsubsequent work. Atapproxi mately this same time a great contribution to the geology of the Ouachita Mountains in Oklahoma was made by Honess (1923, 1924, 1927). More recent mapping and stratigraphic interpretation have been contributed by Harlton (1934, 1938, 1947, 1953), Hendricks (1943), Hendricks and Goldstein (1953),Hendricks et al. (1947), Pitt (1955), Tomlinson and Pitt (1956), Cline (1956a, 1956b, 1960), Misch and Oles (1957), and Shelburne (1960). Mapping by the U.S. Geological Survey Fuels Branch is currently under wayinArkansas (Reinemund and Danilchik, 1957). Petrography of Ouachita Mountains sedimentary rocks has been described by Honess (1923), Goldstein and Reno (1952), Goldstein and Hendricks (1953), Harlton (1953), Bokman (1953), and Goldstein (1959a, 1959b). In 1959 the geology of the Ouachita Mountains was the subject of a symposium volume prepared by the Dallas and Ardmore Geological Societies and including papers by Branson, Cline and Shelburne, Decker, Elias, Flawn, Goldstein, Ham, Harlton, Hendricks, Howell and Lyons, Laudon, Miser, Pitt, Scull, Scull et al., and Tomlinson. Far to the southwest, in the Marathon Basin of Brewster County, Texas, steeply dipping Paleozoic strata of the Ouachita structural belt came to the attention of early reconnaissance geologists such as Yon Streeruwitz (1891), Hill (1900), Udden (1907a, 1907b), and Baker and Bowman (1917). In 1929, P. B. King started work in the Marathon Basin; his field work continued through 1931 and resulted in a classic U.S. Geological Survey Professional Paper (King,1937).More recent investigations in the Marathon Basin have been carried out by Adams and Frenzel et al. (1952);J. L. Wilson (1956a, 1956b), Hall (1956), Fan and Shaw (1956), Berry and Nielsen (1958). Geologic studies inthe Solitario area southwest of the Marathon Basin have been made by Baker and Bowman (1917), Powers (1921), Sellards, Adkins, and Arick (1931), Lonsdale (1940), and Herrin (1959) ;Paleozoic rocks inthe Persimmon The Ouachita System Gap area were described by Maxwell et al. (1949, pp. 27-28), J. L.Wilson (1954a), Lonsdale et al. (1955, pp. 54-59 and map), Hazzard, Maxwell, and Lonsdale (1958), Berry and Nielsen (1958), and Maxwell etal. (MS). Many contributions to the geology of the Ouachita system have been made through the efforts of paleontologists to solve problems of age and correlation. David White (1934) described the plants, C. E. Decker (1936), Ruedemann (1947), and Berry (1960) the graptolites, Henbest (1936) the radiolarians, Cooper (1931, 1935), Ellison (1941, 1946), Ellison and Graves (1941), Graves (1952), and Hass (1950, 1951, 1956) the conodonts, and J. L.Wilson (1954b) the trilobites. For many years it has been known that wells drilled near the Balcones fault zone in Texas pass from Cretaceous rocks into a sequence of steeply dipping clastic sedimentary rocks showing varying degrees of incipient to weak metamorphism. The first published reference to these rocks was made by Udden (1919), who speculated as to their age. After more wells had been drilled, Powers (1928), Cheney (1929b), Miser (1929), Sellards (1930, 1931b), Miser and Sellards (1931), and Van der Gracht (1931a) were able to demonstrate that these rocks were related to folded rocks of Paleozoic age exposed in the Ouachita Mountains of Arkansas and Oklahoma and to those of the Marathon Basin of Texas. They outlined the extent of the folded belt and separated itfrom a hypothetical landmass, Llanoria, which was presumed to have provided the sedimentary material that filled the Paleozoic trough. The concept of Llanoria dates from before the turn of the century and is based on indications that the sedimentary detritus in the Ouachita belt came from the south (J. C. Branner, 1897, pp. 357-377; Miser, 1921, pp.68-71;P.B.King,1937, pp.44, 54, 87-88). Miser (1921) and Sellards (1933) summarized the literature pertaining to Llanoria. With new ideas on the processes of orogeny and the role of island arcs as source areas, the concept of Llanoria as an enduring landmass was modified (Van der Gracht, 1931a; P. B. King,1950, pp. 663668; H.J. Morgan, 1952; Flawn, 1956, pp. 58-61). Barnes (1948) studied some central Texas wells and outlined successive belts of increasing metamorphism from northwest to southeast; he interpreted the phyllites of the subsurface "schist ridge" of Caldwell County, Texas, previously thought to be Precambrian, as metamorphosed Paleozoic rocks. Goldstein and Reno (1952) extended Barnes' concept to include all metamorphosed sediments encountered inwells along the Luling-Mexia- Talco fault system. Kleihege (1948) studied metamorphosed sedimentary rocks inwellsinTerrelland ValVerde counties, Texas, and concluded that they are of Paleozoic age. Masson (1955) and Woods (1956) distinguished and mapped several zones within the subsurface structural belt that are characterized by different degrees of metamorphism ranging from "semislate" to "fine-grained schist." Acknowledgments The writers express their appreciation and sincere thanks to the following members of the petroleum industry ;their generous contribution of time and their continued interest over many years were the greatest single factor inmaking the project possible. They are listed under company affiliation during the time of their contribution to the project, and acknowledgments are due to both individual and company. Special mention is due the Shell Oil Company and the Pan American Petroleum Corporation for making available data collected by Weaver and Goldstein, respectively, over a period of many years. Arkansas Fuel OilCorporation James K.Rogers The Atlantic Refining Company Bruce W. Fox Henry J. Morgan, Jr. Austral OilExploration Company Karl Schneidau Bureau of Economic Geology, The University of Texas Continental OilCompany R. F.Mathews Lloyd J. Ryman General Crude OilCompany J. C. Barker Gulf OilCorporation Roy T. Hazzard J. D. Moody- Humble Oil&Refining Company Fredda BullardLackman Peter H. Masson J. C. Meacham Robert Roth T.H.Shelby, Jr. T.R. Simmons, Jr. R.D. Woods Kent Waddell &Company A.P. Werner Magnolia Petroleum Company J. H. Halsey Robert Pavlovic John R. Sandidge H. A.Sellin R.E. Wills,Jr. Mayflower Minerals, Inc. W. N. Tindell Pan American Production Company DeWitt C. Van Siclen Parker Petroleum Company, Inc. M.W. Eddleman Petroleos Mexicanos Jose Carrillo B. Teodoro Diaz G. Phillips Petroleum Company F. H.Olson Addison Young Pure OilCompany Gregory L. Turner Standard OilCompany of Texas J. E. Adams V.E. Tims Stanolind Oil&Gas Company (Pan American Petroleum Corporation) L.H. Carroll T.A.Hendricks Porter Montgomery J. B.Souther Shell OilCompany R.E. Farmer Phillip Fowler John E. Galley E.M.Hurlbut, Jr. J. L.Lindner Shell OilCompany (continued) Mary C. Magaw R. P. Maner E. J. Theessen E. A. Vogler James L.Wilson W. J. Wilson Skelly OilCompany K.H. Hamilton H.L.Spyres Sun OilCompany R. J. Cordell F. J. Feigl I.B. Hamilton J. W. Lea J. A.Means B.J. Scull S. D. Sumerford D. A. Zimmerman The Texas Company (Texaco Inc.) H.D. Becwar L.A. Coon H. W. Davis R.H. Schweers Union Producing Company Charles A.Stewart Although separate responsibility for the various chapters and illustrations of this report is indicated (pp. iii-vi),the respec tive authors have benefited greatly from exchange of ideas and criticism during the course of the work; each author has reviewed the text of his colleagues and made comments and suggestions. The writers express their appreciation of the continued interest, support, and constructive criticicisms of the late John T.Lonsdale, Director of the Bureau of Economic Geology, and to VirgilE. Barnes, Thomas A. Hendricks, Hugh D.Miser, Peter U. Rodda, Paul L. Applin,and NormanF.Williams,whoread the manuscript critically and made many worthwhile suggestions. Their contribution of time and effort is deeply appreciated. Flawn was ably assisted by Cader A. Shelby and Mary Elizabeth Wheeler and their help is gratefully acknowledged. of Study Method Nature of the problem. —The problem, simply stated, is to map the concealed Oua chita system. Many of the complexly folded and faulted orogenic systems of the world that are exposed at the surface have been studied by geologists for decades and yet such is their complexity that many of their problems are stillunsolved. Itmight seem thus overly ambitious to attempt a study of a concealed orogenic belt on the basis of merely several hundred randomly located boreholes. But from another viewpoint, such a study is comparable to reconnaissance geological studies of mountain systems during the 19th century; this project attempts to solve broad structural relationships and to map large-scale lithologic units through scrutiny of some scattered boreholes over a wide area. The interpretations of subsurface relations are supported by detailed studies of exposed parts of the structural belt, by geophysical data, by new techniques of rock analysis, and by a growing body of knowledge about the behavior and development of orogenic systems (Pol dervaart, 1955). — Petrographic methods. The most fruitfulsource of information is the rocks themselves. Therefore, as a first step, an attempt was made to locate and obtain cores and cuttings from all wells penetrating the Ouachita structural belt. Wellsamples were studied with a binocular microscope; selected samples were studied in thin section and/or by X-ray analysis. Thin sections of cable tool or rotary cuttings do not give information on attitude of beds or larger structures, but through a long sequence of strata that have not been cored they provide a valuable record of mineralogy and texture that cannot be obtained otherwise. Petrographic study of well cuttings, involving preparation of large numbers of thin sections, may appear a very laborious procedure compared to rapid studies of samples with the binocular microscope. However, inspection of sample logs of Ouachita facies rocks demonstrates that obser vations on degree of metamorphism and identification of rock types are commonly in error and have led to serious misinter pretations. The binocular microscope is not a reliable tool for study of weakly meta morphosed rocks. Metamorphic changes in the mineralogy and mineral structure of shales, sandstones, and carbonate rocks in the Ouachita belt (formation of new min erals of metamorphic origin, twinning, grain deformation, and elongation) may go undetected without thin-section study and too much importance may be given to cleavages and the sheen of second-cycle de tritalmica.Hard, brittle shale withlustrous closely spaced partings may suggest a higher metamorphic grade than dull,compact, more massive shale, yet petrographic comparison of the two rocks might show that the lustrous shale has undergone no metamorphic change while the massive, dull shale is a partly reconstituted rock. In the Kinney-Val Verde-Terrell County area of southwest Texas, several wells (pp. 285, 303-311, 319-332) penetrate interlayered fine-grained calcite marble, dolomite marble, phyllite, and metaquartzite. The presence of calcite marble, phyllite, and meta- quartzite inclose association with the dolomite indicates that the entire sequence has experienced the same degree of low-grade metamorphism; this is obvious in the calcite marbles, phyllites, and metaquartzites, but the dolomites commonly show littleindication of metamorphism. Calcite marbles show spectacular twinning and grain- stretching and are commonly rudely foliated; itisclear that they are completely recrystallized even without corroboration from bands of oriented quartz-sericite muscovite and quartz-calcite mosaic. The dolomite, however, strongly resists deformation and displays a characteristic rhombic mosaic; in highly sheared dolomite there is seen locally an orientation of the long axes of the rhombs and rather obscure twinning, but only in the impure rocks where there are patches of deformed calcite grains and sericitic and quartzitic layers can it be clearly demonstrated that Bureau of Economic Geology, The University of Texas the dolomite has in fact experienced low- grade metamorphism. This reluctance of fine-grained dolomite to display signs of metamorphism leads to misinterpretations in conventional binocular descriptions of the rocks where the observer notes metamorphism of the calcitic rocks and concludes that the dolomites are unmetamorphosed. The supposed change from metamorphosed to unmetamorphosed rocks is usually explained by faults or other structural discontinuities. In some wells these structural explanations appear correct, but petrographic scrutiny is necessary to verify them when they are based solely on supposedly "unmetamorphosed" or "normal" dolomite. Petrographic methods can be applied to regional geologic problems of concealed basement or concealed orogenic belts to establish, within the limits of well control, major lithologic and tectonic divisions characterized by differing types and degrees of metamorphism, as well as zones of igneous activity and allochthonous plates. Petrographic methods provide a framework into which geophysical, geochemical, paleontologic, stratigraphic, X-ray, and surface mapping data can be fitted; they furnish information on the present physical state, history, and genesis of the rock itself that cannot be obtained by any other technique. For best results, the petrographic study should be regional in scope because the sample data from wells randomly spaced and commonly widely separated permit recognition of major features only. Insofar as possible, the petrographic work should be done by one individual, to elim inate variations inobservational bias. — X-ray methods. The X-ray is a tool of the mineralogist. Although it yields information on mineral composition and crystal structure, it does not furnish information on rock textures, structures, and mineral relations from which the history of a rock can be deciphered. Itisnevertheless a valuable aid in the study of the very fine- grained rocks whose mineral composition defies resolution by standard petrographic methods. One of the main problems in respect to the Mississippian-Pennsylvanian rocks of the Ouachita structural belt and its frontal basins is the discrimination between the different thick sequences of alternating sandstone and shale of the Stanley, Jack- fork, and Atoka formations. Weaver (1958) has made extensive X-ray studies of the shales penetrated in the structural belt and the adjacent shelf and basin areas. He discovered that shales of foreland facies are characterized by interlayered illitemontmorillonite, whereas shales within the structural belt contain none. He also discovered a correlation between degree of — metamorphism and a new measurement sharpness ratio (SR) (p. 149). The X-ray technique is simple and involves no more than powdering the sample and determining the clay and mica minerals. — Collection of data. In any regional subsurface study the first step is collection of well data, stratigraphic information, and samples. Most of the basic well data and stratigraphic information in this report were secured through correspondence with company geologists in various parts of Texas and Oklahoma, both in operating sections and in research laboratories, and through the cooperation of Petroleos Mexicanos inMexico. Much additional information was obtained during visits with company geologists. Every effort was made toresolve conflicting information by checking back to original sources and by securingadditional informed opinioninmatters of interpretation. Inevitably, some conflicts had to be resolved by the writers' judgment. Location and collection of well samples was a more difficult problem. Once the samples were found and the need for them was made known, they were in most cases generously shipped to Austin by the owner. Many geologists made a great personal effort to find missing samples. The Well Sample Library of the Bureau of Economic Geology contains samples of many wells which are not preserved in any other library; without the foresight of the founders of this library some 45 years ago, this study and others like it would not be possible. Nomenclature Structural and Stratigraphic Nomenclature Through geologic time, a major tectonic system, such as the Ouachita system or Appalachian system, passes through growth and change which produce a linear and commonly arcuate deformed belt or orogen. During geosynclinal development and the subsequent period of deformation, the system is a mobile belt. The mobile belt and the compressed, consolidated, and immobilized deformed belt are manifestations of fundamental processes of continental growth. The name Ouachita system is applied to the southern tectonic system of the North American continent throughout itshistory; the earlier formed Ouachita geosyncline and Ouachita mobile belt and the product of the orogenic paroxysm, the Ouachita structural belt, are sequentially developed phases of the Ouachita system. The name Ouachita is taken from the major exposure of the deformed belt, and its application to the subsurface extensions of the belt seems straightforward and proper. In the literature other names have been applied to the deformed belt. Ouachita foldbelt and Ouachita-Marathon belt are clearly synonymous with Ouachita structural belt. The name Llanoria structural belt has been proposed by Masson (1955, p. 1593) and Woods (1956, pp. 3-11), but in the writer's opinion, perpetuation of the name Llanoria is not desirable. The name Marathon foldbelt has been used for the western limb of the belt in Texas;rocks and structures of the Ouachita structural belt in the Marathon uplift can best be considered as the Marathon salient of the Ouachita structural belt inasmuch as the continuation of the Ouachita structural belt westward around the Llano uplift is no longer in doubt. Many misunderstandings have arisen in regard to the term Ouachita facies. This term properly refers to rocks lithologically and faunally like those exposed in the Ouachita Mountains and unlike rocks infrontal basins and shelf areas on the foreland. Rocks of Marathon facies are lithologically and faunally similar to those exposed in the Marathon region. These are remarkably similar to Ouachita facies rocks and may be called Ouachita facies, although they also show some foreland characteristics. In other areas along the front of the belt there are rocks even more clearly transitional between Ouachita and foreland facies. An erroneous belief has arisen that all Ouachita facies rocks are metamorphosed and/or siliceous and that the term Ouachita facies implies metamorphosed and/or siliceous rocks. Some Ouachita facies rocks have experienced varying degrees of metamorphism but some are unmetamorphosed. The following distinctions are pertinent: (1) rocks of Ouachita facies, (2) rocks of foreland facies, and (3) rocks within the Ouachita structural belt. The latter include (a) rocks of Ouachita facies deformed but not metamorphosed, (b) rocks of Ouachita facies that are deformed and metamorphosed, and (c) rocks of foreland or transitional facies that are deformed and locally slightly metamorphosed. The boundary of the deformed belts transects the facies boundary, which indeed is a transitional boundary in space and has varied through Paleozoic time. In some areas along the front of the Ouachita belt, rocks of foreland facies in the frontal basins are folded. In the Mc- Alester basin where these folds have been mapped on the surface their axes are broadly parallel to structures in the Ouachitabelt; inparts ofthe FortWorth,Kerr, and Val Verde basins where Paleozoic structures are concealed by overlying Mesozoic rocks, cores show that foreland Paleozoic beds along the front dip steeply in some areas. Structures in the foreland basins were produced by the same forces that deformed the Ouachita belt and are products of the Ouachita orogeny; here, then, the problem is where to place the frontal boundary of the Ouachita structural belt. The boundary can be placed easily where strongly deformed Ouachita facies rocks Bureau ofEconomic Geology, The University of Texas have overridden gently deformed foreland facies rocks along low-angle thrust faults, and there is a clear cut structural break between them. A condition of this sort commonly occurs where the Ouachita geosyncline impinged on a stable foreland element. In some areas without frontal overthrusts (e.g., the Ouachita Mountains inArkansas) ,the orogenic front is marked by a rather abrupt change in structural grain or pattern. Within the structural belt there are steep narrow folds, locally overturned, and locally accompanied by high- angle reverse faults; in the frontal basins the folds are broader and more gentle. In still other concealed areas, however, the boundary might not be sharp and Ouachita structures might pass gradually into fore- land structures; perhaps such a condition prevails where the belt is bordered by a deep frontal down warp (such as the Val Verde basin) that in itself achieved incipient mobility. Possibly in west Texas (PI. 2) there are segments of the Ouachita belt where the boundary against the forelandistransitional withinadeformed zone. The terms flysch and molasse have been defined invarious ways and have both been applied to sequences of rocks which differ substantially in stratigraphic character. The utility of the terms has been debated (Eardley and White, 1947), but they con tinue to be used and a number of authors have applied them to late Paleozoic sedimentary sequences within and adjacent to the Ouachita belt (Van der Gracht, 1931a, p. 498; P. B. King, 1937, pp. 87-SB, 135; Cline and Shelburne, 1959, pp. 177, 205206). Broadly speaking, the term flysch has been applied to rhythmically bedded sand- stone-shale sequences that are syn-orogenic in character, that is to say, that were deposited in deep tectonic basins between or infrontofactively risingelements, and the term mp2asse_has been applied to .ppst orogenic sediments^d^JYedjcom erosion of the uplifted deformed_ belt and deposited irj^kdlojwjmter_in_ basins in front of or bordering the orogenic sequences. Ameri can geologists tend to rather rigid de scriptive and genetic definitions of these sequences based on mineralogy, texture, sedimentary structures, fossils, and mode of origin; some definitions require that flysch sequences be composed of turbid ites. There is general acceptance of the principle that flysch must be a deep-water deposit and molasse must be a shallow- water deposit. European geologists, on the other hand, influenced by the classic Alpine flysch and molasse sequences, tend to place more importance on tectonic setting orrelation to tectonic elements in their definitions and are less restrictive inapplying stratigraphic and mineralogic criteria. Consideration of the formation of these sequences through time within a developing orogenic belt suggests that rigid definitions are not in order. Tectonic basins differ in rate of subsidence and amount of filling, symmetry, and nature of source areas. Some flysch basins probably filled up so that the younger part of the sequence was deposited in shallow water; other flysch basins probably never filled; in some the water was warm and inothers it was cold, thus affecting the amount and nature of carbonate rocks in the sequence. Although molasse deposits are considered post-orogenic, the classic molasse basin of the Alps was involved in the later stages of Alpine orogeny and the beds have been folded and broken by thrust faults. They are post-orogenic in the sense that they post-date the main geosynclinal and early orogenic periods. Insome areas the change from flysch to molasse sedimentation was abrupt, in other areas it was gradual; in some areas molasse lies on flysch, in other areas the two facies are tectonically juxtaposed or occur in separate basins. If not too rigidly defined, the terms flysch and molasse are very useful in regional stratigraphic and structural studies. There seems tobe no justification for using them outside of an orogenic setting. Petrographic Nomenclature Early in the project it became evident that there was need for a classification of argillaceous and arenaceous sedimentary rocks showing varied degrees of weak The Ouachita System metamorphism, and that such a classification did not exist. Because many of the samples available for study are limited to well cuttings, the distinguishing criteria of classification had to be those determinable from thin-section study. Rock characteristics that can be observed in outcrops or hand samples cannot be used for classification when the sample is limited to finely chipped bit cuttings. Furthermore, any classification which carried connotations of — genesis was to be avoided the classifica tionhad tobe descriptive. The writer and August Goldstein, Jr., dealt with this problem in earlier studies (Flawn, 1953, 1956) and proposed aclassi fication based on degree of reconstitution of the clay minerals, presence or absence of cleavage or parting, and grain size. The classification finally adopted is a revision of this earlier attempt; it is based on de gree of reconstitution and/or recrystallization and the presence or absence of preferred mineral orientation orparting, slaty cleavage, or foliation (Table 1). The weakness of the classification lies in the difficulty of distinguishing new reconstituted mica and chlorite from degraded, frayed, and fibrous second-cycle mica and chlorite;determination of degree of reconstitution is strongly subjective. However, with practice, the fresh new sprouts of sericite and chlorite can with fair certainty be separated from the faded, washed-out, de graded mica and chlorite. The writer and Goldstein, working independently with the same rocks and commonly on the same thin sections, used this classification successfully. Masson (1955) in a study of the same rocks employed the name semislate, apparently as an alternative name for clay- slate. Susceptibility of rocks to metamorphic changes depends on their original structure, mineralogy, fabric, and grain size. Eskola (1932) noted that presence of finely divided carbon in a rock inhibits metamorphic reactions. Moreover, within a deforming prism of rocks, stresses and temperatures are not everywhere equal—variations in degree of metamorphism occur within a single fold. There should thus be variations in metamorphic grade in se quences of weakly metamorphosed rocks as a result of differences in susceptibility to metamorphism and structural position. A rock reflects the temperature and stress conditions of its environment, commonly preserving a record of changes therein, with over-all control of the final product exerted by its original composition. The classification shown in Table 1 distinguishes three grades of metamorphism below that commonly referred to as low- grade metamorphism, namely, incipient, very weak, and weak. Alternations between unmetamorphosed, incipiently metamorphosed, and very weakly metamorphosed rocks occur in samples from a single borehole where there is no evidence toindicate structural dislocations. Thus, no fine lines of separation can be drawn between slight changes of metamorphic grade, and no great tectonic significance is implied by such changes. But in a broad regional study, plotting of degrees of weak metamorphism on a map establishes definite trends because the areal scope cancels out minor variations. These trends are persistent and have structural significance (Pis. 1and 2). Bokman has called the sandstones of the Stanley "graywackes," defining a graywacke as "...any sandstone containing 20 percent or more argillaceous material" (Bokman, 1953, p. 162).He says further that "Arenites bearing 0-20 percent matrix material and having the poor rounding and sorting characteristic of the gray- wackes (as opposed to the excellent rounding and sorting of the orthoquartzites) are defined as subgraywackes." Although there is much support for this usage of graywacke (Pettijohn, 1949; Krumbein and Sloss, 1951 ;5; 5 and Tallman, 1949), the writer prefers to use the term graywacke for rocks with a particular mineralogical composition, following Krynine (1948) and Folk (1954, 1956) who define the rock on a mineralogical basis as a sedimentary rock containing grains of quartz, chert, 5More recently (Dapples, Krumbein, and Sloss, 1953) these authors have adopted another classification with more of a mineralogical basis. 16 Bureau ofEconomic Geology, The University of Texas (th< (th<(th< ¦ ¦¦ com-gamet gametcom-com-gamet grade phyllite phyllitegradegradephyllite (e.g., (e.g.,(e.g., fine-grainec fine-grainecfine-grainec high highhigh reconstituted, reconstituted,reconstituted,recrystallized) high-rank high-rankrecrystallized)recrystallized) high-rank hornfels hornfelshornfels a aa 3 very very33very to toto is isis schist phyllites phyllitesschistschistphyllites pletely rock rockpletelypletelyrock as asas Medium MediumMedium (100% o o the theo(100%(100% oo othe as asas rocks rocksrocks .2 .2.2 .2 'I eye, 'I.2.2 eye,'Ieye, rocks rocksrocks may metaquartzite high-grade metaquartzitemaymayhigh-grademetaquartzite high-grade or these theseororthese reconstituted, reconstituted,reconstituted, may unaided unaidedmaymayunaided classify classifyclassify such suchsuch 3 33 the thethe grade gradegrade feldspar feldsparfeldspar recrystallized) phyllite, term phyllite,recrystallized)recrystallized) termphyllite,term by byby Low LowLow 100% 100%100% and andand be schist and schistbebe andschistand (Matrix (Matrix(Matrix not low-rank low-ranknotnot low-rank hornfels slate, resolved slate,hornfelshornfels resolvedslate,resolved petrographers petrographerspetrographers be bebe rocks rocksrocks rocks. quartz or orquartzquartzor Some SomeSome cannot cannotcannot metamorphic metamorphicmetamorphic arenaceous reconsti- reconsti-reconsti-feldspar high-rank high-rankfeldsparfeldspar high-rank argillite plates platesargilliteargilliteplates mm. mm.mm. low-grade low-gradelow-grade 0.5 0.50.5 and andand and than thanthan Weak WeakWeakrecrystallized) slate high-rank slaterecrystallized)recrystallized)high-rankslate high-rank and andand high-rank minerals. minerals.high-rankhigh-rank minerals. chlorite chloritechlorite quartz clay clayquartzquartzclay or oror less lessless to toto ; ;; argillaceous (Matrix>so%so%so%2s%2s%2s%xn mobile belt jvas welded^ to_die_craton_Jby late Precambrian orogeny and intrusion and, as the Paleozoic Diablo Platform, formed a stable southern foreland for the Ouachita system (p. 166). The "bay" thus created in the Ouachita system's foreland served to channel the late Paleozoic orogenic forces in this area, and a structural salient was the result. The first indication of tectonic activity in the Marathon segment of the Ouachita belt is recorded by a coarse arenaceous facies in the Early Ordovician beds of the southeasternmost exposures of the belt, by the exotic boulders of the Middle Ordovician Woods Hollow shale, and by the Upper Ordovician basal Maravillas conglomerates. P.B.King(1937, p.42) noted "...evidence of marked upliftand diastrophism in the region near the Middle and Upper Ordovician boundary," and J. L. Wilson (1954a, p. 2455) said: "The Ordovician section of the interior (southeasternmost) folds of the Ouachita-Marathon system suggests that orogenic activity occurred in the system in Ordovician time. . . ." In all probability the stratigraphic evidence of this disturbance visible in exposures today is only a faint northwestern reflection of an extensive Ordovician orogeny that took place to the southeast of the present-day exposures and whose conglomerates and intrusions are now concealed beneath a great thickness of younger sedimentary rocks. Bureau ofEconomic Geology, The University of Texas The hiatus and unconformity between the Caballos novaculite and the Tesnus, and the thin basal conglomerate of the Tesnus are evidence of Mississippian up- lift,probably inthe early or middle part of the period. The advent of Tesnus sedimentation marks the beginning of the late Paleozoic orogeny, and, with the exception of the quiescent period of Dimple limestone deposition, the succeeding stratigraphic column, representing almost continuous sedimentation, carries the evidence of a series of orogenic pulses in flyschmolasse deposition and conglomerate beds. P. B. King (1937, p. 119) has referred to this diastrophism as the "Marathon orogenic epoch" and recognized six episodes from the beginning of Tesnus time through Wolfcamp time, namely, (1) strong uplift of the hinterland, (2) overthrusting in the southeastern part of the area, (3) beginning of folding, including folding of the first overthrusts, (4) strong folding and overthrusting, (5) warping followed by erosion, and (6) tiltingand folding.Recent subsurface evidence that lower Wolfcamp beds were involved in late thrusting (Woods Oil and Gas Company No. 1-47 Mary Decie et al., p. 237) may call for a modification of King's episode No. 6 to include thrust faulting in early Wolfcamp time. The stratigraphic record shows that orogenic activity in the Marathon segment of the Ouachita structural belt began with the Tesnus and ended during Wolfcamp time. Movements were intermittent throughout Late Mississippian, Pennsylvanian, and Early Permian. Hall (1956) deserves credit for recognizing the importance of Wolfcamp orogenic move- merits, but the writer does not concur with him in making a sharp separation between a Lower Pennsylvanian orogeny dated by the Tesnus and an Early Permian (Wolfcamp) orogeny dated by the lower clastic Wolfcamp section. The Dimple limestone does record a period of quiescence between the two orogenic facies sedimentary sections, at least in the area of its occurrence,"> but the flysch character of the Haymond, the boulder beds in the upper Haymond, and the Gaptank conglomerates record continuing tectonism in the Late Pennsylvanian. The Tesnus clastic wedge and the Wolfcamp clastic wedge which Hall cites as evidence of two separate orogenies (separated by epeirogenic movements) merely record the normal progress of geosynclinal deformation and shifting of the axis of maximum deposition toward the foreland. The significance of the rocks and structures of the Marathon Basin was recognized in 1931 by Van der Gracht; he did not have the benefit of the detailed stratigraphic work and well data available today, and in the writer's opinion, the followingquotation (1931a, p.1042) testifies to his remarkable geologic perception. The importance of the Marathon Mountains, as part of a major structural feature, is indicated by- many signs. The wide development of an early Pennsylvanian foredeep, and, farther out, of an early Permian foredeep, and the orogenic facies of the deposits filling these troughs; the asymmetric profile of these foredeeps, and the fact that the depression moved progressively outward from the mountain front in later Pennsylvanian and Permian times; the very great intensity and duration of the Arbuckle phase [name given to an orogenic phase of middle Cisco time]; and, finally, the important flat overthrusting— of the Dugout Creek and Solitario nappes these allin dicate a major orogeny. Itis the history of a largeand important mountain chain. Other Exposures of the Ouachita Belt Peter T. Flawn Central Texas Inthe spring of 1948, Barnes discovered a sequence of steeply dipping dark shales and interbedded sandstones of Carboniferous age along the Colorado RiverinTravis and Burnet counties (Barnes, 1948) .These rocks overlie Marble Falls limestone and were identified as Smithwick (Morrow? Atoka?) ;because of the dark color of the rocks, their general lithology, and their steep dips, Barnes suggested that they might be within the Ouachita structural belt. The Marble Falls formation in the area strikes east of north and dips eastward with progressive inclination ranging from 10 to 15 degrees in the western part of the exposure to 70 degrees in the eastern outcrops; sandstone beds in the overlying shale sequence strike northeast and show dips up to 70 degrees to the southeast. The exposures occur in the bottom of the channelofLakeTravisintheTurkeyBend area and in the bottom of Cypress Creek; they are visible only at times of low water. Because of the limited exposures itcould not be determined whether or not local faulting was responsible for the structure. Thin-section examination of sandstone from within the dark shale sequence indicates that these rocks are not Ouachita facies as the term is used in this paper (p. 13);the rocks are fine-grained, sub- angular to subround, fairly well-sorted, cherty quartz sandstones of foreland type. Their foreland character is confirmed by the normal carbonate facies of the underlying Marble Falls; in the Ouachita sequence the Marble Falls carbonate unit is not present and probably itgrades into a clastic unit east of the Llano uplift. But although the rocks are not of Ouachita facies, their structure suggests that they are within the northwestern margin of the belt. The Turkey Bend exposures are on the southeast side of the Llano uplift and deformed Ouachita facies rocks occur only 5 miles to the southeast. This is the area of maximum deformation of the folded belt where the orogenic forces were directed against the unyielding buttress of the Llano uplift;inthis locus ofmaximum deformation itis reasonable to suppose that the foreland facies rocks mantling the southeast side of the uplift were caught up in the late Paleozoic folding and that, in this area, deformed foreland facies rocks occur within the frontal structures of the Ouachita belt. Solitario Area General Statement The Solitario is a nearly circular uplift, about 9 miles in diameter in southwestern Trans-Pecos Texas wherein northeastsouthwest- trending Paleozoic rocks are completely encircled by a high-standing rim of Cretaceous rocks; the Paleozoic exposures are about 35 miles southwest of the southwesternmost exposed Paleozoic rocks in the Marathon Basin. The geology of the Solitario area has been described by Udden (1907a), Powers (1921), Sellards, Adkins, and Arick (1931), Baker (1935), Lonsdale (1940), J. L. Wilson (1954a), and Herrin (1959).The following discussion is based largely on the work of Herrin (1959). The Paleozoic sequence exposed in the Solitario resembles that of the Marathon area and the same stratigraphic terminology is applicable (Table 3). Recently, Berry (1960, p. 20) noted that in the Soli Bureau ofEconomic Geology, The University of Texas tario and old Jones ranch areas a white to buff quartzose sandstone occurs between the Marathon and Fort Pena formations occupying the same position as the Alsate shale farther north; he proposed the name Rodriguez Tank sandstone for this unit. Cambrian and Lower to Middle Ordovician beds are mostly sandstone and shale; the shale is calcareous and the minor limestone beds in the sequence are nearly all sandy. The Upper Ordovician and the Devonian toLower Mississippian rocks are bedded chert, novaculite, and minor limestone. Upper Mississippian and Pennsylvanian rocks are siliceous black shale and massive quartzite. The rocks have been thrown into sharp asymmetric folds overturned to the northwest; a low-angle thrust, the Solitario thrust, has transported younger rocks over older rocks and is exposed in the interior of the uplift as a result of later folding. Cambrian and Ordovician rocks are exposed in a window of the thrust sheet. Stratigraphic Synopses The base of the stratigraphic sequence is not exposed in the Solitario uplift. The oldest exposed unit is the Dagger Flat sandstone which consists of about 600 feet of drab sandstone and sandy shale; the sandstones in the lower part are poorly sorted and contain angular grains of quartz, feldspar, chert, shale, and mica; higher, the sandstones are more calcareous. The Marathon formation, 1,500 to 3,000 feet thick, rests conformably on Dagger Flat beds and is composed of dark siliceous shale, dark chert, poorly sorted sandstone, and sandy limestone with a few beds of slabby blue limestone; the formation thus contains much less carbonate than in the Marathon area. Alsate shale has not been recognized in the Solitario. The Fort Pena formation is of much the same character as in the Marathon Basin; it is massive sandstone and quartzite, sandy and siliceous limestone, chert, and calcareous shale about 400 feet thick. Between itand the Woods Hollow shale is a transitional unit about 50 feet thick wherein sandy limestone gives way to black shale with thin sandstone partings. The Woods Hol shale, low is 400 feet of black fissile light-colored thin fairly well-sorted sandstone beds, and a few thin beds of flaggy limestone. The Woods Hollow is overlain conformably, but with a sharp change in lithology, by the Maravillas chert, which is bedded black chert 200 feet thick containing sporadic lenses of brown limestone and chert pebble conglomerate. The Maravillas is unconformably overlain by the Caballos formation, 280 feet of light-colored banded chert and novaculite with a red and green shale locally at the base. The youngest Paleozoic unitin the Soli tario area is the Tesnus formation of which about 4,600 feet ispreserved ;itis massive brown siltstone, very fine-grained sandstone, and dark green shale, variably siliceous, like the Tesnus of the Marathon Basin. The sandstone is a fine-grained, angular, poorly sorted, chloritic micaceous feldspathic rock containing fragments of chert, shale, and metamorphic rocks. Tertiary igneous rocks, mostly rhyolite, occur as dikes, sills, and small stocks, and the extrusive Buck Hillseries overlies the older rocks. Stratigraphic and Structural Analysis The Solitario uplift exposes the south- westernmost Paleozoic rocks of the Ouachita belt in the United States. Some units in the Solitario are nearly like those in the Marathon Basin but others differ inmineralogy and texture. Greatest differences are in the older Ordovician beds, such as the Marathon formation, which are more clastic and siliceous (J. L.Wilson,1954a, pp. 2458, 2471; Herrin, 1959, p. 42). The Solitario may lie nearer to the axis of the Ordovician geosyncline than the Marathon area (Herrin, 1959, p. 47), although the source of sediment was still farther south or southeast. The Tesnus contains more rock fragments than inthe Marathon Basin and perhaps, like the Marathon formation, The Ouachita System was deposited nearer to the source than equivalent beds in the Marathon Basin. Folding and thrust faulting in the Solitario is like that in the Marathon area and the Ouachita Mountains. Major structures strike northeast as in the Marathon Basin. The Solitario thrust is mappable for about 4 miles and has a displacement of about 4,000 feet (Herrin,1959, p.123).Presumably the Paleozoic rocks in the Solitario area were deformed at the same time as the rocks of the Marathon area. Although there may be local incipient to very weak alteration in rocks in this area, additional petrographic work willhave to be done to demonstrate the distribution and degree of metamorphism. It is unlikely that these frontal zone rocks experienced regional low-grade metamorphism. Gap and Dog Canyon Persimmon Areas General Statement Paleozoic rocks of Ouachita facies are exposed in the Persimmon Gap and Dog Canyon areas of Brewster County, Texas (Bone Spring quadrangle) ,about 10 miles south of the southernmost exposures of Paleozoic rocks in the Marathon Basin and about 40 miles east-northeast of the Solitario. These rocks have been described by Maxwell et al. (1949, pp. 27-28), J. L. Wilson (1954a ),Lonsdale et al. (1955, pp. 54-59 and map), Hazzard, Maxwell, and Lonsdale (1958), Berry and Nielsen (1958), and Maxwell et al. (MS). Strongly deformed Paleozoic rocks occur in a series of separate exposures in the Santiago Mountains in a northwest-southeast- trending belt about 6 miles long between Persimmon Gap on the northwest and the general area of Dog Canyon on the southeast. The area has been subjected to both Paleozoic and Cretaceous thrust faulting, and many of the exposed Paleozoic rocks are in thrust slices or parts of dislocated plates. The Paleozoic rocks include undifferentiated Ordovician rocks (probably Marathon and Alsate formations) ,Maravillas chert, Caballos novaculite (upper unit), and Tesnus formation. Stratigraphic Synopses According to Maxwell et al. (MS), the oldest Paleozoic unit in the Persimmon Gap-Dog Canyon area is probably a strongly deformed and crumpled mass of flaggy dark shale with minor thin limestone beds which has been thrust over the Georgetown formation and in turn has been overridden by strata of the Fredericksburg group. From their lithology, these rocks appear to be either Marathon or Alsate; thickness does not exceed 100 feet. A slice of Maravillas chert probably about 200 feet thick is exposed in the core of the Santiago Mountains structure resting onbeds oftheTesnus formation;itconsists ofgraytoblack chert,gray,brown,orange, and pink shale (with graptolites in one shale bed),dark brown toblack limestone, and thin chert-limestone pebble conglomerates; all these are extensively jointed and fractured. Several other smaller exposures of Maravillas chert ranging from 15 to 76 feet thick occur in the Persimmon Gap—Dog Canyon area. Near Persimmon Gap there is an exposure of all three subdivisions of the upper unit of the Caballos novaculite (Santiago formation of Berry and Nielsen, 1958).From the base upward they consist of 45 feet of reddish shale and chert, 30 feet of light gray to white novaculite, and 40 feet of inter- bedded dark chert and siliceous shale. These rocks lie unconformably on Mara- villas beds and are overlain unconformably by the Tesnus formation. The major exposure of the Tesnus occurs in Persimmon Gap and consists of hard dark shale and dark fine-grained sandstone cut by veinlets of white quartz (PI. 7, A). The base of the Tesnus is a thin conglomerate composed of dark chert and light-colored novaculite pebbles. The Tesnus in this area is thrust over Cretaceous rocks and overridden by Maravillas chert and has been extensively jointed and fractured. There are also other smaller exposures of Tesnus beds elsewhere. Maxwell et al. (MS) estimate that not more than 500 feet of Tesnus strata is exposed inthe area. Reconnaissance petrographic study of Tesnus sandstones from the Persimmon Gap area shows that the rocks are fine- grained, angular to round, poorly sorted, argillaceous-chloritic feldspathic quartz sandstone or arkose veined by calcite- hematite. Most of the quartz has strongly undulose extinction. The abundant feldspar is mostly plagioclase partly altered to calcite, but subordinate potassium feldspar is also present. Mica shreds, a few fragments of chert and phyllite-schist, and some carbonaceous debris were observed. The The Ouachita System heavy mineral fraction includes large round to subhedral zircons, apatite, rutile, leucoxene, and tourmaline. Stratigraphic and Structural Analysis The Paleozoic rocks of the Persimmon Gap-Dog Canyon area provide a glimpse of the southeasternmost exposures of unmetamorphosed rocks of the frontal zone of the Ouachita structural belt in Trans- Pecos Texas. Although the exposures are small and extensively deformed so that it is difficult to make detailed comparisons with the Marathon Basin sequence, certain broad conclusions can be drawn. The most important is that the major formations of theMarathon Basin sequence persist southward for atleast 10 miles without radical change. The rocks are more jointed and fractured than inthe Marathon Basin, but this appears to result from involvment in Cretaceous deformation rather than an increase in severity of Paleozoic deformation south of the Marathon area. Veining does not seem more extensive than to the north. Because of the fragmentary sections, the only infor mation available on thickness changes pertains to the Caballos novaculite, the upper part of which appears to thin southward (Berry and Nielsen, 1958). Not enough petrographic work has been done to determine whether or not the Tesnus sandstones are more arkosic in this area than to the north. Itis clear that the same type of Paleozoic deformation took place in this area as in the Marathon Basin to the north, and apparently there is no change in the trend of the Paleozoic axes; Paleozoic thrusting was from southeast tonorthwest (Hazzard, Maxwell,and Lonsdale, 1958).Ifthe trend of the Paleozoic structures in the Persimmon Gap-Dog Canyon area is northeast- southwest and the axes are projected northeastward, they strike toward the Jones ranch area in the southeastern tip of the Marathon Basin where pre-Tesnus Oua chita facies rocks are exposed and have been encountered inwells (PI. 2).Perhaps the Persimmon Gap—Dog Canyon and Jones ranch exposures are part of a third great anticlinal structure more or less parallel to the Dagger Flat and Marathon anticlinoria to the north (PL 2). The Subsurface Ouachita Structural Belt in Texas and Southeast Oklahoma Peter T. Flawn General Statement In mapping subcrop geology, the procedure followed is very much like the one used to construct areal geologic maps of the bedrock where itisobscured by heavy soils, glacial deposits, or alluvial cover; the characteristics of the rocks penetrated in a number of wells are plotted on a base map and similar rocks are grouped to form map units. In the frontal zone of the subsurface Ouachita belt where the rocks are unmetamorphosed and can be correlated withformations in the Ouachita Mountains orMarathon region, the problem is one of establishing the course and structural attitude of as many units as well control permits. Inattempting to map metamorphosed rocks inthe interior part of the belt—rocks which do not appear to have outcropping equivalents —the distinction between rock units and belts of metamorphism is important. Rocks of different ages and character might appear to be similar where they have been overprinted, so to speak, with the same degree and kind of meta morphism. This problem manifests itself in the eastern and southern part of the Ouachita beltincentral Texas where belts of differing degrees of metamorphism transect lithologic boundaries. In delimiting mappable lithologic units, the rocks are grouped by basic lithologic and mineralogic characters rather than by degree of reconstitution or similarity of metamorphic structures. The following lithologic units are mapped on the subcrop of the Ouachita belt inTexas and southeast Oklahoma:(1) Cambrian (? ) through Devonian (possibly including Lower Mississippian) rocks of Ouachita facies, pre-Stanley and pre- Tesnus beds; (2) Mississippian-Pennsylvanian rocks of Ouachita facies, including Atoka formation, Jackfork sandstone, Stanley shale, Tesnus formation, and Mississippian- Pennsylvanian rocks undivided; (3) dark fine-grained to coarse-grained clastic rocks of unknown age; and (4) phyllite, slate, metaquartzite, marble, and schist of unknown age. Cambrian (?)—Lower Mississippian Rocks of Ouachita Facies Lithologic Descriptions The pre-Stanley (pre-Tesnus) sequence includes distinctive siliceous units; the major lithologic types are chert and siliceous shale, limestone and dolomite, shale, siltstone, and sandstone. The rocks are commonly veined by quartz, quartz-bitumen, and calcite or dolomite; in the siliceous rocks extensive vein networks are common; in some slightly metamorphosed shale-sandstone samples, reconstitution adjacent to veins is reflected by development of coarse chlorite-sericite (p. 118). In some areas these rocks are unmetamor phosed, inother areas they have been subjected to incipient to very weak metamorphism, and, locally, they are low-grade metamorphic rocks (pp. 121-124 and PL 2) .10.10 In the metamorphosed terranes the rocks are deformed and show foliation, slaty cleavage, and fracture cleavage. In Lamar and Red River counties, Texas, pre-Stanley rocks are variably metamorphosed and are similar to pre- Stanley rocks exposed in the Ouachita Mountains inthe Broken Bow-Benton anti 10 Throughout this report the terms incipient, very weak, weak, and low-grade metamorphism are defined within specific limits (Table 1). Bureau ofEconomic Geology, The University of Texas clinorium (p. 25). Sericite and chlorite phyllite, slate, metaquartzite, metachert, and marble locally showing foliation, slaty cleavage, fracture cleavage, and convolution have been penetrated in this area. In Bentley, Shepherd, and Stevens No. 1 Southern Pine Lumber Company in Red River County, green hornblende occurs in metaquartzite, and the calcite marble in Johnston Petroleum Syndicate No. 1Lady Alice in Red River County is graphitic dolomitic calcite marble (PI. 8, D). Chert-siliceous shale. —Ouachita facies cherts range from light-colored (tan, greenish) to dark (brown, black) micro- granular to cryptocrystalline to chalcedonic chert, commonly dolomitic, argillaceous, pyritic, with abundant dark red- brown to black organic material inmasses, streaks, or evenly distributed in such quantity as to render the rock nearly opaque (PI. 5, B, C, D). The dark cherts commonly are spore-and /or radiolarianbearing and/or spiculitic (PI. 8, C). Siliceous shales are a transitional phase and except for their clay-mica content are similar to the cherts. These siliceous rocks are locally fractured, brecciated, or completely shattered. Incipient to very weak metamorphism is not visibly reflected in them —degree of metamorphism in these sequences is inferred from study of associated shale-sandstone. Limestone-dolomite. —Where limestone and dolomite occur, they are always associated with dark chert and siliceous shale. They are fine-grained limestone, dolomitic limestone, and dolomite, commonly glauconitic, argillaceous, siliceous, pyritic, and slightly fossiliferous, and commonly containing dark organic matter. The fossil material is a fine debris composed mostly of spicules but also including small gastropods, commonly pyritized, and pelmatozoan fragments. These carbonate rocks grade into chert and siliceous shale, and transitional types are common. Except for local twinning, effects of incipient to very weak metamorphism are not evident, but higher metamorphism is recorded in some areas. One well in Red River County (Johnston Petroleum Syndicate No. 1Lady Alice), located on the southwest extension of the Broken Bow-Benton anticlinorium (southwest of McCurtain County, Oklahoma), penetrated a sequence containing a graphitic quartzose dolomitic calcite marble. Stratigraphic relations in Mc- Curtain County indicate an early Paleozoic age, so this marble is probably early Paleozoic; inTerrell County inwest Texas, No. 1Barksdale penetrated R. E. Freeman a sequence of very weakly metamorphosed dark fine-grained dolomitic spiculitic limestone and fine-grained dolomite that is probably correlative with the Marathon limestone intheMarathon region. Shale. —Pre-Stanley shale (excluding siliceous shale) is of two main types: (1) dark gray-green shale, rarely brown or black, commonly containing rhombs or hour-glass porphyroblasts of "pleochroic" carbonate —probably dolomite or siderite, locally micaceous, chloride, pyritic, and silty, and (2) dark red hematitic shale, locally micaceous, chloritic, and silty. Perhaps in some areas the hematitic shale is derived from weathering of the pyriticgray- green shale. These shales readily reflect metamorphism. The most common type is a dark gray-green chloritic micaceous metashale or clay-slate showing incipient foliation or partial development of slaty or fracture cleavage. The mica commonly has a "braided" appearance (from wrinkling?) and commonly shows orientation in two directions at a high angle (one parallel to bedding, the other parallel to an axial plane?). — Siltstone and sandstone. Dark, fine- grained, angular, quartz siltstone, commonly chloritic, micaceous, dolomitic, pyritic, in part feldspathic and carbonaceous, is associated with the shale. Insome areas development of new interstitial mica and chlorite indicates incipient to very weak metamorphism, and the rocks are low-rank metasiltstone. Sandstone is relatively rare inpre-Stanley sequences. Where present, itis associated with siltstone and The Ouachita System is very fine-grained, mostly angular, and fairly well sorted; it is mineralogically similar to the siltstone. Two wells in Red River County (The Texas Company No. 1 Solomon and Magnolia Petroleum Company No. 1 Henry) penetrated fine- grained, angular, poorly sorted, tightly packed, hematitic quartzitic quartz sandstone; Johnston Petroleum Syndicate No. 1 Lady Alice encountered dolomitic meta- quartzite. Stratigraphy and Distribution A reliable stratigraphic succession in subsurface pre-Stan ley (pre-Tesnus) rocks cannot be established at this time from the data available; the rocks can only be com pared with the exposed sections in the Ouachita and Marathon areas, bearing inmind that complex structure and unknown facies relations in the hundreds of miles between the two areas willnot permit identification from apparent position in an apparent stratigraphic sequence; for example, a red shale beneath a green chert cannot be identified as Missouri Mountain simply because it is a red shale under something that looks like Arkansas novaculite. Gross units can be identified with some confidence, however, and a sequence can be established insome wells. The most distinctive subsurface unit is the assemblage of dark chert, siliceous shale, limestone, and dolomite. This is equivalent to the Bigfork chert (Upper Ordovician) of the Ouachita Mountains and can be identified with confidence as far south as Williamson County, Texas. The only unit with which itmight be confused is the Arkansas novaculite which also contains dark chert and siliceous shale but which does not contain the limestone and dolomite characteristic of the Bigfork. Thus, dark cherts are not necessarily Big- fork, but dark chert, siliceous shale, and limestone-dolomite is Bigfork lithology. West of the Llano uplift, dark chert has been encountered in a number of wells (Roland Blumberg No. 1 D. C. Knibbe, Comal County; Fred Turner, Jr., et al. No. 1R. Linder, Kendall County; Plateau Oil Company No. 1 R. D. Garrison, Bandera County).Probably these rocks are Bigfork or Bigfork equivalents, but the only name that can be applied withcertainty is"lower Paleozoic Ouachita facies." The Bigfork equivalent in the Marathon region, the Maravillas chert, has not been recognized inthe subsurface of that area. The other prominent body of siliceous rocks inboth the Ouachita Mountains and Marathon region is the Arkansas novaculite or Caballos novaculite (Devonian- Mississippian) which is distinguished in both areas by prominent beds of white chert or novaculite. One would expect that this unit could be easily recognized in subsurface and could be used as a distinct marker, but white chert or novaculite was only rarely seen in subsurface between the two areas where it is so vividly exposed. Insubsurface, the term Arkansas novaculite is applied to light-colored mostly tan or greenish chert and siliceous shale, commonly slightly dolomitic, which does not appear to be as thick as in the Ouachita Mountains and Marathon region. In the Ouachita Mountains the Arkansas novacu lite includes dark red-brown bituminous pyritic spore-and radiolarian-bearing chert similar to that in the upper part of the Bigfork;Goldstein (personal communi cation, 1958) states that this type of chert occurs in the lower part of the middle member of the Arkansas novaculite. Thus, it is not possible to separate Arkansas novaculite from the Bigfork chert on the presence of dark chert containing organic matter; likewise, because of complex structure, a dark chert immediately overlain by Stanley is not prima facie evidence that the chert is Arkansas novaculite. Dark gray-green to brown chloritic micaceous shale (commonly metashale) and fine chloritic micaceous quartz siltstone is identified as Womble where it occurs beneath a Bigfork sequence. However, where no Bigfork is recognized and penetration is limited, it is difficult to identify these shales and siltstones unless Bureau ofEconomic Geology, The University of Texas an Ordovician age can be established by graptolites. The Womble seems to be a great deal thicker in the Texas subsurface than inthe Oklahoma outcrop (possibly as much as 3,000 feet in Grayson County), but according to Goldstein (personal communication, 1958), no unfaulted section of Womble exists in the Ouachita Mountains, and without a completely cored section in Texas to determine dip, the true thickness cannot be determined. Several other Ouachita Mountain names — have been used in the Texas subsurface Missouri Mountain shale, Blaylock sandstone, Polk Creek shale, Mazarn shale, j Crystal Mountain sandstone, Collier shale, and Stringtown shale. Inasmuch as the facies relations and persistence of these units are not yet fullyknown in the Ouachita Mountains, itseems hazardous to use them casually in subsurface studies. Missouri Mountain shale (Silurian), consistingofhard red and green slaty shale and siliceous shale with minor chert and sandstone, is a distinct unit in the Ouachita Mountains but not all hard red shale encountered in subsurface is necessarily Missouri Mountain. The red color is due to hematite; in north Texas red hematitic shales mark the top of the Paleozoic sequence and are developed by weathering of Stanley and Atoka shales. Blaylock sandstone (Lower Silurian) has been applied to fine-grained, fairly well-sorted, micaceous quartz sandstone which seemingly forms a sequence below light-colored cherts of the Arkansas novaculite, but this usage is hazardous also, as relations of the outcropping unit are not completely known. Blakely, Mazarn, Crystal Mountain, and Collier have been used to describe a metamorphosed sequence penetrated in Red River County (Johnston Petroleum Syndicate No. 1 Lady Alice) close to the McCurtain County outcrop of these formations. In the writer's opinion, it is difficult to justify the use of these formation names. In west Texas in Terrell County, R. E. Freeman No. 1 Barksdale penetrated a long section of black finely dolomitic and calcareous shales, commonly siliceous and containing bituminous material, and dark fine-grained spiculitic limestone, commonly silty, pyjritic, siliceous, bituminous, and slightly fossiliferous; although incipiently to very weakly metamorphosed, these rocks resemble the Marathon limestone and are identified as Marathon(?).Table4lists wellsinwhich formal stratigraphic names have been applied to the pre-Stanley sequence. Inspection of the map (PL 2) shows that in outcrop and subcrop pre-Stanley Ouachita facies rocks occur (1) inrelatively small discontinuous areas along the structural front of the Ouachita belt and (2) in broad anticlinoria in the interior parts of the frontal zone where it is broadly developed in the Marathon and Ouachita salients. Studies in the Ouachita Mountains and data from wells indicate that the older rocks which occur along the front of the belt have been raised along frontal over- thrusts. From Oklahoma to BellCounty in central Texas the oldest unit in the allochthonous Ouachita plates is Womble shale; thus, the displaced Ouachita plates all seem to have slid on Womble shale. West of the Llano uplift a narrow zone of lower Paleozoic Ouachita facies rocks fringes the frontof the Ouachita belt,butitisdifficult to recognize Ouachita Mountains orMarathon area units in this area. Overthrust relations inMagnolia Petroleum Company No.1EdBelow,KendallCounty, thepattern of the rocks in subcrop, and abrupt changes from Ouachita to foreland facies suggest that the same relations prevail as — in the northern limb of the belt that the lower Paleozoic Ouachita rocks in the sub- crop occur along a belt of overthrusting. In the complex area of southern Val Verde County, lower Paleozoic Ouachita rocks form a narrow zone between Val Verde basin sedimentary rocks and highly sheared low-grade metamorphic rocks. The area is interpreted as one in which the Ouachita belt was thrust strongly against a buttress of high-standing Precambrian rocks, and the lower Paleozoic Ouachita The Ouachita System facies rocks are represented on the map as part of a dislocated plate (p. 172 and PL 2). In the Ouachita Mountains the largest exposures of pre-Stanley rocks form a major east-west-trending anticlinorium in Montgomery, Garland, and Saline counties, Arkansas, and inMcCurtain County, Oklahoma— the Broken Bow—Benton anticlinorium. Subsurface information indicates that the anticlinorium trends southwestward into the subsurface inTexas (PI. 2).Smaller exposures ofpre-Stanley rocks in the Ouachita Mountains occur to the northwest along overthrust faults or as windows. In the Marathon area lower Paleozoic rocks are exposed in the Marathon and Dagger Flat anticlinoria. Another anticlinorium, largely concealed, probably occurs southeast of the Dagger Flat structure and includes the Persimmon Gap and Jones ranch exposures of older rocks. More such uplifts probably exist in the concealed area of the Marathon salient. The lower Paleozoic Ouachita rocks in Terrell County may be part of such an anticlinorium. Bureau ofEconomic Geology, The University of Texas Table 4. Wells inwhich pre-Stanley (pre-Tesnus) Ouachita fades formations have been identified. lOUNTY lOUNTYlOUNTY and andand WELL WELLWELL NAME FORMATION INTERVAL FORMATIONNAMENAME INTERVALFORMATION INTERVAL (feet) REFERENCE REFERENCE(feet)(feet) REFERENCE 1 11 — —— BELL BELLBELL COUNTY COUNTYCOUNTY Nolan NolanNolan Bell BellBell Oil OilOilCo. Co.Co. No. No.No. 2 22 Wm. Wm.Wm. Bacon BaconBacon B. B.B. F. F.F. Gilchrist GilchristGilchrist No. No.No.1 11Curb-Fee Curb-FeeCurb-Fee Mellon MellonMellon Oil OilOil Co. Co.Co. No. No.No.1 11Noah NoahNoah Bailey BaileyBailey Shell ShellShell Oil OilOilCo. Co.Co.No. No.No.1 11C. C.C.E. E.E. Massie MassieMassie Eclipse EclipseEclipse Oil OilOil Co. Co.Co. No. No.No. 2 22 Slayden SlaydenSlayden — —— COLLIN COLLINCOLLINCOUNTY COUNTYCOUNTY Deep DeepDeep Rock RockRock Oil OilOilCorp. Corp.Corp. No. No.No.1 11 W. W.W. M. M.M.Sherley SherleySherley — —— COMAL COMALCOMAL COUNTY COUNTYCOUNTY Roland RolandRoland Blumberg BlumbergBlumberg No. No.No. 1 11D. D.D.C. C.C. Knibbe KnibbeKnibbe — —— CORYELL CORYELLCORYELL COUNTY COUNTYCOUNTY General GeneralGeneral Crude CrudeCrude Oil OilOilCo. Co.Co. No. No.No.1 11Earnest EarnestEarnest Day DayDay ELLIS ELLISELLIS COUNTY COUNTYCOUNTY John JohnJohn Mitchell MitchellMitchell No. No.No. 1 11J. J.J. L. L.L.Rush RushRush — —— FANNIN FANNINFANNIN COUNTY COUNTYCOUNTY Sun SunSun Oil OilOilCo. Co.Co.No. No.No.1 11Tucker TuckerTucker GRAYSON GRAYSONGRAYSON COUNTY COUNTYCOUNTY Continental ContinentalContinental Oil OilOilCo. Co.Co. No. No.No.1 11 B. B.B. F. F.F. Armstrong ArmstrongArmstrong A. A.A.G. G.G. Hill HillHillNo. No.No.1 11lone lonelone Carter CarterCarter Olson OlsonOlson Drlg. Drlg.Drlg.Co. Co.Co.No. No.No.1 11Southwestern SouthwesternSouthwesternLife LifeLife Insurance InsuranceInsurance Co. Co.Co. Olson OlsonOlson Drlg. Drlg.Drlg.Co. Co.Co.No. No.No.1 11Utiger UtigerUtiger Pan PanPan American AmericanAmerican Prod. Prod.Prod. Co. Co.Co. No. No.No.1 11 J. J.J. Umphress UmphressUmphress Womble WombleWomble shale(?) shale(?)shale(?) Bigfork BigforkBigfork chert chertchert Arkansas ArkansasArkansas novaculite novaculitenovaculite Bigfork BigforkBigfork chert chertchert Arkansas ArkansasArkansas novaculite novaculitenovaculite Bigfork-Womble Bigfork-WombleBigfork-Womble Silurian SilurianSilurian Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain(?) Mountain(?)Mountain(?) Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert chertchert Woinble WoinbleWoinble shale shaleshale Arkansas ArkansasArkansas novaculite(?) novaculite(?)novaculite(?) Blaylock BlaylockBlaylock sandstone(?) sandstone(?)sandstone(?) Bigfork BigforkBigfork chert(?) chert(?)chert(?) Womble WombleWomble shale shaleshale Arkansas ArkansasArkansas no nonovaculile vaculilevaculile ( ((? ?? ) )) ~\ ~\~\ Bigfork BigforkBigforkchert chertchert \ \\ Womble WombleWomble shale(?) shale(?)shale(?) J JJ Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain MountainMountain shale shaleshale Polk PolkPolk Creek CreekCreek shale shaleshale Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert(?) chert(?)chert(?) Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain(?) Mountain(?)Mountain(?) shale shaleshale Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain MountainMountain shale shaleshale Polk PolkPolk Creek CreekCreek shale shaleshale Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Fault FaultFault and andand Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain MountainMountain shale(?) shale(?)shale(?) Polk PolkPolk Creek CreekCreek shale(?) shale(?)shale(?) Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Arkansas ArkansasArkansas novaculite novaculitenovaculite Missouri MissouriMissouri Mountain MountainMountain shale(?) shale(?)shale(?) Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Womble WombleWomble shale shaleshale T/896 T/896T/896 2 22 1,200-2,015 1,200-2,0151,200-2,015 2,500-3,790 2,500-3,7902,500-3,790 3,500 3,5003,500 ( (( ?)-3,790 ?)-3,790?)-3,790 4,700 4,7004,700 ±-4,800 ±-4,800±-4,800 ± ±± 4,800 4,8004,800 ±-5,050 ±-5,050±-5,050 710-850 710-850710-850 935-1,050 935-1,050935-1,050 940 940940 1,000, 1,000,1,000, 1,050 1,0501,050 3,930-5,400 3,930-5,4003,930-5,400 685-690 685-690685-690 1,340-1,350 1,340-1,3501,340-1,350 1,535-1,540 1,535-1,5401,535-1,540 1,895, 1,895,1,895, 2,015-2,020, 2,015-2,020,2,015-2,020, 2,175 2,1752,175 7,400±-9,27S 7,400±-9,27S7,400±-9,27S T/2,098 T/2,098T/2,098T/2,416 T/2,416T/2,416T/3,793 T/3,793T/3,793T/3,846 T/3,846T/3,846 3,755-3,854 3,755-3,8543,755-3,854 2,100-2,110, 2,100-2,110,2,100-2,110, 2,170-2,180 2,170-2,1802,170-2,180 2,260-2,270 2,260-2,2702,260-2,270 2,470-2,480, 2,470-2,480,2,470-2,480, 2,490-2,500, 2,490-2,500,2,490-2,500, 2,520-2,530, 2,520-2,530,2,520-2,530, 2,570-2,580, 2,570-2,580,2,570-2,580, 2,590-2,600, 2,590-2,600,2,590-2,600, 2,700-2,710, 2,700-2,710,2,700-2,710, 2,810-2,820, 2,810-2,820,2,810-2,820, 2,950-2,970 2,950-2,9702,950-2,970 3,000-3,010 3,000-3,0103,000-3,010 1/2,280 1/2,2801/2,2801/2,370 1/2,3701/2,370T/2,440 T/2,440T/2,440T/2,700 T/2,700T/2,700T/2,185 T/2,185T/2,185T/3,300 T/3,300T/3,300 r/3,500 r/3,500r/3,500 T/4,485 T/4,485T/4,485T/4,790 T/4,790T/4,790T/4,860 T/4,860T/4,860T/4,890 T/4,890T/4,890 T/5,270 T/5,270T/5,270 T/950 T/950T/950 T/1,270 T/1,270T/1,270 T/1,320 T/1,320T/1,320 T/2,030 T/2,030T/2,030 3,730-6,175 3,730-6,1753,730-6,175 Sellards SellardsSellards (1931b, (1931b,(1931b, p. p.p. 821) 821)821) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Sellards SellardsSellards (1931b, (1931b,(1931b, p. p.p. 821) 821)821) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1958) 1958)1958) H. H.H.J. J.J. Morgan, Morgan,Morgan, Jr., Jr.,Jr., (pers. (pers.(pers. comm., comm.,comm., 1956) 1956)1956) W. W.W. J. J.J. Wilson WilsonWilson (pers. (pers.(pers. comm., comm.,comm., 1956) 1956)1956) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) The Ouachita System COUNTY COUNTYCOUNTY and andand WELL WELLWELL NAME FORMATION INTERVAL FORMATIONNAMENAME INTERVALFORMATION INTERVAL (feet) REFERENCE REFERENCE(feet)(feet) REFERENCE 1 11 — —— GRAYSON GRAYSONGRAYSON COUNTY COUNTYCOUNTY (continued) (continued)(continued) Peter PeterPeter and andand Johnson JohnsonJohnson No. No.No.1 11J. J.J. A. A.A.O'Dell O'DellO'Dell W. W.W. J. J.J. Rutledge RutledgeRutledge No. No.No.1 11M. M.M.E. E.E. Williams WilliamsWilliams Simpson-Fells Simpson-FellsSimpson-Fells Oil OilOilCo. Co.Co. No. No.No.1 11 G. G.G. W. W.W. Wall WallWall Starr StarrStarr Oil OilOil Co., Co.,Co., Inc., Inc.,Inc.,No. No.No. 1 11Blankenship BlankenshipBlankenship Verne VerneVerne Dumas DumasDumas Co. Co.Co. et etet al. al.al.No. No.No.1 11 M. M.M. E. E.E. Williams WilliamsWilliams HAYS HAYSHAYS COUNTY COUNTYCOUNTY E. E.E.A. A.A.Bucklin BucklinBucklin No. No.No.1 11A. A.A.A. A.A.Eisner EisnerEisner — —— KENDALL KENDALLKENDALLCOUNTY COUNTYCOUNTY J. J.J. S. S.S. Abcrerombie AbcrerombieAbcrerombie and andand Harrison HarrisonHarrison Oil OilOil Co. Co.Co. No. No.No.1 11Lena LenaLena Kunz KunzKunz and andand Joe JoeJoe Nickel NickelNickel Magnolia MagnoliaMagnolia Petr. Petr.Petr. Company CompanyCompany No. No.No.1 11Ed EdEd Below BelowBelow Fred FredFredTurner, Turner,Turner,Jr., Jr.,Jr.,et etet al. al.al.No. No.No.1 11 R. R.R. Linder LinderLinder — —— LAMAR LAMARLAMARCOUNTY COUNTYCOUNTY Clark ClarkClark& &&Ogg OggOgg No. No.No.1 11Smiley SmileySmiley Coeden CoedenCoeden Petr. Petr.Petr. Co. Co.Co. No. No.No. 1 11W. W.W. T. T.T.Adams AdamsAdams MCLENNAN MCLENNANMCLENNAN COUNTY COUNTYCOUNTY Daniel DanielDaniel Oil OilOil Co. Co.Co. No. No.No. 1 11 Elizabeth ElizabethElizabeth W. W.W. Estes EstesEstesDelta DeltaDelta Drlg. Drlg.Drlg. Co. Co.Co.No. No.No. 1 11C. C.C. Horstman HorstmanHorstmanHodges HodgesHodges et etet al. al.al.No. No.No.1 11Lawrence LawrenceLawrenceSt. St.St.Louis LouisLouis Oil OilOilPool PoolPool No. No.No.1 11Stuart StuartStuart RED REDRED RIVER RIVERRIVER COUNTY COUNTYCOUNTY Johnston JohnstonJohnston Petr. Petr.Petr. Syndicate SyndicateSyndicate No. No.No. 1 11Lady LadyLady Alice AliceAlice Joe JoeJoe White WhiteWhite et etet al. al.al.No. No.No.1 11Kurth KurthKurthLumber LumberLumber Co. Co.Co. — —— TERRELL TERRELLTERRELL COUNTY COUNTYCOUNTY Milham MilhamMilham Oil OilOil Corp. Corp.Corp.No. No.No.1 11Bassett BassettBassett R. R.R.E. E.E. Freeman FreemanFreeman No. No.No.1 11Barksdale BarksdaleBarksdale WILLIAMSON WILLIAMSONWILLIAMSONCOUNTY COUNTYCOUNTY W. W.W. E. E.E. Green GreenGreen No. No.No.1 11Lehman LehmanLehman S. S.S. L. L.L.Carpenter CarpenterCarpenter No. No.No.1 11S. S.S. J. J.J. Seward SewardSeward Missouri MissouriMissouri Mountain MountainMountain shale shaleshale Polk PolkPolk Creek CreekCreek shale shaleshale Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Bigfork BigforkBigfork chert chertchert Stringtown StringtownStringtown shale shaleshale Womble WombleWomble shale shaleshale Bigfork BigforkBigfork chert chertchert (?) (?)(?) Missouri MissouriMissouri Mountain MountainMountain shale shaleshale Polk PolkPolk Creek CreekCreek shale shaleshale Missouri MissouriMissouri Mountain MountainMountain shale(?) shale(?)shale(?) Arkansas ArkansasArkansas novaculito novaculitonovaculito Missouri MissouriMissouri Mountain MountainMountain shale shaleshale (?) (?)(?) Womble WombleWomble shale(?) shale(?)shale(?) Missouri MissouriMissouri Mountain MountainMountain shale shaleshale (?) (?)(?) Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert chertchert and andand Womble WombleWomble shale shaleshale (?) (?)(?) Blaylock BlaylockBlaylock sandstone(?) sandstone(?)sandstone(?) Bigfork BigforkBigfork chert chertchert (?) (?)(?) Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert(?) chert(?)chert(?) Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale Blakely BlakelyBlakely sandstone sandstonesandstone Mazarn MazarnMazarn shale shaleshale Crystal CrystalCrystal Mountain MountainMountain sandstone sandstonesandstone Collier CollierCollier shale shaleshale Bigfork BigforkBigfork chert(?) chert(?)chert(?) Woods WoodsWoods Hollow HollowHollow shale(?) shale(?)shale(?) Marathon MarathonMarathon limestone limestonelimestone (?) (?)(?) Arkansas ArkansasArkansas novaculite novaculitenovaculite or oror Bigfork BigforkBigfork chert chertchert Bigfork BigforkBigfork chert chertchert Womble WombleWomble shale shaleshale 3,530-3,540, 3,530-3,540,3,530-3,540, 3,800-3,810 3,800-3,8103,800-3,810 T/900 T/900T/900 T/1,374(?) T/1,374(?)T/1,374(?) 900-1,552 900-1,552900-1,552 1,552-2,515 1,552-2,5151,552-2,515 2,010-5,230 2,010-5,2302,010-5,230 725-835 725-835725-835 2,252 2,2522,252 1,007-1,365 1,007-1,3651,007-1,365 1,100 1,1001,100 T/1,450, T/1,450,T/1,450, 1,481 1,4811,481 3,195-3,355 3,195-3,3553,195-3,355 2,820-3,065 2,820-3,0652,820-3,065 2,598,2,650 2,598,2,6502,598,2,650 1,120-2,259 1,120-2,2591,120-2,259 1,313-1,600 1,313-1,6001,313-1,600 1,235±-3,500 1,235±-3,5001,235±-3,500 1,673-4,520 1,673-4,5201,673-4,520 2,133-2,139 2,133-2,1392,133-2,139 1,215-3,565 1,215-3,5651,215-3,565 2,470-2,990 2,470-2,9902,470-2,990 (scattered (scattered(scattered samples) samples)samples) 1,630-2,008 1,630-2,0081,630-2,008 (scattered (scattered(scattered samples) samples)samples) Miser MiserMiser and andand Sellards SellardsSellards (1931, (1931,(1931, p. p.p. 815) 815)815) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Miser MiserMiser and andand Sellards SellardsSellards (1931, (1931,(1931, p. p.p. 818) 818)818) V. V.V. E. E.E. Tims TimsTims (pers. (pers.(pers. comm., comm.,comm., 1957) 1957)1957) Sellards SellardsSellards (1931b, (1931b,(1931b, pp. pp.pp. 822, 822,822, 827) 827)827) (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Goldstein GoldsteinGoldstein Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Goldstein GoldsteinGoldstein (pers. (pers.(pers. comm., comm.,comm., 1955) 1955)1955) Sellards SellardsSellards (1931b, (1931b,(1931b, p. p.p. 823) 823)823) Miser MiserMiser and andand Sellards SellardsSellards (1931, (1931,(1931, p. p.p. 812)* 812)*812)* Lewis LewisLewis (1941, (1941,(1941, pp. pp.pp. 78-79) 78-79)78-79) 1 11If IfIfno nono=other other==other reference referencereference is isis given, given,given, the thethe identification identificationidentification was waswas made mademade in inin this thisthis study. study.study. 2 22T/ T/T/ top. top.top. 3 33 Sequence SequenceSequence penetrated penetratedpenetrated in inin well wellwell is isis described describeddescribed as asas "comparable "comparable"comparable in inin lithology lithologylithology to toto . ... ..." ."." the thethe Ouachita OuachitaOuachita Mountain MountainMountain section. section.section. Mississippian-Pennsylvanian Rocks of Ouachita Facies Stanley Shale, Tesnus Formation, and Mijssissippian-Pennsylvanian Rocks Undivided (Tesnus?) The Stanley and Tesnus formations, as well as probably correlative rocks of Mississippian-Pennsylvanian age in the subsurface of south-central Texas, are thick bodies of thinly interlayered shale and sandstone of flysch type; they comprise most of the frontal zone of the Ouachita belt. They are for the most part unmetamorphosed near the foreland margin of the belt and incipiently to very weakly metamorphosed to the south and east. Throughout most of the Ouachita belt they are strongly folded and faulted and locally show incipient to well-developed slaty cleavage. They are commonly veined by quartz, carbonate, quartz-bitumen, and, more rarely, chlorite; chlorite veinlets are restricted to the slightly metamorphosed sequences. Shale. —Stanley-Tesnus shale is mostly dark (dark gray, green gray, and black) clay shale, commonly silty, carbonaceous, micaceous, and chloritic. Weaver (1958, p. 299) described the Stanley shale as dominantly illite-chlorite with kaolinite present in the southern Ouachita Mountains. Fan and Shaw (1956) described the Tesnus shale as illite and mixed-layer chlorite-vermiculite (lower unit) and illite-montmorillonite (upper unit). In some parts of the Ouachita belt these shales have been deformed and subjected to varied degrees of metamorphism (mostly incipient to very weak). Deformed and very weakly metamorphosed shale (meta shale and clay-slate) commonly has a "braided" appearance under the microscope (due to wrinkling?) with two directions of orientation of clay-mica-chlorite at a high angle. Incipient axial plane and fracture cleavage occurs locally. Micachlorite is well developed in the partly reconstituted rocks. — Sandstone. Stanley-Tesnus sandstone ismostly hard gray to greenish-gray, fine- grained (0.10 to 0.20 mm), angular, poorly sorted, argillaceous feldspathic quartz sandstone, commonly carbonaceous, micaceous, and chloritic, and rarely calcareous or dolomitic (PL 6, B, C, D; PI. 7,B,C,D).Calcite and dolomite are more abundant in the western segment of the belt than in the northern segment; conein- cone carbonate occurs in Daniel Oil Company No.1Elizabeth W.Estes inMc- Lennan County, Texas Minerals No. 1 Snowden inFannin County, and Peter Oil and Gas Company, Inc., No. 1Butcher in Grayson County (PI. 8, B). Locally the sandstone contains abundant rock fragments including chert, slate-phyllite, quartz mosaic, and in the western area microgranular feldspathic fragments, as well as micaceous-chloritic material. These rocks are graywackes. Inone area (Medina County, Texas) the rocks probably include conglomerates or breccias made up of sheared granitic rock fragments and fragments of volcanic rocks, schist, and limestone. The quartz of Stanley-Tesnus sandstone consists predominantly of undulose to strongly undulose grains, composite grains, and grains of bubbly vein quartz. The feldspar ismostly plagioclase (albiteoligoclase) with subordinate microcline and microcline microperthite in the western segment. The heavy mineral fraction is garnet, zircon, tourmaline, apatite, magnetite-ilmenite, and leucoxene; much angular garnet occurs in the sandstone in the northern segment between Travis County and the Red River; garnet is less common southwest of the Llano uplift and is very rare farther west. In places the matrix of the sandstone is partly reconstituted through incipient to very weak meta — morphism insome samples the new mica chlorite is oriented and in others direc tional fabric is lacking. Dark, hard, angu lar, fairly well-sorted, argillaceous mica The Ouachita System ceous chloritic quartz siltstone, commonly feldspathic, occurs with the sandstone. In southeast Oklahoma and northern Texas in the vicinity of the buried Arbuckle element, the Stanley is more calcareous and contains morepotassium feldspar than elsewhere; inCarter OilCompany No.1Loyd, Bryan County, Oklahoma, large subhedral potassium feldspar grains and a fragment of granite occur in sandstone from the Stanley, and inDamon No.1Chaffin, Fannin County, Texas, Stanley sandstones contain abundant potassium feldspar. Jackfork Sandstone The Jackfork sandstone forms a large part of the frontal zone of the Ouachita belt in the Ouachita Mountains salient and extends southward in the subsurface into Fannin County, Texas; it has not been recognized farther south. The Jackfork is a thick mass of interlayered sandstone and shale; excepting for local incipient to very weak nietamorphism in areas of maximum deformation, it is not metamorphosed. In places itis cut by veinlets of quartz, carbonate, and bitumen. Like the Stanley, the Jackfork has been strongly deformed, and locally cleavage is developed. Sandstone.— The Jackfork sandstone is hard, gray, fine-to coarse-grained, mostly subangular, mostly well-sorted, quartz sandstone, commonly quartzitic and commonly containing abundant rock fragments (vein quartz, quartzite, chert, minor slatephyllite). The heavy mineral suite includes zircon, rutile, tourmaline, apatite. The low clay-mica and feldspar content of Jackfork sandstones and the absence of garnet make them easy to distinguish from Stanley and Atoka sandstones. In areas of strong deformation, the matrix of the Jackfork sandstones ispartly reconstituted. — Shale. Shale in the Jackfork is dark gray to green clay shale, commonly silty and commonly containing carbonaceous plant debris, locally spiculitic (PI. 8, A). According to Weaver (1958, p. 299), itis illite-chlorite, with amounts of minor kaolinite and mixed-layer illite-montmoril lonite; this shale contains much less chlorite than that of the Stanley. Inareas of strong deformation Jackfork shales show cleavage and partial reconstitution. Atoka Formation The Atoka formation (1) occurs well within the Ouachita belt in the Ouachita Mountains salient; (2) forms a thin band within the front of the belt in some areas in Texas (and probably also in Mississippi) ;and (3) occurs also on the foreland from Mississippi to far west Texas. Although Atoka lithology is mostly sandstone and shale, rocks called Atoka vary greatly in their sandstone/shale ratio and in the character of the sand; along the axes of the deep foreland basins, the Atoka formation ismostly shale but on the margins it is more sandy. Moreover, of the basins the sand within the Atoka was derived from many different sources. In the Mc- Alester basin, the Atoka beds on the side of the basin bounded by the Ouachita belt contain sand from a southern source, but to the northeast the Atoka contains sand derived from the Ozark uplift, and to the west the sand came from the Arbuckle up- lift(C. C. Branson, personal commmunication, 1958) .In the Fort Worth basin, most of the Atoka sand was derived from the Ouachita belt to the east, but in the southern and northern parts of the basin, the Llano uplift and the Muenster arch contributed detritus. Atoka beds locally are strongly deformed and cleavage is developed in the shales; the rocks are cut by veinlets of quartz, carbonate, and quartz- bitumen. For purposes of this report, studies of Atoka lithology were confined to the parts withinorimmediately adjacent to the Oua chita belt. Here, the Atoka is similar to the Stanley and some Atoka sandstones cannot be distinguished from Stanley sandstones, but generally, the sandstones of the two units can be distinguished by differences in mineralogy and texture (p. 18). — Sandstone. Atoka sandstone within the Ouachita belt is hard (locally quartzitic) , Bureau of Economic Geology, The University of Texas gray, fine-to coarse-grained, angular to subround, poorly to fairly well-sorted, quartz sandstone, commonly argillaceous, commonly calcareous, locally micaceous. Inplaces close to the Ouachita front these sandstones contain abundant mica and rock fragments derived from the Ouachita belt, including metamorphic rock fragments (slate, phyllite,metaquartzite) ,chert (Bigfork and Arkansas novaculite types),sandstone, shale, and vein quartz. The quartz in Atoka sandstone is of mixed types with abundant strongly undulose and composite grains and large amounts of bubbly vein quartz. The feldspar is plagioclase, but it occurs in much smaller amounts than in Stanley sandstones (potassium feldspar occurs in Atoka sandstones in the frontal basins where uplifts of the foreland basement contributed detritus). Zircon, garnet, apatite, tourmaline, rutile, leucoxene, and magnetite-ilmenite make up the heavy mineral suite; angular and modified garnet fragments similar to garnet inStanley sandstones occur in some samples, but itis not so common or abundant as in the Stanley. Where the Atoka has been strongly deformed (close to the Llano uplift), incipient reconstitution of the clay- mica matrix is indicated by sprouts of new sericite and chlorite, but metamorphism in Atoka rocks is generally rare. Shale. —Atoka shale within the Ouachita belt is very similar to Stanley shale; it is dark clay shale, commonly silty, micaceous, carbonaceous, chloritic. According to Weaver (1958, p.299),the Atoka shales south of the frontal Choctaw fault in the Ouachita Mountains are illite-chlorite with lesser amounts of kaolinite and mixed- layer clay. Dimple and Haymond Formations The Dimple and Haymond formations (Morrowan and Atokan respectively) in the Ouachita structural belt in the Marathon region (P. B. King, 1937) are not separately distinguished on Plate 2 of this report; their respective outcrops are grouped with the Tesnus formation. They undoubtedly extend beneath the Cretaceous cover into the subsurface east and southwest of the exposures of the Marathon Basin, but wellcontrol is insufficient to attempt to separate them from the Tesnus ortomap themindividually.Inthenorthern part of the Ouachita belt, the post- Stanley beds (Jackfork and Atoka formations) within the frontal zone of the belt seem to be restricted to the broadly developed Ouachita Mountains salient (p. 165) ;likewise, in the western segment the occurrence of younger rocks (post- Tesnus beds) within the deformed belt seems to be more or less restricted to the Marathon salient where the frontal zone is broadly developed. Stratigraphy and Distribution of Mississippian-Pennsylvanian Rocks No attempt is made herein to work out a stratigraphic sequence in the thick strongly deformed body of Mississippian- Pennsylvanian clastic rocks that comprises most of the frontal zone of the Ouachita belt; the main problem is to distinguish major units—Stanley shale, Tesnus formation, Jackfork sandstone, and Atoka formation. A combination of sandstone petrography and X-ray analysis serves to identify these formations within the limits of accuracy required for a regional study. Well samples indicate that the lithology determined in outcrops persists into the subsurface. Tuffaceous beds, siliceous shales, and cone-in-cone carbonate occur in the Stanley in north-central Texas, and siliceous radiolarian-bearing shale occurs in the Jackfork in Fannin County. Scattered cores show that the rocks are steeply dipping, sheared, and slickensided. Because of deformation, faulting, and lack of continuously cored sections, it is uncertain whether there is any major change in the thickness of these units in the subsurface. In the northeast-trending limb of the Ouachita belt between the Ouachita Mountains in southeast Oklahoma and Travis County in central Texas, the frontal zone The Ouachita System of the Ouachita belt is mainly Stanley formation (PI. 2). Throughout this segment, the Stanley appears to be identical with the Stanley shale in the western Ouachita Mountains; Stanley sandstone is characteristically dark, fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone, commonly micaceous and chloritic, with abundant garnet in the heavy mineral fraction. The feldspar is sodic plagioclase and the mica is sericitemuscovite. Tuffaceous material probably correlative with the tuff in the lower part of the Stanley in the Ouachita Mountains (Hatton tufflentil)isfoundinHill-Texas OilCompany No.1C. Weatherby inHill County, Texas, and as hard green tuffaceous siliceous shale at the base of the Stanley in General Crude Oil Company No. 1 Earnest Day in Coryell County. Tuffaceous material is also present in an incipiently to very weakly metamorphosed red shale-siltstone sequence in Hunt County (Humble Oil & Refining Company's No. 1Norman and No. 1 Rutherford) which is probably Stanley; red beds are not typical of the Stanley in the Ouachita Mountains, but innorth Texas a zone of red beds seems to have been formed on the surface of Paleozoic rocks as a result of pre-Cretaceous weathering. Goldstein (p. 340) interpreted the granite and feldspar fragments inthe Stanley in Carter Oil Company No. 1 Loyd in Bryan County, Oklahoma, as probably of pyroclastic origin because the sandstone matrix in the sample (3,649 feet) is tuffaceous. Another possible interpretation is that some clastic material in the Stanley in this area was derived from a foreland uplift (Arbuckle element?) during Mississippian time. The abnormally high amount of calcareous material in the Stanley in this same area might also be the result of forelandderived sediments. Southwest and west of Travis County, Texas, where the Ouachita belt wraps around the Llano upliftand continues westward, Mississippian-Pennsylvanian rocks retain the over-all character of the Ouachita facies but change sufficiently that the name Stanley is no longer applicable. In part, this change is more apparent than real due to the advance of very weak metamorphism farther into the frontal zone (p. 122 and PL 2), but there are also changes in the composition of the sandstone. Here (Hays, Comal, Blanco, Kendall, Bexar, Bander a, Medina, and Uvalde counties) the northern part of the frontal zone of the Ouachita belt seems to consist of very weakly metamorphosed Mississippian- Pennsylvanian and older rocks of Ouachita facies that have been thrust over the foreland; farther to the south, unmetamorphosed Mississippian-Pennsylvanian rocks occur immediately north of the Luling overthrust front (PI. 2). The over all petrography of the Mississippian- Pennsylvanian sandstones shows the characteristics of the Ouachita facies —the rocks are mostly hard, gray to gray-green, fine-grained, angular, poorly sorted, argillaceous micaceous chloritic feldspathic quartz sandstone and dark silty shale. In detail, however, there are significant differences : (1) The feldspar content of the rocks is higher than in the northern segment of the Ouachita belt and many of the sandstones are true arkose; potassium feldspar, rarely seen to the north, is commonly present in this area, although still subordinate to plagioclase in amount. (2) Mica and chlorite are more abundant in this area and include faded and bleached biotite which does not occur in the Stanley to the north. (3) Rock fragments southwest of the Llano uplift, although mainly phylliteslate, chert, and quartz mosaic like those to the north, also include a few fragments of a microgranular feldspathic igneous rock. (4) Calcite and dolomite are commonly present in these sandstones in small amounts. (5) Carbonaceous and bituminous material is relatively abundant. (6) Garnet is not a prominent heavy Bureau ofEconomic Geology, The University of Texas mineral (except in Clarence Newton No. 1 Check Ranch in Kendall County) ;the usual suite is zircon, apatite, tourmaline, and magnetite-ilmenite. Itshould be noted that Weaver (p. 157) reported relatively abundant kaolinite in the shales in this area. The rocks are cut by the same suite of quartz, carbonate, chlorite, and bitumen veinlets; chlorite veinlets are most common in very weakly metamorphosed rocks. The shales show the same structural characteristics as to the north—wrinkling and development of incipient axial plane and fracture cleavage. In samples from John I.Moore No. 1 Alfred J. Wurzbach in Medina County, fragments of muscovite-biotite granodiorite, in part cataclastically altered, as well as fragments of trachyte porphyry, and a few pieces of calcilutite and muscovite schist are associated with sandstone and metashale fragments. The exotic fragments (mostly igneous rocks) in this well are probably in conglomerate or breccia beds within a sandstone-metashale sequence of Mississippian-Pennsylvanian age (p. 157). The frontal zone of the Ouachita belt, which can be mapped as a continuous tectonic unit from western Arkansas to Medina County, Texas, disappears in Duval and Kinney counties. Very little well control is available in this area, but there is a real structural discontinuity in the frontal zone and not an apparent discontinuity caused by a paucity of control points, because farther west in western Kinney and Val Verde counties highly sheared low-grade metamorphic rocks characteristic of the interior zone of the Ouachita belt are bordered on the north by foreland facies rocks and there are no intervening frontal zone Ouachita rocks. IfMississippian-Pennsylvanian rocks were deposited in the Ouachita geosyncline in this area, they must have been overridden by an allochthonous plate of metamorphic rocks of the interior zone of the belt (pp. 172-173). In the Marathon region part of another salient of the Ouachita belt is exposed where the frontal zone is broadly de veloped. Here, the oldest Mississippian- Pennsylvanian rocks of Ouachita facies form the Tesnus formation, a flysch-type unit of interlayered sandstone and shale. East and southwest of the Marathon Basin well control is poor. Tesnus beds, variably metamorphosed, have been identified in wells in Terrell County east of the Marathon area; the Tesnus also crops out south and southwest of the Marathon uplift in Persimmon Gap and in the Solitario. The Tesnus, therefore, probably makes up a large part of the subcrop of the frontal zone of the Ouachita belt in Terrell and Brewster counties. The Tesnus is similar to the Stanley and to the undivided Mississippian- Pennsylvanian rocks south and west of the Llano uplift; in petrographic detail the Tesnus sandstones are more like those south and west of the Llano uplift than like the Stanley beds in the north limb of the belt. Tesnus sandstones contain abundant chlorite, faded second-cycle biotite, and potassium feldspar inaddition to the more abundant plagioclase. The feldspar content of Tesnus sandstones is low compared to the highly feldspathic sandstones of the frontal zone in south- central Texas. Farther south inPersimmon Gap Tesnus sandstones seem to be more feldspathic. The general similarity is such that the Mississippian-Pennsylvanian rocks which comprise the frontal zone of the Ouachita belt in Hays, Blanco, Kendall, Bexar, Bandera, Medina, and Uvalde counties are tentatively assigned to the Tesnus (? ). Dark Clastic Rocks of Unknown Age Lithologic Description metasandstone, commonly calcareous or East and south of the Stanley and pre- Stanley rocks that form the foreland side of the frontal zone of the Ouachita belt is a body of dark clastic rocks that do not crop out in any of the exposed parts of the belt. This unit lies partly in the frontal zone and partly within the highly sheared interior zone, east and south of the Luling overthrust front (PI. 2).The unit includes two distinct metamorphic facies. Superficially, the highly-sheared weakly metamorphosed rocks east and south of the Luling front look very different from the very weakly metamorphosed rocks of the frontal zone, but the basic lithology and — mineralogy are the same inboth zones the rocks are dark fine-grained to coarse- grained clastic sedimentary rocks containing abundant carbonaceous or graphitic material, mica, and dolomite as well as calcite, hematite, and pyrite. The main mineralogical difference between the two zones is that to the southeast, as a result of extreme shearing and higher grade metamorphism, carbonaceous matter was converted to graphite, and argillaceous material, second-cycle mica and chlorite, was to a greater extent reconstituted to new sericite and chlorite. Physical differences between the two zones are much plainer; east and south of the Lulingfront the rocks show pronounced dynamic structures such as slaty cleavage, fracture cleavage, foliation, microfolding and microfaulting, contortion, and flowage structures. In the zone of very weak metamorphism the rocks are mostly (1) gray and black silty micaceous metashale and sericite-chlorite clay-slate, commonly carbonaceous or graphitic, pyritic, locally dolomitic, and siliceous (PI. 9, A); (2) dark angular chloritic micaceous quartz siltstone or metasiltstone, commonly dolomitic (less commonly calcareous), carbonaceous, locally feldspathic, hematitic, and pyritic; and (3) dark, fine-to coarse- grained, angular, poorly sorted, chloritic micaceous argillaceous quartz sandstone or dolomitic, carbonaceous, locally feldspathic and containing abundant fragments of slate-phyllite, metaquartzite, and chert. These rocks have been invaded by numerous and locally massive veins of quartz, dolomite, calcite, chlorite, and bituminous material. The metashale and clay-slate are locally brecciated, crinkled, contorted, and have slaty cleavage. South of the Luling front where shearing is extreme, reconstitution and metamorphic structures are better developed; the rocks are mostly (1) gray to black (rarely green) carbonaceous to graphitic chlorite-sericite slate, withaugen ofbroken quartz veins, locally hematitic, pyritic, siliceous (PI.9,B, C,D);(2) dark angular carbonaceous sericitic chloritic quartz metasiltstone; and (3) dark, fine-grained, angular to subround, very poorly sorted, carbonaceous micaceous quartz metasandstone (rarely metaquartzite), commonly dolomitic, feldspathic, and with abundant rock fragments, locally pyritic. The rocks in this zone of weak metamorphism and high to extreme shearing are cut by both pre-deformation and post-deformation veins of quartz, dolomite, calcite, and chlorite ;pre-deformation veins are broken and sheared into augen; veins are profuse and commonly massive. Metamorphic structures include foliation, slaty cleavage, contortion, and flowage around augen (Pis. 13,14). Several wells penetrating this unit in its western extension have encountered cataclastically altered granitic rock and fractured, sheared, and altered (chloritized- sericitized-albitized) andesite and basalt porphyry (p. 110). The igneous rocks are partly mylonitized—grains are fractured and granulated and feldspar is partly or wholly converted to sericite. Stratigraphy and Distribution On the subcrop of the Ouachita belt, dark clastic rocks of unknown age (not formally named) form an arcuate band Bureau ofEconomic Geology, The University of Texas east, southeast, and south of the Llano up- lift;their maximum subcrop is more than 20 miles wide in Travis County, but they are unknown north of McLennan County and west of Bexar County. In the northern segment of the Ouachita belt, low-grade highly sheared rocks of the interior zone of the belt appear to have overridden very weakly metamorphosed shales and sandstones of this unit,but southward and westward in Travis County, part of the unit was included in the movement of the Luling overthrust front; from Travis County to Medina County extremely sheared black slates with strongly developed flowage structures suggest that the movement along the Lulingfront occurred withinor at the base of these dark elastics. This is supported by the presence of partly mylonitized igneous rocks in Bexar and Medina counties (p. 110). In Bexar County dark sheared and altered andesite or basalt lies within or beneath the sheared slates. Similar sheared and altered dark extrusive rocks occur farther west inMedina County and to the southwest inMaverick County,butinthese areas the dark clastic sequence was not observed. Relations between this sequence and the intermediate to basic lava sequence are therefore uncertain, and itis not known whether the lavas in Bexar County are at the base of or within the sequence. At the southeast edge of the known Ouachita belt, southeast oftheLulingfrontand southeast of the subcrop of the phylliteslate- metaquartzite sequence of the Luling area, one well (Quintana Petroleum Corporation No. 1Lampkin) penetrated extensively veined dark slate and metasandstone similar to the dark clastic sequence. This well leads to speculation that the dark clastic unit might be repeated in the sub- crop by successive thrusts southeast of the Lulingfront. Age and Correlation No fossils have been found in the dark clastic sequence. The carbonaceous material forms sooty masses and irregular streaks and no wood fragments were ob served. The pattern of the outcrop suggests that the sequence is either (1) a large an ticlinorium, thrust faulted to the south, or (2) ahomoclinal (or synclinal) mass resting on the Stanley, dipping east and south, and thrust faulted to the south. Thisunitmay thusbepartof theStanley or a younger Mississippian-Pennsylvanian unit (structural interpretation No. 2).The dark shale-siltstone-sandstone lithology is not incompatible with that of the Stanley, but the rocks ingeneral contain more finer material and more carbonate than the Stanley. Regional relationships indicate that the dark clastic sequence may be closer to the source area than the Stanley of the frontal zone, but ifso, it should not contain more carbonate and fine-grained clastic material than the Stanley. Itis also unreasonable to suppose that these dark elastics are correlative with younger Pennsylvanian units such as the Jackfork or Atoka. The dark clastic unit is stronglydeformed; the most recent deformation occurred prior to the deposition of Pennsylvanian- Permian post-orogenic beds in Bexar County (H. A. Pagenkopf No. 1 Max Blum) perhaps during Dcs Moines time. Earlier deformations are indicated by the flysch facies of the Mississippian-Pennsylvanian sequence. Pre-shearing and post- shearing veins in the dark clastic sequence south of the Luling front show that these rocks were extensively veined and probably metamorphosed before the tectonic movements that caused the extensive shearing. It would thus appear that the deformed dark clastic sequence is older than Middle Pennsylvanian and perhaps considerably older. These rocks may be a near-source facies of lower Paleozoic Ouachita facies rocks (structural hypothesis No. 1 above; Cross Section A-A',PL 2);the associated volcanic rocks in Bexar County may be a product of the same period of volcanism that provided the silica for the lower Paleozoic chert sequences nearer to the fore- land. Phyllite,Slate, Metaquartzite, Marble, and Schist of Unknown Age Lithologic Description Phyllite, slate, metaquartzite, marble, and schist occur in the subcrop east and south of the Luling front (PL 2) and constitute a distinct lithologic group. These rocks show low-to medium-grade metamorphism with a strong shearing component. The rocks are: (a) chlorite-sericite phyllite (or slate), commonly graphitic, hematitic, rutiliferous, locally albitic, biotitic, locally containing muscovite as porphyroblasts or unsheared relicts, rarely garnetiferous (PL10,A,B,C;PL11,C); (b) fine-grained metaquartzite, commonly graphitic, sericitic, chloritic, dolomitic, rutiliferous (includes metachert) (PL 11, A); (c) fine-grained biotite-chlorite-muscovite (and/or sericite) schist, commonly graphitic, garnetiferous, rutiliferous, calcareous; (d) fine-grained amphiboleepidote schist, locally calcareous, chloritic, sericitic; (c) fine-grained calcite marble, commonly dolomitic, quartzose, sericitic, graphitic, hematitic, locally albitic (PL 10, D; PL 11, B); and (f) fine-grained dolomite marble, commonly calcitic, quartzose, sericitic, graphitic, locally talcose(?). The rocks contain pre-and post- deformation veins of quartz, calcite, dolomite, chlorite, and epidote. Metamorphic structures are foliation, slaty cleavage, fracture cleavage, grain stretching, micro- folding, microthrust faulting, micro-imbrication, wrinkling, convolution and contortion, and flowage around augen; the metaquartzites show granulation, suturing, and partial mylonitization; the calcite marbles show extensive twinning and grain deformation. The exposed rocks at the base of the Sierra del Carmen range in Coahuila, Mexico, just south of the Rio Grande (PL 2; PL 11, C) probably belong tothisunit (Flawn and Maxwell,1958). Allof these rocks show dynamic structures produced by strong shearing and a low to medium grade of regional metamorphism (PL 15). Medium-grade metamorphic rocks—indicated by presence of biotite, amphibole, garnets, and porphyro — blastic muscovite occur mostly in the extreme southern part of the belt in Caldwell, Wilson, Bexar, Frio, Zavala, and Val Verde counties. Insome wells in this part of the belt (Plateau Oil Company No. 1 B. S. Harrison et al., Val Verde County; Magnolia Petroleum Company No. 1McKinley, Frio County; Arkansas Fuel Oil Company No. 1George Burkhardt, Bexar County),there isasuggestion ofretrogressive metamorphism —muscovite is sheared to sericite, biotite is frayed and faded, garnets are broken (p.124). The various rock types are gradational and have a common mineral assemblage. They all contain the same essential minerals such as quartz, sericite-muscovite, chlorite, calcite, and dolomite, but the minerals occur in varying proportions to make phyllite-schist, metaquartzite, or marble. Graphitic material and rutile in finely dispersed needles are übiquitous. In addition to the sericite-chlorite quartz-calcite-dolomite assemblage that makes up the bulk of the rocks of this unit, several wells in the southern part of the belt have penetrated highly sheared phyl lite or fine-grained schist containing epi dote and a finely fibrous colorless amphi bole (Husky Oil Company No. 1 Rose- Robertson, Val Verde County; Park and Phillips No. 1Flowers and Ward Ranch, Zavala County; and Bur-Kan Petroleum Company and Stanolind Oiland Gas CompanyNo. 1LeeHubbard, Bexar County). These rocks also contain sericite, chlorite, quartz, and feldspar. They may be sheared igneous bodies included within the Ouachita beltor,inHuskyOilCompany No.1 Rose-Robertson, they may be part of a Precambrian metavolcanic terrane (p. 109). Bureau ofEconomic Geology, The University of Texas Their metamorphic grade is similar to that of associated rocks —their mineralogy reflects their original composition (an igneous rock or a sedimentary rock with sufficient calcium, aluminum, iron, and silica to form amphibole and epidote). Stratigraphy and Distribution Phyllite, slate, metaquartzite, marble, and schist form the subcrop of the Ouachita belt in a continuous band from Navarro County, Texas, southwestward to Frio County, Texas. Continuity is lost in the Zavala and Maverick County area, but to the west phyllite, slate, metaquartzite, marble, and schist make up the subcrop in southern Kinney, Val Verde, Terrell, and Brewster counties, Texas, and northeastern Coahuila, Mexico. Similar rocks are exposed in the base of the western Sierra del Carmen scarp immediately south of Brewster County in northern Coahuila (p. 99). These strongly deformed rocks do not change in over-all lithology and metamorphic character from northeast to southwest and thus resemble the remarkably persistent lithologic units of the frontal zone which are more orless the same from the Marathon region in west Texas to the Ouachita Mountains of Oklahoma and Arkansas. The major difference between the Trans-Pecos metamorphic sequence and the rocks to the east lies in the presence of abundant calcite and dolomite marble to the west, whereas to the east carbonate rocks are comparatively rare. Interpretations from well cuttings, wherein lithologies are intimately mixed through long intervals, and the relations seen in the single exposure in the Sierra del Carmen indicate that in the western segment the sequence is thinly interlayered phylliteschist, marble, fine-grained metaquartzite, and metachert; probably many of the wells drilled very steeply dipping ornearly vertical beds. Eastward in the Luling area and farther northeast the sequence is mostly phyllite with lesser fine-grained meta- quartzite or metachert and rare marble; cores show that inmany wells the rocks are nearly vertical. In Freestone County, about 15 miles southeast of the highly sheared low-grade metamorphic rocks mapped in Navarro County, Humble Oil&Refining Company No. 1Marberry encountered a very different sequence (p. 127). The predominant rock is a hard red quartzitic quartz sandstone containing abundant authigenic feldspar and derived from sedimentary rocks; metamorphism is very weak to weak, with a strong hydrothermal element and lacking the strong shear characteristic of rocks to the east. The rocks are unlike any others penetrated in the Ouachita belt to date; some geologists have speculated that the presence of these apparently very weakly metamorphosed rocks east of highly sheared low-grade metamorphic rocks suggests that the metamorphic terrane is flanked by' unmetamorphosed Paleozoic rocks to the south and east and that the Ouachita belt is therefore relatively narrow. However, it is not sound to attempt large-scale tectonic interpretations on the basis of one well. Inthe Appalachian belt a wide variety of rocks occurs east of the Blue Ridge front, which in itself is discontinuous with many recesses, re-entrants, and windows. Possibly these red beds are post-orogenic rocks altered by younger igneous activity (p. 127). Age and Correlation The age of the highly sheared low-grade phyllite, slate, metaquartzite, marble, and schist is uncertain. Early investigators classed the rocks beneath the Cretaceous in the Luling field as Precambrian because of their metamorphic character and the presence of demonstrably Precambrian metamorphic rocks to the north in the Llano uplift.Asmore was learned about the Ouachita belt and it was recognized that some of the weakly metamorphosed rocks within the belt are Paleozoic, some geologists classed the phyllite, slate, metaquartzite, marble, and schist as Paleozoic in age (Barnes, 1948; Goldstein and Reno, The Ouachita System 1952).The problem isstillunresolved, but the possibilities can be clarified by examining the metamorphic rocks within the regional framework of the Ouachita belt. The phyllite, slate, metaquartzite, marble, and schist sequence is part of an interior zone of the Ouachita belt. In the eastern counterpart of the Ouachita system, the Appalachian system, a zone of similar rocks adjacent to the frontal zone is known as the Blue Ridge province. These rocks are both late Precambrian and early Paleozoic inage, and the same maybe true in the Ouachita belt. Probably rocks of different ages have been tectonically juxtaposed. However, the consistent lithology of the phyllite, slate, metaquartzite, marble, and schist sequence indicates that these rocks constitute a gross lithologic unit as well as a metamorphic zone (p. 79). Therefore, although it is not unlikely that both Paleozoic and Precambrian rocks may occur within the interior of the Ouachita belt, the sequence mapped east and south of the Luling overthrust front probably does not include both Precambrian and Paleozoic rocks. Some rather tenuous and inconclusive evidence suggests that these rocks are early Paleozoic: (1) Absolute age determinations on mica from the Sierra del Carmen exposures, although not con clusive, point to a Paleozoic age for the metamorphism (George Edwards, Shell Development Company, personal communication, 1959) ; (2) small siliceous bodies resembling spicules were observed in Plumber and Schwab No. 1Bud Roark in Brewster County (p. 235) ;(3) pre-Stanley rocks inthe southwestern subsurface extension of the Broken Bow-Benton anticlinorium have been subjected to variable weak to low-grade metamorphism with a high shearing component, and the resulting sequence strongly resembles the rocks of the phyllite, slate, metaquartzite, marble, and schist belt incentral and west Texas and northern Mexico; in Red River County, Texas, in Johnson Petroleum Syndicate No.1Lady Alice (p.301) agraphitic dolomitic calcite marble occurs with sericitechlorite slate and phyllite, and sericitic and chloritic metachert or fine-grained meta- quartzite —this rock is nearly identical with the marble south of the Luling over- thrust front; and (4) where Precambrian rocks have been encountered beneath metamorphosed Ouachita belt rocks inKinney and Val Verde counties, the Precambrian rock is metavolcanic rock lithologically distinct from the phyllite, slate, meta- quartzite, marble, and schist sequence. The Subsurface Ouachita Structural Belt East of the Ouachita Mountains 11 Philip B. King Introduction Inother chapters of this publication all available information, both surface and subsurface, has been assembled to portray the rocks and structures of the Ouachita belt of Paleozoic age from the Ouachita Mountains of Arkansas and Oklahoma, southwestward through Texas into Mexico. This chapter might be termed a reconnaissance survey of these same rocks and structures, eastward from the Ouachita Mountains. In central Arkansas the exposed rocks and structures of Paleozoic age in the Ouachita Mountains pass eastward beneath Cretaceous, Tertiary, and Quaternary deposits of the Mississippi embayment. Obvi — ously, they extend farther but where? Three hundred and fifty miles to the east the rocks and structures of Paleozoic age in the Appalachian Mountains pass southwestward beneath Cretaceous and Tertiary deposits of the Gulf Coastal Plain. Again, these obviously extend farther —but where? What is the relation between these two orogenic systems, both of which grew during about the same parts of Paleozoic time? Ifthey join, what is the nature of their junction? Partial answers to these questions are afforded by the records of wells whichhave penetrated Paleozoic and earlier rocks beneath Mesozoic and younger rocks of the Gulf Coastal Plain and Mississippi embayment. Nevertheless, penetrations of the Paleozoic and earlier rocks have so far not been made in some of the most critical areas, in many of which they lie at great depth. Even where penetrations have been made, some of the data are either meager, equivocal, or not available to this writer. 11 Publication authorized by the Director, U. S. GeologicalSurvey. Because of the fragmentary nature of the record, the interpretations made here are based partly on analogy with known relations in adjacent outcrop areas. To make these interpretations, it is necessary to review amuch wider area than that occupied by the Ouachita system alone, including the exposed Paleozoic and earlier rocks in the southern part of the Appalachian system and the Interior Plateaus, and their subcrop extensions southward beneath the deposits of the Atlantic and Gulf Coastal Plains. This review isbased partly on published and partly on unpublished sources. Drillrecords in the part of Arkansas lying generally eastward from the Ouachita Mountains have been reported on by Renfroe (1949),Maher and Lantz (1953), and Caplan (1954). In addition, Norman F. Williams, State Geologist, and William M.Caplan, both of the Arkansas Geological and Conservation Commission, have generously provided many unpublished data on this part of the State. The writer's compilation on southern Arkansas was much more cursory than elsewhere and consisted only of a review of the easily available literature. Subsurface relations of the Paleozoic rocks innorthern Mississippi and Alabama were summarized in a pioneer paper by Mellen (1947).Further details on some of the wells have been given by the Mississippi Geological Society (Dott and Murray, cd., 1954, pp. 4-7, sheet 1; Mississippi Geol. Soc, 1954, pp. 39-52; Frascogna, cd., 1957, pp. 12, 20, 40, 60, 78, 82, 86, 114,128),byWelch (1959),andbyCropp (1960, pp. 360-362) .A structure contour map on the top of the Mississippian in the Bureau ofEconomic Geology, The University of Texas northern part of the Black Warrior basin isavailable (Everett, 1953,p.36).Inaddition, all non-producing wells in Mississippi, including those which have penetrated Paleozoic rocks, have been listed and mapped by Beikman and Drakoulis (1958a, 1958b) ; these authors indicate the probable age of the lowest formation penetrated in each well but give few other details. In Alabama, all logs of wells drilled prior to 1945 have been assembled by Bowles (1941) andToulmin (1945). Logs of wells drilled in northwestern Alabama prior to 1955 which are based on sample studies have been given by McGlamery (1955).Records of wells drilledinPaleozoic and older rocks in northern Florida, southern Alabama, and southern Georgia are listed and interpreted ina fundamental paper by Applin (1951),and the results of a paleontological study of specimens from many of the same wells have been summarized by Bridge and Berdan (1951, 1952). Besides this published record, the writer has had the use of petrographic reports on cores or samples from some wells drilled in Mississippi and Alabama, made by Peter T.Flawn of the Texas Bureau ofEconomic Geology, August Goldstein, Jr., of the Bell Oiland Gas Company, and Charles Milton oftheU.S.Geological Survey, and theuse of paleontological reports on some other wells by G. Arthur Cooper of the U. S. National Museum and Ellis L. Yochelson of the U. S. Geological Survey. Various petroleum geologists have generously furnished other well data, and their contributions are acknowledged at appropriate places in the summary of well data, Appendix, Part 3. Jean Berdan of the U. S. Geological Survey has informed the writer of results of her work on the Florida Paleozoic which are later than the published record. Isidore Zeitz and other geophysicists of the U. S. Geological Survey have contributed valuable advice on the interpretation of geophysical features. Finally, Paul L. Applin of the U. S. Geological Survey has been an unfailing source of assistance and counsel regarding well data inthe southeastern states. Regional Geology Results of the writer's study are presented on the accompanying map of part of the southeastern United States (PI. 3). This shows the extent of various Paleozoic and older rock units, both in outcrop toward the north and in subcrop beneath the coastal plains toward the south. The units selected for mapping are mainly stratigraphic, but they are also of structural significance. Results of the writer's review can best be presented interms of these units. Tectonic Provinces The area mapped is divisible into various tectonic provinces, which will be referred to in the ensuing discussion. In the Paleozoic and earlier rocks are the following provinces: (A) The southeastern part of the Central Stable Region of North America, where gently tilted Paleozoic rocks form most of the surface, was the foreland of both the Appalachian and Ouachita orogenic systems. Toward the north the Paleozoic rocks ¦are raised in the broad Nashville and Ozark domes. To the southeast along the front of the Appalachian system they are depressed into a shallow longitudinal basin beneath the Cumberland Plateau; to the southwest along the front of the Ouachita system they are depressed into the deeper longitudinal Arkansas basin. In the intervening area, mainly beneath coastal plain deposits, is the Black Warrior basin; this is of triangular rather than longitudinal outline because itlies in a recess between the converging Appalachian and Ouachita systems. (B) The Appalachian system on the southeast consists of folded, faulted, and partly metamorphosed Paleozoic and older rocks, divisible into a succession of longitudinal provinces, and these into subdivisions which are here referred to as "belts." To the northwest is the Valley and Ridge province, consisting of deformed but not metamorphosed strata of Cambrian to Pennsylvanian age. Southeast of it are the Blue Ridge and Piedmont provinces, consisting of weakly metamorphosed sedimentary rocks, metamorphic, and plutonic rocks, partly of the same age as those in the Valley and Ridge province and partly older. Drill data indicate that the Appalachian system extends considerable distances beneath younger deposits in the adjacent coastal plains, both southwestward along the strike and southeastward across the strike. (C) The Ouachita system on the southwest is composed of folded, faulted, and partly metamorphosed Paleozoic rocks; no older rocks are known. Much of its structure in the exposed area resembles that in the Appalachian Valley and Ridge province. Drilldata indicate that the Ouachita system extends southward and southeastward a considerable distance beneath younger deposits of the Gulf Coastal Plain and Mississippi embayment. (D) Innorthern Florida, Paleozoic and older rocks are entirely concealed by younger deposits, but theylieat relatively shallow depth and have been widely penetrated bydrilling.Paleozoic rocks underlie an extensive area, termed the Suwanee basin, inwhich they are flat-lyingorgently tilted and are notmetamorphosed. The Mesozoic and later rocks of the region form broad coastal plains, where they are tilted seaward at low angles. The plains are divided geographically into the Atlantic and Gulf Coastal Plains, but the characteristic stratigraphic and tectonic features of the Atlantic Coastal Plain extend somewhat west of its geographic boundary, into Alabama. Variations in the prevailing structure occur in the Peninsular arch in the northern part of Florida (whichcoincides inpart withtheSuwanee basin in the older rocks) and the Mississippi embayment, a transverse downwarp in the Gulf Coastal Plain that crosses the Bureau ofEconomic Geology, The University of Texas eastern end of the Paleozoic Ozark uplift and extends northward into southern Illinois. Triassic(?) Unfossiliferous rocks that are believed to be of Triassic age have been penetrated in a large area in the Gulf Coastal Plain in southeastern Alabama, southwestern Georgia, and northwestern Florida (McKee et al., 1959, pi. 5). The sedimentary rocks include red arkosic sandstones and shales. Associated with the sedimentary rocks are large volumes of mafic igneous rocks that were emplaced either as flows, shallow intrusives, or both (Applin, 1951, pp. 15-17).Some wells have been drilled from younger Mesozoic rocks, through Triassic(?)rocks, intorocks ofPaleozoic or earlier age, but a well to the west in Alabama (well 112,I 12, Crenshaw County) penetrated 4,285 feet of red clastic rocks without reaching their base, and another well in the Florida panhandle (well 9', Walton County) penetrated 4,297 feet of similar rocks. These red rocks are at least partly of Triassic (? ) age, but they include younger Mesozoic strata at the top. Northeast of the main Triassic (? ) area in Georgia, several outlying wells have penetrated mafic igneous rocks, probably intrusive into a prevailing terrane of metamorphic and plutonic rocks. These mafic intrusives are analogous to the extensive system of diabase dikes inthe exposed part of the Piedmont province from Alabama northeastward, that are believed to be of Triassic age. The dikes in Georgia, which trend generally northwestward, have been described by Lester and Allen (1950) . These Triassic(?) sedimentary and igneous rocks are much like those of the Upper Triassic Newark group, which is exposed in the Piedmont province of the Appalachian system from North Carolina northeastward. The Newark group probably was deposited in longitudinal troughs not much more extensive than the 12 See Appendix, Part 3, for all numbered wells. present outcrop areas. Well data are insufficient to prove the form of the Triassic (?) deposits beneath the coastal plain; they may similarly occupy longitudinal troughs (Braunstein, 1958a ), or they may have accumulated as a widespread blanket along the edge of a primitive coastal plain (McKee et al., 1959, p. 24 and pi. 9),as shown on the map (PI. 3). Permian(?) Farther west, mainly insouthern Arkansas, is the Eagle Mills formation (Weeks, 1938, pp. 962-964; Imlay, 1940a, pp. 815; Hazzard et al., 1947, pp. 484-486), another body of red, unfossiliferous clastic rocks. The Eagle Millsis commonly classed as of Permian (?) age, but its relations to other formations cannot be proved, as itis everywhere overlain unconformably by much younger Upper Jurassic or Cretaceous formations, and as no well has certainly reached its base, although thicknesses of as much as 4,600 feet have been penetrated. The Eagle Mills is evidently younger than the Ouachita orogeny; one well which entered the formation is only 17 miles south of outcrops of deformed Paleozoic rocks inthe Ouachita Mountains. Itisprobably also younger than theMiddle orUpper Pennsylvanian Morehouse formation, penetrated in one well to the south inLouisiana (well23). The Eagle Mills was originally thought to be an updip clastic equivalent of the Werner formation and Louann salt13 farther south beneath the coastal plain, but these units are now generally believed to have been formed during a later sedimentary cycle (Hazzard et al., 1947, p. 483). The Werner and Louann are also classed as Permian (?) by some geologists but as of Jurassic(?) age by others (McKee et al., 1956, p. 2). Red strata have been penetrated beneath 18 The stratigraphic names Werner formation, Louann salt, and Norphlet formation are used here as redefined by Hazzard et al. (1947), although these redefinitions have not been formally adopted by the U. S. Geological Survey. The stratigraphic concepts involved have been generally accepted, but opinions differ as to the validity of the Permian age which was suggested for the first two units. The Ouachita System proved Jurassic formations in some of the deeper wells in Mississippi and Alabama, in the area between typical occurrences of the Eagle Mills and the Triassic(?). Although various correlations of these strata have been proposed by geologists, the present study has not been sufficient to determine whether they are equivalent to the Eagle Mills on the west, the Triassic(?) ontheeast,orwhether theyinclude equivalents of both. Pennsylvanian Rocks of the Pennsylvanian system are extensive in the foreland region northwest of the Appalachian Mountains and north of the Ouachita Mountains. They are generally missing within the Appalachian and Ouachita Mountains, at least partly because of erosion. However, they are preserved in deeper synclines in the southwest part of the Valley and Ridge province near Birmingham, Alabama (Butts, 1926, pp. 208-217).Moreover, the weakly metamorphosed Talladega belt farther southeast in the same region includes the Erin shale which contains fossil plants of probable Pennsylvanian age (p. 92). The Erin is part of the sequence and is actually a slate or phyllite, rather than a "shale" (Griffin,1951, pp.31-48);itisnotina window in a thrust sheet as has been claimed (Park, 1935). In the Ouachita Mountains most of the exposed rocks are older than the Pennsylvanian, but the Pennsylvanian Atoka formation is preserved in some of the deeper synclines. In the Appalachian region and its fore- land the Pennsylvanian rocks have allbeen assigned to the Pottsville formation. They are mainly shale and sandstone but include thin beds of conglomerate. Layers of coal are interbedded throughout, as well as layers containing marine invertebrate fossils, so that the Pottsville must be of mixed continental and shallow-water marine origin. The Pennsylvanian strata which are preserved are about 2,500 feet thick in the foreland area and more than 9,000 feet thick in the synclines in the Valley and Ridge province. At least part of this increase in thickness is the result of depositional variations. Similar Pennsylvanian strata extend westward around the south end of the Nashville dome, across northern Alabama and into the subcrop in northern Mississippi. Here, they thicken southwestward into the Black Warrior basin, some wells penetrating as much as 8,000 feet of Pennsylvanian strata (Cropp, 1960, p. 360) ;the maximum thickness in the basin may exceed 10,000 feet. In the Black Warrior basin, coal layers are recorded throughout the Pottsville, and much of it is probably of mixed continental and marine origin, as farther east. In the Arkansas basin14 of Arkansas, north of the Ouachita Mountains, most of the Pennsylvanian is Atoka formation, although the Hartshorne sandstone and higher formations of Dcs Moines age are preserved above it toward the west. The Atoka is more than 19,000 feet thick close to the front of the Ouachita Mountains (Reinemund and Danilchik, 1957), but it thins northward to a feather edge along the flanks of the Ozark uplift. The Atoka formation west of the Mississippi embayment is on line of strike with the Pottsville formation east of the embayment and is probably correlative. However, its thicker parts are of marine origin and are not of continental origin as is part of the Potts- ville. Along the northwestern front of the Appalachian system most of the Pennsylvanian rocks are gently tilted, but they are turned up steeply on the flanks of marginal folds such as the Sequatchie anticline and are much folded in the synclines within the Valley and Ridge province near Birmingham, Alabama. Moreover, detailed studies in the Cumberland Plateau of Tennessee indicate that wide areas of seemingly little disturbed Pennsylvanian beds have been displaced extensively along vThe term Arkansas basin, and the term McAlester basin mentioned below, refer to different parts of the same feature, lyingrespectively in Arkansas and Oklahoma. The single term Arkoma basin has recently come into wide use for this feature (C. C. Branson, 1956 a; Jordan, 1959). Bureau ofEconomic Geology, The University of Texas bedding-plane thrusts (Wilson and Steams, 1958, pp. 1290-1295). These thrusts may extend southwestward along the front of the Appalachian system, into Alabama. In the Arkansas and McAlester basins of Arkansas and Oklahoma the Pennsylvanian rocks have been folded into a succession of anticlines and synclines, parallel to those in the Ouachita Mountains and diminishing in intensity away from the mountains. Incipient metamorphism is indicated by carbon ratios in the coals (Hendricks, 1935, pp. 946-947) ;although the ratios vary much indetail they increase generally southward, as a result of pressures directed northward from the mountain area. Insubcrop inMississippi similar tilted, folded, and weakly metamorphosed clastic rocks probably form a belt of some width along the southwest flank of the Black Warrior basin; such a belt is indicated on the accompanying geologic map (PI. 3) although itis admittedly somewhat hypothetical. The clastic rocks penetrated by wells inthis belt have been assigned to the Pennsylvanian by many geologists, and no equivalents of the Mississippian Stanley and Jackfork formations have been reported. The rocks would thus seem to be the structural and stratigraphic counterparts of the Pennsylvanian rocks in the Arkansas basin immediately north of the main Ouachita system in the Ouachita Mountains of Arkansas and Oklahoma. The rocks in many of the same wells in Mississippi have been ascribed to a "Ouachita facies" by some geologists, but this can be true onlyinthe gross meaning of that term. In Attala, Neshoba, and Lauderdale counties, east-central Mississippi, wells which have penetrated these rocks (wells 35-38) lie northeast of an extensive subcrop belt of lower Paleozoic carbonate rocks which is here interpreted as an extension of the Appalachian Valley and Ridge province. Petrographic examination of rocks from one of these wells (well 35) by August Goldstein, Jr. (written communication, 1960) indicates that they have been weakly metamorphosed. Nevertheless, the rocks in this well, and others nearby, must be part of a structural element that is different from the Ouachita belt as itis understood farther west. Mississippian The Mississippian system crops out extensively along the front of the Appalachian system, as well as southeastward into the Valley and Ridge province and westward into the foreland area south of the Nashville dome. Along the front of the Appalachian system the Mississippian is about 1,200 feet thick and forms alternating thick limestone units and thinner sandstone and shale units (Butts, 1926, pp. 162-207). The Lower Mississippian is thin, and most of the sequence belongs to the Upper Mississippian, or Chester series, the latter being divided into many thin, widely traceable formations and members. Southeastward in the Valley and Ridge province the Mississippian is preserved in many downfolded or downfaulted remnants, which are more extensive than those of the Pennsylvanian in the same province. Here, the formations of the Chester series are partly or wholly replaced southeastward by the Floyd shale, which overlaps unconformably onto rocks as old as Early Ordovician. The Floyd is succeeded by the more sandy Parkwood formation, which apparently bridges the Mississippian- Pennsylvanian boundary. The Floyd and Parkwood together are broadly of the same age as, and occupy a stratigraphic position similar to, the much thicker Stanley shale and Jackfork sandstone of the Ouachita Mountains (see below),but published descriptions afford little evidence as to what extent the facies of the formations in the two regions differ from or resemble each other. 15 15 H.D. Miser (written communication, 1960) reported that the Parkwood formation, where examined by him, resembles the Stanley formation of parts of the Ouachita Mountains, and that it contains few or no beds resembling the Jackfork sandstone. The Ouachita System Mississippian strata with about the same thickness and age as those along the front of the Appalachian system extend westward on the outcrop and southwestward into the subcrop in the Black Warrior basin, where they have been penetrated in numerous wells in the gas-producing area centering around Monroe County, Mississippi (Everett, 1953; Welch, 1959). Here, many beds can be correlated with those on the outcrop, but the rocks change from dominant limestone to dominant shale, much of which is classed as Floyd shale. The lower part of the overlying sandstones probably includes equivalents of the Park- wood formation (Mellen, 1947, p. 1813; Dott and Murray, 1954, p. 6),although in some published sections they are not differentiated from the Pottsville formation (Welch, 1959). In the Ouachita Mountains the Upper Mississippian (Meramec and Chester) is represented by the Hot Springs sandstone, Stanley shale, and Jackfork sandstone (pp. 34-37).The upper part of the underlying Arkansas novaculite includes beds of Early Mississippian age, but most of Early Mississippian time is represented by a hiatus. The Hot Springs is a thin, local deposit, but the Stanley and Jackfork extend through most of the mountain area and are as much as 20,000 feet thick. Toward the west in Oklahoma the Stanley and Jackfork wedge out before reaching the structural front of the mountains (Hendricks et al., 1947), but the abruptness of the wedging has probably been exaggerated by thrust slicing. Farther east in Arkansas the Stanley and Jackfork have been identified beneath the Atoka formation in wells drilled in the Arkansas basin as much as 30 miles north of the structural front (well12, White County) (Maher and Lantz, 1953). The basin in which they accumulated thus had different outlines from the area which later was strongly deformed intheOuachita Mountains. The Stanley shale and Jackfork sandstone probably extend in subcrop south from the Ouachita Mountains for at least 25 miles beneath the Gulf Coastal Plain, beyond which they are overlapped by Eagle Mills formation and their farther extent is unknown. Here, rocks of Ouachita facies have been penetrated (including wells 42, 43, 44) which, where descrip tions are available, are indurated sandstone and black shale. Rocks of this sort are reported as far east as Grant and Cleveland counties, Arkansas (Spooner, 1935, p.334; Weeks, 1938, p. 962). They resemble the Stanley and Jackfork, and perhaps the Atoka formation. In subcrop east of the Ouachita Mountains, beneath the Mississippi embayment, the Stanley and Jackfork have not been identified, and they may be partly or wholly cut out along the strike by convergence of structural belts. Devonian to Cambrian — Appalachian system. Inthe Valley and Ridge province of the Appalachians the base of the Paleozoic sequence is quartzite and shale of Early Cambrian and Cambrian(?) age (Chilhowee group of Tennessee and Weisner formation of Alabama and Georgia) .This is followed by a great carbonate sequence, nearly 9,000 feet thick, extending from the Lower Cambrian into the Lower Ordovician, and in places into the Middle Ordovician. The Rome and Conasauga formations in the lower part of the carbonate sequence include inter- bedded shale, but the Knox group and related units of Late Cambrian and Early Ordovician age form an uninterrupted body of limestone and dolomite. The Middle and Upper Ordovician series are thin inmost of Alabama and Georgia, but they thicken in Tennessee where they contain much shale and fine-grained sandstone in the southeastern outcrop belts. The Silurian and Devonian are rather inconsequential throughout the southern Appalachians, although red ironores of Silurian age are of economic interest in the Birmingham district, Alabama. Subcrop extensions of Appalachian sys — tem. Lower Paleozoic carbonate rocks like those in the Valleyand Ridge province Bureau ofEconomic Geology, The University of Texas have been penetrated beneath coastal plain deposits in wells drilled southwest of the exposed Appalachian region in Greene, Marengo, and Sumter counties, west- central Alabama, and in Leake, Newton, Neshoba, and Scott counties, east-central Mississippi. The southernmost Paleozoic penetration in Mississippi is in carbonate rocks of early Paleozoic age (wells 51 and 52, Newton County). The only fossils which have been reported from wells drilled in the carbonate rocks are of Middle Ordovician and Silurian age, according toidentifications by G.A.Cooper (well 55, Marengo County, Alabama; well 45, Leake County, Mississippi) .However, no fossils have been observed in much of the sequence and itmay be largely of Late Cambrian and Early Ordovician age; the Knox group and related carbonate rocks of these ages are poorly fossiliferous on the outcrop. The lower Paleozoic carbonate rocks penetrated in Alabama lie on an obvious southwestward extension of those in the Appalachian Valley and Ridge province. The structural relations of the carbonate rocks penetrated in Mississippi are less certain, as they occur in a belt trending northwest parallel to the Ouachita system. They may be on the crest of an independent upliftinfront of that system, but more likely they form an extension of both the subcrop belt in Alabama and the Valley and Ridge province of the outcrop (McKee et al.,1956, pi. 2).Ifthis belt of carbonate rocks is a continuous feature, it "turns the corner" from the Appalachian trend in Alabama into the Ouachita trend inMississippi. In central Mississippi the belt apparently wedges out, either from a westward change in stratigraphic facies or from a structural convergence of the belts on each side of it. Ouachita system. —Cambrian to Devonian rocks emerge intheOuachita Mountains in its central anticlinorium, as well as in outlying anticlines and fault blocks, and are described inmore detail elsewhere in this publication (pp. 25—34).Briefly, they are of facies quite different from those of rocks of the same age inthe Valley and Ridge province in the Appalachians, being a sequence of graptolite-bearing shales and slates, interrupted atintervals by units of sandstone and chert, mainly of Ordovician and Silurian age, which are topped by the siliceous rocks of the Arkansas novaculite, of Devonian and Early Mississippian age. Cambrian to Devonian rocks of Ouachita type are identifiable in wells in Arkansas drilled a short distance east of their outcrops in the Ouachita Mountains (well 56, Pulaski County), but they have not been recognized with certainty farther east. Suwanee basin.16—Innorthern Florida and adjacent parts of Georgia and Alabama, Mesozoic rocks are underlain by Paleozoic rocks at depths of 2,700 to 8,000 feet below sea level (Applin, 1951, pp. 13-15) .These form the Suwanee basin, a triangular area of about 25,000 square miles. The Paleozoic rocks are unmetamorphosed, dip at low angles, or lienearly horizontal. Wells which have penetrated them are widely spaced, so that their gross structure and sequence are poorly known. They adjoin plutonic, metamorphic, and volcanic rocks of the Piedmont province of the Appalachian system on the north with an undetermined relation; they adjoin other crystalline and volcanic rocks on the south, against which they may be down- faulted. Juxtaposition of rocks of different ages orlithologies within the basin may be caused by other faults, whose pattern is as yet undetermined. The Paleozoic rocks are probably not less than 3,000 feet thick, and may exceed 6,000 feet, but the sequence is conjectural because most wells penetrate only one lithologic unit, and no wells penetrate more than two. However, many of the well cores are fossiliferous, and contain various associations of mollusks, brachiopods, trilobites, ostracodes, and other invertebrates ;graptolites have been found in one 18 Originally named the Suwanee River basin by Braunstein (in Frascogna, 1957, p. 1;Braunstein, 1958a), but the shorter term seems adequate and preferable. The Ouachita System well but not in the remainder (Bridge and Berdan, 1951, 1952). Microscopic study has also revealed the presence in some well cores of rich assemblages of chitinozoans and plant spores (Schopf, 1959) . Sandstone probably forms the lowest unit and is at least as old as Early Ordovician; some wells have penetrated it to a thickness of more than 2,000 feet, and one well near the southeastern border of the basin (Sun Oil Company No. 1 H. N. Camp, Marion County, Florida, beyond the map area) drilled through itinto an older unit of volcanic agglomerate. Most of the other strata which have been penetrated are black or dark gray shales, some with sandy laminae, which from well to well contain faunas of Early Ordovician, Middle and possibly Late Ordovician, Silurian, and Middle Devonian ages (Jean Berdan, writtencommunication, 1960).The young est strata may be those in Jackson County, Florida (well62),which are red and gray sandstone and shale of fresh-water or terrestrial origin that contain plant fragments and spores of probable Middle Devonian age. The stratigraphic and tectonic affinities of the Paleozoic rocks of the Suwanee basin are obscure. Lithologically, they are very different from the dominant carbonate rocks of the same ages in the Valley and Ridge province on the opposite side of the Appalachian system, but they somewhat resemble the slaty and sandy rocks of those ages in the Ouachita system. However, their faunas are like those of neither of these provinces nor do they agree closely with those of any other faunas in North America; some of the fossils have their nearest affinities with those in parts of Europe (Jean Berdan, written communication, 1960). Presence of Middle Devonian^) nonmarine deposits suggests that Paleozoic deposition terminated inthe Suwanee basin much earlier than it did in either the Appalachian or Ouachita basins. The writer (King, 1950, pp. 657-658) suggested that the Suwanee basin and its Paleozoic rocks form the southeastern flank of the Appalachian system, but their relations to the Appalachian rocks and structures are uncertain; their map pattern suggests that they extend transversely across the strike of the rocks of the adjacentj acent Piedmont province. Relations of the basin to the Ouachita system are even more remote, as the nearest proved part of that system is several hundred miles to the northwest, inMississippi. Weakly Metamorphosed Rocks The rocks shown in this category on the geologic map (PI.3) are so classed mainly because of their metamorphic and structural character, rather than because of their stratigraphic position or age. Those in the Appalachian system include rocks of both late Precambrian and Paleozoic ages; the age of those in the Ouachita system is undetermined but is probably Paleozoic. Allthese rocks share a weak to moderate metamorphism and are thus intermediate in character between the unmetamorphosed rocks of the forward parts of the Appalachian and Ouachita systems and the thoroughly metamorphosed and plutonized inner parts. Appalachian system. —In the Appalachian system weakly metamorphosed rocks form the Ocoee and Talladega belts, lying between the unmetamorphosed Paleozoic rocks of the Valley and Ridge province and the metamorphosed rocks of the Piedmont province. The Ocoee belt is in the BlueRidge province, but thisprovince ends as a physiographic feature in northwestern Georgia, so that the Talladega belt farther southwest is physiographically part of the Piedmont province. The rocks of both the Ocoee and Talladega belts form a separate thrust slice or slices, which are faulted over the Paleo zoic rocks of the Valley and Ridge province along a discontinuity known in the north as the Great Smoky fault and farther south as the Cartersville fault. The more metamorphosed rocks of the Piedmont province are in turn faulted over the weakly metamorphosed rocks along the Whitestone fault Bureau ofEconomic Geology, The University of Texas on the southeast side of the Ocoee belt, and along a fault which follows the Hillabee sill along the southeast side of the Tal ladega belt. The Ocoee belt, from Cartersville, Georgia, north into Tennessee and North Carolina, is formed mainly of the Ocoee series, a mass of fine to coarse clastic rocks more than 30,000 feet thick (P. B. King et al., 1958, pp. 949-951). Along the northwest side of the belt the series lies in stratigraphic sequence beneath fossiliferous rocks of Early Cambrian age, hence the Ocoee itself is probably of late Precambrian age. The rocks of the Murphybelt, which borders the Ocoee belt on the southeast, may be equivalent to rocks of proved Cambrian age northwest of the Ocoee belt, but they are unfossiliferous. In western North Carolina, in the extreme northeast corner of the map area, the Ocoee series lies unconformably on metamorphic and plutonic rocks of an earlier Precam brian age (pp. 93-94). The Talladega belt extends southwestward from Cartersville, Georgia, across Alabama to the edge of the Gulf Coastal Plain and has been described by Griffin (1951, pp. 28-48), Butts (1926, pp. 4961), and earlier authors. Parts of the belt in Alabama were examined in reconnaissance in the spring of 1961 by the writer, R. B. Neuman, and R. A. Laurence, and their observations largely confirm the published accounts. In Alabama the rocks of the Talladega belt form a southeast-dipping sequencewhose thickness Butts estimates tobe about 30,000 feet. Earlier accounts have suggested that the belt contains equivalents of the Precambrian Ocoee series farther northeast, but ifpresent these are minor. The greater part of the sequence is prob ably of Paleozoic age, although the rocks are more metamorphosed and are of a more clastic facies than the Paleozoic rocks in the Valley and Ridge province which adjoin them on the northwest. The lower part of the sequence is a great body of slates and phyllites, in part tuffaceous and containing rare limestone lenses, which is probably of early Paleozoic age. East of Birmingham this body is followed by the persistent, ridge-forming Cheaha sandstone, from which crinoid stems have been reported and which is probably of middle Paleozoic age; its equivalent south of Birmingham may be the Butting Ram sandstone. The Butting Ram south of Birmingham is overlain by the Jemison chert which contains brachiopods of Devonian age. The Cheaha east of Birmingham is overlain by the Erin slate which contains fossil plants, reported to be of Pennsylvanian age. Pennsylvanian or other later Paleozoic rocks may be preserved else where in the belt; in cuts on the new Birmingham-Montgomery freeway, near the edge of the coastal plain south of Jemison, King, Neuman, and Laurence observed sandstone and carbonaceous shale with interbedded sheared coal; fossil bryozoans have been reported in these rocks by local collectors. The sequence of weakly metamorphosed Paleozoic rocks of the Talladega belt is of interest in the present discussion, because it might be an Appalachian analogue of the sequence of Paleozoic rocks in the Ouachita Mountains. Both sequences approach a eugeosynclinal facies and are dominantly clastic, but from what is pressently known the succession of units in the Talladega belt is not notably like that in the Ouachita Mountains. The rocks of the Talladega belt in the Appalachian system extend southwestward intosubcrop beneath the Gulf Coastal Plain but have not there been identified; however, wellcontrol is very sparse where they might occur. On the geologic map (PL 3), their subcrop extension is indicated theoretically. Ouachita system. —Very weakly to weakly metamorphosed rocks of unknown but probable Paleozoic age have been penetrated inhalf a dozen wells inabelt extending through Arkansas County, Arkansas, and Bolivar County, Mississippi, to Attala County, central Mississippi. Detailed re The Ouachita System ports are available on the rocks penetrated in only a few of these wells, the remainder being reported as of "Ouachita" facies. In one well in Carroll County (well 71), according to Weaver (p. 159 and fig. 7), the sharpness ratio of the clays exceeds 5.0, "which is within the range of values of low-grade metamorphism." Two wells in Attala County to the south (wells 72 and 73) penetrated black slates, siliceous slates, and cherts that have undergone weak to low-grade metamorphism and contain much chlorite and sericite but the sharpness ratio of their clays is less (fig. 7). Except for a few sponge spicules in the siliceous rocks, no fossils have been observed, but the general aspect of the rocks is like that of the older Paleozoic formations of the Ouachita system farther west. These very weakly to weakly metamorphosed rocks may lie on an extension of the central anticlinorium of the Ouachita Mountains to the west as suggested on the map (PI.3),ortheymaybepartsofthrust slices of the inner zones of the Ouachita system. North of the Ouachita Mountains a wide band of Mississippian Stanley shale and Jackfork sandstone intervenes between the older Paleozoic rocks of the anticlinorium and the deformed Pennsylvanian rocks of the Arkansas basin;here the rocks are strongly folded, but available evidence suggests that faulting is minor. By contrast, in central Mississippi the weakly metamorphosed rocks appear to be juxtaposed against deformed Pennsylvanianrocks, suggesting an elimination of some of the structural belts of the outcrop area, probably by thrust slicing. The extent of the weakly metamorphosed rocks farther south in the Gulf Coastal Plain is undetermined, as in this direction the pre-Mesozoic basement is generally beyond reach of drilling. In Cleveland County, Spooner (1935, pp. 392-394) reported a penetration of shale, limestone, and possibly chert, intruded and metamorphosed by peridotite. Two wells in the Smackover oil field of southern Arkan sas (wells 74, 75) are reported to have entered argillaceous rocks beneath the Jurassic (?) Werner formation, intruded and altered by diabase. The affinities of these rocks to those farther north is uncertain, and their metamorphism may result from proximity to the mafic intrusions. Metamorphic and Plutonic Rocks This unit is shown on the geologic map only in the Piedmont province of the Appalachian system and in its subcrop extensions to the southeast and southwest. The rocks so mapped share an extreme metamorphism and plutonism but are heterogeneous in detail, both in lithology and degree of metamorphism (Crickmay, 1952, pp. 50-52; P. B. King, 1955a, pp. 343-363). Extensive areas are formed of monotonous bodies of gneiss and schist, commonly termed "Carolina gneiss" in early reports, but in places there are beds or units of quartzite and marble, and on the southeast side of the belt (mainly in the Carolina slate belt, northeast of the map area) are extensive bodies of volcanic rocks and as sociated slates. The rocks of the Wacoochee belt, near the southeast edge of the exposures in the Piedmont province of Alabama and Georgia, include the thick, persistent Hollis quartzite and the overlying Chewacla marble (Hewett and Crickmay, 1937, pp. 26-30).Embedded in the metamorphic rocks are pods and plutons of all sizes, composed of felsic plutonic rocks, varying fromfoliated tomassive. Inplaces, mainly northeast of the map area, are plutons of more mafic rocks. In the Blue Ridge province in the extreme northeast part of the map area, between the Ocoee belt and the Brevard belt, the metamorphic and plutonic rocks are known to be unconformable beneath the Ocoee series (P. B. King et al., 1958, p. 963), hence to be of an earlier Precambrian age; this is confirmed by a few radiometric determinations. Elsewhere in the Piedmont province, mainly southeast of the Brevard belt, the age of the metamor Bureau ofEconomic Geology, The University of Texas phic rocks is less certain. They may be partly or whollyof Paleozoic age, although no fossils have been found in them. The plutonic rocks which invade them have been dated radiometrically as between 400 and 250 million years, hence are of early to middle Paleozoic age. No radiometric dates of either Precambrian or late Paleozoic age have been reported from the Piedmont province southeast of the Brevard belt. The gross structure of the metamorphic and plutonic rocks is little known and is probably complex. Inmany areas the foliation in the gneiss and schist dips rather gently, and the latest structures imposed on them may have been open anticlinoria and synclinoria. In places, however, are zones of intense shearing and cataclasis. The narrow Brevard belt crosses the province witha nearly straight orgently curved trend and must be a major structural element; its true nature has not been proved, but extensive strike-slip movements may have occurred along it.17 Metamorphic and plutonic rocks like those in the exposed parts of the Piedmont province have been penetrated by wells drilled through the coastal plain deposits in parts of southern Georgia and Alabama (wells 76-88; see also Applin, 1951, pp. 5-11). The rocks are variously described as schist, gneiss, and granite, but the wells are not spaced closely enough to determine details of the bedrock pattern. Insoutheastern Georgia along the north side of the Suwanee basin a well in Atkinson County (well 88) and another to the east in Camden County penetrated altered rhyolitic volcanic rocks (Applin, 1951, pp. 8-11). These rocks are comparable to those penetrated in half a dozen or more wells on the south side of the Suwanee basin in central Florida. These rhyolitic volcanic rocks differ greatly from the Triassic mafic igneous rocks of the same area, 17 Further details on probable strike-slip displacements alongthe Brevard belt are given in a manuscript now in preparationby J. C. Reed, Jr., H. S. Johnson, Jr., Bruce Bryant, and W. C. Overstreet, of the U. S. Geological Survey. These authors record a prominent horizontal linear structure in the metamorphic rocks of the belt inNorth and South Carolina. and their alteration suggests that they are much older. They may underlie the Paleozoic sedimentary rocks of the Suwanee basin, as in one wellincentral Florida they are overlain by quartzitic sandstone of probable Ordovician age (Applin, 1951, p. 14). They are perhaps related to volcanic rocks of the Carolina slate belt in the exposed Piedmont province. The age of the latter is unknown but is generally believed to be of some undetermined part of the Paleozoic. Geophysical Data 18 Geophysical data on the eastern part of the Gulf Coastal Plain supplement the well data and extend the structural picture downward beyond limits of control by drilling. However, results of many past geophysical investigations are unpublished, and results of other investigations now in progress are not yet available. Woollard (1949, 1958) has summarized some of the results of gravity and seismological studies, and Lyons (1950) has published a gravity map of the United States which includes significant information on the region here treated. Results of a more detailed magnetic survey of Florida have been presented byE.R.King(1959). In the eastern United States, gravity maps show a weak positive anomaly (less than plus 20 milligals) along the axes of the Cincinnati and Nashville domes, a strong negative anomaly inthe Blue Ridge province of the Appalachians (more than minus 100 milligals innorthwestern North Carolina), and prevailing positive anomalies in the Piedmont province (plus 20 to 40 milligals from North Carolina to New England) .Southwestward, within the area here treated (fig. 4), the negative anomalies of the Blue Ridge province are concentrated near the Brevard belt, suggesting a fundamental and deep-seated origin for that structure. Northwest of it,in the Blue Ridge and Valley and Ridge provinces, 18 Inpreparation of this discussion the writer is indebted to Isidore Zeitz, Martin Kane, Andrew Griscom, H. K. Joesting, and E. R.King, geophysicists of the U. S. Geological Survey, who have made many helpful suggestions. However, the opinions expressed herein are solely those of the writer. The Ouachita System gravity trends extend diagonally across the trends of the surface structures, confirming the superficial nature of the deformation in those provinces that has been de duced from geological evidence. In the south-central United States gravity maps show well-marked positive anomalies (as much as plus 40 milligals) along the axes of the Wichita, Arbuckle, and related uplifts, reflecting the presence of basement rocks at or near the surface. By contrast, the salient of the Ouachita Mountains which centers in southeastern Oklahoma shows a major negative anomaly (more thanminus 100milligals). These belts of strong positive and negative gravity disappear in the Atlantic and Gulf Coastal Plains and Mississippi embayment, where there are weaker and less well- defined positive and negative areas, some of regional extent, but none showing clear relations to the trends of either the Appalachian or Ouachita systems. Inplaces the change in gravity pattern along the edge of the coastal plain is abrupt, resulting in steep gradients such as those at the edge of the Mississippi embayment in the southeastern part of the Ouachita Mountains of Arkansas and at the southwest end of the exposed Brevard belt in Alabama. The trends of earthquake epicenters associated with the Appalachian system likewise disappear near the edge of the coastal plain (Woollard, 1958, p.1149).Of more obvious origin than the larger gravity features in the coastal plain are small areas of positive gravity anomaly. Those at Jackson, Mississippi, and south of Little Rock, Arkansas, coincide with intrusive bodies in the Mesozoic orolder rocks. Others insouthern Alabama and Georgia probably have a similar origin. In northern Florida near the Suwanee basin narrow but pronounced gravity and magnetic belts trend northeastward (E. R. King, 1959, pp. 2852-2853), reflecting either a grain in the basement parallel to that inthe Piedmont province of the Appalachian system, fault blocks in the Paleozoic and basement rocks of the basin, or both. In southern Florida these belts terminate against a northwest-trending gravity and magnetic grain. This grain may be related to a southeastward prolongation of the Ouachita system and to a southwestward truncation of the Appalachian system as suggested by E. R. King (1959, pp. 2852-2853), but it coincides inposition with the pronounced southwestward thickening of Mesozoic and younger rocks insouthern Florida. Meaning of the gravity, magnetic, and seismic patterns of the region remains elusive. The large negative gravity anomalies (more than minus 100 milligals) in the Appalachian and Ouachita areas indicate the presence of rock masses of less than normal density. Inpart at least, these are bodies of sedimentary rocks that were originally thick and that have been further thickened tectonically, as in the Ocoee belt and the belt of Stanley, Jackfork, and Atoka formations. However, the magnitude of the anomalies would require masses of rock of less than normal density that are 25,000 to more than 100,000 feet thick (Martin Kane, written communication, 1960),so that the density difference must also extend into the basement and into the crust. Disappearance of the well-marked positive and negative trends of the Appalachian and Ouachita systems in the coastal plain area is paradoxical, as drill data indicate that both systems extend unchanged for long distances beneath the coastal plain cover. A geologist is tempted to suspect that this cover in some manner exerts a damping effect on the geophysical manifestations of the underlying rocks; however, for negative anomalies of the magnitude of those in the Appalachian and Ouachita systems this would require a cover much thicker than 10,000 feet (Martin Kane, written communication, 1960). Geophysical considerations thus suggest a notable difference in the nature of the crust between that in the exposed Appalachian and Ouachita systems and that of the coastal plain area. Systems Relations Between Ouachita and Appalachian Evidence and inferences so far presented contribute to a solution of the problem of the relations between the Ouachita and Appalachian systems but are insufficient to solve it, as data are stilllacking inmany critical areas. Nevertheless, some sugges tions can be made. The Ouachita and Appalachian systems are now interrupted by a cover of younger coastal plain deposits, but there is little doubt that they are parts of an originally continuous belt of deformation, whatever the precise nature of their junction. The writer believes that the Appalachian system is too broad and massive a structure to terminate abruptly southwestward, despite its poor geophysical expression in the coastal plain area. The magnitude of the less completely exposed Ouachita system is not as obvious, but many considerations suggest itisequally broad and massive. These inferences seem to be confirmed by available drill data in the coastal plain area. Sediments laid down on the foreland during the deformational epoch are continuous from one system to the other. Both the Mississippian and Pennsylvanian systems thicken and become more clastic, not only southeastward toward the Appalachian system and southwestward toward the Ouachita system but also southward into the intervening Black Warrior basin. So far as they can be traced, structural belts of the Ouachita and Appalachian systems are continuous beneath the coastal plain cover, being most accordant in the foreland area and increasingly discordant toward the inner parts of the systems. The Mississippian outcrop and subcrop belt, well out in the foreland, pursues a gentle curve from the strike of one system to that of the other. The Pennsylvanian outcrop and subcrop belt along the edge of the systems forms a sharper curve from the strike of one to that of the other and expands at the angle between them into the triangular Black Warrior basin. The belt of lower Paleozoic carbonate rocks extends westward from the Valley and Ridge prov ince of the Appalachians into a belt paral lel with the Ouachita system in east-central Mississippi but bends at nearly rightangles inpassing from the trend of one system to that of the other. Ifany connection exists between the belts of weakly metamorphosed rocks farther southeast and southwest in the two systems, their junction must be at an even more acute angle. The writer (King, 1950, p. 668) suggested that the inner, eugeosynclinal, weakly metamorphic and metamorphic belts of the Appalachian system continue westward into the outer belt of the Ouachita system, curving from one trend to another, and eliminating by thrusting the outer miogeosynclinal belt as they do so. Alternatively, E. R. King (1959, p. 2853) has suggested on the basis of geophysical evidence that the Ouachita belt may cut off transversely the southwest end of the Appalachian belt and continue independently into southern Florida. Both suggestions are probably oversimplifications. Amore fruitfulpossibility has been suggested by Woollard (1949, p. 1932), that the junction is comparable to those of island arcs and deep trenches at sea, which may be mobile belts in an early stage of development. From what is known of the island arcs and trenches, their intersections are most complex, with the two trends crossing each other but neither extending far beyond their intersection. Very likely a similarly complex intersection occurs between the inner parts of the Ouachita and Appalachian systems, in the deeply buried area in southern Mississippi and Alabama. The inner part of the Ouachita system differs from the inner part of the Appalachian system in its post-orogenic history. Ithas been strongly susceptible to subsidence and has been deeply covered by younger coastal plain deposits, whereas Bureau ofEconomic Geology, The University of Texas the inner part of the Appalachian system is stillpartly exposed and at most iscovered by thin younger deposits. West of the Mississippi River the edge of the area of deep subsidence corresponds closely to the edge of the inner zone of the Ouachita system. East of the Mississippi River the edge of the area of deep subsidence extends southeastward, beyond the point where the Ouachita and Appalachian systems should intersect, at least as far as southern Florida (E.R.King, 1959, p.2848). Gravity data suggest a fundamental difference between the crustal material beneath the Gulf Coastal Plain, especially in the area of deep subsidence, and that in the Appalachian area. Passage from the characteristic features of the Appalachian system to those of the Ouachita system may result more from such a change in crustal material than from a structural truncation. During the orogenic phase the metamorphic rocks of the Piedmont province of the Appalachians were extensively granitized and were pervasively injected by felsic plutonic bodies. A similar history has been inferred by Flawn (p. 105) for the inner part of the Ouachita system far to the west, beyond the Gulf Coastal Plain in northeastern Mexico. Less is known of the metamorphic and plutonic history of the inner part of the Ouachita system in the intervening area, where it has subsided deeply beneath coastal plain deposits. Pos sibly this part was less pervasively injected by felsic plutonic bodies and was less completely converted to sialic crust than the parts tothe east and west. An extreme alternative, still not to be dismissed, was suggested nearly 30 years ago by Van der Gracht (1931a, pp. 14091051) —that the original felsic or rialic inner part of the Ouachita system has broken away by drift during a postorogenic distention of the Gulf and Caribbean areas. This inner part, and perhaps also the original junction of the Appalachian and Ouachita systems, may thus now be found somewhere in Central America or northern South America. The area of supposed great subsidence of the inner part of the Ouachita system in the Gulf Coastal Plain would instead be the void produced by drift,over whose simatic floor sediments were prograded to the present edge of the continental shelf during Mesozoic and Cenozoic time. The Ouachita Structural Belt in Mexico Peter T. Flawn — General remarks. The rocks and structures of the frontal zone of the Ouachita belt exposed in the Solitario uplift of Trans-Pecos Texas are only 15 miles from the Rio Grande and they strike southwest toward it.From the trend of the Ouachita belt as mapped inTexas (PL 2) and from scattered outcrops and wells in northern Mexico, the Ouachita system must extend southwestward and southward intoMexico. However, itis poorly known there because of the thick concealing cover of Cretaceous Exposures of Pre-Mesozoic Outcrops of pre-Mesozoic rocks in Chihuahua, Coahuila, Nuevo Leon, Tamaulipas, northern Zacatecas, and northern San Luis Potosi are shown on figure 5. Undoubtedly, additional exposures of pre- Mesozoic rocks will be discovered with further geologic mapping. — Sierra del Carmen. Outcrops of pre- Mesozoic metamorphic rocks in the Sierra del Carmen near Boquillas, Coahuila, were discovered by C. L.Baker (Bose, 1923, p. 133 •**£Baker > 1935 > P-146) and nave been described by Flawn and Maxwell (1958). The metamorphic rocks are thinly inter- layered very fine-grained graphitic chloritic sericite schist (or phyllite), fine- grained calcite marble, and fine-grained metaquartzite with gradational types including calcareous schist, schistose or phylliticmarble, and phyllitic metaquartzite. Allhave been subjected to low-grade metamorphism with a high shearing component. Early quartz veins have been sheared, broken, and drawn out into knots or augen; post-shearing quartz veins cut across earlier structures. The rocks are foliated, and commonly the foliation is crinkled and contorted. Determinations of the age of the mica are inconclusive and yielded divergent ages of 240 and 370 million years (George Edwards, Shell De- and younger rocks, complications introduced by strong Laramide deformation, paucity of well control, and general lack of information about the widely separated areas of exposed pre-Mesozoic rocks. Some of the problems of Paleozoic tectonics in Mexico have been discussed by Kellum et al. (1936),R.E.King(1944),Still(1946, 1947), Eardley (1951), P. B. King (1951), Acevedo and Marquez (1952), De Cserna (1956) ,De Cserna and Diaz G. (1956), and Flawn and Diaz G. (1959). Rocks in Northern Mexico velopment Company, personal communication, 1959).The results suggest that the metamorphism occurred during Paleozoic time but do not date the rocks themselves. The rocks are like those encountered in wells in southwest Texas, in Kinney, Val Verde, and Terrell counties. The original sequence may have been thin-bedded impure dark shale and limestone similar to the Marathon formation in the Marathon and Solitario uplifts to the north. Probably these rocks are early Paleozoic in age (p. 81). The exposure in the Sierra del Carmen is the only known outcrop of the interior zone of the Ouachita belt (p. 169 and PI.2). Sierra del Cuervo. —Paleozoic exposures in the Sierra del Cuervo, about 18 miles north of the City of Chihuahua, have been described by Acevedo and Marquez (1952), De Cserna and Diaz G. (1956, p. 47),and Flawn and Diaz G. (1959). Paleozoic rocks in the Sierra del Cuervo are interbedded sandstone and slaty shale containing sporadic limestone lenses. These are strongly deformed, highly sheared, and very weakly to weakly metamorphosed with incipient foliation and local well-developed lineation. The rocks The Ouachita System zoic structures in the Solitario uplift and Marathon Basin in Texas (Ernst Cloos, in Log of Cd. Chihuahua to Sierra del Cuervo field trip, Int. Geol. Cong. XX,Excursion A-13, and Teodoro Diaz G., personal com munication, 1958) . Placer de Guadalupe area. —Paleozoic rocks crop out near Placer de Guadalupe about 60 miles northeast of the city of Chihuahua and have been described by King and Adkins (1946), Still (1946, 1947), De Cserna and Diaz G. (1956, pp. 37-39), and Flawn and Diaz G. (1959).Luther W. Bridges is currently studying the area as part of a doctoral dissertation problem at The University of Texas; preliminary results of this study have been reported (Bridges and DeFord, 1961). Paleozoic rocks exposed in the area of Placer de Guadalupe include about 4,000 feet ofOrdovician, Silurian(?),Devonian, Mississippian, Pennsylvanian, and Permian strata. Most of the sequence is com posed of shaly and cherty' limestone, locally fossiliferous, of shelf or platform facies. The pre-Carboniferous rocks aggregate about 1,800 feet in thickness. In the upper part of the sequence there is about 1,600 feet of Permian (?) rock consisting of dolomitic pisolitic reef (?) limestone containing Wolfcamp fossils and overlain by nonfossiliferous siltstone and conglomerate. Thus, the youngest Paleozoic rocks in the area are Wolfcamp or possibly Leonard in age. The rocks have undergone both pre- Mesozoic and Laramide deformation and hence are much folded. According to Bridges and DeFord (1961, p. 103) "...regional metamorphism has not proceeded farther than recrystallization of the limestone." Analysis of the pre-Mesozoic structure suggests that these rocks are withinor close to the northwestern margin of the Ouachita structural belt. — Las Delicias-Acatita area. The Las Delicias-Acatita area, located in southwestern Coahuila 60 miles north-northwest of Torreon, has been described by Haarmann (1913), Bose (1921), R. E. King (1934), Kellum et al. (1936), Kelly (1936),R.E.Kingetal. (1944),Humphrey (1955), and Newell (1957) ;the significance of these exposures in relation to regional structure has been discussed by the original geologists in the area (above) and by P. B. King (1951), Eardley (1951), De Cserna (1956), and Flawn and Diaz G. (1959). The Paleozoic sequence in the area is as much as 12,000 feet of interlayered sedi mentary and volcanic rocks including phy'llite, slate, shale, quartzite, sandstone, graywacke conglomerate, fossiliferous limestone, lava, and tuff; the sedimentary rocks are steeply folded and intruded by granite and granodiorite. Degree of metamorphism varies in different parts of the area, ranging from incipient to weak with hornfels developed locally as a contact phenomenon. The sedimentary rocks range from Late Pennsylvanian(?) to Permian in age and include beds of Wolfcamp ( ? ), Leonard^ Guadalupe, and Ochoa(?) age, although Leonard and Guadalupe beds make up most of the section and are much thicker than comparable sequences in Texas; the facies is geosynclinal. The granite is either Late Permian or post- Permian and pre-Cretaceous (Albian) in age. Caopas-Rodeo area. —About midway be tween Parras, Coahuila, and Gruxiidora, Zacatecas, pre-Mesozoic rocks are exposed in the core of a northwest-trending fold. This area is briefly discussed byDe Cserna (1956, pp. 13-14 and map) who credits C. L.Rogers and others (inpreparation) with the original work. There is an older sequence of mica schist with thin beds of quartzite and conglomerate (Caopas series) and a younger sequence of interlayered phyllite and altered volcanic rocks (Rodeo formation). The Rodeo isunconformably overlain byMesozoic rocks of the Huizachal group. The Caopas series and Rodeo formation are tentatively considered to be Permo-Carboniferous (Rogers etal.,inpreparation). Bureau ofEconomic Geology, The University of Texas The weakly metamorphosed sedimentary and volcanic rocks inthis area maybe part of the Paleozoic orogenic terrane. — Galeana area. About 98 highway miles south and west of Saltillo and 7 or 8miles from the town of Galeana (near San Pablo), Nuevo Leon, road cuts expose jointed and faulted sandstone (graywacke) intruded by small bodies of fine-grained igneous rock and apparently in fault contact with gypsum of pre-Oxfordian age. These rocks may be Paleozoic or they may be part of the Triassic La Boca formation (R. B. Mixon, personal communication, 1959). Sierra de Catorce.— Baker (1921, 1922) described metamorphic rocks in the Sierra de Catorce innorthern San Luis Potosi as an older series of sericitic and talcose schists and volcanic rocks and a less metamorphosed series of sandy, shaly, and possibly tuffaceous rocks interbedded with conglomeratic quartzites; both are transversed by quartz veins. De Cserna (1956, p. 13) believed that these rocks are upper Paleozoic. Cd. Victoria area.—Pre-Mesozoic rocks are exposed in three areas northwest and west of Cd. Victoria in central and western Tamaulipas. Immediately west and northwest of the city the frontal fold of the Sierra Madre Oriental has been breached by Novillo,Peregrina (La Presa),Caballeros, and La Boca canyons, exposing crystalline rocks, probably Precambrian in age, and Paleozoic rocks. The pre-Mesozoic rocks of this area have been discussed by Baker (1921, 1936), Girty (1926), Muir (1936), Heim (1940), P.B.King(1951), Humphrey and Diaz G. (1953), Bodenlos et al. (1956, p. 63), Chandler (1957), and Flawn and Diaz G. (1959). Althoughthere are many different kinds of crystalline rocks in the area, preliminary reconnaissance suggests there are two main groups: (1) massive light-colored garnetiferous gneiss and (2) dark mica schist, locally graphitic. Strongly deformed slightly metamorphosed Paleozoic rocks are faulted against the crystalline rocks in a number of fault blocks. For many years ithas been known that a thick sequence of interlayered dark shale and sandstone of orogenic (flysch) facies containing Mississippian fossils at the bottom and Permian (Leonard) fossils in the upper part occurs in Peregrina Canyon. Recently, Jose Carrillo B. of Petroleos Mexicanos has discovered in Caballeros Canyon 19 Silurian and Devonian rocks and older sedimentary rocks that are probably Ordovician. Silurian and Devonian rocks are dark siltstone, black shale (containing graptolites) ,lightcolored chert or novaculite, and dark thin- bedded fossiliferous limestone. Although the sequence is still little known and no generalizations can be made, the rocks have many of the characteristics of Ouachita facies rocks or transitional rocks. The more or less unaltered Silurian and possibly Ordovician rocks indicate that the crystalline rocks are probably Precambrian. Southwest of Cd. Victoria at Miquihuana, Baker (1921) reported green talcose and sericitic schists extensively crumpled and cut by quartz veins. Imlay (1944, p. 1142) also reported talcose schists in this area. De Cserna (1956, p. 13) reported a discovery by R. R. Alexandri of phyllites of probable upper Paleozoic age northwest of Cd. Victoria near Aramberri. Potrero de La Mula area.—Granitic rocks are exposed in the Potrero de La Mula in east-central Coahuila. These rocks have been discussed by Tappolet (1928), Kellum et al. (1936), and Flawn and Diaz G. (1959). Kellum et al. and Humphrey (inmanuscript) concluded that these rocks are pre-Cretaceous; Tappolet and Diaz G.interpreted them as post-Cretaceous. Final resolution of the question will require detailed field mapping. 19 Determinations on fossils collected by Jose Carrillo B. of Petroleos Mexicanos were made by W. C. Bell, J. L. Wilson, Otto Majewske, and Thomas Amsden (trilobites and brachio pods), and W. B. N. Berry (graptolites). His report on this area has recently been published (Carillo 8., Jose (1961) Geologia del anticlinoria Huizachal-Peregrina al N-W de Ciudad Victoria, Tamps.:Asociacion Mexicana de Geologos Petroleros, 801. Vol.XIII,no.1y 2, pp. 1-98. Wells Penetrating Pre-Mesozoic Rocks in Northern Mexico Three wells have penetrated pre-Mesozoic rocks innorthern Mexico (fig.5) : 1. No. 2-A Peyotes (82.5 km. S. 22° W. from Eagle Pass, Texas) in northeastern Coahuila. 2. No. 101 Chapa (11,750 m. S. 77°09' E. of Cerralvo) in north-central Nuevo Leon. 3.No.1BarrilViejo (also known as No. 2 San Marcos) (45 km. S. 59° W. from Monclova) in south-central Coahuila. The No. 2-A Peyotes (p. 345) encountered very fine-grained sericite-muscovite schist and sericitic metaquartzite ; metamorphism is low grade with a high shearing component. These rocks are similar in lithology and type of metamorphism to those exposed inthe Sierra del Carmen and encountered in numerous wells in Kinney, Val Verde, and Terrell counties north of the Rio Grande. The No. 101 Chapa (p. 345) penetrated dark sericite- chlorite slate and dark, fine-to medium-grained, angular, poorly sorted, chloritic micaceous feldspathic metasandstone (metagraywacke) containing abundant fragments of slate-phyllite, chert, and quartz mosaic; metamorphism is weak. These rocks are of geosynclinal facies and are similar to those penetrated in the interior part of the frontal zone of the Ouachita belt in central Texas. From a studyofthesamples, theNo.1BarrilViejo (reportedly bottomed in arkose) appears to have penetrated granitic rocks in situ. Analysis of Outcrop and Well Data There are two widely separated areas in northeastern Mexico where strongly deformed and highly sheared late Paleozoic flysch-type orogenic sedimentary rocks are exposed —in the Sierra del Cuervo and Placer de Guadalupe areas in Chihuahua and in the Cd. Victoria area of Tamaulipas. In the Sierra del Cuervo, Wolfcamp fossils occur in limestone lenses in the upper part of the sequence; the rocks near Cd. Victoria have not been adequately studied, but in Peregrina Canyon Mississippian fossils occur in sandstones in the lower part of the section along the contact with the crystalline rocks, and Permian fossils (Leonard) occur higher up in a very strongly deformed sequence. At least part of this flysch is thus Early Permian in age. Strongly deformed rocks of Permian age but of different facies occur inthe northern part of the Placer de Guadalupe area and in the Las Delicias-Acatita area; in these areas no flysch has been described. A thick sequence of volcanic rocks, graywacke, and dark shale in the Las Delicias-Acatita area suggests that these sedimentary rocks are of eugeosynclinal facies. In the northern part of the Placer de Guadalupe area, on the other hand, the rocks are of fore- land facies. Itis tempting to connect the south-or southwestward-striking Ouachita structural belt as exposed in the Marathon and Solitario uplifts in Texas and known outcrops of Paleozoic rocks of geosynclinal facies in northern Mexico, but such correlations are hazardous at present. Kellum etal. (1936),R.E.King(1944),Eardley (1951), and P. B.King (1951) have discussed the possibility that the Ouachita belt strikes south and includes the Pennsylvania^?) and Permian rocks of the Las Delicias-Acatita Another possibility area. is that the Ouachita structures strike southwestward into Mexico and that the front of the belt passes north of the Placer de Guadalupe and Sierra del Cuervo areas, thence turning sharply south toward the Las Delicias-Acatita area (Diaz G., 1956, pp. 9-14) ,20, 20 Stillanother possibility, suggested by R. K. DeFord (personal communication, 1958), is that the Paleozoic folds are offset by a post-Paleozoic strike- slip fault tending northwest-southeast in the approximate position of the Rio Grande trench and that the southwest side has moved northwest. The exposed orogenic facies Paleozoic rocks in northern Mexico include Permian and possibly Pennsylvanian rocks as well as Mississippian rocks near Cd. Victoria; the deformation is known to be post- Leonard in the Cd. Victoria area and post- Wolfcamp in the Sierra del Cuervo;in the Las Delicias-Acatita area, Guadalupe and possibly Ochoa equivalents are deformed. The final orogenic phase in Mexico thus took place in very late Permian time, as compared with the Late Pennsylvanian and possible early Wolfcamp orogeny in the Marathon area. The fundamental Mesozoic feature of northern Mexico was the Coahuila peninsula (Kellum et al., 1936), a relatively stable block or platform defined by (1) absence of Jurassic and Triassic sedimentary rocks and (2) more intense Laramide folding and thrust faulting along the south and west borders. Kellum et al. (1936, pp. 977—978) described the Coahuila peninsula as the foreland of the Mexican geosyncline: (1) In the south this landmass was formed by marine Permian sediments and lavas, byPermian or post-Permian intrusive granites and granodiorites, and by a series of phyllites, quartzites, slates, shales, and conglomerates ofPaleozoic age, probably in part Permian; (2) in central Coahuila itis composed of granitic rocks and associated dikes and quartz veins; and (3) in northern Coahuila it is composed of pre-Cambrian mica schist. The Permian sediments of southern Coahuila are believed by Bb'se, King, and Kelly to have been deposited in the same geosyncline as 20 Diaz G. originally suggested that the orogenic front passed south of the Placer de Guadalupe area, but Bridges'work (p. 101) shows that the Placer de Guadalupe area was affected by the Paleozoic folding. The Ouachita System those of western Texas. The mica schists of Sierra del Carmen, and possibly the granitic rocks of Potrero de La Mula, were part of the land area that existed adjacent to this earlier geosyncline. Thus, Kellum et al. (1936) believed that the Coahuila block was an uplift of the Paleozoic deformed belt and an "adjacent land area." In the last two decades, data have become available which permit a clarification of earlier ideas. There is considerable evidence to indicate a major pre-Mesozoic granitic terrane in northern Mexico lying on the east side of the Coahuila peninsula. There are granitic outcrops at Potrero de La Mula; granodiorite was encountered in the No. 1 Barril Viejo; thick Jurassic (and Triassic?) arkosic sequences arepresent ineastern Coahuila and have been penetrated in wells in Coahuila and Nuevo Leon;21 D. N. Miller (1955) deduced a northern Mexico granitic source for late Permian or Triassic red beds in the Delaware basin in Texas; a few fragments of highly sheared granite occur in red-bed conglomerate beneath Jurassic beds in Humble No. 1 Bandera County School Land inMaverick County; granite pebbles and cobbles occur in the Haymond boulder bed in the Marathon area. 22 This granitic terrane cannot be delineated accurately, butitissouth of the highly sheared low-grade metamorphic rocks (probably early Paleozoic or late Precambrian) that form an interior zone of the Ouachita structural belt in west Texas and northernmost Mexico and crop out in the Sierra del Carmen; itis east of 21The following wells bottomed in arkose: No. 1Treviiio, No. 1Zambrano, No. 1Chupadero, No. 1Garza. For descriptions of Cretaceous arkose sections, see Imlay (1944, p. 1079, figs.8,11,12, 13). 22 The source of the granite pebbles and cobbles in the Haymond boulder bed is not known;if the granite terrane in — Coahuila is the same age as the granite in the Las Dclicias Acatita area (very late Permian or post-Permian) ,the Haymond granite fragments (Atoka age) cannot have been derived from it. the Permian deformed belt partly exposed in the Las Delicias-Acatita area; and it is west of the highly sheared slate and metagraywacke encountered in the No. 101 Chapa inNuevo Leon.Itseems reasonable to suggest that this granitic terrane is em- placed in one of the interior zones of the Ouachita structural belt. It can be dated only as pre-Jurassic. If the numerous granite pebbles and cobbles in the Haymond boulder bed of the Marathon Basin (Atokan) were derived from an uplift of this granitic terrane, it is a pre-Middle Pennsylvanian intrusion;ifitisrelated to the granite intrusions of the Las Delicias- Acatita area, it is very late Permian or post-Permian. IntheCd.Victoriaarea crystalline rocks of probable Precambrian age, and unmetamorphosed upper and lower Paleozoic rocks of geosynclinal and transitional facies, occur only 80 miles from the Gulf of Mexico. Itis difficult to fit these exposures into the tectonic pattern of a Mexican Paleozoic orogenic belt because no regional trends have been established. To the northwest and west there appears to be a broad terrane of variably metamorphosed Paleozoic rocks intruded by granitic igneous rocks, but no information is available on pre-Mesozoic rocks north, east, or south. The crystalline rocks may be part of a massif within the orogenic belt, they may be part of a fore- land (eastern?, western? ),or they may be part of the crystalline core (by analogy to rocks exposed in the Appalachian pied- mont).Ifthey are part of the core, juxtaposition of unmetamorphosed sedimentary rocks of frontal zone type is difficult to explain (p. 102) ;probably the crystalline rocks are part of an ancient massif or part of a foreland mass. Summary The presence of deformed and variably metamorphosed late Paleozoic rocks of geosynclinal facies, metamorphic rocks of unknown age, and granitic rocks indicates that northern Mexico was Paleozoic tectonic land. The difference in the age of the Mexican orogenic facies rocks (Permian as against Mississippian in the Ouachita belt to the north) and the difference in the age of the deformation in Mexico (Late Permian as against Late Pennsylvanian- Early Permian in the Ouachita belt to the north) make it unlikely that there is a direct and simple connection between the Ouachita belt in the United States and the exposures of northern Mexico. Recognizing this, P. B. King (1951, p. 157) sug gested that the Mexican exposures may be a southwestern extension of an interior zone of the Ouachita system. Another possibility is that the Ouachita system in Mexico developed a younger foredeep along its western foreland and that this downwarp was deformed and intruded in late Permian time. The thick Wolfcamp clastic wedge in the Val Verde basin in Texas, younger than clastic wedges in Ouachita foreland frontal basins to the east and north, indicates that mobilitypersisted longer in the southwestern part of the belt in Texas, and perhaps in the Mexican segment the advance of the geosyncline over the foreland was carried a step farther. Igneous Rocks and Vein Rocks in the Ouachita Belt Peter T. Flawn Theoretical Considerations A developing orogen is a zone of crustal weakness and instability and thus a locus of igneous activity; an igneous cycle ac companies the development of the orogenic system from a geosyncline into a mobile belt. One criterion of a eugeosynclinal sedimentary sequence is its interbedded lavas, generally basaltic or andesitic; the deeply depressed core of the geosyncline is the habitat of syn-orogenic batholiths and migmatites ;the consolidated deformed belt, transected by faults and extensively jointed, is commonly invaded by postorogenic intrusions. Geographic association of older deformed belts and much younger intrusive igneous rocks suggests that post-orogenic adjustments along major structural planes and intersections continued to open channelways for the passage of intrusive igneous material into higher parts of the crust. At the close of the orogenic cycle the only trace of the early chain of volcanoes that marked the first arc of the incipient orogenic system may be the bedded siliceous deposits in the sedimentary sequence far away along the foreland margin; a deep- seated post-orogenic batholith concealed in the interior zone of abelt may be indicated only by a retinue of dikes cutting the folded and faulted rocks of the frontal zone; the gneisses, schists, and amphibolites of the crystalline core of a belt may be the altered equivalents of sedimentary wedges (containing volcanic or intrusive rocks) that once were like the folded and faulted sedimentary, volcanic, and intrusive rocks that now constitute the frontal zone. If the orogenic forces are not spent, the frontal zone may in time be downwarped and metamorphosed while a younger zone forms along the foreland boundary of the belt. The Ouachita belt is largely concealed so that the nature of its Paleozoic igneous activity must be reconstructed from very fragmentary evidence. Paleozoic Igneous Activityin the Ouachita Belt Areas ofOutcrop The dikes, sills, and other masses of igneous rock which intrude the Paleozoic rocks of the Ouachita Mountains are of Cretaceous age except for two diorite dikes which intrude Ordovician rocks near Glover in McCurtain County, Oklahoma (Honess, 1923, pp. 210-212, 261; Miser, 1943,p.112; Kidwell,1949,p.14).These diorite bodies are extensively fractured and considered to be pre-Late Pennsylvanian (pre-deformation). The plugs, dikes, and sills which intrude Paleozoic rocks in the Marathon Basin belong to the Tertiary igneous suite with one known exception in the southeast part of the Marathon Basin, 30 miles southwest of Sanderson, where basalt or diabase intrudes Ordovician beds and is unconformably overlain by Cretaceous strata (J. L. Wilson, 1954a, p. 2045). There is thus no direct evidence of Paleozoic igneous activity inthe two major exposures of the frontal zone of the Ouachita structural belt except for two or three small dikes or sills of intermediate orbasic intrusive rock. In the scattered exposures of pre-Mesozoic rocks in northern Mexico, Paleozoic igneous rocks are common. In the Las Delicias-Acatita area lavas are interbedded Bureau ofEconomic Geology, The University of Texas with Permian marine sedimentary rocks, and granitic and granodioritic rocks intrude Permian sedimentary rocks (Kellum et al., 1936, pp. 987-988; R. E. King, 1944, pp. 23, 28).At Potrero de La Mula there are granitic rocks which may be Paleozoic in age (Flawn and Diaz G., 1959, p. 224). Ages of intrusives in the Paleozoic rocks of the Sierra del Cuervo and Placer de Guadalupe area are not yet known. Despite the paucity of direct evidence of Paleozoic igneous activity inthe exposed parts of the belt5 the sedimentary record provides considerable indirect evidence on igneous activity in the concealed interior parts of the belt. Early Paleozoic sedimentary rocks contain little indication of contemporaneous igneous activity. In the Marathon region Cambrian(?) and Ordovician beds have a high feldspar content which seems to in crease southward; in Dagger Flat the writer observed small pebbles of granite in sandy limestone in the Marathon formation. This arkosic material was probably derived from Precambrian crystalline rocks farther south. Some of the early Paleozoic rocks inthe Ouachita Mountains are likewise feldspathic (Goldstein, 1959a, p. 97). The thick sequences of Ordovician and Devonian chert and siliceous shale in the Marathon Basin and Ouachita Mountains strongly suggest widespread contemporaneous volcanic activity in the more tectonically active parts of the belt to the south, the siliceous sediments being derived from fine pyroclastic material and mixed with fine muds along the foreland side of the belt. The thick rhythmically deposited sandstones of the Tesnus and Stanley formations are feldspathic and the Tesnus contains beds of arkose (P. B.King, 1937, p. 60); moreover, the sandstones contain metamorphic rock fragments as well as feldspar so that the source may have been a terrane of mixed metasedimentary and igneous rocks. In the Marathon Basin, the succeeding Haymond formation contains massive arkose beds inits upper part and a number of remarkable boulder beds. The Haymond boulder beds contain a suite of rounded igneous and metamorphic pebbles and cobbles as well as fragments of locally derived Paleozoic rocks. The igneous rocks are muscovite granite and granodiorite, in part rudely gneissic, and sheared volcanic rocks, mostly fine-grained porphyries. These may be well-worn fragments from uplifts of the Precambrian foreland to the north but it seems more likely to the writer that, along with the bulk of the other clastic material, the igneous detritus came from an uplift of an interior zone of the Ouachita belt to the south, probably innorthern Mexico. The crystalline fragments in the Haymond boulder beds must have been derived from a terrane of mixed plutonic, volcanic, and metasedimentary rocks. The plutonic rocks, from their gneissic character, may have been synorogenic granites orpost-orogenic granites subjected to later shearing. The volcanic rocks are strongly sheared and cataclastically altered. In the Ouachita Mountains rocks younger than Stanley are not significantly feldspathic and were apparently derived largely from reworking of pre-existing sedimentary and metasedimentary rocks of the Ouachita belt. The sandstones of the Stanley, how — ever, are markedly feldspathic the feldspar is, with only minor exceptions, plagioclase and was derived from crystalline rocks, possibly including granitic rocks. The feldspar content inthese Mississippian orogenic facies rocks indicates a crystalline source to the south which may have been (1) an uplifted block of Precambrian crystalline rocks or (2) anuplift of early or middle Paleozoic crystalline rocks like the areas of early Paleozoic and middle Paleozoic intrusive rocks in the Appalachian piedmont (Rodgers, 1952; P. B,King, 1955b, pp. 730-732; Grunenfelder and Silver,1958;Hurley,Fairbairn, and Pinson, 1958; Long and Kulp,1958). The Ouachita System Evidence from Subsurface A number of wells drilled in the frontal zone of the Ouachita belt west of the Llano uplift penetrated Mississippian-Pennsyl vanian sandstones that locally contain small fragments of microgranular feldspathic igneous rock, probably volcanic rock, which along with metamorphic rock fragments was probably derived from an uplifted terrane to the south and indicates igneous rocks in the source area. Igneous rocks have been encountered in a number of wells in the subsurface Ouachita belt (Tables 5and 6).Determination of their age is a problem, particularly in the case of fine-grained basalt and andesite, where petrographic study of textures and structures is not sufficient to identify positively the rock as intrusive or extrusive. Ifdiagnostic structures and textures of extrusive rocks can be recognized, it can be established that the igneous rock is a flow within the sedimentary sequence and the same age as the enclosing sedimentary rocks, or at least older than the beds above and younger than the beds below. If the igneous rock is intrusive, its age is less certain. Ifthe igneous rocks contain biotite, zircon, thorium or uranium minerals, several methods can be used to determine its absolute age;these methods willbe improved and broadened to include other groups of minerals in years to come. For other types of intrusive igneous rocks, itis known only that they are younger than the rocks they have invaded. If the igneous rock is deformed or metamorphosed, it is at least older than the deformation ormetamorphism. In the Ouachita structural belt subsurface igneous rocks which are cataclastically altered or metamorphosed must be older than the late Paleozoic orogeny and either Paleozoic or Precambrian in age. Rocks which are not metamorphosed or cataclastically altered belong to the Mesozoic and Tertiary suites of igneous rocks which have been emplaced in this same area probably as a direct or indirect result of deep structural weaknesses associated with the Ouachita belt. These also have a rather characteristic chemical composition and mineralogy. Igneous Paleozoic or Precambrian Rocks Encountered inWells Nine wells drilled in the Ouachita structural belt or the immediately adjacent fore- land have encountered igneous rocks of Precambrian or Paleozoic age (Table 5). Except for Shell Oil Company No. 1Pur cell (Williamson County), which penetrated Precambrian granite gneiss on the foreland edge of the belt, all of these wells are in the western part of the structural belt. In Kinney, Val Verde, and Terrell counties, highly sheared phyllites, schists, marbles, and metaquartzites of the Ouachita belt have been thrust against and over a sequence of sheared metavolcanic rocks of Precambrian age that may be part of the late Precambrian Van Hornmobile belt (Flawn,1956, pp. 32-35). The Havoline Oil Company No. 1 Weatherby (Kinney County) and Hiawatha Oil Company No. 1 Sellars (Val Verde County) encountered metavolcanic rocks of probable Precambrian age. They are mostly highly sheared metarhyolite unlike the general suite of Ouachita rocks and resemble more closely the sheared Precambrian rocks of the Van Horn area to the northwest (P. B. King and Flawn, 1953; Flawn, 1956). In the Sellars well, this metavolcanic sequence underlies highly sheared rocks of the Ouachita belt which are probably overthrust. The Precambrian age of these rocks is assumed from their lithologic character and from stratigraphic relations in Richardson Oil Company No. 1 Martin Rose (600 feet northeast of Havoline No. 1Weatherby) in which an Ordovician fossil occurs in carbonate rocks that lie on the metarhyolite (p. 286). These Precambrian rocks are probably part of a foreland "high" along the northern margin of the Ouachita geosyncline (p. 144 and fig. 2). The sheared basaltic rockinHuskyOilCompany No.1 Rose-Robertson (ValVerde County) to the Bureau ofEconomic Geology, The University of Texas northwest may be either a part of this Precambrian basement or a pre-shearing intrusion into the rocks of the Ouachita belt. In Terrell County, north of the margin of the structural belt, Magnolia Petroleum Company No. 1 Brown and Bassett penetrated Precambrian basement composed of metavolcanic rock, micro- granite, and magnetite-hornblende gneiss and overlain by Cambrian rocks. In Bexar and Medina counties sheared igneous rocks occur inthree wells (PI. 12). The General Crude Oil Company No. 1 Rogers Ranch encountered highly deformed slate containing masses of brecciated and partly mylonitized granitic rock and underlain by fractured and altered greenstone (andesite) .To the west in John I.Moore No. 1Alfred J. Wurzbach, similar fragments of partly mylonitized granitic rock and volcanic rock occur in a meta- shale sequence. No cores were taken but the sporadic nature of the igneous material suggests boulders or boulder beds in a slightly metamorphosed shale sequence. In the Rogers Ranch well, cores indicate that the fragments of brecciated granitic rock were tectonically injected into the slate during extreme shearing. Southwest of these two wells, Humble Oil & Refining Company No. 1E. E. Wilson in Medina County cored brecciated granitic rock overlying sheared and altered greenstone (andesitic and dacitic rocks).Farther southwest in Maverick County, Humble Oil & Refining Company No. 1Bandera County School Land penetrated steeply dipping sheared and altered greenstones (spilitic? basaltic rocks) partly converted to sericitechlorite slate (PL 12). The following interpretations of this complex area are suggested : (1) In the general area of Bexar, Medina, and Maverick counties the Ouachita belt contains volcanic rocks (andesite and basalt) and granitic rocks (granite and granodiorite) .Relict textures suggest that the volcanic rocks are extrusive. (2) The plutonic igneous rocks are brecciated, sheared, and locally mylonitized, and the volcanic rocks are sericitized and chloritized; in Maverick County they are foliated. They are thus older than the final deformation of the Ouachita belt and pre- Middle or Late Pennsylvanian in age. (3) Whether the granite intrudes the volcanic sequence or is older than the volcanic sequence is not known; the occurrence of granite over the volcanics in Humble Oil&Refining Company No. 1E. E. Wilson in Medina County may have been caused by faulting. (4) The granitic terrane was uplifted and shed boulders into an area of shale accumulation to the north. During deformation, these granitic fragments were "squirted" into the shale in the locus of maximum shearing. (5) The presence of "greenstones" suggests that the concealed southern part of the Ouachita belt is eugeosynclinal in nature. Igneous Post-Paleozoic Activityin the Ouachita Belt — General remarks. The area underlain by the Ouachita structural belt has been intruded by both Mesozoic and Tertiary igneous rocks; in places these rocks may be related to Mesozoic or Tertiary fault zones or flexures resulting from renewed movement along pre-existing Ouachita structures. The igneous rocks of the Balcones fault zone area have been described by Hill (1890), Kemp (1890), Osann (1893), Cross (1900), Lonsdale (1927), Romberg and Barnes (1954), and Greenwood and Lynch (1959) ; the igneous bodies in the Marathon Basin have been briefly described by P. B. King (1937) and Graves (1954) ;igneous rocks inthe Solitario area were studied by Lonsdale (1940) and Herrin (1959) ;igneous rocks of the Ouachita Mountains have been described by Kemp (1891), Washington (1900, 1901), Miser (1914), Miser and Ross (1922, 1923), Honess (1923), Lloyd (1923), Ross, Miser, and Stephenson (1928), Croneis and Billings (1929), Miser and Purdue (1929),C.P. Ross (1941) ,Kidwell(1949), Landes, Parks, and Scheid (1933).Moody (1949) and Kidwell (1949, 1951) studied the igneous rocks of the northern Gulf Coastal Plain. Kidwell lists 159 wells that penetrated igneous rocks (including 26 that encountered pyroclastic rocks) in the northern Gulf Coastal Plain and divided the igneous rocks of the Gulf Coastal Plain into two main petrographic provinces: (1) A diabase-diorite petrographic province which is probably Triassic or early Jurassic in age and certainly pre-Cretaceous ;these rocks occur in a relatively narrow eastwestbelt extending fromnortheast Texas to northern Mississippi and more orless coincide with a zone of Tertiary faulting and a zone of pronounced flexingor faulting in the pre-Eagle Mills formations. These faults may be manifestations of a deep- seated fault zone which formed the northern boundary of the Gulf Coastal Plain in late Paleozoic or early Mesozoic time. (2) An alkaline petrographic province which is Upper Cretaceous (Woodbine-Taylor) to Tertiary in age; the rocks appear to be older north and east of the Mississippi embayment and younger in south Texas. These, in turn, can be divided into four groups —the Balcones group, the Ouachita group, the central Mississippi group, and the Appalachian foreland group. Only the first two are within the bounds of this study. The Balcones group of the alkaline province extends more than 200 miles from Austin, Texas, southwestward into Mexico inabeltasmuch as40mileswide. Itsrocks are low-silica basalt and gabbro containing olivine, titaniferous augite (and locally aegirine-augite) , nepheline, and melilite (Lonsdale, 1927) which form plugs, dikes, sills, and possibly flows. The masses of "serpentine" locally associated with this suite are altered pyroclastic rocks, which in at least some localities are nontronite (Weiss and Clabaugh, 1955). Intrusions of the Balcones type are profuse in Uvalde and Kinney counties, Texas, where the Ouachita belt changes trend sharply, which suggests a relation between Paleozoic structures and younger intrusions. To the east, Balcones-type intrusions are less common but occur as far northeast as the Bell-Williamson County area. Their extent southward into Mexico is unknown. The Ouachita group of alkaline rocks extends from central Mississippi tocentral Arkansas in a belt 250 miles long and 100 miles wide which coincides with the Ouachita Mountains and their buried extension to the southeast. Its rocks include nepheline syenite and its fine-grained equivalents, nepheline basalt, and leucite-bearing rocks. Mildly alkaline syenite, diorite, trachyte, and andesite are present in the central part, and these are associated with peridotite, pyroxenite, and various lamprophyres. The Table 5. Paleozoicor Precambrian igneous rocks encounteredinwels in the Ouachita structural belt. metashale-sandstone sequence; granodiorite is Paleozoicor Precambrian apearsto ocuras cobles or bouldersin a granodiorite Alfred J. Wurzbach Granodiorite (with volcanic and other rocks) Cataclasticaly altered 2,890-3,180 P. 295 John I. More No. 1 cambrian and dacite gests complex structural relations or intrusive relations; Paleozoic or Pre- 7,163-7,16 feet, fractured and chloritized andesite incomplete) fractured and altered andesite-dacite sugclasticaly altered granite (samples No. 1 E. E. Wilson Cataclasticaly altered granite overlying 7,065-7,070 feet, cata- 6,980-7,168 P. 295 Humble Oil & Refg. Co. lEDINA COUNTY chlorite slate Paleozoicor Precambrian Shearedsericitized-chloritizedbasalt (spili tic?), partly convertedto sericite- 13,32-13,863TD P. 290 Humble Oil & Refg. Co. No. 1 Bandera County Schol Land tAVERICK COUNTY — OuachitaPrecambrian belt; metarhyoliteis probably Metarhyolite overlain by early Paleozoic carbonate rocks along foreland edge of the Mylonitized (phylonitized) metarhyolite 4,381±-4,398±TD P. 284 HavolineOil Co. No. 1 lINEY Weatherby COUNTY — brian andesite Extremely deformed slate —localy containing augenof breciated granodiorite —resting on altered andesite; Paleozoic or Precam- Breciated granodiorite (as augen in slate) Sericitized and chloritized 5,713 5,894-5,896TD P. 224 General Crude Oil Co. No. 1 Rogers Ranch IEXAJR COUNTY — GEOLOGY and AGE ROCK TYPE INTERVAL (feet) REFERENCE :OUNTY and WEL NAME 112 Bureau ofEconomic Geology, The University of Texas Precamandesite Ouachita Precambrian clasticaly sugincomplete) Preand The Ouachita System 113 granite of Llano uplift) Gneis is overlain by Cambrian beds along foreland edge of Ouachita belt; Precambrian basement (similarto Town Mountain Granite gneis 9,470-9,485TD P. 337 Shel Oil Co. No. 1Purcel WILIAMSON COUNTY— Highly sheared and altered basaltic igneous rocks —grenstone; may be part of Ouachita sequence (Paleozoic), may be part of Precambrian metavolcanic sequence Actinolitic epidote- chlorite-sericiteschist 2,170-2,426 P. 324 Husky Oil Co. No. 1Rose-Robertson probably Precambrian overthrust (?) low-grade metamorphic rocks of the Ouachita belt; metavolcanics are mostly metarhyolite No. 1Selars Metavolcanic sequence underlies sheared Metavolcanic rocks, 2,641-3,502TD P. 322 Hiawatha Oil Co. VAL VERDE COUNTY — brian basement Igneous and metamorphic rocks imediately north of the Ouachita belt on the foreland are overlain by Cambrian beds; Precam- Metavolcanic rocks, microgranite, magnetitehornblende gneis 14,42-14,56TD P. 307 Magnolia Petr. Co. and Western Nat. Gas No. 1 Brown and Basett TEREL COUNTY — Precambrian 114 Bureau ofEconomic Geology, The University of Texas oi over-but over-oioi butover-but part (Bal- (Bal-partpart (Bal-the thethe group) post- post-group)group) post-into intointo of ofof frontal zone (Balcones feet) intrusive intrusivefeet)zonefrontalfrontal (Balconeszone (Balcones feet) intrusive the group) Ouachita group)thethe Ouachitagroup) Ouachita the lower lowerthethe lower of the theofof thein of ofinin of probably zone zoneprobablyprobably zone of the theofof the (Balcones (Balcones(Balcones rocks interiorthe post-metamorphism post-metamorphisminteriorrocksrocks thethe interiorpost-metamorphism occurs (720-890 presence sequence) intrusion intrusionsequence)(720-890occursoccurs presence(720-890 presence sequence) intrusion frontal frontalfrontal (Balcones intrusion intrusion(Balcones(Balcones intrusion zone zonezone andof a in inofandandaof a in belt also the alsobeltbelt thealso the into intointo post-Paleozoic post-Paleozoicpost-Paleozoic Paleozoic Ouachita intrusion rocks rocksOuachitaPaleozoicPaleozoic intrusionOuachita intrusion rocks belt probably probablybeltbelt probably frontal frontalfrontal basalt section sectionbasaltbasalt section fragments indicates Paleozoic post-Paleozoic post-Paleozoicindicatesfragmentsfragments Paleozoicindicates Paleozoic post-Paleozoic the of ofthethe of a aa AGE into poor; the group) group)theintoAGEAGE poor;into poor; the group) belt beltbelt and a the post-metamorphism sheared shearedpost-metamorphismaandand thea the post-metamorphism sheared Ouachita post-Paleozoic post-PaleozoicOuachitaOuachita post-Paleozoic into intointo (olivine Cretaceous well Cretaceous(olivine(olivine wellCretaceous well of the in theofof inthe in belt. GEOLOGY Probably ProbablyGEOLOGYGEOLOGY Probably intrusion zone Paleozoic highly Samples Sampleshighlyzoneintrusionintrusion Paleozoiczone Paleozoic highly Samples and andand group) group)group) belt lying lyingbeltbelt lying abundance of rock Probably Probablyofabundanceabundance rockof rock Probably cones conescones Ouachita OuachitaOuachita A AA structural the thethe = == Ouachita the gabbro nepheline nephelinegabbrogabbro nepheline in wells augite-biotite olivine(?) olivine(?)augite-biotiteaugite-biotite olivine(?) in TYPE olivine microsyenite microgabbro basalt basalt basaltbasaltmicrogabbroolivineTYPETYPE microsyeniteolivine microsyenite microgabbro basalt basalt (contains (contains(contains limburgite) limburgite)limburgite) ROCK Altered Altered Olivine Olivine OlivineOlivineAlteredROCKROCK AlteredAltered Altered Olivine Olivine encountered and andand rocks (feet) (feet)(feet) igneous 1,805-1,820 1,805-1,8201,805-1,820 (samples incomplete) 4,290-4,330 incomplete)(samples(samples 4,290-4,330incomplete) 4,290-4,330 4,960-4,990 4,650-4,685 4,650-4,6854,960-4,9904,960-4,990 4,650-4,685 INTERVAL INTERVALINTERVAL Post-Paleozoic 9 99 6. — —— 219 315 317 315219219 317315 317 P.P. P. P. P.P.P.P.P.P. P. P. Table APPENDIX285 285APPENDIXAPPENDIX285 REFERENCE REFERENCEREFERENCE 2 Co. Co.22 Co. 1 11 NAME Co. Co. Co.NAMENAME Co.Co. Co. Wardlaw Refg. Refg.WardlawWardlaw Refg. No. Anderson AndersonNo.No. Anderson No. & &No.No. & Oil B. L. B.OilOil L.B. L. WELL Petr. Petr.WELLWELL Petr. C. Oil OilC.C. Oil R. R.R. and COUNTY Bell COUNTYandand BellCOUNTY Bell Bacon COUNTY— COUNTY Reasor ReasorCOUNTY—BaconBacon COUNTYCOUNTY— COUNTY Reasor Ezell COUNTY COUNTYEzellEzell COUNTY Nolan NolanNolan Win. Magnolia MagnoliaWin.Win. Magnolia No. L. L.No.No. L. Jesse No. No.JesseJesse No. G. G.G. COUNTY BELL KINNEY 1 TRAVIS UVALDE Humble HumbleUVALDETRAVIS1BELLCOUNTYCOUNTY KINNEYBELL KINNEY 1 TRAVIS UVALDE Humble 1 11 The Ouachita System largest nepheline syenite bodies are at Magnet Cove and Potash Sulphur Springs, Arkansas. Several hundred dikes and sills related to the plutonic syenite masses are scattered through the eastern part of the Ouachita Mountains. These alkaline rocks of the Ouachita groups are controlled by local structures rather than any major structure (Kidwell, 1949, p. 261); the fracturing that permitted their emplace ment was caused by an intersection of the northwest-trending structures of the Ouachita Mountains and northeast-trending structures formed by the downwarp of the Mississippi embayment in Upper Cretaceous time. The alkaline rocks probably formed as differentiates of an olivine basalt magma (Kidwell, 1949, p. 303) which formed deep inthe orogenic belt after the deformation and was tapped by fractures during formation of the GulfCoast basin. Igneous Rocks Encountered inWells Penetrating the Ouachita Belt Post-Paleozoic Table 6 (p. 114) lists a number of wells in which igneous rocks were encountered within the Paleozoic or metamorphic sequence. These rocks are part of the Balcones group intruded after the deformation and are of basaltic or gabbroic composition. No marked contact metamorphic effects have been noted in the regionally metamorphosed host rocks, but they seem to show more variations in degree of regional metamorphism and more fracturing and veining than are seen in rocks that have not been intruded. 23 These variations may result from local thermal effects caused by intrusive bodies. Igneous Rocks Intruded inMesozoic and Tertiary Rocks Overlying or Adjacent to t;he Ouachita Belt The numerous bodies of igneous rocks encountered in Mesozoic and Tertiary 28 No samples of host rocks were available for Nolan Bell OilCompany No. 2 William Bacon (see Table 6), but the position of the well in the frontal zone of the Ouachita belt suggests that the rocks are unmetamorphosed or at the most incipiently metamorphosed. rocks overlying the Ouachita structural belt were discussed by Kidwell (1949, 1951). Since his study, the No. 1 Garza (76 km. S. 87° W. of Nuevo Laredo in Nuevo Leon, Mexico) penetrated dark amygdaloidal igneous rock within an arkose conglomerate of probable Jurassic age; the igneous rocks appear to be andesite orbasalt flows,possibly spilitic.The conglomerates in this well are much like those inHumble Oil &Refining Company No. 1 Bandera County School Land in Maverick County, Texas. In Freestone County, Humble Oil&Refining Company No. 1Marberry penetrated an olivine basalt between 13,226 and 13,452 feet below Upper Jurassic beds (R. D. Woods, per sonal communication, 1957).Beneath the basalt is a sequence of hard red quartzitic quartz sandstone containing streaks of red micaceous siltstone and shale (metashale and clay shale) ; these rocks show very weak to weak metamorphism with a strong hydrothermal element (p. 127) and their age is unknown. Possibly the basalt is a flow on the very weakly metamorphosed quartzitic sandstone terrane. However, E. M. Hurlbut (personal communication, 1958) reported 10 feet of red shale, between the basalt and the quartzitic sandstone, which seems not to be part of the quartzitic sandstone ;he suggested that the basalt mayliewithintheunmetamorphosed Jurassic section and that Jurassic rocks may be faulted against the quartzitic sandstone. In Shelby County' in east Texas, about 150 miles due south of the Ouachita Mountains of western Arkansas, Amerada Petroleum Corporation No. 1 Strickland penetrated igneous rocks at 11,715 feet below a salt and anhydrite sequence of unknown age and bottomed in igneous rock at 12,533 feet. The rocks are altered dacite and altered quartz microdiorite; although some geologists have interpreted this rock as "basement," and therefore probably part of the Ouachita belt, the writer believes it is more likely a younger intrusive body, possibly belonging to the diabase Bureau ofEconomic Geology, The University of Texas diorite petrographic province of Kidwell (1949). This conclusion is based on the location of the body, the mineralogy and fabric of the rock, and the fine grain size of the upper part of the body. Two wells in the foreland sequence immediately adjacent to the Ouachita belt are of interest. The Humble Oil & Refining Company No. 1 H. C. Miller in Collin County penetrated basalt in the Ellen- burger (p. 242). Because of vesicularity and alteration on the upper surface of this body, some geologists have interpreted it as an extrusive rock which would indicate: (1) Ordovician volcanism in an area of carbonate deposition where all other evidence points to stable shelf conditions, or (2) Ordovician volcanism in the Ouachita belt to the east where other evidence suggests that the environment was such as to favor deposition of siliceous mud. Inasmuch as intrusive bodies highly charged with gas are commonly vesicular and show upper contact phenomena similar to those that characterize flow surfaces (staining, alteration, abundant pyrite, etc.), the writer agrees with V.E. Barnes (personal communication, 1959) that this basalt body is most likely intrusive and related to the Mesozoic period of andesite-basalt intrusive activity. In Fish Production Corporation No. 1 Postell in Kinney County, foreland sedimentary rocks show sporadic effects of thermal metamorphism. The rocks in the interval 4,695 to 5,371 feet show local development of biotite and amphibole (including sodic amphibole) of metamorphic originbut no directional fabric. Goldstein (personal communication, 1955), after a thorough study of this well,concluded that the metamorphism was caused by a nearby igneous intrusion. Intrusive igneous rock (serpentinized basaltic or andesitic rock) was penetrated just beneath the surface (355 to465 feet) inthis same well. Veins in Ouachita Facies Rocks — General remarks.-Most Ouachita facies rocks both in outcrops and in well cores and cuttings contain abundant vein ma terial, ranging from tiny microveinlets to massive veins as much as 100 feet wide (Miser, 1943, p. 95). Their size, abun dance, and mineralogy vary in different parts of the structural belt, and their dis tribution and mineralogy appear to have tectonic significance. Miser (1943, 1959) has described quartz veins inthe Ouachita Mountains, but there has been no similar study in the Marathon region. Veins inthe Ouachita Mountains Ouachita Mountains veins are well known for their fine quartz crystals, and a thriving business has grown up inmarketing crystals to collectors, manufacturers of various decorative objects, such as foun tains, memorials, etc., and manufacturers of electronic equipment. According to Miser (1943),most of the quartz veins in the Ouachita Mountains are restricted to a belt 30 to 40 miles wide extending west-southwest fromLittleRock, Arkansas, to Broken Bow, Oklahoma, which coincides with the main anticlinorial part of the mountains (Broken Bow-Benton uplift). The host rocks range from Cambrian through Pennsylvanian; in the central part of the area the veins apparently occur in all types of rocks, but on the periphery' they are best developed in sandstones. The veins are open-space fracture fillings. Quartz (milky, white, vitreous) is the principal mineral, but calcite (and dolomite), dickite, rectorite (a micaceous mineral), chlorite, and adularia occur also. Feldspar (adularia and orthoclase?) is a rare component in Arkansas and inMcCurtain County, Oklahoma (Honess, 1923, p. 40), and a few veins contain sulfide minerals, including antimony, lead, zinc, copper, and mercury. The veinrock has been somewhat fractured and crushed. Introduction of the vein materialprobably tookplace lateintheperiod of deformation, probably late in the Pennsylvanian, following uplift of the central part of the belt (Miser, 1943, p. 99).There appears to be a correlation between degree of metamorphism and abundance of quartz veins. Miser (1943, p. 99; 1959, p. 39) believed that the sulfide-bearing quartz veins are of the same age as the main suite of quartz veins (Late Pennsylvanian) ; other geologists (Hess, 1908; Branner, 1932; Scull, 1959) relate these veins to the period of Cretaceous igneous activity. Ham (1956a) described asphaltite veins in the Ouachita Mountains in southeastern Oklahoma; he pointed out that these veins and fissure fillings are restricted to an east- trending belt about 25 miles wide in the overthrust northern part of the Ouachita Mountains between the Choctaw and Octavia faults, and he concluded that the asphaltic material was derived from underlying normal or Arbuckle facies rocks beneath the allochthonous Ouachita plate. Veins inthe Marathon Basin Veins are not as conspicuous in the exposed rocks of the Ouachita structural belt in the Marathon Basin as they are in the central part of the Ouachita Mountains. The harder beds in the Marathon Basin are commonly jointed, shattered, slickensided, and penetrated by innumerable small veins of calcite; the Woods Hollow shale contains large veins of fibrous calcite where itis strongly crumpled and overlain Bureau ofEconomic Geology, The University of Texas by the competent Maravillas chert, and on the southeast side of the basin the massive sandstones of the Tesnus are transversed by veins of quartz and calcite (King,1937, p. 120). Numerous veins of calcite and quartz penetrate the Tesnus formation in Persimmon Gap south of the Marathon Basin proper. Veins inthe Sierra del Carmen The metamorphic rocks exposed in the Sierra del Carmen (p. 99) are extensively veined by quartz, carbonate, and chlorite; both pre-and post-deformation veins are present. Locally the schist contains masses or"knots" ofmilkyveinquartz. Veins inthe Subsurface Ouachita Structural Belt Well cores and cuttings of Ouachita rocks commonly contain quartz and carbonate vein material. The size of the veins, their mineralogy, and their age differ from one part of the belt to another. Veins are numerous in the frontal zone of the belt but generally are very small. They consist of quartz, calcite, dolomite, or combinations thereof; a distinctive feature is a narrow and irregular concentration of an opaque black bitumen in the center of each veinlet. Veinlets occur in sandstones, cherts, and shales, being most numerous in the first two;the cherts contain numerous fine criss-crossing veinlets. The frequency and habit of the veinlets is a reflection of the type of rock failure. Sandstones and cherts were more prone to fracturing than the shales, and the cherts were susceptible to shattering. The veins appear to be simple fracture or joint fillings em- placed late in or after the deformation. In the zone of incipient to weak metamorphism, chlorite(vermicular tofibrous) is a common constituent of the quartz- carbonate veins, the veins are larger, and bitumen persists. South and east of the Luling overthrust front in the zone of low-grade high-shearing metamorphism, quartz-carbonatechlorite veins are massive and abundant. Some of them contain epidote. Both predeformation and post-deformation veins are present. The early veins are broken, contorted, and drawn out in augen; later veins cut across the earlier sheared veins. No feldspar was observed in the veins which penetrate subsurface rocks of the Ouachita structural belt, even in the zone of low-grade high-shearing metamorphism. Conclusions Veins in rocks of the Ouachita structural belt are distributed as follows: (1) in a belt along the foreland side of the frontal — zone mostly small carbonate and quartz veinlets emplaced inopen tension fractures and in shattered zones after the main period of deformation and containing bitumen deposited still later in the open spaces remaining; (2) in the interior part — of the frontal zone similar to veins on the foreland side but the presence of chlorite reflects higher temperatures; (3) in the — highly sheared interior zone profuse and commonly massive veins of quartzcarbonate- chlorite-epidote (without bitumen) of two generations; the earlier em- placed before the major shearing, and the later veins in tension fractures younger than the main period of compression. The relation between vein mineralogy and degree of metamorphism is very close. Chlorite occurs in veins traversing the incipient to weakly metamorphosed rocks, and both chlorite and epidote occur in veins penetrating the highly sheared low- grade metamorphic rocks. Size and profusion of veins are also closely related to metamorphism. They are larger and more numerous in the incipient to weakly metamorphosed rocks than inunmetamorphosed The Ouachita System rocks and still more profuse and massive show that these rocks were extensively in the highly sheared low-grade metamor-veined and probably metamorphosed bephic rocks. fore they were sheared; the later veins were The twoages of veins in the rocks south emplaced after the thrusting and disloca and east of the Luling overthrust front tion that produced the shearing. Metamorphism in the Ouachita Belt Peter T. Flawn General Regional metamorphism is produced by interaction of thermal, dynamic, and hydrothermal metamorphism, the final product depending on the relative impor tance of the three processes. In most regionally metamorphosed terranes the mineral assemblage results from recrystal lization and reconstitution due to elevated temperatures; the stress environment is reflected in the metamorphic fabric and structures. High pressures and shearing stresses influence the mineral assemblage because some minerals are more stable in high-pressure and/or high-stress environments than others. The hydrothermal component of regional metamorphism islocally important in areas extensively invaded by high-temperature solutions. Adjacent to intrusions the thermal component of metamorphism may produce mineral assemblages unique to the aureole of the invading igneous body (contact metamorphism), whereas in areas of extreme shearing stress the metamorphic products are cataclasites characterized by granulated, sheared (mylonitic) fabrics. Thus, a metamorphic rock is a product of metamorphic environment, and under certain conditions the sum total of its tectonic adventures may be read inits mineralogy and fabric. Retrogressive metamorphism, for example, occurs where a metamorphic rock that has attained equilibrium in a comparatively high temperature environment is brought into an environment characterized by lower temperatures (and commonly high stress) , an environment whichis common inmajor overthrusts and nappes. Ifthe rock adjusts completely to its new environment all traces of its former nature willbe erased,5l5 l but where retrograde metamorphic reactions did not proceed to completion, a Statement record remains in the mineralogy and fabric of the rock. Regional metamorphism is common in orogenic belts, especially in the core and interior zones; it also occurs sporadically in frontal zones. The question of where metamorphism begins and diagenesis ends cannot be resolved by consideration of temperature alone because temperatures in deep wells in foreland-basins approach those at which incipient metamorphic reactions are presumed to take place and yet the rocks show no signs of metamorphism. The presence of belts of very weakly metamorphosed rocks in the frontal zones of orogenic belts where high temperatures were not attained seems toindicate that the key is deformation and that low temperature metamorphic reactions are promoted by penetrative intergranular movements during deformation. The grade of metamorphism attained by a rock unit depends mainly on its position within the orogenic belt. In detail, however, the metamorphic grade attained depends also on the relation of the rock to local structures and the susceptibility of the rock to metamorphism (p. 15). Because of the tectonic significance of metamorphism in the study of the concealed Ouachita belt, Flawn and Goldstein have defined three grades of metamor phism below low-grade metamorphism, namely, incipient metamorphism, very weak metamorphism, and weak metamorphism (Table 1);the divisions are made on the basis of degree of reconstitution, recrystallization, and rock structures (p. 15). Two main metamorphic zones are mapped in the Ouachita belt: (1) a zone of incipient to very weak metamorphism lying irregularly within the frontal zone Bureau ofEconomic Geology, The University of Texas and (2) a zone of weak tolow-grade metamorphism with a strong shearing component which conforms to the interior zone of the belt. Exceptions to these broad generalizations are (a) where metamorphism in the frontal zone is weak or low grade due to local structural conditions, (b) where foreland facies rocks along the frontal margin of the belt are slightly metamorphosed, (c) where rocks of the interior zone approach medium metamorphic grade, and (d) where rocks of the interior zone appeared to have undergone retrograde metamorphism. Zone ofIncipient to VeryWeak Metamorphism Incipiently to very weakly metamorphosed rocks occur in the frontal zone of the Ouachita belt (1) ina broad somewhat irregular arc around the Llano buttress, (2) in the Ouachita Mountains salient where metamorphism increases toward the axis of the Broken Bow—Benton anticlinorium, (3) ina discontinuous band along the northern boundary of the interior zone in Trans-Pecos Texas, (4) associated with local folds and faults in the frontal zone from the Ouachita Mountains to the Solitario, and (5) in a poorly known band along and within the front of the belt extending southeastward from Arkansas County, Arkansas, toBolivar County, Mississippi. While rocks within the anticlinoria in the Ouachita Mountains salient are metamorphosed, rocks within the anticlinoria of the Marathon Basin are not. From the eastern Ouachita Mountains to Travis County, Texas, that part of the Ouachita belt's frontal zone next to the foreland is for the most part unmetamorphosed —neither the early Paleozoic or later Paleozoic rocks are significantly metamorphosed. In this part of the frontal zone incipient to very weak metamorphism (and locally higher grade metamorphism) occurs only in the southern and eastern parts — of the zone in anticlinorial structures in the Ouachita Mountains and in a broad band beginning in McLennan County, Texas, and broadening southwestward toward the Llano buttress. The bordering band of incipient to very weak metamorphism generally follows the broadening subcrop of dark clastic rocks, although the metamorphic zone transgresses lithologic boundaries and includes Stanley rocks. In this part of the Ouachita belt, then, it seems to hold generally true that in the interior of the frontal zone the pre-Stanley rocks (including the dark clastic unit in central Texas) are metamorphosed to a greater degree than the younger rocks. Possibly the pre-Stanley beds in the interior part of the frontal zones were metamorphosed before Stanley time. Goldstein (1959a) reported evidence from study of sandstones of two geosynclinal cycles, one Ordovician and Silurian and another Mississippian and Pennsylvanian. However, where the earlier beds show the greatest metamorphism, the Stanley, Jackfork, and Atoka beds also are more metamorphosed than elsewhere. An alternative hypothesis, therefore, is that metamorphism in the south and east parts of the frontal zone of the Ouachita belt between Arkansas and the Llano uplift occurred during development of large anticlinorial structures wherein deeper and more altered early Paleozoic rocks were uplifted to their present position in the subcrop. The higher metamorphic grade of the pre-Stanley rocks was thus attained deep inthe cores of the anticlinoria. In the Llano area, metamorphism inthe frontal zone was probably intensified by crushing against the Llano buttress, but the general coincidence of the belt of metamorphism with the dark clastic unit suggests that this may be another anticlinorial structure. West of the Llano uplift very weakly metamorphosed Ouachita rocks lie adjacent tounmetamorphosed foreland rocks. The zone of incipient to very weak or weak metamorphism parallels the front and appears to be related to frontal overthrust ing and associated deformation. South of the very weakly metamorphosed rocks there is a belt of little altered Mississip The Ouachita System pian-Pennsylvanian rocks (Tesnus? ) which lie next to the Luling overthrust front. Possibly these rocks were not buried as deeply or deformed as much as the metamorphosed rocks tothe north. In Uvalde and Kinney counties where the continuity of the Ouachita belt is lost, Mississippian-Pennsylvanian beds (Tesnus?) with variable incipient to weak metamorphism and cut by intrusive igneous rock were penetrated inHumble Oil &RefiningCompany No.1R.L.Anderson (Uvalde County). Some of the metamorphic effects observed may be due to contact metamorphism related to profuse Cretaceous- Tertiary igneous intrusions in the area. InKinney and ValVerde counties where the Ouachita belt was crushed against a concealed foreland buttress and the frontal zone of the belt is either overridden or narrowly developed, incipient to weak metamorphism extends irregularly along the concealed Precambrian element and includes the lower Paleozoic foreland rocks which mantle the old buttress (PI. 2). Farther west in Terrell County where the frontal zone of the Ouachita belt iswell developed in the subcrop, Tesnus and pre- Tesnus rocks are very weakly metamorphosed just north of the terrane of over- thrust highly sheared low-grade metamorphci rocks —possibly this is an anticlinorium. Beyond, inBrewster County, rocks of the frontal zone are not metamorphosed. Zone of Low-Grade, High-Shearing Metamorphism A zone of low-grade metamorphism (complete reconstitution and recrystallization) with a high shearing component can be mapped in a continuous arcuate band from Navarro County to Medina County, Texas. Continuity of this zone, and that of lithologic units and tectonic units in the Ouachita belt, is lost in Uvalde County, although its persistence is indicated by wells in Frio and Zavala counties (PL 2). In Kinney, Val Verde, Terrell, and Brewster counties, a zone of low-grade high- shear metamorphism is again well defined and mappable ;itcontinues southward into Mexico, where control is insufficient for mapping (Flawn and Diaz G., 1959).The western and northern edge of the zone of low-grade high-shear metamorphism is sharply drawn on the map (PI. 2) and coincides with a structural boundary that is a province boundary as well. This is the boundary of the interior zone of the Ouachita belt herein called the Luling front. This boundary is nearly linear, although itprobably occurs more orless irregularly within a disturbed belt some miles wide. The east and south boundary of this zone is beyond the down-dip limit of well control. Throughout most of the zone, the low- grade chlorite-sericite assemblage persists, but in south-central Texas garnet occurs in some of the rocks and indicates that meta morphism increases southward. Some evidence indicates that the high shearing effected a retrogressive metamorphism in this same area (p. 79). Low-grade metamorphic rocks also occur in two "metamorphic maxima" in the Broken Bow—Benton anticlinorium in the Ouachita Mountains where metamorphism — is clearly related to structure one "maximum" occurs on the east end of the exposed part of the structure near Little Rock and the other on the west end near Broken Bow (Miser, 1959, pp. 34-37 and fig.I)—but the metamorphism varies considerably within short distances, and it is dubious whether the persistent zone mapped in subsurface can be extended into these areas. More likely, the Ouachita Mountains metamorphism within the frontal zone of the belt resulted from deformation along the axes of the anticlinoria and was weaker away from those major structures. Metamorphism East of the Ouachita Mountains Metasedimentary rocks have been encountered in eastern Arkansas and southeastern Mississippi (p. 91) ; the few samples available show that metamorphic Bureau of Economic Geology, The University of Texas grade ranges from very weak to low grade, but there is not sufficient control to attempt to delineate metamorphic zones. Age of the Metamorphism Attempts to determine by the potassium- argon method absolute ages of the metamorphic rocks in the Sierra del Carmen were inconclusive because divergent ages (240 and 370 million years) were calculated (George Edwards, Shell Development Company, personal communication, 1959). The results do indicate, however, that the metamorphism isPaleozoic, whatever the ages of the rocks themselves. Ad ditional inferences as to the age of the metamorphism can be obtained from stratigraphic and structural relations: (1) In the Ouachita Mountains, Jack- fork and Atoka beds are slightly metamorphosed in the central anticlinorium in Arkansas (Miser, 1959, pp. 34-35). (2) In Bexar County, Texas, postorogenic Permo-Pennsylvanian beds apparently rest on the metamorphic terrane (p. 125) ;in northern Louisiana there are post-orogenic beds of Middle to Upper Pennsylvanian age (p. 125). (3) Atoka sandstones along the front of the belt contain abundant fragments of sheared metasedimentary rocks. (4) The final deformation of the Ouachita belt in the frontal zone of the Ouachita Mountains was post-Boggy and probably occurred during late Dcs Moines time. (5) Metamorphic rocks south of the Lulingfront contain pre-and post-shearing quartz veins and are locally retrograde rocks. These data suggest at least two periods of metamorphism, and possibly three, as follows: (1) Widespread regional metamorphism in the interior of the belt indicated by extensive pre-deformation quartz veins, relict minerals of retrograde rocks, and pre deformation granites. (2) Widespread low-grade regional metamorphism with a strong shearing and cataclastic component in the interior part of the belt resulting in shearing of earlier formed quartz veins, retrograde effects in south Texas, and development of mylonites accompanying displacement of the Luling overthrust front. This metamorphism was pre-Atoka because Atoka beds contain abundant fragments of the sheared rocks. (3) Post-Atoka metamorphism associated with development of anticlinoria in the Ouachita Mountains and intense local deformation in other parts of the frontal zone. This metamorphism was later than the shearing metamorphism in the interior of the belt, (2) above, because Atoka beds contain fragments of sheared rocks. Probably it was post-Atoka and pre-late Dcs Moines, although there was probably an overlap with the same sort of metamorphism going on in different parts of the belt at different times. Post-Orogenic Paleozoic Rocks Lying on the Ouachita Belt Peter T. Flawn — General remarks. Four wells have penetrated undeformed and unmetamorphosed late Paleozoic rocks in areas of the Ouachita belt where other data suggest that rocks of the structural belt are strongly deformed or deformed and metamorphosed. These wells are: (1) Union Producing Company No. 1-E Crossett Lumber Company, Ashley County, Arkansas— l2-19S-7W (2) Union Producing Company No. 1-A—Tensas Delta, Morehouse Parish, Louisiana 9-22N4E (3) H. A. Pagenkopf No. 1Max Blum, Bexar County, Texas (p. 226) (4) Magnolia Petroleum Company No. 1 McKinley, Frio County, Texas (p.258) Discussion of Wells Penetrating Undeformed and Unmetamorphosed Late Paleozoic Rocks According to H. J. Morgan (1952, pp. 2270-2271), the No. 1-E Crossett Lumber Company wellinAshley County, Arkansas, encountered the base of the "Eagle Mills salt" (Louannsalt) at 6,485 feet and penetrated 4,651 feet of red shale and sandstone intruded by a number of sills of igneous rock (6,485 to 11,136 feet TD). Kidwell (1949) lists 14 intervals from 6,485 to 10,040 feet that contain igneous bodies and describes the rock as a tinguaite —a nepheline- aegerine phonolite. Morgan considers the "Eagle Mills salt" as Jurassic rather than Permian and the underlying sequence as Paleozoic; 24 he suggests a correlation with the Morehouse formation of northwestern Louisiana. The No. 1-A Tensas Delta well in Morehouse Parish, Louisiana (p. 350),contains the type section of the Morehouse formation which was proposed to include the * There is some controversy over the position of the base of the Jurassic in this area and the age of the Eagle Mills formation (McKee et al., 1956; this report, p. 86). 1,190 feet of dark silty shale and thin beds of siltstone and sandy limestone in the interval 9,285 to 10,475 feet (Imlay and Williams, 1942, p.1672).H.J.Morgan (1952, p. 2271) noted the presence of a few mottled red strata in the sequence. On the basis of pelecypod studies, Imlay and Williams (1942) concluded that the Morehouse formation is late Paleozoic, probably not older than Pennsylvanian; later, in 1954, Hoffmeister and Staplin (1954, pp. 158-159) examined spores from the interval 10,243 to 10,253 feet and concluded that the Morehouse is Middle to Upper Pennsylvanian in age. InBexar County, Texas, the Pagenkopf No. 1 Blum well penetrated deep into a sequence of red, green, and gray shale, locally carbonaceous, and containing thin beds of fine-grained sandstone and limestone (4,580 to 7,179 feet) in an area where surrounding wells encountered highly sheared low-grade metamorphic rocks (p. 226 and PI. 2). The top of this shale sequence seems to correspond with the general elevation of the pre-Mesozoic metamorphic terrane, a surface which dips south at about 200 feet per mile in this area. Thin-section study shows that the rocks are red, brown, green, and gray micaceous silty shale and fine-grained angular poorly sorted micaceous calcareous quartz sandstone containing carbonaceous trash and plant fragments. Some fern and lepidodendron fragments recovered from the 6,734 to 6,737-foot interval have been identified as Pennsylvanian (identifications by R. W. Brown, U. S. Geological Survey, from material submitted by John R. Sandidge, Magnolia Petroleum Company) . Southwest of the No. 1 Blum, the Magnolia No. 1 McKinley in Frio County, Bureau ofEconomic Geology, The University of Texas Texas, penetrated a sequence of red shale, thin-bedded limestone, sandstone, and conglomerate in the interval 10,380 to 11,910 feet between Lower Cretaceous beds and an underlying terrane of highly sheared low-grade metamorphic rocks. H. J. Morgan (1952, p. 2272) noted that seven limestones between 11,630 and 11,900 feet yielded Lower Permian (Wolfcamp) fusulinids. On the basis of lithologic similarity, he correlated "Wolfcamp" beds in the No. 1 McKinley with the beds in the No. 1 Blum. However, some geologists con sider the sequence in the No. 1McKinley to be Jurassic and explain the presence of Wolfcamp fusulinids as reworked from older beds. Interpretation of Wells Penetrating Undeformed and Unmetamorphosed Late Paleozoic Rocks H. J. Morgan (1952) called attention to the occurrence of undeformed and unmetamorphosed late Paleozoic rocks "south and east of the Ouachita folded belt"; he suggested that these beds mark the southern and eastern boundary of the belt, and that the Ouachita belt is a relatively narrow feature (H.J. Morgan, 1952, fig.1) .Inaddition to the four wells cited herein, Morgan included a discussion of the Standard of Texas No.1MitchellinGrayson County, Texas, to support his thesis. In the writer's opinion, the No. 1Mitchell is not pertinent to this problem. Itis located on the fore- land margin of the Ouachita belt and penetrated a normal foreland basin sequence as follows: base of Cretaceous and top of Strawn, 2,370 feet; top of Atoka, 6,735 feet; top of Viola, 9,130 feet; top of Simpson (Bromide) ,9,300 feet; top of McLish, 9,770 feet; top of OilCreek, 10,100 feet; top of Joins, 11,000 feet; top of Ellen- burger, 11,240 feet; TD, 11,540 feet in Ellenburger. 25 The "hard black abundantly slickensided and polished shales and quartzitic sands" described by Morgan as unconformably underlying gently dipping 23 Stratigraphic data from August Goldstein, Jr., personalcommunication, 1955. Strawn beds are, in the writer's opinion, Atoka and not "Ouachita facies." Apparentlyinthis areaAtokabeds wereinvolved in pre-Strawn orogenic movements along the foreland margin of the Ouachita belt. (Immediately to the east, Ouachita facies rocks have overridden Strawn and Atoka beds so there is a record of both pre-Strawn and post-Strawn movements.) Inthe writer's opinion, the best explanation of the undeformed and unmetamorphosed Middle or Late Pennsylvanian and Early Permian sedimentary rocks encountered in No. 1-E Crossett Lumber Company, No. 1-A Tensas Delta, No. 1 Blum, and No. 1McKinley is that they are post-orogenic Pennsylvanian and Permian beds which were deposited in local structural basins within the deformed and metamorphosed Ouachita belt, possibly while final orogenic movements against the fore- land to the north were stillin progress. Red shale and siltstone, locally with carbonaceous debris, are typical of the youngest group of sediments that characterize an orogenic cycle (Pettijohn, 1957, pp. 636644). Except where preserved in grabens or other structurally low areas, these postorogenic deposits were stripped away by post-Paleozoic and pre-Jurassic (in Louisiana and Arkansas) or pre-Cretaceous (in south Texas) erosion. They may be compared to the Triassic Newark group which is preserved ingrabens in the piedmont of the Appalachian belt. According to this thesis, the occurrence of these deposits does not define the southern and eastern margins of the Ouachita belt as H. J. Morgan suggested (1952) .An interpretation similar to that given herein was presented in 1957 by August Goldstein, Jr., in a paper entitled "Minority Report on the Ouachita Fold- Belt," West Texas Geological Society Guidebook, 1957 Fall Field Trip, pages 26-27. If this interpretation is correct, these Middle or Late Pennsylvanian and Early Permian deposits indicate, in the areas in which they occur, that the main Ouachita orogeny was over by Middle Pennsyl The Ouachita System vanian time. This suggests that Van der Gracht's (1931a,p.1027) ideaofPermian orogenic movements is incorrect and that the youngest Ouachita Mountains defor mation along the foreland edge of the belt which Hendricks et al. (1947) dated as post-Boggy (post-early Desmoinesian) may well be Desmoinesian or upper Middle Pennsylvanian in age. The Problem of Humble] Oil& Refining Company No.1Marberry Another well, Humble Oil & Refining Company No. 1 Marberry in Freestone County, Teyas (p. 257), also penetrated red beds of post-orogenic facies. However, these rocks are very weakly metamorphosed. The metamorphism is characterized by a strong hydrothermal element rather than the strong shearing component typical of rocks of the interior zone of the Ouachita belt in this general area. This sequence is tentatively interpreted as late Paleozoic post-orogenic beds altered by a nearby igneous intrusion. Some support for this interpretation is found in the fact that the red beds are overlain by basalt, suggesting that there was indeed later igneous activity inthe region. Foreland Basin and Shelf Rocks North and West of the Ouachita Structural Belt Peter T. Flawn General Statement From Alabama to west Texas, along the foreland boundary of the Ouachita structural belt, are a number of positive and negative foreland structural features; some of these features are positive elements with an early history of stability —part of the older North American craton. They antedate the Ouachita structural belt and acted as foreland buttresses during the late Paleozoic deformation. The deep foreland basins that margin the Ouachita structural belt were certainly actively negative elements during the last stages of the Ouachita belt's mobility because they contain thick accumulations of Late Pennsylvanian and Permian clastic rocks. If the energy that drove the Ouachita belt against the fore- land had not been spent, no doubt these foreland basins would have been buckled downward and strongly deformed in their turn. The late Paleozoic basins along the front of the Ouachita belt appear to have been foreland shelves or shallow basins in early Paleozoic time because they contain thick lower Paleozoic carbonate sequences; drilling shows this to be so in the Mc- Alester and Fort Worth basins. Recent deep exploration inthe lesser-known Black Warrior, Kerr, and Val Verde basins has proven the presence of sequences of lower Paleozoic carbonate rocks on the order of 2,000 or more feet thick. The principal positive elements bordering the Ouachita belt are the Ozark, Ar- buckle 5 Criner Hills, Muenster, Llano, Devils River, Fort Stockton, and Diablo uplifts. The principal negative elements are the Black Warrior, McAlester, Fort Worth,KerrandValVerde basins. The Frontal Basins Black Warrior Basin The Black Warrior basin is located in northeast Mississippi and northwest Alabama (PI.3);itis bordered on the southeast bythe Appalachian structural belt and onthe southwest by the Ouachita structural belt (p. 85).Ithas been described byMellen (1947), Everett (1953), and Braun- stein (1958a, 1958b). Unlike the other basins along the front of the Ouachita belt, the Black Warrior basin is cradled in the Ouachita-Appalachian junction so that its sedimentary prism includes detritus from both tectonic lands. A major stratigraphic problem in this basin is the separation of Atoka beds derived from the Ouachita belt and Pottsville beds derived from the Appalachian belt. The sequence in the basin includes Cambro-Ordovician, Silurian., Devonian, Mississippian, and Pennsylvanian beds. According to Mellen (1947, p. 1805), the section exposed in the Birmingham quadrangle (excepting post-Clinton Silurian and Devonian) is representative for most of the basin, and a more or less typical Silurian-Devonian section isexposed inthe western valley of the Tennessee River. At the time of Mellen's paper (1947), total thickness penetrated in the Black Warrior basin exceeded 12,000 feet. According to Braunstein (1958a, p. 135), the sequence in the basin is Pennsylvanian (Pottsville) , Mississippian (Chester and Iowa), Devonian (Chattanooga), Ordovician (Trenton and Black River),and Cambro-Ordovician (Knox).Cambrian and Ordovician rocks (about 5,500 feet thick) are a thick Bureau ofEconomic Geology, The University of Texas sequence of dolomite, with subordinate limestone, shale, and sandstone. Silurian and Devonian rocks (less than 1,000 feet thick) are mostly limestone, chert, and shale. Mississippian rocks (about I,ooo+ feet thick) are limestone, shale, and sandstone. Everett (1953) and Welch (1959) discussed problems of Mississippian stratigraphy. The Pennsylvanian sequence (thickening from about 8,500 feet in the north to more than 10,000 feet in th south) is sandstone, conglomerate, arkose, and shale with minor limestone beds. The basin is divisible into two structural provinces. Along the Ouachita front in the southwestern part of the area is an irregu lar zone of thrust faulting where Cambro- Ordovician and Silurian rocks have been juxtaposed with Pennsylvanian rocks (Atoka?) .Farther north in the basin is a northwest-southeast fault zone, along which are eight small gas fields in Upper Mississippian sandstones. Carbon ratios were reported to range from less than 55 percent in the deeper parts of the basin to more than 75 percent in the Appalachian belt (Mellen,1947,p.1816). McAlester Basin (By August Goldstein, Jr.) "McAlester basin" was used originally for that part of the Arkansas-Oklahoma Coal basin inOklahoma, whereas "Arkansas Valley" was used similarly for the Arkansas portion. However, it is more appropriate to use the term "McAlester basin" for the entire basin. Recently the term Arkoma basin has become popular (p. 87). The McAlester basin is an east-westtrending structural and depositional basin about 50 miles wide and 180 miles long, extending from east-central Oklahoma to east-central Arkansas. Itis bounded on the south by the Ouachita Mountains, on the southwest by the Arbuckle Mountains, on the northwest by the Hunton arch, and on the north by the Warner uplift and the Boston Mountains of the Ozark uplift. The basin contains a thick sequence of Atokan and early Desmoinesian strata resting on foreland pre-Atoka strata and folded into a series of long, relatively tight anticlines, locally faulted along their crests, which are separated by broad synclines. The only beds exposed in the McAlester basin proper are of Middle Pennsylvanian age (Hendricks et al., 1936).Pre-Pennsylvanian beds include a nearly complete sequence of Paleozoic rocks of Upper Cambrian to Mississippian age, in which there are numerous unconformities and local overlaps. The sedimentary facies is predominantly Arbuckle Mountains or Ozark uplift type and consists of marine shale, limestone, dolomite, and quartzose sandstone, although Maher and Lantz (1953) reported Ouachita facies rocks inthe basin north of Little Rock (p. 89). The Pennsylvanian strata are a thick sequence of alternating sandstones and shales which locally contain thin limestone beds and many coal beds. Plant material is abundant in the Pennsylvanian and much of it is probably nonmarine, although some beds in the western and northwestern parts of the basin are of marine origin (Hendricks et al., 1936, pp. 1343-1345) . In Oklahoma, the thickest sedimentary column in the McAlester basin is in the extreme southwestern part, where it is as much as 20,000 feet thick, the greatest bulk being in the Arbuckle group and Atoka formation. Few wells in the basin have passed through the Arbuckle group of Upper Cambrian and Lower Ordovician age, and none of them were in its deepest part; however, there may be as much as 5,000 feet of Arbuckle rocks in the southwestern portion of the McAlester basin. The post-Arbuckle Ordovician rocks (Simpson to Sylvan) are relatively thin, not exceeding 1,000 feet. Silurian and Devonian rocks (Hunton group, Woodford) amount to another 400 feet, and the post- Woodford Mississippian (Mayes and Mississippian Caney) may exceed 900 feet. Pre-Atokan Pennsylvanian rocks (Pennsylvanian Caney or "Springer," Cromwell, The Ouachita System Union Valley limestone, Union Valleyshale, and Wapanucka) possibly amount to 3,200 feet. However, the maximum thicknesses of individual formations do not coincide so that the total thickness in any one spot may be much less than the overall total. The Atoka is thickest in the extreme southeast part of the McAlester basin in Oklahoma and thins to the northwest. In southeastern Oklahoma itisreported tobe 9,000 feet thick (Hendricks et al.,1936, p. 1345), but in the Waldron quadrangle, Scott County, Arkansas, it is probably on the order of 19,000 feet thick. Post-Atokan Pennsylvanian strata of the McAlester basin (Hartshorne, McAlester, Savanna, Boggy, Thurman, Stuart, Senora) may be as much as 7,000 feet thick, but this total is not present at any one spot. These strata are thickest in central Pitts- burg County, Oklahoma, inthe west-central part of theMcAlester basin. The McAlester basin varies structurally from place to place. Along its western side the exposed Dcs Moines beds dip westward at a low angle, whereas the deeper lying pre-Atoka beds dip generally eastward at a variable but fairly rapid rate producing a discordance between surface and subsurface structures. This has resulted from basinward thickening of the Atoka strata. Most of the folds and faults in the Mc- Alester basin were produced by horizontal compressive forces related to the Ouachita orogeny. These forces were directed northward and northwestward with decreasing intensity away from the Ouachita Mountains. In the Ouachita Mountains, where the compressive forces were greatest, there is much thrust faulting. In the McAlester basin, there are folds and faults roughly parallel to the front of the intensely folded and faulted Ouachita Mountains and trending approximately parallel to the strike of the thrust faults inthe Ouachita Mountains. Near the south margin of the McAlester basin the anticlines and synclines are tightly folded and are terminated by thrust faults. The rocks of the McAlester basin immediately adjacent to the Ouachita Mountains are not metamorphosed, but the sandstones are commonly silicified and contain solid bitumen. Heat and pressure accompanying deformation apparently caused silicification and converted the indigenous oilinto solid and gaseous fractions. In the central part of the McAlester basin the characteristic structure is an alternation of broad open synclines and long, steeply folded anticlines. Some anticlines (Brazil, Hartford) are open and symmetrical with relatively gentle dips along the flanks, but others (McAlester, Adamson, Backbone) are strongly asymmetrical with vertical and overturned dips along the north limb and high-angle thrust faults along the axis. On the west side of the basin some high- angle faults break through to the surface, but many die out upward so that complexity of structure increases with depth. Many of the faults trend east-west likethose of the Arbuckle Mountains structural province (Hendricks, Curvin, and Goldstein, 1950, p.4),butothers are step faults which trend approximately parallel to the strike of the hinge line of the basin. Along the north margin of the basin the surface strata have a regional west dip, but the underlying pre-Atoka beds dip rapidly southward into the basin. Along the north rim,high-angle step faulting into the basin along the hinge line is intersected by the numerous, subparallel, southwestward- trending faults radiating from the Ozark- Boston Mountain region. Numerous small fault-closed structures formed along the hinge line from this combination of faulting and strong regional south dip in the deeper beds. The faults radiating from the Ozark uplift apparently die out near the north margin of the McAlester basin, but some can be traced in the subsurface considerably farther. The Fort Smith district of Arkansas farther east intheMcAlester basin isdivisible Bureau ofEconomic Geology, The University of Texas into two parts (Hendricks and Parks, 1950).Inthe southern part the rocks are strongly folded and are broken by a few reverse faults as in the Ouachita Mountains. In the northern part, the strata are deformed only by gentle folds and normal faults, as inthe Boston Mountains. The similarities in lithology and thickness of the pre-Atoka of the McAlester basin to the strata in adjacent areas, such as the Seminole uplift and Boston Mountains, suggest that the McAlester basin developed at the beginning of Atoka time (Hendricks, Curvin, and Goldstein, 1950) . The Atoka formation generally thickens southward, and in Atoka time the Mc- Alester basin was only the northern part of a larger basin that also included the Ouachita Mountains. Deformation within the McAlester basin began during Atoka timeand continued at least into post-Thurman (middle Dcs Moines) time, probably culminating even later. Continued deformation is indicated by unconformities at the bases of major sandstone formations, by intraformational conglomerates, and by pronounced thinning of strata over major structures. The absence of the Hartshorne sandstone in the Ouachita Mountains to the south of the McAlester basin suggests that at the end of Atoka time the Ouachita Mountains region was uplifted sufficiently to be above sea level, so that the original limits of the Mc- Alester basin were only slightly different than those defined by present occurrences of the Hartshorne sandstone on the surface and in the subsurface (Hendricks, Curvin, and Goldstein, 1950, p. 6). A final stage in the structural history of the basin was regional westward tilting that probably resulted from uplift in the central part of the basin;itmay have occurred as late as post-Cretaceous time. The entire McAlester basin has possibilities for gas production on favorable structures. Gas has been produced from sandstones of Morrowan, Atokan, and Desmoinesian age, from the Viola limestone (Ordovician) and from the Hunton lime } stone (Silurian-Devonian) .Most of it has been dry gas, but wet gas has been produced from several areas on the eastern side of the basin, and oil was produced from Cromwell sandstones and sandstones of the Simpson group in Coal County, Oklahoma, at the extreme western margin of the basin. Adequate porosity and permeability, low to moderate carbon ratios, and presence of a favorable sedimentary facies suggest that the western and northern rims of the McAlester basin are potentially favorable for the occurrence of oilin suit able structures. Grayson County Area Between the northwest-trending Muensand northwest-trending ter element the Amarillo-Wichita-Criner element is a deep narrow basin variously called the Marietta basin, Marietta-Sherman basin, or Marietta syncline. The Ouachita belt is thrust over the southeastern end of this basin and oil and gas have been discovered immediately west of it.Hence, many well data are available on foreland facies rocks adjacent to the Ouachita belt. No Cambrian beds have been penetrated in the Marietta basin, but as they are known on the Muenster uplift inCooke and Denton counties they probably occur in the deeper parts of the basin. Ordovician beds, including Ellenburger and Simpson groups and Viola limestone, may be as much as 8,000 feet thick, according to Bradfield (1957, pp. 44-45) ;the lower part of the sequence is mostly limestone and dolomite and the upper part, limestone and shale with minor sandstone. In early Paleozoic time the Marietta basin was probably a subsiding shelf or shallow basin. Devonian and Lower Mississippian beds are represented by the Woodford formation, mostly dark shale as much as 1,000 feet thick, which lies disconformably on older rocks. The Marietta basin contains a thick sequence of Pennsylvanian clastic rocks of Morrowan(?) toVirgilianage and consisting of shale and sandstone with thin lime The Ouachita System stone beds, similar to those inbasins to the northeast and south. Pennsylvanian beds truncate older rocks. The thickest units are Atoka (Dornick Hills) and Strawn (Deese) . Folding and faulting during Pennsylvanian sedimentation produced local truncations, so that the thickness of the Pennsylvanian beds varies greatly. According to Bradfield (1957, pp. 26-28), Atokan-Morrowan (?) and Strawn strata attain a maximum thickness of 12,500 feet. Younger Pennsylvanian beds aggregate 2,500 to 3,000 feet thick. Foreland facies beds near the Ouachita front are sharply folded and overturned toward the west and are cut by both high- angle reverse faults and younger normal faults (Bradfield,1957, fig.5).The"Red" Strawn (upper Strawn) thickens and coarsens eastward with an accompanying increase in the amount of varicolored chert fragments of Ouachita derivation. According to Bradfield (1957, p. 37), Ouachita folding and uplift must have preceded or been contemporary with deposition of the "Red" Strawn, and final thrusting was later. The Ouachita front in Grayson County is marked by an overthrust (PL 2 and fig. 13) which brings lower Paleozoic Ouachita facies rocks over Strawn (Deese) beds. Structural relations and lithology of the Strawn beds indicate that overthrusting oc curred within or immediately following Strawn time with tilting and normal faultinglater inthe Pennsylvanian (Missourian or Virgilian). Where Ouachita rocks have been thrust against the Marietta basin they have overridden northwest-trending structures such as the Sherman anticline. A well on the southeast end of the Sherman anticline, Tennessee Gas Transmission Company No. 1 Washburn, penetrated Atoka beds lyingon deeply eroded Simpson rocks (Oil Creek) ,indicating that the northwest- trending structures are pre-Atoka. Oiland gas inthe Grayson County area are produced from Strawn (Deese) ,Atoka (Dornick Hills),and Simpson (OilCreek) formations. Fort Worth Basin The Fort Worth basin is innorth-central Texas (PI. 2).Itis bounded on the east by the Ouachita structural belt, on the south by the Llano uplift, on the north by the Red River uplift (Muenster and Electra elements), and on the west by the Texas arch (insome papers the western boundary isgivenastheBend arch,aMiddleorLate Pennsylvanian axis of tilting). Excellent summaries of the geologic features of this basin are given by O. D. Weaver (1956) and Turner (1958). The sedimentary sequence in the Fort Worth basin includes Cambro-Ordovician, Devonian, Mississippian, and Pennsylvanian rocks, allof which,except the Upper Ordovician, are exposed along the north east side of the Llano uplift. Maximum sedimentary' thickness is about 12,000 feet (Turner, 1958, p. 57);the deepest part of the basin is to the northeast, in western Dallas and southeast Denton counties. Precambrian basement rocks have been encountered at 7,660 feet inParker County and at shallower depths along the south and west margins. The Cambro-Ordovician (possibly at taining a thickness in excess of 3,500 feet inthe eastern part of the basin) is a thick sequence of carbonate rock (Ellenburger) with subordinate sandstone and shale. Upper Ordovician rocks (Simpson and Viola) occur only in the northeast part of the basin. Devonian strata form thin (less than 20 feet thick) patches on the Cambro- Ordovician surface intheLlanoupliftarea but have not yet been found in the subsurface. Mississippian rocks range from 200 to 500 feet thick and are mostly shale and limestone. The Pennsylvanian is mostly elastics (sandstone, shale, and conglomerate) with thin limestone beds to the west and north. According to Turner (1958, p. 65), Morrow and Atoka beds thicken from less than 250 feet inthe north to more than 6,000 feet along the Ouachita front, and their maximum original thickness may have been as much as 10,000 feet. Bureau ofEconomic Geology, The University of Texas The Strawn ranges from 1,500 feet thick in the west to more than 4,500 feet thick inDenton and Wise counties. Canyon and Cisco beds are preserved in the north and west parts of the basin; the Canyon is 750 feet to 2,000+ feet thick and the Cisco is 600 feet toI,ooo+ feet thick. The eastern margin of the Fort Worth basin along the Ouachita orogenic front is poorly known and structurally very complex. In some areas Ouachita facies rocks of lower Paleozoic age have been thrust over Atoka beds. At the south end of the basin in Bell County the minimum displacement on this overthrust front is about 6 to 8 miles (PI. 2). Paleozoic rocks of the Fort Worth basin must have been strongly folded and faulted near the Ouachita front. On the north near the Muenster uplift the basin is bordered by northwest-and west-trending faults which have raised basement rocks about 5,000 feet on the northeast; this faulting was pre-Canyon and probably post-Mississippian. Lower Atoka beds near the faults contain arkose derived from the uplifted basement rocks in the Muenster and Electra elements. Positive movements of the Llano uplift are also pre-Canyon; according to Cheney and Goss (1952, pp. 2237, 2246, 2262), the area was one of alternating uplift and subsidence subsequent to deposition of Ellenburger rocks. Structural contours on top of the Ellen- burger show a regional slope of about 50 feet per mile from the outcrop inthe Llano uplift area to a —10,000-foot contour against the fault zone on the southwest side of the Muenster uplift. In early Paleozoic time the area was apparently a shelf or shallow carbonate basin. Whatever Silurian and Devonian sediments were deposited in the area were removed by pre- Mississippian erosion. The thin dark phosphatic shales and spiculitic-crinoidal lime stones of Mississippian and earliest Penn sylvanian age indicate restricted calcium carbonate and mud deposition. During Late Mississippian time orogenic activityinthe Ouachita belt was advancing westward toward the Fort Worth basin, and a thick clastic wedge of Stanley beds was being deposited to the east. As this Stanley trough was deformed, uplifted, and pushed westward, a rapidly subsiding Atoka trough formed on the site of the Fort Worth basin and received Ouachita-belt detritus from the east and MuensterElectra- uplift detritus from the north. Deformation and uplift of the Atoka deposits along the eastern margin of the basin with thrusting of Ouachita facies rocks over them resulted in a shift of the major axis of Strawn deposition to a position west of that of the Atoka. Ouachita orogenic activity continued into Strawn time, as Big- fork and Womble rocks (lower Paleozoic Ouachita facies) are thrust over Strawn beds in Grayson County, northeast of the Fort Worth basin. Farther south, however, there is no recognizable Strawn along the Ouachita front, and Ouachita facies rocks are thrust over the Atoka. Turner (1958, p.76) mapped the subcrop contact between Atoka and Strawn northeast from its outcrop in the Llano uplift in Mills County, through Hamilton, Hood, Tarrant, and northwest Dallas counties. The position of the present subcrop contact is the result of post-Canyon erosion; Cheney and Goss (1952,p.2251) stated: Epeirogeny of the Ouachita Mountain region and westward tilting of the central Texas region apparently did not begin until after Canyon time. This conclusion is based on (1) eastward thickening of Atoka to Canyon beds, (2) eastward deepening of channels in the upper Canyon, and (3) westward thickening of Cisco and Permian beds. Three possible interpretations account for the absence of Strawn along the Ouachita front in the Fort Worth basin: (1) Strawn beds were never deposited because of local post-Atoka —pre-Strawn uplift; the major period of frontal thrusting, as dated in the Grayson County area, was late Strawn orpost-Strawn. (2) Frontal thrusting along the Ouachita belt in the Fort Worth basin was post-Atoka and pre- Strawn (earlier than in Grayson County), The Ouachita System and any Strawn rocks deposited after the overthrusting have been removed by erosion. (3) Strawn beds were involved in the frontal structures of the Ouachita belt and are preserved therein but have not been recognized because they are of a different facies than the western Strawn rocks; according to this hypothesis, the thick wedge of tectonic sediments deposited along the front of the Ouachita belt in the Fort Worth basin includes both Atoka and Strawn but the Strawn limestones (containingthe Strawn fauna) were developed only farther west, at some distance from the front. The third hypothesis derives some support from Turner's observation (1958, p. 71) that there seems to be no significant unconformity between Strawn and Atoka beds, and that their lithologic differences are minor. Strawn shales are less micaceous than Atoka shales, and Strawn conglomerates to the north are more arkosic than those lower in the sequence. However, in Grayson County, on the other side of the Muenster upliftfrom the Fort Worth basin, lower Paleozoic Ouachita facies rocks are thrust over normal Strawn beds. Unless the frontal thrust in this area has a much greater displacement than farther south so that the facies change has been overridden, there was no marked facies change in Strawn beds deposited close to the Ouachita front. The writer favors hypothesis (1) above and believes that the abundant chert and novaculite fragments in the upper Strawn and lower Canyon conglomerates are stratigraphic evidence that the structural belt was an active source area at this time, probably as a result of the orogenic paroxysm that culminated in the frontal overthrusts. The complex structures which are concealed along the eastern edge of the Fort Worth basin are probably similar to those along the southwestern edge of the Val Verde basin and the northern edge of the Marathon region;inboth areas deep drilling has proved the presence of a normal basin section below overthrust Ouachita facies rocks (p. 57). In the eastern part of the Fort Worthbasin, Bigfork chert and Womble shale have been thrust over Atoka beds (Strawn and Atoka in Grayson County) which in turn are underlain by a normal lower Paleozoic basin sequence; along the northern edge of the Marathon Basin, Caballos novaculite has been thrust over Pennsylvanian and Wolfcamp(?) beds which overlie a normal lower Paleozoic basin sequence. In the southern end of the Fort Worth basin there are northeast-trending normal faults which can be traced into the subsurface from the outcrop inthe Llano uplift (Cheney, 1929b, PI. VIII;Turner, 1958, p. 74). Oiland gas production inthe Fort Worth basin is mainly from Mississippian and Pennsylvanian rocks in the northern and western parts of the basin and to a lesser extent from Ordovician rocks in this same area. There is also some small gas production from Lower Pennsylvanian rocks (Marble Falls limestone) on the south margin of the basin. Trough East the Llano Uplift Paleozoic and South of East and south of the Llano uplift in parts of Bell, Travis, Blanco, Hays, and Kendall counties, wells and seismic studies indicate a narrow, arcuate, very thick body of Paleozoic rocks between rocks of the Llano uplift and the Ouachita facies rocks in the Ouachita structural belt. The intervening rocks appear to be foreland facies rocks deformed when the Ouachita prism was crushed against the Llano buttress. The trough in which they lie apparently connects the Fort Worth and Kerr basins around the southeast bulge of the Llano uplift. Seismic interpretations indicate that the sedimentary rocks are more than 12,000 feet thick26 in western Hays and Travis counties so that the Precambrian basement rocks exposed in the Llano uplift drop off sharply to the southeast. Most wells along the southeastern edge 26 Personal communication ;source prefers to remain anonymous. Bureau ofEconomic Geology, The University of Texas of the Llano uplift penetrate a typical shelf sequence of Atoka, Marble Falls, Barnett, and Ellenburger, but insome wells Cretaceous rocks rest directly on Ellen- burger. Along the southeastern margin of the shelf, however, the Atoka sandstones are of orogenic facies and contain abundant chert and phyllite fragments and a higher percentage of feldspar (10 to 15 percent more) than normally. The shales are brecciated and deformed, and there is an indication of incipient metamorphism in both shales and sandstones. These rocks reflect active tectonism in their source areas and apparently took part in subsequent orogenic movements (Shell Oil Company No. 1 Harwell, Hays County; Summerow No. 1Reimers, Franklin No. 1 Reimers, and Cypress Creek Drilling Association No. 1 Romberg, Travis County).One of the most significant wells in this trough is Shell OilCompany No. 1 Purcell inWilliamson County, whichpenetrated over 6,000 feet of Atoka beneath which are Marble Falls —Barnett, Ellen- burger, Cambrian, and Precambrian granite gneiss of Town Mountain type. This well demonstrates the abrupt southeastward thickening of Pennsylvanian beds into the trough. Kerr and ValVerde Basins West of the Llano uplift, the Ouachita structural belt is bordered on the north by a long narrow Pennsylvanian-Permian basin which trends west-northwest. Its eastern part, in parts of Kerr, Bandera, Real, Edwards, Uvalde, and Medina counties, is the Kerr basin; the western part, including parts of Edwards, Kinney, Val Verde, Terrell, Crockett, and Pecos counties, is the ValVerde basin. The boundary between the two basins is an arch extending approximately north-south throughEdwards County where the Pennsylvanian sequence thins. Although related structurally, the two basins differ in stratigraphy. The Kerr and Val Verde basins are bordered on the north by the Llano uplift, Eastern shelf, and the south end of the Central Basin Platform. The western end of the ValVerde basin connects northwestward with the Delaware basin. A Late Permian successor of the Val Verde basin is known as the Sheffield channel. Despite extensive drilling for oil north of the Kerr and Val Verde basins, surprisingly little is known about them. The Val Verde basin is the subject of current wildcat efforts, and more is known about this area than about the eastern part of the basin. The sequence intheKerrbasinissimilar to that in the Fort Worth basin, and the same stratigraphic terminology can be used. Its sequence includes Ordovician (Simpson and Ellenburger) ,Mississippian (Barnett-Chappel) , Pennsylvanian (Marble Falls and Atoka), and Lower Permian (Wolfcamp) .Mississippian rocks are mostly restricted to the east and Simpson beds to the west. Pre-Cretaceous and post-Ellenburger rocks in the Kerr basin are 8,000 to 9,000 feet thick and are mostly dark elastics of Atokan age. A thinMississippian section occurs between the Atoka and Ellenburger to the east. To the west the upper part of the dark clastic rocks is considered by some geologists to be of Wolfcamp age. Some wells in the Kerr basin have penetrated Ellenburger carbonate rocks but were abandoned after drillinga thousand feet orless into Ordovician strata. Presumably Cambrian rocks underlie the Kerr basin but no wells have reached Cambrian orbasement inthe basin proper. 27 One of the thickest sections in the Kerr basin was penetrated in Phillips Petroleum Company No. 1-A Carson in Edwards County: top of Wolfcamp, 1,090 feet; top of Pennsylvanian, 3,140 feet; top of Simpson, 9,500 feet; top of Ellen- burger, 9,657 feet; total depth, 9,970 feet inEllenburger. The Val Verde basin to the west contains 27 The Magnolia Petroleum Company No. 1 Ed Below, Kendall County, on the eastern edge of the Kerr basin penetrated a pre-Pennsylvanian Llano upliftsection including Marble Falls, Barnett, Chappel, Doublehorn, Ives, Ellenburger, Wilberns, Morgan Creek, Welge, Lion Mountain, and Cap Mountain. The Ouachita System a thicker sequence which is more like the west Texas Permian basin section than the Llano uplift section. The only basement test in the basin topped Precambrian rocks at 15,442 feet (Magnolia Petroleum Company No. 1 Brown and Bassett, Terrell County) ; a deeper test in Val Verde County (Phillips Petroleum Company No. 1 Wilson) was abandoned in Cambrian beds (Wilberns) at 16,456 feet. Another Phillips well (No.1Elsinore Cattle Company) drilled on the Sierra Madera in Pecos County spudded inLeonard and was abandoned in Pennsylvanian (Cisco) at 12,096 feet. The Sierra Madera is an anomalous structure so that the thickness penetrated inthis well cannot be used in a general stratigraphic picture. The deepest well in the Val Verde basin and currently the deepest well in the world is Phillips Petroleum Company No. 1-EE University, which bottomed in Ellenburger at 25,340 feet. Addison Young (1960) estimated that the bottom of the well is about 1,000 feet above the basement. About 7 miles to the north, Shell Oil Company (Humphries) No. 1 University encountered basement rocks at 4,809 feet on the southern edge of the Pecos arch (Fort Stockton high),demonstrating a structural displacement of more than 21,000 feet. The ValVerde basin contains a complete Paleo — zoic sequence including Cambrian (100 feet), Ordovician (Ellenburger, 1,500 ± feet; Simpson, 500 to 1,200 feet), Silurian( 300±feet),Devonian (500±feet), — Mississippian (50 feet), and Pennsyl — vanian-Permian (13,000 feet). More than 13,000 feet of the total 16,000 to 17,000 feet of known section isPennsylvanian- Permian, and Frenzel (1957, p. 2) estimated that as much as 10,000 feet of Lower Permian (Wolfcamp) rocks may be present in Terrell and Pecos counties. Addison Young (1960) calculated maximum Wolf- camp thickness as close as 14,000 feet. The sequence from Cambrian through Strawn in the Val Verde basin appears to be normal west Texas basin sequence of carbonates and elastics without excessive thick ness of Atoka and Strawn rocks. The Ellenburger is of typical carbonate facies throughout the Val Verde basin, whereas younger Paleozoic beds change in facies from predominantly clastic facies in the basin proper to a carbonate facies farther north. The Pennsylvanian-Permian boundary north of the Marathon area and in the Val Verde basin has been much debated ;new fusulinid evidence suggests that much of the dark clastic rocks that had been considered post-Strawn Pennsylvanian are of Wolfcamp age. However, the type section of the Wolfcamp in the Wolfcamp Hills northeast of Marathon consists of only 500 to 600 feet of shales, thin limestones, and conglomerates resting on older rocks with strong unconformity and overlain by Leonard beds. This strong unconformity is also present in the western Glass Mountains (Decie ranch area) where it is marked by a coarse conglomerate at the base of the fossiliferous Wolfcamp beds. P. B. King (personal communication, 1957) remarked that the new fusulinid data indicate several possibilities: (a) Beds both above and below the unconformity in the Decie ranch area are equivalent to parts of the Wolfcamp at its type locality, that is, the unconformity corresponds to some level within the Wolf- camp at the type section, (b) The beds below the unconformity inthe Decie ranch area contain fusulinids of Wolfcamp type but are pre-Wolfcamp and post-Virgil in age, representing deposits laid down rapidly along the edge of the mobile belt when little was deposited elsewhere, (c) Wolfcamp-type fusulinids {Pseudoschwagerina and Schwagerina) range down into the Virgil series, or to a lower level than heretofore supposed. The imputations of Wolfcamp age for the beds below the conglomerate fail to consider the collections of fossils made earlier from the Gap- tank formation west of Marathon and the vicinity of the Decie ranch which include fusulinids, ammonoids, brachiopods, etc., — that range from Dcs Moines to Virgil Bureau ofEconomic Geology, The University of Texas these include collections made between the Decie ranch and milepost 580 on the railroad that contain Tritidtes secalius, a Virgil fusulinid (P. B. King, 1937, pp. 80-82 ).The important question raised by King (personal communication, 1957) is whether the Wolfcamp series should be defined on the basis of beds correlative with those of the type section, or on the basis of occurrence of Pseudoschwagerina, Schwagerina, and other alleged Wolfcamp index fossils, regardless of where they occur inthe sequence. The question of the age of the thick clastic section in the Val Verde basin is far from academic because these sediments record orogenic movements in the structural belt and therefore serve to date the orogeny in this part of the belt. The difference between the Val Verde basin and frontal basins to the east and north is that itsmajor downwarp was post-Strawn rather than Atoka. Tectonic activity (uplift of source area and downwarp of frontal basin) in this area, therefore, continued — later than inthe area to the east throughout the Pennsylvanian ifthe clastic wedge ispost-Virgiland intoLower Permian time ifthe clastic wedge is Wolfcamp. Farther southwest in Mexico weakly metamorphosed but strongly deformed Paleozoic rocks are of Wolfcamp age (p. 104).Ifthe thick post-Strawn clastic sequence if of Wolfcamp age, the Canyon and Cisco beds must be missing, so that the Wolfcamp rests directly on Strawn. The southern margin of the Kerr and ValVerde basins is structurally very complex. As in the other frontal basins, the Ouachita mobile belt was thrust against the basin from the south, and in some areas Ouachita facies rocks have overridden fore- land rocks along the south side of both the Kerr and Val Verde basins. The trace of one such fault, the Dugout Creek overthrust, crops out in the Marathon Basin (PL 2). As an additional complicating factor, there is a concealed Precambrian buttress in Kinney and Val Verde counties along the south edge of the Val Verde basin (p. 144). Although no commercial oil fields have been discovered in the Kerr and Val Verde basins, there are commercial gas fields in Terrell, Val Verde, and Kinney counties (Goode, Pan- dale, Morrison, Vinegarone fields). A major gas discovery was made in 1957 in Magnolia Petroleum Company No. 1 Brown and Bassett in Terrell County. Gas is being produced in the basin from Ellen- burger, Devonian, Pennsylvanian, and Permian rocks. Drilling in the Val Verde basin has revealed steeply tilted beds and thrust or reverse faults. Thus, as in the McAlester basin, paroxysms of the Ouachita orogeny folded and faulted the sedimentary rocks of the basin. The southern boundary of the Kerr basin in Uvalde and Kinney counties is not known. The Ouachita belt itself cannot be traced, and there are abundant intrusions of Cretaceous-Tertiary igneous rocks. Basins East and South of the Known Course of the Ouachita Belt In northern Florida, southern Georgia, and southeastern Alabama, some wellshave encountered lower Paleozoic beds of Cambrian to Devonian age whose composite thickness is more than 6,000 feet (Applin, 1951; Bridge and Berdan, 1952; Braun- stein, 1958a, p. 137). These Paleozoic rocks, mostly shales and sandstones, are termed the Suwanee River basin by Braun- stein (1958a, p. 137) and the Suwanee basin inthis report (p. 90).If this basin, like the Black Warrior, McAlester, Fort Worth, Kerr, and Val Verde basins, is a frontal basin whose development was initiated by the Ouachita orogeny, its location suggests that the Ouachita belt borders it on the southwest (PI. 1) .However, its lack of late Paleozoic rocks indicates that it differs from the other frontal basins so that comparison with them must be made with reservations. P. B. King (1950, pp. 657658) suggested, with reservations, that this basin marks the southeast flank of the Appalachian system. The Ouachita System Some Paleozoic rocks are exposed in the poorly known area of northern Mexico south of the last exposure of the Ouachita structural belt in the Solitario uplift of west Texas (PL1and fig.5).Part of the rocks are flysch-type orogenic sediments which resemble the Tesnus and may be Ouachita facies, but other exposures seem to be foreland rocks (p. 99). Perhaps a Paleozoic frontal basin exists in northeast ern Chihuahua northwest of Ojinaga and north of Placer de Guadalupe. Summary The stratigraphic record and the structure of the frontal basins of the Ouachita structural belt provide much information useful in reconstructing the history and development of the Ouachita system. The lower Paleozoic sequence shows that the early Paleozoic foreland of the Ouachita geosyncline was a more or less stable shelf on which thick carbonates and fine elastics were deposited. The abundant siliceous material inthe chert and siliceous shale of the Devonian and other systems is a fore- land reflection of distant volcanic activity in the mobile area to the south and east. Mississippian shales indicate continued fine clastic deposition inthe foreland while the geosyncline was advancing closer toward the craton. Pennsylvanian (Atoka and early Strawn) clastic wedges in the Black Warrior, McAlester, Fort Worth, and Kerr basins record strong foreland downwarps in response to the thrust of the mobile belt against the foreland; later Strawn-Canyon rocks in this area are postorogenic products derived from the uplifted geosynclinal rocks. The latest fore- land basin downwarp in the Val Verde basin to the west was of post-Strawn and possibly mainly Wolfcamp age. Orogenic activity thus probably continued longer in the western part of the Ouachita belt. Uplifts North and West of the Ouachita Belt Ozark Uplift The Ozark uplift is a slightly elliptical domical area in southern Missouri, north ern Arkansas, and northeastern Oklahoma whose long axis extends nearly 400 miles northeast-southwest. Its highest part exposes Precambrian, Cambrian, and Ordovician rocks, and Mississippian and Pennsylvanian beds dip away around the periphery of the uplift (Dake and Bridge, 1932; Huffman, 1958). The exposed Precambrian of the Ozark uplift is granite and rhyolite porphyry. Upper Cambrian sandstone, locally con glomeratic, is overlain (in ascending order) by thick dolomite, limestone, shale, and dolomite, which were deposited on a hillyPrecambrian surface with as much as 1,300 feet of relief inOklahoma and nearly 2,000 feet of relief inMissouri (Dake and Bridge, 1932, p. 630). The Cambrian ranges from a thin veneer to as much as 1,000 feet thick; most of itlies flat, but in places there are steep initial dips of 30 degrees in the lower part. Lower Ordovician rocks overlap the Cambrian sediments and inplaces rest directly on the Precambrian; the Ordovician is dolomite overlain bylimestone, dolomite, sandstone, and shale; it is as much as 1,500 feet thick in the central area and attains 3,500 feet in southwest Arkansas. No Silurian and Devonian rocks occur at the surface except in scattered outcrops, but both systems are represented in subsurface on the flanks of the uplift. Silurian and Devonian rocks are thin limestone, chert, and shale with minor sandstone; the Silurian is as much as 250 feet thick and the Devonian is as much as 600 to 700 feet thick on the flanks of the uplift.The older Paleozoic rocks are overstepped by Mississippian and Pennsylvanian beds, and Pennsylvanian beds may have covered the dome completely at one time (L.H. White, 1926, PL 1).The Mississippian rocks are black shale, fossiliferous limestone, and chert which are overlain by limestone and sandstone that grade upward into a sandstone-shale sequence of Atoka age and pass into a shale-coal section. Mississippian rocks are about 500 feet thick in the central area and 1,500 feet in central- eastern Missouri; Pennsylvanian rocks are as much as 2,500 feet thick. The Pennsylvanian sequence thickens very rapidly into the adjoining basins. The Ozark uplift was positive throughout much of Paleozoic time. The earlier Paleozoic rocks thin toward the crest of the uplift and the younger Paleozoic beds are unconformable on the older rocks. Mississippian and Pennsylvanian beds rest directly on Lower Ordovician rocks in the area of maximum uplift. Successive unconformities record both uplift and tilting. Epeirogeny occurred in Upper Cambrian time (pre-Potosi) ,at the end of Silurian time,inlateDevonian orpre-Mississippian time, late inthe Mississippian, and inEarly and Middle Pennsylvanian time (Huffman, 1958, pp. 105-109) . Although the present uplift is more or less domical, the pre- Mississippian feature was elongate east- west or northwest-southeast, perhaps connecting with the Ellis, Chautauqua, and Hunton arches farther west. Northwest- trending faults and folds cross the Ozark uplift and there are northeast-trending faults in the southwest part of the dome. According to Huffman (1958, p. 109), major deformation in the area is the result of tension in Middle Pennsylvanian time produced by basin loading and cessation of the compressional forces of the Ouachita orogeny. River terraces along the Grand and Arkansas Rivers may indicate intermittent Pleistocene uplift (Huffman, 1958, p.109). Following transgression of the Cambrian seas overahillytomountainous surface of Precambrian rocks, the Ozark region was an area of carbonate deposition on a fairly shallow warm marine shelf on which some The Ouachita System islands of Precambrian rocks remained emergent as late as Early Ordovician time. Silurian and Devonian rocks —limestones, shales, and cherts —were deposited in basins flanking the uplift and may also have been thinly deposited on the older Paleozoic rocks of the uplift. During middle Paleozoic time there was epeirogenic uplift and tilting which resulted inerosion at the end of the Silurian and at the end of the Devonian periods. Mississippian black shales were deposited in deep water over the eroded earlier Palozoic rocks. The succeeding Mississippian fossiliferous limestones, cherts, and black shales indicate continued marine shelf conditions with a limited supply of fine elastics. Broad uplift at the end of the Mississippian was followed by deposition of Pennsylvanian sandstones and fossiliferous limestones with sand and clay more abundant higher in the section. The Atoka sequence is predominantly marine and nonmarine sandstone and shale with thin limestone beds. The post-Atoka beds are shales and coals. During the Pennsylvanian there was an increase in tectonic activity south of the Ozark uplift and an invasion of the earlier shale-limestone marine environment by sands until the entire area was blanketed by sands, probably including the crest of the structure. The post-orogenic Pennsylvanian deposits in the Ozark area were laid down in shallow seas and extensive marine swamps. Arbuckle Uplift The Arbuckle uplift trends northwest- southeast in southeastern Oklahoma; its Precambrian and early Paleozoic rocks are exposed inMurray, Pontotoc, and Johnston counties, and it extends southeastward beneath the coastal plain into Atoka, Bryan, and Marshall counties. The uplift has been discussed by TafE (1902, 1903, 1904), Van der Gracht (1931a), Dott (1934), Ham (1955, 1956b), and others. Precambrian rocks are overlain by a Cambrian through Mississippian sequence which has been divided by Ham (1956b, p. 425) into a southwestern basin province with 12,000 feet of pre-Pennsylvanian sediments and a northwestern shelf province with 7,000 feet of pre-Pennsylvanian sediments. More than two-thirds of the pre-Pennsylvanian rocks are of Ordovician age and are chiefly carbonates. Pennsylvanian rocks which were deposited in the central and northern parts on the site of the pre-Pennsylvanian shelf are about 5,000 feet of marine clastic rocks, including conglomerate, and interbedded limestones; the basin to the southwest (Ardmore basin) received about 17,000 feet of fine-grained Pennsylvanian clastic rocks. This Pennsylvanian basin was more or less congruent with the earlier basin. Epeirogenic uplift of the northeastern part of the Arbuckle area began early in Middle Pennsylvanian with the rise of the Hunton anticline which was emergent and shed clastic sediments and conglomerates in Middle and Late Pennsylvanian time. Granite fragments in Stanley sandstone southeast of the Arbuckle uplift suggest that possibly there were earlier Mississip pian movements of the concealed southeast end of the structure (p. 73). During the uplift the basin to the southwest continued to subside. Tectonism in this southwestern area was Late Pennsyl vanian and was orogenic instead of epeirogenic; the sediments were strongly folded, thrust faulted, and uplifted. The structural uplift was so great that probably 16,000 feet of sediments were stripped from the area (Ham, 1956b, p.426). The Arbuckle uplift includes major northwest-trending folds and faults; at least two faults have a strike-slip component of movement (Ham, 1956b, p. 426). The Arbuckle uplift is a compound epeirogenic and orogenic tectonic element and thus differs from the other frontal uplifts of the Ouachita system. Before Pennsylvanian time the stratigraphic record indicates that it did not differ markedly from other foreland areas except for a thicker sedimentary sequence in the south Bureau ofEconomic Geology, The University of Texas western basin; its deposits included Cambrian sandstones and thick Ordovician carbonates and succeeding Ordovician, Silurian, Devonian, and Mississippian shales, limestones, and sandstones of foreland shelf type. The epeirogenic rise of the northeastern area or Hunton anticline in Middle Pennsylvanian time follows the pattern of other frontal uplifts. An unusual feature was the development of an intracratonic deep trough, the Ardmore basin, south of the Hunton uplift and its subsequent deformation during the Arbuckle orogeny. Deformation in the Arbuckles was of Late Pennsylvanian (Virgil) age according to Ham (1956b, p. 425) and was thus more or less contemporary with the last phases of orogenic activity in the Ouachita Mountains. Muenster Arch The Muenster arch is a northwest-southeast- trending uplift that forms the southeast end of the Red River upliftunder parts of Denton, Cooke, and Montague counties, Texas, and Jefferson County, Oklahoma (PI. 2).Itis a Paleozoic subsurface feature and is not expressed in the overlying Meso zoic rocks. On the crest of the uplifted core of the Muenster arch, Precambrian igneous and metasedimentary rocks are overlain directly by Late Pennsylvanian beds which truncate the older Paleozoic rocks (Cambrian, Ordovician —including Simpson and Viola—and Mississippian) still preserved on the flanks. The arch is faulted on the southwest where basement rocks on the northeast orupthrown side are raised about 5,000 feet. The faulting is of post-Mississippian and pre-Canyon (Upper Pennsylvanian) age. The first Paleozoic movement of the Muenster element is indicated by the shale and sandstone in the Late Mississippian and Early Pennsylvanian deposits adjacent — to it these pass into carbonate rocks and black shale in the basin to the south. Atoka elastics overlap the flanks of the upliftand Strawn sandstones and conglomerates are arkosic on its flanks. Apparently, the Muenster uplift became active in Late Mississippian time and its major positive impulses occurred during Atoka and Strawn time; itwas positive and emergent during Early and Middle Pennsylvanian time and shed arkosic elastics southwest and northeast. Upper Pennsylvanian Canyon beds thin over the structure, indicating continued positive tendency but the Cisco shows only a very slight thinning. In some areas the Upper Pennsylvanian lies directly on the Precambrian, showing that disconnected high areas persisted as islands in Middle Pennsylvanian time. Permian beds overlie the Upper Pennsylvanian conformably. The Muenster arch, which is part of the Red River uplift, was raised inlate Paleozoic time; there is no evidence to suggest that it had any positive tendency earlier in the Paleozoic. The Red River upliftmay have been controlled by a Precambrian structural trend (Flawn, 1956, pp.38-39). Llano Uplift The Llano upliftof central Texas raises Precambrian and Paleozoic rocks to the surface inBurnet, Llano,Blanco, Gillespie, Mason, Kimble, Menard, McCulloch, and San Saba counties and extends as a structural unit into the subsurface farther north and west. This area was stabilized by profuse granitic intrusions during Precambrian time (Flawn, 1956, pp. 26-27) and at the beginning of Paleozoic time formed a great southern lobe on the North American craton which profoundly influenced subsequent geologic history; it has had intermittent positive tendencies since Precambrian time and acted as a firm buttress against the forces of the Ouachita orogeny. The area is now a topographic basin floored by Precambrian metasedimentary, meta- igneous, and igneous rocks and partly surrounded by a rim of Paleozoic rocks that also are downfaulted in grabens within the basin. Along the southern margin is a scarp of Cretaceous rocks. Inthe Llano uplift there are about 1,200 The Ouachita System feet of Upper Cambrian and Lower Ordo vician sediments, mainly sandstone and calcarenite, deposited on a hilly surface with a maximum relief of about 800 feet. A thin remnant of Upper Ordovician limestone is preserved in a collapse structure in the eastern part of the uplift (Barnes, Cloud, and Duncan, 1953) ,but no Silurian rocks are known. A thin and fragmentary record of once extensive Devonian rocks consisting of dark shales, commonly phosphatic, and local chert breccia is preserved in scattered outcrops mostly along the eastern edge (Cloud, Barnes, and Hass, 1957) . The Mississippian is mostly dark shale, commonly phosphatic, and crinoidal limestones generally 40 to 50 feet thick but insome localities more than 100 feet thick. Lowermost Pennsylvanian rocks are mostly dark cherty limestone and dark shale, succeeded by sandstone, shale, conglomerate, and thin limestone of Middle and Upper Pennsylvanian age. The maximum thickness of the Pennsylvanian in the Llano uplifetotals about 1,000 feet for the limestone- shale sequence and about 1,400 feet for the overlying clastic rocks. According to Cloud and Barnes (1957, pp. 194-209), the first Paleozoic sea to invade central Texas submerged a land with considerable relief; the environment was one of moderately deep cool water and abundant available detritus, probably with a number of protruding islands. Toward the end of the Cambrian and the beginning of Ordovician time the waters grew warmer and shallower and shoal conditions prevailed. At the beginning of Ordovician time either the Ouachita trough was in existence or the hinterland to the—south and east had been reduced to a peneplain perhaps both (p. 209). The presence of a channel or trough south and east of the Llano uplift in the Ordovician is indicated by the absence of water-borne detritus in Ellenburger rocks. Evidently, the Llano area was relatively stable in Early Ordovician time, but prior to Simpson time the Ellenburger rocks were truncated (Cloud and Barnes, 1957, p. 209).Before the end of the Ordovician the Llano area was probably uplifted as the south end of the Concho or Texas arch (Cheney and Goss, 1952, pp. 2244, 22622263; Adams, 1954, p. 4). There is no record of Silurian history. In Devonian and Mississippian time the Llano uplift area received a thin deposit of dark phosphatic muds, indicative of slow restricted marine sedimentation. The black shales transgress truncated Ordovician carbonates. Structural movements in the Llano up liftarea began inthe Lower Pennsylvanian and continued into Middle Pennsylvanian time inresponse to tectonic activity in the Ouachita mobile belt. Pennsylvanian sedimentation started withlimestone and shale on a more orless stable platform. As movements in the geosyncline to the southeast came to a climax, the Llano area was uplifted and block faulted; the flanks were blanketed with sandstone, conglomerate, and shale, withthinlimestone inthehigher part of the sequence. North-and northeast- trending block faulting occurred during Middle Pennsylvanian (Strawn) time and at some time after Upper Pennsylvanian (Canyon) time the entire area was tilted westward. Fort Stockton High (Pecos Arch) The Fort Stockton high, or Pecos arch, is a west-northwest-trending uplift extending through Sutton, Crockett^ Terrell, and Pecos counties which forms the northern boundary of the ValVerde basin; itis the southern end of a larger uplift known as the Central Basin Platform. On itscrest Permian beds liedirectly on Precambrian rocks (Scobey et al., 1951), but on its steeply dipping or faulted flanks Permian beds truncate Ordovician through Pennsylvanian beds which dip north and south away from the axis of uplift.On the south side Pennsylvanian beds lie unconformably on Ordovician and Devonian rocks and are in turn overstepped by Permian strata; on the north side Permian Bureau ofEconomic Geology, The University of Texas rocks rest unconformably on the Devonian (Scobeyetal., 1951). The major uplift of the Fort Stockton high occurred inLate Pennsylvanian (post- Virgil) and pre-Permian time (Wolf camp), but there may have been earlier movements (Adams et al., 1951, p. 2600, fig.1; P. B. King, 1942, pp. 718-763) as well as later Wolfcamp movements. Whether this block was raised as a horst or whether its high position resulted from downwarp of the basins to the south and north, the Fort Stockton high was positive and emergent inLate Pennsylvanian time. Paleozoic rocks mantling it were stripped off by erosion and the basement was exposed. The Fort Stockton high probably had no pre-Pennsylvanian history as a persistent positive element; it is a late Paleozoic foreland structure. Devils River Uplift Wells drilled in southwest Kinney and southeast Val Verde counties and across the Rio Grande inMexico indicate a structurally high area that appears to trend northwest-southeast; Galley (1958, p. 397) named this the Devils River uplift, but itis also known locally as the Del Rio uplift; its structure has been discussed briefly by Flawn (1959c). There is insufficient well control to delimit the structure accurately, but contours on pre- Mesozoic and Precambrian basement rocks suggest that itis about 100 miles long and 40 miles wide (fig. 2 and p. 172).Plate 2, Section C-C, shows a schematic northeast- southwest cross section of the Devils River uplift which consists of a mass of Precambrian rocks, apparently mostly metavolcanic rocks, mantled by lower Paleozoic carbonate rocks (Ordovician?). On the south side the Devils River uplift has been overridden by sheared and thrust- faulted low-grade metamorphic rocks of the Ouachita structural belt, and the fore- land Paleozoic rocks on the uplift have been sheared and slightly metamorphosed. To the north a clastic sequence of Pennsylvanian rocks thickens rapidly basinward. The Precambrian age of the metavolcanic rocks is indicated by their mantle of lower Paleozoic carbonate rocks and by their lithology, which is not like the metamorphic rocks of the Ouachita belt but resembles late Precambrian metarhyolite exposed in the Van Horn area. Cretaceous rocks rest on the Paleozoic carbonate rocks and possibly in some areas rest directly on the Precambrian. The upliftmay have a mild expression in Cretaceous rocks; Calvert'smap (1928, p.81) shows an anticlinal axis which in part corresponds to the inferred position of the subsurface feature. The sheared and slightly metamorphosed nature of the Paleozoic carbonate rocks overlying the Precambrian suggests that the Devils River uplift played a role in the Ouachita orog — eny similar to that of the Llano uplift a resistant buttress against which the Ouachita system was thrust. Unlike the Llano uplift, the Cretaceous cover of the Devils River uplift was not breached by erosion, although there may have been some post- Cretaceous epeirogenic uplift. Three wells which disclose the presence of the Devils River uplift are Havoline Oil Company No.1Weatherby, Kinney County (p.284);Richardson OilCompany No.1 Martin Rose, Kinney County (p. 286) ;and Hiawatha OilCompany No.1Sellars, Val Verde County (p.322).The concept of the Devils River uplift is based on an interpretation of samples from these wells. The samples are difficult to interpret because they include three types (and probably at least two ages) of sheared metamorphic — rocks (a) an allochthonous sequence of low-grade highly sheared Ouachita rocks including marble, slate, metaquartzite, and phyllite, commonly hematitic, rutiliferous, and graphitic, thrust infrom the south and probably Paleozoic inage; (b) an autochthonous sequence of slightly metamorphosed foreland facies Paleozoic carbonate rocks, mostly dolomitic limestone and dolomite, overridden by (a) above and underlain by (c), an autochthonous se The Ouachita System quence of sheared metavolcanic rocks of probable Precambrian age. Present information does not permit detailed reconstruction of the history of the Devils River uplift.The early Paleozoic carbonate sequence suggests that it was a shelf in early Paleozoic time. Whether middle and late Paleozoic rocks were deposited inthe area and later stripped off followingPennsylvanian uplift,or whether the area was positive and emergent inmiddle and late Paleozoic time is a matter for conjecture. In the writer's opinion, the location of the feature and its relations to the Ouachita belt indicate that it is a craton-margin positive element similar to the Llano uplift. Diablo Platform The Diablo Platform is a northwest southeast-trending element in Culberson, Hudspeth, Jeff Davis, Brewster, and Presidio counties, Texas, extending northwestward into New Mexico. The northwestern and southeastern parts are little known and poorly denned, but inthe central part (Van Horn area and Sierra Diablo) Precambrian, Ordovician, Silurian, Devonian, and Mississippian rocks truncated by Wolf- camp beds are exposed (P. B. King,1942, figs. 18, 19; 1949). Strongly deformed and metamorphosed Precambrian rocks are unconformably overlain by about 750 feet of late Precambrian (? ) red sandstone, arkose, and conglomerate, which in turn are unconformably overlain by about 1,300 feet of Ordovician strata including a basal sandstone and a succeeding carbonate section. Thin Silurian, Devonian, and Mississippian rocks crop out only on the northeast side of the Sierra Diablo, but there is no indication in their lithology of any nearby shore orland so probably they covered the structure and were later eroded (P. B. King,personal communication, 1959). The Diablo Platform was intermittently positive. Following late Precambrian orogeny and deposition of post-orogenic late Precambrian (?) rocks (Van Horn sand stone), there was tilting and faulting before transgression of the Ordovician rocks (King and Flawn, 1953, pp. 115117). Late in the Pennsylvanian, rocks of the Diablo Platform were folded, faulted, and deeply eroded prior to transgression of Wolfcamp beds. Another cycle of emergence, faulting, and erosion occurred after Permian and before Cretaceous time. Ordovician, Permian, and Cretaceous rocks all rest directly on Precambrian in the central part of the uplift (King, in P. B. Kingand Flawn,1953,p.97). It appears that the Diablo Platform extends southward into Presidio and western Brewster counties. Two wells west of the Marathon uplift (Sun Oil Company No. 1McElroy and Pure OilCompany No. 1Massie West, both in Brewster County) either passed from Permian beds directly into Devonian and Ordovician or penetrated a relatively thin Pennsylvanian section. Close spacing of the folds and thrust faults inOuachita facies rocks inthe western part of the Marathon Basin suggests that they may have been crowded against a foreland buttress to the west or northwest during the late Paleozoic deformation (p. 166). Summary Foreland uplifts marginal to the Ouachita structural belt are of two types :(1) large, more or less domical uplifts with a history of positive tendency throughout the Paleozoic (Ozark and Llano uplifts) and (2) smaller elongate-faulted uplifts of late Paleozoic age (Muenster and Fort Stockton (or Pecos) uplifts). The Devils River and Diablo uplifts are not well enough known for classification. The large persistently positive features antedate the formation of the Ouachita system; they are old fundamental elements of the North American craton and to a great extent influenced the course of the Paleozoic Ouachita system, which was a craton-margin mobile belt. Faulted uplifts (2, above) probably formed in part as a response to the orogenic thrust of the Ouachita belt against the craton. Probably the Bureau ofEconomic Geology, The University of Texas form and trend of at least the Muenster and Fort Stockton (or Pecos) elements were controlled by Precambrian structural trends, and the Ouachita thrust was resolved along these pre-existing zones of weakness. Although orogenic forces of the Ouachita belt may not have been directly responsible for large foreland uplifts such as the Central Basin Platform, the thrust of the Ouachita system against the oraton contributed to the general mobility which existed in the foreland area during the late Paleozoic. The Arbuckle uplift is not solely — an epeirogenic uplift its rocks were deformed and raised during an independent intracratonic orogeny and formed a buttress against the late thrust of the Ouachita orogeny. The Ouachita System — Explanation of symbols and ratios. The following abbreviations are used in this section and pertinent illustrations: K= kaolinite; Ch=chlorite; I=illite; M— montmorillonite; ML=mixed-layer illitemontmorillonite; F = 20 =plagioclase = feldspar ; F 24 =potassium feldsp ar; SR=sharpness ratio;10/7=ratio of height of illite X-ray peak (10A) to the combined (ifboth are present) chlorite and kaolinite (7A) X-ray peak. For equal amounts of clay, chlorite and kaolinite commonly afford a 7A peak approximately 2.5 times as large as the 10A illitepeak. Thus a 10/7ratio of 2 means that illiteis approximately 5 times as abundant as the chlorite and kaolinite combined. — Acknowledgments. -The writer wishes to thank the many Shell Oil Company geologists who have supplied samples for this study and management of Shell and Continental Oil Companies for generously allowing him to participate in this project. Special acknowledgment is made to A. R. Edwards, J. E. Galley, W. S. Pike, F. T. Connolly, and R. G. Stevenson for their help and encouragement in various phases of this work. X-ray analyses were made in the Shell OilCompany's Research Labora tory. SHARPNESS RATIO In analyzing X-ray data, the relative sharpness of the illite 10A reflection appears to be related to the degree of metamorphism as determined by microscopic studies. In general, large flakes and well- crystallized clays afford sharper X-ray reflections than small, poorly crystalline clayminerals. Inanattempt toobtain some measure of the relative sharpness of the 10A peak, a plastic overlay 6.7 inches long withparallel vertical lines representing the 10.0Aand the 10.5Aspacings was placed so that the top of the 10.0Aline coincided with the tip of the 10.0 Aillite peak and was perpendicular to the horizontal base of the chart paper; the values from the base of the 10.0Apeak to the point where the 10.5Avertical line intersected the side of the peak were measured and the total peak height was measured; the ratio of these two values appears to give a reason able measure of the relative sharpness of the 10.0Apeak (fig. 8). (As the shape of the left-hand side of the 10.0Apeak is rela tively constant, it was not necessary to measure values for both sides of the peak and calculate akurtosis value.) SR values range from less than 1inunmetamorphosed foreland facies rocks to more than 12 inmetamorphic rocks of the interior zone of the Ouachita belt. GENERAL REMARKS ON MINERALOGY Kaolinite occurs in nearly all foreland sediments and is rarely present in Ouachita facies sediments. Illite (70%) and chlorite (30%) together comprise the great bulk of the clay minerals in the sediments studied; the relative abundance of illiteand chlorite does not appear to have relation to the degree of metamorphism. The samples with low SR values contain mixed-layer illite-montmorillonite (predominant ratios 9:1 to 7:3, i.e., 9 parts illite to 1part montmorillonite).The first detectable effects of regional metamorphism by X-ray diffraction are the removal of the interlayer water from the montmorillonite layers and the reduction of their thickness to near 10A. Further metamorphism causes increased orientation and anincrease incrystal size (Bates, 1947). The illiteinboth the Ouachita and fore- land rocks and in low-grade metamorphic and unmetamorphosed rocks has a 2M (muscovite-type) structure. The metamorphosed illites,ingeneral, have sharper and stronger reflections in the region from 3.20 Ato 2.70 Athan do the unmetamorphosed samples. Many rocks of the Ouachita belt are traversed by veinlets and microveinlets which in some areas contain abundant chlorite (p. 118) ;thus, X-ray analysis of The Ouachita System 151 en enen •z •z•z¦z > >¦z¦z > SYS- SYS-SYS-TEM TEMTEM z zz SE-> >SE-SE->o o M ooo Mo M nn nnnn RIES^ RIES^RIES^ Atoka Elvira Elvira Homberg Design Ste. Louis Salem SalemLouisSte.DesignHombergElviraAtokaAtoka ElviraElvira Elvira Homberg Design Ste. Louis Salem St. St.St. GROUP Morrow Pre-Morrow Genevieve Warsaw WarsawGenevieveMorrowGROUPGROUP Pre-MorrowMorrow Pre-Morrow Genevieve Warsaw Post-New NewPost-Post-New '11l '11l'11l ka' . .ka'ka' . ika ikaika :lawa: At. Pr Ate AteAt.:lawa::lawa: PrAt. Pr Ate III! Upper Mississippia UpperIII!III! MississippiaUpper Mississippia INI! INI!INI!.shale Mississippian'limestone limestoneshale..Mississippian'shale Mississippian'limestone [i [i[i ™i|| ™i||™i|| rocks. alena Upper or Upperalenaalena orUpper or HUECO Middle MiddleHUECOHUECO Middle Magdalena Lo dagc ¦I ¦ILoMagdalenaMagdalena dagcLo dagc ¦IHelms Lower LowerHelmsHelms Lower Helms and/ and/HelmsHelms and/ 1 clay clay11 clay Pennsylvanian ' '' "I "I"I .RATHON Haymond Dimple Upper Lower LowerUpperHaymond.RATHON.RATHON DimpleHaymond Dimple Upper Lower Tesnus TesnusTesnus \ \\ Tesnus Montmorillonite MontmorilloniteTesnusTesnus Montmorillonite mixed-layer mixed-layermixed-layer Lower .1 .1.1 y 111 111yy 111 Tj TjTj1[ [ 11[ Fa. Falls FallsFa.Fa. Falls and 1 11 11 1111 I 11 11II 11 .tokay,a .tokay,a.tokay,aif ififpper pperpper sle 3wer jle 111 1113werslesle jle3wer jle 111 | || I II j jj LLANO Barnett BarnettLLANOLLANO Barnett 1 11 I II j jj11 1111 M | |MM |II IIII f ffMarl vlarb: 1 vlarb:MarlMarl 1vlarb: 1 I II , 1 1,, 1Mississippian ir. .> .irir.>. .> I II Atoka Che' lowa Che'AtokaAtoka lowaChe' lowa \i \i\i JWARRIOR WARRIORJJWARRIOR Upper J> rnec chlorite rnecJ>J> chloriternec chlorite ai aiai Upper UpperUpper ottsville J>J> of Central Atoka Bloyd Hale Pitkin Fayetteville -> L/X/V/j L/X/V/j->FayettevillePitkinHaleAtokaCentralCentral BloydAtoka Bloyd Hale Pitkin Fayetteville -> L/X/V/j McALESTER McALESTERMcALESTER 1, 1,1, Distribution Caney CaneyCaney Atoka -', Morrow Spr Spr-',AtokaAtoka Morrow-', Morrow Spr: w w:: wvk Chester 4J Chestervkvk 4JChester 4J 9. ANADARKO ANADARKOANADARKO /Ol niite niite/Ol/Ol niite Fig. f ff \ \\ Atoka :erville Jolliff Springer Caney Cvvvvi CvvvviCaneySpringer:ervilleAtokaAtoka Jolliff:erville Jolliff Springer Caney Cvvvvi 1. 1.1. ARDMORE Primrose life. PrimroseARDMOREARDMORE life.Primrose life. O1 O1O1 41 4141 .oka .mi* .mi*.oka.oka .mi* :ka Springer Caney Springer:ka:ka CaneySpringer Caney At AtAtS.V S.VS.V x xx Eastern EasternEastern McALESTER Wap; Limesto: m^pHi Cromwell Cromwellm^pHiWap;McALESTERMcALESTER Limesto:Wap; Limesto: m^pHi Cromwell !l !l!l . Valley] Valley].. Valley] Atoka Upper UpperAtokaAtoka Upper Stanley Lower LowerStanleyStanley Lower Stanley StanleyStanley OUACHITA jjohns Jackfork jjohnsOUACHITAOUACHITA Jackforkjjohns Jackfork Distribution of Clay Minerals in the Ouachita Belt Oklahoma In Oklahoma, pre-Upper Mississippian sediments generally contain a relatively simple illite-chlorite clay suite, whereas the post-Lower Mississippian sediments usually contain montmorillonite, mixed- layer illite-montmorillonite (and frequentlyintergrowths of chlorite), and kaolinite inaddition toilliteand chlorite (fig.9). This difference is more pronounced in the foreland sediments than inthe geosynclinal sediments. Analysis of approximately 75 outcrop and 25 subsurface samples from the pre- Upper Mississippian rocks of the Ouachita Mountains area indicates that illiteis the only clay in approximately 40% of the samples and illite with chlorite occurs in 60%. Most of the samples contain only 5% to 10% chlorite and none contain more than 40%. Kaolinite is relatively minor but occurs scattered throughout the section. Scattered samples (55) of foreland facies rocks in the Arbuckle Mountains and the Ardmore, Anadarko, and Fort Worth basins resemble those of the geosynclinal facies, although kaolinite is more abundant; mixed-layer illite-montmorillonite (4:1-2 :3) 28 is abundant in the Simpson and upper Arbuckle; mixed-layer chlorite-montmorillonite (1:1) is abun dant in the upper and middle Arbuckle. The post-Lower Mississippian formations of Ouachita facies —Stanley, Jack- fork, Johns Valley,and Atoka—are similar in composition, being predominantly illite (70%) and chlorite (30%) with minor amounts of kaolinite and mixed-layer illitemontmorillonite. The Stanley sediments generally contain less kaolinite and mixed- layer illite-montmorillonite and more feldspar than the sediments of the three younger formations. Equivalent formations of foreland facies 28 4:1indicates 4 parts illite to 1part montmorillonite. are the Caney, Chester, Springer, Morrow and Atoka. The Caney is composed predominantly of illite, the Chester and Springer of montmorillonite and/ormixed-layer illite-montmorillonite,and the Morrow and Atoka contain abundant illite and significant amounts of kaolinite, chlorite, and mixed-layer illite-montmorillonite. The following discussion of the transition between the geosynclinal and foreland sediments is taken from Weaver (1958). Figure 10 is a generalized cross section showing distribution of the major clay mineral facies in southern Oklahoma. True Ouachita facies sediments in the Ouachita Mountains lie south of the Ti Valleyfault (PL2).Between theTiValley and Choctaw faults, 2 to 10 miles north, is a series of sediments which is thought by Hendricks et al. (1947) to be transitional between the Ouachita sediments on the south and the Arbuckle sediments on the north. Sediments north of the Choctaw fault are typical Arbuckle facies (foreland facies) sediments. Outcrop samples were collected from McCurtain County, Oklahoma, in the extreme southern part of the Ouachita Mountains, south of the Ti Valley fault, in the northern part of the Ouachitas, and between the Choctaw and TiValley faults. The lower part of the Stanley in Mc- Curtain County consists of several hundred feet of hard black shale which is overlain by a 90-foot tuff bed. The shale and tuff are of Meramecian age and are generally believed to be the equivalent of the black Caney shales of Arbuckle facies (Hass, 1950). The basal black shale consists of illiteand abundant chlorite and kaolinite, the latter being in sharp contrast to the Caney shales which are characterized by a low chlorite and kaolinite content. The gray shale adjacent to the tuff beds contains illite and mixed-layer chlorite-ver miculite, the mixed-layering probably Bureau ofEconomic Geology, The University of Texas 1M 1M being due to weathering of chlorite. The main tuff bed contains a green, iron-rich 29 illite (glauconite-celadonite) ;however, several of the thinner beds which have been identified as tuff beds contain well-crystallized 2Millite(muscovite type) which has a Sr-Rb age of 500 millionyears. The large discrepancy between this age and the Mississippian age of the Stanley suggests that theillitemeasured isanolder detrital mineral and not the product of Mississippian volcanism. The basal black shale a few miles south of the TiValley fault (approximately 70 miles northwest of the McCurtain County outcrops) consists of illite and only minor amounts of chlorite and kaolinite; it is more similar to the Caney shales. The gray Stanley shales throughout the rest of the section consist uniformly of varying amounts of illite (2M) and chlorite (weathered to chlorite-vermiculite). In addition to quartz, nearly all the Stanley shale samples contain minor amounts of feldspar. The Jackfork shales contain illite (2M) and mixed-layer illite-montmorillonite and minor amounts of chlorite and kaolinite. The Johns Valley shale is similar to the Jackfork but contains considerably more chlorite and kaolinite, which appear to increase higher in the section. The Atoka shales are similar to the Johns Valley shales but have even more chlorite and kaolinite and resemble the Atoka shales from the Ardmore and Anadarko basins. Montmorillonite-rich shales which occur sporadically throughout the foreland Atoka and Morrow were not found in the AtokaorJackfork inthis area. Scattered samples taken from between the Choctaw and TiValley faults in Hendricks' transitional zone (Hendricks et al., 1947) indicate that their clay mineral content is, in general, similar to that of foreland facies sediments. The Atoka shales are the same as those of foreland facies, and the Wapanucka limestone and associated shales (Morrow) are similar to the Ardmore basin Morrow, that is, the shales 28 1M=one-layer monoclinic; 2M=:lwo-layer monoclinic. are highly micaceous and the bioclastic limestones contain abundant montmorillonite. The lower few hundred feet of Springer and the upper portion of the black Caney shales are montmorillonitic and have a clay-mineral suite similar to the Chester and, somewhat less so, to the Springer shales of the Ardmore and Anadarko basins; either montmorillonite or mixed-layer illite-montmorillonite may be dominant; illite, chlorite, and kaolinite are present in amounts more characteristic of the Chester than the Springer. The lower Caney shales are largely illitic,and although they do not contain any mixed- layer clays they are similar to the Ardmore basin Caney. At Grants Gap, 10-IS-12E, about one- quarter mile south of the Ti Valley fault, a section of lower Stanley shale was sampled. The lower few hundred feet contains an abundance of montmorillonite and resembles the Springer more than the Stanley; however, chlorite, illite,and feldspar increase upward where the shales are more like typical Stanley shales. The distribution of the clay minerals in the Springer between the Ti Valley and Choctaw faults and in the southeast Ardmore and southwest McAlester basins indicates that this is the area of transition between the western montmorillonitic facies and the southeastern illiticfacies. Trans-Pecos Texas The distribution of clay minerals in the Ouachita belt in the Marathon region (fig. 9) is similar to that in the Ouachita Mountains. Analysis of 30 outcrop samples of pre-Upper Mississippian rocks shows that illite is the only clay in approximately 30% of the rocks and illite with chlorite (and often minor mixed-layer illitemontmorillonite) comprises 60%. Mixed- layer illite-montmorillonite is abundant in the Woods Hollow shale and Fort Pena formation (Middle Ordovician). Mixed- layer chlorite-montmorillonite is abundant in the Alsate shale, Marathon limestone (Lower Ordovician) t and Dagger Flat for The Ouachita System mation (Upper Cambrian).Smallamounts of kaolinite were found in five samples. Scattered subsurface samples and out crop samples from the Franklin Mountains and Llano region, inthe foreland area, are similar in composition to those examined from the Marathon area. The Tesnus formation (post-Lower Mississippian) resembles the Stanley. The lower Tesnus shales, in general, contain about 70% illite,30% chlorite, and possibly minor amounts of kaolinite. The chloritic material is a mixed-layer chlorite vermiculite (or chlorite-montmorillonite) which is thought to have been formed by the recent weathering of chlorite. As in the Stanley, these lower Tesnus shales grade upward into shales which have an increased illite content. Here the chlorite is more weathered and is actually a vermiculite. The Tesnus shales, like the Stanley shales, also contain feldspar. Upper Tesnus shales contain, in addition to illite and chlorite, a mixed-layer illitemontmorillonite (7:3) similar to that found in the Chester and Morrow rocks of the foreland. The lower part of the Dimple formation has a similar clay mineral suite. Throughout the remaining Dimple, mixed- layer illite-montmorillonite and/or montmorillonite are dominant and illite and chlorite are only minor. The lower part of the Haymond formation contains illiteand lesser amounts of mixed-layer clay, chlorite, and kaolinite. The Dimple, of probable Morrow age, is mineralogically similar to the lower Magdalena of known Morrow age. The lower Haymond has a typical Atokan suite of clay minerals. The heavy minerals of montmorillonitic Dimple shales contain about 50% apatite and varying amounts of collophane, zircon, tourmaline, biotite, and rutile. The abundant apatite and biotite indicate that some of these clays were derived from igneous rocks (possibly volcanic material). In the Hueco Mountains of west Texas, the Meramecian is represented by lower Helms limestone and shales > and the Chester by upper Helms shales and sandy shale. The Helms is overlain by 1,300 feet of Magdalena limestone. The basal beds are of Morrow age and are overlain by approximately 300 feet of Atokan limestones. The clay suite from the lower Helms consists largely ofilliteand minor amounts of mixed-layer clay and resembles that of the Caney of Oklahoma and Barnett of central Texas. The upper Helms (Chester) and the lower Magdalena (Morrow) contain similar clay suites composed mostly of mixed-layer illite-montmorillonite (7:3) and a lesser amount of illite. Illite and kaolinite increase upward in the Magdalena section until in the Atoka interval they are generally more abundant than the mixed-layer clay. Thus,inthis area the Chester shales have the high mixed-layer content characteristic of the Chester rocks in general. The Morrow and Atoka clays are similar in composition and sequence to the Morrow (Marble Falls) —Atoka rocks on the southern Bend arch (fig. 11). These Mississippian-Pennsylvanian rocks contain less chlorite and kaolinite than is usual in this interval inother areas- Farther northeast, in the center of the Delaware basin (Humble Oil & Refining Company No. 1 Federal-Wiggs, 31-24527E, Eddy County, New Mexico), Lower Mississippian shale (90 feet),Mississippian limestone (300 feet),Upper Mississippian shale (320 feet), and Lower Pennsylvanian (pre-Atoka?) shale (860 feet) are composed largely of a mixed- layer (7:3) clay of the type found in the upper Helms (Chester) and the lower Magdalena (Morrow). Varying amounts of chlorite, kaolinite, and illite are also present. The Atoka shales consist of inter- bedded mixed-layer shales and illitic shales. The illiticshales contain considerable chlorite, some mixed-layer clay, and minor amounts of feldspar and are quite similar to the Atoka shales from the southern Fort Worth basin. The data from this well indicate that both the Meramec and Chester contain The Ouachita System creases from north to south on the Bend arch as the southwest Texas foreland source area is approached. Buried Ouachita Belt In Texas Only a few pre-Mississippian samples from the belt and adjacent foreland were examined inthis area. The clay fraction of the Ellenburger is predominantly mixed- layer illite-montmorillonite and illite.Clay in the Polk Creek shale is almost entirely illite. The Bigfork chert, Missouri Moun tain shale, and Arkansas novaculite con tain similar clays largely of illiteand chlo rite with minor amounts of mixed-layer illite-montmorillonite. The clay suites of these formations in subsurface are similar to those of the exposed formations in the Ouachita Mountains. Clay in the Stanley shale is approxi mately 60% illite,30% chlorite, and less than 10% mixed-layer illite-montmorillo nite. Feldspar is present in all Stanley shale samples. The Jackfork resembles the Stanley but generally contains more mixed-layer illitemontmorillonite and no feldspar. The Atoka is also like the Stanley, though most samples contain more mixed-layer illitemontmorillonite. Feldspar is usually present. The Atoka contains kaolinite (less than 5% to 10%) which distinguishes it from the Stanley and Jackfork. The line marking the appearance of kaolinite (fig. 6) in most places coincides with the foreland facies —Ouachita facies boundary (PI. 2). Insouthern Kendall and Blanco counties there are three wells (J. S. Abercrombie and Harrison Oil Company No. 1 Lena Kunz and Joe Nickel; Clarence Newton No. 1Check Ranch; and Theodore Hicks No. 1 Albert Specht) wherein shales contain from 20% to 30% kaolinite. This is a much higher kaolinite content than was observed in other shale samples in the Ouachita belt and may reflect the presence of a local granitic source to the south (p. 76). Flawn (PI. 1) places these wells in the Ouachita structural belt, but the relatively high content of mixed-layer clay suggests that they might be transitional or foreland facies sediments. Some of the low-grade metamorphic rocks (Texas Gulf Sulphur Company No. 1 Baker, Milam County; Rimrock-Tide lands, Inc., No. 1 W. F. Crawford, Milam County; Humble Oil&Refining Company No. 1 M.Holderman, HillCounty; Clar ence Newton No. 1 Check Ranch, Kendall County; and Anderson-Prichard Oil Cor poration No. 1 E. H. Yturri, Bexar County) contain appreciable amounts of kaolinite. Southern Appalachians, Black Warrior Basin, and Buried Eastern Segment of the Ouachita Belt Seven hundred fifty samples representing 50 formations of pre-Upper Mississippian rocks of the southern Appalachians indicate that illite is the only clay in approximately 30% of the samples; 60% contain both illite and chlorite; 10% are composed predominantly of mixed-layer illite-montmorillonite and chlorite-montmorillonite. Sixty percent of the samples containing illiteand chlorite contain from less than 5% to 10% chlorite, and about 20% contain more than 20% chlorite. Kaolinite is present in approximately 5% of the samples, generally in amounts less than 20%. The clay suite of the pre-Upper Mississippian rocks of the Black Warrior basin (13 wells) is similar to that in the Ar- buckle Mountains and the west Texas area. Illiteand chlorite predominate (withillite Being by far the most abundant) ;mixedlayer illite-montmorillonite is relatively common as an accessory. Mixed-layer chlorite-montmorillonite is abundant and frequently dominant through much of the Lower Ordovician Knox. Ordovician carbonate rocks along the northeastern border of the Ouachita structural belt contain clay suites similar to those of the Ordovician carbonate rocks in the center of the Black Warrior basin. Samples of the Upper Mississippian Bureau ofEconomic Geology, The University of Texas Mauch Chunk shale from the Appalachian Mountains in central Pennsylvania are composed of illite and a slightly lesser amount of chlorite and are similar incomposition to the Stanley and Tesnus shales. Post-Lower Mississippian samples were examined from 10 wells from near the center of the Black Warrior basin (fig. 9). The residues from the Meramecian limestones consist predominantly of illite with minor amounts of chlorite. The clay- mineral suite resembles that in the Meramecian limestones of the Illinois basin and the black Caney shales of Oklahoma and Texas. The lower half of the Chester section 30 contains shales which have ap proximately 30% chlorite and kaolinite and 70% illite and mixed-layer illitemontmorillonite, the latter, which has a 7:3 ratio, being two to four times as abundant as the illite. The clay-mineral suite of these shales is similar to that of the Chester shales of Illinois but, in general, contains less mixed-layer clay than the Chester shales of Arkansas and Oklahoma. The upper Chester shales and the overlying 80 Based on the Chester "top"currently inuse by subsurface geologists inthe area. Pennsylvanian Morrow-Atoka shales consist largely of illite,chlorite, and kaolinite and contain only minor amounts of mixed- layer clay. These Morrow-Atoka shales have less mixed-layer clay than those from Oklahoma and are similar to those of the Illinois basin. The change in clay-mineral composition which occurs within the upper Chester section is similar, though less pronounced, to that which occurs between the Mississippian and Pennsylvanian rocks of Oklahoma, Arkansas, Texas, and the Illinois basin. This could mean a Pennsylvanian age (Morrowan?) for the upper Chester or that orogenic movement (change of source) occurred earlier inthe Black Warrior basin. The few outcrop samples examined of Parkwood, Pennington, and Floyd shale suggest a sequence of clay-mineral suites similar to the subsurface well samples. The lower Chester Floyd formation has considerable mixed-layer clay, whereas the geosynclinal upper Chester Pennington and Mississippian-Pennsylvanian Park- wood formations are composed largely of illite, chlorite (mixed-layer chloritevermiculite), and kaolinite. Metamorphism Figure 6 shows the distribution of sharpness ratio values in the Ouachita structural belt. The highest grade of metamorphic rocks outcropping in the Ouachita Mountains is in the southern portion of McCurtain County, Oklahoma. Samples from outcrops range in age from the Upper Cambrian (?) Lukfata to Upper Mississippian Stanley. The regional metamorphism is variable, ranging from incipient to low grade. The sharpness ratio values in the McCurtain County area range from 4 to 10, averaging approximately 6 (the average for the Stanley is 8).Illite-rich samples from the pre- Upper Mississippian rocks of foreland facies have an average sharpness ratio of approximately 3. Stanley samples from outcrops slightly northwest of the area of maximum metamorphism have an average sharpness value of 4.3. Farther to the north in the vicinity of the Choctaw and Ti Valley faults, outcrop and subsurface samples of the Stanley, Jackfork, and Atoka have values of less than 2. Sharpness values for samples in the foreland facies of the Ardmore basin range fromless than 1to1.8. The distribution of sharpness ratios shown in figure 6 is based on average values obtained on the same bulk samples that were examined under the petrographic microscope by Flawn. Most values represent an average of several samples (2 to 15).Most of the values greater than 5 fall in the region of low-grade metamorphism. Most of the values between 2.5 and 5 are in the region of incipient to weak metamorphism. Values less than 2.5 occur inthe areaofnometamorphism. Thelatter include rocks of both foreland and Ouachita facies; however, in most instances, the presence or absence of kaolinite serves to distinguish between the two facies. Table 7lists the average SR values for the metamorphic zones in the subsurface Ouachita belt in Texas (all data are from X- ray patterns of bulk samples) .Questionable values were omitted; for example, samples fromKorshoj No.1Simon-Ferguson in McLennan County which were classed petrographically as showing in cipient to very weak metamorphism have an SR of 9.0, which is several times larger than the SR value of the other samples in the same class. This anomalous ratio may be the result of contamination. Table 7. Average sharpness ratios inrocks of the belt in Texas. subsurface Ouachita Average AverageAverage SR SRSR Low-grade Low-gradeLow-grade metamorphism.... 12.1 12.1metamorphism....metamorphism.... 12.1 Weak WeakWeak to toto very veryvery weak weakweak metamorphism.. 6.3 6.3metamorphism..metamorphism.. 6.3 Incipient IncipientIncipient to toto weak weakweak metamorphism—-. .metamorphism—-metamorphism—-. 4.5 4.54.5 Incipient IncipientIncipient metamorphism 2.3 2.3metamorphismmetamorphism 2.3 Unmetamorphosed UnmetamorphosedUnmetamorphosed Stanley.— 2.3 2.3Stanley.—Stanley.— 2.3 Unmetamorphosed UnmetamorphosedUnmetamorphosed Atoka... 1.8 1.8Atoka...Atoka... 1.8 Figure 7 is a plot of the SR values obtained on the less-than-2-micron fraction of Paleozoic samples from wells near the margin of the buried eastern segment of the Ouachita structural belt. Ordovician illitesfrom the center of the Black Warrior basin and east of the Ouachita structural belt have an average SR value of 2.0; those samples from wells in the southwestern portion of the basin close to the Ouachita belt have an average value of 3.5. Lower Pennsylvanian shales near the center of the Black Warrior basin have an average SR value of 1.9. SR values near the western edge of the basin range from 3.5 to 8.0 and average 5.25. Ifthe data obtained from the Texas segment are extended to this area, the one well with an SR value of 8 (The Texas Company No. 1 Whitehead) is the only one which is within the range of values representative of low-grade metamorphism. The other high values are in the range of incipient to weak metamorphism. Kaolinite is present in most wells, suggesting that rocks in the frontal zone of the Ouachita belt in this area may be of foreland facies. Regional Several distinctive clay mineral suites appear to have regional distribution (fig. 12) .A zone of mixed-layer chlorite-montmorillonite (whose mineralogy and chemistry have been discussed previously (Bradley and Weaver, 1956) ) occurs inthe Upper and Lower Ordovician and can be traced from the western portion of the southern Appalachians to the Franklin Mountains of extreme west Texas. This mixed-layer chlorite-montmorillonite zone extends from slightly above the top of the Cambrian to slightly below the base of the Chazyan (Arbuckle-Knox-Ellenburger) . There is little clue to the origin of this relatively raretypeofclay;itislikelythat the clay was originally a montmorillonite and that layers ofbrucite wereprecipitated between approximately half the layers. The montmorillonite may have been formed from volcanic material, weathered chlorite, and/or weathered illite. The absence of diagnostic heavy minerals of volcanic origin and the fact that the montmorillonite- like layers appear to have a relatively 31 high tetrahedral charge (LiCl treatment (Greene-Kelly, 1955) indicates that the expanded layers have a predominantly tetrahedral rather than an octahedral charge) suggest that the clay was more apt tohave been derived by the leaching of potassium from micas and illite and/or the leaching of brucite from chlorite. Expanded clays (montmorillonite, vermiculite, mixed-layer chlorite-montmorillonite, and chlorite vermiculite) are the common weathering products of illiteand chlorite in instances where leaching is not thorough enough to form kaolin-like minerals. DuringMiddle Ordovician time (Black River) periodic volcanism occurred which resulted in the formation of at least 14 separate ash falls in the eastern United States. The volcanic material was altered and preserved as a mixed-layer illite-mont 31Ifexpanded clays are saturated with LiCl and heated at 200° to 300° C. for 24 hours, the Liis believed to migrate into the vacant octahedral sites and nullifythe octahedral charge. Ifthe clay originally had a predominantly octahedral charge, after treatment the clay will not expand and willresemble talc. Ifthe original charge was predominantly tetrahedral, the clay willcontinue to expand after treatment. Trends morillonite (7:3) (Weaver, 1953). These "K-bentonite" beds have been traced as far west as Minnesota and as far south as Alabama. Discrete ash beds do not appear to have been preserved in the Oklahoma and Texas sediments; however, abnormally abundant mixed-layer illite-montmorillonite exists in the Simpson of Oklahoma and the Woods Hollow and Fort Pena formations of the Marathon area. A montmorillonite zone of regional extent occurs in Upper Mississippian rocks. This zone can be traced all through the eastern and central United States and at least as far west as Nevada. The montmorillonite and/or mixed-layer illitemontmorillonite commonly comprise 40% to 80% of the clay suite. Figure 9 shows the approximate top and bottom of this zone in the basins flanking the Ouachita structural belt. The clay zone underlying this montmorillonite zone is composed predominantly of illite,perhaps averaging as high as 90% in most foreland formations. The clay suite overlying the montmorillonite zoneis,innearly allareas, acomplex suite containing illite (approximately 50%), mixed-layer illite-montmorillonite, chlorite, and kaolinite (Weaver, 1959). This latter clay suite is believed to have been derived largely from source areas to the east and south, and the mineralogic change between the montmorillonite zone and the overlying complex clay suite is believed to reflect orogenic uplift in the Appalachian and Ouachita structural belts. It is interesting to note that in the Black Warrior basin this mineralogic break occurs within the Chesteran (see footnote 30, p. 158), in Oklahoma near the end of Chesteran, and inwest Texas in the Lower Pennsylvanian. This suggests that the tectonic activity responsible for the change in clay mineralogy occurred later in the western area. In the Black Warrior basin, the Knox, Wells Creek, and Stones River formations The Ouachita System 161 Fig. 12. Generalized corelation chart for clay-mineral zones. loriloni K-f elds par abundant K-fld lorilonite and/ or mom ate -montm orilonite Plagioclase feldspar abundant Ilite, chlorite, kaolinite, mixed-layert Plagioclase = atmorilonite riorilonite Mixed-layer chlorite-mo: M Mixed-laye.r ilite -monta -i:-: -/erilite-monta I&iox, >per Canadian mantown1 XChep .rbuckli '??" "EUenburae Plagipclase s>Mar?thonX; ¦kT ORDOVICIAN . Mohawkian i:z-- ¦ igioclase Pl Plagioclac Womble? :ld ?-? X- 1 Niagaran Medinan Cincinatian SILURIAN Gayugan Predominantlyilite PredominantlyilUte Predominantlyilite Predominantlyilite Predominantlyilite Predominantly' ilite Erian Ulsterian DEVONIAN Senecan man iautau Predominantlyilite .gioclase .giocla pi IS din ian isa: •lagioclas SIPIAN Men £s MISIS - iri; sha iiss. »er Ilitechlorite T; Tesnus orowan' ;ta ¦•"-. x-SS lower Atoka^ Atolca »MSJ smoinesian Jlite, chlorite, 1 -kaolinite, ML ian •i Yir SYSTEM SERIES Warior Basin Marathon SouthernApalachians Ouachitastructuralbelt ArdmoBreasin and ArbuckleMtns. Llano and NE Texas DelawareBasin Bureau ofEconomic Geology, The University of Texas contain predominantly potassium feldspar and the overlying rocks of Trenton age, predominantly a plagioclase feldspar. An examination of Ordovician samples indicates that this change in the type of feldspar is of regional extent. Upper Cambrian and Lower Ordovician outcrop samples from the southern Appalachians (Tennessee and Virginia) and from central Pennsylvania contain predominantly potassium feldspar, and samples from Upper and upper Middle Ordovician contain plagioclase. Sufficient samples were not available to determine the exact position of the boundary. Scattered samples from the Lower Ordovician ElPaso-Ellenburger of west Texas all contain potassium feldspar. Samples fromtheoverlyingMontoya werenotavailable. In the Arbuckle Mountains of southeastern Oklahoma, potassium feldspar is found inthe Arbuckle, Simpson, and Viola formations. Itis much more abundant in the Arbuckle than in the other two formations. X-ray analysis of slate, phyllite, and schist samples from the southern Appalachians and northern Mexico shows that plagioclase is the dominant and usually the only feldspar. Itseems quite plausible that much of the plagioclase feldspar in the Middle and Upper Ordovician was derived from this eastern and southern meta- sedimentary source. The outcropping early Paleozoic Ouachita Mountain sediments are predominantly clastic sediments. This detritus was apparently derived from a metasedimentary source to the south. Thus, the Upper Cambrian and Ordovician sediments of the Ouachita Mountains are presumably more similar to the sediments which comprised the eastern part of the Appalachian geosyncline. X-ray analysis of Ouachita samples indicates that plagioclase is the dominant and usually the only feldspar present in these early Paleozoic rocks (extending from the Upper Cambrian Lukfata formation through the Lower Pennsylvanian Atoka). In the Marathon region, early Paleozoic rocks contain potassium feldspar and plagioclase. These data suggest that detrital feldspar in the early Paleozoic was derived from two major types of source rocks, probably granitic rocks in the interior shield and metasedimentary rocks from an area which was located east or southwest of the present Appalachian and Ouachita Mountains. The distribution of the two types of feldspar may be a function of the relative effectiveness of these two areas insupplying detritus to the basin of deposition. Possibly the feldspars could be used to distinguish between pre-Middle Ordovician Ouachita and foreland facies sediments. Tectonics Peter T. Flawn General Statement These minimum dimensions show that the The maps (Pis. 1, 2, and 3) show the Ouachita belt as a narrow band extending from southwest Alabama into Mexico. In most segments the Ouachita front or side toward the North American craton or fore- land is rather well defined. The southeastern limitof the belt as shown on Plate 1 is not a boundary but merely the down-dip limit of well control. Therefore, the apparent narrowness of the belt is an illusion and merely indicates lack of data. Widths of the belt measured across the two major salients (Ouachita Mountains and Marathon uplift) from the structural front to the down-dip limit of well control are 90 and 70 miles, respectively, but these distances are not actual widths. The known length of the belt inthe United States is at least 1,300 miles, and itmay extend southward into Mexico for at least 300 miles. Ouachita belt ranks with the Appalachian belt in order of magnitude and is a major continental structural feature. The front of the Ouachita belt as mapped is strongly sinuous, curving toward and over the craton in broad salients and recessed around massifs or buttressing elements along the craton margin; the salients of the belt perhaps mark the position of "bays" in the old craton where the craton margin subsided deeply during formation of the Ouachita geosyncline or during orogeny. The course of the Ouachita front as itexists today was strongly modified by the behavior under stress of tectonic elements on the margin of the old craton; the course of the pre-existing Ouachita geosyncline was determined by the margin of the old craton as itwas before the orogeny. Basis for Subdivision Theoretical Considerations During recent decades the accumulation of geologic and geographical data on orogenicbelts overtheworldhas ledtoamuch better understanding of their origin and development. Many modern ideas are summarized in a recent symposium volume, Crust of the Earth (Poldervaart, 1955) .In a synthesis of data available on the western Alps and southern Appalachian deformed belts, Bucher (1955) stated that in these typical belts there are three major structural zones between foreland and hinterland: (1) an outer belt of shallow folds and thrusting, (2) a marginal belt of piled-up thrusts and nappes, and (3) a belt of crustal folds involving metamorphic and plutonic rocks. In the outer zone, the deformation is mainly surficial and does not involve the basement; inthe marginal zone the thrust masses are allochthonous plates which may be detached from their original base (Bucher, 1955, pp. 348, 351, 353, 356). In the southern Appalachians the outer zone of shallow folds and thrusting corresponds to the Valley and Ridge structural province, the interior marginal zone of piled-up thrusts corresponds to the northwestern part of the Blue Ridge structural province, and the belt of crustal folds of metamorphic and plutonic rocks takes in the Piedmont structural province and the southeastern part of the Blue Ridge province. Boundaries between the three main subdivisions of a typical orogenic belt are not everywhere sharply defined and in many places passage from one province to an other is marked only by a general change in the structural grain or occurs within a Bureau ofEconomic Geology, The University of Texas rather broad zone. P. B. King (1950, pp. 646—647) comments as follows regarding the boundary between the Valley and Ridge province and the Blue Ridge province inthe southern Appalachians : Along a line somewhere in the southeastern part of the Valley and Ridge province, a change takes place in the mode of deformation. This change in structural habit is wellillustrated by recent work of Cloos ... in South Mountain, Maryland. ... The folds northwest of South Mountain are flexure folds in which the strata are merely bent, the distortion being taken up by gliding between the beds...; cleavage and other metamorphic effects are nearly lacking. By contrast, the folds in South Mountain are shear folds, in which the whole mass of stratified rocks, and the underlying basement as well, were deformed as a unit by laminar flow, resulting in extensive development of slaty cleavage, and in marked tectonic thickening of strata along the axes of the folds. The present writer [King] believes that this change in structural habit, as much as any other character, serves to separate the Valley and Ridge province from the Blue Ridge province, next on the southeast. Many geologists have believed that the Valley and Ridge province is separated from the Blue Ridge province by a continuous low-angle thrust fault, or faults, styled the 'Blue Ridge over- thrust' ...; but faulting along the boundary is actually discontinuous. ... In some places, low-angle thrust faults along the boundary between the two provinces are strikingly developed, for example, throughout the segment in Tennessee. ...Here, the Great Smoky thrust and Holston Mountain thrust have carried the rocks of the Blue Ridge province northwestward over those inthe Valley and Ridge province, and many windows reveal the overridden rocks for as much as 35 miles behind the northwestern boundary of the province. ... The low-angle thrust faults inTennessee, like the folds in South Mountain, Maryland, extend into the basementrocks, and thus differ fundamentally from those inthe Valleyand Ridge province. Farther southeast in the Appalachian belt, the boundary between the metamorphic and plutonic rocks of the core of the orogenic belt and the Blue Ridge tectonic province is indefinite and includes an apparently transitional zone (P. B. King, 1950,p.650).According toBucher (1955, p. 360) the belt of metamorphic and plutonic rocks in the southern Appalachians includes the southeastern half of the Blue Ridge province (the physiographic Blue Ridge province) and most of the Piedmont province, and fades out southeastward into a less-metamorphosed and less-deformed "hinterland." The tectonic analysis of the Ouachita belt which follows draws heavily on the general analysis of orogenic belts made by Bucher (1955) and specifically on the synthesis of P. B. King in the southern Appalachians (1950, 1955a, 1955b). Interpretations of tectonic relations in the poorly exposed Ouachita belt are in large part interpretations by analogy with more completely exposed and studied orogenic belts elsewhere, in particular with the southern Appalachians. Rocks of the Ouachita Belt Rocks of the Ouachita belt fallinto two broad groups: (1) unmetamorphosed to very weakly metamorphosed sedimentary rocks showing the effects of strong deformation but without any pronounced directional fabric and (2) sedimentary rocks showing weak to low-grade metamorphism with a high shearing component and the metamorphic structures associated with high shear (foliation, slaty cleavage, fracture cleavage, wrinkling, rucking, microimbricate structures, flowage around augen) ;sheared and altered igneous rocks make up a minor part of this group. Rocks transitional between these two major groups are relatively scarce. The two major petrographic groups form long belts parallel to the general strike of the Ouachita structural belt (Pis. 1 and 2); group (1), composed of unmetamorphosed to very weakly metamorphosed sedimentary rocks, forms a belt bordering the foreland, and group (2), composed of highly sheared rocks showing weak to low-grade metamorphism, forms an interior belt to the south and east of the rocks of group (1). Transitional rocks, where present, are in a zone along the boundary of the two major rock groups or occur withinthe area of group (1) in zones of strong deformation (p. 122).The belt of rocks adjacent to the foreland is the frontal zone of the Ouachita belt, and the belt of rocks lying south and east of the frontal The Ouachita System zone is the interior zone of the Ouachita is recognized only in a relatively narrow belt; the frontal zone has known limits on strip along the southeast side of the frontal both sides, but the less known interior zone zone (Pis. 5-15). The Frontal Zone 32 — General remarks. Rocks and structures of the frontal zone of the Ouachita belt are exposed in the Ouachita Mountains and Marathon salients of the Ouachita belt and include the Solitario and Persimmon Gap areas in Trans-Pecos Texas and a small outcrop near Turkey Bend of Lake Travis in central Texas. The Ouachita Mountains of Oklahoma and Arkansas constitute by far the largest exposure, but heavy vegetation and soil cover obscure the relations inmuch of the area;inTrans-Pecos Texas and especially in the Marathon region the structure of the frontal zone of the Ouachita belt is exposed in wonderful clarity. In both the Ouachita Mountains and Marathon areas the Paleozoic rocks are strongly folded; the folds are commonly overturned toward the foreland and are broken by thrust faults, reverse faults, and tear faults, and the older thrust faults are folded. Inboth areas the structure isof Appalachian type and has been interpreted as the product of several orogenic periods or intermittent orogenic pulses extending through a considerable span of late Paleozoic time. Major Structures of the Salients The structures in the Marathon Basin consist of two northeast-southwest-trending anticlinoria separated by a synclinorium (P. B. King, 1937) ; from northwest to southeast these are named the Marathon anticlinorium, the Perla Colorado synclinorium, and the Dagger Flat anticlinorium. These features occur in the uplifted western part of the area; to the northeast is a depressed area. The two doubly-plunging anticlinoria expose lower Paleozoic rocks. The northwest side of the Marathon anticlinorium was ruptured by 32 Not to be confused with Hendricks' "frontal belt of the Ouachita Mountains" which refers to the area of the Ouachita Mountains lying between the Choctaw and Ti Valley faults (Hendricks, 1943 and subsequent publications). the Dugout Creek overthrust, along which the rocks of the Ouachita belt have been displaced over the foreland for a distance of at least 8 miles. According to estimates by P. B. King (1937, p. 131), the minimum amount of crustal shortening as a result of deformation in the Marathon area is15miles and probablyitisconsiderably more. Only part of the salient is exposed in the Marathon Basin, and other anticlinoria probably occur in the concealed part farther southeast (PI. 2);a third anticlinorium southeast of and more or less parallel to the Dagger Flat anticlinorium probably includes the lower Paleozoic exposures of the Jones ranch and Persimmon Gap areas, and perhaps part of another such feature is exposed in the Solitario. In the subcrop in southern Terrell County, slightly metamorphosed lower Paleozoic rocks indicate an uplifted area of the frontal zone. Synclinoria probably occur between these concealed anticlinoria. In the Marathon salient, then, a series of complexly faulted anticlinoria have raised the older lower Paleozoic rocks and these have been locally thrust over younger rocks —in Terrell County very weak metamorphism seems to be associated with the uplifted structure. Beds as young as Atoka in age are preserved in the depressed structures. In the Ouachita Mountains salient the major structures are: (1) A large central anticlinorium, trending east-west in the eastern part of the area and northeast- southwest in the western part, which reflects the trend and shape of the entire salient; this includes the large uplift in Montgomery, Garland, and Saline counties, Arkansas, and the so-called "core" of the Ouachita Mountains inMcCurtain County, Oklahoma (Pitt, 1955) ;recently this anticlinorium has been called the Broken Bow Bureau ofEconomic Geology, The University of Texas Benton uplift(Miser,1959).(2) Athrustfaulted synclinorium north and northwest of the Broken Bow-Benton anticlinorium which includes the complexly thrust- faulted frontal belt of the Ouachitas studied by Hendricks (Hendricks et al., 1947) ;in it, older rocks come to the surface in the Potato Hillsand at Black Knob Ridge. (3) A synclinorial area which lies south of the Broken Bow-Benton uplift, largely in Arkansas. The minimum amount of movement on the faults in the frontal belt of the mountains seems to be in excess of 50 miles (Hendricks, 1959, pp. 48-50) ;the rocks south of the TiValley fault probably have been thrust north-northwestward for a distance of 20 ormore miles (Miser, 1934c, p.1065; 1959, p.32),and there mayhave been a total minimum shortening of 70 miles inOklahoma and 50 miles in Arkansas (Miser, 1929, p. 12). The youngest beds preserved in the synclinoria in the Ouachita Mountains are part of the Atoka formation. The two structural salients of the Oua chita belt show many interesting simi larities: (1) The frontal zone is broad and has Appalachian-type structure; major structural axes are convex toward the foreland. (2) The western part of each salient impinges on a foreland buttressing element with pronounced thrust faulting; in the Ouachita Mountains salient this buttress is the Arbuckle element; in the Marathon salient the buttress is the southeastern extension of the Diablo Platform. In both salients folds are the dominant structures inthe eastern part. (3) Major anticlinoria and synclinoria whose axes parallel the trend of the belt occur in both salients; the anticlinoria have raised lower Paleozoic rocks into the outcrop or subcrop, whereas beds as young as Atoka occur inthe synclinoria. (4) Rocks along the axes of the anticlinoria have been metamorphosed in parts — of both areas in the Ouachita Mountains salient along the Broken Bow—Benton anti clinorium in what was probably the most deeply buried part of the salient and in the Marathon salient in the concealed southern Terrell County structure. The major differences between the two areas are in structural scale (P. B. King, 1937, p. 134) as the amplitude of the Marathon salient structures is considerably less than in the Ouachita Mountains. Metamorphism was also more intense and extensive in the Ouachita Mountains salient. This may indicate that deformation of the Ouachita Mountains salient occurred under a much thicker cover than deformation in the Marathon region (P. B. King, 1937, p.134). Concealed Frontal Zone of the Ouachita Belt Between the Salients South of the Ouachita Mountains salient, between Dallas and Uvalde counties, Texas, the frontal zone is narrower than in either the Ouachita Mountains or Marathon salients. Although there are minor sinuosities in the course of the front, there are no major bulges or convexities. This segment of the Ouachita belt can be called the Llano recess because the Llano buttress here dominates the path of the deformed belt. In the frontal zone are Stanley and pre-Stanley rocks of Ouachita facies and narrow belts of foreland rocks of Morrow and Atoka ages that were involved in the deformation against the Llano buttress. Pre-Stanley rocks occur in subcrop along the front of the belt along faults or faulted folds. In northeastern Williamson County pre-Stanley rocks form the subcrop farther southeast in the frontal zone, perhaps inan anticline. In the southeastern part of the frontal zone the subcrop is a lithologic unit of unknown age which may be a near- source facies of the early Paleozoic rocks; ifso, there isamajor upliftintheinterior part of the frontal zone (p. 78). From scattered cores and from micro- structures seen in thin section, itis evident that the over-all structure in the frontal zone of the belt in this area is much like that in the exposed parts of the salients — The Ouachita System the beds are steeply dipping and have been fractured, slickensided, and cut by numer ous veins. The only major structures that can be discerned in the frontal zone in this segment of the belt are frontal thrusts, suggested by the juxtaposition of Ordovician Ouachita facies rocks and foreland facies Pennsylvanian rocks in the subcrop and locally proved by wells which drilled through the dislocated Ouachita plates into underlying foreland facies rocks (PL 2). In McLennan and Coryell counties there is more than 5,000 feet difference in altitude between the top of the Bigfork in St. Louis OilPool Company No. 1Ella V. Stuart (Stewart) and the top of the Big- fork in General Crude OilCompany No. 1 Earnest Day about 5 miles away. A major structure thus occurs in this area, and many other such structures probably occur elsewhere in the area. The frontal zone of the belt in Uvalde and western Medina counties islittleknown and poorly defined. Here several wells have - penetrated Mississippian Pennsylvanian rocks characteristic of the frontal zone, but control is inadequate to determine trend. In Kinney and Val Verde counties, the frontal zone, which is continuously and broadly developed to the east and west, disappears abruptly, and a change in the trend and character of the Ouachita belt is indicated. The area of disappearance of the frontal zone coincides with a concealed area of high-standing Precambrian rocks — the Devils River uplift. Two hypotheses may account for the missing frontal zone: (1) The Ouachita geosyncline formed south of the area of the Devils River uplift and the frontal zone developed in that area; subsequently, the rocks of the frontal zone were completely overridden by the metamorphosed rocks of the interior zone. (2) Because of the area of high-standing Precambrian rocks which formed a southern projection on the craton, the Ouachita geosyncline in this area was attenuated and the frontal zone of the belt developed in a restricted form. Insubcrop, a narrow thrust slice of slightly metamorphosed pre- Tesnus rocks occurs north of the metamorphicrocks of the interior zone and indicates that at least some lower Paleozoic Ouachita facies rocks were deposited. The Devils River uplift appears tohave influenced the location and development of the Ouachita geosyncline, and itcertainly was a resistant element during deformation of the belt as the foreland facies lower Paleozoic rocks which mantle the Precambrian rocks are deformed and very weakly metamorphosed. This is the only area known where foreland facies rocks are metamorphosed. Frontal Zone East of the Ouachita Mountains The nature and extent of the frontal zone of the Ouachita belt east of Arkansas and south of Texas arelittleknown. Drillingin southeastern Mississippi indicates a disturbed zone wherein foreland beds of lower and upper Paleozoic age are juxtaposed with weakly metamorphosed Ouachita slates and phyllites (p.93).This zone probably marks the front of the Ouachita belt but nothing is known about the interior of the belt south of the front. The presence of weaklymetamorphic rocks adjacent toforeland rocks suggests that either (1) frontal zone rocks are metamorphosed here as they are in the Broken Bow-Benton anticlinorium of the Ouachita Mountains salient and the anticlinorium extends southeastward or (2) the frontal zone of Ouachita facies rocks has been overridden by rocks of the interior zone of the belt, as in the Kinney- Val Verde County area of Texas (PL 2). The band of deformed and weakly metamorphosed Pennsylvanian rocks which parallels the belt (PL 3) may in part lie within the frontal zone. Frontal Zone inMexico Rocks like those in the frontal zone of the Ouachita belt in the United States occur in widely separated areas of northern Mexico (p.99),butcontrol is not sufficient to map the trend and course of the frontal zone in this region. Scattered outcrops and Bureau ofEconomic Geology, The University of Texas wells suggest that frontal zone rocks occur in eastern Chihuahua and western Coahuila and that most of the remainder of Coahuila is occupied by metamorphic and igneous rocks of an interior zone. Differences Between the Salients Texas Segment and the Concealed The map (PL 2) indicates a general contrast between the pattern of the Ouachita belt in the two major salients and in the Texas segment between them. The salients are strongly convex toward the craton, and within them the frontal zone of the belt is very broad. Between, the frontal zone is narrow, and inKinney, Val Verde, and Terrell counties itis completely missing. Besides their general differences in tectonic pattern, the salients and the concealed recess inTexas differ as follows: (1) Both salients were affected by marked post-orogenic uplift so that they are now exposed or partly exposed as a result of post-Cretaceous doming. (2) In both salients beds as young as Atoka occur well within the belt and form synclinoria in the frontal zone, whereas between the salients these younger rocks are preserved only where they were involved in deformation along the frontal margin. Between the salients most of the frontal zone is composed of Stanley, Tesnus, and older rocks of Ouachita facies. (3) In both salients the frontal zone includes rocks of transitional and foreland facies along their northern margin. In the concealed segment in Texas the facies boundary nearly coincides with the structural boundary, and the zone where fore- land facies rocks occur within the structural belt is either much narrower or absent. Development of the Salients Differences between the Ouachita Mountains and Marathon salients and the interim segment suggests that the salients were originally wide asymmetric foredeeps that received foreland deposits along their northern and more gently sloping sides and Ouachita detritus from an interior uplift of the belt along their deeper and steeper southern sides. These basins were depressed and received sediments in Jackfork and Atoka time while the frontal zone of the Ouachita belt in north and central Texas was already undergoing uplift. This is well illustrated by the distribution of the Jack- fork sandstone in Fannin County, Texas, and the southwestern Ouachita Mountains (PL 2). This area was the southwestern end of a great complex northeast-plunging syncline in which the Ouachita Mountains sedimentary rocks were deposited; Jack- fork sandstone was preserved along the axis of the syncline in Fannin County. Deformation of the very thick sedimentary rocks in the salients intensified and concentrated their sedimentary loads. Subsequent epeirogenic uplifts in both the Ouachita Mountains and Marathon salients reflect the buoyancy of this great mass of sedimentary rocks. Interior Zone of the Ouachita Belt — General remarks. The interior zone of the Ouachita belt comes to the surface in only one place, along the west-facing scarp of the Sierra del Carmen south of the Rio Grande near Boquillas, Coahuila, Mexico. Other exposures of metamorphic and igneous rocks in northern Mexico are perhaps part of this interior zone but correlations are uncertain (Flawn and Diaz G., 1959). The discontinuous outcrops in the Sierra del Carmen are interlayered very fine-grained sericite-muscovite-chlorite schist and phyllite, very fine-grained metaquartzite, and calcite marble. These are highly deformed and sheared and include quartz veins that are cut bylater post- deformation quartz veins. Local rapid changes in dip and small folds and faults indicate a highly folded and faulted sequence. Sporadic cores from the interior zone between the Sierra del Carmen and north- central Texas show effects of a similar strong deformation and likewise contain two ages of veins. Allof the field, megascopic, and microscopic observations indicate that the rocks of the interior zone are extensively folded, faulted, veined, and sheared and have been subjected to weak to low-grade regional metamorphism with a strong shearing component. Extent and Nature of the Interior Zone The interior zone of the Ouachita belt has been mapped from Navarro County in north-central Texas southward into Caldwell and Gualalupe counties, thence westward toBrewster County, and thence southwestward intoMexico. The actual extent of the zone is unknown, as well control is restricted to a relatively narrow belt adjacent to the frontal zone; however, present knowledge indicates that the interior zone is an elongate belt more orless parallel to the general course of the Ouachita structural belt. Continuity of the zone is lost in Uvalde County, but wells in Zavala and Maverick counties (PI. 2) suggest that it is present south of Uvalde County. Farther west, inKinney, Val Verde, Terrell, and Brewster counties, the interior zone is again mappable. Two lithologic units occur in the interior zone. Most ofitis fine-grained schist - phyllite -slate metaquartzite -marble (p. 79),but from Travis County westward to Bexar County there is a narrow east-westtrending belt of black graphitic slate along the northern border (p. 78).This slate was intensely sheared and microstructures reveal that the rock deformed almost plastically. Cores from widely separated wells (Woodward No.1Schubert, Hays County; Stanolind Oil and Gas Company No. 1 Schmidt, Guadalupe County;General Crude Oil Company No. 1Rogers Ranch, Bexar County; PI. 2) are nearly identical. In Bexar County and farther west in Medina and Maverick counties, sheared and altered volcanic rocks appear to occur within the interior zone. Boundary Between the Interior and Frontal Zones The boundary between the frontal and interior zones of the Ouachita belt is shown on the map (PI. 2) as a continuous line called the Luling front,but this is a simplification. In some areas, the boundary appears to be relatively sharp, with a change in short distance from unmetamorphosed Mississippian-Pennsylvanian rocks of the frontal zone to highly sheared low-grade metamorphic rocks of the interior zone. In these areas the interior zone seems to be allochthonous and bounded by a zone of overthrusting. Elsewhere, the boundary appears to be more transitional, particularly in south-central Texas where it cuts across the dark clastic lithologic unit so that very weakly metamorphosed rocks in the frontal zone are adjacent to highly sheared weakly metamorphosed Bureau ofEconomic Geology, The University of Texas rocks in the interior zone, and the over-all lithologyissimilar onboth sides. However, even in this area the two zones can be distinguished by the strong shearing which occurred in the interior zone. The extraordinary high shearing in the black slate adjacent to the Luling overthrust front suggests that this was an incompetent unit along which the interior zone was displaced. Partly mylonitized igneous rocks occur along the same trend farther west. The interior zone of the Ouachita belt is thus distinguished by its deformational features rather than by any particular lithology. By analogy with the Blue Ridge tectonic province of the Appalachians, deformation in the interior zone of the Ouachita belt east and south of the Luling overthrust front probably involved basement rocks, while deformation in the frontal zone was superficial. Gravity Anomalies of the Ouachita Belt The structural grain of the Ouachita belt is wellexpressed on regional gravity anomaly maps of the southern United States as a series of maxima and minima strongly elongated parallel to the strike of the belt. These are better defined in Texas than in the area of the Mississippi embayment to the east where the reflection of the Ouachita belt is subdued by a thick cover of younger rocks. Gravity features of the area east of the Mississippi River are discussed in some detail by P. B. King in another section of this report (p. 94 and fig.4). The foreland side of the Ouachita belt ismarked by a band ofpronounced gravity minima which more or less seems to correspond with the frontal zone of the belt and suggests that the prism of folded and faulted sedimentary rocks is very thick. Southeast of the line of strong minima are a series of disconnected maxima overlying the interior zone of the belt.Itseems likely that those anomalies are caused by changes in lithology within the interior zone, perhaps by a series of intrusions, but no data are available on the nature of the rocks underlying the anomalies. Geophysics of the Ouachita Mountains have been discussed by Howell and Lyons (1959) ;they report a "truly great negative anomaly" over the area of the mountains (which lieentirely withinthe frontal zone of the Ouachita belt).The conclusions of Howell and Lyons (1959, pp. 57-58), based on gravity data and limited magnetic data, are summed up as follows: (1) The Ouachita Mountains are a very thick prism of sedimentary rocks; (2) the basement is deep and irregular with local uplifts; (3) folding and faulting were accompanied in some areas by intrusion of magnetite-bearing igneous rock. Southeast of the great minima of the Ouachita Mountains, the course of the Ouachita belt across the Mississippi embayment issuggested by anumber of rather weak and vague northwest-southeast elongated anomalies in Mississippi and Alabama; these appear to intersect the south- west-trending Appalachian gravity pattern at nearly right angles in southwest Alabama (fig.4),but relations are not clearly shown. Insummary, regional gravity data indicate that: (1) The frontal zone of the Ouachita belt is a thick sedimentary mass, and (2) the interior zone is made up of masses of rock of different densities. Problem Some parts of the Ouachita structural belt present vexing problems in tectonic interpretation, especially the area of the Ouachita-Arbuckle junction in southeast Oklahoma and northern Texas and the area of Uvalde and Kinney counties, Texas, where there is a major structural discontinuity or divergence in the belt. Ouachita-Arbuckle Junction In southeastern Oklahoma the outcropping rocks and structures of the Ouachita Mountains are overlapped by Cretaceous rocks along a line which extends approxi mately east-west through McCurtain, Pushmataha, Atoka, and Johnston counties; south of this line the Ouachita belt is concealed. The Cretaceous blanket obscures the junction of the Ouachita belt and the Arbuckle element, anditisinthis zone of extreme structural complexity that the continuity of the Ouachita belt is lost. Thus, with one exception, none of the major structures that have been mapped in the Ouachita Mountains can be projected with confidence into the subsurface in Texas. The exception is the axis of the Broken Bow—Benton anticlinorium which can with fair certainty be extended southwestward into Red River and Lamar counties, Texas. Along the northwestern front of the Ouachita belt inAtoka County a series of major thrust faults (Jackfork Mountain, Windingstair, Ti Valley, Pine Mountain, and Choctaw faults) strike southwestward beneath the Cretaceous overlap. The rocks involved include the Stanley, Jackfork, Johns Valley, and Atoka formations as well as a thin slice of pre-Stanley rocks; where last seen these faults are converging, so that as projected, they intersect the southeast-plunging Arbuckle structures at nearly right angles within a distance of 10 miles (PL 2). Well spacing insouthwest Atoka,Bryan, and Marshall counties, Oklahoma, is sufficiently dense to map the southeastern Areas extent of the Arbuckle element. Arbuckle facies rocks have been encountered in the subcrop in southeastern Bryan County close to the Red River about 30 miles from the edge of the overlapping Cretaceous rocks (PI. 2) so that there is a very abrupt structural recess in the front of the Ouachita belt in this area. The telescoped thrust-faulted sequence of Ouachita rocks on the northeast side of the Arbuckle element suggests large-scale tear faulting, wherein the deformed Ouachita rocks were moved northwestward relative to the Arbuckle rocks (Flawn, 1959b).The discontinuity in the Ouachita belt is thus not merely a discontinuity due to the concealing cover but a major structural discontinuity caused by an unyielding Arbuckle buttress. On the southwest side of the Arbuckle element the situation appears to be much the same. In Grayson County, Texas, the Ouachita front ismarked by an overthrust that has been penetrated in a number of wells (minimum displacement, 6 miles);moreover, well density is adequate to map broadly the subcrop contact between pre-Stanley rocks and the Stanley shale (PI. 2 and fig. 13). In Grayson County and in southern Marshall County, Oklahoma, dislocated Ouachita rocks occur many miles northwest of the Arbuckle facies rocks which form the subcrop in Bryan County, Oklahoma. The pattern is one which suggests tear faulting with the southwest side moving northwest. The frontal overthrust of the Ouachita belt southwest of the Arbuckle element in Grayson County is not necessarily correlative with the Choctaw frontal fault on the northeast side of the Arbuckle element. Because of the intervening foreland mass no correlation can be made, and the Grayson County fault may be equivalent to one of the interior thrusts of the Ouachita Mountains. In the northeastern and northern Ouachita Mountains, the thrust during the Bureau ofEconomic Geology, The University of Texas Ouachita orogeny was absorbed by the tremendous mass of sediments in the Arkansas basin without any major dislocation. Farther west the Ouachita rocks were thrust against the unyielding Arbuckle buttress which caused both extensive over- thrusting and large-scale transverse faulting with a probable minimum displacement of 30 miles. Most of the northwestern movement of the Ouachita Mountain mass was probably effected by thrust faulting and tear faulting along the northeast side of the Arbuckle element (fig. 13), as suggested earlier by Miser (1929, pp. 12-25; 1959, pp. 32-33),Hendricks et al. (1947), and Hendricks (1959, pp.48-50). Position of the Ouachita Front in Grayson and Collin Counties, Texas Figure 13 shows two interpretations of the position of the Ouachita front in Grayson and Collin counties Texas, based on different interpretations of the stratigraphic sequence penetrated in Rutledge No. 1 Williams (p. 263), Verne Dumas Company et al. No. 1 Williams (p. 259), and Deep Rock Oil Corporation No. 1 Sherley (p. 241).The answer to the problem hinges on interpretation of well samples— whether the Ouachita facies Bigfork chert fragments in the Williams wells are derived from tectonically transported Ouachita rocks or from pebbles and cobbles in Pennsylvanian conglomerates, and whether the lower sequence in the No. 1Sherley is Ouachita facies Womble or foreland facies Pennsylvanian. Although in the regional view the problem is not of great importance, production of oil and gas from foreland rocks immediately adjacent to the Ouachita front in this area makes an accurate delineation of the front a problem of economic significance. Coring of the pre- Cretaceous section in this area would contribute a great deal of valuable information on the nature, attitude, and intensity of jointing and fracturing in these rocks. Uvalde and Kinney Counties, Texas In Bexar and Medina counties, Texas, the Ouachita belt, with a well-developed frontal zone and a well-marked boundary between the frontal zone and interior zone, strikes westward into a problem area in Uvalde and Kinney' counties. Farther west, in Val Verde County, the Ouachita belt trends northwest toward the Marathon salient, and the frontal zone is either missing or is extremely narrow. The geology of the problem area is as follows: (1) Aburied Precambrian buttress, the DevilsRiveruplift,liesinsouthern Kinney and Val Verde counties; it is mantled by lower Paleozoic foreland rocks and is overridden or partly overridden by rocks of the interior zone of the Ouachita belt. (2) Frontal zone Ouachita rocks occur in northern Uvalde County, north of fore— land rocks in Kinney County this indicates that the Ouachita front in western Uvalde County turns southwest, almost at right angles to the trend of the belt in Kinney and ValVerde counties (PI. 2). (3) This area of sharp change in trend of the Ouachita belt is also an area of profuse intrusion of Cretaceous-Tertiary igneous rocks. Association of a discontinuity in the Ouachita belt and an area of high-standing Precambrian rocks is probably more than a coincidence, and the writer (Flawn, 1959c) suggested that: (a) At the beginning of Paleozoic time the area of the Devils River upliftin southern Kinney and Val Verde counties formed a stable lobe on the southern edge of the craton, much like the Llano uplift farther to the east. The Cambro-Ordovician sequence on the Devils River uplift (p. 144) and on the Llano uplift is similar so that the two areas must have had a similar early Paleozoic history. (b) The Ouachita geosyncline, with perhaps a somewhat restricted frontal trough, formed south of this uplift,whereas farther west and east the foreland side of the geosyncline was more broadly developed (figs.2,3). (c) Deformation of the geosyncline was affected by the Devils River uplift; south of it the frontal zone was crushed against the buttress and the interior zone overrode History of the Ouachita System 33 Philip B. King Preceding parts of this publication set forth the facts available regarding the Ouachita system of Texas and adjacent states and the inferences that can reasonably be derived therefrom. This summary is more speculative and is colored by the predilections of its author, not only regarding the origin and development of the Ouachita system but of orogenic systems ingeneral. Precambrian Framework Much isknown of the history of Precambrian time in the Canadian Shield in the heart of the continent, and in recent decades this history has been strengthened by many radiometric determinations of "absolute" ages. Nevertheless, many uncertainties remain (James, 1960, pp. 108113). These uncertainties are compounded insurrounding parts of the Central Stable Region and in the orogenic belts beyond, where Precambrian rocks emerge from the cover of younger rocks in few places, and only scattered information is available from drillingin intervening areas. Flawn (1956, pp. 23-52),Thiel (1956, pp. 10851093), and Burwash (1957, pp. 96-101) have interpreted the Precambrian of parts of the region outside the Canadian Shield, similar investigations are inprogress elsewhere, and Gastil (1960, pp. 9-10) has made a more generalized interpretation of the whole region. The margins of the continent in Precambrian time are even less known. Precambrian rocks are exposed across part of the Appalachian and Cordilleran systems on the east and west, but not near their oceanward edges, and none reach the surface in the Ouachita system on the south, where the lowest exposed strata are probably considerably above the base of the Paleozoic column. A basement of sialic metamorphic and plutonic rocks which has yielded radiometric ages of a billion years or more emerges in the Appalachians as far east as the Blue Ridge, and inthe Cordillera somewhat farther west than the Grand Canyon representing margins of the continental plate that were downwarped beneath the miogeosynclines of later time. Precambrian basement rocks are exposed in few places nearer the oceans, in the eugeosynclinal areas of later time (Gilluly, 1955, p. 12),and the Precambrian age of some of the reported occurrences is questionable (as in the Klamath Mountains of northern California). The floor on which the later eugeosynclinal deposits were laid might have been simatic and oceanic crust, rather than sialic and continental, and the eugeosynclinal areas may only have been added to the continent by later accretions and consolidations (Wells,1949,p.1927). Regardless of the nature of their base ment, geosynclines originated along the eastern and western sides of the continent before the beginning of Paleozoic time. Earliest Cambrian strata in the Blue Ridge province of the central and southern Appalachians are separated from basement plutonic and metamorphic rocks by thick stratified sequences which must be oflate Precambrian age, as in many places there is no clear discordance between them and the earliest Cambrian. In Virginia these strata include the Catoctin greenstone and related volcanic rocks and the meta- sedimentary Lynchburg gneiss;inTennessee, North Carolina, and Georgia they include the even thicker mass of gray- wackes and other clastic rocks of the Ocoee 83 Publication authorized by Director, U. S. Geological Survey. series. Allthese strata have some of the Bureau ofEconomic Geology, The University of Texas features of eugeosynclinal deposits of later time, although the analogy is not complete. Precambrian geosynclinal deposits in the Cordilleran region are best exemplified by the Belt series (Purcell series of Canada) in the northern Rocky Mountains whose eastern phases, with units of limestone, red argillite, and other shallow- water deposits, are typically miogeosynclinal but which pass farther west into more dominantly clastic eugeosynclinal rocks. The Belt is known to overlie older basement rocks toward the east but its base is not visible farther west. Surprisingly ancient dates of more than a billion years have been determined from veins in the Belt series (Eckelmann and Kulp,1957, p. 1130),suggesting that geosynclinal conditions along this segment of the continent began during orbefore the final consolidation of the Canadian Shield itself. The ancient age of the Belt is further attested by its unconformable relations with the succeeding and equally thick Windermere series of Canada, which is apparently of latest Precambrian age as itis conformable with the succeeding geosynclinal deposits of Paleozoic time. Precambrian geosynclinal deposits are more fragmentarily preserved farther south in the Cordillera but include the quartzites and slates of the Uinta Mountain group and related units inUtah, the Grand Canyon series of northern Arizona, and the Pahrump series and Apache group to the west and south. The Grand Canyon, Pahrump, and Apache include units of limestone, sandstone, shale, and minor lava and seem to be typically miogeosynclinal. Their ages are undetermined, but all of them are at least younger than basement rocks, which in the Grand Canyon have yielded a radiometric date of about 1.3 billion years (Aldrich, Wetherill, and Davis, 1957, p. 656). Precambrian history along the southern margin of the continent, adjoining the Ouachita system, is less understood than along the east and west margins. Information, stillpartly unpublished, indicates that during later Precambrian time rhyolitic lava covered an extensive part of the Central Stable Region in Oklahoma, Texas, and New Mexico. Lopolithic intrusions of gabbro and granophyre in the Wichita Mountains of Oklahoma have yielded the very late Precambrian date of about 0.6 billion years (Hamilton, 1956, p. 1325). In west Texas, perhaps also late in Precambrian time, strata resembling the Grand Canyon series and its allies were strongly deformed and were welded to the continent as the Van Horn orogenic belt (P. B. King and Flawn, 1953, pp. 131132; Flawn, 1956, pp. 32-35). Some resistant massifs of earlier basement rocks can be identified along the southern margin of the Central Stable Region, including the Llano upliftinTexas and the Arbuckle Mountains inOklahoma, whose rocks have yielded radiometric ages in excess of a billion years (Flawn, 1956, p. 27; Hamilton, 1956, p. 1328) . Some other massifs, including the Devils River uplift southwest of the Llano uplift,are now whollyburied but may be of similar nature. Precambrian rocks are unknown within the Ouachita system itself. However, ifthe Ouachita system is similar to the Appalachian and Cordilleran systems itislikely that awidepartofitonthe side toward the continent is underlain by sialic basement rocks, downflexed before the beginning of Paleozoic time to permit at least local accumulations of younger Precambrian geosynclinal deposits. This initial downflexing would have influenced the course of the Ouachita geosyncline during Paleozoic time and, in turn, the pattern of the Ouachita orogenic system. Present sinuosities of the Ouachita system were clearly accentuated by thrusting of the Paleozoic geosynclinal rocks into the salients during the orogenic phase, but one of the recesses is opposite themassif oftheLlanouplift.This massif resisted the thrusting of later Paleozoic time, and it may also have deflected the zone in which the basement was down- flexed during later Precambrian and earlier Paleozoic time. EARLYGEOSYNCLINAL PHASE (CAMBRIANTO DEVONIAN) The Appalachian and Cordilleran sys tems were well differentiated from the Central Stable Region by the beginning of Paleozoic time. The farthest inland extent of the Lower and Middle Cambrian series on the east and west is near the edges of the geosynclines as they existed through most of the later part of the era (Kay, 1951b, pp.7-11;P.B.King,1959, pp.2526), and only the Upper Cambrian series overlaps widely over the Central Stable Region. A comparable differentiation has not been established south of the Central Stable Region. The basal Paleozoic deposit in the Arbuckle and Wichita Mountains of southwestern Oklahoma is the Reagan sandstone, whose Late Cambrian age indicates that the geosyncline of the Wichita system originated much later than those of the Appalachian and Cordilleran systems. In the Ouachita system the oldest fossiliferous rocks are of comparable age or younger. In the Marathon region these include the Dagger Flat sandstone and Marathon limestone, with fossils of Late Cambrian, early Early Ordovician (Tremadocian), and Early Ordovician age (J.L.Wilson,1954b, p.254; Berry, 1960, p.5).Inthe Ouachita Mountains the oldest fossiliferous beds, in the Mazarn shale, contain graptolites no older than those in the upper part of the Marathon limestone (zone 4, above Monument Spring member; Berry, 1960, p.35). The Mazarn is underlain by the unfossiliferous Crystal Mountain sandstone, Collier shale, and Lukfata sandstone of W. D. Pitt (1955), parts of which have been assigned to the Cambrian, but none of which may be older than the earliest Ordovician (Ham, 1959, pp. 81-82). Nevertheless, geosynclinal conditions probably began much earlier inPaleozoic time in the Ouachita system than in the Wichita system. No basement rocks like those in the Wichita system emerge in any Ouachita area, and the oldest Paleozoic rocks exposed there are probably not near the base of the stratified sequence. The characteristic folds and fault slices in the Ouachita Mountains and Marathon region could have formed only over a thick mass of incompetent strata (King,1937, p. 22), and the existence of such strata is attested by one 14,000-foot hole in the Marathon region (Turner No. 1Coombs, in the Dagger Flat anticlinorium),which penetrated only sandstones and shales to the bottom. Even though these rocks are highly deformed, they could scarcely have been derived from a sequence that was originally thin. These inferences are confirmed by gravity data. Allthe uplifts in the Wichita system, where basement rocks are known to be at or near the surface, show positive anomalies, whereas none of the anticlinoria in the Ouachita Mountains produce any variation inthe prevailing large negative anomaly of that region (Howell and Lyons, 1959,p.57).Asimilar,but smaller, negative anomaly occurs in the Marathon region, where the older rocks of the Ouachita system are again exposed. The age of the inferred mass of strata beneath the exposed rocks of the Ouachita system is unknown, except that itisolder than latest Cambrian. During Paleozoic time miogeosynclinal belts were extensive east and west of the continent, in the Appalachian and Cordilleran systems. The lower halves of the deposits laid down in the miogeosynclinal belts are dominantly units of carbonate rocks with subordinate shale and sandstone, formed in water of moderate to shallow depth. They resemble the deposits laid down in the continental interior but are much thicker, due to greater subsidence in the miogeosynclinal belts. Eugeosynclinal belts were farther away from the continent to the east and west — certainly in the northern Appalachians, Bureau ofEconomic Geology, The University of Texas less certainlyinthe southern Appalachians, and nearly continuously along the ocean- ward side of the Cordillera. Miogeosynclines and eugeosynclines were either parts of single troughs or were separated by barriers, but rocks of the two sequences are now mostly1 juxtaposed along structural discontinuities. Various absolute criteria have been used for identification of eugeo — synclinal sequences presence of volcanic rocks and chert; sandstone of the graywacke suite rather than of the quartzite suite; subordination of carbonate deposits; a distinctive biofacies such as that dominated by graptolites in early Paleozoic time; greater thicknesses of deposits than in the miogeosynclinal or interior sequences; and sedimentation in waters of greater depth. But the combinations of these criteria vary from one eugeosynclinal sequence to another, or even from one part to another of a single sequence, and in many sequences one or more of the criteria are inapplicable. Nevertheless sedimentation in all eugeosynclinal sequences was controlled to a greater extent by tectonic forces than in depositional realms nearer the continental interior. Classification of the early Paleozoic deposits south of the continent is more perplexing than that of the deposits to the east and west. The early Paleozoic sequence in the Wichita system of southwestern Oklahoma much resembles the miogeosynclinal sequence of the southern Appalachians, but itlacks the thick Lower and Middle Cambrian elements of that area. Within the Ouachita system a miogeosynclinal belt is indicated only in places. Carbonate rocks like those of the miogeosynclinal belt of the southern Appalachians extend in sub- crop into east-central Mississippi, where they seemingly wedge out against the main belt of the Ouachita system (pp. 89-90) . In the part of the Ouachita Mountains of Oklahoma north of the TiValley fault the Devonian Pinetop chert and underlying limestone approach a miogeosynclinal aspect; rocks beneath them are not exposed and their character is undetermined (Hendricks etal.,1947).Ordovician rocks of the Ouachita system in the Marathon region contain fossiliferous boulders derived from Upper Cambrian and Lower Ordovician carbonate rocks that are inpart older than any known nearby in the interior region (J.L.Wilson,1954b, pp. 254258), which may have been derived from a narrow intervening miogeosynclinal belt. Nevertheless, it seems unlikely that a miogeosynclinal belt could ever have been extensive along the front of the Ouachita system or could have been much concealed by later thrusting. This situation is not unique, as widths of miogeosynclinal belts vary inother orogenic systems because of local tectonic peculiarities. The miogeosynclinal belt in the segment of the Cordilleran system in the Great Basin is nearly 300 miles broad yet is less than 100 miles broad in the segment in Alberta and British Columbia. The miogeosynclinal belt is as much as 100 milesbroad inthecentral and southern Appalachians, yet in a 500-mile segment farther north, between Vermont and Gaspe, it is lacking on the outcrop so that Cam brian and Ordovician eugeosynclinal rocks abut the foreland on the northwest (Cady, 1960, p. 558). These rocks, like those in the Ouachita system, contain fossiliferous boulders of miogeosynclinal carbonate rocks, but itis doubtful whether these rocks were ever extensive. Local tectonic peculiarities that could inhibit the development of a miogeosynclinal belt are speculative; they might include a more abrupt downflexing of the continental margin than elsewhere, or a lack of barrier ridges be tween the eugeosyncline and the continent so that eugeosynclinal sediments could spreal freely over the whole geosynclinal tract. Although the early and middle Paleozoic deposits of the Ouachita system form a distinctive suite, their features do not correspond exactly to any of the usual classes of geosynclinal deposits, and even their geosynclinal origin has been questioned The Ouachita System (J. M. Barton, 1945, p. 1346; Harlton, 1953, p. 796; Ham, 1959, p. 85). Early and middle Paleozoic deposits of the Ouachita system exposed in the Ouachita Mountains and Marathon region include distinctive units of chert and other siliceous deposits (the Middle Ordovician Fort Perta formation, the younger Ordovician Bigfork and Maravillas cherts, and the Devonian and Mississippian Arkansas and Caballos novaculites) 34 Units of shale .34. and slate are associated with the siliceous strata, which in the Ouachita Mountains include interbedded layers and a few thicker units of sandstone, but in the Marathon region they are more calcareous and include much flaggy argillaceous lime stone. Few linkages exist between the Ouachita sequence and its fossils and the carbonate rocks and their fossils in the Wichita system and other parts of the interior region. The earliest link is by means of the Monument Spring dolomite member of the Lower Ordovician Marathon limestone in the Marathon region, which marks a momentary incursion of the carbonate facies and its fossils into a prevailing graptolite-bearing facies. The cherts and limestones of the later Ordovician Mara- villas and Bigfork formations are part of a blanket of deposits that also spread widely into the interior region, where it includes the Montoya and Viola limestones. All these formations have been classified from time to time and from one part to another as of Trentonian, earlyCincinnatian, and late Cincinnatian age, and no doubt they vary somewhat inscopefromplace toplace by addition orsubtraction of beds at the base and top, but their general continuity is beyond question. The Devonian and Mississippian Caballos and 84The writer does not accept the radical restriction of the Caballos novaculite proposed by Berry and Nielsen (1958) but believes that the term should be applied, as it has been for more than 40 years, to the whole body of novaculites and cherts that intervene between the Maravillas and Tesnus formations. Used in this sense, the Caballos is nearly or whollyidentical, even in subdivisions, with the Arkansas novaculite of the Ouachita Mountains. In both areas these subdivisions, probably with a wide range of Devonian and Early Mississippian ages, will no doubt eventually be denned as named formations, at which time both Caballos and Arkansas nova culites should be redefined as groups. Arkansas novaculites link with the Wood- ford chert. Thicknesses of exposed sequences of the early and middle Paleozoic rocks in the Ouachita system are not impressive, compared with sequences of equivalent age in the Wichita system and the West Texas basin (J. M.Barton, 1945, p.1338; Ham, 1959, p. 84).In the Ouachita Mountains the exposed pre-Silurian strata are about 5,000 feet thick and the Silurian and Devonian 2,700 feet, compared with thicknesses of 11,000 and 900 feet, respectively, for equivalent strata inthe Arbuckle Mountains. In the Marathon region the thickness of the Caballos novaculite and exposed older strata is about 2,900 feet, whereas the thickness of equivalent strata in the West Texas basin is nearly twice as great. The dominant fact of sedimentation in the Ouachita system during much of early and middle Paleozoic time was a stagnant sea, inhibiting the growth of a bottom fauna, so that most of the preserved fossils are pelagic forms such as graptolites. The novaculite formations, deposited later than the time of the graptolites, contain sapropelic spore-bearing layers, which also indicate at least intermittent stagnant conditions (Goldstein and Hendricks, 1953, p. 440).Nevertheless, sedimentary structures throughout the Ordovician sequence in the Marathon region show that itaccumulated inprevailingly shallow water (King,1937, p. 45; Berry, 1960, pp. 32-34). Less is known regarding depth of water during accumulation of the sediments of the Ordovician and Silurian sequence in the Ouachita Mountains area, although indications of shallow-water origin are reported in some layers (Miser and Purdue, 1929, pp. 127-131). Unconformities have been reported at various levels in the sequences of both the Ouachita Mountains and Marathon region, but their origin and the amount of hiatus represented by each is uncertain. In the Marathon region the Maravillas chert and Caballos novaculite are separated by a dis Bureau ofEconomic Geology, The University of Texas conformity whose hiatus represents all of Silurian time or longer, yet itis questionable whether there was much uplift, emergence, or erosion of the underlying beds. Moreover, some of the units were formed during long spans of time—the Maravillas chert during part of Middle Ordovician and all of Late Ordovician time (Berry, 1960, p. 33), the Arkansas and Caballos novaculites during much of Devonian and — part of Early Mississippian time suggesting prolonged stability and slow accretion of sediments. Unconformities are indicated by physical evidence at various levels in the Ordovician of the Marathon region, but Berry (1960, pp. 5-8) believed that the sequence of graptolite zones is complete; the supposed breaks may thus represent little or no hiatus. Less can be determined regarding the magnitude of unconformities observed between the various Ordovician and Silurian units in the Ouachita Mountains, because detailed zonation is prevented by wide spacing of fossiliferous horizons and localities. Early and middle Paleozoic deposits of the Ouachita system are more shaly, sandy, and siliceous than deposits of corresponding ages in the interior region. The sandstones in different parts of the Ouachita Mountains sequence are variously classifiable as orthoquartzites, protoquartzites, subgraywackes, and lithic graywackes(Goldstein, 1959a,p.107),and those inthe Marathon sequence of the Cambrian and Ordovician are mostly classed as subgraywackes (Berry, 1960, pp. 32-34).Each of these varieties implies differences in the nature, and perhaps in the position, of the source area. Some of the orthoquartzites, like those in units near the base of the Ouachita Mountains sequence, might have been derived from low lands in the interior region. Other sandstones, most of which are less well-sorted subgraywackes or gray- wackes, were derived from within the Ouachita system, as shown by increasing sandiness of limy or shaly formations southeastward across the area of exposure, and the wedging in of sandstone units in the same direction. These sandstones might have been derived from intermittent pulses of uplift in varied tectonic lands within the geosynclinal area. Although the ultimate sources of all the sands were crystalline rocks, at least some of them were resedimented from earlier deposits. Source areas need not have been directly opposite the sites of deposition, as longitudinal filling of sedimentary basins was a more common event than has been generally supposed (Kuenen, 1957).Allthe directional structures observed by Berry (1960, pp. 32-33) in the Marathon Ordovician sequence indicate transport of sediments to the northeast, probably along rather than across the trend of the depositional basin. Some of the pulses of upliftrecorded by the sandstone wedges may reflect early times of orogeny within the Ouachita system, akin to the Taconian or Acadian orogenies of the inner parts of the Appalachian system. Aminor pulse is suggested by the Blakely sandstone in the Ouachita Mountains and the Rodriguez Tank sandstone ofBerry(1960,p.20)inwestTexas, both of early Middle Ordovician age, and a greater pulse is suggested by the thicker Blaylock sandstone of the Ouachita Mountains, of Early Silurian age. The polymetamorphic fabrics observed by Flawn in many well cores from the interior zones of the Ouachita system in central Texas ("Metamorphism," pp. 121-124) suggest that one or more orogenies occurred before the climactic late Paleozoic orogeny, some of which may have been as early as Silurian or Ordovician time. However, the boulder beds inthe Middle and Upper Ordovician formations in the Marathon region are not orogenic products but resulted merely from faulting along the northwest margin of the depositional area during times of unusual subsidence (J. L. Wilson, 1954b, p. 258). Bedded cherts and other siliceous rocks are among the most perplexing of sediments. Even the classic radiolarian cherts of the Franciscan formation inCalifornia, The Ouachita System whose spatial relations to spilitic lava are obvious and whose genetic relation is likely, contain little internal indications of source. Silica-secreting organisms such as radiolarians and sponges clearly are no more than incidental constituents, although their remains are common inthe chert. The cherts and siliceous rocks of early and middle Paleozoic age in the Ouachita system share the perplexities of their class and have been diversely interpreted. The most convincing hypothesis is that of Goldstein and Hendricks (1953, pp. 440-441), that they were derived ultimately from falls of siliceous volcanic ash, which were altered diagenetically on the sea floor during long exposure and slow burial. The Upper Ordovician chert formations and the Devon ian and Mississippian novaculite formations are thought to have formed during times of greatest volcanism and ash falls, when there was littleinflux of clastic sediments into the area of deposition. We can now revert to the classification of the environment of the early and middle Paleozoic deposits of the Ouachita geosyncline, a problem unlikely tobe resolved by application of a few absolute criteria. There is a tantalizing resemblance between them and the "leptogeosynclinal" deposits of parts of the Alpine geosyncline (Trumpy, 1960, pp.865-869),as both are relatively thin sequences representing a long time span and include significant volumes of siliceous sediment. However, available evidence suggests that most of the deposits of the Ouachita geosyncline were laid down in shallow water, whereas those in the Alps are believed to have been laid down in deep water. Nevertheless, the deposits of the Ouachita geosyncline were probably not merely a thinned shoreline facies of the dominant carbonate deposits of the interior region overlapping toward a theoretical land "Llanoria," although this has been inferred (Miser, 1921, pp. 87-89; P.B.King,1937,p.44; andlater authors) .Shoreline deposits would hardly create such remarkably persistent rock and faunal facies for long distances along the system, and differences between the ex posed sequences inthe Ouachita Mountains and Marathon region would have been greater. The exposed lower and middle Paleozoic rocks are probably only a part of the deposits laid down at that time in the Ouachita geosyncline, as Flawn's study of drill data indicates that they are marginal to a much broader orogenic belt. Itis reported that where lower and middle Paleozoic formations can be identified in drill holes southeast of the outcrops, they are much thicker (Goldstein, 1959a, p. 108) ;rocks in some of the buried southeastern belts described by Flawn may include units of early and middle Paleozoic age but of unrecognizable facies. Moderate tectonic and volcanic influences on sedimentation are indicated by the sandstone, chert, and novaculite units, whose sediments were probably derived from tectonic lands and volcanic areas within or flanking the Ouachita geosyncline. The exposed early and middle Paleozoic rocks of the Ouachita system are marginal to the inner zones of the system, like the miogeosynclinal rocks of equivalent age in the southern part of the Appalachian system. They are unlike the usual miogeosynclinal sediments but were deposited in a — similar manner mainly in shallow water on a slowly subsiding foundation. The sediments themselves are more like those of the eugeosynclinal realm than any other. In the Ouachita system extensive development of the usual carbonate rocks of the miogeosynclinal realm was somehow inhibited, and deposits of eugeosynclinal type might thus have been able to spread from the inner zones across the marginal zone, into an area whose structural behavior, at least, was miogeosynclinal. LATE GEOSYNCLINAL PHASE (MISSISSIPPIAN AND EARLY PENNSYLVANIAN) The upper part of the sequence in the miogeosynclinal belts of the Appalachian and Cordilleran systems differs fundamentally from the lower in both nature and origin (P. B.King,1959, p.59).The lower part is dominantly carbonate rocks, and the few interbedded clastic layers were derived mainly from the continental interior. The upper partis dominantly clastic rocks, which thicken and coarsen toward the inner zones of each system, where the eugeosynclinal belts were in process of deformation. The clastic rocks overspread the miogeosyncline in a succession of wedges, the edges of some of which extend wellinto the interior region. These clastic sequences vary from place to place, depending on the local tectonic history. Insome segments of the Appalachian system clastic wedges appear in the Middle or Upper Ordovician, in others in the Silurian, Devonian, orevenhigher;in some segments of the Cordilleran system they first appear near the top of the Pale- zoic.Inplaces the difference between lower and upper parts of the miogeosynclinal sequence is absolute, with clastic rocks dominating from the first wedge upward. In others, clastic and carbonate wedges interlock, indicating several widely separated pulses of deformation before the climactic orogeny. A Mississippian clastic wedge thus spreads widely across the central Great Basin from the Antler orogenic belt on the west but interlocks eastward with miogeosynclinal carbonate rocks that were not deformed untilMesozoic time (Roberts etal., 1958, p. 2838). Many of the earlier clastic deposits are localized within the miogeosynclinal belts and accumulated in deep, linear, rapidly subsiding troughs near the source areas, as did the European flysch (Triimpy, 1960, p. 873).Many of the later clastic deposits are broad wedges or blankets, formed in a complex of continental, estuarine, and shallow- water environments, as did the European molasse (Triimpy, 1960, p.880).In places successively younger clastic deposits are juxtaposed, each farther inland, indicating progressive consumption by orog eny of the earlier eugeosynclinal and miogeosynclinal tracts. Inthe exposed parts of the Ouachita system a fundamental change in sequence like that in the Appalachian and Cordilleran miogeosynclines occurs at the top of the Arkansas and Caballos novaculites. Whereas the sequence from the novaculites downward is dominated by thin, widely spread argillaceous or siliceous units, with a few clastic wedges, the sequence above is a great mass of clastic rocks of Late Mississippian (Meramec and Chester) and of Early Pennsylvanian (Morrowand Atoka) ages. These clastic rocks comprise the Hot Springs sandstone, Stanley shale, Jackfork sandstone, and Atoka formation of the Ouachita Mountains, and the Tesnus and Haymond formations of the Marathon region. The clastic formations follow the novaculite formations with a hiatus which represents part of Early Mississippian time. In places in the Ouachita Mountains of Arkansas the basal clastic unit is the quartzose Hot Springs sandstone, which probably wedges out by overlap elsewhere. An unconformity is reported at the top of the novaculite formations at many places in both the Ouachita Mountains and Marathon region, with conglomerate at the base of the succeeding deposits, but the break between them maynot have been subaerial, and itmight represent merely a cessation of sedimentation. Thinning of the inland margin of the clastic deposits was probably more by wedging out of each unit than by overlap. These clastic deposits have many features in common and are of similar origin, but three principal rock facies occur: (1) The Stanley shale and Tesnus formation include thin to thick, to very thick units of dark shale, which alternate with thin to thick sandstone layers. The sand The Ouachita System stone layers are dark, argillaceous, chloritic in part, and are subgraywackes or lithic graywackes which contain much detrital feldspar, mica, and rock fragments. Rocks of thisfacies are widespread, both in the outcrop areas in the Ouachita Mountains and Marathon region and in the sub- crop between the Ouachita Mountains and central Texas, where Flawn observed that they contain abundant detrital biotite, granitic fragments, and high-kaolin shales. The facies resembles the more sandy rocks of Franciscan type inthe Mesozoic of California. (2) The Jackfork sandstone is a thick- bedded, light-colored sandstone, withshale partings. The sandstones are protoquartzites or subgraywackes and are coarser than those of the preceding facies. Their detrital grains are dominantly quartz, although they include appreciable minor constituents. Sandstones of this kind are widespread inthe Ouachita Mountains but have been identified only a short distance southward insubcrop into Texas. They are represented in the Marathon region by only a few lenses in the thicker parts of the Tesnus. That part of the Atoka formation which is preserved in the Ouachita Mountains contains many sandstone beds similar to those inthe Jackfork. (3) The Haymond formation of the Marathon region is mostly thinly and rhythmically interbedded sandstone and shale, interrupted by some thick lenses of feldspathic arkose and by boulder beds. This facies is not represented inother parts of the Marathon sequence; it occurs in the Ouachita Mountains in the Johns Valley shale and lower part of the Atoka formation, without the arkose lenses (T. A. Hendricks, writtencommunication, 1960). These thin-bedded sandstones and shales resemble those of the Mesozoic Knoxville and Paskenta formations in California. Minor constituents of the clastic sequence of the Ouachita system include a thinunit of volcanic tuff in the lower part of the Stanley shale in the interior of the Ouachita Mountains, and eight or nine thin,persistent beds of siliceous shale dis tributed through the Stanley, the Jackfork, and the lower part of the Atoka. The shales contain conodonts, radiolarians, and other siliceous fossils and are probably of ulti mate volcanic origin (Goldstein and Hendricks, 1953, p. 440). Similar beds of siliceous shale occur in the Tesnus formation of the Marathon region. Minor constituents also include several remarkable boulder beds whichcontain not only pebbles, cobbles, and boulders but also angular blocks and slabs of diverse earlier Paleozoic sedimentary rocks, some more than a hundred feet across. Boulder beds in the Ouachita Mountains are mainly in the Johns Valley shale of Late Mississippian and Early Pennsylvanian age, but there are a few in the underlying Jack- fork sandstone (T. A.Hendricks, written communication, 1960).Those intheMarathon region are somewhat higher in the sequence, in the Haymond formation of Atoka age. In the Ouachita Mountains the boulders and blocks are from formations of the foreland region, such as those now exposed in the Arbuckle Mountains and Ozark uplift, but boulders and blocks in the Marathon region appear to have been derived not only from the foreland region but from uplifts within the geosynclinal area. The Upper Mississippian and Lower Pennsylvanian clastic rocks are notable not only for their great thickness but for their close restriction to the Ouachita belt itself. The Tesnus formation can be traced on the outcrop across the Marathon region from a near feather edge into exposures on the southeast where itis more than 7,000 feet thick (P. B. King, 1937, pp. 55-56). Abrupt southeastward thickening of the Stanley and Jackfork formations occurs from one thrust slice to the next in the western part of the Ouachita Mountains of Oklahoma (Hendricks et al., 1947), part of which is surely a sedimentary variation, although it has been accentuated by later thrusting. Farther east these units wedge out more gradually, as they have been identified beneath the Arkansas basin north of LittleRock, Arkansas (Maher and Bureau ofEconomic Geology, The University of Texas Lantz, 1953) (see well 12 in Appendix, Part 3). Within the Ouachita Mountains the Stanley shale is as much as 12,000 feet thick, the Jackfork sandstone is as much as 7,000 feet, and the Atoka formation preserved above them is as much as 7,000 feet thick; along the mountain front in western Arkansas the Atoka is probably more than 19,000 feet thick (Reinemund and Danilchik, 1957). In the southeastern part of the Marathon region the Tesnus formation is as much as 7,000 feet thick and the Dimple limestone 1,000 feet thick, with incomplete sequences of the overlying Haymond formation more than 3,000 feet thick. The sequence inthe Marathon region is impressive but is thinner than that in the Ouachita Mountains, either from a less complete development of the clastic deposits, orbecause the part exposed is northwest of the depositional maximum. These clastic deposits of great thickness were derived from tectonic lands within the Ouachita system, which might have been uplifted wedges of basement rocks, deformed geosynclinal rocks, orboth. They were not the product of an accidental juxtaposition of unrelated orogenic systems created during markedly differentiated orogenies (Hall,1956, p.2254) but record pulsations of a continuing process of orogeny, by which the original geosynclinal area was being converted into an orogenic system. Flawn's observation shows that the clastic formations are most extensive areally in the salients of the Ouachita Mountains and Marathon region, both in outcrop and subcrop, whereas they form either narrow belts or are missing entirely in the intervening area in Texas. Part of this relation is caused by later structure and erosion, butitsuggests that the salients may coincide with the widest and deepest basins of the late geosynclinal stage, and the most vigorously raised tectonic lands, so that a greater volume of clastic sediments accumulated here than elsewhere. The mass of clastic deposits must have accumulated in a long trough or troughs, so deep that sediments were mostly con fined to the troughs except for the youngest deposits in the Atoka formation. Subsidence of the troughs was so rapid that it exceeded the rate of deposition and created areas of deep water, into which much of the coarser material was transported by turbidity currents. Some parts of the sequence have been interpreted as of continental origin, perhaps because of included plant remains and other terrigenous material (Fan and Shaw, 1956, p. 266), but these ideas are as archaic as early notions that graywackes in the Ocoee series of Tennessee and the Franciscan for mation of California were subaerial piedmont or flood-plain deposits (Barrell, 1925, p.12;E.F.Davis, 1918, pp.29-10). On the contrary, most of the clastic deposits contain flute casts, load casts, groove casts, convolute bedding, graded bedding, and pelagic fossils, and lack cross-bedding, — ripple marks, orbenthonic fossils indicating that they accumulated in moderately deep to very deep water (Cline and Shel burne, 1959, p. 206; Cline, 1960, pp. 87-100). In the Ouachita Mountains directional observations indicate movement of sediments westward along the axis of the trough; in the Marathon region no directional observations have been recorded in the Mississippian and Pennsylvanian rocks, but it will be recalled that in the Ordovician rocks Berry (1960, pp. 32-33) has which sug made directional observations gest northeastward transport along the axis of the basin. The Dimple limestone, which interrupts the clastic sequence in the Marathon re- gion,probably expresses merely acessation of influx of clastic material, rather than shoaling of the bottom. Aside from layers of the of foraminiferal limestone, most contain only shell debris and occa strata sional pelagic cephalopods. Anapparently analogous facies forms the Chickachoc chert on the margin of the Ouachita geosyncline in Oklahoma, which contains a varied fauna, including abundant sponges. Absence of ripple marks, uniform lamination of the sediments, and the fact that brachiopod valves are still joined indicate The Ouachita System that the water in which the Chickachoc accumulated was moderately deep (T. A. Hendricks, written communication, 1960). The boulder-bearing layers which interrupt the sequence inplaces are the expectable products of the rapidly deepening troughs. During times of excessive subsidence the margins of the troughs were downflexed and inplaces faulted. From the submarine scarps thus created, both shelf deposits and blocks of the bedrock slumped or slid into the basin, where they were transported for considerable distances with the aid of turbid flows (P. B.King,1958, p.1735). OROGENIC PHASE (MAINLYPENNSYLVANIAN) Inorogenic systems the late geosynclinal phase blends into the orogenic phase, or the two overlap completely. The orogenic climaxes are commonly interpreted from relations in the marginal parts of the systems, where deformation occurred after that of the inner parts of the systems. Details of the orogenic phase in the Appalachian system are no longer preserved, but Pennsylvanian coal measures that are infolded with the miogeosynclinal rocks in Alabama and Pennsylvania, and are preserved elsewhere only in the fore- land, resemble the molasse of European areas, suggesting that they formed in a very late stage of the orogenic cycle. Credence to this inference is afforded by the many clastic wedges derived from orogenic belts farther southeast which occur in the sequence of middle Paleozoic rocks that underlie the Pennsylvanian in the miogeosynclinal area, and radiometric ages of 280 to 400 million years obtained in the crystalline rocks farther southeast, which suggest that the inner part of the system had been deformed during several orogenies, extending as far back as Middle Ordovician time (P. B. King, 1959, pp. 57-60, 64-65). Although the deformation in the miogeosynclinal and foreland belts was Pennsylvanian or younger, it was marginal to an earlier and greater deformation inthe interior of the system. In the Cordilleran system the frontal parts of the Rocky Mountains were deformed during the Laramide orogeny of Late Cretaceous and Paleocene time, but the record of earlier deformation in the central part of the system is better preserved than in the Appalachians. One or more orogenies during Early Cretaceous and Late Cretaceous time occurred in the western Rocky Mountains and eastern Great Basin (Spieker, 1946, pp. 149-156) . Moreover, the Nevadan orogeny of Jurassic time nearer the Pacific Coast, once thought to have created an independent orogenic system, represents merely the orogenic climax in the Cordilleran eugeosyncline. The record of orogeny is more complete in the Ouachita system than inthe Appalachian system, butitismostlyinthemarginalparts, where deformation was mainly during Pennsylvanian time but extending inplaces into Permian time. We willdeal mainly with the orogenic record in these marginal parts, although, as indicated earlier, the interior zones of the system were already in process of deformation as far back as later Mississippian time, with still earlier orogenic pulses suggested by minor wedges of clastic rocks in the Silurian and Ordovician. In the Ouachita Mountains of Oklahoma and the McAlester basin to the north rearrangement of the patterns and environments of the depositional basins began in Atoka time and continued intoDcs Moines time, probably accompanied by a mounting crescendo of orogeny within the present mountain area. The total thickness of the Atoka formation that was originally deposited over the site of the Ouachita Mountains is unknown, but the 19,000 feet preserved along the mountain front may have been near the depositional maximum. The formation thins rapidly northward and northwestward from the mountain front toward the Ozark and Hunton uplifts, passing from a deep-water geosynclinal deposit into a mixed shallow-water and nonmarine deposit less than 500 feet thick. Disturbances must have occurred inthe Ouachita Mountains during Atoka time, as in places in the mountains the Atoka is unconformable on underlying formations, and as west of the mountains it contains beds of chert conglomerate. No Pennsylvanian rocks younger than the Atoka are preserved within the Ouachita Mountains, but strata of Dcs Moines age are as much as 7,000 feet thick in the McAlester and Arkansas basins immedi The Ouachita System ately to the north, where they are sandstones and shales, with many coal beds. According to Hendricks (written communication, 1960),"Turbidites occur not only in the Atoka, but in the McAlester and Savanna formations. Marine fossils which have been collected from them include more than 30 species and numerous individuals, whose shells are characteristicallystilljoined. Muchof thedeposition must have been in fairly deep water, and the basin filledup to sea level only at times of coal deposition." Absence of beds of Dcs Moines age from the Ouachita Mountains is probably not merely an accident of erosion, as that area was probably in process of deformation. From Stanley and Jackfork time, through Atoka time, into Dcs Moines time the axis of the depositional trough shifted from the interiorofthemountains toitsmargin, and thence into the foreland area beyond. The depositional environment also changed progressively to shallower water, with oc casional coal swamps toward the end. Deformation thus presumably began in the Ouachita system during Atoka time and continued through Dcs Moines time. Moreover, the Dcs Moines strata in the McAlester and Arkansas basins are thrown into linear folds parallel with those in the Ouachita Mountains that diminish in intensity outward to the north and northwest, indicating that thrusting from the Ouachita area continued even later. During these times of deformation, the Ouachita rocks were extensively thrust toward their fore- land—probably on the order of 50 miles in the western part of the exposed area (Hendricks, 1959, p. 55). Flawn (1959a, p.2013) suggests that there was also lateral movement of the Ouachita rocks on transverse faults at the sides of the Arbuckle massif insubcrop which was on the order of 30 miles (p. 171). The inferred deformational history in the Ouachita Mountains area is probably representative of much of the salient of the Ouachita system between Mississippi and central Texas, but in the salient to the west,'» centering intheMarathon region, deformation apparently reached its climax later. Strata which accumulated near the time of the orogenic climax are exposed in two areas in the Marathon region, but these areas exhibit strangely contrasting his tories: In the northeastern Marathon Basin, near the type areas of the Wolfcamp and Gaptank formations, the characteristic clastic deposits of the Haymond formation are succeeded by the more varied Gaptank and Wolfcamp deposits, formed in a shallower, less stable marine environment. Many conglomerate beds in the middle of the Gaptank contain water-worn cobbles not only of the Dimple limestone and other older formations but also of the basal limestone member of the Gaptank itself. They record the first strong pulse of orogeny in the exposed part of the Marathon region and are approximately of Missouri age, or younger than any of the orogenic sediments in the Ouachita Mountains region. Nevertheless, the exposed sequence of Haymond, Gaptank, and Wolfcamp formations seems to be structurally conformable, despite übiquitous local channeling at many levels, so that the steep folding of the Haymond passes gradually northward into the gentle tiltingof the upper part of the Gaptank and the Wolfcamp. The first decided unconformity is at the top of the Wolfcamp formation as defined, at what has been called the base of the Leonard series, although it is now known that the zone of Pseudoschwagerina extends above it (C. A. Ross, 1959, p.300). Inthe northwestern Marathon Basin the later Pennsylvanian, mapped as Gaptank and Haymond formations, is a thick mass of highly deformed shale and of thinlayers of sandstone, sandy limestone, and chert- pebble conglomerate. More than 6,600 feet of similar strata were drilled through in the Slick-Urschel No. 1Decie well before entering older rocks. These strata are so different from the type Gaptank that it is hardly surprising that they were assigned tothe Tesnus formation during the first sur Bureau of Eonomic Geology, The University of Texas vey (Baker and Bowman, 1917, pp. 104105); like the Tesnus they were probably deposited in water of much depth in a rapidly subsiding trough, rather than on an unstable shelf. Nevertheless, fossils from many localities indicate a wide range of later Pennsylvanian ages (Dcs Moines, Missouri, and Virgil) (P. B. King, 1937, pp. 80-82),and all the clastic strata in the Decie well have been assigned to the Wolf- camp (Hall, 1956, pp. 2253), perhaps be cause they include part of the zone of Pseudoschwagerina. The Decie well demonstrates that these strata overlie a foreland sequence of older Paleozoic rocks like that beneath the West Texas basin. Moreover, fieldrelations show that they are overridden from the south east for many miles along the Dugout Creek thrust by a plate of older Paleozoic rocks of the Ouachita sequence, a relation confirmed by the Decie well and the Gulf Oil Corporation No. 1D. S. C. Coombs well farther southeast, both of which drilled through the plate into the overridden rocks. Both overridden and overriding rocks are overlain on the north by the Wolfcamp formation, with great angular unconformity and coarse basal conglomerate, thus establishing the culmination of deformation and thrusting as within the early part of the zone of Pseudoschwagerina. The strata in the northwest part of the Marathon Basin are an exposed fragment of a much more extensive mass of deposits, laiddowninaforeland trough that extends eastward beneath the surface, north of the Marathon region and into the Val Verde basin of Terrell and Val Verde counties (Galley, 1958, pp. 424-428). There, as much as 14,000 feet of Late Pennsylvanian and Early Permian clastic rocks have been reported, the greater part of which have been called Wolfcamp. Along at least part of its length, the trough must be overridden from the south by thrust plates of rocks of the Ouachita system, comparable to the plate above the Dugout Creek thrust in the exposed area. In this setting, the relatively thin sequence of shallow-water deposits of the type Gaptank and Wolfcamp formations in the northeastern Marathon Basin is anomalous. However, this sequence lies within the Ouachita system rather than in the foreland, and the deep foreland trough rilled by contemporaneous deposits must lie north of it. The environment in which the sequence accumulated was a product of an earlier orogenic pulse of Missouri age, which destroyed the deep basins within the Ouachita system that had existed during Haymond and earlier times and converted the marginal part of the system into a geanticline or unstable shelf, covered only by shallow seas. This review demonstrates that in each segment of the Ouachita system the belts of deformation and deposition migrated withtimefrom theinner part ofthe system toward its foreland. The review also suggests that the climactic orogeny in the Ouachita system migrated westward with — time the orogeny in the salient centering in the Ouachita Mountains being of Middle Pennsylvanian age, and that in the salient centering in the Marathon region being of Late Pennsylvanian and Early Permian age. This westward migration may also have extended into the little-known prolongation of the Ouachita system in Mexico, where the Permian includes thick accumulations of graywacke, other clastic rocks, and volcanic rocks, and where some of the Permian sequences (as that near Las Delicias, Coahuila) were strongly deformed late in Permian time or shortly thereafter. POST-OROGENIC PHASE Modern surface features of the mountain belts around the borders of North America were created during the post orogenic rather than the orogenic phase. Even in the Cordilleran system, where the orogenic phase persisted later than in the other systems, the rugged mountains are products of the succeeding heterogeneous local orogenies, or of the final epeirogeny. In the older Appalachian system the mountains are products of epeirogeny and are erosional remnants in areas of regional uplift. Even greater areas in the Appalachian system have regionally subsided, have been buried by younger sediments, or have been lost beneath the sea (P. B. King, 1959, pp. 41-42; Billings, 1960, pp. 376-380).In the Ouachita system, epeirogenic uplift has been less extensive than in the Appalachian system, so that no more than 275 miles of its length is now exposed, out of an original thousand — or more in the Ouachita Mountains, the Marathon dome, and a few smaller areas. Regional subsidence has been much more extensive; the inner part of the system, especially, has been peculiarly susceptible to collapse, so that most of it is deeply buried by the Mesozoic and Cenozoic deposits of the GulfCoastal Plain. Late Paleozoic post-orogenic deposits are extensive in the continental interior of the south-central states, especially near the uplifts of the Wichita system. InOklahoma they are largely of continental origin and include the Late Pennsylvanian conglomerates of the Pontotoc group that overlap the Arbuckle Mountains, and the Permian red beds that half-bury the Wichita Mountains. In west Texas, where marine conditions persisted through Permian time, the uplifts are masked and buried by carbonate deposits, including extensive reefs. Except in the Glass Mountains, along the northern edge of the Marathon region, few of the post-orogenic deposits of the continental interior extend onto the deformed (PERMIAN AND LATER) rocks of the Ouachita system. However, within the inner part of the system some wells have passed from strata of proved Mesozoic age into undisturbed shales, red beds, and coarser clastic rocks, whereas adjacent wells have entered thoroughly de formed and metamorphosed rocks of Ouachita facies (see "Post-orogenic Paleo zoic rocks lying on the Ouachita belt," pp. 125-127) .Some of the undisturbed rocks are certainly Paleozoic, as invertebrate and plant fossils of Pennsylvanian and Early Permian age have been identified in them in Morehouse Parish, northern Louisiana, and in Bexar and Frio counties, central Texas. Some of the others, from which no fossils have been obtained, might be of early Mesozoic age, like the Triassic New ark group of the inner part of the Appa lachian system. The most extensive of these undisturbed rocks are the unfossiliferous red beds of the Eagle Mills formation, classed doubtfully as of Permian age, which have been penetrated inmany wells along the south flank of the Ouachita Moun tains from southern Arkansas into north eastern Texas. The other undisturbed rocks are recorded only in single wells, so that nothing can be told of their structural relations. By analogy with late Paleozoic post-orogenic deposits of the northern Appalachians (in the Maritime Provinces of Canada) those of the inner part of the Ouachita system might have formed in local basins of various sizes, between ridges of deformed earlier rocks. Perhaps only sometime after these strata had been deposited were the modern uplifts and depressions within the Ouachita sys tem differentiated. In the continental in terior, and along the margins of the Oua chita system, Lower Cretaceous strata lie on a deeply eroded, truncated, and pene — planed surface of the Paleozoic rocks the Wichita paleoplain of Hill (1901, p. 363) —which had been perfected during earlier parts of Mesozoic time. This surface may Bureau of Economic Geology, The University of Texas combine effects of several periods of erosion in the inner part of the Ouachita system, as various unconformities are recorded between and beneath the Jurassic and Cretaceous rocks inthe Gulf Coastal Plain. Exposures of the Ouachita system inthe Ouachita Mountains result from epeirogenic uplift. Within the mountain area is a large and abrupt gravity minimum of more than 100 milligals, caused, probably, by a great thickness of light sediments, even now uncompensated, which have been rising since the orogenic climax. Ridge-crest profiles of the mountains suggest the existence of a former Ouachita peneplain (Miser and Purdue, 1929, pp. 136-139) , which is seemingly traceable southward into the Wichita paleoplain beneath the Lower Cretaceous strata of the coastal plain. However, uplift of the Ouachita Mountains is more complex than thus suggested, as Upper Cretaceous rocks south of the mountains bevel Lower Cretaceous rocks eastward, and as both these and the deformed Paleozoic rocks of the Ouachita system are beveled inturn near LittleRock, Arkansas, by Paleocene and Eocene rocks of the Mississippi embayment. In the Marathon region, uplift of the rocks of the Ouachita system was probably more orogenic than epeirogenic. A deficiency of gravity occurs here, probably due to excessive thickness of light sediments as in the Ouachita Mountains, but this is a rather minor feature. Lower Cretaceous rocks perfectly truncate the Paleozoic structures along the Wichita paleoplain, but this was not distorted until after Cretaceous time. The Marathon dome, in which rocks of the Ouachita system are exposed, was produced primarily by resistance offered by the transverse-striking Ouachita structures to compression from the west during the Cordilleran orogenies. The dome was raised during at least two periods, near the end of the Cretaceous and early in the Tertiary (P. B. King, 1937, pp. 139-140) . Subsidence of the remaining part of the Ouachita system began primarily inMesozoic time and was accentuated during Cenozoic time. The first extensive deposits over the inner part of the system comprise the Werner formation and Louann salt— the latter the source of the salt domes over — much of the Gulf Coastal Plain which are probably younger than the Eagle Millsformation (Hazzard et al.,1947, p. 483).The Werner and Louann have been called Permian, like the Eagle Mills,but are more likely the first deposits of the Mesozoic transgression (McKee et al., 1956, pp. 1-2). They are followed by a great sequence of Upper Jurassic and Lower Cretaceous rocks, only the highest of which persist updip to the outcrop, and these by the Upper Cretaceous and Tertiary. The area of subsidence corresponds to the Gulf Coastal Plain and is related to differentiation of the Gulf of Mexico as a tectonic feature. Nevertheless, as indicated earlier byMiser (1934c,pp.1067-1072), the inner edge of the area of subsidence, from Texas eastward to Mississippi, corresponds remarkably to the marginal part of the Ouachita system. Zones of normal faulting along the edge of the area of subsidence, such as the Balcones fault zone of Texas and others farther east, and zones of igneous activity of Cretaceous and early Tertiary age, closely follow the Ouachita trend. This relation may be coincidental, but at the very least, the structures associated with the subsidence of the Gulf of Mexico utilized lines of weakness already created by the Ouachita system. More likely, the Ouachita system and the Gulf of Mexico are manifestations of a single continuing process, the structural features of the latter being inherited from those of the former. Economic Possibilities August Goldstein, Jr., and Peter T. Flawn General Statement From an economic point of view, the Ouachita structural belt is the least known and most poorly understood structural trend inthe southern United States; itisa 1,300-mile long nonproductive swath which is flanked by areas of large oil and gas production and reserves in the coastal plain to the south and east and in the basins to the north and west. Miser (1934c) has emphasized how the Ouachita structural belt separates the Paleozoic production of the Mid-Continent region on the north and west from the Mesozoic and Tertiary production on the south and east. Most of the data and conclusions in this chapter are taken from an earlier paper by Goldstein andFlawn (1958). Most petroleum geologists have considered the rocks of the Ouachita structural belt as being highly metamorphosed, and the trend is commonly called the "schist" belt. Of the more than 200 wells which have encountered the rocks of the structural belt, most have been abandoned after penetrating only a short section of rocks of Ouachita facies, largely because the rocks were regarded as metamorphosed and unsuitable for oil and gas reservoirs. Medium to high-grade metamorphic rocks have been encountered in a few wells, but in others the so-called "schist" is actually highly sheared and contorted shale. "Black granite" reported from north-central Texas wells is a local name for steeply dipping black shales of the structural belt; this cognomen certainly tends to discourage deeper drilling. In addition to the rather limited vertical penetration of the rocks of the structural belt, the average drilling density along the entire structural belt is so thin that the belt as a whole must be classified as unexplored. There are two possible petroliferous provinces associated with the Ouachita structural belt. Although related tectonically, they differ widely in lithology and environment of deposition and require entirely different exploration techniques and "exploration thinking" for proper evaluation of their petroleum possibilities. There are, first, the possibilities of oiland gas production in the rocks of Ouachita (geosynclinal) facies and, second, the petroleum potentialities of the rocks of foreland (Arbuckle or "normal") facies both underlying and adjacent to the fold- belt. POSSIBILITIES OF PETROLEUM PRODUCTION IN ROCKS OF OUACHITA FACIES In the western part of the Ouachita Mountains of Oklahoma, the northern limit of the Ouachita Mountains is generally considered tobe the Choctaw fault.A wide variety of rocks of Ouachita facies ranging in age from Cambrian (?) to Atokan occur from the Choctaw fault southward to where the Ouachita Mountains are overlapped by Cretaceous sediments. Paleozoic beds in — this area are not all metamorphosed some show practically no alteration. At other places, the rocks show intense crushing, contain numerous quartz vein- lets, and are recrystallized due to metamorphism. These latter areas are unfavorable for petroleum production; limited data suggest strongly that the oil is dissipated long before any observable metamorphic changes occur. Furthermore, it is probable that reduction or virtual elimination of pore space in potential reservoir beds occurs very early in low-grade re Bureau ofEconomic Geology, The University of Texas gional metamorphism, possibly before there are any positive microscopic indications of mineralogical changes due to metamorphic reorganization. In the areas of the Ouachita Mountains where rocks are essentially unmetamorphosed, there seems tobe no reason whyit isnotpossible tofind reservoirs of oiland gas. There is considerably more reason to doubt that these deposits willbe economically profitable except under unusual circumstances. Most of the potential reservoir beds are in the sandstones of the Stanley, Jackfork, and Atoka formations. These rocks typically have low porosity and very low permeability. Local development of fracture porosity possibly could create suitable reservoir rocks out of these tight argillaceous sandstones. The quartzose sandstones of the Crystal Mountain and Blakely occur mostly in the more metamorphosed terranes of the Ouachita Mountains and cannot be regarded as suitable reservoir beds on the basis of their observed properties where they crop out. The Blaylock sandstone is both generally tight and very limited in its areal distribution. The sandstone development in the Womble occurs in the more highly metamorphosed portion of the Ouachita Mountains, and the Womble is largely shale in the unmetamorphosed areas. Structurally, the conditions for trapping oil and gas are not very favorable. Large faulted anticlines are present in the Ouachita Mountains, and presumably there are large anticlinal structures in the buried rocks of the foldbelt. However, it willbe difficult tolocate and map closed structural traps in these rocks. Moreover, the numerous faults provided a means for escape of oiland gas. Nevertheless, a completely pessimistic approach to the petroleum possibilities in rocks of Ouachita facies seems unwarranted. Oilhas been produced from shallow wells in Stanley sandstone near Redden, Atoka County, Oklahoma. These wells, originally drilled as early as 1914, produce at a depth of 500 feet from steeply dipping, tight sandstone sealed up-dip by asphalt impregnation. The amount of production obtained and the periods during which the wells have produced are not known to the writers. The oil at Redden may have migrated from some of the older, more petroliferous, underlying rocks that were faulted against sandstones of the Stanley. Hendricks et al. (1947), Ham (1956a), and Howell and Lyons (1959) reported on the many oilseeps and veins and irregular bodies of grahamite or asphaltite (solid hydrocarbon) within the Ouachita Mountains. Ithas been suggested that the petro leum in the seeps and that which formed the grahamite probably originated in the strata of foreland facies underlying the overthrust beds, and that this oil subsequently migrated into rocks of Ouachita facies. Oil-stained sandstones and scattered noncommercial gas shows have been observed in Stanley-Jackfork strata penetrated by deep wells in the Ouachita Mountains of Oklahoma. Insome wells the beds with oil or gas shows overlie thou sands of feet of Ouachita facies rocks, and the hydrocarbons are unquestionably indigenous rather than derived from underlying rocks of foreland facies. In the subsurface Ouachita structural belt in Texas, small amounts of asphaltic material are fairly common in sandstones and cherts. A possible approach to this problem is to concentrate exploratory efforts in unmetamorphosed areas withlarge structures (to drain as large an area as possible), where massive thick beds of sandstone are present at shallow depths (to make up for generally low porosity and permeability) . Only under such conditions would oil or gas deposits insediments of Ouachita facies prove tobe economically attractive. POSSIBILITIES OF PETROLEUM PRODUCTION INROCKS OF FORELAND FACIES UNDERLYING OR ADJACENT TO THE OUACHITA STRUCTURAL BELT Evaluation of the possibilities of petroleum production inrocks of foreland facies underlying or adjacent to the Ouachita structural belt involves a number of factors. Among these factors are the validity of the carbon ratio theory, relative proximity to the foldbelt front, geologic section present, age, intensity, and nature of the structural movements, and productive history of the adjoining area. There are a number of reasons why the oilproduction possibilities of these foreland rocks have not been tested adequately heretofore. (1) Most wells that have been drilled on structures associated with or involved in the frontal zones of the orogenic belt have encountered a high degree of secondary silicification in pre-Atokan sandstones. This silicification is coincident withhigh carbon ratios incoals of the overlying Dcs Moines series. If a fixed carbon ratio in excess of 62.5 is considered tobe thelimitingparameter for oilproduction, the studies by Fuller (1919) and Hendricks (1935) appear to condemn for oil production part of the frontal area adjacent to the Ouachita structural belt. (2) Because of the complexity of the highly faulted and strongly folded areas adjacent to the foldbelt front, conventional subsurface geologic and geophysical methods of exploration are of limited value. (3) Most of the drilling for prospects adjacent to the structural belt, and all of the drilling for prospects underlying thrust sheets, requires deep wells. Drillingof thick sections of steeply inclined beds of hard shale and quartziticsandstone presents many problems, such as excessive well deviation and use of numerous bits;well costs inthis area are high. (4) Statistical compilations such as those by Knebel and Rodriquez-Eraso (1956) and the classic study of Wei- rich (1953) suggest that the stable (shelf) side of a basin contains more oilthan themobile side. (5) Some geologists believe that the oil and gas found in Ellenburger and Arbuckle reservoirs had its source in Mississippian or Pennsylvanian beds of foreland facies, and that exploration is not justified unless these late Paleozoic "source beds" are in contact with the older Paleozoic carbonate rocks. These arguments make itclear whylarge sums of money have not been allotted to exploration for oil in rocks of foreland facies immediately adjacent to or underlying the Ouachita structural belt. Some of these arguments are still valid today, but others deserve re-examination. There is serious doubt that carbon ratios derived from coals of Desmoinesian age have any meaning when applied to the underlying sedimentary rocks of lower Paleozoic age. Most of the major Ouachita Mountains overthrusts (sole thrusts) in the frontal area follow closely along the bedding of incompetent shale which acted as a lubricant. Dynamic metamorphism duetothismovementisrestricted toarelatively narrow zone adjacent to the thrust plane. (See David Young (1957) for a discussion of the thrust zone at the base of the Cumberland block in the Appalachian area.) Underlying sediments of foreland facies should not be considered as metamorphosed simply because of superjacent thrust faulting. Secondary silica cementation of quartzose sandstones, such as those of the Simpson group ("Wilcox"),may be purely a sedimentary process not related to metamorphism. Porosities in Simpson sandstones encountered in deep wells in Bureau ofEconomic Geology, The University of Texas Coal and Atoka counties, Oklahoma, have been generally adequate in wells drilled close to the frontal zone of the Ouachita Mountains, and some production has been obtained. However, this is not an area of high carbon ratios, and oil production in these counties does not prove or disprove any lack of relationship between high carbon ratios inDcs Moines beds and silicified lower Paleozoic sandstones. It is con sidered probable, however, that deep Ordovician production (Simpson, Ellen- burger-Arbuckle) willbe obtained eventually from areas of high carbon ratios adjacent tothe frontalorogenic zone. High well costs and lack of satisfactory exploration methods are merely challenges to oil men, not insurmountable barriers. No one doubts that they can be overcome ifenough drilling is done. After a number of rank wildcat tests have provided a base of general stratigraphic and structural information, geophysical data interpreted by geologists experienced in the geology of folded and thrust-faulted mountains should provide a more scientific basis for prospecting. Statistical compilations of the production on the mobile and stable parts of a basin may be misleading. The mobile side of a basin is much more difficult to prospect than the stable side, and the drilling density on the stable side is usually much greater. Entrapment of oil and gas along an orogenic front is in no way unusual; many fields in different parts of the world produce from rocks involved in Appalachian or Alpine-type deformation. Condemnation of the vast area along the front of the Ouachita structural belt on the basis of the theory that oiland gas can only be found where Mississippian or Pennsylvanian source beds overlie directly the Ordovician carbonate rocks seems completely unwarranted to the writers. This theory is regarded as not proven, but even if it were correct it could not be used to condemn the frontal zone of the Ouachita belt because of the complex stratigraphic and structural conditions which obtain there. It can be reasonably expected that almost every possible source bed could be in contact with a possible reservoir bed at some place along the structural belt. Itis difficult, except in a very general way, to select parts of the Ouachita belt as more favorable for prospecting than others because of the lack of any significant amount of exploratory drilling. Studies of the belt indicate that the trace of the buried front is not a continuous straight line but is marked by salients, recesses, and allochthonous plates (PL 1). Each local area must be considered separately on its own merits. The segments of the belt which have been crushed against the Llano and Devils River buttresses do not appear to be favorable because of the severity of the deformation. Compared to this area, the frontal zone of the Ouachita Mountains and the adjacent McAlester basin structures appear to be excellent places for further exploratory drilling. Frontal zone structures in the Fort Worth, Kerr, and Val Verde basins and in the Sheffield channel likewise seem relatively promising. In Collin and Grayson counties of north Texas, in Bell County in central Texas, and in the northern part of the Marathon Basin in Brewster County, Texas, wells have penetrated large thicknesses of unmetamorphosed rocks of fore- land facies beneath overthrust Ouachita facies rocks. In prospecting Ordovician carbonate facies rocks (Arbuckle-Ellenburger) along the Ouachita front, three factors should be considered: (1) the change in carbonate lithology from foreland to deep trough, (2) the amount of structural displacement of the Ouachita facies rocks, and (3) post- Ordovician downwarping of the foreland section. Itis generally true that carbonate rocks on foreland shelves include permeable dolomites which make excellent reservoirs, whereas the carbonate rocks deposited in deep troughs are dense fine- grained unfossiliferous rocks without significant reservoir capacity. If Ouachita facies rocks have been thrust over shelf The Ouachita System facies carbonate rocks, oil prospects are good; there is a possibility, however, that wells drilled some distance back of the front may penetrate the Ouachita facies only to encounter dense fine-grained Ordovician carbonate rocks unsuitable for the accumulation of oiland gas. CONCLUSIONS Oil possibilities of rocks of foreland facies underlying or adjacent to the Ouachita structural belt are far superior to the oil possibilities of rocks of geosynclinal facies. These foreland rocks have produced tremendous quantities of oilinTexas and Oklahoma. They have been thoroughly explored in much of their normal area of deposition, and the opportunity for major "oil finds" lessens as more and more deep tests are drilled and the untested areas diminish. The widespread occurrence of these foreland rocks in and adjacentj acent to the Ouachita structural belt and the lack of adequate exploration to date make this area one of the largest remaining untested, possibly petroliferous, provinces in the southwestern United States. Bibliography Aberdeen, E. J. (1940) Radiolarian fauna of the Caballos formation: Jour. Paleont., vol. 14, pp. 127-239. Acevedo, F. C, and Marquez, B. C. (1952) Reconocimiento geologico de la parte norte y noreste del Estado de Chihuahua. [Private report for Petroleos Mexicanos.] Adams, J. E. (1954) Mid-Paleozoic paleography of central Texas: Shale Shaker, vol. 4, no. 6, pp. 4-5. ,Frenzel, H. N., et al. (1952) Marathon Basin, Brewster and Pecos counties, Trans-Pecos Texas: West Texas Geol. Soc, Guidebook, Spring Field Trip, May 23-24, 1952, 78 pp. , , Rhodes, M. L., and Johnson, D. P. (1951) Starved Pennsylvanian Midland basin: Bull. Amer. Assoc. Petrol. Geol., vol. 35, pp. 2600-2607. ,Newell, N. D., et al. (1949) The Permian rocks of the Trans-Pecos region:West Texas Geol. Soc, Guidebook, FieldTripNo. 4, Nov. 6-9, 1949, 94 pp. Adkins, W. S. (1923) Geology and mineral resources of McLennan County [Texas]:Univ. of Texas Bull.2340, 202 pp. — ,and Arick, M. B. (1930) Geology of Bell County, Texas: Univ. Texas Bull. 3016, 92 pp. Albritton, C. C. (1928) Stratigraphy and structure of the Malone Mountains, Texas: Bull. Geol. Soc. Amer., vol. 49, pp. 1747-1827. Aldrich, L. T., Wetherill, G. W., and Davis, G. L. (1957) Occurrence of 1350 million-yearold granitic rocks in western United States: Bull.Geol. Soc. Amer., vol. 68, pp. 655-656. Anonymous (1940) Well logs and field data of active oil areas: south-central Oklahoma: Oil and Gas Jour., vol. 39, no. 27, Nov. 14, pp. 122-123, map, logs. (1950 a) Reports by areas: Oil and Gas Jour., vol. 49, no. 13, Aug. 3, pp. 96-107. (1950b) Reports by areas: Oil and Gas Jour., vol. 49, no. 16, Aug. 24, pp. 204-217. (1951) Discovery and development data for 1950's new pools and new pays: Oil and Gas Jour., vol. 49, no. 38, Jan. 25, pp. 261 308. (1953a) Areal field reports: Oiland Gas Jour., vol. 51, no. 47, March 30, pp. 221 238. (1953b) Areal fieldreports: Oiland Gas Jour., vol. 51, no. 48, April6, p. 170. (1957) Slick-Urschel, Decie No. 1, in Glass Mountains: West Texas Geol. Soc, Guidebook, Fall Field Trip, Oct. 24-25, 1957, fig. 7, p. 13. Applin, P. L. (1951) Preliminary report on buried pre-Mesozoic rocks in Florida and adjacent states :U.S. Geol. Survey Circ. 91, 28 pp. (1957) in Reeside, J. 8., Jr., et al. (1957) Correlation of the Triassic formations of North America exclusive of Canada: Bull. Geol. Soc. Amer., vol. 68, pp. 1451-1514 (note 62, pp. 1486-1489). and Applin, E. R. (1947) Middle and early Upper Cretaceous rocks inAlabama, Georgia, and north Florida: U.S. Geol. Survey Oiland Gas. Inv.Chart 26, 3 sheets. Ardmore Geological Society (1956) Ouachita Mountains Field Conference, 72 pp., Ardmore, Oklahoma. Ashley, G. H. (1897) Geology of the Paleozoic area of Arkansas south of the novaculite region: Amer. Philos. Soc, Proc, vol. 36, pp. 217-318. Baker, C. L. (1921) Geologic studies in northeast Mexico. [Unpublished manuscript.] (1922) General geology of the Ca torce mining district: Trans. Amer. Inst. Mm. Met. Eng., vol.66, pp. 42-48. (1932) Erratics and arkoses in the Middle Pennsylvanian Haymond formation of the Marathon area, Trans-Pecos Texas: Jour. Geol., vol.40, pp. 577-603. (1935) Structural geology of Trans- Pecos Texas, in The geology of Texas, Vol.11, Structural and economic geology: Univ. Texas Bull. 3401 (Jan. 1, 1934),pp. 132-214. (1936) Historical geology of the Antillean-Caribbean region, etc., by Charles Schuchert, a review:Bull.Amer. Assoc. Petrol. Geol., vol. 20, pp. 496-508. ,and Bowman, W. F. (1917) Geologic exploration of the southeastern Front Range of Trans-Pecos Texas: Univ. Texas Bull.1753, pp. 61-172. Barrell,Joseph (1925)Thenature andenvironment of the Lower Cambrian sediments of the southern Appalachians: Amer. Jour. Sci., sth ser., vol. 9, pp. 1-20. Barnes, V.E. (1940) Pre-Cambrian of the Llano region with emphasis on tectonics and intrusives: Excursion 4, Geol. Soc. Amer. 53rd Ann.Meeting, pp. 44-55. (1948) Ouachita facies in central Texas: Univ. Texas, Bur. Econ. Geol. Rept. Inv.No. 2, 12 pp. (1959) Stratigraphy of the pre- Simpson Paleozoic subsurface rocks of Texas and Southeast New Mexico: Univ. Texas Pub. 5924, 836 pp. , Cloud, P. E., Jr., and Duncan, Helen (1953) Upper Ordovician of central Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 37, pp. 1030-1043. 1 ( and Warren, L. E. (1947) Devonian rocks of central Texas: Bull. Geol. Soc. Amer., vol. 58, pp. 125-140. Barton, D. C. (1936) Surface fracture system of south Texas, in Gulf Coast oil fields, A symposium, Amer. Assoc. Petrol. Geol., pp. 251 269. Barton, J. M. (1945) Pre-Permian axes of maximum deposition in west Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 29, pp. 1336-1348. Bates, T. F. (1947) Investigation of the micaceous minerals in slates: Amer. Mm., vol. 32, pp. 625-636. Bureau ofEconomic Geology, The University of Texas Beikman, H. M., and Drakoulis, Sophie (1958 a) Records of unsuccessful test wells drilled for oil and gas in Mississippi as of July1, 1956: U.S. Geol. Survey Bull. 1072-A, pp. 1-66. (1958b) Map of Mississippi showing oil and gas fields, unsuccessful test wells, saltdomes, and pipelines: U.S. Geol. Survey Oil and Gas Inv.Map OM-200. Berry, W. B. N. (1958) Depositional environment of the Ordovician succession inthe Marathon region, Texas: Jour. Sed. Petrology, vol. 28, pp. 389-405. (1960) Graptolite faunas of the Marathon region, west Texas :Univ. Texas Pub. 6005, 179 pp. ,and Neilson, H. M. (1958) Revision of Caballos novaculite in Marathon region, Texas :Bull.Amer. Assoc. Petrol. Geol., vol. 42, pp. 2254-2259. Billings, M. P. (I960) Diastrophism and mountain building: Bull.Geol. Soc. Amer., vol. 71, pp. 363-398. Bodenlos, A. J., et al. (1956) Estratigrafia del Cenozoico y del Mesozoico a lo largo de la Cer retera entre Reynosa, Tamps, y Mexico, D. F. Tectonica de la Sierra Madre Oriental. Vul canismo en el Valle de Mexico. Excursions A-14 y C-16, Congreso Geologico Inter. XX, 323 pp. Bose, Emil (1921) On the Permian of Coahuila, northern Mexico:Amer. Jour, of Sci., sth ser., vol. 1, pp. 187-194. (1923) Vestiges of an ancient continent innortheast Mexico: Amer. Jour. Sci., sth ser., vol. 6, pp. 127-136, 199-214, 310-337. Bokman, J. W. (1951) Petrology and genesis of the Stanley and Jackfork formations: Ph.D. Dissertation, Univ. Chicago. (1953) Lithologyand petrology ofthe Stanley and Jackfork formations: Jour. Geol., vol. 61, pp. 152-170. Borden, J. L. (1943) Developments in Oklahoma in 1942: Bull. Amer. Assoc. Petrol. Geol., vol. 27, pp. 790-805. Bowles, Edgar (1941) Well logs of Alabama: Alabama Geol. Survey Bull.50, 357 pp. Bradfield, H. H. (1957) The petroleum geologyof Grayson County, Texas, in The geology and geophysics of Cooke and Grayson counties, Texas, Dallas Geol. Soc. and Dallas Geophys. Soc, pp. 15-69. Bradley, W. F., and Weaver, C. E. (1956) A regularly interstratified chlorite-vermiculite clay mineral:Amer. Mm., vol. 41, pp. 497-504. Branner, G. C. (1929) Geologic map of Arkansas, Arkansas Geol. Survey. Scale, 1:500,000. (1932) Cinnabar insouthwestern Arkansas: Arkansas Geol. Survey Inf. Circ. 2, 51pp. Branner, J. C. (1896) Thickness of the Paleozoic sediments in Arkansas: Amer. Jour. Sci., 4th ser., vol.2,pp. 229-236. —— (1897) The former extension of the Appalachians across Mississippi, Louisiana, and Texas: Amer. Jour. Sci., 4th ser., vol. 4, pp. 357-371. (1909) Bibliography of the geology of Arkansas, in The slates of Arkansas, Arkansas Geol. Survey, pp. 97-164. Branson, C. C. (1956) Tentative correlation chart of Ouachita facies rocks with Arbuckle facies and with northeastern Oklahoma: Ardmore Geol. Soc, Guidebook to Ouachita Mountains Field Conf., p. 15. (1956 a) Pennsylvanian history of northeastern Oklahoma: Tulsa Geol. Soc. Digest, vol. 24, p. 83. (1959) Regional relationships of Ouachita Mississippian and Pennsylvanianrocks, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 118-121. Braunstein, Jules (1958a) Eastern Gulf Coast oiland gas geology:WorldOil,vol.146,no.7, June, pp. 133-139. (1958b) Habitat ofoilineastern Gulf Coast, in Habitat of oil, Amer. Assoc. Petrol. Geol., pp. 511-522. Bridge, Josiah, Barnes, V.E., and Cloud,P. E., Jr. (1947) Stratigraphy of the Upper Cambrian, Llano uplift, Texas: Bull. Geol. Soc. Amer., vol.58, pp. 109-124. ,and Berdan, J. M. (1951) Preliminary correlation of the Paleozoic rocks from test wells in Florida and adjacent parts of Georgia and Alabama: U. S. Geol. Survey Press Release, 8 pp. , (1952) Idem. Florida Geol. Survey Guidebook, Assoc. Amer. State Geol. 44th Ann. Meeting Field Trip, pp. 29-38. Bridges, L. W., and DeFord, R. K. (1961) Pre- Carboniferous Paleozoic rocks in central Chihuahua, Mexico: Bull. Amer. Assoc. Petrol. Geol., vol. 45, pp. 98-104. Bucher, W. H. (1955) Deformation in orogenicbelts, inCrust of the earth: Geol. Soc. Amer. Spec. Paper 62, pp. 343-368. Burwash, R. A. (1957) Reconnaissance of subsurface Precambrian of Alberta: Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 70-103. Butts, Charles (1926) The Paleozoic rocks, in Geology of Alabama: Alabama Geol. Survey Spec. Rept. 14,pp. 41-230. Cady, W. M. (1960) Stratigraphic and geotectonic relationships in northern Vermont and southern Quebec: Bull. Geol. Soc. Amer., vol. 71, pp. 531-576. Calvert, W. R. (1928) Geologic features of Val Verde County, Texas, and adjacent areas: Oil and Gas Jour., vol. 26, no. 36, Jan. 26, pp. 81 85. Cannon, R. L., and Cannon, Joe (1932) Structural and stratigraphic development of south Permian basin, west Texas: Bull.Amer. Assoc. Petrol. Geol., vol.16,pp. 189-204. Caplan, W. M. (1954) Subsurface geology and related oiland gas possibilities of northeastern Arkansas: Arkansas Resources and Devel. Comm., Div. Geology Bull. 20, 124 pp. Carney, Frank (1935) Glacial beds of Pennsylvanian age in Texas (abst.) :Geol. Soc. Amer., Proc. 1934, p. 70. Chandler, C. E. (1957) A petrographic study of sedimentary rocks of Peregrina Canyon, Tamaulipas, Mexico: M. S. Thesis, Louisiana State Univ., 62 pp. Cheney, M. G. (1929a) History of the Carboniferous sediments inthe Mid-Continent oilfield: The Ouachita System Bull. Amer. Assoc. Petrol. Geol., vol. 13, pp. 557-594. (1929b) Stratigraphic and structural studies in north-central Texas: Univ. Texas Bull.2913, 29 pp. ¦ ,and Goss, L. F. (1952) Tectonics of central Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 36, pp. 2237-2265. Christner, D. D., and Wheeler, O. C. (1918) The geology of Terrell County [Texas]:Univ. Texas Bull.1819, 32 pp. Cline, L. M. (i956a) Mississippian-Pennsylvanian stratigraphy of central Ouachita Mountains, Oklahoma: Ardmore Geol. Soc. Field Conference, Southeastern Oklahoma, Guidebook, pp. 20-24. (1956b) Some stratigraphic studies of the Mississippian and Pennsylvanian rocks of the Ouachita Mountains, Oklahoma: Tulsa Geol. Soc. Digest, vol. 24, pp. 100-106. (1959) Black-shale flysch facies of the Ouachita Mountains, southeastern Oklahoma (abst.) :Bull. Geol. Soc. Amer., vol. 70, p. 1582. (1960) Late Paleozoic rocks of the Ouachita Mountains: Oklahoma Geol. Survey Bull.85, 113 pp. ,and Moretti, Frank (1956) Two measured sections of Jackfork group in southeastern Oklahoma: Oklahoma Geol. Survey Circ. No. 41, 20 pp. ,and Shelburne, O. B. (1959) Late Mississippian —Early Pennsylvanian stratigraphy of the Ouachita Mountains, Oklahoma, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 175-208. Cloos, Ernest (1954) Appalachian profile in Maryland (abst.):Bull.Geol. Soc. Amer., vol. 65, p. 1258. Cloud, P. E., Jr., and Barnes, V. E. (1957) Early Ordovician sea in central Texas, in Paleoecology: Geol. Soc. Amer. Memoir 67, pp. 163-214. , , V. E. Haas, W. H. (1957) Devonian-Mississippian transition in central Texas: Bull. Geol. Soc. Amer., vol. 68, pp. 807-814. Comstock, T. B. (1888) Report upon the geology of western central Arkansas, with especial reference to gold and silver: Arkansas Geol. Survey, Ann. Rept. for 1888, Vol. I,pp. 1-299. Cooper, C. L. (1931 ) Conodonts from the Arkansas novaculite, Woodford formation, Ohio shale, and Sunbury shale: Jour. Paleont., vol. 5, pp. 143-151. (1935) Conodonts from the upper and middle Arkansas novaculite, Mississippian, at Caddo Gap, Arkansas: Jour. Paleont., vol. 9, pp. 307-315. Cram, I.H. (1948) Cumberland oilfield, Bryan and Marshall counties, Oklahoma, in Structure of typical American oilfields, Vol. 111, Amer. Assoc. Petrol. Geol., pp. 341-358. Crickmay, G. W. (1952) Geology of the crystalline rocks of Georgia: Georgia Geol. Survey Bull. 58, 56 pp. Croneis, Carey (1930) Geology of the Arkansas Paleozoic area, with special reference to oil and gas possibilities: Arkansas Geol. Survey Bull.3, 457 pp. ,and Billings, M. P. (1929) New areas of alkaline igneous rocks in central Arkansas: Jour. Geol., vol. 37, pp. 542-561. Cropp, F. W. (1960) Pennsylvanian spore floras from the Warrior basin, Mississippi and Alabama: Jour. Paleont., vol. 34, pp. 359-367. Cross, Whitman (1900) Petrographic descriptions of igneous rocks, in. Description of the Uvalde quadrangle: U.S. Geol. Survey Geol. Atlas,UvaldeFolio (No.64),7pp. Culbertson, Tom, et al. (1957) Developments in west Texas and southeastern New Mexico in 1956: Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 1117-1134. Dake, C. L. (1921) The problem of the St. Peter sandstone: Univ. Missouri, School Mines and Met.Bull.,vol.6,pp. 1-225. ,and Bridge, Josiah (1932) Buried and resurrected hills of central Ozarks: Bull. Amer. Assoc. Petrol. Geol., vol. 16, pp. 629 652. Dapples, E. C, Krumbein, W. C, and Sloss, L. L. (1953) Petrographic and lithologic attributes of sandstones: Jour. Geol., vol. 61, pp. 291-316. Darby, William (1818) Emigrants' guide to the western and southwestern states and territories, Kirkand Merceine, 311 pp., New York. Darton, N. H., Stephenson, L. W., and Gardner, Julia A. (1937) Geologic map of Texas, U.S. Geol. Survey. Scale, 1:500,000. Davis, C. E. (1955) Developments in north Texas in 1954: Bull. Amer. Assoc. Petrol. Geol., vol. 39, pp. 930-940. (1956) Developments in north Texas in 1955: Bull. Amer. Assoc. Petrol. Geol., vol. 40, pp. 1192-1202. Davis, E. F. (1918) The Franciscan sandstone: California Univ., Dept. Geol. Sci. Bull., vol. 11, pp. 1-44. Decker, C. E. (1936) Some tentative correlations on the basis of graptolites of Oklahoma and Arkansas: Bull.Amer. Assoc. Petrol. Geol., vol.20, pp. 301-311. (1959) Correlation of lower Paleozoic formations of the Arbuckle and Ouachita areas as indicated by graptolite zones, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 92-96. Decker, LaVerne (1927) Structural trends in southern Oklahoma: Oklahoma Geol. Survey Bull.40-P, 13 pp. De Cserna, Zoltan (1956) Tectonica de la Sierra Madre Oriental de Mexico entre Torreon y Monterrey: Congreso Geologico Inter. XX, 87 pp. ¦ , and Diaz G., Teodoro (1956) Estratigraffa Mesozoica y tectonica de la Sierra Chihuahua; Permico de Placer de Guadalupe, Chih.; geohidrologfa de la Region Lagunera; estratigraffa Mesozoica y tectonica de la Sierra Madre Oriental entre Mapimi, Dgo. yMonterrey, N.L.:Excursion A-13, Congreso Geologico Inter. XX,120 pp. Bureau ofEconomic Geology, The University of Texas DeFord, R. K. (1951) Trans-Pecos province, west Texas and southeastern New Mexico: Bull. Amer. Assoc. Petrol. Geol., vol. 35, pp. 347-352. Diaz G., Teodoro (1956) Generalidades sobre la geologfa del Norte Mexico, in Estratigrafia Mesozoica y tectonica de la Sierra de Chihua hua, etc.: Excursion A-13, Congreso Geologico Inter. XX,pp. 9-14. Dixon, E. E. L. (1931) The Ouachita basin of Oklahoma vis-a-vis the Craven Lowlands of Yorkshire: Geol. Mag., vol. 68, no. 806, pp. 337-344. Dott, R. H. (1927) Notes on Pennsylvanian paleogeography, withspecial reference tosouthcentral Oklahoma: Oklahoma Geol. Survey Bull.40-J, 22 pp. (1934) Overthrusting inthe Arbuckle Mountains: Bull. Amer. Assoc. Petrol. Geol., vol. 18, pp. 567-602. — ,and Murray, G.E., cd. (1954) Geologic cross-section of Paleozoic rocks, central Mississippi to northern Michigan, Amer. Assoc. Petrol. Geol., 32 pp., 5 sheets. Drake, N. F. (1897) A geological reconnaissance of the coal fieldsof the Indian Territory:Amer. Philos. Soc, Proc, vol. 36, pp. 361-372. Dumble, E. T. (1920) The geology of east Texas: Univ. Texas Bull.1869 (Dec. 10, 1918),pp. 11 13. Eardley, A. J. (1951) Structural geology of North America, Harper & Bros., 624 pp., New York. (1954) Tectonic relations of North and South America: Bull.Amer. Assoc. Petrol. Geol., vol.38, pp. 707-773. ,and White, M.G. (1947) Flysch and molasse: Bull. Geol. Soc. Amer., vol. 38, pp. 979-989. Eckelmann, W. R., and Kulp, J. L. (1957) Uranium-lead method of age determination; Part 2, North American localities: Bull. Geol. Soc. Amer., vol. 68, pp. 1117-1140. Eifler, G. K. (1943) Geology of the Santiago Peak quadrangle, Texas: Bull. Geol. Soc. Amer., vol. 54, pp. 1613-1644. Elias, M. K. (1959) Some Mississippian conodonts from the Ouachita Mountains, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 141-165. Ellison, S. P., Jr. (1941) Revision of the Pennsylvanian conodonts: Jour. Paleont., vol. 15, pp. 107-143. (1946) Conodonts as Paleozoic guide fossils: Bull. Amer. Assoc. Petrol. Geol., vol. 30, pp. 93-110. ,and Graves, R.W., Jr. (1941) Lower Pennsylvanian (Dimple limestone) conodonts of the Marathon region, Texas :Univ.Missouri, School Mines and Met. Bull., Tech. Ser., vol. 14, 21pp. Eskola, Pentti (1932) Conditions during the earliest geological times: Annales Academiae Scientiarum Fennicae, Ser. A., Tom. XXXVI, pp. 24-28. Everett, Rizer (1953) Certain stratigraphic problems in the Warrior basin: Trans. Gulf Coast Assoc. Geol. Soc, Vol.111, pp. 31-43. Ewing, Maurice, Worzel, J. L., Ericson, D. 8., and Heezen, B. C. (1955) Geophysical and geological investigations in the Gulfof Mexico, pt. 1: Geophysics, vol. 20, pp. 1-18. Fan, P. H., and Shaw, D. B. (1956) The Tesnus formation of Trans-Pecos Texas: Jour. Sed. Petrology, vol. 26, pp. 258-267. Fisher, D. J. (1936) Carbon ratios north of the Ouachitas: Bull. Amer. Assoc. Petrol. Geol., vol.20, pp. 102-105. Flawn, P. T. (1953) Petrographic classification of argillaceous, sedimentary, and low-grade metamorphic rocks in subsurface: Bull. Amer. Assoc. Petrol. Geol., vol. 37, pp. 560-565. ¦ (1956) Basement rocks of Texas and southeast New Mexico: Univ. Texas Pub. 5605, 261 pp. (1958) Genesis of Haymond boulder beds: Bull. Amer. Assoc. Petrol. Geol., vol. 42, pp. 1734-1735. (1959a) Ouachita belt and Arbuckle element: Interpretation: Bull. Amer. Assoc. Petrol. Geol., vol. 43, pp. 2012-2015. (1959b) The Ouachita structural belt, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 20-29. (1959c) Devils River uplift, in Geology of the ValVerde basin:West Texas Geol. Soc, Field Trip Guidebook, Nov. 5-8, 1959, pp. 74-78. ,and Diaz G., Teodoro (1959) Problems of Paleozoic tectonics in north-central and northeastern Mexico:Bull.Amer. Assoc. Petrol. Geol., vol. 43, pp. 224-230. ,and Maxwell, R. A. (1958) Metamorphic rocks in the Sierra del Carmen, Coahuila, Mexico:Bull. Amer. Assoc. Petrol. Geol., vol. 42, pp. 2245-2249. Fohs, F. J., and Robinson, H. M. (1923) Structural and stratigraphic data of northeast Texas petroleum area: Econ. Geol., vol. 18, pp. 724 727. Folk,R.L.(1954) The distinctionbetween grain size and mineral composition in sedimentary- rock nomenclature: Jour. Geol., vol. 62, pp. 344-359. (1956) The role of texture and composition in sandstone classification: Jour. Sed. Petrology, vol.26, pp. 166-171. Fowler, Philip (1957) South-central Texas' faults and folds: Oil and Gas Jour., vol. 55, no. 2, Jan. 14, pp. 162-171. Frascogna, X.M., cd. (1957) Mesozoic-Paleozoic producing areas of Mississippi and Alabama, vol. 1, Mississippi Geol. Soc, 139 pp. Frenzel, H. N. (1957) Introduction, in Wolf- camp of the Glass Mountains and the Permian basin: Field Conference Guidebook, S.E.P.M. Permian Basin Section, Spring 1957, pp. 1-3. Fuller, M.L. (1919) Relation of oil to carbon ratios of Pennsylvanian coals in north Texas: Econ. Geol., vol. 14, pp. 536-542. Galley, J. E. (1957) Maps of Wolfcamp series, in Wolfcamp of the Glass Mountains and the Permian basin: Field Conference Guidebook, S.E.P.M. Permian Basin Section, Spring 1957, pp. 34-38. (1958) Oil and geology in the Permian basin of Texas and New Mexico, in Hab The Ouachita System itat of oil, Amer. Assoc. Petrol. Geol., pp. 395 446. Gastil, Gordon (1960) The distribution of mineral dates inspace and time:Amer. Jour. Sci., vol. 258, pp. 1-35. Gatling, J. L. (1956) Developments in east Texas in 1955:Bull. Amer. Assoc. Petrol. Geol., vol. 40, pp. 1230-1238. Getzendaner, F. M. (1931) Mineral resources of Uvalde, Zavala, and Maverick counties: Univ. Texas, Bur. Econ. Geol., pp. 93-140. (1943) Problems of the pre-Trinity deposits in south Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 27, pp. 1228-1244. Gilluly, James (1955) Geologic contrasts be tween continents and ocean basins, in Poldervaart, Arie,cd., Crust of the earth: Geol. Soc. Amer. Special Paper 62, pp. 7-18. Girty, G. H. (1905) The relations of some Carboniferous faunas: Proc. Washington Acad. Sci., vol.7,p. 10. (1909) The fauna of the Caney shale of Oklahoma: U. S. Geol. Survey Bull. 377, 106 pp. (1911) Fauna of the Moorefield shale of Arkansas: U. S. Geol. Survey Bull. 439, 148 pp. (1926) A new area of Carboniferous rocks in Mexico: Science, n.s., vol. 63, pp. 286-287. Goldich, S. S., et al. (1948) Green Valley- Paradise Valley field trip: West Texas Geol. Soc, Guidebook, Fall Field Trip, October 2931,1948, 67 pp. Goldstein, August, Jr. (1957) Minority report on the Ouachita fold-belt, in Glass Mountains: West Texas Geol. Soc, Guidebook, Fall Field Trip,October 25-26, 1957, pp. 26-27. (1959 a) Petrography of Paleozoic sandstones from the Ouachita Mountains of Oklahoma and Arkansas, inThe geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 97 116. ¦ (1959b) Cherts and novaculites of Ouachita facies, in Silica in Sediments Symposium: Soc. Econ. Paleont. and Mm., Special Pub. 7, pp. 135-149. ,and Flawn, P. T. (1958) Oil and gas possibilities of Ouachita structural belt in Texas and Oklahoma: Bull. Amer. Assoc. Petrol. Geol.,vol.42,pp.876-881. ,and Hendricks, T. A. (1953) Siliceous sediments of Ouachita facies in Oklahoma: Bull.Geol. Soc. Amer., vol. 64, pp. 421 441. ,and Reno, D.H. (1952) Petrography and metamorphism of sediments of Ouachita facies: Bull. Amer. Assoc. Petrol. Geol., vol. 36, pp. 2266-2274. Gould, C. N. (1925) Index to the stratigraphy of Oklahoma: Oklahoma Geol. Survey Bull. 35, 115 pp. (1929) Johns Valley boulders: Okla homa Acad. Sci., Proc, vol. 8, pp. 144-146 (Univ.Oklahoma Bull.n.s. 410). ,and Wilson, R. A. (1927) The upper Paleozoic rocks of Oklahoma: Oklahoma Geol. Survey Bull.41, pp. 5-21. Graves, R. W., Jr. (1952) Conodonts from the Caballos novaculite, in Marathon Basin, Brewster and Pecos counties, Trans-Pecos Guidebook, Texas: West Texas Geol. Soc, Spring FieldTrip,May 23-24, 1952, pp. 65-66. (1954) Geology of Hood Spring quadrangle, Brewster County, Texas: Univ. Texas, Bur. Econ. Geol. Rept. Inv. No. 21, 51 pp. Greene-Kelly, R. G. H. (1955) Dehydration of the montmorillonite minerals: Mm. Mag., vol. 30, pp. 604-615. Greenwood, Robert, and Lynch, V.M. (1959) Geology and gravimetry of the Mustang Hill laccolith, Uvalde County, Texas: Bull. Geol. Soc. Amer., vol.70, pp. 807-828. Griffin,R. H. (1951) Structure and petrography of the Hillabee sill and associated metamorphics of Alabama: Alabama Geol. Survey Bull. 63, 74 pp. Griswold, L. S. (1892) Whetstones and the novaculites of Arkansas: Arkansas Geol. Survey, Ann. Rept. for 1890, vol. 3, 443 pp. Grout, F. F. (1932) Petrography and petrology, McGraw-Hill Book Company, Inc., 503 pp., NewYorkand London. Gruenfelder, Marc, and Silver, L. T. (1.958) Radioactive age dating and its petrologic implications for some Georgia granites (abst.) : Bull.Geol. Soc. Amer., vol. 69, p. 1574. Haarmann, Erich (1913) Geologische Streifziige in Coahuila: Zeitschr. Deutsche Geol. Gesell., vol.65, pp. 19-47. Hall, W. E. (1956) Marathon folded belt in Big Bend area of Texas: Bull.Amer. Assoc. Petrol. Geol., vol.40, pp. 2247-2255. (1957) Genesis of Haymond boulder beds, Marathon Basin, Bull.Amer. west Texas: Assoc. Petrol. Geol., vol. 41, pp. 1633-1637. Ham, W. E. (1955) Regional stratigraphy and structure of the Arbuckle Mountain region: Ardmore Geol. Soc, Guidebook, Spring Field Trip,1955, pp. 28-35. (1956 a) Asphaltite in the Ouachita Mountains of southeastern Oklahoma: Oklahoma Geol. Survey Mm. Rept. 30, 12 pp. (1956b) Structural geology of the Arbuckle Mountain region (abst.): Bull. Amer. Assoc. Petrol. Geol., vol. 40, pp. 425 426. (1959) Correlation of pre-Stanley strata in the Arbuckle-Ouachita Mountain region, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 71-86. Hamilton, W. B. (1956) Precambrian rocks of Wichita and Arbuckle Mountains, Oklahoma: Bull.Geol. Soc. Amer., vol. 67, pp. 1319-1330. Harlton, B.H. (1933) Micropaleontology of the Pennsylvanian Johns Valley shale of the Ouachita Mountains, Oklahoma, and its relationship to the Mississippian Caney shale: Jour. Paleont., vol. 7, pp. 3-29. (1934) Carboniferous stratigraphy of the Ouachitas with special study of the Bendian: Bull.Amer. Assoc. Petrol. Geol., vol. 18, pp. 1018-1049. (1938) Stratigraphy of the Bendian of the Oklahoma salient of the Ouachita Moun Bureau ofEconomic Geology, The University of Texas tains:Bull. Amer. Assoc. Petrol. Geol., vol. 22, pp. 852-914. (1947) The siliceous shale members of the Stanley-Jackfork deposits in the Ouachita Mountains, Oklahoma, withnotes on the Johns Valley shale: Tulsa Geol. Soc, Field Conference, May 8-10, 1947, Western part of the Ouachita Mountains in Oklahoma, Guide book, pp. 41-43. (1953) Ouachita chert facies, southeastern Oklahoma: Bull. Amer. Assoc. Petrol. Geol., vol. 37, pp. 778-796. — (1959) Age classification of the upper Pushmataha series in the Ouachita Mountains, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 130-139. Hass, W. H. (1950) Age of lower part of Stanley shale: Bull. Amer. Assoc. Petrol. Geol., vol. 34, pp. 1578-1584. (1951) Age of the Arkansas novacu- lite:Bull. Amer. Assoc. Petrol. Geol., vol. 35, pp. 2526-2541. (1956) Conodonts from the Arkansas novaculite, Stanley shale, and Jackfork sandstone: Ardmore Geol. Soc. Field Conference, Southeastern Oklahoma, Guidebook, pp. 25-33. Hazzard, R.T.,Maxwell,R. A.,and Lonsdale, J. T. (1958) Paleozoic rock exposures, Persimmon Gap-Dog Canyon areas, Brewster County, Texas: Bull. Amer. Assoc. Petrol. Geol., vol.42, p. 887. — •, Spooner, W. C, and Blanpied, B. W. (1947) Notes on the stratigraphy of formations which underlie the Smackover limestone in south Arkansas, northeast Texas, and north Louisiana, in 1945 Reference report on certain oil and gas fields of north Louisiana, south Arkansas, Mississippi, and Alabama, vol. 2, Shreveport Geol. Soc, pp. 483-503. Heim, Arnold (1940) The Front Ranges of the Sierra Madre Oriental, Mexico, between Ciudad Victoria and Tamazunchale: Eclogae Geol.Helvetiae, vol.33, pp. 313-352. Henbest, L.G. (1936) Radiolaria in the Arkansas novaculite, Caballos novaculite, and Big- fork chert: Jour. Paleont., vol. 10, pp. 76-78. Hendricks, T. A. (1932) Classification of the coals of the Arkansas-Oklahoma field: Trans. Amer. Inst. Mm. Met. Eng., vol. 101, Coal Division, pp. 117-124. -— -— (1934) Some features of stratigraphy in the Arkansas-Oklahoma coal basin (abst.), with discussion: Tulsa Geol. Soc. Digest, vol. 6, pp. 24-27. ¦ (1935) Carbon ratios in part of Arkansas-Oklahoma coal field: Bull. Amer. Assoc. Petrol. Geol., vol.19, pp. 937-947. (1936) Stratigraphy of the pre- Carboniferous rocks of Black Knob Ridge, Oklahoma (abst.), with discussion: Tulsa Geol. Soc. Digest, vol. 8, pp. 50-55. (1937a) Pennsylvania sedimentation in Arkansas coal field: Bull. Amer. Assoc. Petrol. Geol., vol. 21, pp. 1403-1421. (1937b) Geology and fuel resources of the southern part of the Oklahoma coal field, Pt. 1, The McAlester district, Pittsburg, Atoka, and Latimer counties:U. S. Geol. Survey Bull. 874-A, iv,90 pp. (1939a) Geology and fuel resources of the southern part of the Oklahoma coal field, Pt. 4, The Howe-Wilburton district, Latimer and Le Flore counties :U. S. Geol. Survey Bull. 874-D, pp. iv, 255-300. — (1939b) Geologic interpretations of gravity anomalies inAtoka and Bryan counties, Oklahoma (abst.) :Oil Weekly, vol. 93, no. 3, March 27, p. 72. (1943) Geology of the Black Knob Ridge area, Atoka County, Oklahoma: U. S. Geol. Survey Oiland Gas Inv.Prelim. Map1 (text). (1959) Structure of the frontal belt of the Ouachita Mountains, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 44-56. ,and Averitt,Paul (1947) Measured section of a middle Stanley siliceous shale: Tulsa Geol. Soc, Field Conference, May 8-10, 1947, Western part of the Ouachita Mountains in Oklahoma, Guidebook, pp. 10-38. ,Curvin, B. A., and Goldstein, August, Jr. (1950) Geology of the McAlester- Arkansas Valley basin: Amer. Assoc. Petrol. Geol., Mid-Continent Regional Meeting, oral presentation, 11 pp. [Unpublished.] ,Dane, C. H., and Knechtel, M.M. (1936) Stratigraphy of Arkansas-Oklahoma coal basin: Bull. Amer. Assoc. Petrol. Geol., vol. 20, pp. 1342-1356. ,Gardner, L. S., Knechtel, M. M., and Averitt, Paul (1947) Geology of the western part of the Ouachita Mountains of Oklahoma: U. S. Geol. Survey Oil and Gas Inv. Prelim. Map 66, 3 sheets (with text). ,and Goldstein, August, Jr. (1953) Siliceous sediments of Ouachita facies in Oklahoma: Bull.Geol. Soc. Amer., vol.64, pp. 421 442. , Knechtel, M. M., and Bridge, Josiah (1937) Geology of Black Knob Ridge, Oklahoma (with discussion) :Bull. Amer. Assoc. Petrol. Geol., vol. 21, pp. 1-29. ,and Parks, Bryan (1937) Geology and mineral resources of the western part of the Arkansas coal field: U. S. Geol. Survey Bull.947-E, pp. iv.189-224. 1 (1950) Geology of the Fort Smith district, Arkansas: U. S. Geol. Survey Prof. Paper 221-E, 94 pp. ,and Read, C. B. (1934) Correlations of Pennsylvanian strata in Arkansas and Oklahoma coal fields: Bull. Amer. Assoc Petrol. Geol., vol.18, pp. 1050-1058. Herrin, Eugene (1959) Geology of the Solitario area, Trans-Pecos Texas. [Unpublished manuscript.] Hess, F. L. (1908) The Arkansas antimony deposits: U. S. Geol. Survey Bull. 340, pp. 241252 Hewett, D. F., and Crickmay, G. W. (1937) The warm springs of Georgia; their geologic rela tions and origin: U. S. Geol. Survey Water-Supply Paper 819, 40 pp. Hill,R. T. (1890) Pilot Knob: A marine Cretaceous volcano: Amer. Geol., vol. 6, pp. 286 292. The Ouachita System ¦ (1891) Notes on a reconnaissance of the Ouachita Mountain system in Indian Ter ritory: Amer. Jour. Sci., 3d ser., vol. 42, pp. 111-124. (1900) Physical geography of the Texas region: U. S. Geol. Survey Topog. Atlas, Folio (No.3), 12pp. (1901) Geography and geology of Black and Grand Prairies: U. S. Geol. Survey 21st Ann.Rept., pt.7, 666 pp. and Vaughan, T. W. (1898) Geology of the Edwards Plateau and Rio Grande Plain: U. S. Geol. Survey 18th Ann. Rept., pt. 2, pp. 195-322. — Hills,J. M. (1942) Rhythm of Permian seas A paleogeographic study: Bull. Amer. Assoc. Petrol. Geol., vol. 26,pp. 217-255. — ,Jones, T. S., and King, R.E. (1941) Possible future oil provinces of west Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 25, pp. 1527-1538. Hoffmeister, W. S., and Malloy, R. E. (1955) Geologic range of Paleozoic plant spores in North America: Micropaleontology, vol. 1, pp. 9-27. ,and Staplin, F. L. (1954) Pennsylvanian age of Morehouse formation of northeastern Louisiana: Bull. Amer. Assoc. Petrol. Geol., vol.38, pp. 158-161. Hollingsworth, R. V. (1933) Paleontological notes concerning Savanna formation inMcAles ter quadrangle, Oklahoma (abst.) :Pan-Am. Geol., vol. 59, p. 237. (1934) Union Valley sandstone (abst.) :Geol. Soc. Amer., Proc. 1933, pp. 364 365. Honess, C. W. (1920) Structural features of the southern Ouachita Mountains, Oklahoma (abst.), with discussion by H. D. Miser: Bull. Geol. Soc. Amer., vol. 31, pp. 121-122. (1921a) The Stanley shale of Oklahoma: Amer. Jour. Sci., sth ser., vol. 1, pp. 63-80. (1921b) Field work in the Ouachita Mountains: Bull. Amer. Assoc. Petrol. Geol., vol.5,p. 679. (1923) Geology of the southern Ouachita Mountains of Oklahoma: Oklahoma Geol. Survey Bull. 32, Pt. I,278 pp., Pt. 11, 76 pp. (1924) Geology of southern Le Flore and northwestern McCurtain counties, Oklahoma: Bureau of Geology, Norman, Oklahoma, Circ. 3, 23 pp. (1927) Oil and gas in Oklahoma: Geology of Atoka, Pushmataha, McCurtain, Bryan, and Choctaw counties, Oklahoma: Oklahoma Geol. Survey Bull. 40-R, 32 pp. Hoot, Carl (1951) Good drilling-activity potential at Sandusky, Grayson County, Texas: Oiland Gas Jour., vol. 49, no. 40, Feb. 8, pp. 106-107. [Table giving well, survey, elevation, formation tops, producing formation and depth, barrels, etc., of eleven wells.] (1951) Progress report: Sanduskyfields, Grayson County, north Texas: Oil and Gas Jour., vol. 50, no. 29, Nov. 22, pp. 62, 8687, map. Hopkins, O. 8., Powers, Sidney, and Robinson, H.M.(1923) The structure ofthe Madill-Denison area, Oklahoma and Texas, withnotes on oil and gas development: U. S. Geol. Survey Bull.736, p. 21, pi.5. Howell, J. V. (1947) Glossary of structural terms especially applicable to Ouachita [Mts. Oklahoma] type of folding: Tulsa Geol. Soc, Field Conference, May 8-10, 1947, Western part of the Ouachita Mountains in Oklahoma, Guidebook, pp. 52-53. ,and Lyons, P. L. (1959) Oiland gas possibilities of the Ouachita province, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 57-61. Huffman, G. G. (1958) Geology of the flanks of the Ozark uplift: Oklahoma Geol. Survey Bull. 77, 28 pp. Hull, J. P. D., Jr. (1957 a) Humble Oil and Refining Co. No. 1 N. D. Blackstone, in Notes on well sections, in Wolfcamp of the Glass Mountains and the Permian Basin: Field Conference Guidebook, S.E.P.M. Permian Basin Section, April26-27, 1957, p. 88. (1957b) Slick-Urschel OilCo. No. 1 Mary Decie-Sinclair, in Notes on well sections, in Wolfcamp of the Glass Mountains and the Permian Basin: Field Conference Guidebook, S.E.P.M. Permian Basin Section, April 2627,1957, pp. 96-98. Humphrey, W. E. (1955) Permian glaciation in northern Mexico?: Bull.Geol. Soc. Amer., vol. 66, pp. 1319-1324. , and Diaz, G., Teodoro (1953) A.M.G.P. Primera Convencion, Mexico, D. F., Febrero 9 al 15. Hurley, P. M., Fairbairn, H. W., and Pinson, W. H., Jr. (1958) Intrusive and metamorphic rock ages inMaine and surrounding areas: Bull. Geol. Soc. Amer., vol. 69, p. 1591. Hutchinson, L. L. (1911) Preliminary report on the rock asphalt, asphaltite, petroleum, and natural gas inOklahoma: Oklahoma Geol. Survey Bull.2, 256 pp. Imlay, R. W. (1936) Evolution of the Coahuila Peninsula, Pt. IV, Geology of the western part of the Sierra de Parras: Bull.Geol. Soc. Amer., vol. 47,pp. 1091-1152. (1940a) Lower Cretaceous and Jurassic formations of southern Arkansas and their oil and gas possibilities: Arkansas Geol. Survey Inf.Circ. 12, 64 pp. (1940b) Neocomian faunas of northern Mexico: Bull. Geol. Soc. Amer., vol. 51, pp. 117-190. (1943) Jurassic formations of Gulf region: Bull. Amer. Assoc. Petrol. Geol., vol. 27, pp. 1407-1533. (1944 ) Cretaceous formations of Central America and Mexico: Bull. Amer. Assoc. Petrol. Geol., vol. 28, pp. 1077-1195. ,and Williams, J. S. (1942) Late Paleozoic age ofMorehouse formation ofnortheastern Louisiana: Bull. Amer. Assoc. Petrol. Geol., vol. 26, pp. 1672-1673. James, Problems H. L. (1960) of stratigraphy and correlation of Precambrian rocks withparticular reference to the Lake Superior region: Amer. Jour. Sci., vol. 258A, pp. 104-114. Bureau ofEconomic Geology, The University of Texas Johnson, R.H., Jr. (1954) Geology of the Medicine Springs area, Pushmataha County, Oklahoma: M. S. Thesis, Univ. Oklahoma. Jones, W.B.(1960) Warriorbasin;prospects are bright, exploration needed:WorldOil,vol.150, pp. 89-91. Jordan, Louise (1958) Petroleum and natural gas, in Fifty years' progress, semi-centennial report of the Director to the Governor of the State of Oklahoma, July 25, 1908 to July 24, 1958, Oklahoma Geol. Survey, pp. 27-61. (1959) Arkoma basin: Oklahoma Geol. Survey Geology Notes, vol. 19, pp. 235 236. Geological Society (1931) Guidebook, Kansas Fifth Annual Field Conference (Oklahoma-Arkansas)^? pp. Kay, G. M.(1951a) North American geosynclines and continental origin: Oiland Gas Jour., vol. 49, no. 51, April26, p. 124. Kay, G. M. (1951b) North American geosynclines: Geol. Soc. Amer. Memoir 48, 143 pp. Kellum, L. B. (1936) Evolution of the Coahuila Peninsula, Pt. 111, Geology of the mountains west of the Laguna district: Bull. Geol. Soc. Amer., vol.47, pp. 1039-1090. (1937) The geology and biology of the San Carlos Mountains, Tamaulipas, Mexico: Univ.Michigan Studies, Sci. Ser., vol. 12, 341 pp. ,Imlay, R. W., and Kane, W. G. (1936) Evolution of the Coahuila Peninsula, Pt. I, Relation of structure, stratigraphy, and igneous activity to an early continental margin: Bull. Geol. Soc. Amer., vol. 47, pp. 9691009. Kelly, W. A. (1936) Evolution of the Coahuila Peninsula, Pt. 11, Geology of the mountains bordering the valleys of Acatita and Las Delicias: Bull.Geol.Soc. Amer.,vol.47,pp. 1009 1038. Kemp, J. F. (1890) Notes on a nepheline basalt from Pilot Knob, Texas: Amer. Geol., vol. 6, pp. 292-294. (1891) The basic dikes occurring outside of the syenite areas of Arkansas, in The igneous rocks of Arkansas: Arkansas Geol. Survey, Ann. Rept. for 1890, Pt. II(1891), pp. 392-406. Kidwell,A.L. (1949) Mesozoic igneous activity in the northern Gulf Coastal Plain: Ph.D. Dis sertation, Univ. Chicago, 316 pp. (1951) Mesozoic igneous activity in the northern Gulf Coastal Plain: Trans. Gulf Coast Assoc. Geol. Soc, Vol.I,pp. 182-199. Kiene, J. R., and McMahon, B. E. (1952) De velopments inNorth Texas:Bull. Amer. Assoc. Petrol. Geol., vol. 36, pp. 1157-1168. King, E. R. (1959) Regional magnetic map of Florida: Bull. Amer. Assoc. Petrol. Geol., vol. 43, pp. 2844-2854. King, P. B. (1931) Pre-Carboniferous stratigraphy ofMarathonuplift,west Texas(withdis cussion by H. D.Miser):Bull. Amer. Assoc. Petrol. Geol., vol.15, pp. 1059-1085. (1932) Large boulders in the Haymond formation of west Texas (abst.) :Bull. Geol. Soc. Amer., vol. 43, p. 148. (1935 ) Outline of structural development of Trans-Pecos Texas:Bull.Amer. Assoc. Petrol. Geol., vol. 19, pp. 221-261. (1937) Geology of the Marathon region, Texas: U. S. Geol. Survey Prof. Paper 187,148 pp. [1938]. (1940) Older rocks of the Van Horn region, Texas:Bull.Amer. Assoc. Petrol. Geol., vol.24, pp. 143-156. (1942) Permian of west Texas and southeastern New Mexico: Bull. Amer. Assoc. Petrol. Geol., vol. 26, pp. 535-763. (1949) Regional geologic map of parts of Culberson and Hudspeth counties, Texas: U. S. Geol. Survey Oil and Gas Inv. Prelim. Map 90 (with text). (1950) Tectonic framework of southeastern United States: Bull. Amer. Assoc. Petrol. Geol., vol. 34, pp. 635-671. (1951) The tectonics ofmiddleNorth America, Princeton Univ. Press, pp. 119-159, Princeton, N.J. (1955 a) A geologic section across the southern Appalachians; an outline of the geology in the segment inTennessee, North Carolina, and South Carolina, in Russell, R. J., cd., Guides to southeastern geology: Geol. Soc. Amer. 1955 Ann. Meeting, pp. 332-373. (1955b) Orogeny and epeirogeny through time, in The crust of the earth: Geol. Soc. Amer., Spec. Paper 62, pp. 723-740. (1958) Problems of boulder beds of Haymond formation, Marathon Basin, Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 42, pp. 1731-1735. (1959) The evolution ofNorth America, Princeton Univ. Press, Princeton, New Jersey, 190 pp. ,Baker, C. L., and Sellards, E. H. (1931) Erratic boulders of large size in the west Texas Carboniferous (abst.): Bull. Geol. Soc. Amer., vol. 42, p. 200. ,and Flawn, P. T. (1953) Geology and mineral deposits of pre-Cambrian rocks of the Van Horn area, Texas: Univ. Texas Pub. 5301, 218 pp. ,Hadley, J. 8., Neuman, R. 8., and Hamilton, Warren (1958) Stratigraphy of Ocoee series, Great Smoky Mountains, Tennessee and North Carolina: Bull.Geol. Soc. Amer., vol.69, pp. 947-966. King,R.E.(1934) ThePermianofsouthwestern Coahuila, Mexico: Amer. Jour. Sci., sth ser., vol. 27, pp. 98-112. (1942) Paleozoic stratigraphy of Mexico: Proc. Bth Amer. Sci. Cong., Washing- ton,D.C, 1940, vol.4,pp.109-199. (1944) Geology, Pt. 1 of Geology and paleontology of the Permian area northwest of Las Delicias, southwestern Coahuila, Mex ico: Geol. Soc. Amer., Spec. Paper 52, pp. 3-33. ,and Adkins, W. S. (1946) Geology of a part of the lower Conchos Valley, Chihuahua, Mexico: Bull.Geol. Soc. Amer., vol. 57, pp. 275-294. ,et al. (1942) Resume of geology of the south Permian basin, Texas and New Mexico: Bull. Geol. Soc. Amer., vol. 53, pp. 539 560. (1944) Geology and paleontology of the Permian area northwest of Las Delicias, The Ouachita, System southwestern Coahuila, Mexico: Geol. Soc. Amer. Spec. Paper 52, 172 pp. Kleihege, B. W. (1948) Metamorphism ofPaleozoic sediments in Val Verde and Terrell coun ties, Texas: Master's Thesis, Univ. Kansas, 59 pp. Knebel, G. M., and Rodriquez-Eraso, Guillermo (1956) Habitat of some oil: Bull. Amer. Assoc. Petrol. Geol., vol. 40, pp. 547-561. Kramer, W. B. (1933) Boulders from Bengalia: Jour. Geol., vol.41, pp. 590-621. ¦ (1934) En echelon faultsin Oklahoma (with discussion byR.H. Dott):Bull.Amer. Assoc. Petrol. Geol., vol. 18, pp. 243-250. — ,King,P.8.,andMiser,H.D. (1936) Ouachita boulder problem, Oklahoma and Arkansas: Bull. Amer. Assoc. Petrol. Geol., vol. 20, pp. 479-491. Krumbein, W. C, and Sloss, L.L. (1951) Stratigraphy and sedimentation, W. H. Freeman & Co., 497 pp., San Francisco. , , and Dapples, E. C. (1949) Sedimentary tectonics and sedimentary environments: Bull. Amer. Assoc. Petrol. Geol., vol.33, pp. 1859-1891. Krynine, P.D. (1948) The megascopic study and field classification of sedimentary rocks: Jour. Geol., vol.56, pp. 112-117. Kuenen, P. H. (1953) Significant features of graded bedding: Bull. Amer. Assoc. Petrol. Geol., vol.37, pp. 1044-1066. (1957) Longitudinal fillingof oblong sedimentary basins: Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig Genootschap, Geol., ser., dccl 18, pp. 189-195. Landes, K.X.,Parks, Bryan, and Scheid, V.E. (1933) Magnet XVI Inter. Cove, Arkansas: Geol. Cong. Guidebook 2, pp. 104-112. Laudon, L.R., and Bowsher, A. L. (1949) Mississippian formations of southwestern New Mex ico: Bull.Geol. Soc. Amer., vol. 60, pp. 1-88. Laudon, R. B. (1959) Some age relationships of Chesterian and Morrowan rocks ineastern Oklahoma, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 122-129. Lee, F. W., Swartz, J. H., and Hemberger, S. J. (1945) Magnetic survey of the Florida peninsula: U. S. Bur. Mines Rept. Inv. 3810, 44 pp. Lester, J. G., and Allen,A. T. (1950) Diabase of the Georgia Piedmont: Bull. Geol. Soc. Amer., vol. 61, pp. 1217-1224. Levorsen, A. I. (1955) Where willtomorrow's oil be found: World Oil, vol. 140, no. 5, April, pp. 76-85. Lewis, F. E. (1941) Position of San Andres group, west Texas and New Mexico: Bull. Amer. Assoc. Petrol. Geol., vol. 24, pp. 78-79. Lloyd, E. R. (1923) Igneous rocks, inDescription of the Hot Springs district: U. S. Geol. Survey Geol. Atlas, Hot Springs Folio (No. 215), pp. 7-8. Logue, L.L. (1954) Gravity anomalies of Texas, Oklahoma, and the United States: Oil and Gas Jour., vol. 52, no. 50, April19, pp. 132-135. Long,L.E.,andKulp,J.L.(1958) Isotopicages of rocks in the vicinity of the City of New York (abst.):Bull.Geol. Soc. Amer., vol. 69, p. 1605. Lonsdale, J. T. (1927) Igneous rocks of the Balcones fault region of Texas: Univ. Texas Bull. 2744, 78 pp. ¦ (1940) Igneous rocks of the Terlingua- Solitario region, Texas:Bull.Geol. Soc. Amer., vol. 51, pp. 1539-1636. ,Maxwell, R. A., Wilson, J. A., and Hazzard, R. T. (1955) Big Bend National Park, Texas:West Texas Geol. Soc. Guidebook, Field Trip, March 18-19, 1955, pp. 54-60. Love,D.W.,Kirkland,R.A.,andRichey, W.E. (1957) Developments in east Texas in 1956: Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 1171-1180. Lyons, P. L. (1950) A gravity map of the United States: Tulsa Geol. Soc. Digest, vol. 18, pp. 33-43. McCoy, A. W. (1921) A short sketch of the paleogeography and historical geology of the Mid-Continent oil district: Bull. Amer. Assoc. Petrol. Geol., vol.5, p. 562. McCullough, E. L. (1954) Geology of the Finley area, Pushmataha County, Oklahoma: M. S. Thesis, Univ.Oklahoma. McGlamery, Winnie (1955) Subsurface stratigraphy ofnorthwest Alabama:Alabama Geol. Survey Bull.64, 503 pp. McKee, E. D., et al. (1956) Paleotectonic mapsj of Jurassic system: U. S. Geol. Survey Misc.] Geol. Inves. Map 1-175, 6 pp., 9 pis. (1959) Paleotectonic maps of the Triassic system:U. S. Geol. Survey Misc. Geol. Inv.Map 1-300, 33 pp., 9 pis. Maher, J. C, and Lantz, R. J. (1953) Correlation of pre-Atoka rocks inthe Arkansas Valley, Arkansas:U. S. Geol. Survey Oiland Gas Inv. Chart OC-51. Maravich, M. D. (1953) Developments in Oklahoma in 1952: Bull. Amer. Assoc. Petrol. Geol., vol.37, pp. 1340-1351. Masson, P. H. (1955) Metamorphism in the Llanoria structural belt, Trans-Pecos Texas (abst.) :Bull.Geol. Soc. Amer., vol. 66, p. 1593. Mather, K. F. (1915) The fauna of the Morrow group of Arkansas and Oklahoma: Scientific Lab., Denison Univ. Bull., vol. 18, p. 83. (1917) Pottsville formations and faunas of Arkansas and Oklahoma:Amer. Jour. Sci., 4th ser., vol.43, pp. 134-135. Maxwell, R. A., Lonsdale, J. T., Goldich, S. S., and Smith, J. F., Jr. (1949) Marathon region, — Big Bend, Green Valley Paradise Valley region, Sierra Blanca region: West Texas Geol. Soc, Guidebook Field Trip No. 1, Nov. 6-9, 1949, 111 pp. , , Hazzard, R. T., and Wilson, J. A. (MS) Geology of Big Bend National Park. Mead, W. J. (1925) Geologic role of dilatancy: Jour. Geol., vol. 33, pp. 685-698. Mellen, F. F. (1947) Black Warrior basin, Alabama and Mississippi: Bull. Amer. Assoc. Petrol. Geol., vol. 31, pp. 1808-1816. (1958) Cretaceous shelf sediments of Mississippi: Mississippi Geol. Survey Bull. 85, 112 pp. Melton, F. A. (1929) A reconnaissance of the joint systems in the Ouachita Mountains and central plains of Oklahoma: Jour. Geol., vol. 37, pp. 729-746. Bureau ofEconomic Geology, The University of Texas (1930) Age of the Ouachita orogeny and its tectonic effects: Bull. Amer. Assoc. Petrol. Geol., vol. 14, pp. 57-72. (1954) Natural mounds of north eastern Texas, southern Arkansas, and northern Louisiana: The Hopper, vol. 14, no. 7, pp. 88-120, Oklahoma Geol. Survey. Miller, B. W. (1955) Geology of the western Potato Hills, Latimer and Pushmataha counties, Oklahoma: M. S. Thesis, Univ. Oklahoma. Miller,D. N. (1955) Petrology of Pierce Canyon red beds, Delaware basin, Texas and New Mexico: Ph.D. Dissertation, Univ. Texas, 148 pp. Miller,E. T., and Ewing, Maurice (1956) Geomagnetic measurements in the Gulf of Mexico and inthe vicinity of Caryn Peak: Geophysics, vol.21, pp. 406-432. Miller, R. D. (1957) Developments in north Texas in1956:Bull.Amer. Assoc. Petrol. Geol., vol. 41, pp. 1135-1143. Mills, J. M., Jones, T. S., and King, R. E. (1941) Possible future oil provinces of west Texas, Edwards Plateau, Trans-Pecos province: Bull. Amer. Assoc. Petrol. Geol., vol. 25, pp. 1530-1534. Misch, Peter, and Oles, K. F. (1957) Interpretation of Ouachita Mountains of Oklahoma as autochthonous folded belt, preliminary report: Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 1899-1905. Miser, H. D. (1914) New areas of diamond-bearing peridotite in Arkansas: U. S. Geol. Survey Bull.540, pp. 534-546. (1917) Manganese deposits of the Caddo Gap and DeQueen quadrangles, Arkansas: U. S. Geol. Survey Bull. 660, pp. 59-122. (1920) Mississippian tuff in the Ouachita Mountain region: Bull. Geol. Soc. Amer., vol. 31, pp. 125-126. (1921) Llanoria, the Paleozoic land area in Louisiana and eastern Texas: Amer. Jour. Sci., sth ser., vol. 2, pp. 61-89. (1926) Geologic map of Oklahoma, U. S. Geol. Survey. Scale, 1:500,000. (1929) Structure of the Ouachita Mountains of Oklahoma and Arkansas: Okla homa Geol. Survey Bull.50, 30 pp. (1931) Discussion, in Pre-Carbonferous stratigraphy of Marathon uplift, west Texas, by P. B.King:Bull.Amer. Assoc. Petrol. Geol., vol.15, p. 1083. (1932) Oklahoma structural salient of the Ouachita Mountains (absts.): Bull. Geol. Soc. Amer., vol. 43, p. 138; Pan-Am. Geol., vol. 57, p. 67. (1933a) Oklahoma structural salient of the Ouachita Mountains (abst.): Jour.Washington Acad. Sci., vol. 23, pp. 110-112. (1933b) Some problems of the Ouachita Mountains (abst.): Tulsa Geol. Soc. Digest, pp. 35-38. — (1934 a) Structural relations of Oua chita geosyncline of Arkansas, Oklahoma, and adjacent states (abst.) :Pan-Am. Geol., vol. 61, pp. 155-156. (1934b) Carboniferous rocks of Ouachita Mountains: Bull. Amer. Assoc. Petrol. Geol., vol. 18, pp. 971-1009. Abst., Jour. Washington Acad. Sci.,vol.24,pp.494-495. (1934c) Relation of Ouachita belt of Paleozoic rocks to oil and gas fields of Mid- Continent region: Bull. Amer. Assoc. Petrol. Geol., vol. 18, pp. 1059-1077. Abst., Pan-Am. Geol., vol. 59, pp. 227-228, 1933. — (1936) Structural relations of Ouachita geosyncline of Arkansas, Oklahoma, and adjacent states: 16th Inter. Geol. Cong. (1933), Rept., vol. 2, pp. 997-998. (1943) Quartz veins in the Ouachita Mountains of Arkansas and Oklahoma, their relations to structure, metamorphism, and metalliferous deposits: Econ. Geol., vol. 38, pp. 91-118. (1954) Geologic map of Oklahoma, U. S. Geol. Survey. Scale, 1:500,000. (1959) Structure and vein quartz of the Ouachita Mountains of Oklahoma and Arkansas, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 30-43. , and Honess, C. W. (1927) Age relations of the Carboniferous rocks of the Ouachita Mountains of Oklahoma and Arkan sas: Oklahoma Geol. Survey Bull. 44, 48 pp. ,and Purdue, A. H. (1918) Asphalt deposits and oil conditions in southwestern Arkansas: U.S. Geol. Survey Bull. 691, pp. 271-292. — ,¦ (1929) Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U.S. Geol. Survey Bull. 808, 195 pp. — ,and Ross, C. S. (1922) Peridotite dikes in Scott County, Arkansas: U.S. Geol. Survey Bull.735, pp. 271-278. , (1923) Diamond-bear ing peridotite in Pike County, Arkansas: U.S. Geol. Survey Bull.735, pp. 279-322. ,and Sellards, E. H. (1931) Pre- Cretaceous rocks found inwellsinGulf Coastal Plain south of Ouachita Mountains: Bull. Amer. Assoc. Petrol. Geol., vol. 15, pp. 801-818. Mississippi Geological Society (1954) Paleozoic rocks, central Tennessee and northwest Alabama: Mississippi Geol. Soc. 11th Field TripGuidebook, 67 pp. Moody, C. L. (1949) Mesozoic igneous rocks of northern Gulf Coastal Plain: Bull. Amer. Assoc. Petrol. Geol., vol. 33, pp. 1410-1428. Moore, R. C. (1928) Framework of southeastern North America: Bull. Geol. Soc. Amer., vol. 39, pp. 181-182. (1934) The origin and age of the boulder-bearing Johns Valley shale in the Ouachita Mountains of Arkansas and Oklahoma: Amer. Jour. Sci., sth ser., vol. 27, pp. 432-453. (chairman) (1944) Correlation of Pennsylvanian formations of North America: Bull.Geol. Soc. Amer., vol. 55, pp. 657-706. ,and Thompson, M. L. (1949) Main divisions of Pennsylvanian period and system: Bull. Amer. Assoc. Petrol. Geol., vol. 33, pp. 275-302. Morgan, G. D. (1924) Geology of the Stonewall quadrangle, Oklahoma: Bureau of Geology, Norman, Oklahoma, Bull.2, 248 pp. Morgan, H. J., Jr. (1952) Paleozoic beds south and east of Ouachita folded belt: Bull. Amer. Assoc. Petrol. Geol., vol. 36, pp. 2266-2274. The Ouachita System Mum, J. M. (1936) Geology of the Tampico region, Mexico, Amer. Assoc. Petrol. Geol. 280 pp. Nelson, L.A. (1940) Paleozoic stratigraphy of the Franklin Mountains, west Texas: Bull. Amer. Assoc. Petrol. Geol., vol.24, pp. 157-172. Nettleton, L. L. (1949) Geophysics, geology, and oilfindings: Geophysics, vol. 14, pp. 273 289. Newell, N. D. (1957) Supposed Permian tillites in northern Mexico are submarine slide deposits: Bull. Geol. Soc. Amer., vol.68, pp. 15691575. North Texas OilScouts Association (1954) Texas, north, inOiland gas fielddevelopment 1953: National Oil Scouts and Landmen's Assoc. Yearbook, 1954, vol. 24, pp. 716-767. Nuttall, Thomas (1821) A journal of travels into the Arkansas Territory during the year1819, 296 pp., Philadelphia. Oakes, M. C. (1948) Chert River, an inferred Carboniferous stream of southeastern Oklahoma: Oklahoma Acad. Sci. Proa, vol. 28, pp. 70-78. Oil and Gas Division, Texas Railroad Commission (1955) Annual Report, pp. 197, 198, Austin. Osann, C. A. (1893) Melilite-nepheline basalt and nepheline-basanite from southern Texas: Jour Geol., vol. 1, pp. 341-346. Park, C. F., Jr. (1935) Notes on the structure of the Erin shale of Alabama: Washington Acad. Sci. Jour., vol. 25, pp. 276-279. Penrose, R. A. F. (1892) The iron deposits of Arkansas: Arkansas Geol. Survey, Ann. Rept. for1892, Vol.I,pp. 59-103. Pettijohn, F. J. (1949) Sedimentary rocks: Harper &Bros., 526 pp., New York,N.Y. (1957) Sedimentary rocks, 2d cd., cd., Harper and Brothers, 718 pp., New York. Petty, J. K. (1952) Val Verde basin offers big gas possibilities: World Oil, vol. 135, no. 5, October, pp. 128-135. Pitt, W. D. (1955) Geology of the core of the Ouachita Mountains of Oklahoma: Oklahoma Geol. Survey Circ. 34, 34 pp. (1959) Summary discussion of the geology of the core areas of the Ouachita Mountains, Arkansas and Oklahoma, in The geologyof the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 87-91. Poldervaart, Arie,cd. (1955) Crust of the earth (a symposium) :Geol. Soc. Amer., Spec. Paper62, 762 pp. Powers, Sidney (1921) Solitario uplift, Presidio- Brewster counties, Texas: Bull. Geol. Soc. Amer., vol. 32, pp. 417-428. (1928) Age of folding of the Okla homa Mountains, the Ouachita, Arbuckle, andWichita Mountains of Oklahoma and the Llano- Burnet and Marathon uplifts of Texas: Bull. Geol. Soc. Amer., vol. 39, pp. 1031-1072. Price, W. A. (1951) Building of Gulf of Mexico: Trans. Gulf Coast Assoc. Geol. Soc, Vol. I, pp. 7-39. Priddy, R. R., and McCutcheon, T. E. (1943) Montgomery County mineral resources : Missis sippi Geol. Survey Bull. 51, 115 pp. Purdue, A. H. (1909a) Structure and stratigraphy of the Ouachita Ordovician area, Arkan sas (abst.):Bull.Geol. Soc. Amer., vol.19, pp. 556-557. -— ¦ (1909b) The slates of Arkansas: Ar kansas Geol. Survey, pp. 1-95. (1910) The slates of Arkansas: U. S. Geol. Survey Bull.430, pp. 317-334. ,and Miser, H. D. (1923) Description of the Hot Springs district: U. S. Geol. Survey Geol. Atlas, Hot Springs Folio (No. 215), 12pp. Reed, J. J. (1957) Petrology of the lower Mesozoic rocks of the Wellington district:New Zealand Geol. Survey, Bull.n.s. 57, 60 pp. Reeside, J. 8., et al. (1957) Correlation of the Triassic formations ofNorth America exclusive of Canada: Bull.Geol. Soc. Amer., vol. 68, pp. 1451-1514. Reinemund, J. A., and Danilchik, Walter (1957) Preliminary geologic map of the Waldron quadrangle and adjacent areas, Scott County, Arkansas: U. S. Geol. Survey Oil and Gas Inv. Map OM192 (with text). Renfroe, C. A. (1949) Petroleum exploration in eastern Arkansas with selected well logs: Arkansas Resources and Devel. Comm., Div. Geology, Bull.14, 159 pp. Rich, J. L. (1927) Generation of oilby geologic distillation during mountain-building: Bull. Amer. Assoc. Petrol. Geol., vol. 11, pp. 1139 1149. Richards, H. G. (1945) Subsurface stratigraphy of Atlantic Coastal Plain between New Jersey and Georgia: Bull. Amer. Assoc. Petrol. Geol., vol. 29, pp. 885-955. Roberts, J. R., and Nash, J. P. (1918) The geology of Val Verde County [Texas] :Univ. Texas Bull.1803, 51pp. Roberts, R. J.,Hotz,P.E.,Gilluly,James, and Ferguson, H. G. (1958) Paleozoic rocks of north-central Nevada: Bull. Amer. Assoc. Petrol. Geol., vol. 42, pp. 2813-2857. Rodgers, John (1952) Absolute ages of radioactive minerals from the Appalachian region: Amer. Jour. Sci., vol. 250, pp. 411-427. Roe, N. C. (1955) Geology of the eastern Potato Hills, Latimer and Pushmataha counties, Oklahoma: M.S. Thesis, Univ. Oklahoma. Rogers, C. L., De Cserna, Zoltan, Ojeda, Jesus, Tavara, Eugenio, and Van Vloten, Rogelio (In preparation) Estudio de reconocimiento de los depositos de fosfato en la parte nortecentral de Mexico:Inst. Nacl. Invest. Recursos Minerales and U. S. Geol. Survey. Romberg, Frederick, and Barnes, V.E. (1954) A geological and geophysical study of Pilot Knob (south), Travis County, Texas: Geophysics, vol. 19, pp. 438-454. Ross, C. A. (1959) The Wolfcamp series (Permian) and new species of fusulinids, Glass Mountains, Texas:Washington Acad. Sci.Jour., vol.49, pp. 299-316. Ross, C. P. (1941) The quicksilver deposits of the Terlingua region, Texas: Econ. Geol., vol. 36, pp. 115-142. Ross, C. S. (1928) Altered Paleozoic volcanic materials and their recognition: Bull. Amer. Assoc. Petrol. Geol., vol. 12, pp. 143-164. Bureau ofEconomic Geology, The University of Texas ¦ ,Miser, H. D., and Stephenson, L.W. (1928) Water-laid volcanic rocks of early Upper Cretaceous age in southwestern Arkan sas, southeastern Oklahoma, and northeastern Texas: U. S. Geol. Survey Prof. Paper 154, pp. 175-202. Ruedfmann, Rudolf (1947) Graptolites ofNorth America: Geol. Soc. Amer., Mem. 19, 652 pp. Rutten, M. G. (1955) Orogenese et edification dcs montagnes :Revue de geomorphologie dynamique, 6e6 e anee, no. 2, pp. 49-53. Schopf, J. M. (1959) Sargassoid microfossil assemblage from black shale of early Paleozoic age in Florida and Georgia: Bull. Geol. Soc. Amer., vol.70, pp. 1671-1672. Schuchert, Charles (1923) Sites and nature of the North American geosynclines :Bull. Geol. Soc. Amer., vol. 34, pp. 151-229. — (1935) Historical geology of the An tillean-Caribbean region, John Wiley & Sons, Inc., 811 pp., New York. Scobey, W. 8., et al. (1951) North-south cross section, Permian basin of west Texas, West Texas Geol. Soc, Midland. Scull, B. J. (1959) The age of mineralization in the Ouachita Mountains of Arkansas and Oklahoma, in The geology of the Ouachita Mountains, A symposium :Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 62-70. ,Glover, G. D., and Planalp, Roger (1959) The Atoka of the McAlester basin- Arkansas Valley region, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 166 174. Seeley, D. R. (1955) Geology of the Talihina area, Latimer, Le Flore and Pushmataha counties, Oklahoma: M.S. Thesis, Univ. Oklahoma. Sellards, E. H. (1919) The geology and mineral resources of Bexar County [Texas]:Univ. Texas Bull.1932, 202 pp. (1920) On the underground position of the Ellenburger formation in north-central Texas: Univ. Texas Bull.1849 (Sept. 1, 1918), p. 11. (1928) Well records of Bell County: Univ. Texas, Bur. Econ. Geol. Well Records Circ. 6, 17 pp. (mimeographed) . (1929) Preliminary map of underground position of pre-Cambrian in Texas: Univ. Texas, Bur. Econ. Geol., 2 pp. (mimeo graphed). —— ¦ (1930) Pre-Cretaceous rocks of the Balcones fault zone of Texas (abst.) :Pan-Am. Geol., vol. 53, pp. 233-240. (1930a) Mineral resources of Williamson County: Univ. Texas, Bur. Econ. Geol., pp. 70-92. (1931a) Erratics in the Pennsylvanian of Texas: Univ. Texas Bull.3101, pp. 9-18. (1931b) Rocks underlying Cretaceous in Balcones fault zone of central Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 15, pp. 819 827. — (1933) The pre-Paleozoic and Paleozoic systems in Texas, in The geology of Texas, Vol. I,Stratigraphy: Univ. Texas Bull. 3232 (Aug. 22, 1932), pp. 127-140, 187-192. (1935) Balcones zone of faulting and folding, in The geology of of Texas, Vol. 11, Structural and economic geology: Univ. Texas Bull.3401 (Jan. 1, 1934), pp. 49-61. ——— , Adkins, W. S., and Arick, M. B. (1931 ) Geologic map of the Solitario of Texas, Univ. Texas, Bur. Econ. Geol. Shannon, C. W., and Trout, L. E. (1915) Petroleum and natural gas in Oklahoma, Pt. I: Oklahoma Geol. Survey Bull.19, 133 pp. Shea, E. F. (1941) Developments in Oklahoma during 1940: Bull. Amer. Assoc. Petrol. Geol., vol. 25,pp. 1090-1102. Shelburne, O. 8., Jr. (1960) Geology of the Boktukola syncline, southeastern Oklahoma: Oklahoma Geol. Survey Bull.88, 84pp. Sheldon, M.G. (1954) Sample descriptions and correlations for selected wells in northern Arkansas: Arkansas Resources and Devel. Comm., Div. Geology Inf.Circ. 17, 222 pp. Shreveport Geological Society (1947) 1945 reference report on certain oiland gas fields of north Louisiana, south Arkansas, Mississippi, and Alabama, vol. 1: Shreveport Geol. Soc, 328 pp. Siever, Raymond, and Potter, P. E. (1956) Sources of basal Pennsylvanian sediments in the eastern Interior Basin, Pt. 2, Sedimentary petrology: Jour. Geol., vol.64, pp. 317-335. Singewald, Q. D. (1936) Evolution of the Coahuila Peninsula, Pt. V,Igneous phenomena and geologic structure near Mapimi: Bull. Geol. Soc. Amer., vol.47, pp. 1153-1176. Skinner, J. W. (1946) Correlation of Permian of west Texas and southeast New Mexico :Bull. Amer. Assoc. Petrol. Geol., vol. 30, pp. 1857 1874. Smith, L. 8., Jr. (1953) Developments in north Texas in1952: Bull. Amer. Assoc. Petrol. Geol., vol. 37, pp. 1384-1391. Snider, L. C. (1911a) Preliminary report on the clays and clay industries of Oklahoma: Okla homa Geol. Survey Bull.7, 270 pp. — (1911b) Preliminary report on the road materials and road conditions of Oklahoma: Oklahoma Geol. Survey Bull.8, 191 pp. (1912) Preliminary report on the lead and zinc of Oklahoma: Oklahoma Geol. Survey Bull.9, 97 pp. (1913) Petroleum and natural gas in Oklahoma, The Harlow-Ratliff Co., 196 pp., Oklahoma City. Spangler, G. W., and Fulk, F. F. (1942) Pan American Petroleum Corp. [Company report.] Spieker, E. M. (1946) Late Mesozoic and early Cenozoic history of central Utah: U.S. Geol. Survey Prof. Paper 205, pp. 117-161. Spooner, W. C. (1935) Oil and gas geology of the Gulf Coastal Plain in Arkansas: Arkansas Geol. Survey Bull.2,474 pp. Stenzel, H.B. (1932) Pre-Cambrian of the Llano uplift, Texas: Bull. Geol. Soc. Amer., vol. 43, pp. 143-144. Stiles, Edward, Roper, F. C, and McCammow, J. H. (1955) Val Verde basin cross sections, in San Angelo Geol. Soc, Geol. Contributions, 1955. Still,J. T. (1946) A geologic report on the Cuchillo Parado area, Chihuahua, Mexico. [Pri vate report for Petroleos Mexicanos.] The Ouachita System (1947) Report on an area in the northeastern part of the State of Chihuahua, Mexico. [Private report for Petroleos Mexicanos.] Stille, Hans (1940) Einfiihring in den Bau Amerikas, Gebriider Borntraeger, Berlin, 717 pp. Stone, J. A., and Cooper, C. L. (1929) Geology of Haskell, Latimer, Le Flore and Sequoyah counties, Oklahoma: Oklahoma Geol. Survey Bull. 40-11, vol. 3, pp. 411-430. Stovall, J. H., Dorbandt, L. W., and Ammon, W. L. (1948) Developments in north and west- central Texas in 1947: Bull. Amer. Assoc. Petrol. Geol., vol.32, pp. 988-996. Sundstrom, R. W., Hastings, W. W., and Broadhurst, W. L. (1948) Public water supplies in eastern Texas: U. S. Geol. Survey Water-Supply Paper 1047, 285 pp. Swain, F. M. (1944) Stratigraphy of the Cotton Valley beds of northern Gulf Coastal Plain: Bull. Amer. Assoc. Petrol. Geol., vol. 28, pp. 577-614. Swartz, F. M. (1949) Muscle marks, hinge and overlap features, and classification of some Leperditiidae: Jour. Paleont., vol. 23, pp. 306 327 Taff, J. A. (1899) McAlester-Lehigh coal field, Indian Territory: U.S. Geol. Survey 19th Ann. Rept., pt. 3, pp. 423-456. (1900) Structural features of the Ouachita Mountain range in Indian Territory (abst.) :Science, n.s., vol.11, pp. 187-188. (1901a) A comparison of the Oua chita and Arbuckle Mountain sections, Indian Territory (abst.) :Science, n.s., vol. 13, pp. 271-272. (1901b) Description of the Colgate quadrangle [Indian Territory]:U.S. Geol. Survey Geol. Atlas, Colgate Folio (No. 74), 6 pp. (1902) Description of the Atoka quadrangle [Indian Territory]:U.S. Geol. Survey Geol.Atlas, AtokaFolio (No.79),8pp. (1903) Description of the Tishomingo quadrangle [Indian Territory]:U.S. Geol. Survey Geol. Atlas, Tishomingo Folio (No.98), 8 pp. (1904) Preliminary report on the geology of the Arbuckle and Wichita Mountains in Indian Territory and Oklahoma: U.S. Geol. Survey Prof. Paper 31, 97 pp. (1905) Some erratic boulders in middle Carboniferous shale inIndian Territory (abst.):Science, n.s.,vol.21,p. 225. (1909) Grahamite deposits of southeastern Oklahoma: U.S. Geol. Survey Bull. 380, pp. 286-297. (1910) Ice-borne boulder deposits in mid-Carboniferous marine shale: Bull. Geol. Soc. Amer., vol. 20, pp. 701-702. Abst., Science, n.s., vol. 29, p. 637, 1909. Tallman, S. L. (1949) Sandstone types: Their abundance and cementing agents: Jour. Geol., vol. 57, pp. 582-591. Tappolet, W. (1928) Reconnaissance in central Coahuila. [Private report for Mexican Aguila Petroleum Company. Petroleos Mexicanos files.] Thiel. Edward (1956) Correlation of gravity anomalies with the Keweenawen geology of Wisconsin and Minnesota: Bull. Geol. Soc. Amer., vol. 67, pp. 1079-1100. Tomlinson, C. W. (1959) Ouachita problems, in The geology of the Ouachita Mountains, A symposium: Dallas Geol. Soc. and Ardmore Geol. Soc, pp. 1-19. , and Pitt, W. D. (1955) Recent studies in the Ouachita Mountains: Tulsa Geol. Soc. Digest, vol. 23, pp. 89-97. f (1956) Recent studies in the Ouachita Mountains [Oklahoma], reprinted, in Ardmore Geol. Soc, Guidebook Ouachita Mountains Field Conf. 1956, pp. 20 24. Toulmin, L. D. (1945) Well logs of Alabama, 1940-1945; Alabama Geol. Survey Bull. 57, 177 pp. Trumpy, Rudolf (1960) Paleotectonic evolution of the central and western Alps: Bull. Geol. Soc. Amer., vol.71, pp. 843-908. Turner, G. L. (1958) Paleozoic stratigraphy of the Fort Worth basin: Abilene and Fort Worth Geological Societies 1957 Field Trip, October 25-26, 1957, Guidebook, pp. 57-77. Tyrrell, G. W. (1929) The principles of petrology, E. P. Dutton and Company, Inc., 349 pp., New York. Udden, J. A. (1907 a) Report on a geological survey of the lands belonging to the New York and Texas Land Company, Ltd., in the upper Rio Grande embayment in Texas: Augustana Lib.Pub. No.6, pp.50-103. (1907b) Sketch of the geology of the Chisos country, Brewster County, Texas: Univ. Texas Bull.93 (Sci. Ser. 11), 101 pp. (1919) Observations on two deep borings near the Balcones faults: Bull. Amer. Assoc. Petrol. Geol., vol. 3, pp. 124-131. Ulrich, E. O. (1911) Revision of the Paleozoic systems: Bull. Geol. Soc. Amer., vol. 22, pp. 352 (footnote), 477, 528. (1927) Fossiliferous boulders in the Ouachita "Caney" shale and the age of the shale containing them: Oklahoma Geol. Survey Bull.45, 48 pp. Van der Gracht, W. A.J. M.van Waterschoot (1931a) Permo-Carboniferous orogeny insouthcentral United States: Bull. Amer. Assoc. Petrol. Geol., vol. 15, pp. 991-1057. (1931b) The pre-Carboniferous exotic boulders in the so-called "Caney shale" in the northwestern front of the Ouachita Mountains of Oklahoma: Jour. Geol., vol. 39, pp. 697-714. (1936a) The late Paleozoic orogeny in the North American continent (abst.) :16th Inter Geol. Cong. (1933), Rept., vol. 2, p. 993. (1936b) Ouachita boulder problem: Bull. Amer. Assoc. Petrol. Geol., vol. 20, pp. 1125-1127. Yon Streeruwitz, W. H. (1891) Report on the geology and mineral resources of Trans-Pecos Texas: Geol. Survey Texas, 2nd Ann. Rept. (1890), pp. 605-738. Washington, H. S. (1900) Igneous complex of Magnet Cove, Arkansas: Bull. Geol. Soc. Amer., vol. 11, pp. 389-416. Bureau ofEconomic Geology, The University of Texas (1901) The foyaite-ijolite series of Magnet Cove: Jour. Geol., vol. 19, pp. 607622, 645-670. Weaver, C. E. (1953) Mineralogy and petrology of some Ordovician K-bentonites and related limestone: Bull. Geol. Soc. Amer., vol. 64, pp. 921-943. (1958) Geologic interpretation of argillaceous sediments, —Pt. 11, Clay petrology of Upper Mississippian Lower Pennsylvanian sediments of central United States :Bull. Amer. Assoc. Petrol. Geol., vol. 42, pp. 272-309. (1959) The clay petrology of sedi ments, in Clays and clay minerals, Sixth Natl. Conf., 1957, Pergamon Press, pp. 154-187, New York. Weaver, O.D.,Jr. (1956) Anintroduction to the Fort Worth basin, in Symposium on the Fort Worth basin area, etc.:S.E.P.M. Permian Basin Section, Spring Meeting and Field Symposium, May 11-12, 1956, Guidebook, pp. 10-18. Weeks, W. B. (1938) South Arkansas stratig raphy withemphasis on the older coastal plain beds: Bull. Amer. Assoc. Petrol. Geol., vol. 22, pp. 953-983. Weirich, T. E. (1953) Shelf principle of oil origin, migration, and accumulation: Bull. Amer. Assoc. Petrol. Geol., vol. 37, pp. 2027 2045. Weiss, E. J., and Clabaugh, S. E. (1955) Mineralogy of the "serpentine" at Pilot Knob near Austin, Texas: Texas Jour. Sci., vol. 7, no. 2, pp. 136-148. Welch, S. W. (1959) Mississippian rocks of the northern part of the Black Warrior basin, Ala bama and Mississippi: U. S. Geol. Survey Oil and Gas Inv.Chart OC-62. Weller, J. M., et al. (1948) Correlation of the Mississippian formations of North America: Bull.Geol. Soc. Amer., vol. 59, pp. 91-196. Wells, F. G. (1949) Ensimatic and ensialic geo synclines (abst.) :Bull. Geol. Soc. Amer., vol. 60, p. 1927. West Texas Geological Society (1941) Possible future oilprovinces of west Texas, in Possible future oil provinces of the United States and Canada: Bull. Amer. Assoc. Petrol. Geol., vol.25, pp. 1527-1538. White, David (1934) The age of the Jackfork and Stanley formations of the Ouachita geosyncline as indicated by plants: Bull. Amer. Assoc. Petrol. Geol., vol. 18, pp. 1010-1017. (1937) Fossil plants from the Stanleyshale and Jackfork sandstone in southeastern Oklahoma and western Arkansas: U. S. Geol. Survey Prof. Paper 186-C, pp. 43-67. White,L.H. (1926) Subsurface distribution and correlation of the pre-Chattanooga ("Wilcox sand") series of northeast Oklahoma: Okla homa Geol. Survey Bull. 40, pp. 21-48. Whittington, H. B. (1953) A new Ordovician trilobite from Florida: Breviora, no. 17, 6 pp. Williams, Howel, Turner, F. J., and Gilbert, C. M. (1954) Petrography, W. H. Freeman & Company, 406 pp., San Francisco. Willis, Bailey (1907) A theory of continental structure applied to North America: Bull. Geol. Soc. Amer., vol. 18, pp. 394-395. , (1912) Index to the stratigraphy of North America:U. S. Geol. Survey Prof. Paper 71, 894 pp. Willis,P. D. (1954) Geology of the Snow area, Pushmataha County, Oklahoma: M.S. Thesis, Univ. Oklahoma. Wilmarth, M. G. (1938) Lexicon of geologic names of the United States (including Alaska): U. S. Geol. Survey Bull.869 (2 parts), 2396 pp. Wilson, C. W. (1939) Probable connection of the Nashville and Ozark domes by a complementary arch:Jour. Geol., vol. 47, pp. 583-597. and Steams, R. G. (1958) Structure of the Cumberland Plateau, Tennessee: Bull. Geol. Soc. Amer., vol.69, pp. 1283-1296. Wilson, J. L. (1954a) Ordovician stratigraphy in Marathon folded belt, west Texas: Bull. Amer. Assoc. Petrol. Geol., vol. 38, pp. 2455 2475. (1954b) Late Cambrian and Early Ordovician trilobites from the Marathon up lift,Texas: Jour. Paleont., vol. 28, pp. 249-285. Winland, H. D. (1953) Petrography of Ouachita facies sandstones: Univ. Tulsa, 55 pp. [Unpublished report.] Woods, R. D. (1955) Spores and pollen, a new stratigraphic tool for the oil industry: Micro- paleontology, vol. 1, pp. 369-375. (1956) The northern structural rim of the Gulf basin: Trans. Gulf Coast Assoc. Geol. Soc, Vol.VI,pp. 3-11. Woodworth, J. B. (1912) Boulder beds of the Caney shale at Talihina, Oklahoma:Bull.Geol. Soc. Amer., vol. 23, pp. 457-462. Abst., Science, n.s., vol. 35, p. 319. Woollard, G. F. (1949) Regional gravity study in the Appalachian Mountain system (abst.) : Bull.Geol. Soc. Amer., vol.60, p. 1932. (1955) Gravity studies of major tectonic units in the United States (abst.) :Bull. Geol. Soc. Amer., vol. 66, no. 12, pt.2, p. 1638. (1958) Areas of tectonic activity in the United States as indicated by earthquake epicenters: Amer. Geophys. Union Trans., vol. 39, pp. 1135-1150. Young, Addison (1952) Geologic section in Phillips Petroleum Company's Elsinore Cattle Company No. 1, in Marathon Basin, Brewster and Pecos counties, Trans-Pecos Texas: West Texas Geol. Soc, Guidebook, Spring FieldTrip,May23-24, 1952, pp. 72-73. (1960) Paleozoic history of the Fort Stockton-Del Rio region, west Texas: Univ. Texas Pub. 6017, pp. 87-109. Young,David (1957) Deep drillingthrough Cum berland overthrust block in southwestern Virginia: Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 2567-2573. Appendix Part 1. Summary Reports on Wells Penetrating Rocks of the Ouachita Belt and Immediately Adjacent Foreland in Texas Peter T.Flawn Information on the following wells was compiled from many different sources. Few of the data were available inpublished material. The bulk of the basic well data and stratigraphic data was taken from the files of operating companies and from the files of the Bureau of Economic Geology. Except where credited to another source, all of the petroraphic data are original. Allof the X-ray determinations were made by C. E. Weaver. The following symbols and ratios are used to express X-ray data: X—kaolinite; Ch=chlorite;I= illite;M=montmorillonite;ML=mixed layer illite-montmorillonite; — = F=2o=plagioclase feldspar;F 24 potassium feldspar;SR=sharpness ratio;10/7= ratio of height of illite X-ray peak (10A) to the combined (ifboth are present) chlorite and kaolinite (7A) X-ray peak Nimeans that no information was available. — County. Bandera. — Wellname. General Crude OilCompany No.1Anderson. Location.—Section 21, GH&SA survey; 3,245 feet FNWL, 300 feet FNEL; 25 mi. NW of Bandera. Elevation.— l,B43 feet, derrick floor. Total depth.— lo,626 feet. Completed.— l9ss. — Top ofPaleozoic rocks.-1,097 feet. Elevation ofPaleozoic rocks.—+746 feet. — Thinsection coverage (depth infeet). shell oilcompany: 3040-50. — Description of Paleozoic rocks.-The wellpenetrated a normal foreland basin sequence north of the Ouachita structural belt. Top of Ordovician is 7,500 feet (Barnes, 1959). The sample from 3,040 3,050 feet is a dark, bentonitic silty shale which indicates the presence of volcanic material in the sequence. X-raydata.—l>ML>Ch>X;10/7 1.5;F=.20. References.— Barnes (1959, p. 334). — County. Bandera. — Wellname. Humble Oil& Refining Company No. 1Thompson. — Location. J.A.Delgado survey;750feetN,2,500feetEofSWcor.ofThompson 934acres. Elevation.—l,66o(?) feet. Totaldepth.—3,67o feet. Completed.—l924. —— TopofPaleozoic rocks. 800 feet.ElevationofPaleozoic rocks. +860(?) feet. — Thinsection coverage (depth infeet). None. Description of Paleozoic rocks.-—Paleozoic rocks encountered in this well are considered to be Upper Mississippian and LowerPennsylvanian; no reliable subdivision has been made (Woods, 1957). This well is probably north of the Ouachita structural belt in foreland basin rocks. No samples were examined. — X-ray data. None. — References. Personal communication: R. D. Woods, Humble Oil & Refining Company, 1957. — County. Bandera. Well name.—H. L.Mcßride No. 1Fee. — Location.-J. F.Davenport survey; NW cor. on Privilege Creek, 4mi.NEBandera. — Elevation. —1,345 feet, derrick floor. Total depth.— ll,oso feet. Completed. 1952. —— TopofPaleozoic rocks. 870 feet.Elevation ofPaleozoic rocks. f-475 feet. Bureau ofEconomic Geology, The University of Texas — Thinsection coverage (depth infeet). None. Description of Paleozoic rocks.— Two core fragments from the interval 870 to 1,179 feet are strongly deformed and fractured dark shale veined by carbonate. This well seems to have penetrated Mississippian-Pennsylvanian rocks of Ouachita facies in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Robert Pavlovic, Magnolia Petroleum Company, 1959. — County. Bandera. — Well name. MiktonNo. 1Stelzer. Location—H.E. Rogers survey; 1,650 feetFEL, 2,800 feetFSL; 1.5 mi.FW,7.1mi.FS County line. — —— Elevation. -1,742 feet, derrick floor. Total depth. 8,515 feet. Completed. 1952. —— Top of Paleozoic rocks. 1,040 feet. Elevation of Paleozoic rocks. +702 feet. — Thin section coverage (depth infeet). None. Description of Paleozoic rocks.—Young (1957) reported base of Cretaceous at 1,040 feet; the sequence from 1,040 feet to total depth consists of alternating gray shale and sandstone. These rocks are probably all Pennsylvanian, but itis possible that the upper part of the sequence includes Wolf- camp beds. This wellis north of the Ouachita structural belt in foreland basin rocks. — X-ray data. None. — References. Personal communication: Addison Young, Phillips Petroleum Company, 1957. — County. Bandera. — Well name. Plateau (Peerless) OilCompany No.1R.D Garrison. Location.—Section 506, GC&SF survey; 2,900 feet FNL, L9OO feet FWL; 9 mi. NW of Tarpley. —— Elevation.— l,B3s feet. Total depth. 5,365 feet. Completed. ]935. —— Top of Paleozoic rocks. 1,150 feet. Elevation of Paleozoic rocks. 1-685 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 1220-40, 1381-98, 1440-44, 2186-87, 2224-25, 2400-20, 2510-12, 2588-90, 2674-77, 3160-80, 3200-07, 3750-70, 3790-3810 (2), 3830-50, 4610-30, 5090-5110, 5130-50, 5230-50. <=hell oilcompany: 1160-80. Description of Paleozoic rocks. —Sample descriptions inthe files of the Bureau of Economic Geology indicate base of Cretaceous at 1,150 feet and describe the sequence between 1,150 and 5,365 feet, total depth, as dark gray, greenish-gray, reddish-brown, and light green schistose shales with thin streaks of gray quartzitic sandstone and quartzite cut by quartz and calcite veinlets; the upper part of the sequence is red due to weathering. This well penetrated a sequence of dark, angular, poorly sorted, chloride micaceous siltstone and dark silty shale with lesser amounts of fine-grained, angular to subangular, poorly sorted, micaceous chloritic feldspathic quartz sandstone and dark, pyritic argillaceous cryptocrystalline to microgranular chert; locally the rocks are extensively invaded by chlorite-quartz-calcite veinlets. Some of the quartz veinlets contain bitumen. The entire sequence shows varying degrees of metamorphism, mostly incipient but ranging up to very weak and weak in some intervals; 1,160-1,180-foot interval is composed of silty sericite-chlorite clay-slate and sericitic chloritic metasiltstone ;3,830-3,840-foot and 4,610-4,630-foot intervals are com posed of sericite-chlorite slate and chloritic micaceous metasiltstone; the slate with"hourglass" carbonate porphyroblasts is similar to that seen in Turner No. 1Linder in Kendall County, Blumberg No. 1 Knibbe and Newton No.1Check Ranch wellsinComal andKendall counties, and other wellsto the northeast (p. 66). This well is close to the northern limit of the Ouachita belt, and the degree and variation of metamorphism suggest folding and possibly thrusting along this frontal segment of the belt. (See Blumberg No. 1Knibbe, p. 243.) Such advanced metamorphism and extensive veining are not common along the frontal margin of the belt to the west or along the course of the belt north of the Llano uplift. The rocks penetrated in this well are interpreted as upper Paleozoic Ouachita facies overlying lower Paleozoic Ouachita facies, but possibly the entire sequence is lower Paleozoic. An interpretation suggested by Maner (1958) is that the sequence is composed of Stanley beds overlying Atoka beds containing abundant detritus from early and middle Paleozoic Ouachita facies rocks; according to this hypothesis, slightly metamorphosed pre-Stanley Ouachita facies rocks somewhere to the south were uplifted (by thrusting?) to form a provenance for Atoka detritus and subsequently the Atoka beds were overthrust by Stanley rocks. — X-ray data. None. The Ouachita System References.— Goldstein and Reno (1952, fig.10-B, p. 2283). Bureau of Economic Geology files. Personal communication:R.P.Maner, ShellOilCompany, 1958. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bandera. — Wellname. RayPoolDrillingCompany No.1E.L.Rainey. Location—Section 16, GH&SA survey; 2,600 feet FSWL, 1,500 feet FNWL. Elevation.—l,737 feet. Totaldepth.—s,oo9 feet. Completed— -1947. — TopofPaleozoic rocks.—I,ooo± feet.Elevation ofPaleozoic rocks. +737± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. A sample log shows that the well penetrated Paleozoic rocks at 1,020 feet (Sandidge, 1957). This wellis probably in foreland basin rocks north of the Ouachita structural belt. — X-ray data. None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Bandera. — Well name. Rossman (Stan-Ross) No. 1Goodenough. Location.—]. B. Gobies survey; 660 feet FSWL, 660 feet FSEL; 2]/2 mi. NE of Bandera. —— Elevation. 1,347 feet. Total depth. —5,508 feet. Completed. 1953. — — TopofPaleozoicrocks. 840feet.ElevationofPaleozoicrocks. +507feet. — Thin section coverage (depth in feet). bureau of economic geology: 855-58 (2), 1245-50, 1425-30, 2245-50 (2), 2470-75 (2), 3590-3600 (2), 4080-90 (3), 5490-5500. — Description of Paleozoic rocks. The sequence is composed of angular to subangular, poorly to fairly well-sorted, micaceous chloritic argillaceous feldspathic quartz sandstone and dark, carbonaceous silty shale and metashale, both commonly invaded by quartz veinlets;the sandstones contain abundant rock fragments, mostly phyllite. Locally the sandstones are dolomitic. The sequence is composed of upper Paleozoic Ouachita facies rocks; metamorphism varies fromnone to incipient. ThiswellisinthefrontalzoneoftheOuachitastructural belt. The writer was unable to identify individualunits in this sequence; Maner (1958) suggested that the sequence is composed of Stanley beds thrust over Atoka and compared it to the section penetrated inPlateau No.1Garrison (p.212). X-raydata.—l>Ch;10/7 ~->0.8;F=20;SR=3.2. — References. Personal communication:R.P.Maner, ShellOilCompany, 1958. — County. Bandera. — Wellname. G.L.Rowsey No.1Fee. Location.—Section 3,BS&Fsurvey;1,080 feetFWL,1,384 feetFSL;8mi.NEofBandera. Elevation.—l,7s7 feet, derrick floor; 1,747 feet, ground. Total depth.— 6,2oo feet. Completed.— l9s4. — —— Top of Paleozoic rocks. 940 feet. Elevation of Paleozoic rocks. |— 817 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Information from scout cards indicates top of Ellenburger, 4,412 feet and top of Hickory, 5,750 feet. These data indicate that the well penetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. None. — County.-Bandera. — Well name. G. L.Rowsey No. 2Fee. Location.—]. M. Shipp survey; 1,120 feet W and 550 feet NFSW cor. of BS&F survey; 10 mi.NW of Bandera. —— Elevation. 1,809 feet, derrick floor; 1,798 feet, ground. Total depth. —6,970 feet. Completed. 1953. —— TopofPaleozoic rocks. ni.ElevationofPaleozoic rocks. ni. — Thinsection coverage (depth infeet). None. Bureau ofEconomic Geology, The University of Texas — Description of Paleozoic rocks. Scout card reports top of Marble Falls, 4,000 feet; top of Ellen- burger, 4,495 feet; top of Hickory, 6,833 feet. The well penetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. References.— Barnes (1959, p. 341). — County. Bandera. — Well name. G.L.Rowsey No. 5Fee. Location.—]. M. Shipp survey; 4,000 feet F most N'ly NL,330 feet F most N'lyEL; 10 mi. NNW of Bandera. Elevation.—1,848 feet. Total depth. —5,069 feet. Completed.— l9sB. — Top of Paleozoic rocks. —I,ooo± feet. Elevation of Paleozoic rocks. -f-848± feet. Thinsection coverage (depth infeet).—bureau of economic geology: 1,700±. — Description of Paleozoic rocks. Information from scout card indicates top of Marble Falls, 4,738 feet; top of Ellenburger, 4,960 feet. The single sample available for study is a dark, carbonaceous silty shale veined with quartz, probably Atoka. This well penetrated foreland basin rocks north of the Ouachita belt; quartz veins in the Atoka(?) shale suggest proximity to the front of the Ouachita belt. — X-ray data. None. — References. None. — County. Bandera. — Wellname. WoodTexasOilCompany No.1A.E.Clayton(alsocarriedasH.W.Clayton). — Location. GM&D survey; % mi. Nof Vanderpool. Elevation.—1,900 feet (fromtopographic map).Total depth.— 4,o2o feet. Completed.— l92o(?). — Top of Paleozoic rocks.— 96o feet. Elevation of Paleozoic rocks. -+940 feet. — Thin section coverage (depth infeet). None. DescriptionofPaleozoic rocks.—SampledescriptionsinthefilesoftheBureauofEconomicGeology are as follows: top of Pennsylvanian, 960 feet; top of Ellenburger, 4,020± feet; the Pennsylvanian sequence is composed of gray slickensided sandstone and quartzitic sandstone and dark to black, slickensided shale; quartz veins are rare. Although the top of Ellenburger was identified inthis well, there isnothing inthe sample descriptions tosubstantiate the determination. — X-ray data. None. — References. Bureau ofEconomic Geology files. — County. Bandera. Additionalwellnotshownonmap(PI.2)andnotstudiedbecause oflackofsamplesorbasicdata: — G.L.Rowsey No.1Gus Evans Location: George Ball survey; 330 feet FNEL, 330 feet FNWL; 6 mi. N of Bandera. Elevation: 1,397 feet, derrick floor; 1,389 feet ground. Total depth: 6,500 feet. Completed: 1958. Top of Paleozoic rocks: 770 feet (Pennsylvanian sand). County.—Bastrop. — Well name. Skelly OilCompany and Sunray Midcontinent OilCompany No. 1Itha Ray. Location.—Ed. Gritten survey; 330 feet F Caldwell County line, 2,500 feet FTravis County line. — —— Elevation. 605 feet. Total depth. 3,928 feet. Completed. 1956. — Top of metamorphic rocks. 3,720 feet. Elevation of metamorphic rocks. 3,115 feet. — Thin section coverage (depth in feet). rureau of economic geology: 3750-75, 3800-25, 3900-25. — Description of metamorphic rocks. The sequence is composed of dark carbonaceous (graphitic?) sericitic chloritic metasiltstone and dark carbonaceous (graphitic?) sericite-chlorite slate; quartzchlorite veinlets are common. The abundance of opaque carbonaceous or graphitic material—instreaks, layers, and disseminated "clouds" makes itdifficult to assess the degree of metamorphism probably itis weak. Foliation is expressed by mica and chlorite orientation and streaks of opaque matter, but theshearing elementisnotashighasinotherpartsofthiszone(PI.2). This wellpenetrated the black slate beltinthe interior zone ofthe Ouachita belt. The Ouachita System — X-ray data. None. — References. None. — County. Bell. — Wellname. Bell County OilCompany No.1T.R.Holcomb. — Location. LouisWalkersurvey; 3mi.WofBelton. —— Elevation. 760 feet (from topographic map). Total depth.—1,640 feet. Completed. 1921. — Top of Paleozoic rocks. 1,107 feet. Elevation of Paleozoic rocks. 347 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Sellards (1933) reported quartzitic sandstone. Udden (Bur. Econ. Geol. files) described a sample from1,150 feet as dark, sheared, quartzitic sandstone. This wellprobably penetrated the Stanley. — X-ray data. None. References— Sellards (1928, p. 12; 1931b, p. 821; 1933, p. 187). Bureau of Economic Geology files. — County. Bell. — Well name. Bell Williams OilCompany No. 3 John Kolls. Location.—2% mi.NW ofBelton,EofNo.1Kolls,Sof No.1Hair. —— Elevation. 625 feet (from topographic map). Total depth. l,4O5(?) feet; 1,446 (?) feet. Com- pleted.—Before 1930. —— TopofPaleozoic rocks. ni.ElevationofPaleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. According to Adkins and Arick (1930), the well penetrated black shale and quartzite. Bureau of Economic Geology files report total depth 1,405 feet in black limestone. This wellprobably penetrated the Stanley. — X-ray data. None. — References. Adkins and Arick (1930, pp. 16, 86). Bureau ofEconomic Geology files. — County. Bell. — Wellname. BellWilliamsOilCompany No.1B.F.Warrick. Location.—E. Ingram survey; 6.7 mi. NW of Jarrell; location is SofJ. B. Hartman No. 18. F. Warrick. — —— Elevation. 864 feet (by aneroid barometer). Total depth. -2,203 feet. Completed. Before 1925. TopofPaleozoicrocks.—1,200feet.ElevationofPaleozoicrocks. 336feet. — Thin section coverage (depth in feet). bureau of economic geology: 1190-1255 (2), 1304-07, 1336-73, 1372y2,1535, 1660, 1765 (2), 2203 (2). — Description of Paleozoic rocks. Sellards (1931b, 1933) described the section as "hard shale and quartzitic sandstone." Udden (Bur. Econ. Geol. files) described scattered samples from 1,190 to 1,373 feet as dark to black schistose shale and greenish to dark gray indurated sandstone. The sequence is composed of dark silty shale and angular, poorly sorted, argillaceous feldspathic quartz sandstone cut by quartz veinlets. The rocks are Ouachita facies and are identified as Stanley; some samples show incipient metamorphism. — X-ray data. None. References.— Barnes (1948) ;Sellards (1931b, p. 821; 1933, p. 135). Bureau of Economic Geology files. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bell. — Well name. Davidson et al. No. 2 Warrick. Location—E.Ingram survey; 2,250 feet FNEL, 900 feet FNWL. —— — Elevation. ni. Total depth. 3,600 feet. Completed. 1934. —— Top ofPaleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. Bureau ofEconomic Geology, The University of Texas — Thinsection coverage (depth infeet). None. — Description ofPaleozoic rocks. See other wellsinE.Ingram survey (p.215). — X-ray data. None. — References. None. — County. Bell. — Well name. Downs, Perry, and Hughes No. 4 John Kolls. — Location. 2% mi. NW of Belton. —— Elevation. 625 feet (from topographic map). Total depth. 1,405(?) feet; 1,446 (?) feet. Completed.— l9l6. TopofPaleozoic rocks.—1,194 feet.Elevation ofPaleozoic rocks. 569 feet. — Thinsection coverage (depth in feet).¦ None. — Description of Paleozoic rocks. According to Adkins and Arick (1930), this well penetrated black shale and quartzite. Description of samples in Bureau of Economic Geology files shows dark limestone in the interval 1,269 to 1,324 feet, dark sandstone and shale at 1,400 feet, and total depth 5 feet into black limestone. This well probably penetrated the Stanley. — X-ray data. None. References.— AdkinsandArick(1930,pp.16,86);Sellards (1928,p.12). Bureau ofEconomic Geology files. Samples are inBureau ofEconomic Geology WellSample Library. — County. Bell. — Wellname. E.A.Dunham No.1J. E.Hunt. Location.— Wm. Brown survey; 900 feet FWL, 330 feet FNL. — —— Elevation. 809 feet, kelly bushing; 799 feet, ground. Total depth. 3,960 feet. Completed. 1954. —— Top ofPaleozoic rocks. -700 feet. Elevation of Paleozoic rocks. -1-109 feet. — Thin section coverage (depth in feet). Bureau of Economic Geology: 700-10 (2), 750-60 (2), 760-70 (2), 800-10 (2), 840-50 (2), 999-00 (2), 1100-10, 1200-10, 1300-10, 1400-10, 1600-10, 1700-10, 1800-10, 1900-10, 2000-10, 2100-10, 2200-10, 2300-10, 2400-10, 2500-10, 2600-10, 2700-10, 2790-00 (2), 2900-10 (2), 3000-10 (2), 3100-10 (2), 3200-10 (2), 3300-10 (2), 3370-80 (2). — Description of Paleozoic rocks. This well penetrated a foreland basin section consisting mostly — ¦ of dark, micaceous carbonaceous silty and sandy shale (probably Atoka) overlying Marble Falls Barnett and Ellenburger formations. Sorting is poor in the Atoka sandstones, and sand-silt fractions are angular. The Ellenburger is very fine-grained dolomitic calcilutite and dolomite (grain size dolomite 0.01 to 0.1 mm). The following tops are given by Fowler (1955): top of Paleozoic and — Pennsylvanian, 700 feet; top of Marble Falls Barnett, 2,670 feet; top of Ellenburger, 2,720 feet. X-ray data.—l>ML>Ch>X;10/7'—'l.3; F=20; SR=2.4. Shales are composed of mixed illite-chlorite and montmorillonite-illite;montmorillonite is characteristic of foreland wells. The amount of montmorillonite decreases at a depth of about 2,600 feet, but small quantities are present to total depth. The upper section of the wellresembles Atoka. — References. Personal communication :P. T. Fowler, Shell OilCompany, 1955. — County. Bell. Well name. —Eclipse OilCompany No. 2 Slayden. — Location. 7 mi.S ofKilleen. — — Elevation. 900 feet (by aneroid barometer). Total depth. —1,216 feet. Completed. Before 1921. —— Top of Paleozoic rocks. 811 feet. Elevation of Paleozoic rocks. +89 feet. — Thin section coverage (depth in feet). bureau of economic geology: 811, 850, 940, 945, 950 (5), 1000 (3), 1050 (3). — Description of Paleozoic rocks. According to Sellards (1931b), novaculite is found at depths of 935 to 1,050 feet and underlies what seems to be Silurian found at depth of 710 to 850 feet; the inversion may be due to overthrusting. Sellards referred to Miser and said that the boundary between Silurian and basal Devonianinthe wellisindoubtbutthesample at 935 feet isthefirstbasal Devonian sample. Samples 940 to 945, 950, 1,000, and 1,050 feet are Devonian;samples from 710 to 850 feet are Silurian. The Ouachita System Sample descriptions in files of the Bureau of Economic Geology report radiolarians in the intervals 850 and 940-945 feet. Samples 850, 935, and 940 feet are described as red, green, and maroon slate, spiculiferous and cut by veins; 945 and 950 feet are spiculitic gray and green chert; 1,000, 1,050, and 1,216 feet are black chert, dolomitic, spiculitic, bituminous, and cut by quartz veins. These last three samples are almost surely Bigfork chert. Goldstein (1955) reported the following determinations: in Paleozoic (Stanley?) at 811 feet, in Missouri Mountain (?) at 940 feet, in Bigfork at 1,000 feet, last sample (1,050) in Bigfork. He noted that the samples may be mixed. The sequence is composed mostly of siliceous shale and chert of Ouachita facies containing spines and radiolarian tests. Rocks include dark, micaceous siliceous dolomitic shale containing angular quartz sand and fragments of quartz mosaic, and dark, argillaceous chert rich in organic material. One section marked 950 feet is an angular argillaceous feldspathic quartz sandstone which resembles Stanley; a section marked 1,050 feet is a fine-grained cherty limestone containing a trace of glauconite whichsuggests MarbleFalls lithology.The presence ofMarble Fallsinthis wellwouldindicate an overthrust; the alternative and most likely interpretation is that this rock is a limestone of the Bigfork. Thewellpenetrated thefrontalzoneoftheOuachitabeltandiswestofShellNo.1Massie,inwhich an overthrust was intersected. Itis possible, therefore, that deeper drilling inthis area willdisclose a foreland section beneath an allocthonous Ouachita plate. — X-ray data. None. References.— Adkins and Arick (1930, pp. 18-20) ;Barnes (1948) ;Sellards (1928, p. 13; 1931b, p. 821; 1933, p. 187). Bureau of Economic Geology files. Personal communication :August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Bell. Well name.—B. F.Gilchrist No. 1Curb-Fee. Location.—Trimmer Creek School block, J. E. Evitts survey; 330 feet FNL, 330 feet FWL; 4 mi. S of Killeen. Elevation.— B2s feet. Totaldepth—2,o2s feet. Completed.—l949. — Top of Paleozoic rocks. 828 (?) feet. Elevation of Paleozoic rocks. 3(?) feet. — Thin section coverage (depth in feet). shell oil company: 1240-45. pan American petroleum corporation: 1215-20, 1220-25, 1270-75, 1350-55, 1450-55, 1455-60, 1500-05, 1585-90, 1665-75, 1720-25, 1795-1805, 1870-75, 2010-15. — Description of Paleozoic rocks. The sequence consists of dark chert containing organic material, commonly dolomitic, dark siliceous shale rich in organic material, and fine-grained pyritic siliceous dolomitic limestone, locally spiculitic. The rocks are typical Bigfork. There is no visible metamorphism. ThiswelliswithinthefrontalzoneoftheOuachita belt. — X-ray data.-None. — References. Personal communication: J. B. Souther, Pan American Petroleum Corporation, 1956. — County.-Bell. Well name.—]. B. Hartman No. 1B. F. Warrick. Location.—Abner Webb survey; 135 feet FSL, 1,000 feet FEL, 6.8 mi. NW ofJarrell. — —— Elevation. 944 feet (by aneroid barometer). Total depth. 2,807 feet. Completed. 1925. — Top of Paleozoic rocks. 973 feet. Elevation of Paleozoic rocks. 29 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1560, 2320 (2), 2440, 2515, 2520. — Description of Paleozoic ricks. According to Sellards (1931b), two wells on the Warrick ranch in southern Bell County passed through slickensided black somewhat schistose shales and greenish quartzitic sandstone from the base of the Cretaceous at or near 973 feet to 1,373 feet in one well and 2,772 feet inthe other, and the section is probably Stanley-Jackfork. The sequence is composed of angular, poorly to fairly well-sorted, argillaceous feldspathic quartz sandstone containing garnet in the heavy mineral fraction and dark shale;quartz veinlets are common. The rocks are unmetamorphosed Ouachita facies showing typical Stanley lithology; cf. Bell Williams No. 1 Warrick. This well penetrates the frontalzone of the Ouachita belt. X-ray data.—None. References— Sellards (1928, p. 16; 1931b, p. 826; 1933, p. 188). Samples areinBureau ofEconomic Geology WellSample Library. Bureau ofEconomic Geology, The University of Texas — County. Bell. Wellname.—].B.Hartman No.2B.F.Warrick. — Location. 6.8 mi. NW of Jarrell. Elevation.—9oo± feet. Totaldepth.— 2,ll2 feet. Completed— ni. — Top of Paleozoic rocks. 973 feet. Elevation of Paleozoic rocks. 73± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. See No. 1Warrick, page 217. — X-ray data. None. — References. See No. 1Warrick, page 217. — County. Bell. — Wellname. A.B.Johnson No.1F. C.Howard. Location—-W'. P. Johnston survey; 80 feet FNEL, 1,900 feet FNWL; 2l2l/2 mi. Sof Moody. — Elevation. 729 feet, derrick floor; 725 feet, ground. Total depth.—2,264 feet. Completed. —1951. — Top of Paleozoic rocks. 1,415 feet. Elevation of Paleozoic rocks. 686 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1420-30, 1470-80, 1550-60, 1900-10, 2200-10. — Description of Paleozoic rocks. The sequence in this wellis composed of fine-grained, mostly angular, poorly sorted, argillaceous micaceous feldspathic quartz sandstone and dark shale; angular garnet is present in the sandstones in some intervals. The rocks are veined with calcite. The lithology is Stanley. This wellpenetrated unmetamorphosed Stanley shale in the frontal zone of the Ouachita belt. X-raydata.—l>Ch>ML>X;10/7 —1;F=20; SR=1.8. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. — County. Bell. — Wellname. MellonOilCompany No.1Noah Bailey. — Location. James Evitts survey;7mi. S,4mi.EofKilleen. — —— Elevation. 700 feet (by aneroid barometer). Total depth. 3,790 feet. Completed. Before 1928. — Top of Paleozoic rocks. 798 feet. Elevation of Paleozoic rocks. 98 feet. — Thin section coverage (depth infeet). pan American petroleum corporation: 860, 1761-1822, 1920, 2640-55, 2655-75 (2), 2740, 2890-2915, 3015-22, 3350-60, 3540-50, 3645-55, 3678-82, 3770-73. bureau of economic geology: 1920, 3370-80, 3380-85 (5), 3390-00, 3470-75, 3475-80, 3480-85, 3485-00 (2), 3500-05 (2), 3505-10, 3540-45 (6), 3540-50 (2), 3550-60 (2), 3560-70 (2), 3570-80, 3575-80 (2), 3590-05 (4), 3605-15 (4), 3615-25 (2), 3625-40 (2), 3640-45 (2), 3640-50 (4), 3645-50 (2), 3650-55 (2), 3655-60 (2), 3660-72, 3690-95, 3695-00, 3720-25, 3728-32, 3735-40, 3750-55, 3770-73, 3785-90. — DescriptionofPaleozoicrocks. Sellards(1931b),referringtoMiser,reportedthatthiswellentered black shales at 860 feet, and that these shales are probably Stanley. At 2,500 feet the wellencountered novaculite of probable Devonian age. Stanley was encountered again between 2,930 and 3,160 feet due to complicated folding. The well terminated in novaculite. Miser was quoted as follows: "Samples from this well from depth 2,500-3,800 are chiefly and possibly entirely novaculite although itis possible that due to complicated folding the Stanley shale may come into the section at approximately 2,930 to 3,160 feet. The samples immediately under the Cretaceous in this wellat 860 and at about 1,900 are regarded as Stanley. The brown shale at 2,640 to 2,655 is not exceptional for the Devonian since brown shales are found occasionally in the upper part of the novaculite. Fossils were found from 3,640-3,650." Sample descriptions in trie files of the Bureau of Economic Geology report that radiolarians were found in the intervals 2,640-2,670, 2,730-2,740, 2,750-2,760, 2,850-2,860, 3,310-3,400, 3,490-3,500, 3,520-3,540, and 3,640-3,650 feet. Goldstein (1955) reported first sample in Paleozoic (Stanley) at 860 feet, base of Stanley at 2,640 feet,topofBigforkat3,500( ?)feet, totaldepth3,790 feetinBigfork. The sequence is composed of angular to subangular, poorly sorted, chloritic and micaeous feldspathic quartz sandstone, dark shale, and metashale overlying a dominantly siliceous section. In the upper part, the siliceous section is composed of light and dark cherts, commonly argillaceous, micaceous, anddolomiticand/orsideritic,anddarksandychloriticandmicaceous metashale;thechertsare fractured and cut by quartz veinlets. The main part of the siliceous section is composed of greenish, The Ouachita System pyritiferous argillaceous dolomitic and/or sideritic chert and siliceous shale withlesser amounts of dark, red and brown silty shale; these rocks are veined with quartz, quartz-chlorite, and chlorite and contain radiolarians, spores, and dark organic material. Toward the bottom of the sequence the cherts are darker and contain more organic material. The section is Ouachita facies and the shales show local incipient to very weak metamorphism. The upper greenish cherts are similar to the Arkansas novaculite, but the dark cherts toward the bottom are more typically Bigfork;the sandstone and shale at the top of the Paleozoic sequence are Stanley. This wellpenetrated the frontal zone of the Ouachita beltina structurally complex area. Shell No.1 Massie, about 2 miles to the southeast, intersected a thrust beneath Ouachita facies rocks and bottomed inforelandrocks; deeper drillingintheareaofMellonNo.1Baileymightencounter forelandrocks. — X-ray data. None. References.— AdkinsandArick(1930,pp.18-20,86);Barnes(inSellards,1933,pp.134-135; 1948); Goldstein and Reno (1952, p. 2285) ;Sellards (1928, pp. 4-11; 1931b, p. 821; 1933, p. 135). Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bell. — Well name. Nolan Bell OilCompany No. 1WilliamBacon. — Location. Vincent Evans survey; 3.9 mi. W of Nolanville, 6.4 mi. E of Killeen, 0.6 mi. S of public road. — —— Elevation. 820 feet (by aneroid barometer). Total depth. 2,962 feet. Completed. 1928. — Top of Paleozoic rocks. 905± feet. Elevation of Paleozoic rocks. 85± feet. — Thin section coverage (depth in feet). bureau of economic geology: 1100-10. — Description of Paleozoic rocks. Sellards (1928) described the Paleozoic section as black slaty shale. The single section examined is a very dark, slightly calcareous siliceous (?) shale. There are no indications of metamorphism. The well penetrated the frontal zone of the Ouachita belt; more informationisavailableonacompanion well,theNo.2Bacon. — X-ray data. None. References.— Adkins and Arick (1930, pp. 13, 86);Sellards (1928, pp. 2-3). Samples are inBureau of Economic Geology WellSample Library. — County. Bell. — Well name. Nolan Bell OilCompany No. 2 WilliamBacon. — Location. VincentEvans survey;3.9mi.W.ofNolanville,6.4mi.E.ofKilleen,0.6mi.Sofpublic road. — — Elevation. 820 feet (by aneroid barometer). Total depth.—1,820 feet. Completed. 1928. — Top of Paleozoic rocks. 896 feet. Elevation of Paleozoic rocks. 76 feet. — Thinsection coverage (depth infeet). shelloilcompany: 1805-15, 1815-20. bureau of economic geology: 1820. — Description of Paleozoic and igneous rocks. According to Sellards (1931b), the Bacon well in Bell County [whether this was the No. 1 Bacon or the No. 2 Bacon was not specified] entered a black shale which contains graptolites;these were identifiedbyE. O.TJlrich as probably Ordovician but possibly ranging as high as the base of the Silurian. Adkins and Arick (1930, p. 13) described the sequence in the No. 2 Bacon as indurated black shale overlying a dark greenish crystalline rock; there was some discussion as to whether a sample at 1,100 feet might be Ellenburger, withthe weight of opinion in the negative. A complete sample description by H. T. Kniker and E. B. Stiles was given in Sellards (1928, p. 3) in which itwas suggested that the crystalline rock might be pre-Paleozoic withthe overlying rocks Ellenburger and Barnett. — Allof the thin sections examined for this study (see above) were altered igneous rock fine-grainedolivine gabbro and augite-biotite microsyenite ;undoubtedly, this is the dark greenish crystalline rock referred to inthe sample descriptions. Wells immediately to the south of the Bacon wells (Gilchrist No. 1Curb-Fee, Mellon No. 1Bailey) penetrated Ouachita facies Ordovician rocks; the presence of the Ordovician graptolites noted by Sellards (1931b) therefore indicates that the black shales in the Bacon wells are Ouachita facies Ordovician rocks. The igneous rock in the No. 2 is probably a younger intrusion rather than Precambrian basement. The presence of olivine gabbro suggests a relationship to the Cretaceous-Tertiary basic intrusives of the Balcones fault zone, the nearest of which occur to the south in Williamson andTraviscounties (p.Ill);deepwellsintheOuachitabelttothenorthinCoryellCountyandto the southeast in Bell County were in sedimentary rocks at total depth of 9,275 and 7,927 feet (No. 1 Bureau ofEconomic Geology, The University of Texas Day and No. 1Massie, respectively) and make itvery unlikely that Precambrian basement rocks were encountered at such a shallow depth as 1,800 feet. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data.-None. References.— Adkins and Arick (1930, pp. 13, 86);Barnes (1948);Sellards (1928, pp. 3-4; 1931b, p. 827; 1933, p. 187). Samples areinBureau ofEconomic Geology WellSample Library. — County. Bell. — Wellname. Petoskey OilCompany No.1John Kolls. — Location. 2% mi. NW of Belton. — —— Elevation. 625 feet (from topographic map). Total depth. ni. Completed. Before 1930. — — InPaleozoic rocks. 1,170 feet. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth infeet). bureau of economic geology: 1800±. — Description of Paleozoic rocks. Sample descriptions inthe files of the Bureau of Economic Geology for the intervals 1,170, 1,187, 1,190, 1,193, 1,197, and 1,198 feet show that the sequence is composed of dark gray shale and sandstone. The single sample examined in this study is dark red, hematitic metashale, locally brecciated and extensively veined withquartz;metamorphism isincipient. This well probably penetrated the frontal zone of the Ouachita belt; the rocks appear to be in cipiently metamorphosed Stanley, but the sample is insufficient for a positive identification. — X-ray data. None. — References. Adkins and Arick (1930, p. 86). Bureau of Economic Geology files. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bell. — Well name. Rio Grande OilCompany No. 1. D. W. Hair. — Location. LewisWalker survey; 2X,42X,4 mi.NEofBelton. — —— Elevation. 625 feet (from topographic map). Total depth. 2,002 feet. Completed. 1929. — Top of Paleozoic rocks. 1,157± feet. Elevation of Paleozoic rocks. 532± feet. Thin section coverage (depth in feet).—bureau of economic geology: 1305-1310, 1305+. — Description of Paleozoic rocks. Sellards (1931b) described the sequence as black shale and grayquartzitic sandstone. Thin section examination shows fine-to medium-grained, angular, very poorly sorted, slightly argillaceous micaceous feldspathic quartz sandstone veined by quartz-bitumen and containing angular garnet in the heavy mineral fraction; the lithology is Stanley. There are indications of incipient metamorphism. This well penetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Adkins and Arick (1930, pp. 17, 86);Barnes (1948);Sellards (1931b, p. 821; 1933, p. 187). Samples are inBureau of Economic Geology WellSample Library. — County. Bell. — Wellname. Shambeck and Casey No.1Sudie Baugh. — Location. E&Fsurvey,Arochagrant; 8mi.E.ofTemple. —— Elevation. 590 feet, derrick floor; 584 feet, ground. Total depth.—4,473 feet. Completed. 1953. Top of Paleozoic r0ck5.— 3,360 feet. Elevation of Paleozoic rocks. 2,770 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4000-10, 4010-20, 4090 4100, 4190-4200, 4240-50 (2),4340-70 (2),4410-20, 4450-60. Description of Paleozoic rocks.—Top of Paleozoic and Pennsylvanian rocks was established at 3,360 feet according to operator (Fowler, 1955). This sequence is composed of (1) dark, fine-grained, angular, poorly sorted, dolomiticcarbonaceous chloritic micaceous feldspathic quartz sandstone containing abundant rock fragments (slate, chert, quartz mosaic);(2) dark, fine-grained, angular, dolomitic carbonaceous chloritic micaceous felds pathic quartz siltstone; (3) dark, micaceous chloritic silty metashale; (4) in the 4,340 to 4,370-foot The Ouachita System interval —light-colored, microgranular to cryptocrystalline chert (Arkansas novaculite type) containing a few relict radiolarian tests and spicules, and in the 4,410 to 4,420-foot interval—dark, fine- grained dolomite. The dark, fine-grained dolomitic clastic sequence is similar to the section encountered in other wellsin this area, but the presence of Arkansas novaculite fragments is difficultto explain;one possible answer is that the sequence of fine, dark elastics is a near-source facies of the chert sequence and that thin chert beds persist in this eastern area (p. 78). Degree of metamorphism is difficult to assess in these rocks because of the obscuring effect of the carbonaceous debris, but it appears to be lower than in other rocks in this part of the frontal zone; metamorphism is estimated as incipient ( ? ). This well penetrated incipiently metamorphosed dark clastic Ouachita facies rocks in the interior part ofthe frontal zone of the belt. = X-raydata.—l>Ch;10/7 —1;F 20;SR=3.8. — References. Personal communication: P. T. Fowler, Shell Oil Company, 1955. — County. Bell. — Wellname. ShellOilCompany No.1C.E.Massie. — Location. Wm. Leftwich survey; 12mi. SW of Belton. Elevation.—624: feet. Total depth— l,92l feet. Completed.— l9s6. — Top of Paleozoic rocks. 720 feet. Elevation of Paleozoic rocks. 96 feet. — Thin section coverage (depth in feet).-bureau of economic geology: 790-00, 850-60 (2), 920-30 (2), 1780-90 (2), 2480-90 (2), 3000-10 (2), 4210-20 (2), 4270-80 (3), 4760-70 (3), 5060-70 (2),6130-40 (2),6650-60 (2),7130-40 (2). — Description of Paleozoic rocks.-Because of apparent structural complexity the following identi fications are tentative. They are based on Shell Oil Company descriptions and identifications modified by Bureau of Economic Geology sample descriptions and thin section studies: Stanley, 720 to 4,700± feet; Arkansas novaculite, 4,700± to 4,800± feet; probable fault, 4,800± feet; probable Womble (possibly including Bigfork), 4,800dt to 5,050 feet; major tectonic break, probably an overthrust, 5,050 feet; Atoka-type Pennsylvanian, 5,050 to 6,350 feet; mixed lithologic types including Marble Falls, Barnett-Chappel, and Ellenburger, 6,350 to 6,700 feet; Ellenburger, 6,700 to 7,927 feet total depth. The Stanley inthis wellis composed of fine-grained, angular, poorly sorted, feldspathic quartz sandstone, locally argillaceous, and containing a high percentage of garnet inthe heavy mineral fraction, and dark silty shale and metashale, locally containing carbonaceous debris; quartz, quartz-bitumen and quartz-calcite veinlets are common. The shales are commonly contorted. The interval 4,760 to 4,770 feet contains green cryptocrystalline chert;some fragments are argillaceous and some contain elliptical carbonate bodies. The chert is cut by quartz and quartz-chlorite veinlets, and some of the quartz veinlets have bituminous centers. This green chert is identified as Arkansas novaculite. Dark,micaceous metashale beneath the green chert is tentatively considered to be Womble. Atoka beds are fine-grained, angular to subround, poorly sorted, argillaceous calcareous feldspathic quartz sandstone and dark, silty shale. The interval 6,130 to 6,140 feet in the mixed section is comprised of fossiliferous dolomitic calcilutite and dark spiculitic dolomitic argillaceous chert rich in organic material (possibly Marble Falls). The Ellenburger section is composed of fine granular dolomite, dolomitic calcilutite, and calcareous dolomite. This wellpenetrated the frontalzone of the Ouachita belt, intersected an overthrust, and bottomed in foreland Ellenburger dolomite. The shales in the allochthonous Ouachita plate show incipient meta morphism. Shell No. 1 Massie demonstrates that deep drilling inthe area of its location willencounter foreland rocks. — X-ray data.--Arkansas novaculite, Womble, and Atoka allhave relatively similar clay suites: I]> Ch — >ML; 10/7 —1; SR = 1.6 (Atoka). Ellenburger and Chappel are similar: I>ML>Ch; 10/7 8; SR = 1.0. — References. Personal communication :R. P. Maner and E. J. Theessen, Shell Oil Company, 1956. Samples are inBureau ofEconomic Geology WellSample Library. — County. Bell. — Well name. U.S. ArmyNo.1McCloskey Hospital Water Well. — Location. McCloskey Hospital. — Elevation. 678 feet. Total depth.— 2,323 feet. Completed.— -1944. — TopofPaleozoic rocks. 2,318 feet.ElevationofPaleozoic rocks. 1,640 feet. Thin section coverage (depth infeet).—bureau ofeconomic geology: 2319±. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology report hard, tough, gray, laminated, metamorphosed shale cut by quartz veins. Bureau ofEconomic Geology, The University of Texas The single sample examined in this study is dark silty hematitic chlorite-sericite metashale or clay- slate veined with quartz and calcite; locally the rock is brecciated. Metamorphism is very weak. The well penetrated very weakly metamorphosed dark clastic Ouachita facies rocks in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. Samples are inBureau ofEconomic Geology Well Sample Library. — County. Bell. — Wellname. J.E. Winans &Forbes No.1Ferguson. — Location. James Bowers survey; 7 mi. NW of Belton. — — Elevation. 550 feet (from topographic map). Total depth.—1,780 feet. Completed. 1929. — TopofPaleozoic rocks. 821±feet.Elevation ofPaleozoic rocks. 271±feet. — Thin section coverage (depth in feet). bureau of economic geology: 1294, 1320, 1367, 1406, 1512, 1745. — Description of Paleozoic rocks. Sellards (1931b) reported that cores at intervals from 1,200 to 1,700 feet are prevailingly of noncalcareous black shales and quartzitic sandstones; the rock is cut by calcite veins and the shale shows slickensiding. He concluded that the sequence is Stanley-jack fork. Thin sections show that the sequence is composed of dark silty shale and fine-grained, angular, poorly sorted, argillaceous and chloritic feldspathic quartz sandstone veined with quartz-calcite and containing abundant angular garnet inthe heavy mineral fraction. The rocks are Stanley. Some of the samples show incipient metamorphism. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. (1948) ;Sellards (1931b, p. 821; 1933, p. 187). References.— Adkins and Arick (1930, p. 86);Barnes Samples areinBureau ofEconomic Geology WellSample Library. County.— Bell. Additional wells not shown on map (PI. 2) and not studied because of lack of samples or basic data: — W. S. StanfieldNo.2Ludwick Location: 1 mi. NNE of Bland. Elevation: 600 feet (topographic map). Total depth: 1,510 feet. Completed: 1924 (? ).Topof Paleozoic rocks: 1,200 feet. — Killeen-BellOilCompany No.1Swope Location: (?). Elevation: 888 feet (aneroid barometer). Top of Paleozoic rocks: 850 feet or higher. "Pyritic micaceous gray sandstone on dump." U. S. ArmyNo. 2Wilson— Location: NW of Belton. Elevation: 532 feet. Total depth: 964 feet. Completed: 1942. Top of Paleozoic rocks: 945 feet. "Red, brown and green shales and micaceous schist." — U.S. ArmyNo.1Bloomer Location: 3 mi. NW of Belton. Elevation: 533.5 feet. Total depth: 999 feet. Top of Paleozoic rocks: 982 feet. "Red, brown and green clays and sandy shales." U. S. ArmyNo. 1Odell— Elevation: 603.4 feet. Completed: 1941. U. S. ArmyNo.1Safely— Elevation: 547.7 feet. Total depth: 932 feet. Top of Paleozoic rocks: 925 feet. "Dark blue, brown and red shales." — U. S. ArmyNo. 1Jarrell Location: 3% mi. SW of Belton. Totaldepth: 956 feet. Top of Paleozoic rocks: 939 feet. — C.J.Foster DrillingCompany No.1G.W.Tyler Est. Location: O. T. Tyler survey; 3,045 feet FNWL, 1,150 feet FNEL (Leon River), % mi. E of Belton. Elevation: 513 feet. Total depth: 1,720 feet. Completed: 1953. — Layne-Texas No.3 Cityof Temple Elevation: 528 (?) feet. Total depth: 1,259 feet. Completed: 1951. — Meyers &Sons No.1Brazos RiverElectric Totaldepth: 1,358 feet. Completed: 1948. The Ouachita System — Meyers & Sons No. 1Sanderford Total depth: 822 feet. Single sample in Bureau of Economic Geology Well Sample Library (797 to 822 feet) is fine-grained, angular, poorly to fairly well-sorted, chloritic feldspathic quartz sand stone, probably Stanley. — County. Bexar. — Wellname. Anderson-Prichard OilCorporation No.1E.H.Yturri. — Location. Adam Stafford survey; 10 mi. SE of San Antonio. Elevation.—s9Bfeet. Totaldepth—4,301feet. Completed.—l94B. — Top of metamorphic rocks. 4,260 feet. Elevation of metamorphic rocks. 3,662 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 4298. bureau of economic geology: 4268, 4276. — Description of metamorphic rocks. The sequence is composed of fine-grained sericitic dolomitic metaquartzite and chloriticsericite phyllite; locally the rock is a quartzose dolomite marble. Some of the fragments contain opaque graphitic ( ? ) material and some are cut by quartz and dolomite vein- lets. One phyllite fragment contains abundant fine rutile needles. Metamorphism is low grade witha high shearing component ;foliationis expressed insheared micas and stretched grains. This wellpenetrated theinterior zone of the Ouachita structural belt. —' X-raydata.—l>Ch>ML;10/7 1. — References. Personal communication: P. T. Fowler, Shell OilCompany, 1955; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bexar. — Wellname.— Arkansas FuelOilCompany No.1GeorgeBurkhardt. Location. Alfonso Steele survey; from N cor. of Manjaros survey SSE 3,000 feet along its NEL, thence 330feetENEtolocation;7mi.NEofElmendorf. Elevation.—s63 feet. Totaldepth.—s,o97 feet. Completed.—-1947. — Topofmetamorphic rocks. 5,060 feet.Elevation ofmetamorphic rocks. 4,497 feet. — Thin section coverage (depth in feet). bureau of economic geology: 5000-15, 5045-60, 5090-95, 5095-98. — Description of metamorphic rocks. The sequence is made up of sericitic metaquartzite and sericite chlorite phyllite; the metaquartzite is composed of large unreduced augen of quartz in a matrix of finer crushed and granulated quartz containing scattered rhombs and cross-cutting veinlets of dolomite. One fragment of phyllite contains garnet. Except for the presence of garnet, metamorphism appears tobelowgradewithahighshearing component;structures arefoliationwithgrainstretching and deformation. There are two possible explanations for the presence of garnet in these rocks: (1) The rocks were at one time of higher metamorphic grade and were subjected to retrograde metamorphism during extreme shearing; muscovite and possibly potassium feldspar were converted to sericite. In such retrograde reactions, however, garnet commonly is converted to chlorite and there is no evidence that the garnet has undergone retrogressive metamorphism. (2) The garnet in these rocks may be a manganese garnet stable at lower temperatures than the common almandine garnet of regionally metamorphosed terranes. This wellpenetrated the interior zone of the Ouachita structural belt. — X-ray data. I> Ch; 10/7-—'1; (poor pattern). — References. Personal communication: J. K. Rogers, Arkansas Fuel OilCompany, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Bexar. — Well name. Bur-Kan Petroleum Company and Stanolind Oiland Gas Company No.1Lee Hubbard. — Location. Block 75, Ignacio Tejada grant (Wm. Miller survey) ;660 feet FSL, 660 feet FEL of Lot7;2mi. Eof Lytle. Elevation.—-735 feet, derrick floor; 725 feet, ground. Total depth.— s,2o3 feet. Completed.— l94B. — Top of metamorphic rocks. 4,940 feet. Elevation of metamorphic rocks. 4,205 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4960^70, 5040 -50,i5100-10, 5150-60, 5190-00. — Description of metamorphic rocks. The sequence is composed of pyritic calcareous sericite-chloriteepidote phyllite and amphibole-epidote phyllite or very fine-grained schist. The rock is veined by massive calcite. Crumpling, wrinkling, contortion, and grain stretching are common. The general plane of the foliation dips about 45 degrees in a core. Metamorphism is low grade with a high shearing element. Bureau ofEconomic Geology, The University of Texas The wellpenetrated the interior zone of the Ouachita structural belt. — X-raydata. Ch;F=20 (MLfromcaved material?):amphibole. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; J. B. Souther, Pan American Petroleum Corporation, 1955, 1956. — County. Bexar. — Wellname. Fair and WoodwardNo.1Pauline Lyro. Location—J.M.Bustillossurvey; 660feetFSEL,660feetFNEL;1mi.NofSt.Hedwig. — — Elevation. 602 feet, derrick floor;592 feet, ground. Total depth.—4,607 feet. Completed. 1946. — Top of metamorphic rocks. 4,433 feet. Elevation of metamorphic rocks. 3,831 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4466-77, 4488-4501, 4501-13, 4535-46. — Description of metamorphic rocks. The sequence is composed of chlorite-sericite phyllite and chloritic sericitic metaquartzite ;the rocks are cut by both pre-shearing and post-shearing quartzveinlets. Locally, the foliation is thrown into microfolds. Metamorphism is low grade with a high shearing element. This wellpenetrated the interior zone of the Ouachita structural belt. — X-ray data. None. — References. Personal communication: P. T. Fowler, Shell OilCompany, 1955; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomicGeology WellSampleLibrary. — County. Bexar. — IFellname. Gas Ridge Syndicate (Clark OilCompany) No.1Pepper. Location.—Bßß&Csurvey; 200FEL,1,200 feetFSL; 14mi.WofSan Antonio. Elevation—93s feet. Totaldepth.— 3,7B3 feet. Completed.—l92l. — Topof Paleozoic rocks. 2,845 feet. Elevation ofPaleozoic rocks. 1,910 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1963-68, 1987-98, 2579-82, 2903-09, 2905-09, 2985-91, 3308, 3402-14, 3475-80, 3480-90, 3540-57 (2), 3568-80, 3629 (3), 3676-80 (2), 3702, 3748, 3770-76. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Ge ology show a sequence of indurated, black, slightly micaceous sandy shale, locally slickensided, with gray sandstone abundant toward the bottom;fragments of white calcite and milky quartz veinmaterial are present. The sequence is composed of unmetamorphosed, fine-grained, angular, poorly sorted, argillaceous chloritic micaceous feldspathic quartz sandstone and arkose, commonly dolomitic, argillaceous micaceous siltstone, and dark, silty shale. Carbonaceous material is common in the shales. The rocks contain abundant veinlets of quartz, quartz-dolomite, and quartz-chlorite, and massively veined rocks show incipient metamorphism. Sellards (1931b) identified this section as probably Stanley-Jackfork. This wellpenetrated the southern part of the frontal zone of the Ouachita belt; the extensive veiningand high percentage ofquartz sand of probable metamorphic origin (stretched quartz mosaic fragments; abundant composite grains and grains withundulose extinction) and of vein origin indicate the proximity of a metamorphic terrane which could only be to the south. The rocks are probably upper Paleozoic Ouachita facies. — X-ray data. None. References.— Sellards (1931b, p. 822; 1933, p.188). Personal communication: P. T. Fowler, Shell Oil Company, 1955; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Bureau of Economic Geology files. Samples are inBureau ofEconomic Geology WellSample Library. — County. Bexar. — Wellname. General Crude OilCompany No.1Rogers Ranch. Location.—]. S. Collard survey; 1,100 feet FWL, 1,950 feet FNL; 8 mi. W of San Antonio. — —— Elevation. 812 feet, derrick floor; 801 feet, ground. Total depth. 5,896 feet. Completed. 1954. — Top of metamorphic rocks. 2,560 feet. Elevation of metamorphic rocks. 1,748 feet. The Ouachita System — Thin section coverage (depth in feet). bureau of economic geology: 2673, 2676, 3055-60, 3160, 3161, 3170 (2), 3267-68, 4081, 5713, 5894 (2), 5895. shell oil company: 5713-23 (3), 5893-96. — Description of metamorphic rocks. The upper part of the sequence, through the 5,713-5,723-foot interval, is composed of dark carbonaceous (graphitic?) sericitic and chloritic slate and dark, slaty, carbonaceous sericitic chloritic feldspathic metasiltstone ;quartz and carbonate veins are abundant. The following structures were observed: bedding, incipient foliation, microfolding and microfaulting, parallel shear planes, contortion, and convolution. In the 5,713-foot interval the slate includes large augen of brecciated chlorite-biotite-albite granodiorite, locally sericitized; their inclusion in the slate combined withthe other structures indicates extreme shearing, probably associated with overthrusting (PL 2). The slate sequence in general shows weak regional metamorphism with extreme shear and extensive soaking by vein-forming solutions; in many samples the widespread hydrothermal effects make it difficultto assess regional metamorphism. The slate sequence lies on almost completely sericitized and chloritized andesite. This rock consists of relict plagioclase laths invarious stages of sericitization in a mass of chlorite speckled with sphene leucoxene and extensively invaded by quartz. Itis not known whether the slate sequence is in fault contact, depositional contact, or intrusive contact with the igneous section. This well penetrated highly sheared rocks of the black slate belt inthe interior zone of the Ouachita structural belt immediately south of the Luling overthrust front. — X-raydata.—l>Ch;10/7 1.3;F=20;SR=3.8. — References. Personal communication: J. B. Souther, Pan American Petroleum Corporation, 1955. Cores areinBureau ofEconomic Geology WellSample Library. — County. Bexar. Well name.— General Crude OilCompany No. 1J. H. Talley. — Location. T.R.Edmondson survey; 14mi. W ofSan Antonio. —— Elevation. 881 feet. Total depth. 2,622 feet. Completed.—-1954. — TopofPaleozoic rocks. 2,600 feet.ElevationofPaleozoic rocks. 1,719 feet. Thin section coverage (depth infeet).—bureau of economic geology: 2615-22 (2). — Description of Paleozoic rocks. The single sample examined in this study is fine-grained, angular, poorly sorted, argillaceous micaceous feldspathic quartz sandstone veined by quartz and carbonate; the rock is probably upper Paleozoic Ouachita facies;there isno metamorphism. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. B. Souther, Pan American Petroleum Corporation, 1955. A coreisinthe Bureau ofEconomic Geology Well Sample Library. — County. Bexar. — Well name. Hickok &Reynolds No. 1Ewert. — Location. Thomas Yorksurvey; 6,750 feet E ofELof Sarah Taylorsurvey, 1,150 feet SW of SWL of BBB&Csurvey;15mi.NW ofSan Antonio. — —— Elevation. 995 feet. Total depth. 3,004 feet. Completed. 1938. — TopofPaleozoic rocks. 2,630 feet.Elevation ofPaleozoic rocks.—-1,635 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2640-50, 2650-2704, 2715-30, 2820-30, 2969-73. shell oilcompany: 2640-50. — Description of Paleozoic rocks. Sample log (P. S. Morey, Bureau of Economic Geology) shows top of Pennsylvanian at 2,640 feet in dark gray to black shaly sandstone. Sample descriptions in Bureau of Economic Geology files report the interval 2,630 to 3,014 feet total depth as sandstone. Thin section examination shows that the sequence is composed of fine-grained, angular, poorlysorted, argillaceous micaceous feldspathic quartz sandstone cut by quartz veinlets; the rocks are probably upper Paleozoic Ouachita facies. Locally, the presence of new chlorite suggests incipient metamorphism. This well penetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology Well Sample Library. Bureau ofEconomic Geology, The University of Texas — County. Bexar. — Wellname. Mid-TexProduction Company No.1C.G.Walker. Location.—S. N. Dobie survey; 3,100 feet FNEL, 3,300 feet FNWL; 10 mi. Nof San Antonio. — Elevation.— -840 feet, derrick floor. Total depth. —2,132 feet. Completed. 1935. Top ofPaleozoic rocks.—2,110(?) feet.ElevationofPaleozoic rocks. 1,270(?) feet. — Thin section coverage (depth infeet.) shell oilcompany: 2118-24. — Description of Paleozoic rocks. Descriptions of samples in the Bureau of Economic Geology files show very black shale or slate withsome quartz in the interval 2,116 to 2,132 feet. The single section examined in this study is fine-grained, angular, poorly sorted, micaceous feldspathic quartz sandstone cut by quartz-calcite veinlets; rocks are upper Paleozoic Ouachita facies with incipient metamorphism. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. Samples are in Bureau of Economic Geology Well Sample Library. — County. Bexar. — Wellname.-H.A.Pagenkopf No.1MaxBlum. Location.—MariaF.Rodriguez survey;400feetFWL,4,800 feetFNL;10mi.SWofSanAntonio. — —— 714 feet. Totaldepth. 7,179 feet. Completed. 1946. Top of Paleozoic rocks. 4,580 feet. Elevation of Paleozoic rocks. 3,866 feet. Elevation. — — Thin section coverage (depth in feet). bureau of economic geology: 4760-75, 4775-90, 50955110, 5643-50, 6090-6108, 6123-38, 6648-69, 6745-64, 7085-7113. — Description of Paleozoic rocks.-According to Goldstein (1955), the base of Cretaceous gravels andtopofJurassic(?) is3,900(?)feetwithtotaldepthat7,197feetinJurassic(?).Morgan(1952) remarked that this well passed from Comanche rocks at 4,500 feet into red and gray shale with thin sandstone and limestone beds to a total depth of 7,179 feet; he believed that the pre-Cretaceous section is Permo-Pennsylvanian on the basis ofsimilarity to the section inMagnolia No.1McKinleyin Frio County. The age of the lower unmetamorphosed clastic section inthis wellis stillbeing argued, but general stratigraphy and study of plant remains seem to support a Permo-Pennsylvanian age over a Jurassic age. This well is anomalous in that it penetrates an unmetamorphosed section of Paleozoic rocks (presuming the Permo-Pennsylvanian age is correct) in an area where other wells have encountered highly sheared and altered pre-Cretaceous rocks, mostly phyllites. The rocks are brown, red, and gray micaceous silty shale and fine-grained, angular, poorly sorted, micaceous calcareous sandstone; carbonaceous trash and plant fragments are present. Some fern and Lepidodendron fragments from 3s the 6,734 to 6,737-foot interval were identified as Pennsylvanian. The most reasonable explanation is that this wellpenetrated Paleozoic (probably post-Atokan) post-orogenic sedimentary rocks preserved ina downfaulted block withinthe deformed and metamorphosed terrane (p.125). — X-ray data. None. — H. J.Morgan (1952). References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; C. A.Stewart, Union Producing Company, 1956. Sample log by P. S. Morey, Bureau of Economic Geology. Samples are in Bureau of Economic Geology Well Sample Library. — County. Bexar. — Wellname. Reenlee OilCorporation No.1A.Theis. Location.—-L.Kneippsurvey; 660 feetFNWL,6,625 feetFNEL;3mi.SofWetmore. — —— Elevation. 806 feet, derrick floor. Total depth. 2,105 feet. Completed. 1955. —— Top of Paleozoic or metamorphic rocks. 2,060 feet. Elevation of Paleozoic or metamorphic rocks. -1,254 feet. ¦ — Thin section coverage (depth infeet). None. — Description of Paleozoic or metamorphic rocks. ni. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957; J. R. Sandidge, Magnolia Petroleum Company, 1957. Samples from upper part of well are in Bureau of Economic Geology Well Sample Library. 86Identification by R. W. Brown of the U.S. Geological Survey on core fragments submitted by John R, Sandidge of the Magnolia Petroleum Company. The Ouachita System — County. Bexar. Wellname.—Security DrillingCompany No.2Englemann. — Location. Juan Vasquez survey; 660 feet F most Ely NWL, 330 feet FNEL; 1mi. SW Selma. Elevation.—B3B feet, derrick floor. Total depth.— 2,sBl(?) feet; 2,682(?) feet. Completed— l9ss. Topofmetamorphic rocks.—2,480 feet.Elevationofmetamorphic rocks. 1,642 feet. — Thin section coverage (depth infeet).-None. — Description—of metamorphic rocks. ni. X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957; J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Bexar. — Well name. Union Producing Company No. 1L.S. McKean. Location.—Fernando Rodriguez survey; 4,500 feetFmost W'lyEL, 3,300 feet F most N'lyNWL. —— Elevation. 605 feet, derrick floor; 595 feet, ground. Total depth. —4,426 feet. Completed. 1949. Topofmetamorphic rocks.—4,370feet.Elevationofmetamorphic rocks. 3,765 feet. — Thin section coverage (depth infeet) None. — Description of metamorphic rocks. ni. — X-day data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957;C. A.Stewart, Union Producing Company, 1957. — County. Bexar. — Well name. U. S. Government No. 1Camp BullisWater Well. — Location. Camp Bullis Military Reservation, 14 mi. NNW of San Antonio, 5 mi. S of Leon Springs, on old—Gerter Estate. — Elevation. 1,050 feet (from topographic map). Total depth.—1,910 feet. Completed. Before 1919. TopofPaleozoic rocks.—1,770 feet. Elevation ofPaleozoic rocks. 720 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. J. A. Udden (Bur. Econ. Geol. files) described these samples as red,purple,green, darkgrayschist,locallyblackgraphiticschist,andveinquartz. In an early report, Sellards (1919) quoted Udden's determination that this well encountered dark gray graphitic schist;ina later report, however, he described the pre-Comanche sequence as "altered shale" (Sellards, 1931b). No samples were located, but from descriptions of the rocks, itis probable that the Camp Bullis well penetrated dark carbonaceous shale or metashale, possibly slickensided, veined withquartz. The age of the shale is unknown. From the location of the well (PI. 2), the rocks could be either upper or lower Paleozoic Ouachita facies. — X-ray data. None. References.— Sellards (1919, pp. 131-135; 1931b, p. 821. Bureau of Economic Geology files. — County. Bexar. — Wellname. U.S.Government No.1LeonSprings Water Well. Location.—Camp Stanley RifleRange, LeonSprings MilitaryReservation; 2mi.NEofLeon Springs. —— Elevation.—1,156 feet (from topographic map). Total depth. 2,500 feet. Completed. 1909. Topof Paleozoic rocks.—l,o46 feet. Elevation of Paleozoic rocks. [-110 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. In an early report, Sellards (1919) quoted a description by Alexander Deussen classifying the pre-Comanche rocks as "slate seamed with quartz." In a later report Sellards (1931b) described these rocks as "altered shale." Udden (1919) described them as dove-gray toblackslatymaterialseamedwiththinstraight quartzveins.DescriptionsbyUddenintheBureauof Economic Geology files, dated 1916, show a sequence composed of hard, gray to black fine-textured schist-like slickensided shale veined withquartz, locally micaceous, and withcleavage at an angle to the bedding; intwo intervals, one 1,750 feet, one unmarked, Udden described extreme deformation by irregular shearing with quartz veins complexly folded and faulted. In the Cretaceous conglomerate overlying this sequence (1,010 to 1,015-foot interval) he noted the presence of fragments of flint, Bureau of Economic Geology, The University of Texas greenish sandstone, vein quartz, agate, micaceous shale or schist, marble, quartzite, limestone, and slate. From available descriptions, it would appear that the rocks are dark hard carbonaceous Pennsylvanian shale or metashale veined withquartz. From the location of the well (PI.2), the rocks could be either upper orlowerPaleozoic Ouachita facies. — X-ray data. None. References.— Sellards (1919,pp.129-131;1931b,p.821);Udden (1919,p.127). Bureau of Economic Geology files. — County. Bexar. Well name.—]. M. West No. 1Timberlake. Location.—]. M.Urrighas survey; 1,650 feet FWL, 1,900 feetFNL;% mi.NofAltaVista. — Elevation. 573 feet. Total depth.—4,630 feet. Completed.— l94B. — Topof metamorphic r0ck5.—4,240 feet. Elevation of metamorphic rocks. -3,667 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4243-53 (2), 4263-73, 431020, 4420-30', 4500-10, 4600-10. — Description of metamorphic rocks. The sequence is composed of rutiliferous graphitic chloritesericite phyllite and phyllitic metaquartzite ;metamorphism is low grade with a high shearing element; principal structures are foliation, grain stretching, microfolding, contortion, and flowage around augen of quartz. The rocks are penetrated by both pre-and post-deformation quartz veins and probably the quartz augen are broken veins. This wellpenetrated the interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957;J.R.Sandidge, Magnolia Petroleum Company, 1957. Samples areinBureauofEconomic GeologyWellSample Library. — County. Blanco. — Wellname. Roland K.Blumberg No.1Wagner. Location.—Henry Manton League;1,980 feet FWL,1,320 feet FSEL (oflease). —— Elevation.—1,250 feet (fromtopographic map). Totaldepth. 3,318 feet. Completed. 1955. — Top of Paleozoic rocks. 130 feet. Elevation of Paleozoic rocks.— +l>l2o feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. This well penetrated Ellenburger rocks directly beneath the Cretaceous. According to Barnes (1956), top of Ellenburger is 130 feet, top of Cambrian sequence is at 1,940 feet, and at 3,318 feet, total depth, the wellis in the Cambrian Hickory sandstone. Thiswellpenetrated forelandrocksnorthoftheOuachitabelt. — X-ray data. None. References.— Barnes (1959, p. 348). Personal communication: V. E. Barnes, Bureau of Economic Geology, 1956; Robert Pavlovic, Magnolia Petroleum Company, 1955. — County. Blanco. — Well name. Theodore Hicks No.1AlbertSpecht. Location.— T. M.Fowler survey; 273 feet FWL, 3,355 feet FSL; 22 mi. Sof Johnson City. —— Elevation. 1,330 feet. Total depth. —1,635 feet. Completed. 1931. — — Top of Paleozoic rocks. 690 feet. Elevation of Paleozoic rocks. +640 feet. — Thin section coverage (depth in feet). bureau of economic geology: 718-80, 1180-1240, 1250, 1380, 1430, 1480. DescriptionofPaleozoic rocks.—DescriptionsinthefilesoftheBureauofEconomic Geologyreport dark sandy shale, 690 to 1,270 feet, and red and green shale, 1,270 to 1,430 feet. Sellards (1933) described these samples as "altered shale." The sequence consists of dark sheared and brecciated chert invaded by vein quartz and containing dark organic material, dark argillaceous and micaceous siltstone, dark silty shale, locally pyritic, and red hematitic shale. The shales are invaded by quartzveinlets, and locally small blebs of new chlorite indicate incipient metamorphism. Carbonized plant fragments and spore fragments were noted in some of the cuttings. The shale in the 1,430-foot interval contains ellipsoidal grains of "pleochroic" carbonate, possibly siderite, similar to that The Ouachita System seen in Turner No. 1 Linder in Kendall County. Ingeneral, the section consists of unmetamorphosed Ouachita facies rocks. A small fragment of microgabbro in the 1,430-foot interval is probably the result of contamination. This well penetrated Ouachita facies rocks of probable lower Paleozoic age in the frontal zone of the Ouachita belt. — X-ray data—I>X>ML>Ch; 10/7' ,0.9; SR=1.75. Chlorite-illiteshales of Ouachita structuralbelttypebutthese shalescontainmorekaolinitethanisfoundinwellsinthenorthernlimb of the belt. References.— Barnes (1948) ;Sellards (1933, p. 188). Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Blanco. — Well name. Johnson (R. A. Rodson et al.) No. 1Glasscock. Location.— W. W. McDonald survey; 600(?), 1,156(?) feet FNL, 600(?), 859(?) feet FWL; 8 mi. NofBlanco, 6.8 mi. S of Johnson City. Elevation.—l,3oo feet (from topographic map). Total depth.—l,oos(?) feet; 968(?) feet. Com- pleted.—-Before 1932. — Topof Paleozoic rocks. 704 feet. Elevation of Paleozoic rocks. (-596 feet. — Thin section coverage (depth infeet). bureau of economic geology: 954-958. Description of Paleozoic rocks.—According to Barnes (1956), this wellencountered Ordovician Ellenburger beds directly beneath the Cretaceous. The single section examined for this study was Ellenburger dolomite. This wellpenetrated foreland rocks north of the Ouachita belt. — X-ray data. None. References.— Barnes (1948) ;Sellards (1933, p. 192). Personal communication: V. E. Barnes, Bureau of Economic Geology, 1956; J. B. Souther, Pan American Petroleum Corporation, 1955. — County. Blanco. — IFellname. Johnson CityOilCompany No.1Waller (also known as Winan &Forbes No.1Bruckner, Bruckner Water Well). — Location. Z.J.Hemphillsurvey;1mi.SofJohnson City. Elevation.—l,2so feet. Totaldepth.—l,ss2 feet. Completed.—l929 and 1933. —— Top of Paleozoic rocks. 240 feet. Elevation of Paleozoic rocks. +l>olo feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. First sample at 240 feet is Ellenburger; last sample at 1,255 feet isEllenburger. This wellpenetrated forelandrocksnorthoftheOuachita belt. — X-ray data. None. References.— Barnes (1948) ;Sellards (1933, p. 192). Samples areinBureau ofEconomic Geology WellSample Library. — County. Blanco. — Well name. Lile and Adams No. 1 Leeder (also known as Adams &Lyles No. 1Leeders). — Location. NoelNixonsurvey;2%mi.N,3mi.WofBlanco. —— — Elevation.-ni. Total depth. 530 feet. Completed. Before 1932. —— Top of Paleozoic rocks. 405 feet. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. According to Barnes (1956), the entire Paleozoic section penetrated is Ellenburger. This wellpenetrated foreland rocks north of the Ouachita belt. — X-ray data. None. References.— Barnes (1948);Sellards (1933, p. 192). Personal communication :V. E. Barnes, Bureau of Economic Geology, 1956. Samples are inBureau ofEconomic Geology WellSample Library. Bureau ofEconomic Geology, The University of Texas — County. Blanco. Well name.—D. J. Meeks No.1E. W. Walker. — Location. Noel Nixon survey; 4,445 feet FNL, 1,000 feet FWL; llll/2 mi. Eof Blanco. — — Elevation. 1,400± feet (from topographic map). Total depth.—l,o7s feet. Completed. 1931. — TopofPaleozoic rocks. 635 feet. Elevation ofPaleozoic rocks. f-765± feet. — Thin section coverage (depth in feet). bureau of economic geology: 660, 800, 900. Description of Paleozoic rocks.—According to Barnes (1956), this wellpenetrated a Pennsylvanian sandstone and shale. The sequence is composed of dark shale, locally sandy, silty, calcareous, micaceous, and fine- grained, angular to subround, very poorly sorted, calcareous argillaceous slightly feldspathic silty quartz sandstone; these rocks are probably Atoka. Thewellpenetrated forelandrocksnorthoftheOuachitabelt. — X-ray data. None. — References. Personal communication: V.E. Barnes, Bureau of Economic Geology, 1956. Samples are inBureau ofEconomic Geology WellSample Library. — County. Blanco. Well name.—E. L.NixonNo. 3 C. E. Crist. — Location. John McClenechen survey;3mi.SE ofBlanco. —— Elevation.—l,4oo± feet. Total depth. 1,264± feet. Completed. ni. —— Top ofPaleozoic rocks. 500± feet. Elevation of Paleozoic rocks.--|-900± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in files of the Bureau of Economic Geology are as follows: below 1,082 feet, dark greenish finely micaceous siltstone; 1,264 feet, dark shale and fine-grained quartzitic sandstone. This wellprobably penetrated Pennsylvanian beds of Atoka age close to the Ouachita front. — X-ray data None. — References. Bureau ofEconomic Geology files. — County. Blanco. — Well name. E. L.Nixon No. 2 Hohenberger. — Location. Q.C.Stephens survey; 4mi.SofBlanco. — —— Elevation. 1,460 feet (from topographic map.). Total depth. 1,191 feet. Completed.-1937. —— Top of Paleozoic rocks. 470 feet. Elevation of Paleozoic rocks. -j-990 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in Bureau of Economic Geology files report Ellenburger directly beneath Cretaceous rocks at 470 feet. This wellpenetrated foreland rocks north of the Ouachita belt. X-ray data.—None. — References. Bureau ofEconomic Geology files. County.—Bosque. — Wellname. American LibertyOilCompany No.1Clanton. — Location. WilliamMcFarlandsurvey; 660feetFNL,660feetFEL;1mi.SofIredell. — —— Elevation. 981 feet, derrick floor; 972 feet, ground. Total depth. 6,995 feet. Completed. 1949. — Top of Paleozoic rocks. 530 feet. Elevation of Paleozoic rocks.—^-f-451 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1900-30, 2320-50, 2770-00, 2980-10, 3580-3600, 4150-80, 4330-60, 4620-30 (2),5060-70. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Pennsylvanian, 650± feet; top of Marble Falls, 4,330 feet; top of Barnett, 4,618 feet; top of Ellenburger, 4,720 feet; total depth 6,982 feet, in Ellenburger. Petrographically, the sequence is divided into the following gross units: (1) fine-grained, angular to subround, fairly well-sorted, slightly argillaceous (chloritic) and feldspathic quartz sandstone, locally calcareous, locally dolomitic, angular to subangular micaceous quartz siltstone, and very dark The Ouachita System silty shale; (2) dark, fine-grained, slightly glauconitic calcareous spiculite and black spiculitic and calcareous shale; and (3) fine-grained, equigranular dolomite and slightly fossiliferous and pelletif — erous calcilutite. Unit (1) is Atoka, unit (2) is Marble Falls Barnett—both rich in dark organic — material and unit (3) is Ellenburger. This wellpenetrated rocks of foreland facies west of the Ouachita structural belt. = X-ray data.—l>Ch>ML >X;10/7 1;F 20;SR = 2.0. References.— Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; Robert Roth, Humble Oil&Refining Company, 1955. — County. Bosque. — Well name. American Liberty OilCompany (Southland OilCompany) No.1R.T. Green wade. Location.—MaryColesurvey; 660feetFSL,8,752feetFEL;10mi.EofWhitney. — —— Elevation. 664 feet, derrick floor. Total depth. 7,231 feet. Completed. 1949. — Top of Paleozoic rocks. 720 feet. Elevation of Paleozoic rocks. 56 feet. — Thin section coverage (depth in feet). bureau of economic geology: 6800-10, 7110-20. — Description of Paleozoic rocks. Goldstein (1955) reported top of "Atokan" Smithwick, 720 feet; top of Ellenburger, 7,192 feet;totaldepth 7,230 feet, inEllenburger. Thin sections show fine-grained, angular, poorly sorted, dolomitic feldspathic quartz sandstone (6800-6810) and black spiculitic cal — careous shale (7110-7120) .The deeper sample is Marble Falls Barnett. This wellpenetrated foreland rocks west of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Bosque. — Wellname. AmericanLibertyOilCompany No.1Reichert. Location.—JosephHarlansurvey;660feetFNL,2,850 feetFEL;7mi.NWofValleyMills. — —— Elevation. 852 feet, derrick floor. Total depth. 8,000 feet. Completed. 1948. — TopofPaleozoic rocks. 1,150 feet.ElevationofPaleozoic rocks. 298 feet. — Thin section coverage (depth infeet). bureau of economic geology: 3970-80, 4360-70. — Description of Paleozoic rocks. Goldstein (1955) reported top of "Atokan" Smithwick, 6,730 feet; top of Big Saline, 6,830 feet; top of Ellenburger, 6,900 feet; total depth 8,000 feet, in Ellenburger. Thin sections and samples examined for this study show a sequence of dark silty shale, fine-grained subangular to subround, fairly well-sorted, slightly argillaceous and feldspathic quartz sandstone and angular to subangular chloritic micaceous quartz siltstone. The sandstones are Atoka type. This wellpenetrated foreland facies rocks west of the Ouachita belt. X-raydata.—l>ML>Ch(X=Tr?);10/7 1.2;F==20;SR=1.50. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; Robert Roth, Humble Oil&Refining Company, 1955. — County. Bosque. — Wellname. Coleman and Wasson OilCompany No.1R.M.Cox. — Location. Ross McClellan survey;l/2 mi.Sof Walnut Springs. — — Elevation. 1,000 feet (from topographic map). Total depth. —3,960 feet. Completed. 1920. — — Top of Paleozoic rocks. l,ooo± feet. Elevation of Paleozoic rocks. Sea level datum±. — Thin section coverage (depth infeet). bureau of economic geology: 3900-4000. — Description of Paleozoic rocks. Notes in files of the Bureau of Economic Geology describe the rocks from 3,900 to 4,000 feet as dark shale and hard quartzitic sandstone; top of Paleozoic, as in terpreted fromdriller'slog,is1,000±feet. The single sample examined for this study is a fine-grained, angular to subround, fairly well-sorted, slightly calcareous, argillaceous and feldspathic quartz sandstone, containing fragments of darkshale, chert, slate-phyllite, and quartz mosaic. This wellpenetrated Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. Bureau ofEconomic Geology, The University of Texas County. —Bosque. — Wellname. ProfitNo.1Henry. — Location. AmonB.Kingsurvey;%mi.SofMosheim. — —— Elevation. 1,150 feet. Total depth. 6,224 feet. Completed. 1953. — TopofPaleozoic rocks.—1,060 feet. ElevationofPaleozoic rocks. +90 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The following information is from scout reports: base of Cre taceous and top of Pennsylvanian, 1,060 feet; top of Strawn, 2,952 feet; top of Ellenburger, 5,815 feet. The reported "Strawn" is probably Atoka. This wellis located west of the Ouachita belt. — X-ray data. None. — References. Personal communication: H. A. Sellin, Magnolia Petroleum Company, 1958. — County. Bosque. — Wellname. Telegram OilCompany No.1J.W.Burns. — Location. Justin Castanie (Castino) survey. — —— Elevation. 700 ± feet (from topographic map). Total depth. 4,575 feet. Completed. 1922. — Top of Paleozoic rocks. 1,000±(?) feet. Elevation of Paleozoic rocks. 300±(?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology report black shale, gray sandstone, and light-colored sandstone between 4,310 and 4,500 feet; top of Paleozoic, asinterpreted fromdriller'slog,is1,000±feet. This wellprobably penetrated Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. — County. Bosque. — Wellname. Telegram Oil Company No.1M.B.Myrick. — Location. Martha Baker survey; 4 mi.NW ofKopperl. —— Elevation. 610 feet. Totaldepth.—6,loo feet. Completed. 1925. —— Top of Paleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 4825(?), 5800. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology report the wellin Pennsylvanian at 4,700 feet and describe a series of samples between 4,700 and 6,100 feet, total depth, as black shale, gray sandstone, and some clear quartz. Petrographic study shows a sequence of dark silty shale, fine-grained argillaceous quartz siltstone, locally micaceous, and fine-grained, angular to subround, fairly well-sorted, argillaceous quartz sandstone, locally calcareous, micaceous, chloritic; the sandstone contains fragments of shale, chert, and slate-phyllite. This wellpenetrated Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. County. —Bosque. Additionalwellnotshownonthemap (PI.2)andnot studied because oflackofsamples orbasic data: — SinclairOiland Gas Company No.1A.M.White Location: Joseph Taylor survey, NW corner. Completed: 1919. Top of Paleozoic rocks: from driller'slog,1,200± feet. — County. Bowie. — Wellname. A.M.Sutton No.1J.G.Newkirk. Location.— Jessie Dean survey; 500 feetFSL, 1,980 feet FWL; 9mi.NW ofDeKalb. — —— Elevation. 390 feet. Total depth. ni. Completed.-ni. The Ouachita System Top of Paleozoic rocks.— 4,l7o feet. Elevation of Paleozoic rocks. 3,780 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 3895, 4250, 4293. — Description of Paleozoic rocks. Base of Cretaceous and top of Paleozoic (Stanley?) is reported at 4,170 feet (Goldstein, 1955). Thin section studies show that the sequence is composed of fine- grained, angular, poorly sorted, argillaceous micaceous feldspathic quartz sandstone (or metasandstone) and calcareous micaceous siltstone (or metasiltstone) invaded by fine quartz veinlets; the rocks show incipient to very weak metamorphism. — This well penetrated Stanley (?) southeast of the Broken Bow Benton uplift of the Ouachita Mountains. — X-ray data.-None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955, — County. Bowie. Wellname.—J. K.Wadley No.1E.Blackman. Location.—]. C.Hayssurvey; 1,190feetFNL,466feetFWL;3%mi.NofMalta. —— — Elevation. 355 feet. Total depth. 5,548 feet. Completed. 1955. — TopofPaleozoic rocks. 5,460 feet.Elevation ofPaleozoic rocks.-—5,105 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. p. 1237). References.— Gatling (1956, Personal communication :B. W. Fox, The Atlantic Refining Company, 1956. — County. Bowie. — Wellname. J.K.Wadley No.1Bentley Johnson. Location.—John Tisdale survey; 1,800 feetFNL,1,400 feetFEL; 6mi.NofMalta. —— — Elevation. 354 feet. Total depth. 5,091 feet. Completed. 1955. TopofPaleozoic rocks.—5,003 feet. ElevationofPaleozoic rocks. 4,649 feet. — Thin section coverage (depth in feet). bureau of economic geology: 5020-30, 5070-80. Description of Paleozoic rocks.— Thin sections are fine-grained angular to subround, poorly sorted, argillaceous feldspathic quartz sandstone; in the 5,070 to 5,080-foot interval the sandstone is veined withcalcite and has a calcareous matrix. These rocks are probably Stanley. There isno metamorphism. — This well penetrated Stanley (?) southeast of the Broken Bow Benton uplift of the Ouachita Mountains. — X-ray data. None. References.— Gatling (1956, p. 1237). Personal communication: B. W. Fox, The Atlantic Refining Company, 1956. — ICounty. Brewster. — IWell name. Brewster No. 1 Fee. — Location. Section 45, block G-15, GC&SF survey. Elevation.—3,l99(?) feet. Total depth.— l,93s feet. Completed.— l93o. — TopofPaleozoic rocks. 100±feet. Elevation ofPaleozoic rocks.—+3,099± (?) feet. — Thin section coverage (depth in feet). shell oilcompany: 415-25 (2), 425-35, 435-50 (2), 45075 (2), 475-540 (2), 540-75, 575-615 (2), 620-40, 640-45, 645-65, 665-75 (2), 675-700 (3), 720-95, 795-05, 805-60, 860-925, 925-85 (2), 1080-00, 1100-1230, 1230-50 (2), 1250-70 (2), 1275-00 (2), 1300-10, 1310-50, 1350-70, 1375-90, 1390-95, 1400-05, 1405-10, 1425-30, 1450-00, 1500-25, 1550-60, 1600-25 (2), 1625-50, 1675-00, 1700-25, 1800-25, 1850-70 (2), 1870-85 (2). Description of Paleozoic rocks.—According to Olson (1958), this well penetrated Marathon limestone, probably dipping steeply. The sequence is composed of: (1) dark, very fine-grained, angular to subround, fairly well-sorted, dolomitic and calcareous feldspathic quartzitic quartz sandstone and siltstone, locally containingbitumen, locally pyritic, micaceous, and rich in heavy minerals (layers of abundant leucoxene, tourmaline, zircon, rutile);the rocks are veined withcalcite, quartz, and streaks of bituminous material; locally calcite is very abundant and the fine-grained sandstone grades into a silty and sandy lime Bureau ofEconomic Geology, The University of Texas stone or dolomitic limestone;the feldspar is plagioclase and commonly so abundant that the rock is an arkose;in some sections the rocks show dimensional grain orientation and mica orientation, calcite is commonly twinned, and insome fragments there is severe crushing; (2) very dark shale, commonly containing dark organic material, locally silty,micaceous, dolomitic, or calcareous. Although the calcite is commonly twinned extensively, the rocks do not appear to be metamorphosed except for local incipient to very weak metamorphism inzones of more intense shearing. The sequence is identified as lower Paleozoic Ouachita facies, probably a clastic and siliceous facies of the Marathon limestone. — X-ray data. None. — References. Personal communication: J. P. Olson, Shell OilCompany, 1958. — County. Brewster. — Wellname. Dodson (Hinton) No.1Texas American Syndicate. Location—Section 66,block10,GH&SAsurvey; 660feetFNL,660feetFEL. Elevation—4,233 feet. Totaldepth.—9,oss feet. Completed.—l944. — Top of Paleozoic rocks. 875 feet. Elevation of Paleozoic rocks. [-3,358 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The following information is taken from a sample log: base of Cretaceous, and top of Triassic (Bissett), 875 feet; top of Paleozoic (Capitan?), 1,125(?) feet; igneous intrusion, 4,455 to 4,710 feet [analcite microsyenite, Flawn, 1956]; top of Mississippian ( ? ), 5,120 feet;top of Devonian, 5,665 feet;top of Montoya, 6,000 feet;igneous intrusion, 6,078 to 6,458 feet [aegirine-arfvedsonite microgranite, Flawn, 1956];top of Simpson, 6,680 feet; top ofEllenburger, 8,350 feet. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — Flawn (1956, p. 65). Personal communication :J. P. Olson, Shell OilCompany, 1958. Samples are inBureau of Economic Geology Well Sample Library. References. — County. Brewster. — Wellname. John C. Grasdorf (Grostorf ) No.1Trans-Pecos Oiland Gas Company. Location.—Section 18, block G-15, GC&SF survey; 920 feet FNL, 2,500 feet FEL; SE of Horseshoe Mountain. Elevation.—3,o73 feet. Totaldepth.— 2,B2o feet. Completed.—l933. —— TopofPaleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. — Thin section coverage (depth infeet). bureau of economic geology: 1900-10, 2350-60, 2730-45. — Description of Paleozoic rocks. The sequence is composed of fine-grained, dark, locally graphitic, siliceous dolomite and dolomitic chert, brecciated and sheared, and veined with quartz-carbonatebitumen. This wellpenetrated lower Paleozoic (probably Ordovician) Ouachita facies rocks just south of the Marathon Basin. X-ray data.—{l) 1,900 feet: Ch>l; 10/7-^0.3. (2) 2,730 feet:I> Ch; 10/7-^4; F=20; SR =7.0. — References. Personal communication :J. P. Olson, Shell OilCompany, 1958. — County. Brewster. — Wellname. GulfOilCorporationNo.1D.S.C.Coombs. Location.—Section16,block4,GC&SFsurvey; 660feetFSL,1,980feetFEL;1mi.SEofMarathon. — — Elevation. 4,114 feet, derrick floor. Total depth.—9,500 feet. Completed. 1956. Topof Paleozoic rocks.36 Elevation of Paleozoic rocks. 1—4,1.14 feet. — Thin section coverage (depth in feet) shell oil company: 2900-05 (5), 3880 (7), 3900 (2), 4000 (2),4020, 4850-00, 5830 (2),6200 (2),9370 (4). — Description of Paleozoic rocks. Wilson (1957) reported as follows: The well was spudded in Woods Hollow shale; top ofFort Pena, 320 feet; top of Alsate, 710 feet; top ofMarathon, 810 feet; top of Dagger Flat, 4,840 feet; base of thrust plate in interval 5,840 to 6,100 feet (samples missing) ; 6,100 feet to total depth, Pennsylvanian-type sandstone and shale. Andesitic( ?) intrusions occur inthe 38 Well was spudded inWoods Hollow shale. The Ouachita System interval 3,870 to 3,910 feet; trilobites of Marathon age (Lower Ordovician) were found at 4,050 feet in the thrust plate, and fusulinids of Pennsylvanian and Wolfcamp ( ? ) age occur inbeds beneath. Thin section examination gives the following information:2,900-2,905 feet, very fine-grained dolo mitic limestone; 3,880, 3,900, 4,000, 4,020 feet altered andesite(?); 4,850-4,900 feet, fine-grained sandy intraclastic limestone; 5,830 feet, fine-grained sandy limestone, indications of metamorphism in extensively twinned calcite; 6,200 feet, fine-grained, angular to subangular, fairly well-sorted, tightly packed, dolomitic feldspathic quartz sandstone of Mississippian-Pennsylvanian (foreland?) type; 9,370 feet, angular to subround, fairly well-sorted, feldspathic quartz sandstone, locally tightly packed, locally slightly argillaceous, dolomitic, cherty. This wellpenetrated lower Paleozoic Ouachita facies rocks, intersected a thrust fault, and bottomed in strata of probable Mississippian-Pennsylvanian age and foreland type; itsupports the concept that at least the north part of the Marathon salient is an allochthonous plate. — X-ray data. None. — References. Personal communication: J. D. Moody, Gulf Oil Corporation, 1957; J. L.Wilson, Shell Oil Company, 1957. — County Brewster. — Wellname. King&Franklin No.1A.S. Gage. — Location. Section 138, block 22, GH&SA survey; 7mi. SE ofMarathon. Elevation.—4,244 feet. Totaldepth.—l,6l3feet. Completed.—l93s. Top of Paleozoic rocks. 31 Elevation of Paleozoic rocks. f-4,244 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 130-40, 255-62, 290-95, 335-41, 508-12, 835-39, 885-90, 929-30, 934-38, 1086-90, 1100-05, 1112-15, 1131-35, 1190-93, 1193-98, 1215-21. — Description of Paleozoic rocks. According to Goldstein (1955) there are three interpretations of the section penetrated inthis well: Baker and Carsey (King, 1937) Spangler and Fulk (1942) Goldstein (Feet) (Feet) (Feet) Fort Pena 0-114 Quaternary 0-114 Middle and Lower Alsate 114-465 Tesnus 114-1060 Ordovician 0-1060 Marathon 465-1613 Caballos 1060-1565 Caballos 1060-1516 The sequence from the surface to 1,060 feet consists of gray calcareous silty shale, locally dolomitic and locally containing calcareous spines, clay pellets, and a trace of glauconite, and calcareous argillaceous siltstone, overlying fine-grained, subangular, fairly well-sorted, tightly packed, calcareous quartzitic sandstone, locally fossiliferous. The intervals 927 to 930 and 934 to 938 feet are fine- grained fossiliferous calcareous dolomite. Veinlets of quartz, carbonate, and bituminous material are common. The deeper part of the well from 1,060 feet to total depth is composed mostly of siliceous rocks, chiefly dark argillaceous microgranular to microspherulitic chert locally containing abundant organic material;the cherts are commonly fractured and brecciated. The rocks are unmetamorphosedOuachita (Marathon) facies. This well spudded in lower Paleozoic Ouachita facies rocks and bottomed in rocks of the same age and facies. IfGoldstein's interpretation is correct, there is a thrust faultin the sequence. — X-ray data. None. References— P.B.King(1937, p. 29);Spangler andFulk (1942). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Brewster. — Well name. Plumber and Schwab No. 1Bud Roark. — Location. Section 64, block G-18, TC survey. — Elevation. —2,172 feet. Totaldepth. —3,007 feet. Completed. ni. — Top of metamorphic rocks. 1,848 feet. Elevation of metamorphic rocks. (-324 feet. — Thin section coverage (depth infeet). shell oilcompany: 1848-65 (2),1865-20, 1920-60, 1960-00, 2000-10, 2110-55, 2155-05 (2), 2241-85, 2288-20, 2320-62, 2362-10, 2410-47, 2447-93 (2), 2536-74, 2574-00, 2600-40, 2640-65, 2665-31 (2), 2731-60, 2750-57, 2804-33, 2933-35, 2938-77, 2977-07 (2). bureau of economic geology: 1865, 2000, 2205, 2535, 2804, 3007. 37 Well was spudded inOuachita (Marathon) facies rocks. Bureau ofEconomic Geology, The University of Texas — Description of metamorphosed Paleozoic(?) rocks. The sequence in this wellis composed of: (1) dark gray to black rutiliferous graphitic sericite-chlorite-quartz phyllite and black pyritic rutiliferous siliceous (finely quartzose) graphitic slate; (2) very fine-grained graphitic dolomitic meta- quartzite, locally sericitic (phyllitic), calcareous, rutiliferous, locally feldspathic in the lower part of the well; and (3) below 2,600 feet in the lower part of the sequence, fine-grained siliceous (finely quartzose) dolomitic calcite marble, locally pyritic, graphitic. Dolomitic metachert occurs in the 3,007-foot interval. Metamorphism is weak to low grade with a strong shearing element in certain intervals; foliation is expressed in stretched quartz and calcite grains and orientation of graphitic streaks; locally the phyllites show wrinkling. Some of the fine-grained metaquartzite samples in the lowerpartofthe sequence showrelictroundsand grainsinamosaic offinerquartz. This well penetrated metamophosed rocks of the interior zone, but metamorphism is not so advanced as in other wells in this belt or as in the Sierra del Carmen outcrop in Coahuila, Mexico. The nature of the rocks suggests that the wellencountered a weakly metamorphosed sequence of pre- Tesnus Marathon facies rocks, possibly a southern facies of the Marathon limestone similar to that exposed in the Dagger Flat area of the Marathon Basin. This is significant in that itsuggests a Paleozoic age for the more metamorphosed rocks to the south and east. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Brewster. — Well name. Pure OilCompany No.1Massie West. — Location. Section 548, block 8. — —— Elevation. 5,026 feet. Total depth. 5,634 feet. Completed. 1956. — Top of Paleozoic rocks. 3,520 feet. Elevation ofPaleozoic rocks.— +1,506 feet. — Thin section coverage (depth in feet). None. — Description of Paleozoic rocks. This well was spudded involcanic rocks, drilled through Permian and Ellenburger beds, and bottomed in Precambrian granite (Culbertson et al., 1957). Itis located westoftheOuachitastructuralbelt(cf.SunOilCompany No.1McElroy). — X-ray data. None. — References. Culbertson et al. (1957, p. 1128). — County. Brewster. — Well name. Sun OilCompany No. 1McElroy. Location.—Section 5,block 212, T&STLsurvey; 2,300 feet FNL,2,100 feet FEL. —— Elevation. 3,708 feet, derrick floor. Total depth. —8,455 feet. Completed. 1955. Top of Paleozoic r0ck5.— 2,495 (?) feet, 2,570(?) feet. Elevation of Paleozoic rocks— +1,213(?) feet, +1,138 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Olson (1960) reported that probably more than 1,000 feet of lower Paleozoic Ouachita facies rocks overlie a normal foreland sequence. Lithologies include chert conglomerate, dark green and gray shale, dark siliceous argillaceous limestone, and varicolored cherts. Dips in cores range from 35° to vertical. Identification of formations is difficult; the interval 2,495 feet (or 2,570 feet) to about 2,850 feet resembles Fort Pefia and the interval 2,850 feet to about 3,760 feet resembles Woods Hollow. If these tentative identifications are correct the sequence is overturned. Rocks in the interval 3,760± feet to 5,536 feet are probably Wolfcamp but may include Pennsylvanian beds as well. The following stratigraphic data are taken from an earlier report by Zimmerman (1957): top of Woodford, 5,536 feet; top of Silurian-Devonian, 5,613 feet; tentative top of Montoya, 6,288 feet; tentative top of Ellenburger, 7,244 feet; top of basal Ellenburger sand (Cambrian?) ,8,292 feet; totaldepth 8,456 feet. This wellpenetrated lower Paleozoic Ouachita facies rocks, transected a thrust fault (westward extension of the Dugout Creek overthrust?) and bottomed in foreland facies rocks. The well is probably located just south of the Ouachita front. The relatively thin Permo-Pennsylvanian (?) sequence suggests uplift (and erosion?) prior to overthrusting. — X-ray data. None. — References. Personal communication: D. A. Zimmerman, Sun OilCompany, 1957; John P. Olson, Shell OilCompany, 1960. The Ouachita System — County. Brewster. — Wellname. Fred Turner, Jr., No.1D.S. C. Coombs et al. Location.—Section 37,block21,GH&SAsurvey;433feetFSL,2,406feetFWL. — — Elevation. 3,469 feet, derrick floor. Total depth. —13,980 feet. Completed. 1957. Top ofPaleozoic rocks. 38Elevation of Paleozoic rocks. [-3,469 feet. — Thin section coverage (depth in feet). bureau of economic geology: 90-100, 200-10, 700-10, 840-50, 1400-10, 1530-40, 1610-20, 2120-30 (2), 2590-00 (2), 2730-40, 2960-70, 3230-40, 3290-00, 4090-00, 4580-90, 5300-10, 5850-60, 6690-00, 7190-00, 8690-00, 9480-90, 10,690-00, 12,010-20, 13,970-80. — Description of Paleozoic rocks. According to Merkt (1958),this wellwas spudded inDagger Flat sandstone. From the surface to about 1,600 feet the sequence is composed of interbedded sandstone and shale. The sandstone is gray, fine-to medium-grained, angular, poorly sorted to fairly well-sorted, feldspathic quartz sandstone or arkose containing a trace of glauconite, commonly dolomitic or calcareous, locally micaceous, argillaceous, quartzitic, pyritic; the rock is veined with quartz, carbonate, and bituminous material;the mica ismostly faded biotite,potassium feldspar issubordinate to plagioclase, and some samples contain phosphatic fragments. The shale is dark slightly glauconitic silty shale, locally brecciated and deformed. Locally in the sequence the calcareous sandstone grades into silty and sandy limestone. From 1,600 to 13,980 feet (total depth) the sequence consists of interbedded shale, limestone, and sandstone. In the upper part of the section, shale and limestone predominate and sandstone beds are few; sandstone increases downward and below 8,400 feet the section is mostly shale and sandstone with minor limestone. Chert (including siliceous shale) is present between 2,120 and 3,300 feet. The rock types are as follows: (1) dark very fine granular dolomiticlimestone (intraclasts cemented by sparry calcite), locally siliceous, argillaceous, silty or sandy, pyritic, containing dark organic ma — terial, in some intervals containing fossil fragments (2,730 to 2,740 feet spines and shells), veined by twinned sparry calcite, dolomite, bituminous material, and quartz or fine silica; (2) very fine-grained calcilutite, locally dolomitic, pelletiferous, sandy or silty, veined by twinned sparry calcite; (3) fine granular dolomite, veined by dolomite and twinned sparry calcite; (4) dark cryptocrystalline chert, commonly dolomitic or calcareous, locally argillaceous, locally containing dark organic material, veined with twinned sparry calcite, quartz, bituminous material; (5) dark shale, commonly very finely dolomitic,locally sandy orsilty,siliceous, richindark organic matter, veined by twinned sparrycalcite, quartz, bituminous material, locally brecciated and deformed; (6) gray fine-grained mostly angular (subround in some intervals) poorly sorted to fairly well-sorted calcareous and dolomitic feldspathic quartz sandstone or arkose, locally quartzitic, micaceous, argillaceous, locally containing dark organic matter and traces of glauconite, veined by twinned sparry calcite, dolomite, quartz, and bituminous material. The samples are very fine;toward the bottom of the hole there is a mixed sample suite that shows little variation; possibly the sequence is very thin bedded and standing at a high angle, possibly therehasbeen amixingofsamples inthemudstream. This well appears to have penetrated a long sequence of lower Paleozoic Ouachita facies rocks (Cambro-Ordovician) ;the sandstones (containing potassium feldspar, glauconite) do not resemble the late Paleozoic sandstones of the area. = X-raydata.—(l) 840 feet: Ch>ML>I;10/7—'0.4; F 20; SR=1.3. (2) 13,970 feet:I>Ch; = 10/7 ~->0.6;F 20, 25;SR=2.3. — References. Personal communication :E.E. Merkt, GulfOilCorporation, 1958. — County. Brewster. — Well name. Woods Oiland Gas Company No. 1-47 Mary Decie et al. (also known as Slick-Urschel Oil Company No. 1Mary Decie-Sinclair). — Location. Section 47,block4,GC&SFsurvey; 6mi.W,3mi.NofMarathon. — —— Elevation 4,461 feet. Total depth. 9,741 feet. Completed. 1956. Top of Paleozoic rocks.39 Elevation of Paleozoic rocks. f-4,461 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Galley (1957) reported that the wellspudded in Caballos novaculite and encountered the base of the Caballos at 160 feet; beneath the Caballos is a continuous section of normal foreland facies rocks including Permian, Pennsylvanian, Mississippian, Woodford, Devonian, Fusselman, Montoya, Simpson, and Ellenburger; top of Ellenburger, 9,400 feet; total depth, in Ellenburger. Woods (1957) remarked that the well started in a klippe of Caballos and cut several thrust sheets in the upper section. Hull (1957b) noted that the Wolfcamp series is folded and faulted; top of Wolfcamp, 165 feet; base of Wolfcamp, 6,820 feet overlying Strawn. He said: "These 6,655... feet of shale, fine-grained sandstone, and fragmental limestone [Wolfcamp] were deposited in a basin and then folded before the Wolfcamp formation at Wolf Camp Hills was deposited." 38 Well was spudded in Dagger Flat sandstone. 30Well was spudded in Caballos movaculite. 238 Bureau ofEconomic Geology, The University of Texas The following log is given in the West Texas Geological Society Field Trip Guidebook for the Glass Mountains area, 1957: spudded in Caballos novaculite, Dugout Creek overthrust, 160 feet; top of Gaptank formation of Wolfcamp age, 160 feet; possible thrust fault (sole thrust of Marathon Basin allochthonous plate?), 1,600 feet; top of Strawn, 6,820 feet; top of Woodford, 6,980 feet; top of Siluro-Devonian, 7,270 feet; top of Montoya(?), 8,070 feet; top of Simpson, 8,250 feet; top ofEllenburger, 9,385feet;totaldepth, 9,637feet,inEllenburger. This well is important to the structural interpretation of the Marathon salient in that (a) it demonstrates a foreland facies section beneath overthrust Ouachita (Marathon) facies beds, and (b) it suggests that there are deformed Wolfcamp beds older than those exposed in the Wolfcamp Hills (p. 54). I— 1 X-ray data. None. IReferences.— Hull (1957b, p. 96);Anonymous (1957, p. 13). Personal communication: J. E. Galley, Shell Oil Company, 1957; R. D. Woods, Humble Oil & Refining Company, 1957. — County. Burnet. — Wellname. AlBelanger No.1NellaT.Evans. — Location. Spicewood area,10mi.EofMarbleFalls. — —— Elevation. 925 feet (from topographic map). Total depth. 734(?) feet. Completed. ni. —— Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology report Marble Falls limestone at 526 to 704 feet, Barnett shale at 704 to 728 feet, and Ellenburger dolomite at 728 to 734 feet. Apparently this well penetrated foreland rocks close to the edge of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Burnet. Well name.— Bertram City Well No. 1. — Location. Bertram, Texas. — Elevation. 1,265 feet. Total depth.—2,395 feet. Completed.— -ni. —— TopofPaleozoic rocks. ni. ElevationofPaleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 2320-25, 2385-88, — Description of Paleozoic or metamorphic rocks. A driller's log in the files of the Bureau of Economic Geology reports "schist" from 1,767 to 2,395 feet and quartzite in a core from 2,395 feet. The location of the well suggests that the identification of "schist" is probably in error. The two samples available for study are dark silty micaceous shale containing carbonaceous debris and very fine carbonate; the rocks are deformed and locally show two orientations of mica intersecting at a high angle. These rocks are probably deformed Atoka beds lying close to the Ouachita front (PL 2). = X-raydata.—l>ML>Ch>X;10/7 <--'1.5;F 20;SR=1.55. — References. Bureau of Economic Geology files. — County. Burnet. — Well name. E. A.Dunham and Hensman DrillingCompany No.1W.F.Day. Location.—GC&SFsurvey; 330 feetFSL,330 feetFWL;9mi.NEofBriggs. Elevation.— -919 feet. Total depth—-4,790 feet. Completed.—l9ss. —— Top of Paleozoic rocks. 450 feet. Elevation of Paleozoic rocks. -J-469 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. A sample log in the Bureau of Economic Geology files reports base of Cretaceous, 450 feet; Pennsylvanian shale, 450 to 2,390 feet; Ellenburger, 2,390 to 4,790 feet (total depth).Sample descriptions in files of Bureau of Economic Geology indicate that the interval — 450 to 2,390 feet includes Atoka resting on Marble Falls Barnett. This wellpenetrated foreland rocks west of the Ouachita belt. The Ouachita System — X-ray data. None. — References. Bureau of Economic Geology files. Personal communication :E.J. Theessen, Shell OilCompany, 1956. — County. Burnet. — Well name. Twin Cities Oiland Gas Company No. 1Taylor. — Location. 3mi.EofVictorLakeonRocker ranch, 8mi.NofBertram. Elevation.—l,3B2feet. Totaldepth.—2,3oo feet. Completed.— l92o. —— Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thinsection coverage (depth infeet.). None. — Description of Paleozoic rocks. Asample log in the Bureau ofEconomic Geology files reports the following information: in Smithwick at 465 feet, in Ellenburger at 570 feet. Sample descriptions in files of the Bureau of Economic Geology indicate that the intervals 465, 488, and 500 feet are Marble Falls—Barnett. Sellards (1933) gives the following data: top of Mississippian, 550 feet; top of Ordovician, 575 feet;total depth, 2,300 feet. This wellpenetrated foreland facies rocks west of the Ouachita front. — X-ray data. None. References.— Sellards (1933, p. 197). Bureau ofEconomic Geology files. Samples are in Bureau ofEconomic Geology Well Sample Library. — County. Caldwell. — Wellname. GulfCoast DrillingCompany No.1Schawe. — Location. Thomas Maxwell survey. — Elevation.—6o4 feet. Total depth. —3,445 feet. Completed. Before 1932. Topof metamorphic rocks. —3,415 feet. Elevation of metamorphic rocks. 2,811 feet. — Thinsection coverage (depth infeet). None. — Description of metamorphic rocks. According to Sellards (1931b, 1933), this well penetrated shale. Its location indicates, however, that itencountered highly sheared weakly metamorphosed rocks in the black slate belt of the interior zone ofthe Ouachita belt. — X-ray data.-None. References.— Sellards (1931b, p. 822; 1933, p. 188). — County. Caldwell. — Well name. Magnolia Petroleum Company No. 1 Hardeman (salt-water disposal well);also known as United North and South No. 1-A T.C. Gideon. Location—M.G.Dykes survey; 900feetFmost W'lyNEL,1,250feetFmostN'lyNWL. —— Elevation. 470 feet, derrick floor. Totaldepth. —4,845 feet. Completed. ni. — Top of metamorphic rocks. 4,810 feet. Elevation ofmetamorphic rocks. 4,340 feet. — Thinsection coverage (depth infeet). None — Description of metamorphic rocks. From its location, this well probably penetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County Caldwell. Well name. —Magnolia Petroleum Company No. 40 AlfMercer. location—Nancy Reaville survey; 1,535 feet FSEL, 5,535 feet FSWL; 6 mi. NW of Luling. —— — Elevation. 487 feet. Total depth. 4,720 feet. Completed. 1953. Topofmetamorphic r0ck5.—4,697 feet.Elevation ofmetamorphic rocks. 4,210 feet. — Thinsection coverage (depth infeet). bureau ofeconomic geology: 4710-20. — Description of metamorphic rocks. The single sample examined is pyritic sericite phyllite veined by dolomite. Metamorphism is low grade witha high shearing element;the rock is wellfoliated and locally shows development of fracture cleavage. Thiswellpenetrated metamorphic rocksintheinteriorzoneoftheOuachitabelt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. References.— Personal communication: R. E. Wills, Magnolia Petroleum Company, 1953. — County. Caldwell. — Wellname. UnitedNorthandSouthDevelopment CompanyNo.1Gideon. Location— M. G. Dykes survey; 1,300 feet F most N'ly NWL, 1,330 feet FNEL of Caldwell survey. —— Elevation. 470 feet. Total depth. 5,345 feet. Completed.—l929. — Top of metamorphic rocks. 5,335 feet. Elevation of metamorphic rocks. 4,865 feet. — Thin section coverage (depth infeet). None. — Description of metamorphic rocks. From its location, this wellprobably penetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication :R. E. Wills,Magnolia Petroleum Company, 1953. — County. Caldwell. — Wellname. UnitedNorthandSouthDevelopment Company No.1George Kelly. Location.—Nancy Reaville survey; 525 feet FSWL, 725 feet FSEL. —— Elevation. 463 feet. Totaldepth.—l,Bs4 feet. Completed. 1928. Topof metamorphic rocks.—4,750 feet. Elevation of metamorphic rocks. 4,287 feet. — Thin section coverage (depth in feet). bureau of economic geology: 6900, 7103, 7150 (2), 7240. — Description of metamorphic rocks. Sellards (1931b) described rocks encountered in this well as "schist." Barnes (in Sellards, 1933) reported "green schist with cleavage dipping at 16°." Samples examined for this study are graphitic sericite-chlorite phyllite;some samples contain abundant rutile needles. Locally the foliation shows crumpling, convolution, and micro-thrust faulting. Metamorphism islowgrade withahigh shearing element. This wellpenetrated metamorphic rocks in the interior zone of the Ouachita belt. — X-ray data. None. References.— Barnes (1948) ;Goldstein and Reno (1952, p. 2281) ;Sellards (1931b, p. 822; 1933, p. 133). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; R.E.Wills,Magnolia Petroleum Company, 1953. Core fragments from 6,900 feet are in Bureau of Economic Geology Well Sample Library. County.— Caldwell. — Well name. United North and South Development Company No. 8 W. H. Tabor. Location.—Nancy Reaville survey; 7,550 feet FNEL, 120 feet FSEL. —— Elevation. 492 feet. Total depth.—4,852 feet. Completed. 1927. — Topof metamorphic rocks. 4,796 feet.Elevation ofmetamorphic rocks. 4,304 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4822, 4831, depth unknown. — Description of metamorphic rocks. Bailey (in Sellards, 1933, p. 132) described samples from this well as calcite-quartz-sericite schist containing pink garnets. Samples examined in this study are sericite phyllite veined with carbonate and showing well-developed fracture cleavage; foliation is sharply wrinkled between cleavage planes and locally there is micro-thrust faulting. Carbonate veinlets are severely strained and show a herringbone structure. Metamorphism is low grade with a strong shearing element. Thiswellpenetrated metamorphic rocksintheinteriorzoneoftheOuachitabelt. — X-ray data. None. References.— Barnes (1948) ;Goldstein and Reno (1952, p. 2284) ;Sellards (1931b, p. 822; 1933, pp. 132-133). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; R.E.Wills,Magnolia Petroleum Company, 1953. Samples areinBureau ofEconomic Geology WellSample Library. — County. Caldwell. — Well name. United North and South Development Company No. 2 Tiller (also known as No. 1 Tiller).40 40 Apparently there has been some confusion in marking samples; the No. 1 and No. 2 are most probably the same well. The Ouachita System Location.—John Henry survey; 7,300 feet FNEL, 5,550 feet FSEL. Elevation.—43B feet. Total depth.— 7,499 feet. Completed.— l92B. — Topof metamorphic rocks. 4,808 feet.Elevation ofmetamorphic rocks. 4,370 feet. — Thinsection coverage (depth infeet). shell oilcompany: 5957-58. bureau of economic geology: 6696 (2), 7169-71, 7483. Description of metamorphic rocks.—Barnes (in 'Sellards, 1933, p. 133) described this rock as sericite- chlorite schist with the schistosity dipping at 15° in the core and bedding crossing the schistosity at a high and irregular angle. Samples examined for this study are graphitic sericite-chlorite phyllite; in some sections the mica is muscovite rather than sericite ;tiny needles of rutile are abundant, and in one thin section albite makes up a substantial portion of the rock. Foliation is commonly wavy and fracture cleavage is locally developed; rucking and herringbone structures occur between closely spaced cleavage planes. Metamorphism islowgrade witha highshearing element. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. References.— Barnes (1948) ;Sellards (1931b, p. 822; 1933, pp. 132-133). Personal communication :August Goldstein, Jr., Pan American Petroleum Corporation, 1955;R. E. Wills,Magnolia Petroleum Company, 1953. Samples areinBureau ofEconomic Geology WellSample Library. — County. Caldwell. Well name.—J. S. Woodward, Incorporated, No. 1P. S. King. — Location. Sampson Connell survey; 2,000 feet FEL, 2,650 feet FSEL; 2 mi. S of Lytton Springs. — Elevation.—595 feet, derrick floor. Total depth.—4,516 (?) feet. Completed. 1955. Top of metamorphic rocks. —4,430 feet. Elevation of metamorphic rocks. 3,835 feet. — Thinsection coverage (depthinfeet). bureau ofeconomic geology: 4440-50, 4500-10. — Description of metamorphic rocks. The sequence is composed of rutiliferous hematitic chloritesericite phyllite and phyllitic metaquartzite veined withmassive quartz, locally containing vermicular chlorite, and carbonaceous (graphitic?) dolomitic sericitic and chloritic metaquartzite containingchert grains and showing a relict clastic fabric. Metamorphism is low grade with a high shearingelement ;grain stretching is pronounced inthe metaquartzites. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957; J. R. Sandidge, Magnolia Petroleum Company, 1957. Samples are in Bureau of Economic Geology Well Sample Library. — County. Caldwell. — Wellname. J. S. Woodward, Incorporated, No.1Taylor. Location.—J.P.Bellsurvey; 1,850feetFmostN'lyNWL,6,050feetFmostW'lySWL;4mi.NWof Lockhart. Elevation.—4B3 feet. Total depth.— 4,239 feet. Completed.-— 1955. Topof metamorphic rocks.—4,205 feet. Elevation of metamorphic rocks.— -3,722 feet. — Thinsection coverage (depth infeet). bureau ofeconomic geology: 4190-4200, 4220-30. — Description of metamorphic rocks. The samples examined are chlorite-sericite phyllite, locally graphitic and locally containing abundant rutile needles. Metamorphism is low grade with a strong shearing element. Thiswellpenetrated metamorphic rocksintheinteriorzoneoftheOuachitabelt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957;J.R.Sandidge, Magnolia Petroleum Company, 1957. Samples areinBureau ofEconomic Geology WellSample Library. — County. Collin. Wellname.—Deep Rock OilCorporation No.1W.M.Sherley. Location.—D.VanWinklesurvey; 3,500feetFSL, 5,385 feetFEL;3mi.SofWestminster. — Elevation. 586 feet. Total depth.—8,887 feet. Completed.-— 1952. — Topof Paleozoic rocks. 3,932 feet. Elevation of Paleozoic rocks. 3,346 feet. Bureau ofEconomic Geology, The University of Texas — Thin section coverage (depth in feet). pan American petroleum corporation: 3950-60, 3980-90 (2), 4010-20, 4020-30, 4100-10, 4170-80, 4320-30, 4360-80, 4480-90, 5420-30, 5980-90, 5990-00, 6550-60, 6560-70, 6570-80, 6690-00, 6820-30, 6880-90, 7050-60, 7650-60, 7660-70, 7680-90, 7690-00, 7710-20. — Description of Paleozoic rocks. Goldstein (1959) reported base of Cretaceous and top of Bigfork, 3,932 feet; top of Womble, 4,385 feet; and total depth 8,887 feet, in lower Womble. According to Morgan (1955) this wellmay have passed through a thrust fault into Strawn beds. Hazzard (1958) called attention to steep dips. Three units can be recognized in the Paleozoic section in this well: (1) dark chert containingabundant organic material overlying dark shale (Bigfork-Womble section), (2) fine-grained quartzitic sandstone, and (3) fine-grained fossiliferous sandy dolomitic limestone. Quartz veins carrying bituminous material are common in the upper dark chert-shale section. The lower two units, beginning at about 5,400 feet, may be Mississippian-Pennsylvanian rocks of foreland facies, or they may be Womble (Goldstein, 1959). Thiswellpenetratedunmetamorphosed lowerPaleozoicOuachita faciesrocksinthefrontalzoneof the Ouachita belt and possibly passed through a thrust fault into younger beds of foreland facies. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955,1959;R.T.Hazzard,GulfOilCorporation, 1958;H.J.Morgan,Jr.,TheAtlanticRefining Company, 1955. — County. Collin. Wellname.—HumbleOil&Refining Company No.1H.C.Miller. Location—L.Searcy survey; 110 feet FNL,840 feet FWL; 3% mi.WofMcKinney. — —— Elevation. 603 feet, derrick floor; 591 feet, ground. Total depth. 11,407 feet. Completed. 1954. —— Top of Paleozoic rocks. -3,051 feet. Elevation ofPaleozoic rocks. -2,448 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3600-10, 3870-80, 4250-60, 5560-70, 6240-50, 7100-10, 7600-10, 8000-10, 8450-60, 9000-10, 10,729, 10,743, 10,778, 10,806, 10,834, 10,865, 10,870. — Description of Paleozoic rocks. The following tops are reported by Shelby (1958) :top of Paleozoic (Strawn), 3,051 feet; top of Ordovician, 9,152 feet; he noted that older Pennsylvanian rocks probably are present between known Strawn beds and the top of the Ordovician sequence. Accord- ingtoBarnes(1959),thiswellencountered Ellenburgerrocksat9,152feet;foradescriptionofthis section (9,152 feet to total depth), see Barnes (1959). The wellpenetrated a body of basaltic rock withinthe Ellenburger section whichisprobably a sill. The sequence overlying the Ellenburger rocks in this wellconsists of interbedded dark gray shale and sandstone with thin limestone beds. The sandstones are mostly gray, fine-to medium-grained, rarely coarse-grained, subangular to subround, fairly well-sorted, cherty quartz sandstone, commonlycalcareous, locally argillaceous, micaceous, dolomitic, quartzitic, slightly feldspathic, and commonly containing abundant grains of shale and chert (dark cryptocrystalline chert, commonly dolomitic, — spiculitic, rich in dark organic material Ouachita type; probably Arkansas novaculite or Bigfork chert) as wellas sporadic large grains of both quartz and chert. Shales are dark gray, silty and sandy. Limestones are mostly fine-grained silty and sandy fossiliferous calcilutite. The sequence is identified as Strawn-Atoka. This wellpenetrated foreland basin rocks west of the Ouachita belt. — X-ray data.-None. References.— Barnes (1959, p. 369). Personal communication: T.H. Shelby, Jr., Humble Oil&Refining Company, 1958. — County. Collin. — Wellname. Pure OilCompany No.1Finley. — Location. Martha Herron survey; center of Finley 290-acre tract. — — Elevation.—707 feet. Totaldepth. 6,000 feet. Completed. 1944. TopofPaleoozic rocks.—2,850 feet. ElevationofPaleozoic rocks. 2,143 feet. Thinsection coverage (depth infeet).—None. — Description ofPaleozoic rocks. The followingstratigraphic data arereported byGoldstein (1955): base of Cretaceous and top of Pennsylvanian (Strawn), 2,850 feet; top of Ellenburger, 5,510 feet; total depth 6,000 feet, in Ellenburger. This well penetrated foreland rocks west of the Ouachita belt. — X-ray data. None. The Ouachita System — communication: August Goldstein, Jr., Pan American Petroleum Corporation, References. Personal 1955; H.J.Morgan,Jr., TheAtlanticRefining Company, 1957. — County. Collin. — Wellname. Pure OilCompany No.1Light. — Location. J. Ragsdale survey. — — Elevation. 641 feet. Total depth. —5,966 feet. Completed. 1944. — Top of Paleozoic rocks. 2,510 feet. Elevation of Paleozoic rocks. 1,869 feet. Thin section coverage (depth in feet).— BUREAU OF ECONOMIC GEOLOGY: 4030-40 (5), 4100-10 (4), 4200-10 (3), 4300-10 (2), 4400-10 (2), 4600-10, 4840-50 (3), 4900-10 (4), 5400-10, 5500-10, 5600-10 (2), 5960-66 (2). — Description of Paleozoic rocks. Goldstein (1955) reported top of Pennsylvanian (Strawn), 2,510 feet; top of Ellenburger, 4,110 feet; total depth, 5,966 feet, in Ellenburger. Thin section examination shows a sequence of dark silty shale overlying fine-grained dolomitic limestone, more or less fossiliferous. The rocks are normal foreland rocks west of the Ouachita structural belt. X-ray data.—l> ML> Ch> X; 10/7-^1.4; F= 20; SR=1.51. Shales are composed of mixed layer illite-montmorillonitewithminor kaolinite characteristic of foreland shales. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Comal. — Wellname. Roland Blumberg No.1D.C.Knibbe. Location.—John M.Christian survey; 330 feet FWL, 330 feet FSL; llll/2 mi. SE ofKendalia. — — Elevation.—1,075 feet (from topographic map). Total depth. 3,105 feet. Completed. 1958. —— TopofPaleozoic rocks. 540 feet. ElevationofPaleozoic rocks. -f-535 feet. — Thin section coverage (depth in feet). bureau of economic geology: 525-30, 545-50, 685-90 (3), 1340-45, 1535-40, 1800-20, 1895-00, 2015-20, 2175, 2705 (2), 2930. — Description of Paleozoic rocks. The Paleozoic sequence in this wellindicates structural complexity. The upper unit is composed of dark sericite-chlorite clay-slate, locally pyritic, silty, and siliceous; dark chloritic micaceous metasiltstone;and dark, fine-grained, angular, very poorly sorted, micaceous chloritic feldspathic quartz sandstone. Underlying this unit is a sequence of dark cryptocrystalline dolomitic chert and dark red-brown argillaceous chert or siliceous shale rich in brown organic material and containing small (0.05 mm) round siliceous bodies (radiolarians?) ;the cherts are fracturedand fractures are filledwithveinquartz.Beneath thesiliceous rocksisa sequence ofdarksandy chloritic micaceous feldspathic quartz siltstone and dark chloritic micaceous metashale or clay-slate, locally strongly deformed. The deepest unit penetrated is a fine-grained, subangular to subround, poorly to fairly well sorted, slightly feldspathic to feldspathic argillaceous quartz sandstone. Metamorphism ranges from incipient to weak and is higher in the upper unit; structures are foliation and contortion (in clay-slates and metashales) and fracturing (in the cherts). The deepest unit is not metamorphosed. The incipiently to weakly metamorphosed upper clastic unit is probably Mississippian-Pennsylvanian; possibly it is correlative with the Stanley but the lithology is not typically Stanley. The chert- siliceous shale sequence below has characteristics of both Arkansas novaculite and Bigfork chert. Goldstein (1958) reported the following tentative identifications: 525 to 530 feet, probably Mississippian- Pennsylvanian; 685 to 690 feet, closely resembles upper Arkansas novaculite; 1,340 to 1,350 feet, closely resembles Blaylock sandstone; 1,535 to 1,540 feet, either lower middle member of Ar kansas novaculite orBigfork,probably the latter. The chert-siliceous shale sequence is very similar to that seen in the No. 2 Slayden and No. 1 Bailey wells in Bell County. The siltstone-metashale sequence beneath the siliceous rocks is tentatively identified as Womble;it shows incipient metamorphism. Underlying the Womble(?) is an unmetamorphosed quartz sandstone of Mississippian-Pennsylvanian type. This rock cannot be positivelyidentified as Ouachita facies (Stanley) or foreland facies (Atoka);ifitis foreland facies (Atoka) a major frontal displacement is indicated inthis area; ifitis Ouachita facies itmerely indicates over- thrusting or reverse faulting inthe frontal zone of the Ouachita belt withlower Paleozoic Ouachita rocks thrust over Stanley. This well penetrated incipiently to weakly metamorphosed upper and lower Paleozoic Ouachita facies rocks, intersected a thrust fault, and passed into Mississippian-Pennsylvanian sandstone (fore land facies?). Itis located in the frontal zone of the Ouachita belt south of the Llano uplift. — X-ray data. None. — References. Personal communication: Roland Blumberg, 1957; August Goldstein, Jr., Bell Oil and Gas Company, 1958;J. R. Sandidge, Magnolia Petroleum Company, 1957. Bureau ofEconomic Geology, The University of Texas — County. Comal. — Wellname. Caldwell&LanierNo.1T.J.Byler. Location.—HE&WT survey; 1,028 feet FNL, 486 feet FWL; extreme N part of County. —— — Elevation. 1,220 feet (from topographic map). Total depth. 948 feet. Completed. 1932. — Top of Paleozoic rocks. 615 feet. Elevation of Paleozoic rocks.— -f-605 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 722. — Description of Paleozoic rocks. The single sample examined for this study is composed of dark green shale or metashale showing incipient metamorphism ;possibly this sample is lower Paleozoic Ouachita facies, but a positive identification cannot be made. The wellisin the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. Samples are in Bureau of Economic Geology WellSample Library. — County. Comal. — Well name. W. W. Connell, Incorporated, No. 1Casey. Location.—HE&WTsurvey; 2,700 feetFNL,660feetFEL. —— Elevation.—1,325 feet. Totaldepth.--1,300 feet. Completed. 1947. —— TopofPaleozoic rocks. 875(?) feet. Elevation ofPaleozoic rocks. -|-450(?) feet. Thinsection coverage (depth in feet).—None. Description of Paleozoic rocks.—Scout card shows "top slate, 875." The wellprobably penetrated very weakly metamorphosed Ouachita facies rocks (lower Paleozoic?) in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Comal. — Well name. Oblate Fathers Water Well. — Location.-Guadalupe Herrera survey; 600 feet FSL, 4,500 feet FWL; 1mi. SSW of Bulverde. — —— Elevation. 1,300 feet (from topographic map). Total depth. 1,300 feet. Completed. 1954. —— TopofPaleozoic rocks. 900± feet. Elevation ofPaleozoic rocks. +400± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Goldstein (1958) reported that a single sample from 1,320 feet is composed ofsilty clay-slate and argillaceous low-rank metasiltstone. This well seems to have penetrated very weakly metamorphosed rocks of Ouachita facies (lower Paleozoic ? ) inthe southern part of the frontal zone. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Bell Oil and Gas Company, 1958; Robert Pavlovic,Magnolia Petroleum Company, 1955. — County. Comal. — Wellname. YatesNo. 2Heidrick. Location—A.M.Holbrooksurvey;1,800 feetFNWL,1,850feetFSWL. Elevation.—999 feet. Total depth.—l,B67 feet. Completed.—l937. — Top of Paleozoic rocks. 1,822 feet. Elevation of Paleozoic rocks. 823 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. — Personal communication: Porter Montgomery, Pan Corporation, 1957; J. R. Sandidge, Magnolia Petroleum Company, 1957. References. American Petroleum — County. Coryell. Wellname.—BuckeyeandMid-TexOilCompany (Mid-Kansas?) No.1G.A.Strickland. The Ouachita System Location.—John Winn survey; 5,000 feet FEL, 4,300 feet FSL; 17 mi. SW of Gatesville. Elevation.—946(?) feet;9l2(?) feet. Total depth.—3,62B feet. Completed.—l9l9. —— TopofPaleozoic rocks. 615(?) feet.ElevationofPaleozoic rocks. -}-331(?) feet. — Thinsection coverage (depth infeet). bureau of economic geology: 1050-70, 1494-1520 (2), 19902005, 2170-80 (2), 3470-75, 3507-12. Description of Paleozoic rocks.—Adkins and Arick (1930) reported 1,600 feet of Strawn, 375 feet of Smithwick, 140 feet of Marble Falls, and 13 feet of Ellenburger; they placed top of Ellenburger at 3,615 feet, which is the same figure given by Sellards (1933) as top of Ordovician. Sample descrip tions in the files of the Bureau of Economic Geology suggest the following sequence: top of Atoka, 615± feet; top of Marble Falls —Barnett, 3,100± feet; top of Ellenburger, 3,620 feet. Thin section studies show a sequence of fine-grained, angular to subround, fairly well-sorted, quartz sandstone and dark silty shale of Atoka type overlying siliceous spiculitic limestone identified as Marble Falls. No study of the underlying Ellenburger was made. The rocks are foreland facies, and the wellislocated west of the Ouachita structural belt. X-raydata.—l> Ch>ML>K(?);10/7 13;F=20;SR=2.1. References.— Adkins and Arick (1930, pp. 8-10) ;Sellards (1933, p. 206). Bureau ofEconomic Geology files. Personal communication: Robert Roth, Humble Oil&Refining Company, 1955. Samples are inBureau of Economic Geology Well Sample Library. County.—Coryell. — Wellname. Cockburn No.1Kearny (Kernay, Kearday). — Location. James Butterworth survey; 330 feet FSL, 1,650 feet FEL; 10 mi. SE of Gatesville. — Elevation.-ni. Total depth.-—4,520 feet. Completed.— l9so. —— Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 1955-70, 2030-40, 2150-60, 2305-10, 2795-05, 3400-10, 4200-10, 4210-20, 4355-60. — Description of Paleozoic rocks. Information from sample log shows that the wellis in "Strawn" at 1,950 feet with total depth 4,520 feet in "Strawn"; lithology is given as hard gray quartzitic sand stone. The sequence is composed of dark silty shale and fine-grained, mostly subangular to subround, fairlywell-sorted, slightly argillaceous and feldspathic quartz sandstone, locally containing shale and chert fragments. The rocks show no evidence of metamorphism. This section is probably Atoka rather than Strawn. This wellpenetrated foreland basin rocks west of the Ouachita belt. = X-raydata.—l>ML>Ch>X;10/7 <-->1.8;F 20. References.— -Personal communication: J. C. Barker, General Crude OilCompany, 1957. — County. Coryell. — Wellname. Coryell CountyOilCorporation No.1J.Q.Davidson. — Location. Neil Robinson survey. — — Elevation. ni. Totaldepth. —4,400± feet. Completed. 1933 ( ? ). —— Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology indicate that the wellis inAtoka at total depth. The wellis west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Coryell. — Well name. E. A.Dunham (New York Syndicate) No.1Tienert. Location.—Elizabeth Jones survey; 3,000 feet FSL, 3,400 feet FWL. Elevation.—l,o94 feet. Totaldepth.—3,72s(?) feet. Completed.—l92l. — TopofPaleozoic rocks. 800(?)feet.ElevationofPaleozoic rocks. 1-294(?) feet. — Thinsection coverage (depth infeet). bureau of economic geology: 3467 (2). — Description of Paleozoic rocks. Adkins and Arick (1930) reported 1,900 feet of Strawn, 430(?) feetofBend,and21feetofEllenburger withtopofEllenburger at3,579 feet.Sellards (1933) noted Bureau ofEconomic Geology, The University of Texas top of Ordovician at 3,384 feet. The—"Strawn" and "Bend" sequence reported by Adkins and Arick is probably Atoka and Marble Falls Barnett. The single thin section (3467) available for this study is fine-grained Ellenburger dolomite. This wellis inforeland facies rocks west of the Ouachita structural belt. — X-ray data. None. References.— Adkins and Arick (1930, pp. 8-10); Barnes (1948); Sellards (1933, p. 206). Personal communication: Robert Roth, Humble Oil&Refining Company, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Coryell. — Well name. General Crude OilCompany No. 1Earnest Day. — Location. R.T.Davidsonsurvey;660feetFSL,2,550feetFEL;5mi.WofMoody. — —— Elevation. 732 feet, derrick floor. Totaldepth. 9,275 feet. Completed. 1957. TopofPaleozoicrocks.—1,190 feet.Elevation ofPaleozoicrocks. 458feet. — Thin section coverage (depth in feet). bureau of economic geology: 1340-50, 1400-10, 1500-10, 1620-30, 2590-00, 3550-60, 3620-30, 5700-10, 5741-50, 5880-90, 6360-90, 6530-40, 6600-10, 6700-10, 6750-60, 6770-80, 6800-10, 6870-80, 6990-00, 7300-10, 7380-90, 7700-10, 7740-50 (3), 7990-00 (3),8650-60, 9200-10. — Description of Paleozoic rocks. The following divisions are based on sample examination: top of Stanley, 1,190 feet; top of pre-Stanley, 6,800± feet; top of carbonate beds, 7,380 feet; top of sandstone and shale section, 7,405 feet (siliceous shale, 7,530 feet) ;top of dense limestone and shale, 7,580 feet; top of dark chert and shale, 8,090 feet. Graptolites from7,540 to 7,550 and 7,560 to 7,570 feet are Bigfork-Womble. Petrographically, the upper sequence is composed of fine-grained, angular, poorly sorted, argil feldspathic laceous — quartz sandstone containing angular garnet in the heavy mineral fraction and dark silty shale itis typical Stanley. There is a hard green siliceous tuffaceous shale at the base ofthe Stanley (samples 6,700-6,710, 6,750-6,760, 6,770-6,780 feet) which shows relict vitroclastic fabric. Samples at 6,800 to 6,810 and 6,870 to 6,880 feet are mostly light-colored to dark argillaceous micro- angular to cryptocrystalline radiolarian cherts, containing dark organic material, sparsely dolomitic, and very dark brown siliceous shale rich in brown organic matter, locally dolomitic; —this sequence resembles Arkansas novaculite. The lower section shows characteristic Bigfork lithology fine-grained argillaceous dolomitic limestone, locally spiculitic, dark siliceous dolomitic shale, and dark argillaceous dolomiticchert, allcontaining abundant dark organic material. Dark brown slightly micaceous shale and micaceous chloritic quartz siltstone in the last two samples thin sectioned (8650-60 and 9200-10) are probably Womble. Maner (1958) believed that this wellintersected a thrust and passed into Atoka beds at about 9,000 feet. These rocks are unmetamorphosed toincipiently metamorphosed Ouachita facies rocks ofbothupperand lower Paleozoic age;except in the cherts, there is a lack of the quartz and calcite veinlets which characterize similarrocks elsewhere. This wellpenetrated the frontalzone of the Ouachita structural belt. = X-raydata.—l>Ch>ML;10/7<-'1;F 20; SR=2.15. References.— Personal communication: J. C. Barker, General Crude Oil Company, 1957; W.B.N. Berry,University ofHouston, 1957;R.P.Maner, ShellOilCompany, 1958. Samples areinBureau ofEconomic Geology WellSample Library. — County. Coryell. — Wellname. Kansas CitySyndicate No.2 Thomas Young. — Location.-Thomas Young survey;4.8 mi.NofKilleen. — —— Elevation. 838 feet (by aneroid barometer). Total depth. 2,985 feet. Completed. 1920. — Topof Paleozoic rocks. 665± feet. Elevation ofPaleozoic rocks. 1-173± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 1008, 1785, 1955, 2340, 2790. — Description of Paleozoic rocks. Notes inthe Bureau of Economic Geology files indicate that the wellbottomed inAtoka. The sequence consists of: (1) fine-grained, angular to subround, fairly well-sorted to poorlysorted, calcareous quartz sandstone, commonly argillaceous, silty, locally quartzitic; (2) dark siltyshale; (3) angular argillaceous quartz siltstone; and (4) dark fine-grained fossiliferous limestone containing angular quartz silt-sand. This wellpenetrated Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. The Ouachita System County.— Coryell. — Well name. Keystone Texas OilCompany No.IJ. S. Clark. — Location. G. W. Carlile survey; 10 mi. SW of Gatesville. —— — Elevation. ni. Total depth. 3,630 feet. Completed. 1919. — — Top ofPaleozoic rocks. 695± feet. Elevation of Paleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Descriptions of samples in the files of the Bureau of Economic — Geology suggest the following sequence: top of Paleozoic (Atoka), 695 feet; top of Marble Falls Barnett, 3,311 feet; top of Ellenburger, 3,665 feet. This wellpenetrated foreland basin rocks west of the Ouachita belt. — X-ray data. None. — Bureau of Economic Geology files. References. County.—Coryell. — Wellname. New YorkSyndicate No.1Charles Gotcher. — Location. W. T. Whitely survey; 4 mi. SW of Copperas Cove. — —— Elevation. 1,130 feet. Total depth. 3,192 feet. Completed. 1919. — Top of Paleozoic rocks. 620± feet. Elevation of Paleozoic rocks. r-510± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2900. — Description of Paleozoic rocks. Adkins and Arick (1930) reported 1,700 feet of Strawn, 125 feet of Bend, and 57 feet of Ellenburger; top of Ellenburger is given as 3,035 feet. Sellards (1933) reported topofOrdovicianat3,025 feet.AccordingtoGoldstein (1955), thiswellwasinMarbleFallsorBar nett at 2,900 feet. Sample descriptions inthe files of the Bureau of Economic Geology suggest the following sequence: top of Atoka, 620 feet; top of Marble Falls—Barnett, 2,892 feet; top of Ellen- burger, 3,043 feet. The single sample studied from 2,900 feet is a black spiculiferous pyritic calcareous shale, probably Marble Falls. This wellpenetrated foreland rocks west of the Ouachita structural belt. — X-ray data. None. References.— Adkins and Arick (1930, pp. 8-10) ;Barnes (1948) ;Sellards (1933, p. 206). Bureau ofEconomic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; Robert Roth, Humble Oil&Refining Company, 1955. Samples are inBureau of Economic Geology Well Sample Library. County.—Coryell. Additionalwellsnotshownonmap(PI.2)andnotstudiedbecause oflackofsamplesorbasicdata: U.S. Army Water Well No. 1— Location: Gatesville area. Total depth: 760 feet. Top of Paleozoic rocks: 748 feet. Dark gray compact clay and hard quartzitic cherty sandstone. U.S.ArmyWater WellNo.2— Location: Gatesville area. Total depth: 688 feet. Completed: 1943. Top of Paleozoic rocks: 674± feet. Blue gray shale. U. S. Army Water WellNo. 3— Location: Gatesville area. Total depth: 721 feet. Top of Paleozoic rocks: 700 feet. Black hard brittleshale. U. S. Army Water Well No. 6— Location: Gatesville area. Total depth: 735 feet. Top of Paleozoic rocks: 730 feet. Yellow-red — clay old soil? U. S. Army Water Well No. 7— Location: Gatesville area. Total depth: 745 feet. Top of Paleozoic rocks: 740 feet. Green-gray clay. U.S. Army Water WellNo. 10— Location: Gatesville area. Total depth: 764 feet. Completed: 1943. Top of Paleozoic rocks: 762 feet. Dark maroon and red silty clay. U.S. ArmyWaterWellNo.11— Location: North Camp Hood. Total depth: 755 feet. Completed: 1943. Top of Paleozoic rocks: 735 feet. Dark fine-grained hard quartzitic sandstone. Bureau ofEconomic Geology, The University of Texas U.S. ArmyWater WellNo.12— Location: North Camp Hood. Total depth: 755 feet. Completed: 1943. Top of Paleozoic rocks: 730 feet. Dark gray almost black hard cherty quartzitic sandstone. — Summary of Army Wells The above wells apparently penetrated a weathered zone at the top of the Atoka formation and underlying Atoka sandstone and shale. R. T.ElliottWell— Location: 3% mi. NW of Copperas Cove. Total depth: 1,875(?) feet. Completed: 1919. Top of Paleozoic rocks: 500(?) feet. Driller'slog suggests Atoka lithology; wellis % mi. E of Dunham No. 1 Tienert (p. 245). — Columbia Texas OilCompany No.1W.L.Sadler Location: 19 mi. Sof Gatesville. Elevation: 900 ± feet. Total depth: 4,360 feet. Completed: 1920. Driller's log suggests total depth inAtoka. — County. Dallas. Wellname.—CityofDallas No.45 WaterWell. — Location. NE corner of Hillcrest Avenue and Walnut Lane, Dallas, Texas. — — Elevation. 640 feet. Totaldepth.— 3,osB feet. Completed. 1956. Topof Paleozoic rocks.—3,039 feet. Elevation ofPaleozoic rocks. 2,399 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3037-42, 3042-47. — Description of Paleozoic rocks. The rocks are composed of very dark gray to red silty and sandy shale and dark, fine-grained, angular to round, poorly sorted, argillaceous micaceous feldspathic quartz sandstone containing angular garnet in the heavy mineral fraction; the rocks are cut by calcite veinlets. Sample coverage on this wellis poor. The lithology appears to be Stanley type; the wellprobably entered the frontal zone of the Ouachita structural belt. X-ray data.— None. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1958. — County. Dallas. Wellname.— CityofDallas No. 46 Water Well. — Location. \l/i\l/i mi. N of Carrollton; 1% mi. N, % mi. W of intersection of the old Denton and Beltline roads. —— — Elevation. ni. Total depth. 2,321 feet. Completed. 1957. — — Topof Paleozoic rocks. 2,260 feet. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 2260-70, 2300-10. — Description of Paleozoic rocks. The rocks penetrated in this well are dark silty shale, locally micaceous, locally dolomitic. The facies cannot be identified withcertainty. — X-raydata.—ML>I>X>Ch;10/7 '0.8;SR=1.0.AbundantMLwithhighmontmorillonite content suggests foreland facies. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1958. — County. Dallas. — Well name. Garland City Water Well (J. L.Myers & Sons, Federal Works Agency Docket). — Location. J. W. Keen survey, W/2 section 25;1mi. WofGarland. — —— Elevation. 550± feet. Total depth. 3,629 feet. Completed. 1943. — Top of Paleozoic rocks. 3,570 feet. Elevation of Paleozoic rocks. 3020± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Top of Paleozoic by electric log is 3,570 feet. — X-ray data. None. References.— Bureau of Economic Geology files. — County. Dallas. Wellname.— Lacey and Guiberson No.1Meyers (Moyer?). Location.—Thomas Johnson survey; 660 feetFNEL,1,980 feetFSWL; 17mi.SE ofDallas. The Ouachita System —— Elevation. 366 feet. Totaldepth. —4,843 feet. Completed. 1943. Top of Paleozoic rocks.—4,440 feet. Elevation ofPaleozoic rocks. 4,074 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 4370-84, 4468-84, 4484-00, 4523-39, 4616-32. shell oilcompany: 4455. — Description of Paleozoic rocks. According to Goldstein (1955), base of Cotton Valley and top of Paleozoic rocks, Stanley(?), is 4,440 feet, and total depth is 4,843 feet inStanley(?). Thin section study shows a sequence composed mostly of micaceous chloritic argillaceous siltstone veined with quartz and quartz-calcite. The rocks are Ouachita fades; on general lithology and location, the sequence is probably Stanley. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Dallas. Wellname.—McNeil&Mathews No.1W. W.Seaton. Location.—J.G.Garrettsurvey; 400feetFEL,1,900 feetFmostSlyline;2mi.NofBritton. — —— Elevation. 755± feet. Totaldepth. 2,660 feet. Completed. 1928. Top of Paleozoic rocks.-—2,197(7) feet; 2,090(?) feet. Elevation of Paleozoic rocks. 1,442(?) feet; -1,335(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 2240, 2300, 2400, 2435, 2485, 2655. — DescriptionofPaleozoic rocks. Adriller'sloginBureau ofEconomic Geology filesindicates topof Paleozoic rocks at about 2,090± feet; cores at 2,435 and 2,655 feet are described as black slickensided shale and hard black shale. Sellards (1933) gave approximate top of Paleozoic rocks as 2,435 feet and described the rock as "black shale." Thin section studies show the entire sequence penetrated is dark gray silty shale;no quartz or calcite veins werenoted. Inallprobability these rocks are Atoka. This wellpenetrated foreland rocks west of the Ouachita structural belt. X-raydata.—l>ML>Ch>X;10/7 —^1.1;F=20;SR=1.55.Shales showamixedlayerillitemontmorillonite mineralogy of Atoka type. References.— Sellards (1933, p. 188). Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. Samples (incomplete) areinBureau ofEconomic Geology WellSample Library. — County. Dallas. — Wellname. Magnolia Petroleum Company No.1Trigg. — Location. T.W.Cousey survey; 660 feetN,660 feetEofNEcor.ofSA&MGsurvey. —— Elevation. 526 feet, derrick floor. Total depth.—10,231 feet. Completed. 1955. — Topof Paleozoic rocks. 2,043 feet. Elevation of Paleozoic rocks. 1,517 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. H. A.Sellin (1957) reported base of Cretaceous and top ofPenn sylvanian(?), 2,043 feet; top of Strawn, 3,173 feet; top of Atoka(?), 5,485 feet; top ofMarble Falls, 8,055 feet; top of Barnett(?), 8,658 feet; top of Viola,9,057 feet; top of Simpson, 9,357 feet; top of Ellenburger, 9,742 feet; totaldepthinEllenburger. This wellpenetrated foreland basin rocks west of the Ouachita structural belt. — X-ray data. None. — References. Personal communication: H. A. Sellin, Magnolia Petroleum Company, 1957. — County. Dallas. — Wellname. Mark Raley No. 1Morris. Location—C.Gibbssurvey; 129feetFNL,1,483 feetFWL;2mi.SofGrandPrairie. — — Elevation. 488 feet. Total depth. —2,636 feet. Completed. ni. Top of Paleozoic rocks. —2,000± feet. Elevation of Paleozoic rocks. 1,512± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. From its location, this well probably penetrated Atoka rocks west ofthe Ouachita belt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. — References. None. — County. Dallas. — Wellname. Texas Water Wells,Incorporated, No.40 CityofDallas. — Location. J. Nealy Bryan survey; 310 Cadiz Street, Dallas, Texas. — —— Elevation. 400 feet. Totaldepth. 2,800 feet. Completed. 1953. —— Top ofPaleozoic rocks. 2,790 feet. Elevation ofPaleozoic rocks. -2,390 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2790. — Description of Paleozoic rocks. The single sample examined for this study is red and gray siltyshale, locally dolomitic. No reliable determination of facies can be made from this sample. The well is located close to the projected course of the Ouachita front and may be inforeland rocks or within the frontal zone of the structural belt. — X-ray data. —None. References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Dallas. — Wellname. TexasWater Wells,Incorporated,No.41CityofDallas. — Location. BeltlineRoad, Dallas, Texas. Elevation.—mi feet. Totaldepth— 3,o7s feet. Completed— -1952. — Topof Paleozoic rocks. 3,066 feet. Elevation of Paleozoic rocks. 2,659 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Dallas. — Wellname. Texas Water Wells,Incorporated, No. 42CityofDallas. — Location. 2700 Singleton Boulevard, Dallas, Texas. —— — Elevation. 422 feet. Totaldepth. 2,563 feet. Completed. 1952. Top ofPaleozoic rocks. —2,530 feet. Elevation ofPaleozoic rocks. 2,108 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Edwards. — Wellname. HumbleOil&RefiningCompany No.1Collins. Location.—Section 73,block13,GC&SFsurvey;1,980 feetFSL,1,980 feetFWL;10mi.Sof Rocksprings. — —— Elevation. -2,274 feet, derrick floor. Total depth. 7,861 feet. Completed. 1953. —— Top ofPaleozoic rocks. 1,500 feet. Elevation of Paleozoic rocks. +774 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The following stratigraphic data are reported: top of Paleozoic, 1,500 feet; top of Marble Falls, 7,700 feet; top of Simpson, 7,782 feet; top of Ellenburger, 7,810 feet. This wellpenetrated foreland basin rocks north ofthe Ouachita belt. — X-ray data. None. — References. Personal communication: J. C. Meacham, Humble Oil& Refining Company, 1957. — County. Edwards. — Well name. Hunt OilCompany No. 1Allison. Location.—Section1,blockDA6,GC&SFsurvey; 330 feetFSL,330 feetFEL;18mi.SEofRocksprings. The Ouachita System Elevation.—l,9o3 feet. Totaldepth—6,slo feet. Completed.—l94B. Topof Paleozoic rocks.—1,070 feet. Elevation of Paleozoic rocks.— +833 feet. — Thin section coverage (depth in feet). None. — Description of Paleozoic rocks. Goldstein (1955) reported first sample in Trinity at 930 to 940 feet; secondsampleinPaleozoic rocksat1,300feet;baseofSmithwickandtopofMarbleFalls(?), 5,320 feet; topofEllenburger, 5,460 feet; totaldepth 6,512 feet,inEllenburger. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. E. Galley, Shell Oil Company, 1956; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Edwards. Wellname.—PhillipsPetroleum Company No.1-ACarson. Location.—Solomon Page survey; 9,500 feet FSWL, 1,320 feet FNWL; 6 mi. WSW of Barksdale. — Elevation.—1,684 feet, derrick floor. Total depth.—9,970 feet. Completed. 1954. — TopofPaleozoic rocks.—1,090 feet. Elevation ofPaleozoic rocks. +594 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Young (1957) reported top of Wolfcamp, 1,090 feet; top of Pennsylvanian, 3,140 feet; top of Simpson, 9,500 feet; top of Ellenburger, 9,657 feet; total depth 9,970 feet, in Ellenburger. Galley (1957) stated that base of Wolfcamp is in the interval 2,600 to 3,200 feet. This wellpenetrated foreland basin rocks north of the Ouachita structural belt. — X-ray data. None. — References. Personal communication: J. E. Galley, Shell OilCompany, 1957; Addison Young, Phillips Petroleum Company, 1957. — County. Edwards. — Wellname. ShellOilCompany No.1Honeycutt. Location.—Section 7, TCRR survey; 669 feet FEL, 1,997 feet FSL; 12 mi. W and 3 mi. N of Rock- springs. Elevation.— 2,2oo feet, derrick floor. Totaldepth.— B,93l feet. Completed.— -1945. — Topof Paleozoic rocks. 1,120 feet. Elevation ofPaleozoic rocks.— +1,080 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1168-75, 1202-08, 1350-60, 2150-60, 3050-60, 4050-60, 5150-60, 7150-60. — Description of Paleozoic rocks. R. E. Farmer (1959) reported base of Cretaceous, 1,120 feet; topof Ellenburger, 7,220 feet; top of Cambrian sandstone, 8,890 feet. The sequence between the base of Cretaceous and top of Ellenburger is described as gray shale and siliceous sandstone with a few thin beds of fossiliferous limestone toward the bottom. Possibly the bottom part of this sequence is Atoka. Petrographic study shows that the sequence frombase of Cretaceous to top of Ellenburger is com posed of (1) dark silty shale, locally micaceous; (2) fine-grained, angular to subround, poorly sorted to fairly well-sorted quartz sandstone ranging from argillaceous to calcareous or dolomitic to siliceous (quartzitic);the sandstone contains shale and chert grains, feldspar content is low; and (3) fine- grained, angular and subangular, argillaceous calcareous — and dolomitic quartz siltstone. Therocksareforeland facies thewell islocatednorthoftheOuachitabelt. — X-ray data. None. — References. Personal communication: R.E.Farmer, ShellOilCompany, 1959. — County. Ellis. — Well name. American Liberty OilCompany No. 1McClain. — Location. Section 8,R.Pena survey; 4mi.NEofPalmer. — Elevation.—4o2 feet. Totaldepth. 4,270 feet. Completed.— l9s4. — Top ofPaleozoic rocks. 4,200 feet. Elevation of Paleozoic rocks. 3,798 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. On the basis of location, this wellprobably encountered the Stan leyformationinthefrontalzoneoftheOuachita structuralbelt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. — References.-None. — County. Ellis. — Well name. Bechner (Dallas Oil Company, United Petroleum Company) No. 1Howard Garvin. — Location. Coleman Jenkins survey ;3 mi. SE ofMidlothian. Elevation.—7so± feet. Totaldepth.—s,22o feet. Completed.—l92s(?). — Top of Paleozoic rocks. 2,598 ( ? ) feet. Elevation of Paleozoic rocks. -1,848 (?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The only available information is a driller's login the files of the Bureau of Economic Geology. Interpretations therefrom indicate that this wellpenetrated a sequence of black shale and gray to brown sandstone, probably Stanley, in the frontal zone of the Ouachita structural belt. — X-ray data. None. — Bureau of Economic Geology files. References. — County. Ellis. — Wellname. Hickey and WhiteNo. 2Medford. Location.—lsaac Carrollsurvey;2,300 feetFSWL,1,980feetFSEL;3mi.SofMaypearl. —— — Elevation. 506 feet. Total depth. 2,312 feet. Completed. 1954. — Top of Paleozoic rocks. 2,193(?) feet. Elevation ofPaleozoic rocks. 1,687(?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. On the basis of location, itis believed that this wellprobably encountered the Stanley formation inthe frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: H.J. Morgan, Jr.,The AtlanticRefining Company, 1956. — County. Ellis. — Wellname. Lesco (Lasco?) No.1Lesage (water well). Location.—E.D.Harrison survey; 330 feetFNEL,330 feetFSEL; 3mi.NW ofItaly. Elevation.—722 feet. Total depth.—2,9l2 feet. Completed.—l944. — Top ofPaleozoic rocks. 2,520 feet. Elevation of Paleozoic rocks. 1,798 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 2600-10, 2620-30. bureau of economic geology: 2520-30, 2720-30 (2). — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic, 2,520 feet; total depth inPaleozoic (Stanley?). Thin section study shows that the sequence is fine- grained, poorly sorted, argillaceous feldspathic quartz sandstone and dark shale, locally carbonaceous — a typical Stanley lithology. This wellpenetrated Stanley inthe frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955;H.J.Morgan,Jr.,TheAtlanticRefiningCompany, 1956. Samples inBureau ofEconomic Geology WellSample Library. — County. Ellis. — Well name. John MitchellNo. 1J. L.Rush. Location.—]. Chambles survey; 330 feet FNL, 800 feet FWL of J. L. Rush tract; 2 mi. W of Midlothian. Elevation.—662 feetL&S. Totaldepth.—4,o6l feet. Completed.—l9s3. — Top ofPaleozoic rocks. 2,098 feet. Elevation of Paleozoic rocks.— -1,436 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2330-60, 2410-50, 2710-40 (2),3250-80, 3780-20, 3910-40, 4030-60. The Ouachita System Description of Paleozoic rocks.—The following data are reported by Morgan (1956):top of Paleozoic, 2,080 feet; top of Arkansas novaculite, 2,098 feet; top of Missouri Mountain, 2,416 feet; top ofPolk Creek, 3,793 feet;top ofBigfork,3,846 feet. Petrographic study shows the following sequence (from top to bottom): (1) light-colored cryptocrystalline to chalcedonic argillaceous chert, locally containing organic matter and veined with quartz (Arkansas novaculite) ;(2) dark red to opaque hematitic shale, locally silty, and green shale, locally pyritic withsporadic carbonate grains (dolomite?, siderite?) (Missouri Mountain shale) ;(3) black pyritic bituminous rock (Polk Creek shale?) ;and (4) dark cryptocrystalline to microgranular chert containing masses of dark organic material, locallydolomitic,locallypyritic,veined withquartz, carbonate, and bitumen; some fragments intensely shattered (Bigfork chert). Hazzard (1958) reported dips of 45° to 60° in this sequence. This well penetrated lower Paleozoic Ouachita facies rocks in the frontal zone of the Ouachita rocks (Atoka) belt, probably close to the orogenic front; it is close to wells penetrating foreland inthe subrrop and their proximity suggests— overthrusting inthis area (PL 2). X-raydata.—l>Ch>ML>X;10/7 1.0; SR=1.9. — References. Personal communication: R.T.Hazzard,GulfOilCorporation, 1958;H.J.Morgan,Jr., The Atlantic Refining Company, 1956. — County. Ellis. Wellname.—]. B.Stoddard No.1W.E.Smith. Location.—]. B.Edwards survey; 660 feet FNWL,1,550 feet FSWL. —— — Elevation. 480 feet. Totaldepth. 5,020 feet. Completed. 1942. — Top of Paleozoic rocks. 4,847 feet. Elevation ofPaleozoic rocks.— -4,367 feet. — Thin section coverage (depth in feet). bureau of economic geology: 4909-10 (3), 4960-70 (2), 5000-10 (2). — Description of Paleozoic rocks. This wellencountered fine-grained, angular, poorly sorted, feldspathic quartz sandstone and gray and red silty shale; the rocks are cut by quartz-calcite veins. The sequence is Stanley. The wellpenetrated the frontalzone of the Ouachita belt. X-ray data—l>Ch>K; 10/7 —'2.5; SR= 2.3. (Kaolinite occurs only in 4,909 to 4,910-foot sample.) The shales are of Ouachita type and show good crystallinity withoutmixedlayering of illite-montmorillonitetypical of the foreland;chlorite content islow. — References. Personal communication :H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Ellis. — Well name. Triangle Corporation No. 1Hale. — Location. Benj. Smith survey; 1mi. SE of Avalon. — — Elevation. 455 feet. Totaldepth. —3,190 feet. Completed. 1930. — — Top of Paleozoic rocks. 3,060(?) feet. Elevation of Paleozoic rocks. .-2,605(?) feet. — Thin section coverage (depth infeet). bureau of economic geology: 3155-70 (2). — Description of Paleozoic rocks. Cellards (1931b, 1933) described cores at 3,060 and 3,155 to 3,190 feet as slickensided shale and quartzitic sandstone, probably Stanley-Jackfork. The single core sample examined for this study is composed of fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone of Stanley type. The wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Sellards (1931b, p. 822; 1933, p. 188). Samples are inBureau of Economic Geology Well Sample Library. — County. Falls. — Wellname. Humble Oil& Refining Company No. 1Carroll. Location.—L.Stephens survey;330feetFNWL,1,275feetFSWL;5.1mi.SEofWestphalia. Elevation— -502 feet. Total depth.— -3,717 feet. Completed.— l9sl. — Topof metamorphic rocks. 3,610 feet. Elevation of metamorphic rocks. 3,108 feet. — Thin section coverage (depth infeet). None. — Description of metamorphic rocks. Goldstein (Goldstein and Reno, 1952) described a thin section of a core (3,614 feet) as a metamorphosed, sheared argillaceous sandstone of Ouachita facies. The general location of the wellindicates that it penetrated highly sheared metamorphosed rocks in the interior zone ofthe Ouachita belt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. References.— Goldstein and Reno (1952, p. 2284) — County. Falls. — Wellname. HumbleOil&Refining Company No.1Pucek. Location.—L. Thurner survey; 2,917 feet FSWL, 217 feet FSEL; 4 mi. W and 6.5 mi. Sof County Line. Elevation.—426 feet. Totaldepth—3,s76 feet. Completed—l929. — Topof metamorphic rocks. 3,535 feet. Elevation of metamorphic rocks. 3,109 feet. Thin section coverage (depth in feet).—bureau of economic geology: two sections unmarked as to depth. — Description of metamorphic rocks. Sellards (1931b) reported that the core from 3,535 feet is similar to the Missouri Mountain slate; in a later publication (Sellards, 1933) he described the rock as phyllite. Samples examined for this study are gray, reddish topurplish sericite slate veined withquartz. The reddish color is due to disseminated tiny grains of hematite; locally rutileneedles are abundant. Metamorphism is weak; the original bedding intersects foliationand slaty cleavage at a high angle. The wellpenetrated the interior zone of the Ouachita belt. X-raydata.—l>>X(Tr);10/7~>20;F=24?;SR=10+;hematite, rutile(?). References.— Sellards (1931b, p. 822; 1933, p. 188). — County. Fannin. — Wellname. Callery,Incorporated, No.1R.G.Robinson. Location—S.M.Rainer survey; 1,980 feetFEL,660 feetFNL. —— Elevation. 714 feet. Totaldepth. —5,598 feet. Completed. 1952. TopofPaleozoic rocks.—3,214 feet. ElevationofPaleozoic rocks. 2,500 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3240-50, 3500-10, 3650-60, 4300-05, 4700-05 (2), 5590-95. — Description of Paleozoic rocks. -The rocks inthis wellare fine-grained, angular, poorly sorted, feldspathic quartz sandstone and dark silty metashale; the intergranular material in the sandstone is a mat of clay-sericite-chlorite which is slightly reconstituted. The heavy mineral fraction contains abundant angular garnet. The sequence is identified as Stanley. This wellpenetrated the frontal zone of the Ouachita belt. X-raydata.—l>Ch>ML(Tr)>K(?);10/7 0.7;F=20;SR=2.5. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Fannin. — Wellname. CoxDrillingCorporation No.1S.F.Leslie. — Location. Maria Ignacio Giminez survey; 660 feet FSL, 467 feet FEL; % mi. W of Ector. — —— Elevation. 648 feet, kelly bushing; 638 feet, ground. Total depth. 4,116 feet. Completed. 1957. — TopofPaleozoic rocks. 2,560 feet. Elevation ofPaleozoic rocks. 1,912 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2620-30, 3100-10 (2), 3500 10,3900-10,4100-10(2). — Description of Paleozoic rocks. The sequence penetrated in this well is composed of: (1) fine- grained, mostly subangular to subround, fairly well-sorted, quartz sandstone, locally slightly dolomitic, feldspathic, or argillaceous; (2) angular to subangular well-sorted tightly packed micaceous and chloritic quartz siltstone; and (3) dark shale, locally pyritic, siliceous, or spiculitic. Radiolarianbearing siliceous shale occurs at 4,100 feet. The rocks are cut by quartz veinlets; locally there appears to be incipient metamorphism. Although these rocks occur ina terrane where the neighboring wells have encountered Stanley beds, they do not resemble Stanley. Goldstein (1959) reported that the sample from 2,620 feet may be Atoka and that the deeper samples are Jackfork sandstone. This wellpenetrated the frontal zone of the Ouachita structural belt. — X-ray data.—l>ML>Ch;10/7 1.3; SR=l.5. The absence of feldspar is characteristic of Jackfork. — References. Personal communication: R. A. Hall, Pan American Petroleum Corporation, 1957; August Goldstein, Jr., BellOiland Gas Company, 1959. Samples areinBureau ofEconomic Geology WellSample Library. The Ouachita System — County. Fannin. — Wellname. Damon OilCompany No.1Chaffin. — Location. J.Kuetchem survey; 4mi.NEofBonham. Elevation.—s6B feet. Totaldepth—3,2o4 feet. Completed—l942. — Top ofPaleozoic rocks. 3,115 feet. Elevation of Paleozoic rocks. 2,547 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 3100, 3130, 3150, 3200. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic (Stanley? ) at 3,115 feet withtotal depth 3,204 feet inStanley (? ). The sequence is composed of fine-to very coarse-grained, angular, poorly sorted arkose. The rocks are unmetamorphosed, and although several samples show a resemblance to Stanley lithology, there appears to be more feldspar, particularly potassium feldspar, than is typical. Possibly the feldspar was derived from an uplifted foreland element such as the Muenster or Arbuckle blocks. The wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955;H.J.Morgan,Jr.,TheAtlanticRefiningCompany, 1955. — County. Fannin. Wellname.—ElkayOiland Gas Company No.1WilsonLane. Location.—l.Bourland survey; 2,200 feet FWL, 1,700 feet FNL; 2 mi. NW of Ector. — —— Elevation. 700± feet. Total depth. 3,134 feet. Completed. 1921. — Top of Paleozoic rocks. 2,338(?) feet. Elevation of Paleozoic rocks. 1,638±(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 2375-80 (2), 2387-2410, 2430, 2440, 2450, 2454-56, 2460, 2500, 2515, 2530 (2), 2535, 2545, 2560, 2570, 2575, 2590, 25972605, 2610, 2625-30, 2630-40, 2640-58, 2658-70, 2675-94, 2694-2792, 2795, 2834, 2865, 2876-95. Description of Paleozoic rocks. —Sample descriptions in the Bureau of Economic Geology files report gray to black shale locally slickensided, and indurated brown to gray sandstone from 2,338 to 3,134 feet; spicules were noted at 2,895, 3,007, and 3,127 feet. Miser and Sellards (1931) identified the sequence penetrated in this well as Stanley shale; Sellards (1933) described it as black shale and sandstone. The section is unmetamorphosed to incipiently metamorphosed shale, siltstone, and fine-grained sandstone. The shales are dark colored, commonly contain fine quartz silt, carbonaceous debris, and mica shreds, and locally contain finely dispersed carbonate. The sandstones are fine-grained, tightly packed, mostly angular, poorly sorted argillaceous micaceous quartz sandstone containing chert grains and shale fragments. Goldstein (1959) reported the following petrographic determinations: 2,530 to 2,575 feet, Atoka; 2,590 to 2,630 feet, Atoka(?) ;2,630 to 2,895 feet, Jackfork. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Miser and Sellards (1931, pp. 812-813) ;Sellards (1933, p. 188). Personal communication: August Goldstein, Jr., Bell Oiland Gas Company, 1959. Samples are in Bureau of Economic Geology Well Sample Library. — County. Fannin. — Wellname. Hamilton-Powell DrillingCompany No.1Losche. Location.—RobertKerrsurvey; 4,010 feetFNL,990feetFEL;18mi.NofBonham. —— — Elevation. 565 feet. Total depth. 6,408 feet. Completed. 1952. Topof Paleozoic rocks.—2,200 feet. Elevation of Paleozoic rocks. 1,635 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2500-10, 2700-10, 2800-10, 3020-30, 3250-60 (2), 3530-40, 3920-30 (2), 4820-30 (3), 5550-60 (3), 6350-60 (3). — Description of Paleozoic rocks. Coon (1955) reported top of Paleozoic 2,190 to 2,210 feet; the Paleozoic sequence consists of alternating dark shale and fine-grained greenish-gray sandstone and siltstone, locally quartzitic. Thin section study shows the sequence is primarily dark carbonaceous and micaceous shale and fine-grained angular to subround, poorly to fairly well-sorted quartz sandstone, locally feldspathic. One section (2700-10) contains metashale, but in general the rocks are unmetamorphosed. The sandstones show better rounding and sorting, contain less clay, less feldspar, and more carbonate than Bureau ofEconomic Geology, The University of Texas typical Stanley sandstone and do not contain garnet in the heavy mineral fraction. The rocks are identified as Jackfork sandstone. The wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: L. A. Coon, The Texas Company, 1955; H. J. Morgan, Jr., The Atlantic Refining Company, 1955; August Goldstein, Jr., BellOiland Gas Company, 1959. County.— Fannin. — Well name. E. V.Parsons (George L.Pace?) No. 1R. E.Morgan. — Location. J. C.English survey; 3mi.E,1mi.NofSavoy. — —— Elevation.-666 feet. Total depth. 3,048 feet. Completed. 1930. Top ofPaleozoic rocks. —2,280 feet. Elevation of Paleozoic rocks. 1,614± feet. — Thin section coverage (depth in feet). bureau of economic geology: 3515-18, 3521-22, 3546-48, 3598-99 (2),3641-44 (2),3656-60, 3664-65, 5534-36. — Description of Paleozoic rocks. Innotes in the Bureau of Economic Geology files, Sellards described samples from 2,794, 2,999, 3,042, 3,045, and 3,048 feet as gray quartzitic siltstone. Miser and Sellards (1931) identified samples from this wellas Stanley shale; later Sellards (1933) described the sequence as hard shale and sandstone. Thin section study shows a sequence composed of fine-grained, angular, poorly to fairly well-sorted quartz sandstone, commonly argillaceous, micaceous, calcareous, and/or slightly feldspathic, dark silty shale, and calcareous micaceous siltstone. Quartz veins are present. The sandstones differ from Stanley sandstones in that they contain less clay and feldspar, are generally better sorted, and do not have thecharacteristic garnet inthe heavy mineralfraction (cf.Hamilton-PowellNo.1Losche). There is no metamorphism. The rocks are identified as Jackfork sandstone. This wellpenetrated the frontal zone of the Ouachita belt. — —— X-ray data.I>Ch (MLTr?);10/7 '4; SR 1.6. The absence of feldspar is characteristic of Jackfork sandstone. References.-— Miser and Sellards (1931, pp. 813-814) ;Sellards (1933, p. 188). Samples are in Bureau of Economic Geology Well Sample Library. — County. Fannin. — Well name. Sun OilCompany No. 1Tucker. — Location. Juan M.Zepada survey;3mi.NofLeonard. —— — Elevation. 660 feet. Totaldepth. 3,854 feet. Completed. 1955. — Top of Paleozoic rocks. 3,755 feet. Elevation ofPaleozoic rocks. 3,095 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3760-70, 3790-00, 3820-30. — Description of Paleozoic rocks. Means (1956) reported base of Cotton Valley and top of Paleozoic brown chert, 3,755 feet; top of black chert and black siliceous shale, 3,790 to 3,800 feet. Thin section shows dark cryptocrystalline chert rich in dark organic material, commonly containing cavities lined with chalcedony and filled with black bituminous material; quartz veins are common and bitumen occurs inthe centers of the veins. The rocks are Bigfork chert. The wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. A. Means, Sun Oil Company, 1956. — County. Fannin. — Wellname. TexasMineralsNo.1Snowden (Wharton? ). Location.-—WilliamRice survey; 1,060 feet FEL, 2,580 feet FSWL; 2 mi.E and slightly S of White- wright. — Elevation. 707 feet. Totaldepth.—4,100 feet. Completed.—l944. — TopofPaleozoic rocks. 3,210 feet. Elevation ofPaleozoic rocks. 2,503 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3395-3425 (2), 3456-86 (2), 3537-42 (2), 3542-47 (2), 3557-62 (2). — Description of Paleozoic rocks. The sequence is composed of dark silty shale and fine-grained, angular to subangular, poorly sorted, feldspathic quartz sandstone, locally argillaceous and micace The Ouachita System ous; there is a high percentage of garnet in the heavy mineral suite. The rocks are identified as Stanley shale. — This wellpenetrated the frontal zone of the Ouachita belt. ' X-raydata.—l>Ch>ML>K(?);10/7 1;F=20;SR=2.5. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955; H. A. Sellin, Magnolia Petroleum Company, 1956. — County. Fannin. — Wellname. U.S. Epperson Underwriting Company No.1-A W.L.Helton. — Location. Daniel Young survey; 467 feet S along ELofDalton survey, thence 617 feet E to location. — Elevation. 602± feet. Total depth.— s,9l6 feet. Completed.— l9s2. Top of Paleozoic r0ck5.—3,440 (?) feet. Elevation of Paleozoic rocks. 2,838±(?) feet. — Thinsection coverage (depth in feet). None. — Description of Paleozoic rocks. This wellwas drilled as "a tight hole." A scout inferred the pres ence of steeply dipping beds because the driller was unable to maintain a straight hole with normal drillingweight. Based on location, this wellpenetrated the frontal zone of the Ouachita beltin an area where the subcrop might be either Stanley orpre-Stanley Ouachita facies rocks. — X-day data. None. — References. Personal communication: E. M.Hurlbut, Jr., Shell OilCompany, 1956; H. J. Morgan, Jr., The Atlantic Refining Company, 1957. — County. Freestone. — Wellname. Humble Oil&Refining Company No.1Marberry. Location.—S.P.Flintsurvey; 660feetFSL,660feetFWL. — —— Elevation. 459 feet. Total depth. 13,595 feet. Completed. 1952. — Top of Paleozoic rocks. 13,452 feet. Elevation ofPaleozoic rocks. 12,993 feet. — Thin section coverage (depth in feet). bureau of economic geology: 13,270, 13,279, 13,373, 13,387, 13,452, 13,453, 13,457-62, 13,462-67, 13,472-76, 13,481-86, 13,486-91, 13,496-01, 13,501-06, 15,530-35, 13,540-45, 13,545-50, 13,550-55, 13,560-61, 13,561-64, 13,567-73, 13,577-90. — Description of Paleozoic rocks. According to Woods (1956), this wellpenetrated a normal section of upper Jurassic rocks and encountered olivine basalt from 13,266 to 13,452 feet; from 13,452 feet tototaldepth thesequence iscomposedofbrecciatedredhematiticquartziticsandstone withstreaks of red sandy shale. Thin section shows cataclastic and hydrothermal metamorphism of slate grade (determination byP. H.Masson). Hurlbut (1958) noted the presence of10 feet of red shale beneath the basalt; he believed that this red shale (possibly Eagle Mills) is separated from the quartzite sequence below by a fault. Another possibility is that the red shale is a weathered zone at the top of the metamorphosed sequence. The predominant rock type in the sequence beneath the basalt is a hard, red, fine-grained, angular to round, fairly well-sorted to poorly sorted, hematitic argillaceous feldspathic quartzitic quartz sandstone containing abundant chert grains, locally dolomitic, calcareous, chloritic, or sericitic, and commonly veined with hematite, quartz, chlorite, and/or dolomite; there are minor amounts of angularhematitic micaceous feldspathic quartzitic siltstone with shaly or slaty layers in the sandstone sequences. Mica in the siltstone-shale is second-cycle mica and new sericite and is commonly welloriented; some of these rocks are micaceous clay-slates. In the upper part of the sequence the sandstones contain detrital feldspar (both microcline and sodic plagioclase) and relatively large rock fragments of quartzite (silica-cemented standstone) and chert; lower—in the sequence there is abundantalkali feldspar interstitial to secondarily enlarged quartz grains this feldspar appears to be authigenic and comprises as much as 50 percent of the rock.In some parts of the rock quartz grains are completely welded together by silica cement. Inone section hematite and chlorite occur as pseudo- morphs after magnetite (? ). The provenance of these sandstones seems to have been older sedimentary rocks as indicated by thegrains of quartzite and the diverse characters of the quartz grains which include straight extinguishing quartz (locally withinclusions of biotite), weakly undulose quartz, and strongly undulose quartz and composite grains. It is very difficult to assess the degree of metamorphism because of the obscuring effects of hematite and clay (white reflecting, montmorillonite? ) which seem to have leached down from the overlying section of altered basalt, and because of the relatively simple quartz-feldsparmineralogy. Reconstituted mica-chlorite in some of the slaty rocks suggests a very weak or weakmetamorphism; the abundant authigenic feldspar indicates a strong hydrothermal element. This wellis east of highly sheared low-grade metamorphic rocks of the interior zone;the relation ship of these rocks to the more highly metamorphosed sequence isunknown and their age is unknown. General lithology indicates a Paleozoic age. Goldstein (1959) believed that these rocks are low-grade Bureau ofEconomic Geology, The University of Texas — metamorphic rocks—equivalent in grade to other rocks of the interior zone but possibly metamorphosed by nearby igneous intrusion. Another possibility is that they are post-orogenic late Paleozoic rocks altered by nearby igneous activity;the lithology is compatible witha post-orogenic facies. — X-ray data. None. — References. Personal communication: E. M. Hurlbut, Shell Oil Company, 1958; R. D. Woods, Humble Oil&Refining Company, 1956; August Goldstein, Jr., BellOiland Gas Company, 1959. Samples areinBureau ofEconomic Geology WellSample Library. — County. Frio. — Well name. Magnolia Petroleum Company No. 1McKinley. Location.—Davidson survey; 1,320 feet FNL, 660 feet FWL; 6% mi.NE of Pearsall. —— Elevation.—^l4 feet. Totaldepth. 11,951 feet. Completed. 1947. Top of metamorphic rocks.—11,910 feet. Elevation of metamorphic rocks. 11,296 feet. — Thin section coverage (depth infeet). shell oilcompany: 11,945-51. Description of metamorphic rocks. —Morgan (1952 ) stated that this wellpassed out of the Comanche at 10,380 feet and encountered mica schist at 11,910 feet. The interval between is occupied by red shale with thin-bedded reddish to white limestone, red sandstone and conglomerate; Morgan re ported that fusulinids of Wolfcamp age were found inseven limestone beds between 11,630 and 11,900 feet, and he identified thissequence as Permo-Pennsylvanian inage. IfMorgan is correct in this age assignment, the most likely explanation is that these sandstones and shales are late Paleozoic post-orogenic beds preserved in a structural low withinthe metamorphic terrane (cf. Pagenkopf No. 1Blum in Bexar County). An alternative explanation is that they are Mesozoicbeds (Jurassic) containing reworked older fusulinids. The metamorphic rocks in this well are garnetiferous biotite-chlorite-muscovite-quartz schists; spongy garnet porphyroblasts are with chlorite, suggesting retrogressive meta- commonly associated — morphism. Locally, the foliation is convoluted. Metamorphism is low to medium grade the schist in this well shows as high a metamorphic grade as has been encountered in the Ouachita structural belt. The wellpenetrated the interior zone of the Ouachita belt and provides one of the southernmost control points. — X-ray data. None. References.— GoldsteinandReno(1952,p.2289);H.J.Morgan(1952,p.2272). — County. Gonzales. — Well name. Quintana Petroleum Corporation No. 1Lampkin. Location.— Winslow Turner League; 660 feet FSEL, 1,980 feet SW of highway; V/i mi. NW of Slayden. — Elevation—MO feet. Totaldepth.— 9,l77 feet. Completed. 1944. Top of metamorphic rocks.—B,sBo feet. Elevation of metamorphic rocks. 8,240 feet. — Thin section coverage (depth in feet). bureau of economic geology: 8580-85, 8600-05, 8617-21, 8738-53 (2), 8770-76 (2), 8815-30, 8935-50 (2), 9058-75 (2), 9150-56 (2). — Description of metamorphic rocks. The sequence is composed of dark-colored, fine-to coarse- grained, angular to subround, very poorly sorted, sericitic chloritic high-rank metasandstone and dark-colored pyritic carbonaceous sericite slate, both extensively veined with quartz. Quartz sand grains are undulose, fractured, and commonly consist of fragments of broken quartz veins. Rocks are foliated and fracture cleavage is developed. Metamorphism is weak with a high shearing element. The rocks resemble the dark, sheared slate sequence found in northern Guadalupe and Caldwell counties rather than the phyllite-metaquartzite sequence immediately to the north in Caldwell County(PI. 2). Metamorphism appears to be less intense than in areas to the north closer to the Luling front. This well suggests that perhaps the black slate belt is repeated in the subcrop south of the phyllitemetaquartzite belt. — X-ray data. None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1956. — County. Grayson. — Well name. Burton et al. (Burton Syndicate, Zee-Tex OilCompany) No. 1Cannon. — Location. Alex.Martinsurvey;SWofcorner;1mi.NofTioga. Elevation—m. Total depth.—l,9s6(?) feet. Completed— -1922. The Ouachita System —— TopofPaleozoic rocks. ni. ElevationofPaleozoic rocks. ni. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Information in the Bureau of Economic Geology files indicates that this wellbottomedina gray-banded sandstone ofPennsylvanian age. From the location, it appears that the wellpenetrated Strawn or Atoka beds west of the Ouachita front. — X-ray data.-None. — Bureau of Economic Geology files. References. — County. Grayson. — Wellname. Continental OilCompany No. 1B.F. Armstrong. — Location. Ignatius Carrico survey; 660 feet FSL, 1,700 feet FWL; 3 mi. NE of Sherman. — — — Elevation. 710 feet, derrick floor. Total depth. 10,150 feet. Completed. 1957. Topof Paleozoic rocks.—1,919 feet. Elevation of Paleozoic rocks. 1,209 feet. — Thin section coverage (depth in feet).' bureau of economic geology: 2100-10 (2), 2170-80, 2260 70, 2470-80, 2490-2500, 2520-30, 2570-80, 2590-2600, 2700-10, 2810-20, 2950-70, 3000-10, 3140 50,3360-70,3460-70,3550-60,3620-30,3650-60. — Description of Paleozoic rocks. Creager (1957) reported the following determinations: base of Cretaceous and top of novaculite, 1,920 feet; top of Missouri Mountain, 2,245 feet; top of Polk Creek, 2,460 to 2,480 feet; top of Viola (Bigfork), 2,480 feet; top of Dcs Moines (Pennsylvanian), 3,490 feet. The following subdivision of the sequence is based on thin section examination: (1) samples2,100 to 2,110 and 2,170 to 2,180 feet are dark black argillaceous spiculitic cryptocrystalline chalcedonic chert containing dark organic material, locally dolomitic, and light-colored spiculitic cryptocrystalline chalcedonic chert containing local masses of dark organic matter and scattered dolomite rhombs—Arkansas novaculite;(2) samples 2,260 to 2,270 feet are dark red and green shale—probably Missouri Mountain; (3) samples 2,470-2,480, 2,490-2,500, 2,520-2,530, 2,570-2,580, 2,590-2,600, 2,700-2,710, 2,810-2,820, and 2,950-2,970 feet are dark dolomiticspiculitic argillaceous chert containing dark organic material, dark dolomitic spiculitic siliceous shale rich in organic matter, fine- grained dolomite, locally containing dark organic material, and fine-grained spiculitic dolomiticlime — stone, locally shaly Bigfork chert; (4) samples 3,000 to 3,010 feet are dark gray-green shale or metashale — Womble; (5) samples 3,140 to 3,150 feet are fine-grained, round, well-sorted, slightly dolomitic quartzitic quartz sandstone— Strawn (?); (6) samples 3,360-3,370, 3,460-3,470, 3,5503,560, 3,620-3,630, and 3,650-3,660 feet are unmetamorphosed fine-grained, subangular to round, fairly — well-sorted, slightly argillaceous quartz sandstone, crushed and fractured Atoka. The Ouachita facies rocks are veined withquartz, carbonate, and bituminous matter. This well penetrated unmetamorphosed pre-Stanley Ouachita facies rocks, intersected a thrustfault, and bottomed in Pennsylvanian (Strawn-Atoka) sandstone and shale. There appears to be some discrepancy between the top of the Dcs Moines picked from sample examination and the petrographic determination of Strawn(?) (but definitely Pennsylvanian) at 3,140 to 3,150 feet. The wellisinthefrontalzoneoftheOuachita beltclose tothewestern margin. — X-ray data. None. — References. Personal communication: N.G.Creager, Continental OilCompany, 1957; R.F.Mathews, Continental OilCompany, 1957. — County. Grayson. — Wellname. VerneDumas Company etal.No.1M.E.(Mollie)Williams. Location.—BenNixsurvey; 360 feetFWL, 350 feetFSL; 3.9mi.NEofVanAlstyne. Elevation.—79o feet. Totaldepth—s,o46(7) feet. Completed.—l933. Top of Paleozoic rocks.—3,loo(?) feet; 3,425(?) feet. Elevation of Paleozoic rocks. 2,310(?) feet;-2,635(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 3469, 3572-87, 4585-00, 4720-35. Description of Paleozoic rocks. —Descriptions of sporadic samples (Bur. Econ. Geol. files) show red shale at 3,160 to 3,499 and 3,572 to 3,633 feet and note that fragments of brown chert occur in deeper samples— 3,633-4,509, 4,535-4,562, 4,555-4,615, 4,585-4,660, 4,660-4,921, 5,046 feet; sandstone fragments are described in the last sample, 5,046 feet. Samples examined for this study are composed of dark cryptocrystalline to microgranular chert, locally containing dark organic material and dark silty metashale ;the lithology is typically Bigfork. This well penetrated lower Paleozoic Ouachita facies rocks in the frontal zone of the Ouachita Bureau ofEconomic Geology, The University of Texas structural belt. An alternate interpretation is that the Ouachita facies rocks occur as fragments in Strawn conglomerates and the wellis west of the Ouachita front. — X-ray data. None. References.— Sellards (1933, p. 189). Personal communication: August Goldstein, Jr., Bell Oiland Gas Company, 1959; W. T. Smith, Pan American Petroleum Corporation, 1955. Samples areinBureauofEconomic GeologyWellSample Library. — County. Grayson. — Well name. Gace MillingCompany No. 1Exstein. Location—McMullen&McGloinsurvey;1mi.SofRedRiver,10mi.FW County line,13mi. Wof Denison. — —— Elevation. ni. Totaldepth. ni.Completed. ni. — — Top of Paleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. Thinsection coverage (depth infeet).—None. — DecriptionofPaleozoic rocks. Informationinthe Bureau ofEconomic Geology files indicates that the sample at 2,742 feet is probably Strawn. This wellis in foreland rocks west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Grayson. — Wellname. A.G.HillNo.1loneCarter. — Location. Ignatius Carrico survey; 330 feet FSL, 1,575 feet FWL. — —— Elevation. 704 feet, derrick floor; 694 feet, ground. Total depth. 6,938 feet. Completed. 1955. — Top of Paleozoic rocks. 1,920 feet. Elevation of Paleozoic rocks. 1,216 feet. — Thinsection coverage (depth in feet). None. — Description of Paleozoic rocks. The following data were reported by Wilson (1956): base of Cretaceous and top of Stanley(?), 1,920 feet; top of Arkansas novaculite, 2,280 feet; top of Missouri Mountain shale, 2,370 feet; top of Polk Creek shale, 2,440 feet; top of Bigfork chert, 2,700 feet; top of Womble shale, 3,185 feet; top of Bigfork chert and thrust fault, 3,300 feet; top of Womble shale, 3,500 feet; top ofPennsylvanian and thrust fault,3,700 feet. According to the sample determinations above, this wellpenetrated a normal Ouachita facies section with the lower part repeated by faulting, intersected a thrust fault, and bottomed in foreland Pennsylvanian rocks (lithology not described). The wellpenetrated an allochthonous plate in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication :W. J. Wilson, Shell OilCompany, 1956. — County. Grayson. — Wellname. HowellandHowellNo.1J.C.Mulder. — Location. J. Barefoot survey; Mulder field. — — Elevation. 692 feet. Total depth.—7,888 feet. Completed. 1951. — Top of Paleozoic rocks. 1,670 feet. Elevation of Paleozoic rocks. 978 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Kiene and McMahor (1952) reported production from Ellenburger rocks. This wellpenetrated foreland rocks west of the Ouachita belt. — X-ray data. None. — References. Kiene and McMahon (1952). — County. Grayson. — Well name. Olson Drilling Company No. 1Southwestern LifeInsurance Company (Mauldin). — Location. Section665,J.C.Jamisonsurvey(J.C.Butler?survey);1,160feetFNL,1,627feetFEL, 6Y2mi. W,4mi.NofDenison. Elevation.— 77o feet. Totaldepth.— s,B9o feet. Completed.—l936. The Ouachita System TopofPaleozoic rocks.—1,010 feet. Elevation ofPaleozoic rocks. 240 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 1460-70 (2), 1510-20, 205060 (2), 2600-10, 3280-90, 4030-40, 4455-61, 4461-63, 4720-30, 4820-30, 4870-76, 4950-60, 509000, 5300-10, 5450-60, 5800-10. Description of Paleozoic roc&s.—Goldstein (1955) reported base of Trinity and top of Stanley, 1,010 feet; top of Arkansas novaculite, 4,485 feet; top of Missouri Mountain(?), 4,790 feet; top of Polk Creek(?), 4,860 feet; top of Bigfork, 4,890 feet; top of Womble, 5,270 feet; total depth 5,890 feet, in Womble. — Thin section examination shows typical Stanley lithology dark shale and metashale interlayered withfine-grained, mostly angular, poorly sorted, argillaceous feldspathic quartz sandstone inthe upper partofthesequence. Thelowerbedsaredarkdolomiticargillaceous chertcontainingorganicmaterial, dark dolomitic argillaceous limestone, dark fine-grained argillaceous dolomite, commonly siliceous, and dark metashale; Bigfork and Womble lithologies are clearly recognizable. The shales show incipient metamorphism throughout the sequence. Graptolites in core fragments were studied by Berry (1959) who reported as follows: 4,879 to 4,891 feet, Climacograptus(?) cf. C. eximius Ruedemann; 5,453 to 5,454 feet, Retiograptus geinitzianus (Hall), Dicellograptus sextans (Hall), Glyptograptus sp., Cryptograptus tricornis (Carruthers), Glossograptus hincksii (Hopkinson), Leptograptus flaccidus var. spinifer mut. trentonensis Ruedemann; 5,457 feet, Dicellograptus sextans (Hall), Glyptograptus cf. G. teretiusculus (Hisinger), fragments of Retiograptus geinitzianus (Hall), and Cryptograptus tricornis (Carruthers). Berrynoted that these graptolite forms are characteristic of the lower part of the Womble and Woods Hollow shales and are mid-MiddleOrdovician in age. The wellpenetrated upper and lower Ouachita facies rocks inthe frontal zone of the Ouachita belt. — X-raydata. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; W. T. Smith, Pan American Petroleum Corporation, 1955; W. J. Wilson, Shell Oil Com pany, 1956; W. B. N. Berry, University of California, 1959. Samplesare inBureau ofEconomic Geology WellSample Library. — County. Grayson. — Wellname. Olson DrillingCompany No.1Utiger. Location.—P. P. Cudy (Cady?) survey; center of survey. Elevation—-722 feet. Totaldepth.—6,ooo feet. Completed— l937'. — Top ofPaleozoic rocks. 950 feet. Elevation of Paleozoic rocks. 228 feet. — Thin section coverage. shell oilcompany: 1700-10. bureau of economic geology: 960-70, 1060 70,1360-70,1450-60 (2),1920-30, 2050-60, 2500-10, 4100-10, 5150-60. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Arkansas novaculite, 950 feet; top of Missouri Mountain(?), 1,270 feet; top of Bigfork, 1,320 feet; top of Womble, 2,030 feet; total depth 6,000 feet, inWomble. Thin section examination shows a typical pre-Stanley Ouachita facies sequence composed of dark- colored dolomitic cherts containing organic material, locally spiculitic, and dark siliceous metashales. The 1,450 to 1,460 interval is fine-grained fossiliferous siliceous dolomitic limestone and dark green metashale containing "pleochroic" carbonate porphyro blasts (siderite?). The wellpenetrated pre-Stanley Ouachita facies rocks showing incipient metamorphism in the frontalzone ofthe Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955;W.T.Smith,Pan AmericanPetroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. County.—Grayson. — Wellname. Pan AmericanProduction Company No.1J.Umphress. Location.—EliJones (Jonas?) survey; 2,000 feet FNL,1,950 feet FWL; 5% mi. SW of Whitewright. Elevation.— 664 feet. Totaldepth.— B,B96 feet. Completed.— l9s2. Topof Paleozoic rocks.—3,304 feet. Elevation ofPaleozoic rocks. 2,640 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 4520-30, 4540-504610-20, 4690-00, 4820-30, 6190-00, 6220-30, 6230-40, 6330-40, 6350-60, 6390-00, 6440-50,6500-10, 6530-40, 7010-20, 7080-90 (3), 7130-40, 7150-60, 7450-60, 7560-70, 7600-10, 7760-70,7975-80, 7980-00, 8180-90, 8330-40, 8520-30, 8710-20, 8800-10, 8830-50. Bureau ofEconomic Geology, The University of Texas — Description of Paleozoic rocks. Goldstein (1955) reported top of Bigfork,3,346 feet; top of Womble (graptolite-bearing), 3,750 feet; top of Pennsylvanian of foreland facies (boulder-bearing mudstone — or conglomerate), 6,175 feet. Morgan (1955) stated that Pennsylvanian (Deese beds Strawn) is reported beneath Ouachita facies rocks at 6,180 feet. The sequence below 6,175 feet is composed of a mixture of various types of chert, fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone with more or less carbonate, carbonate rocks containing abundant sand and silt, and fairly well-sorted and rounded argillaceous to calcareous quartz sandstone. The heterogeneous suite of rocks associated with Pennsylvanian type sandstone suggests a conglomerate or some type of sedimentary rock carrying exotic fragments (see Goldstein's interpretation above). Ifthe interpretation of a thrust fault at 6,175 feet is correct, this wellpenetrated pre-Stanley rocks of Ouachita facies and bottomed in Pennsylvanian rocks, probably of Atoka or Strawn age. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955, 1959; H.J.Morgan, Jr.,The AtlanticRefining Company, 1955. — County. Grayson. — Wellname. Peter andJohnson (McCartyOilCompany) No.1J.A.O'Dell. — Location. T.R. Shannon survey ;2 mi. SE ofDenison. — —— Elevation. ni. Totaldepth. ni. Completed. 1927. —— Top ofPaleozoic rocks. 1,560± feet. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 1945(2). Description of Paleozoic rocks.—Sample descriptions in the Bureau ofEconomic Geology files show red and gray shale from1,780 to 1,945 feet. Miser (Miser and Sellards, 1931) examined samples from 1,580 to 1,945 feet and identified the sequence as Missouri Mountain shale and Polk Creek shale. Getzendaner (1943) commented on the pre-Trinity red sandstones, shales, and conglomerates in this and other wellsinthe area. Cuttings from 1,945 feet are dark silty shale containing varied amounts of mica, bitumen, and fine "pin-point" carbonate ;the rocks cannot be identified from this single sample. IfMiser's identification is correct, this wellpenetrated older Ouachita facies rocks in the frontal zone of the Ouachita belt. — X-ray data. None. References.— Getzendaner (1943, p. 1229) ;Miser and Sellards (1931, p. 815). Samples are inBureau of Economic Geology Well Sample Library. — County. Grayson. — Well name. Peter Oiland Gas Company, Incorporated, No. 1Butcher (also known as Peter No. 1). — Location. PollyAnnBoon survey; SE corner; 3mi.E ofDenison. — Elevation.—l2s feet. Totaldepth. 4,025 feet. Completed.—l922. — TopofPaleozoic rocks. 1,511 feet. Elevation ofPaleozoic rocks. 786 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 3340 (2). bureau of economic geology: 1678 (4), 1702, 1945, 1970 (2), 2070, 2435, 2460 (2), 2530-75 (2), 2960-75, 3340 (5),3345, 3800, 3888-3919, 3945-4003, 3975, 4023. — Description of Paleozoic rocks. Sample descriptions in the Bureau of Economic Geology files report a sequence of black shale, locally slickensided, and gray sandstone; cone-in-cone limestone occurs in the sample at 3,340 feet; black siliceous shales occur in the lower part of the sequence. White calcite veins are present, but Udden noted that the samples are not so extensively veined as in wells in Bell and Williamson counties. An excerpt (undated) from a letter from the United States Geological Survey to H. A. Jones notes that the sequence was identified by K.C. Heald as probably Stanley. Miser (Miser and Sellards, 1931) identified the rocks as Stanley; Sellards (1933) described the sequence as black shale and sandstone. The rocks are dark shale and fine-grained, mostly angular, poorly sorted, argillaceous feldspathic quartz sandstone, commonly containing a substantial amount of garnet in the heavy mineral fraction; thin limestone beds in the sequence have cone-in-cone structure. Thiswellpenetrated Stanley bedsinthefrontalzoneoftheOuachitabelt. — X-ray data: None. References.— Miser and Sellards (1931, p. 815);Sellards (1933, p. 189). Samples inBureau ofEconomic Geology WellSample Library. The Ouachita System — County. Grayson. — Wellname. Peter Oiland Gas Company, Incorporated, No.1Jackson. — Location. WilliamWright survey; SE corner; 2mi.SofDenison. Elevation.— 7oo± feet. Total depth.— l,7oB(?) feet. Completed.— l92o. — TopofPaleozoicrocks. 828± feet.ElevationofPaleozoic rocks. 128=fc feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in the Bureau of Economic Geology files report a sequence ofred, purple, green-gray, and brownshales from1,400 to1,700 feet. Getzendaner (1943) reported 500 feet of red shale, sandstone, and conglomerate of pre-Trinity age. The age and facies of these rocks are unknown. — X-ray data. None. — References. Getzendaner (1943, p. 1229). Samples areinBureau ofEconomic Geology Well Sample Library. County. —Grayson. — Wellname. Peter Oiland Gas Company, Incorporated, No.1Munson (No.2Munson; alsoknown as Preston No.1Munson and Preston No.2Munson). — Location. Ramon Rubio survey; 2%mi.NofDenison. — —— Elevation. 605 feet (from topographic map). Total depth. 3,640 feet. Completed. 1922. — Top ofPaleozoic rocks. 2,370± feet. Elevation of Paleozoic rocks. 1,765± feet. — Thin section coverage (depth infeet). bureau of economic geology: 2700-30, 3147, 3250. — Description of Paleozoic rocks. Notes in the Bureau of Economic Geology files report black shale and gray sandstone from scattered samples between 2,525 and 3,260 feet;reference ismade to observa tionsbyK.C.Heald,whoreported darkgraytoblacksiliceousshale,tentativelyidentifiedasStanley. Miser and Sellards (1931), discussing the No.1Munson, stated that K.C. Heald examined samples from 3,140 to 3,260 feet and identified them as Stanley. Miser and Sellards (1931, p. 816) discussed a No. 2 Munson well2% miles north ofDenison, and Miser said that the cuttings from 2,370 to 3,260 feet are Stanley; the sequence is described by Sellards (1933) as black shale and sandstone. This seems to be the same as the No.1Munson. Three samples available for study are dark, angular, bituminous micaceous chloritic calcareous argillaceous quartz siltstone, dark bituminous shale, and fine-grained, angular to subround, poorlysorted, micaceous chloritic calcareous quartz sandstone; scattered siliceous spicules occur in the siltstone. These three samples are non-diagnostic. The sandstone and siltstone contain too much calcite and too littlefeldspar tobe typical Stanley lithology. Thiswellpenetrated Stanley(?)inthefrontalzoneoftheOuachitabelt. — X-ray data. None. References.— Miser and Sellards (1931, pp. 815-816) ;Sellards (1933, p. 189). Samples are inBureau of Economic Geology Well Sample Library. — County. Grayson. Well name.— W. J. Rutledge No. IM.E. (Mollie) Williams. — Location. Solomon Nixsurvey; 3% mi.NEofVan Alstyne. — —— Elevation. 790 feet, derrick floor. Total depth. 5,309 feet. Completed. 1938. Top ofPaleozoic rocks.—3,460 feet. Elevation of Paleozoic rocks. 2,670 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 3530-40, 3800-10, 4910-20. Description of Paleozoic rocks.—Sample descriptions by E. R. Applin in the files of the Bureau of Economic Geology show chert pebble conglomerate (Strawn conglomerate) and red and greenshale from 3,460 to 4,500 feet and mostly green, red-brown, and gray shale from 4,500 to 5,309 feet. The first two thin sections above (3530-40, 3800-10) are dark argillaceous microgranular to cryptocrystalline chert containing dark organic material (Bigfork formation);the 4910-20-foot interval contains calcareous sandy and silty brown shale and calcareous argillaceous quartz sandstone. The sandstone is Pennsylvanian (Strawn) type. Two interpretations of this wellmerit consideration: (1) The wellpassed out of the Cretaceous and directly into Pennsylvanian conglomerates containing chert pebbles from the Bigfork chert, or (2) the wellpassed from Cretaceous rocks into Bigfork chert (and Womble shale?), intersected a thrust fault, and penetrated Pennsylvanian beds. The existence of an overthrust fault in this area is demonstrated by other wells to the north and east and perhaps to the south (p. 172; PI. 2). If Applin's interpretation from sample studies is correct and the wellpassed directly into Strawn beds, there would appear to be a re-entrant in the overthrust (due to pre-Cretaceous erosion) or a fensterinthis area. Bureau ofEconomic Geology, The University of Texas — X-raydata. None. — References. Bureau ofEconomic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology Well Sample Library. County.—Grayson. Wellname.—Seitz, Comegys and Seitz No.1W.P. Mackay (Mackoy) (McKay) (MacKey). — Location. J. Bridges survey;3 milesSE ofWhitesboro Mackoy field,Macomb area. Elevation.—76o feet. Totaldepth.— 3,B34 feet. Completed.— l9s2. Top ofPaleozoic rocks.—1,790 feet. Elevation of Paleozoic rocks. 1,030 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Smith (1953) reported total depth in Strawn with production from Strawn sand. This wellislocated west of the Ouachita belt and penetrated foreland rocks. A sec ond wellin this area, No. 2 W. P. Mackay, achieved production from Ellenburger rocks. — X-ray data. None. References.— Smith (1953, p. 1387);Bradfield (1957, p. 24). County. —Grayson. — Wellname. ShellOilCompany No.1R.O.Brown. Location.—]. W. Vandever survey; 330 feet FNL, 330 feet FWL; 2 mi. S of Pottsboro; South Pottsboro field. — — Elevation. 710 feet, derrick floor. Total depth. —8,500 feet. Completed. 1954. — TopofPaleozoic rocks. 1,993feet.ElevationofPaleozoicrocks. 1,283 feet. — Thin section coverage (depth in feet). bureau of economic geology: 23031/4> 3590-3600 (2), 3790-3800, 4590-4600, 5790-5800, 6590-6600, 7140-50, 7390-7400, 7690-9 iy2. — Description of Paleozoic rocks. Wilson (1959) reported top of Paleozoic (Dcs Moines) at 1,993 feet; top of Atoka at 8,135 feet. The sequence is composed of (1) dark silty and sandy shale and siltstone; (2) fine-to medium- grained, angular to subround, fairly wellsorted to poorly sorted, argillaceous quartz sandstone commonly containing abundant fragments of shale and chert, locally containing calcite cement; and (3) dark fine-grained fossiliferous limestone (7,140 to 7,150-foot interval). Fragments of chert in the 3,590 to3,600-foot intervalare probably derived frompebbles. The rocks are Strawn and Atoka; the well penetrated foreland rocks immediately west of the Ouachita belt. — X-ray data. None. — References. Personal communication :W. J. Wilson, Shell OilCompany, 1959. — County. Grayson. — Wellname. Sherman City Well. Location.—Sherman, Texas. — —— Elevation. 720 feet. Totaldepth. 2,366 feet. Completed. 1922. Topof Paleozoic rocks.—2,350± feet. Elevation of Paleozoic rocks. 1,630± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Getzendaner (1943) listed this well as having penetrated about — 500 feet of pre-Trinity beds composed of red shale, sandstone, and conglomerate age unknown. — X-ray data. None. — References. Getzendaner (1943 ). Samples are inBureau ofEconomic Geology WellSample Library. — County. Grayson. Wellname.—Simpson-Fells OilCompany No.1G.W.Wall. Location.—George B. Reeves survey; 42 feet FWL, 965 feet FNL; 8 mi. WNW of Denison. Elevation— -734 feet. Total depth.— 2,sls feet. Completed.—l927. — Top of Paleozoic rocks. 900± feet. Elevation of Paleozoic rocks. 166 ± feet. The Ouachita System — Thin section coverage (depth in feet). bureau of economic geology: 972, 987-89, 1065, 1137-38, 1178, 1187 (2), 1198 (2), 1202-04, 1220-24, 1240, 1269-73, 1274-80, 1291-94, 1300-02, 1300-03, 1305-13, 1327-32, 1367-70, 1390-93, 1432-42, 1506-15, 1532-40, 1583-93, 1618-45, 2084-86, 2217-39. — Description of Paleozoic rocks. Miser (Miser and Sellards, 1931) described the section from 900 to 1,552 feet as flint, calcareous chert, and siliceous limestone of the Bigfork chert, and the lower unit, 1,552 to 2,515 feet, as Stringtown shale containing graptolites of the same fauna as found in the Womble. Sellards (1933) placed the top of the Paleozoic at 963 ± feet. Goldstein (1955) reported base of Trinity and top of Bigfork,900 feet; possible top of Womble, 1,374 feet; definitely inWomble, — 1,739 feet; inWomble at 2,515 feet last sample. Thin section study shows a sequence of dark, fine-grained, commonly spiculiferous argillaceous dolomitic limestone and dark chert containing organic matter, commonly spiculitic, and commonly containing carbonate rhombs, overlying dark pyritic locally dolomitic slightly silty shale. Fine- grained light gray limestone is present in the 2,084 to 2,086 and 2,217 to 2,239-foot intervals. This well penetrated lower Paleozoic Ouachita facies rocks including Bigfork chert and Womble shale in the frontal zone of the structural belt. — X-ray data. None. References.— Miser and Sellards (1931, pp. 817-818) ;Sellards (1933, p. 189). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Grayson. — Wellname. H.W.Snowden etal.No.1A.M.Bryant. — Location. E. M. Jones survey; 1,768 feet S, 1,060 feet W ofNW cor. A. Hilburn survey. — — Elevation. 782 feet, derrick floor. Totaldepth. —4,471 feet. Completed. 1946. — Top of Paleozoic rocks. 3,285 feet. Elevation of Paleozoic rocks. 2,503 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. According to Davis (1959), this wellpenetrated Ouachita facies rocks: top of Arkansas novaculite, 3,285 feet; top of Missouri Mountain shale, 3,770 feet; top of Bigforkchert, 4,140 feet; totaldepth4,471feet,inBigforkchert. This wellpenetrated lower Paleozoic Ouachita facies rocks in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: H. W.Davis,The Texas Company, 1959. County. —Grayson. — Well name. Snuggs and Cox No. 2 M.M. Davis et al. — Location. W. G.Millersurvey; Collinsvillefield. Elevation.—69l feet. Totaldepth.—3,99o feet. Completed.— l9ss. — Top of Paleozoic rocks. 1,810 feet. Elevation of Paleozoic rocks. 1,119 feet. Thin section coverage (depth in feet).—None. — Description of Paleozoic rocks. This well achieved production from foreland facies rocks west of the Ouachita belt. X-ray (tea.— None. C. E. Davis (1956, p. 1197). References.— — County. Grayson. — Wellname. Snuggs and Neal No.1Q.Little. — Location. W.M.Allensurvey;BigMineralfield. —— — Elevation. 669 feet. Total depth. 3,629 feet. Completed. 1951. — TopofPaleozoic rocks. 1,750 feet. ElevationofPaleozoic rocks. 1,081feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. This well achieved production from Strawn beds; other wells in the field penetrated lower Paleozoic foreland facies rocks. This wellis located west of the Ouachita front. — X-raydata. None. — References. None. Bureau ofEconomic Geology, The University of Texas — County. Grayson. — Wellname. Standard OilCompany ofTexas No.1Mitchell. — Location. J. McNair survey;2 mi.NW of Sherman. —— Elevation. 751 feet. Total depth.—11,541 feet. Completed. 1946. — TopofPaleozoic rocks. 2,370 feet. ElevationofPaleozoic rocks. 1,619 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 4140-50, 4240-50, 4640-50, 6370-80, 6560-70, 6700-10, 6710-20, 6960-70, 7740-50, 8260-70, 8580-90, 8590-00 (2), 8600-10, 8700-10, 9420-30, 10,140-50, 11,000-10. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Strawn, 2,370 feet; top of Atoka, 6,735 feet; top of Viola, 9,130 feet; top of Simpson (Bromide), 9,300 feet; top ofMcLish, 9,770 feet; top ofOilCreek, 10,100 feet; top of Joins, 11,000 feet; top of Ellenburger, 11,240 feet; total depth 11,540 feet, in Ellenburger. Morgan (1952) made the following analysis: base of Comanche, 2,370 feet; 2,370 to 6,757 feet, red and gray shales, sandstones, and insome places — conglomerates, with a—few thin limestone beds at the base the rocks show no metamorphism and cores show a low dip a fusulinid of Strawn age was found at 6,740 to 6,750 feet; from 6,785 to 9,117 feet the beds are hard black abundantly slickensided and polished shales and hard quartziticsandstones which in two cores showed nearly vertical dips; 9,117 to 9,298 feet, limestone similar to the Viola; 9,298 feet to total depth, beds resembling Simpson. According to Morgan's interpretation, late Paleozoic beds overlie Ouachita facies rocks and the unconformity can be dated as pre-Strawn, post-Bend; Morgan made no explanation of the foreland facies Ordovician rocks beneath the strata he calls Ouachita facies except to compare the situation encountered in Magnolia No. 1Wardlaw in Kinney County. Thin section examination shows that the clastic section is composed mostly of fine-grained, poorly to fairly well-sorted, calcareous and/or feldspathic argillaceous quartz sandstone; beds of fine- grained fossiliferous limestone occur in the sandstone sequence. These rocks more closely resemble Pennsylvanian rocks of foreland facies than Ouachita facies; it appears that Strawn and Atoka beds rest on foreland facies Ordovician rocks and the wellpenetrated a foreland facies section west of the Ouachita belt. Apparently, the Atoka sequence was deformed prior to Strawn deposition (see p. 126). — X-ray data. None. H. J. Morgan (1952, pp. 2271-2272). References.— Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Grayson. — Wellname. Standard OilCompany ofTexasNo.1O'Hanlon. Location.—A.T. Cooke survey; 615 feet FSL, 660 feet FEL; 3 mi. NW of Sherman. —— Elevation.—B7B feet, derrick floor. Totaldepth. 10,312 feet. Completed. 1955. — Top ofPaleozoic rocks. 2,090 feet. Elevation ofPaleozoic rocks. 1,212 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Bradfield (1957) presented the following section: red Strawn (Deese), gray Strawn (Deese), Dornick Hills, Viola(?). Wilson (1959) reported top of Paleozoic (Dcs Moines) at 2,090 feet and top of Atoka at 8,540 feet. This wellencountered foreland facies rocks very close to the Ouachita front. — X-raydata. None. References.— Bradfield (1957, p. 41). Personal communication :W. J. Wilson, Shell OilCompany, 1959. — County. Grayson. — Wellname. StarrOilCompany, Incorporated, No.1Blankenship. — Location. Seymour Bradley survey; 6mi.SE ofPottsboro. — —— Elevation. 696 feet. Total depth. 6,542 feet. Completed. 1953. Top of Paleozoic rocks.—2,005 feet. Elevation ofPaleozoic rocks. 1,309 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3400-10, 3600-10 (2), 370010, 4400-10, 5295-00. — Description of Paleozoic rocks. According to Morgan (1955) this well encountered Ordovician strata of Ouachita facies below the Comanche, penetrated a thrust fault, and bottomed in Pennsylvanian (Deese beds—Strawn). Tims (1957) reported base of Cretaceous and top of Ouachita facies (Womble), 2,010 feet; thrust fault and top of Pennsylvanian (Bruhlmeyer sand ofDeese formation), 5,230 feet; totaldepth 6,542 feet,inBruhlmeyer sand. The Ouachita System Thin section examination shows a sequence of dark shale and metashale, locally brecciated, fine- grained argillaceous glauconitic fossiliferous limestone, light-colored cryptocrystalline to microgranu lar chert, and dark red shale containing organic material, overlying fine-grained, subangular to subround, fairly well-sorted quartz sandstone. The upper part of the Paleozoic sequence is composed of Ordovician Ouachita facies rocks, probably Bigfork-Womble, although X-ray data do not confirm — this identification (see below);the lower sandstone is of foreland facies Strawn. This well penetrated lower Paleozoic Ouachita facies rocks in the frontal zone of the Ouachita belt, transected a thrust fault, and bottomed inforeland rocks. — X-ray data. ML>l>K>Ch; SR =1.0. Womble(?). The upper sample is composed predomiantlyofmixed- layerillite-montmorillonite,whichisnotcharacteristic ofOuachitafaciesrocks. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955; V.E.Tims, Standard OilCompany of Texas, 1957. Samples are inBureau ofEconomic Geology WellSample Library. — County. Grayson. Wellname.— Starr OilCompany, Incorporated, No. 1W. A.Moser. — Location. J.C.Parkssurvey;1,100feetFSL,660feetFEL;3mi.SEofPottsboro. — —— Elevation. 732 feet, derrick floor. Total depth. 5,427 feet. Completed. 1952. — Topof Paleozoic rocks.-2,030 feet. Elevation ofPaleozoic rocks. 1,298 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks.-Wilson (1959) reported top of Paleozoic rocks (Dcs Moines) at 2,030 feet. No samples were available for study. From its location, this wellis close to the Ouachita front, probably just to the west in Dcs Moines beds. Without samples no positive determination can be made. — X-ray data. None. — References. Personal communication :W. J. Wilson, Shell OilCompany, 1959. — County. Grayson. — Wellname. Tennessee Gas Transmission Company No.1Washburn. — Location. Aaron Burleson survey; 72 feet FSL, 1,506 feet FEL. —— Elevation. 681 feet, derrick floor. Total depth.—13,421 feet. Completed. 1955. — TopofPaleozoic rocks. 2,750 feet. ElevationofPaleozoic rocks. 2,069 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. The following stratigraphic information is reported (Davis, 1959) : base of Cretaceous and top of Strawn, 2,750 feet; top of Atoka, 9,033 feet; top of Simpson, 12,555feet;topofArbuckle,13,273 feet;totaldepth13,421feet,inArbuckle. This well penetrated foreland facies rocks close to the Ouachita front; the Atoka sequence, abnormally thick for this area, overlies truncated Ordovician rocks. — X-ray data. None. — References. Personal communication: H. W. Davis, The Texas Company, 1959. — County. Grayson. — Wellname. TheTexas Company No.1JohnMarshall. — Location. A.Tuttle survey; 2% miles S of Sandusky; Sandusky field. Elevation.—-703 feet. Totaldepth.—7,BBs feet. Completed.— l9so. — TopofPaleozoic rocks. 1,523 feet. Elevation ofPaleozoic rocks. 820 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The following stratigraphic information is reported: top of Simpson, 6,668 feet; top ofOilCreek, 7,270 feet; top ofEllenburger, 7,543 feet; the wellwas completed as an Ellenburger producer. This wellpenetrated foreland rocks west of the Ouachita structural belt. — X-ray data. None. References. —Anonymous (1951, p. 269). County.—Grayson. — Ifellname. Westover et al. (Westover OilCompany) No.1Easton (Peter Oiland Gas Company, Incorporated, No. 2 Easton). Bureau ofEconomic Geology, The University of Texas Location.—Polly Stamps survey; 1,050 feet FWL, 2,150 feet FNL; 9 mi. NW of Denison. Elevation.—69o feet. Totaldepth.—l,o7o feet. Completed.—l92o. — Top of Paleozoic rocks. 830± feet. Elevation ofPaleozoic rocks. 140± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Sellards (Bur. Econ. Geol. files) described a core from 1,015 feet as black shale and hard sandstone withbedding dipping at 55° to 60°;he compared the rock with cores from Griffiths et al. No. 1 Evans (Sunset ranch) in Travis County and remarked that the core from the No. 1Easton is not so indurated or extensively veined as the rock from Travis County. Miser and Sellards (1931) reported Stanley shale dipping at 60°; Sellards (1933) described the rock as hard sandstone. Thiswellpenetrated Stanley shaleinthefrontalzoneoftheOuachitabelt. — X-ray data. None. References.— Miser and Sellards (1931, p. 818) ;Sellards (1933, p. 189). Personal communication: W. T. Smith, Pan American Petroleum Corporation, 1955. County.—Guadalupe. — Wellname. DiamondHalfOilCompany No.1Bibbs. — Location. J.B.Robinson survey; 660feetFNEL,660feetFSEL. —— Elevation. 509 feet. Total depth.—5,508 feet. Completed. 1937. Topof metamorphic rocks.—5,440 feet. Elevation of metamorphic rocks. 4,931 feet. — Thin section coverage (depth in feet). bureau of economic geology: 5440-50, 5450-60(?). — Description of metamorphic rocks. The rocks penetrated inthis wellare partly mylonitized meta- quartzite, locally sericitic, and talc-dolomite marble. Metamorphism is low grade witha high shearing and crushing element. The wellpenetrated the interior zone of the Ouachita belt. = X-raydata.—l,F=22(?);SR 17.2. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. County.— Guadalupe. — Wellname. Frank Gravis No.1Weyel. — Location. E. de los Santos Coy survey; 3% mi. NW of Marion. — —— Elevation. 798 feet, derrick floor. Total depth. 2,588 feet. Completed. 1946. Topof metamorphic rocks.—2,500 feet. Elevation of metamorphic rocks.-— -1,702 feet. — Thin section coverage (depth in feet). bureau ofeconomic geology: 2574-76. — Description of metamorphic rocks. The single sample examined for this study is a green chloritesericite slate containing quartz grains and fragments of sheared vein quartz; micaceous minerals are bent around the quartz grains. Metamorphism is weak witha high shearing element. This wellpenetrated the black slate beltinthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. County.—Guadalupe. — Wellname. CecilHagen No.1Henry Calvert etal. Location.—John Ussery survey; 5,400 feet FWL, 3,150 feet FSL; 4% mi. W of Kingsbury. —— Elevation. 559 feet, derrick floor; 552 feet, ground. Total depth. 4,391 feet. Completed.—1947. — Top of metamorphic rocks.—4,260(?) feet; 4,238(?) feet. Elevation of metamorphic rocks. -3,701 ( ? ) feet;-3,679 ( ? ) feet. — Thinsection coverage (depth infeet). None. — Description of metamorphic rocks. On the basis of location, this wellprobably penetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. The Ouachita System — County. Guadalupe. — Wellname. Magnolia Petroleum Company No.1Frances Baker. Location.—H.Cottlesurvey; 10,175 feetFSWL,330feetFNWL;6mi.NWofLuling. —— — Elevation. 402 feet. Totaldepth. 4,705 feet. Completed. 1952. Top of metamorphic rocks.—4,682 feet. Elevation of metamorphic rocks. 4,280 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 4693-97 (2). — Description of metamorphic rocks. Samples examined are sericite phyllite, locally hematitic. Metamorphism is lowgrade witha strong shearing element; structures include foliation, slaty cleav age, and fracture cleavage. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. X-raydata.—l>Ch> X;10/7 <—3;F=24(?);SR=14.4. — References. Personal communication: R. E. Wills, Jr., Magnolia Petroleum Company, 1953. Samples are in Bureau of Economic Geology Well Sample Library. — County. Guadalupe. — Wellname. Magnolia Petroleum Company No.1Murphy Pfulman. Location.— G.W. Williamson survey. —— Elevation. 509 feet. Totaldepth.— s,l46 feet. Completed. 1948. Top of metamorphic rocks. —5,140 feet. Elevation of metamorphic rocks. 4,631 feet. — Thinsection coverage (depth infeet). shell oilcompany: 5140-42, 5142-44, 5145-46. Description of metamorphic rocks.—Samples examined are highly sheared metaquartzite;metamorphism is low grade with a strong shearing component; structures are foliationand grain-stretching. This well penetrated metamorphic rocks in the interior zone ofthe Ouachita belt. — X-ray data. None. — References. Personal communication: R. E. Wills, Jr., Magnolia Petroleum Company, 1953. County.— Guadalupe. IFellname.—AdolphSeiderman (New Braunfels OilCompany) No.1AlvinaSeiderman. Location.— A. Maria Esmaurrizar survey; from SE cor. N along EL 26,600 feet, thence W 35,200 feet; 2% mi. SE of New Braunfels. — —— Elevation. 628 feet, derrick floor; 625 feet, ground. Total depth. 2,955 feet. Completed. 1934. — Topof metamorphic rocks. 2,853 feet. Elevation of metamorphic rocks. 2,225 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2636, 2695-2713, 2767-71, 2850-51, 2954-55. — Description of metamorphic rocks. According to scout report, top of Trinity is 2,576 feet, top of Pennsylvanian is 2,650 to 2,660 feet, and top of schist is 2,885 to 2,895 feet. A second well,the No. 2 Alvina Seiderman, was drilled 150 feet from the No. 1and reportedly topped black schist at 2,639 feet. This wellpenetrated a sequence of highly sheared and deformed dark chlorite-sericite slates which vary from dark red hematitic slates to black pyritic and graphitic slates. Pre-shearing vein quartz occurs as brecciated masses and augen; post-shearing quartz veins are abundant. Metamorphism is weak with a very strong shearing component; structures are foliation, shear fractures, wrinkling, contortion, and brecciation. The wellpenetrated the black slate beltin the interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. Samples areinBureau ofEconomic Geology WellSample Library. — County. Guadalupe. — Well name. Stanolind Oiland Gas Company No. 1Schmidt. — Location. Gustavus Bunson survey; 1,320 feet FNWL, 660 feet FNEL; 4 mi. E of Selma. —— Elevation.— Bls feet. Total depth. 2,641 feet. Completed. 1954. Topof metamorphic rocks.—2,582 feet. Elevation of metamorphic rocks. 1,767 feet. Bureau ofEconomic Geology, The University of Texas — Thin section coverage (depth in feet). bureau of economic geology: two sections marked core No. 38. — Description of metamorphic rocks. Cores and thin sections are dark gray to black sericite slate containing masses of crushed and sheared vein quartz. Metamorphism is weak witha very high shearingelement; slaty cleavage is welldeveloped. This wellpenetrated weakly metamorphosed highly sheared rocks of the black slate belt in the interior zone of the Ouachita belt. X-raydata.—l>Ch;10/7~'1.5; SR=3.9. — References. Personal communication: J. B. Souther, Pan American Petroleum Corporation, 1956. Cores areinBureau ofEconomic Geology WellSample Library. County.— Hays. — Wellname. BobAntibusetal.No.1J.Howe. Location.—L.Wortelsurvey; 375 feetFSL,1,800 feetFEL;1%mi.SWofBuda. Elevation.—76o feet, derrick floor. Total depth.— 2,3Bo(?) feet; 2,830(?) feet. Completed.—l939. — Top of Paleozoic rocks. 2,240 feet. Elevation of Paleozoic rocks. 1,480 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2240-62, 2338(2). — Description of Paleozoic rocks. The few samples available for study are dark, fine-to medium- grained, angular, poorly sorted, carbonaceous (?) chloritic micaceous feldspathic low-rank metagraywacke and dark pyritic silty metashale or clay-slate veined by quartz. The abundant rock fragments in the graywacke are mostly chert, quartz mosaic, and slate-phyllite ;new sericite and chlorite fibers penetrate grain boundaries. Metamorphism is very weak. These rocks appear to be part of the dark clastic unit of unknown age that forms the subcrop in the southeastern part of the frontal zone of the Ouachita belt. — X-raydata.—l>Ch;10/7 1.2;F=20(?);SR=5.4. — Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. References. — County. Hays. Wellname.—E. A.Bucklin No.1A.A.Eisner. — Location. S. J. Fowler survey; 3 mi. S of Dripping Springs. — —— Elevation. 1,075 feet (from topographic map). Total depth. 2,460 feet. Completed. 1929. — TopofPaleozoic rocks. 700± feet. ElevationofPaleozoic rocks.—-f-375± feet. — Thin section coverage (depth in feet). shell oilcompany: 1400. bureau of economic geology: 725-50, 795-815, 815-830, 1025, 1285, 1420 (2), 1585, 2330, 2425. — Description of Paleozoic rocks. Sellards (1931b, p. 822) reported sandstone and black shale and (p. 827) quoted Miser's opinion that the interval 725 to 835 feet resembles Missouri Mountain slate withthe bottom samples possibly Polk Creek shale. Goldstein (1955) stated that the wellpenetrated slightly altered greenish-gray shale beneath the Cretaceous and drilled maroon and gray-green shale from 720 to 835 feet; below this point samples consist of black altered shale, siltstone, and silty fine- grained quartz sandstone. Sample descriptions inthe files of the Bureau of Economic Geology are as follows: 688 to 1,135 feet, brown, red, green, gray, and black shale; 1,135 to 2,300 feet, black shale cut bycalciteveins;2,300 to2,425feet,blackshalewithsomechert. Thin section examination shows a sequence of sericitic and chloritic clay-slate and micaceous dolomitic siltstone invaded by quartz and carbonate veinlets; most of the silica is in veinlets, but in one sample (siliceous clay-slate) silica was disseminated. The siltstone is generally poorly sorted and composed of angular quartz grains with minor plagioclase and more or less clay. Metamorphism ranges fromincipient to very weak and the clay-slate shows incipient foliation. This wellpenetrated Ouachita facies rocks (lower Paleozoic?) — inthe frontal zone of the Ouachita belt possibly inan area of overthrusting (PI.2). — — X-raydata.I>Ch;10/7 '0.6;F=20;SR=4.5.The sequence shows well-crystallized chloriteillitewithno mixedlayering. References.— Sellards (1931b, pp. 822, 827). Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau ofEconomic Geology WellSample Library. The Ouachita System — County. Hays. — Wellname. Harley and Whittington No.1Heidenreich. Location.—Pace, Hemphill, and Carson survey; 720 feet FSEL; 253 feet FSWL; 3 mi. SE of Kyle. Elevation.— 632 feet. Total depth.— 2,767 feet. Completed.— l93l. Top of metamorphic rocks.—2,750± feet. Elevation of metamorphic rocks. 2,118± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2757, 2767. — Description of metamorphic rocks. Sellards (1931b) described the rock as dark schistose shale. Sample descriptions in files of Bureau of Economic Geology are as follows: 2,750 feet, hard black metamorphosed shale with streaks of green material; 2,767 feet, dark green schistose shale and vein quartz. Thin section study shows that the sequence is composed of dark siliceous sericite slate, sheared and brecciated, and invaded bymassive quartz-carbonate-chlorite veinlets. This well penetrated highly sheared rocks of the black slate belt in the interior zone of the Ouachita belt. — X-ray data. None. References.— Sellards (1931b, p. 822;1933, p. 189). Samples areinBureau ofEconomic Geology WellSample Library. — County. Hays. — Wellname. Mann No.1Reeder. Location.—R. Vaughn survey; 3,520 feet FNL, 2,750 feet FEL. Elevation.—l,lolfeet, derrick floor; 1,100 feet, ground. Total depth.— 3,37o feet. Completed.—l939. — Top ofPaleozoic rocks. 900± feet. Elevation ofPaleozoic rocks.— +201± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 875-85, 890-900, 920-35(2), 985-1000, 1025-40(2), 1055-70. — Description of Paleozoic rocks. Maner (1958) identified the sequence in this wellas Stanley(?). The sequence is composed of (1) fine-grained (locally containing coarse grains and pebbles), angular, very poorly sorted, micaceous chloritic feldspathic quartz sandstone containing abundant rock fragments (metaquartzite, schist, phyllite, vein quartz mosaic, metasiltstone, chert, shale, micro- granular volcanic rock); locally the sandstone contains fine interstitial carbonate; (2) angular, micaceous chloritic feldspathic sandy quartz siltstone, locally containing dark streaks of pyriticbituminous material; and (3) dark silty carbonaceous metashale. One carbonate veinlet was observed. The second-cycle mica includes faded biotite; the only common heavy mineral is zircon. Metamorphism ranges from incipient to very weak. These rocks are Mississippian-Pennsylvanian rocks of Ouachita facies; probably correlative with Stanley-Tesnus. X-raydata.—l> Ch;10/7 ~>2;SR= 2.7. — References. Personal communication :R. P. Maner, Shell OilCompany, 1958. County.—Hays. — Wellname. ShellOilCompany No.1Harwell. — Location. M.H.Denham survey; 7%mi.SW ofDripping Springs. — —— 1,387 feet. Total depth. 4,661 feet. Completed. 1956. Elevation. — — TopofPaleozoicrocks. 820feet.ElevationofPaleozoicrocks. -(-567feet. — Thin section coverage (depth in feet). bureau of economic geology: 860-70 (2), 866-76 (2), 1040-50, 1050-60, 1480-90 (3),1840-50 (3),2330-40 (2). — Description of Paleozoic rocks. The following stratigraphic information is reported: top of Pennsylvanian, 820 feet; top of Mississippian, 2,420 feet; top of Ellenburger, 2,430 feet; total depth 4,661 feet, in Ellenburger. The lower part of the sequence is composed of Marble Falls and Ellenburger rocks; the Marble Falls is a dark spiculiferous limestone containing a mixture of clay and organic material. The overlying Pennsylvanian beds are fine-to medium-grained, angular to subround, poorly to fairly well- sorted, argillaceous calcareous feldspathic quartz sandstone and dark, locally silty shale or metashale ; the shales are deformed and brecciated. The sandstones contain abundant chert and phyllite fragments and as much as 10 to 15 percent plagioclase feldspar. In allprobability the Pennsylvanian sequence is Atoka; the abundant plagioclase is not typicalof the Atoka west of the structural belt in the Fort Worth basin, but over-all sandstone lithology and stratigraphic — position (overlying Marble Falls) suggest Atoka. The change from a normalEllenburger Marble Falls foreland sequence to a clastic sequence containing metamorphic rock fragments, feldspar, and showing incipient metamorphism reflects tectonism in this part of the structural belt immediately before and during Atoka deposition. The source of these sediments was prob Bureau ofEconomic Geology, The University of Texas ably a belt of overthrusting immediately to the south (see PI. 2); post-Atoka orogeny and the proximity of the Llano buttress resulted in deformation and incipient metamorphism of the Atoka beds. This wellpenetrated incipiently metamorphosed foreland rocks close to or within the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication :P. T.Fowler, Shell OilCompany, 1956. Samples areinBureau ofEconomic Geology WellSample Library. — County. Hays. — Wellname. Woodward No.1Schubert. — Location. Lot 26, Otis G. Eels survey; % mi. NW of Niederwald. Elevation— s9o feet. Total depth.— 3,33B feet. Completed.— l9ss. — Topof metamorphic rocks. 3,290 feet. Elevation of metamorphic rocks. 2,700 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3297-3305, 3305-33, 3333-38. — Description of metamorphic rocks. The sequence is composed of dark dolomitic quartzitic meta- sandstone, micaceous dolomitic metaquartzite, and black graphitic augen slate. Metamorphism is weak tolowgrade withstrong shearing element;foliationislocally warped and folded. The wellpenetrated highly sheared rocks of the black slate belt inthe interior zone of the Ouachita belt. X-ray data.—l>Ch;10/7 ~>1.1;F=20 and 24?. — References. Cores areinBureau ofEconomic Geology WellSample Library. — County. Hill. — Well name. California-Texas OilCompany No. 1Mastin (Maston). — Location. James Ship survey; SVz mi. SW of Grandview. —— Elevation. 750 feet (from topographic map). Total depth. —3,870 feet. Completed. ni. — Top of Paleozoic rocks. 1,600± feet. Elevation ofPaleozoic rocks. 850± feet. — Thin section coverage (depth infeet). bureau ofeconomic geology: 3370, 3765. — Description of Paleozoic rocks. A driller's log in the files of the Bureau ofEconomic Geology reports a sequence of dark to black shale and gray sandstone. The two samples available for study are non-diagnostic dark silty shale. From the location of the welland the samples and sample descriptionsavailable, this wellprobably penetrated Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Hill. Well name.—Hillsboro City WellNo. 1. — Location. 0.6mi.WofCourthouse, atcitywaterworks,Hillsboro,Texas. —— — Elevation. 635 feet. Total depth. 2,136 feet. Completed. 1912. — Topof Paleozoic rocks. 1,900± feet. Elevation ofPaleozoic rocks. 1,265± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Barnes (in Sellards, 1933, p. 135) described the rocks fromthis well as quartzite and phyllite and said "... the less resistant rocks of this series show considerable re crystallization." No samples were available for study, but from the location of the well, the amount ofmetamorphism reportedbyBarnesisanomalous; thewelliswithinthefrontalzoneoftheOuachita belt. — X-ray data. None. References.— Sellards (1933, pp. 135, 189) ;Sundstrom et al. (1948, p. 159). — County. Hill. — Wellname. HillsboroCityWellNo.2(WhiteandGreenDrillingCompany). — Location. Near Well No. 1, 0.6 mi. W of Courthouse, at city water works, Hillsboro, Texas. (This may be the same as CityWellNo. 1.) The Ouachita System Elevation.—634 feet. Totaldepth.—2,ls2 feet. Completed.—l9l9. — Topof Paleozoic rocks. I,Blo± feet. Elevation of Paleozoic rocks. 1,176± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology report a sequence of gray to black shale (red shale at top) and hard sandstone. Sellards (1931b) described the sequence as shale and quartzitic sandstone. From the location of the welland the general lithology, itprobably penetrated Stanley shale in the frontal zone of the Ouachita belt. — X-ray data. None. References.— Sellards (1931b, p. 822; 1933, p.189) ;Sundstrom et al. (1948, p. 159). — County. Hill. Wellname.—HillsboroCityWellNo.3 (Market Square Well). — Location. 0.1mi.NEofWellNo.1;0.6mi.WofCourthouse, Hillsboro,Texas. Elevation.—62s feet. Total depth.—l,B3Bfeet. Completed— -1922(?);1930(?). — TopofPaleozoic rocks. 1,794± feet. ElevationofPaleozoic rocks. 1,169 feet. — Thinsection coverage (depthinfeet). shelloilcompany:1838. — Description of Paleozoic rocks. Sellards (1931b) reported shale and quartzitic sandstone. Thin section study shows the rocks are fine-grained, angular, poorly sorted, feldspathic, silty quartz sandstone — witha substantial amount of garnet in the heavy mineral fraction Stanley lithology. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Sellards (1931b, p. 822) ;Sundstrom et al. (1948, p. 159). Samples are inBureau ofEconomic Geology Well Sample Library. — County. Hill. — Well name. Hill-Texas OilCompany (B. H. Harrison et al.) No. 1C. Weatherby (Weatherbee). Location.—W.O.Merriwethersurvey; 330 feetFSL,330 feetFEL;3%mi.SE ofHillsboro. Elevation.—lllfeet. Total depth.—4,ooo+ feet. Completed— -1929. — Top ofPaleozoic rocks. 2,305 feet. Elevation of Paleozoic rocks. 1,528 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 2835-45, 3761-70. — Description of Paleozoic rocks. Sellards (1931b) identified the sequence in this wellas probably Stanley-Jackfork ;later (1933) he described the rocks as black shale and quartzitic sandstone. Gold stein (1955) reported top ofPaleozoic, 2,305 feet; totaldepth 4,000 feet, inStanley ( ? ). The two samples examined for this study are altered sandy and silty volcanic tuff and fine-grained micaceous siltstone. The rocks are unmetamorphosed. The presence of tuff suggests that the rocks are Stanley, which contains tuff beds in the lower part. The well penetrated the frontal zone of the Ouachita belt. — X-ray data. None. References— Sellards (1931b, p. 826; 1933, p. 189). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology Well Sample Library. — County. Hill. — Well name. Humble Oil& Refining Company No. 1M. Holderman. — Location. C.Sullivantsurvey; 750 feetFNL,1,667 feetFmostElyEL. — —— Elevation. 659 feet, derrick floor. Total depth. 3,398 feet. Completed. 1935. Top of metamorphic rocks.—3,337 feet. Elevation of metamorphic rocks. 2,678 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 3350-56. — Description of metamorphic rocks. The single sample examined for this study is a calcareous chloritic sericite phyllite; metamorphism is low grade witha pronounced shearing element. The well penetrated the interior zone of the Ouachita belt. X-raydata.—Ch>I>X;10/7 0.2;SR=20. — References. Personal communication: T.H. Shelby, Jr., Humble Oil & Refining Company, 1956,1957. Bureau ofEconomic Geology, The University of Texas — County. Hill. — Wellname. J. H.Humphrey No.IJ.E. Osborne. Location.— E. S. Cabler survey; 5,650 feet FSWL, 1,500 feet FSEL; 5Yz mi. SE ofLive Oak. — —— Elevation. 747 feet, derrick floor. Total depth. 8,287 (? ) feet. Completed. 1953. — Top ofPaleozoic rocks. 1,490 feet. Elevation of Paleozoic rocks. 743 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1350-60, 2850-60, 3390-00, 4140-50, 4440-50, 4830-40, 5000-10, 6250-60, 6830-40, 6850-60, 6870-80, 7350-60, 7550-60, 7895-05, 7925-35. — Description of Paleozoic rocks; Turner (1957) reported top of Atoka, 1,490 feet; top of Marble Falls, 6,949 feet; top of Mississippian ( ? ),7,276 feet; top of Barnett, 7,495 feet; top of Ellenburger, 7,863 feet. — The upper part of the sequence is typical Atoka lithology interbedded dark silty shale and fine- grained, angular to subround, fairly well-sorted, quartz sandstone, locally slightly argillaceous and/or — feldspathic and/or calcareous. Marble Falls Barnett is dark fine-grained siliceous spiculitic limestone, locally sandy, containing dark organic matter and traces of glauconite, and black calcareous siliceous spiculitic shale, richinorganic matter. The Ellenburger is composed of fine-grained dolomite and fossiliferous dolomiticcalcilutite, locallypelletiferous. This wellencountered foreland facies rocks west of the Ouachita belt. — X-ray data. None. — References. Personal communication:G.L.Turner,Pure OilCompany, 1957. — County. Hill. — Well name. Hunt OilCompany No. 1E. W. Wright. — Location. JohnHayssurvey;660feetFSL,660 feetFWL;3mi.SEofGrandview. —— Elevation. 620 feet. Totaldepth.— 6,693 feet. Completed. 1948. — Topof Paleozoic rocks. 1,780 feet. Elevation ofPaleozoic rocks. 1,160 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1890-00, 2050-60, 2890-00 (2), 3200-10 (2), 6100-10 (2), 6670-80 (2). — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleo zoic (Pennsylvanian), 1,780 feet; total depth 6,693 feet, inPennsylvanian of normal(?) facies. Thin section examination shows a sequence of fine-grained, angular to subround, poorly to fairly well- sorted, calcareous quartz sandstone and dark silty and sandy shale which is probably Atoka. This wellpenetrated rocks of foreland facies west of the Ouachita belt. = X-ray data.—l>Ch>ML>X(?);10/7 <-'1.3;F20;SR=2.3. References.— Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology Well Sample Library. — County. Hill. — Well name. A.P.MerrittNo. 1Henry Nors. — Location. F.A.Tabor survey;3mi.SE ofAquila. —— — Elevation. 535 feet. Total depth. 3,127 feet. Completed. ni. TopofPaleozoic rocks.—1,624feet.ElevationofPaleozoicrocks. 1,089feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 1940-50, 2130-40, 2260-70. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic Ouachita facies, 1,624 feet; total depth 3,127 feet, in Pennsylvanian ( ? ).Thin section examination shows a sequence of fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone and dark shale. The sandstone contains garnet in the heavy mineral fraction and is identified as Stanley. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. The Ouachita System — County. Hill. Wellname.—PhillipsPetroleum Company No.1-APosey. — Location. E. S. Wyman survey; 2,400 feet FWL, 467 feet Fmost N'ly S line; 2 mi. S of Brandon. ——— Elevation. 599 feet. Total depth. 6,622 feet. Completed. 1956. — Top of Paleozoic rocks. 2,615 feet. Elevation of Paleozoic rocks. 2,016 feet. — Thin section coverage (depth infeet). bureau of economic geology: 2620-30, 2680-90 (2), 272030, 2730-40, 2770-80, 2817, 2880-90, 2993, 3407 (3), 3830-40 (2), 3910, 3947, 4200-10, 4609 (2),5182, 5192, 5383-98, 5480-90 (2),6112-20, 6410-20 (2),6620-21 (2). — Description of Paleozoic rocks. This wellencountered the top of the Stanley shale at 2,615 feet and bottomedinStanleyat6,622 feet.Acorefromthe3,900to3,910-footintervalshowsadipof75°to80°. The sequence is composed of fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone and dark metashale; the sandstone contains abundant garnet in the heavy mineral fraction. Locally quartz veins are numerous. Metamorphism ranges from none to incipient and occurs mostly in theshales; locally,veryweakmetamorphism ispresent adjacent toquartz veins. This wellpenetrated the frontal zone ofthe Ouachita belt. = X-raydata.—l>Ch;10/7 1;F 20;SR=1.5(shallow),3.1(deep). — References. Personal communication: F. H. Olson, Phillips Petroleum Company, 1956, 1957. — County. Hill. Wellname.—PhillipsPetroleum Company andGarrett No.1J.R.Rose. — Location. Francis Baldez survey; 1,300 varas FNL, 125 varas FEL; 5 mi. SSW of Whitney. Elevation.—46o feet. Totaldepth.—3,349 feet. Completed.—l92s. — Top of Paleozoic rocks. 1,600 feet. Elevation of Paleozoic rocks. 1,140 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1660, 1700, 1800, 1900-10, 1911, 2040, 2160, 2762, 2772. — Description of Paleozoic rocks. Sample descriptions in the Bureau of Economic Geology files re port dark slickensided shale, dark gray carbonaceous siltstone, and hard gray sandstone, locally quartzitic. A driller's log indicates base of Cretaceous may be as high as 1,364 feet. Goldstein (1955) reported top of Paleozoic (probably Pennsylvanian), 1,600 feet; total depth 3,349 feet, in Pennsylvania^?). The sequence is composed of fine-grained, mostly angular, poorly sorted, argillaceous micaceous quartz sandstone and siltstone, and dark silty shale containing abundant carbonaceous debris; locally, the sandstones are calcareous or quartzitic. This sequence is tentatively identified as Atoka. The sandstones are more angular and less sorted than most Atoka sandstones, but possibly this is due to proximity to the Ouachita front. Apparently, Atoka sandstones change infacies in this area and become more angular, less sorted, and contain more feldspar, mica, and rock fragments. This well is located close to the Ouachita front, possibly in the frontal zone of the Ouachita belt, possibly west ofit. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology Well Sample Library. — County. Hill. — Wellname. Sherman DrillingCompany (Clarence Houseman et al.) No.1J.F.Griffith. — Location. Samuel Waddell survey; SE corner; 10 mi. W of Hillsboro near Bethel Church. —— Elevation. 625 feet (from topographic map). Total depth.—2,835 feet. Completed. 1930. TopofPaleozoicrocks.—1,575±feet.ElevationofPaleozoicrocks. 950±feet. — Thin section coverage (depth in feet). bureau of economic geology: 2250-57, 2800-20. Description of Paleozoic rocks.—Sample descriptions inBureau of Economic Geology files reportblack shale and hard sandstone withsome red shale at the top of the sequence. Two samples available for study are fine-to very fine-grained, fairly well-sorted, calcareous argillaceous quartz sandstone, locally quartzitic, locally slightly feldspathic and micaceous, and containing minor amounts of chert, stretched quartz mosaic, shale, and slate-phyllite. This well encountered Atoka beds west of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. Bureau ofEconomic Geology, The University of Texas — County. Hunt. — Well name. American LibertyOilCompany No.1McNatt. Location.— E. Murphy survey; 4,750 feet FSL, 850 feet FEL. Elevation.—s73 feet. Total depth—6,B9o feet. Completed.—l942. Topof Paleozoic rocks.—6,870 feet. Elevation of Paleozoic rocks. 6,297 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. A sample log (source unknown) shows "red slate." The lithology isprobably similartotheNo.1NormanandNo.1Rutherford wellsimmediately tothesouth. — X-ray data. None. References.— Personal communication :Ann Carter, Shell OilCompany, 1958. — County. Hunt. — Wellname.-HumbleOil&Refining Company No.1E.M.Anderson. — Location. J. Porter survey. —— Elevation. 599 feet. Total depth. —6,273 feet. Completed. 1944. — Top ofPaleozoic rocks. 6,198 feet. Elevation of Paleozoic rocks. 5,599 feet. Thinsection coverage (depthinfeet).—bureau ofeconomic geology: 6267-73 (3). — Description of Paleozoic rocks. The driller's log reports "red slate." This sequence is composedof hematitic micaceous clay-slate (?) and hematitic chloritic micaceous quartz siltstone; the rocks are veined by quartz, carbonate, hematite, and chlorite. Metamorphism is difficult to assess because — of the obscuring effect of the finely disseminated hematite it appears to be very weak. This wellseems to have penetrated very weakly metamorphosed rocks of Ouachita facies, possibly weathered Stanley beds, possibly lower Paleozoic Ouachita facies beds. On the basis of tuff associated withsimilar red beds to the south in the No.1Norman, the sequence is identified as Stanley ( ? ). The wellis inthe frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Ann Carter, Shell OilCompany, 1958; R. D. Woods, Humble Oil& Refining Company, 1958. — County. Hunt. — Wellname. Humble Oil&Refining Company No.1Norman. — Location. Hiram Thompson survey ;720 feet FNL, 4,665 feet FWL. —— — Elevation. 559 feet. Total depth. 7,157 feet. Completed. 1944. — Topof Paleozoic rocks. 7,142 feet. Elevation of Paleozoic rocks. 6,583 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 7135-50 (2),7150-55. — Description of Paleozoic rocks. This sequence consists of fine-grained, argillaceous silty devitrified tuff veined with quartz overlying dark red hematitic metashale, locally brecciated, hematitic micro- granular chert, and dark red hematitic chloritic micaceous feldspathic quartz siltstone veined with quartz. Metamorphism is incipient. The tuffaceous rocks in this wellsuggest Stanley because tuff occurs in the lower part of the Stanley in the Ouachita Mountains and no tuffaceous rocks are known from the lower Paleozoic Ouachita facies sequence. The abundant hematite probably indicates deep weathering of the Paleozoic rocks. The wellis inthe frontal zone of the Ouachita belt. — X-ray data. None. References.— Personal communication; R.D.Woods, Humble Oil&Refining Company, 1958. — County. Hunt. — Well name. Humble Oil&Refining Company No. 1Rutherford. — Location.-Samuel Lindsey survey. — —— Elevation. 540 feet. Total depth. 7,483 feet. Completed. 1943. — Top of Paleozoic rocks. 7,460 feet. Elevation of Paleozoic rocks. 6,920 feet. — Thin section coverage (depth in feet). bureau of economic geology: 7455-60, 7460-65. — Description of Paleozoic rocks. This sequence is composed of fine-grained slightly hematitic sandy devitrified rhyolite( ? ) tuff overlying dark hematitic shale veined with quartz and dark micaceous The Ouachita System chloritic quartz siltstone veined with quartz and quartz-bitumen. Metamorphism ranges from none to incipient. The tuffaceous rocks in this well suggest Stanley because tuff is known to occur in the basal part of the Stanley in the Ouachita Mountains and itis not known in older rocks. The abundant hematite probably indicates deep weathering of the Paleozoic rocks. Thewellisinthe frontalzone oftheOuachitabelt. — X-ray data. None. — References. Personal communication: R.D. Woods,HumbleOil&Refining Company, 1958. — County. Hunt. — Wellname. Westmount DrillingCompany No.1Clark. Location.—-W'.H. Williams survey; 440 feet FEL, 1,225 feet FNL. Elevation.— 677 feet. Total depth— 5,314 feet. Completed—l939. Top ofPaleozoic rocks.—4,800± feet. Elevation of Paleozoic rocks. 4,123± feet. — Thin section coverage (depth infeet). None. Description of Paleozoic rocks.—According to Trowbridge (1958), Paleozoic rocks encountered in this well are dark shale. On the basis of location, this well probably penetrated the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Ann Carter, Shell Oil Company, 1958; R. M. Trowbridge, Tyler, Texas, 1958. — County. Johnson. — Well name. Alvarado OilCompany No. 1M. S. Richardson. — Location. Seth Morris survey; 3% mi. W of Alvarado. —— Elevation. 850 feet. Total depth. —3,538 feet. Completed. 1926. TopofPaleozoic rocks.—1,600± feet. Elevation ofPaleozoic rocks. 750± feet. Thinsection coverage (depth infeet).—bureau of economic geology: 3232. — Description of Paleozoic rocks. The driller's log in the files of the Bureau of Economic Geology reports a sequence of dark shale and light (gray) sandstone. The single sample studied is com posed of fine fragments of dark silty shale and fine-grained, angular to subround fairly well-sorted, calcareous and argillaceous quartz sandstone, locally quartzitic, micaceous. The sequence is probably Atoka. The wellis west of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Johnson. — Well name. Christie et al. No.1N.Peikoff. Location—¥m. Hickman survey; 3,725 feet FNEL, 6,100 feet FNWL; 2 mi. NW of Venus. —— Elevation. 677 feet, derrick floor. Total depth.—B,Bo9 feet. Completed.-1955. — TopofPaleozoic rocks. 1,840(?) feet. Elevation ofPaleozoic rocks. 1,163(?) feet. — Thin section coverage (depth in feet). None. Description of Paleozoic rocks.— Turner (1957) reported top of Atoka, l,840(?) feet; top of Barnett, 7,800 feet; top of Simpson(?), 8,185 feet; top of Ellenburger, 8,283 feet. This wellpenetrated foreland rocks west of the Ouachita belt. X-ray data.— None. — References. Personal communication: G. L. Turner, Pure Oil Company, 1957. — County. Kendall. — Wellname.-J.S.Abercrombie andHarrisonOilCompany No.1LenaKunzandJoeNickel. — Location. J. W. Cormack survey; 2,100 feet FNL, 550 feet FEL; 7 mi. N and 1mi. E of Boerne. Elevation.— l,3s2 feet. Total depth.— 2,2s2 feet. Completed.— l93o. — Topof Paleozoic rocks. 785 feet. Elevation of Paleozoic rocks.— -f-567 feet. Bureau ofEconomic Geology, The University of Texas — Thin section coverage (depth in feet). pan American petroleum corporation: 2055-61, 2167-70. BUREAU OF ECONOMIC GEOLOGY: 2250. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology are as follows: 1,895 feet, metamorphosed indurated black shale; 2,185, 2,205 to 2,210 feet, indurated metamorphosed black shale, green chloritic schist, reddish quartzite; 2,200 feet, light green micaceous schist. Sellards (1931b) reported top of altered Paleozoic at 1,895± feet and described the rock as schistose shale; he noted that unaltered Paleozoic beds were first encountered at about 800 feet. Goldstein (1955) noted first sample in Pennsylvanian at 1,840 feet; total depth 2,252 feet in Missouri Mountain(?). The three samples available for examination are angular argillaceous quartz siltstone, fine-grained, angular, poorly sorted, argillaceous chloritic and sericitic silty sandstone, and chloritic siliceous metashale; all samples contain massive quartz, quartz-chlorite, and quartz-carbonate veinlets. The rocks show incipient metamorphism, possibly due in part to the massive veining. Notwithstanding the X-ray data, the section appears to be Ouachita facies, probably including Stanley beds overlying older rocks. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data.—l>K>ML>Ch;10/7 '0.4; SR=1.7. Shale shows mixed layer structures resembling shales of the foreland but also has a high content of kaolinite, which is anomalous. References.— Sellards (1931b, p. 823; 1933, p. 189). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology WellSample Library. — County. Kendall. — Well name. Boerne City Well. — Location. 1mi. N of Boerne, Texas. — Elevation.—l,soo± feet. Totaldepth 1,118 feet. Completed.— Before 1930. — (-575± feet. Topof Paleozoic rocks. 925± feet. Elevation ofPaleozoic rocks. — Thin section coverage (depth in feet). None. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology for the intervals 1,012, 1,075, and 1,118 feet report dark gray shale. Sellards (1931b) described the rocks as schistose shale. From its location, this wellprobably penetrated Ouachita facies rocks in the frontal zone of the belt. — X-ray data. None. References.— Sellards (1931b, p. 822). — County. Kendall. — Wellname. Dixon OilCompany, Incorporated, No.1Ottmer Behr. Location.—}. W. Wilson survey; 1,400 feet FEL, 823 feet fromGuadalupe River. Elevation—l,274 feet. Totaldepth— -2,783 feet. Completed— -1932. — — Top of Paleozoic rocks. Inthe interval 425-570 feet. Elevation of Paleozoic rocks. In the interval +704 to -f-849 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology report the following information:base of Cretaceous and top of Pennsylvanian in the interval 425 to 570 feet; from 570 to 1,640 feet the sequence is composed of "partly metamorphosed" black shale and minor gray sandstone; top of Ellenburger occurs at 1,640 feet. The interval 570 to 1,640 feet isprobably Atoka. This wellpenetrated foreland rocks north of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. — County. Kendall. — Wellname. Magnolia Petroleum Company No.1EdBelow. — Location. Section 881, B. Ficklin Irrigation Company survey; 2,786 feet Fmost Sly SWL, 1,085 FSEL (inside line);6 mi. Wof Welfare. — — Elevation. 1,724 feet, derrick floor; 1,712 feet, ground. Total depth.—6,512 feet. Completed. 1953. The Ouachita System —— ¦ Topof Paleozoic rocks. 1,007 feet. Elevation of Paleozoic rocks. +717 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1104-08, 1142-46, 1160-65, 1220-25 (2), 1245-50 (2), 1290-95, 1340-45, 1365-70, 2260-65, 2805-08, 3040-50, 3150-55, 3200-05, 3285-90, 3540-45, 3675-80, 3820-50, 3850-55, 3890-95, 3911, 3920, 3942-47. shell oil company: 3820-25 (2),3850-55, 3890-95. — Description of Paleozoic rocks. Barnes (1958) studied cores from 3,905 to 6,512 feet, total depth andreported the followingsequence: 3,905 feet,inMarble Falls; topofBarnett, 3,934.5 feet; topof Chappel, 3,962.5 feet; top of Doublehorn, 3,964.0 feet; top of chert bed—lyes(?), 3,976.5 feet; top of Ellenburger, 3,977.0 feet; top of Wilberns, 5,490.0 feet; top of Morgan Creek, 6,195.0 feet; top of Welge, 6,340.0 feet; top of Lion Mountain, 6,360.0 feet; top of Cap Mountain, 6,400.0 feet; total depth in Cap Mountain. This is a normal foreland facies sequence. Sparry calcite veinlets with extensive twinning and bent twinlamellae cut these rocks and suggest deformation. Marble Falls rocks are overlain by a sequence of Ouachita facies rocks, showing incipient to very weak metamorphism accompanied by fracturing and brecciation, which are divided into an upper sequence of dark shale, siliceous shale, and chert, and a lower sequence of dark shale, sandstone, and tuff. The upper sequence (1,007 to 1,365 feet) is composed largely of (1) dark metashale (locally clay-slate), commonly siliceous, chloritic, micaceous, dolomitic, commonly containing pyritized spicules, and fragments ofradiolarian capsules, locally tuffaceous (?);commonly the rock is fractured, sliced, or brecciated and invaded by quartz, carbonate, and bitumen veinlets; and (2) dark micro- granular to cryptocrystalline chert, commonly dolomitic, spiculitic, argillaceous, commonly fractured, brecciated, and invaded by quartz, carbonate, and bitumen veinlets. These rocks are identified as pre- Mississippian rocks of Ouachita facies and include Arkansas novaculite, Missouri Mountain (? ),and Womble(?) lithologic types; possibly Stanley beds occur at the top of the sequence directly beneath the Cretaceous and overlying Arkansas novaculite. The lower sequence (1,365 to 3,890 feet) is composed largely of (1) dark shale or metashale, locally silty, siliceous, and veined with quartz, carbonate, and bitumen; (2) fine-grained, angular to subround, poorly sorted, argillaceous micaceous chloritic feldspathic quartz sandstone, locally slightly calcareous or dolomitic, and containing a relatively high percentage of garnet inthe heavy mineral fraction; the mica includes faded biotite; the rocks are veined with quartz, carbonate, and bitumen; and (3) fine-grained argillaceous chloritic siliceous tuff (1,365 to 1,370-foot and 2,805 to 2,808-foot intervals). This sequence is composed of Mississippian- Pennsylvanian rocks of Ouachita facies which closely resemble the Stanley. Insummary, the sequence penetrated in this wellfrom top to bottom consists of: (1) lower Paleo zoic (pre-Mississippian) rocks of Ouachita facies showing incipient to very weak metamorphism; (2) upper Paleozoic rocks of Ouachita facies showing incipient to very weak metamorphism (Stanley type);(3) unmetamorphosed upper Paleozoic rocks of foreland facies (Marble Falls-Barnett- Chappel) ;and (4) unmetamorphosed lower Paleozoic rocks of foreland facies (Ellenburger and older rocks). Descriptions of the lower beds are based on cores (3,900 feet to total depth). Descriptions of the upper beds are based on core chips and cuttings. The division of the Ouachita sequence into two groups is not clear cut but rather suggested by relative amounts of rock types. Possibly the rocks were mixed by complex faulting and folding; possibly the sequence contains abundant conglomerate and the rocks were mixed by sedimentary processes. This wellis interpreted as having penetrated a zone of overthrusting where Mississippian-Pennsylvanian rocks of Ouachita facies were thrust over Marble Falls rocks and in turn overridden by lower Paleozoic Ouachita facies rocks. The wellis probably a short distance south of the Ouachita front. Analternative interpretation is that the rocks overlying Marble Falls beds are of Atoka age and made up of fragments of Ouachita rocks; according to this interpretation, the wellislocated a short distance north of the Ouachita front. = X-ray data.— Samples above 3,900 feet:I> ML> X> Ch; 10/7 »-'1.0; F20; SR =1.6; hema tite. — References. Barnes (1959, p. 456). Personal communication: V.E. Barnes, Bureau of Economic Geology, 1958, 1959; J. R. Sandidge, Magnolia Petroleum Company, 1957. Cores and samples areinBureau ofEconomic Geology WellSample Library. — County. Kendall. — Wellname. A.S.MowinkleNo.1J.Kasten (Kaston). Location.—GeorgeWernersurvey; 150feetFNL,2,660feetFEL;1%mi.WofKendalia. Elevation.—l,392 feet. Totaldepth—l,s43feet. Completed.—l93o. —— TopofPaleozoic rocks. 470 feet. ElevationofPaleozoic rocks. +922 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology are as follows: 513 to 568 feet, green pyritic shale; 568 to 670 feet, gray and greenish-gray sandstone, sandy shale, and shale; 670 to 1,003 feet, dark unctuous glossy shale, locally slickensided;824 feet, Bureau of Economic Geology, The University of Texas quartzitic sandstone. The sequence from 470 to 1,003 feet is probably Atoka. The top of the "Bend" is placed at 1,003 feet; 1,003 to 1,062 feet, dolomitic fossiliferous limestone; 1,062 to 1,127 feet, black pyritic siliceous limy spiculiferous shale. This is probably a Marble Falls-Barnett section. The top of the Ellenburger is placed at 1,127 feet. Goldstein (1955) reported probable top of Paleozoic, 470 feet; definitelyinPaleozoic (Pennsylvanian) at 545 feet; base ofSmithwick and top ofMarbleFalls, 1,003 feet; top of Barnett(?), 1,092 feet; top of Ellenburger, 1,118 feet; total depth 1,545 feet, in Ellen- burger. This well penetrated foreland rocks north of the Ouachita belt. — X-ray data. None. — Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. References. Samples are inBureau ofEconomic Geology WellSample Library. — County. Kendall. — Wellname. Clarence NewtonNo.1Check Ranch. Location.—G.W.Lindsey survey; 165feetFNEL,467feetFWL;3mi.SWofKendalia. — — Elevation. 1,320 feet. Total depth.—2,339 feet. Completed. 1950. — Top ofPaleozoic rocks. 600 feet. Elevation of Paleozoic rocks. [-720 feet, — Thin section coverage (depth in feet). bureau of economic geology: 640-50, 770-810, 970-80, 1350-60, 1600-40, 1870-80, 2320-30 (2). — Description of Paleozoic rocks. The sequence consists of dark red hematitic metashale overlying a sequence of dark metashale, locally silty, and fine-grained mostly angular, poorly sorted, argillaceous micaceous chloritic feldspathic quartz sandstone. The abundant hematite in the upper part of the section is probably due to weathering. Metamorphism is incipient. This sequence is composed of Mississippian-Pennsylvanian beds of Ouachita facies (Stanley-Tesnus) . The wellpenetrated the frontalzone of the Ouachita belt south of the Llano uplift. X-ray data.—l>X>Ch>ML(Xrelatively abundant);10/7—'0.9; SR=1.9; hematite. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Kendall. — Wellname. Permian OilCompany No.1Bowles. — Location. F.delaLunasurvey;150feetFNL,150feetFWL;6mi.NofBoerne. Elevation.—l,4lo feet. Total depth.— l,sso(?) feet;2,485 (?) feet. Completed.— l93o. — TopofPaleozoic rocks. 1,195± feet. ElevationofPaleozoic rocks. |-215± feet. — Thin section coverage (depth in feet). bureau of economic geology: 1545-50. — Description of Paleozoic rocks. Sample descriptions in the files of the Bureau of Economic Geology for the intervals 1,195 to 1,200, 1,420 to 1,425, and 1,545 to 1,550 feet report indurated shale and quartzitic sandstone. Sellards (1931b) described the rock as schistose shale. Thin section examination shows that the rocks are dark silty shale and angular micaceous argillaceous quartz siltstone. The rocks are unmetamorphosed. This sequence is probably composed of Mississippian-Penn sylvanian rocks of Ouachita facies. This wellpenetrated the frontal zone of the Ouachita belt. = X-raydata.—l>Ch;10/7^1;F 20;SR=3.0(1sample). References.— Sellards (1931b, p. 822; 1933, p. 189). — County. Kendall. — Wellname. Seaboard Oiland Gas Company No. 1W. H. Askey. — Location. MigueldelTorosurvey; 8mi.W,4mi.NofKendalia. —— — Elevation. ni. Total depth. 1,005 feet. Completed. 1930. —— Top of Paleozoic rocks. 565 feet. Elevation of Paleozoic rocks. ni. — Thinsection coverage (depth infeet). None. DescriptionofPaleozoic rocks.—Descriptionsinthe filesoftheBureauofEconomic Geologyreport graytoblackshale. Fromitslocation,thiswellisprobablyinAtokabedsnorthoftheOuachitabelt. — X-ray data. None. — References. Bureau of Economic Geology files. The Ouachita System — County. Kendall. — Wellname. P.B.Sterling et al.No.1McCracklin. Location.—B. G. Owen survey; l,350(?), l,800(?) feet FNL, 250(?), 150(?) feet FEL; SY2 mi. NWofKendalia. Elevation.— l,39B feet. Total depth.— l,4Bo feet. Completed.— l93o. — InPaleozoic at 500 feet. Elevation of Paleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sample descriptions inthe files of the Bureau of Economic Geology report hard gray carbonaceous sandstone from 550 to 735 feet and black shale from 735 to 756 feet. Top of Ellenburger dolomitic limestone is placed at 756 feet. The upper clastic section is probably Atoka-Marble Falls-Barnett. Sellards (1933) listed top of Ordovician at 752 feet. This wellpenetrated foreland rocks north of the Ouachita belt. — X-raydata. None. References.— Barnes (1948);Sellards (1933,p.215). Personal communication :j.R. Sandidge, Magnolia Petroleum Company, 1956. Samples are inBureau ofEconomic Geology WellSample Library. — County. Kendall. Wellname.—P.B.Sterling No.IW.Werner. Location.—JohnF.Torreysurvey; 150 feetFNL,2,432 feetFEL;3mi.EofSisterdale. — —— Elevation. 1,403 feet. Total depth. 926 feet. Completed. 1930. —— Top ofPaleozoic rocks. 548 feet. Elevation of Paleozoic rocks. +855 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sample descriptions inthe files of the Bureau of Economic Geology are as follows:736, 745 feet, gray sandstone and hard gray shale (Atoka?);780, 790, 798, 835 feet, brown dense spiculitic crinoidal limestone (Marble Falls-Barnett?) ;886 to 916 feet, hard dolomitic limestone (Ellenburger) .Sellards (1933) records top ofOrdovician at 780 feet. This wellpenetrated foreland rocks north of the Ouachita belt. — X-ray data. None. References.— Barnes (1948); Sellards (1933, p. 215). Personal communication :J. R. Sandidge, Magnolia Petroleum Company, 1956. Samples areinBureau ofEconomic Geology WellSample Library. — County. Kendall. — Wellname. FredTurner,Jr.,etal.No.1R.Linder. Location.—].C.Brownsurvey; 290feetFSWL,1,610feetFSEL;6mi.SofComfort. Elevation—l,67Bfeet. Totaldepth—l,49ofeet. Completed—l939. — TopofPaleozoic rocks. 940 feet. ElevationofPaleozoic rocks. [-738feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 900-07, 963-70, 988-94, 1135-40, 1165-70, 1198-1202, 1400-10, 1478-81 (2). — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic, 940feet;inMissouriMountain(?), 1,100feet;topofBigfork,1,450feet;lastsampleinBigforkat 1,481 feet. Farmer (1958) described the following section below the base of the Cretaceous; 15 feet of gray, green, and brown chert; 100 feet of gray slickensided shale withminor interbedded siltstone; 65-foot sample skip; 225 feet of bright red and green slickensided micaceous shale; 50 feet of gray shale; 70 feet of green shale; 25 feet of dark brown to black hard shale; black spicular chert and brown dolomite. He suggested that this might represent an Arkansas novaculite-Missouri Mountain-Bigfork sequence. Thin section examination shows a sequence of calcareous argillaceous siltstone and sideritic sericitic metashale or clay-slate, locally siliceous, underlain by dark slightly calcareous and argillaceous chert containing dark organic material; quartz-bitumen veins are common. The rocks show incipient to very weak metamorphism. This well penetrated lower Paleozoic Ouachita facies rocks in the frontal zone of the Ouachita structural belt, possibly in an allochthonous plate. Magnolia No. 1Below (p. 278), 6,000 feet to the northeast, has a normal pre-Mississippian foreland facies section. — X-ray data. None. Bureau of Ecojiomic Geology, The University of Texas — References. Personal communication: R.E.Farmer, ShellOilCompany, 1958; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Kerr. — Wellname. Evans et al.No.2 Love. Location.—Section 1594, CCSD & RGNG survey; 660 feet FSL, 1,320 feet FWL; y2y2 mi. FS, 1mi. FW County line. Elevation.—2,3Bo feet. Total depth.— s,B7B feet. Completed.— Before 1932. — Top ofPaleozoic rocks.—1,490 feet. Elevation ofPaleozoic rocks. H-890 feet. — Thinsection coverage (depthinfeet). None. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic (Pennsylvanian), 1,490 feet; top of Marble Falls(?), 5,540 feet; top of Ordovician, 5,580 feet; total depth 5,872feet,inEllenburger. Sellards(1933)listedtopofOrdovicianat5,605feet. This wellpenetrated rocks of foreland facies north of the Ouachita belt. — X-raydata. None. References.— Sellards (1933, p. 215). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Kerr. Wellname.—OhioOilCompany No.1J.H.Soul (Saul?). Location.—Section 47, TWNG survey; 330 feet FEL, 1,650 feet FNL; 6 mi. SW of Center Point. — Elevation.—l,7s6 feet. Total depth. —5,070 feet. Completed. 1945. — Top ofPaleozoic rocks. 950 feet. Elevation of Paleozoic rocks. [-806 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Pennsyl vanian,950 feet;topofEllenburger, 3,580 feet;totaldepth 5,070 feet,inEllenburger. This wellpenetrated foreland rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Kerr. — Well name. G.L.Rowsey No.1R.B.Nowlin. — Location. Juan Corona survey; 1,924 feet FNL, 661 feet FWL; 2 mi. NW of Camp Verde. —— Elevation.—1,695 feet, derrick floor; 1,685 feet, ground. Totaldepth. 6,363 feet. Completed. 1954. — TopofPaleozoicrocks. 970(?)feet.ElevationofPaleozoicrocks. 1-725(?)feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks.-A scout card reported the following data: top of sand, 970 feet; top of Ellenburger, 4,580 feet. Ifthese data are correct, the well penetrated foreland rocks north of the Ouachita belt. — X-ray data. None. — References. None. — County. Kerr. Wellname.—G. L.RowseyNo.2R.B.Nowlin. Location.—George Smith survey; 805 feet FSL, 770 feet FWL; 1% mi.SW of Camp Verde. — — Elevation. 1,680 feet, derrick floor; 1,670 feet, ground. Total depth.—7,902 feet. Completed. 1954. —— Top of Paleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. A scout card reported top of Marble Falls at 4,626 feet and top of Ellenburger "around 4,800 feet." Barnes (1959) reported top of Ellenburger at 5,320 feet. Apparently, this wellpenetrated foreland rocks north of the Ouachita belt. The Ouachita System — X-raydata. None. References.— Barnes (1959, p. 470) — County. Kerr. Additional wellnot shown on map (PI. 2) and not studied because of lack of samples or basic data: — G.L.Rowsey No.1ElderHenderson LewisEt Al. Location: J. E. Bellner survey; 1,971 feet FSL, 330 feet FWL; 1% mi. NW of Camp Verde. Elevation: 1,640 feet. Total depth: 4,756 feet. — County. Kinney. Well name.— Austral Oil Exploration Company, Incorporated, No. 1-A Wardlaw-Whitehead Estate. Location.—Melton Valdez Grant; 23,660 feet FNWL, 13,550 feet FSWL. Elevation.— l,o49 feet. Total depth.— 4,37B feet. Completed.— l9s3. Topof metamorphic rocks.—4,110 feet. Elevation of metamorphic rocks. 3,061 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 4202-17. — Description of metamorphic rocks. The single sample examined is a graphitic sericite slate showing well-developed foliation and slaty cleavage; metamorphism is low grade with a high shearing element. A sample log shows that the sequence is composed of interlayered slate and metaquartzite. Thiswellpenetrated shearedmetamorphicrocksintheinteriorzoneoftheOuachitabelt. — X-ray data. None. — communication: Karl Schneidau, Austral OilExploration Company, Incorpo- References. Personal rated, 1954 (withsample description and electric log). — County. Kinney. — Wellname. Fish Production Corporation No.1Roy Henderson. Location.—Section 53,block11,I&GNsurvey; 600 feetFmost Ely"WL,660 feetFmost N'lyNL; 14mi.N.20° W.ofBrackettville. Elevation.—l,sBB feet. Total depth— -2,699 feet. Completed.— l9sl. Top ofPaleozoic rocks. —2,140 feet. Elevation of Paleozoic rocks. 552 feet. — Thin section coverage (depth in feet). shell oil company: 2150-60, 2210-20, 2230-40, 2320-30, 2440, 2470-80, 2630, 2689-90. — Description of Paleozoic rocks. This wellencountered pre-Cretaceous rocks intruded by andesite porphyry. According to a sample log, Cambrian beds were identified in this sequence. The intrusive rocks range from albite andesite porphyry to trachyte and rhyolite porphyry; all of the igneous rocks show extensive alteration, and large volumes of the groundmass are composed of chlorite, epidote, calcite, and secondary amphibole. The host rock is fine-grained, angular to subround, fairly well-sorted, hematitic feldspathic quartzitic quartz sandstone and metaquartzite variably metamorphosed by in- trusions;some fragments show completely recrystallized quartz mosaic containing clusters ofsericite. The age of the rocks is unknown, and samples are too scanty and alteration too advanced to determine facies. Probably the host rocks are upper Paleozoic. Metamorphism is of the contact type, static, without a high shearing element. This wellis north of the Ouachita belt. — X-ray data. None. — Personal communication: J. B. Souther, Pan American Petroleum Corporation, 1953. References. — County. Kinney. — Wellname. Fish Production Corporation No.1Postell. Location.—Salitha Banks survey; 3,600 feet FNL, 4,620 feet FEL; 12 mi. N. 30° E. of Brackettville. —— Elevation.—1,586 feet. Total depth. 5,374 feet. Completed. 1952. — Top ofPaleozoic rocks. 2,740 feet. Elevation of Paleozoic rocks. 1,154 feet. Thin section coverage (depth in feet).—shell oil company: 3200, 3770-80, 3938-50, 3980-90, 4680-90, 4910-20, 5370-71. bureau of economic geology: 5170-80, 5250-60, 5280-90. Description of Paleozoic rocks.—According to Goldstein (1955), the pre-Cretaceous section can be dividedinto fiveunits, fromthe top down: (1) conglomeratic arkose and black shale, (2) fossiliferous and siliceous limestone of Atokan age, (3) sandy limestone and sandy dolomite, (4) dolomiticsand Bureau ofEconomic Geology, The University of Texas stone and sandy dolomite, (5) weakly metamorphosed sandstones and carbonate rocks. He classified the sequence as normal foreland facies which has undergone local thermal metamorphism from a nearby igneous intrusion. Farmer (1957) reported a normal section including Atoka, Marble Falls, Ellenburger, and Cambrian with the Cambrian section correlative with the Llano uplift Cambrian section; base of Cretaceous, 2,732 feet; top of Ellenburger, 4,200—feet; top of Cambrian, 4,450 feet. This wellpresents problems ininterpretation. Metamorphism-of a static thermal or hydrothermal — type without pronounced shearing is variable in certain intervals. The clastic rocks (Atoka) in the upper part of the sequence are coarse-grained, angular, poorly sorted, feldspathic quartz sandstones or arkoses containing abundant fragments of metamorphic rock (muscovite schist) ; they were probably derived from a metamorphic terrane immediately to the south and as such support the position of the Luling front as drawn in this area (PI. 2). Metamorphism is not the same kind that characterizes rocks of the Ouachita belt in this area and is probably due to local intrusions of igneous rock which are known in the area but do not appear in this boring. Except for the abundance of metamorphic detritus in the upper part of the sequence, the rocks penetrated in this wellappear to — be of normal foreland facies the wellis located north of the Ouachita belt. — X-raydata. None. — References. Personal communication: R. E. Farmer, Shell OilCompany, 1957; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic GeologyWellSample Library. — County. Kinney. — Wellname. HavolineOilCompany (Haveline,Havolind,Havolien)No.1Weatherby (Weatherbee). Location.—Section 21, block 5, I&GNsurvey; 500 feet FNL, 2,640 feet FEL; 14 mi.NE of Del Rio. Elevation.—l,22o feet. Totaldepth.— 4,39B± feet. Completed.— -1927. — TopofPaleozoic rocks.—2,010 feet.ElevationofPaleozoic rocks. -790 feet. Top of metamorphic rocks.—4,381± feet. Elevation of metamorphic rocks. 3,161± feet. — Thin section coverage (depth in feet). shell oil company: 4450. bureau of economic geology: 2088-2103,2340,2350,4400 (3). — Description of Paleozoic and metamorphic rocks. Sellards (1933) described the rock as altered shale. According to Kleihege (1949) the section is composed mostly of gray crystalline dolomite with subordinate quartzite;the quartzites show sutured contacts and wavy extinctions. Rocks from the bottom of the hole are pale green schist. Sample descriptions in the Bureau of Economic Geology files indicate that the pre-Cretaceous sequence is mostly dark quartzitic dolomite and dolomitic quartzite withminor sandstone to a depth of 4,000 feet. "Rock salt" is reported from 4,000 to 4,057 feet, where a hard siliceous carbonate rock was encountered. The alleged presence of salt in this sequence is anomalous, and unfortunately samples from the interval are not available. Thiswellpasses fromCretaceous rocksintoasequence ofquartziticdolomitesandquartzites show ing varied amounts of incipient to weak metamorphism ;sample coverage is poor but a similar section in the nearby No. 1 Martin Rose (p. 286) contains sparse fossil remnants that indicate an early Paleozoic age (Ellenburger?) (Wilson, 1958). The No. 1 Weatherby bottoms in a highly sheared — rhyolite (the pale green schist of Kleihege) which is partly mylonitized (phyllonitized) the potassium feldspar is nearly all converted to sericite except for a few remnant phenocrysts; the rock resembles Precambrian metarhyolite exposed to the northwest in the Van Horn area and is probablyPrecambrian. The well is located on the Devils River uplift, a structurally high area of Precambrian rocks, immediately north of overthrust metamorphic rocks of the interior zone of the Ouachita structural belt (PI. 2). This allochthonous plate of metamorphic rocks has overridden foreland facies sedimentary rocks (see Magnolia No. 1Wardlaw, p. 285). In the area of the No. 1 Weatherby the Paleozoic foreland carbonate rocks lying on the Precambrian metarhyolite show the effects of incipient to weak metamorphism. Probably this extension of metamorphism into foreland facies rocks was caused by the advance of the Ouachita belt against the resistant DevilsRiver uplift. — X-ray data. None. References.— Kleihege (1949, pp. 34-35 );Sellards (1933, p. 190). Bureau of Economic Geology files. Personal communication: J. E. Galley, Shell Oil Company, 1956; E. J. Theessen, Shell OilCom pany, 1956;J.L.Wilson, ShellDevelopment Company, 1957, 1958. Incomplete samples areinBureau ofEconomic Geology WellSample Library. — County. Kinney. — Wellname. Josey, Incorporated, No.1A.F.Beidler. Location.—Melton Valdez survey; 6,400 feet FNEL of GH&SA survey, 2,450 feet FSEL of M.Valdez survey. The Ouachita System — Elevation. 1,043 feet. Totaldepth.—4,006 feet. Completed. —1952. — Top of metamorphic rocks. 3,760 feet. Elevation of metamorphic rocks. 2,717 feet. — Thin section coverage (depth in feet). shell oilcompany: 3760-70, 3780-90, 3790-00, 3800-10, 3830-40, 3840-50, 3890-00, 3940-50, 3970-80, 3980-90, 3990-00. bureau of economic geology: 3990-00, 4000-06. — Description of metamorphic rocks. There are two interpretations of the sequence encountered in this well: (1) base of Cretaceous and top of Ordovician (Ellenburger), 3,760 feet; top of Hickory, 3,890 feet; top of Precambrian, 3,920 feet; or (2) base of Cretaceous and top of metamorphic rocks, 3,920 feet. The section in question is composed of beds of fine-grained inequigranular dolomite, sandy at the base, which lie on a metaquartzite sequence. The dolomite and basal sand show no signs of metamorphism; some geologists believe these beds are Ellenburger and some consider them basal Cretaceous. The correct answer is important because if they are Ellenburger, it means that the underlying metamorphic rocks are Precambrian, but ifthe dolomite is Cretaceous, the underlying metamorphic rocks could wellbe displaced metamorphic rocks of the Ouachita structural belt. There fore, in order to map the correct position of the Ouachita front in this area, itis necessary to resolve the problem of the dolomite sequence. In the writer's opinion, the Cretaceous probably rests directly on metamorphic rocks in this welland there are no intervening Paleozoic beds. The metaquartzite is a highly sheared low-grade metamorphic rock which is partly mylonitized in one sample; locally, itis sericitic and dolomitic. Structures are foliation and grain-stretching. This wellis tentatively considered to have penetrated the interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: R. E. Farmer, Shell OilCompany, 1957; J. B. Souther, Pan American Petroleum Corporation, 1953. County. —Kinney. — Wellname. Magnolia Petroleum Company No.1C.B.Wardlaw. Location.—Melton Valdez survey; 2,640 feet FSL, 2,640 feet FWL; 16 mi. W of Brackettville. Elevation.—99B feet; 988(?) feet. Total depth.— s,2Bo feet. Completed.— l93l. —— Top of metamorphic rocks. 3,430 feet. Elevation of metamorphic rocks. -2,432 feet. Top of Paleozoic rocks.—s,oso (?) feet. Elevation of Paleozoic rocks. 4,052 (?) feet. — Thin section coverage (depth in feet). pan American petrolem corporation: 3440, 3450, 3510, 3840, 4220, 4290, 4300, 4300-10, 4310-20, 4315, 4320, 4715, 4960, 4960-61, 4985, 5235. bureau of economic geology: 4202-07. — Description of Paleozoic and metamorphic rocks. Goldstein (1955) reported base of Cretaceous and top of altered Paleozoic (Ordovician?), 3,450 feet; top of dolomite, 5,050 feet; total depth5,280 feet, in dolomite; two igneous intrusive bodies were encountered in the metamorphosed sequence above the dolomite at 4,290 to 4,330 feet and 4,960 to 4,990 feet. He noted that the unaltered dolomite section is generally referred to as Ellenburger of normal foreland facies. P. S. Morey (sample log) logged top of metamorphic rocks at 3,430 feet and top of dolomite marble at 5,020 feet. Sellards (1933) reported top of Paleozoic at 3,450 feet and remarked that the wellpassed through more or less altered rock from 3,450 to near 5,050 feet, entered unaltered Ellenburger facies, and terminated at 5,280 feet. The metamorphosed sequence is composed of schistose marbles, commonly sericitic, chloritic, and graphitic, and interlayered graphitic or hematitic sericite phyllite; metamorphism is low grade, fabrics range from porphyroblastic and poikiloblastic to cataclastic, structures are foliation and dimensional grain orientation. The intrusive rock is microgabbro, partly sericitized, and largely replacedby calcite; itshows no signs of metamorphism. The bottom samples are fine-grained equigranular dolomite, not metamorphosed. The following structural history is suggested: (1) thrusting of metamorphosed Ouachita rocks over unmetamorphosed lower Paleozoic rocks of carbonate foreland facies; (2) intrusion of gabbroicrocks. This well penetrated the interior zone of the Ouachita belt. Minimum displacement on the overthrust is 6 to 8 miles. — X-ray data. None. — References. Goldstein and Reno (1952, p. 2286) ;P. S. Morey, Bureau of Economic Geology sample log; Sellards (1933, p. 189). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Kinney. — Wellname. Mud Creek Oiland Gas Company No.1J.0.Taylor. — Location. %mi.NofAmanda Siding,2mi.WofStandart. Bureau ofEconomic Geology, The University of Texas — — 1,100 feet (from topographic map). Total depth. —2,798 feet. Completed. 1919. Elevation. —— TopofPaleozoic rocks. ni.ElevationofPaleozoic rocks. ni. — Thin section coverage (depth infeet). None. — Description of Paleozoic or metamorphic rocks. Notes in the files of the Bureau of Economic Geology report Cretaceous rocks at 2,688 feet and splintery blue-black shale at 2,798 feet, total depth. From its location, this wellis probably ina structurally complex zone close to or withinthe Ouachita front. X-ray data.—None. — Bureau of Economic Geology files. References. County.—Kinney. — Wellname. George Proctor No.1Wardlaw-Whitehead. Location.—Melton Valdez survey; 19,100 feet FSEL, 19,800 feet FSWL; 5,800 feet NW of Pinto Creek, 1,160 feet SW of Southern Pacific Railroad. —— Elevation. —1,070 feet, derrick floor. Totaldepth. 4,507 feet. Completed. 1948. — Top of metamorphic rocks. 4,090(?) feet. Elevation of metamorphic rocks. 3020(?) feet. — Thinsection coverage (depth infeet). bureau ofeconomic geology: 3095-3105, 3400-10, 3500-06, 3600-08, 3701-05, 3800-02, 3894-3907, 4090-4107, 4302-05. — Description of metamorphic rocks. Cuttings from this wellare very fine grained. The wellis in rocks of the Ouachita belt at 4,090 feet. Samples are composed of fragments of (1) fine-grained, sheared, graphitic sericitic chloritic dolomiticmetaquartzite or high rank metasandstone; (2) sericitic and chloriticmicrogranular metachert, locally graphitic and dolomitic; and (3) fine-grained siliceous sericitic metadolomite. Between 3,400 and 4,090 feet the cuttings are a mixture of Cretaceous limestone, locally sandy and silty, quartz grains (probably derived from sandstone), chert, and dolomite of unknown age, and fragments of metasandstone and clay shale apparently derived from the Ouachita belt. Either there has been some mixing of the samples or the Ouachita fragments occur as sand grains and pebbles inyounger rocks. The rocks of the Ouachita belt have been subjected to weak to low-grade high-shear metamorphism ; they are similar to rocks of the interior zone penetrated in other Kinney and Val Verde County wells. — X-ray data. None. — References. -None. County.—Kinney. — Wellname. Richardson OilCompany No.1MartinRose. Location—Block5,I&GNsurvey; 600 feetNEofHavolineNo.1Weatherby. Elevation.—l,22s feet. Totaldepth.— -2,675 feet. Completed.— l9s6. TopofPaleozoicrocks.—1,959feet.ElevationofPaleozoicrocks. 734feet. — Thin section coverage (depth in feet). bureau of economic geology: 2593-2664 (5). — Description of Paleozoic rocks. The pre-Mesozoic rocks are quartzose dolomite and dolomitic quartzitic metasandstone showing varying degrees of incipient to weak metamorphism. According to Wilson (1956, 1958), fossil fragments found in cores indicate a Paleozoic age, probably earlyPaleozoic;agastropod fragment wasidentifiedas Ordovician. Metamorphism in this sequence is not as intense as that to the south. In allprobability these are early Paleozoic foreland facies carbonate rocks weakly metamorphosed by the thrust of the Ouachita belt against a local Precambrian buttress (cf. Havoline No. 1 Weatherby, p. 284). The well is located immediately north of allochthonous metamorphic rocks of the interior zone of the Ouachita belt (PI. 2). — X-ray data. None. References.— Personal communication: E. J. Theessen, Shell Oil Company, 1956; J. LWilson, Shell Development Company, 1956, 1958. Core chips are inBureau ofEconomic Geology WellSample Library. — County. Lamar. — Wellname. BaileyDevelopment Company No.1AlexFord. — Location. ParkerS.Dosssurvey;9mi.S,8mi.WofParis. — Elevation. 565 feet. Total depth. —1,930 feet. Completed. —Before 1925. The Ouachita System — Topof Paleozoic rocks. 1,880 feet. Elevation of Paleozoic rocks. 1,315 feet. — Thinsection coverage (depth infeet). bureau of economic geology: 1912-17 (2). — Description of Paleozoic rocks. Sample descriptions in the Bureau of Economic Geology files re port dark gray quartzitic sandstone and hard black slaty shale from 1,880 to 1,900 feet. Miser and Sellards (1931, p. 812) reported that cuttings below 1,880 feet are either Stanley shale or a shale and quartzite formation of Ordovician age. Thin section examination of the single sample available shows fine-grained, angular poorly sorted, slightly feldspathic quartz sandstone and dark shale; probably these rocks are Stanley but no unequivocal determination can be made from one sample. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. References— Miser and Sellards (1931, pp. 812-813); Sellards (1933, p. 190). Bureau ofEconomic Geology files. Incomplete samples areinBureau ofEconomic Geology WellSample Library. — County. Lamar. — Well name. Clark and Ogg No. 1Smiley. Location.-—T.M.Clarksurvey; 330feetFNL,330feetFEL;3mi.NofBrookston. —— — Elevation. 582 feet. Total depth. 3,351 feet. Completed. 1944. — Top ofPaleozoic rocks. 3,195 feet. Elevation of Paleozoic rocks. 2,613 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 3261, 3274-76, 3295, 3305, 3320, 3335. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous (Trinity) and top of Paleozoic Ouachita facies at 3,195 feet; total depth 3,351 feet, inPaleozoic rocks. The upper part of the sequence is light to very dark brown cryptocrystalline to microgranular chert, locally argillaceous, and commonly fractured and veined with quartz; small spherical lighter colored siliceous bodies (radiolarians?) are common. The chert is underlain by dark chloritic sideritic(?) metashale or clay-slate veined with quartz-chlorite. The bottom sample is fine-grained, angular, very poorly sorted, micaceous argillaceous silty quartz sandstone. — The very weakly metamorphosed chert-metashale sequence is pre-Stanley Ouachita facies probably Bigfork-Womble. The unit encountered at the bottom of the hole resembles Stanley and there is, therefore, a possibility of overthrusting or an inverted section inthis well. This wellpenetrated — the frontal zone of the Ouachita belt in the projected southwestern extension of the Broken Bow Benton uplift of the Ouachita Mountains. — X-ray data. —None. References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Lamar. — Wellname. Cosden Petroleum Company No. 1W. T. Adams. — Location. J. H. Gibson survey. — —— Elevation. 511 feet. Total depth. 3,065 feet. Completed. 1944. — Top of metamorphic rocks. 2,820 feet. Elevation of metamorphic rocks. 2,309 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 2820, 2835, 2860, 2865, 2890, 2895, 3035. — Description of metamorphic rocks. Goldstein (1955) reported base of Cretaceous and top of Ouachita fades Paleozoic (Blaylock?), 2,820 feet; total depth 3,065 feet, inBlaylock(?). The sequence is composed of fine-grained chloritic sericitic metaquartzite, locally pyritic anddolomitic, chlorite slate, and chlorite-sericite slate or phyllite cut by chlorite-quartz-carbonate vein- lets. Reconstitution is complete ;metamorphism is weak to low grade. — This well penetrated the southwestern subsurface extension of the Broken Bow Benton uplift of the Ouachita Mountains; the rocks are weakly metamorphosed lower Paleozoic beds of Ouachita facies. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Bureau ofEconomic Geology, The University of Texas — County. Lamar. — Well name. Doyle and Jondreau No. 1Joe Horn (Martin). Location.—R.P.Mayo survey; 2,200 feetFNL,1,000 feetFEL;12mi.NEofParis. — — 1932. Elevation. 532 feet. Total depth. 2,958 feet. Completed. — — TopofPaleozoic rocks. 2,860 feet. Elevation ofPaleozoic rocks. 2,328 feet. Thin section coverage (depth infeet).—bureau of economic geology: 2860-80 (2). — Description of Paleozoic rocks. Notes in the Bureau of Economic Geology files report white and gray indurated siliceous rock witha schist-like character. Paleozoic rocks are dark cryptocrystalline to microgranular argillaceous chert and dark slightly silty shale ormetashale. On the basis of lithology and location, this well appears to have penetrated incipiently metamorphosed lower Paleozoic Ouachita facies rocks in the southwestern subsurface extension of the Broken — Bow Benton uplift of the Ouachita Mountains. — X-ray data. None. — Bureau of Economic Geology files. Personal communication: B.W.Fox,The AtlanticRefiningCompany, 1957;H.A.Sellin,Magnolia Petroleum Company, 1957. References. — County. Lamar. Wellname.—A.T.Walker etal.No.1Federal LandBank. — Location. A.T.Norwellsurvey; 5% mi.NofBlossom. ——— Elevation. 501 feet. Totaldepth. 2,685 feet. Completed. Before 1937. —— TopofPaleozoic rocks. ni.Elevation ofPaleozoic rocks. ni. — Thinsection coverage (depth infeet). bureau of economic geology: 2680-85. — Description of Paleozoic or metamorphic rocks. Barnes (Bur. Econ. Geol. files) described a core from 2,680 to 2,685 feet as a phyllite containing small porphyroblasts and noted that metamorphism is not extreme ;cleavage dips at a low angle. The single sample available is light-colored argillaceous microspherulitic chert and siliceous metashale or clay-slate containing "porphyroblasts" of dark "pleochroic" carbonate and sporadic grains of quartz sand; metamorphism is very weak. These rocks are lower Paleozoic rocks of Ouachita facies, possibly Arkansas novaculite. This well penetrated the — southwestern subsurface projection of the Broken Bow Benton uplift of the Ouachita Mountains. — X-ray data. None. — References. Bureau of Economic Geology files. County.—Lampasas. — Wellname. MarkAlexander etal.No.1AlexanderBrothers. — Location. S. Berry survey; 6 mi. SE ofLampasas. —— Elevation.—l,o2s feet. Totaldepth. ni. Completed. Before 1932. —— Top ofPaleozoic rocks. 1,000 feet. Elevation of Paleozoic rocks. +25 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sellards (1933) recorded top of Ordovician at 1,000 feet. This well apparently penetrated foreland rocks west of the Ouachita belt. — X-ray data. None. References.-— Sellards (1933, p. 216). Asingle sample isinBureau ofEconomic Geology WellSample Library. — County. Lee. — Wellname. SkellyOilCompany and Sunray MidcontinentOilCompany No.1Cornell, location.—Albert Nantz survey; 6,800 feet FNEL,2,550 feet FSEL; approx. 8,900 feet F Williamson County line,12,400 feetFBastrop County line. — —— Elevation. 534 feet, derrick floor; 523 feet, ground. Total depth. 6,826 feet. Completed, 1957. — Top of metamorphic rocks. 6,610 feet. Elevation of metamorphic rocks. 6,076 feet. — Thinsection coverage (depthinfeet). bureau ofeconomic geology: 6745-50. — Description of metamorphic rocks. The sequence is composed of dark graphitic chlorite-sericite phyllite cut by numerous quartz veins; graphitic material is concentrated along shear planes. Structures are foliation, well-developed fracture cleavage, crinkling and rucking; metamorphism is low grade witha strong shearing element. This wellpenetrated the interior zone of the Ouachita belt. The Ouachita System — X-ray data. None. — References. Personal communication:K.H.Hamilton,SkellyOilCompany, 1957. — County. Limestone. — Wellname. FarrellDrilling Company No.1J. R. Gillam. Location.—].S.Spencer survey;1,536 feetFNWL,1,426feetFNEL;2mi.EofMart. Elevation.—s2l feet. Total depth.— 4,B67 feet. Completed.— l94l. — Topof metamorphic rocks. 4,750 feet. Elevation of metamorphic rocks. 4,229 feet. Thin section coverage (depth in feet).—pan American petroleum corporation: 4185, 4245, 4305, 4365, 4385, 4425, 4475, 4485, 4600-4760, 4615, 4685, 4760-4869, 4765, 4835, 4860. bureau of economic geology: 4860-70. — Description of metamorphic rocks. The sequence in this wellconsists of highly sheared sericitechlorite phyllite and sericitic metaquartzite ;in the phyllite, porphyroblasts of muscovite are oriented parallel to and at right angles to the foliation. Metamorphism is low grade with a high shearing element. Goldstein and Reno (1952, p. 2281) figured a photomicrograph of a core fragment from 4,867 feet as "meta-argillite." This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. X-raydata.—l(100%);SR= 5.5.Micaiswellcrystallized. References.— Goldstein and Reno (1952, p. 2281). Personal communication: B. W. Fox, The Atlantic Refining Company, 1956; August Goldstein, Jr., Pan American Petroleum Corporation, 1955; H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. Limestone. Well name.—Pure OilCompany No. 16-T W.H.Kendricks. — Location. Mexia field. Elevation.—sl9 feet. Total depth.— B,2B4 feet. Completed— -1937 (? ). — Top of metamorphic rocks. 8,235± feet. Elevation of metamorphic rocks. 7,716± feet. — Thin section coverage (depth in feet). bureau of economic geology: 8233-38 (2), 8251-59,8278-84. — Description of metamorphic rocks. Barnes (Bur. Econ. Geol. files) described the sequence as composed of unmetamorphosed shales and sandstones overlying a chloritic quartzite (8,233 to 8,238 footinterval). Turner (1957) reported total depth inthe Smackover formation. Available samples are fine to coarse-grained, angular, poorly sorted, siliceous graywacke composedof abundant fragments of sheared sericite-chlorite phyllite, sericitic metachert, vein quartz, microlitic igneous rock, quartz, feldspar, mica and chlorite cemented by silica. In some fragments the calcite and dolomite cement has partly replaced the rock fragments. The rocks studied appear to be late Paleozoic or Mesozoic clastic rocks derived from the Ouachita belt and in large part from the interior zone of metamorphic rocks. According to Barnes (above), rocks of the interior zone of the Ouachita belt were encountered beneath the deepest samples avail able for study (8,284 feet). — X-ray data. None. — References. Bureau of Economic Geology files. Personal communication: G.L.Turner, Pure OilCompany, 1958. — County. Limestone. — Wellname. The Texas Company No.1Keeling. — Location. AlexWhitaker survey; 6% mi. SW of Coolidge. — —— Elevation. 546 feet. Totaldepth. 6,018 feet. Completed. 1942. — Top of metamorphic rocks. 6,000 feet. Elevation of metamorphic rocks. 5,454 feet. — Thin section coverage (depth infeet). None. — Description of metamorphic rocks. Goldstein (1955) reported top of Paleozoic at 6,000 feet; samples are described from 6,004 to 6,007 feet and classified by Goldstein as chlorite-sericite meta quartzites containing swarms of opaque needles (rutile altered to leucoxene?). He noted that theserocks are similar to metasedimentary rocks from the Luling field and that they are possibly a metamorphosed equivalent of the Blaylock formation. This well penetrated metamorphosed rocks inthe interior zone of the Ouachita belt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Maverick. — VPellname. HumbleOil&RefiningCompany No.1Bandera County School Land. Location.— Bandera County School Land survey; 660 feet FSL, 660 feet FEL; 19 mi. NE of Eagle Pass. Elevation.— 9o9 feet. Totaldepth.— l3,B63 feet. Completed.— l9s6. Top of metamorphic rocks.—13,332(?), 13,462(?) feet. Elevation of metamorphic rocks. 12, 423(?),-12,553(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 7890-7920, 8570-8600, 860004, 10,140-70 (2), 11,460-70 (8), 11,590-93, 12,362-72, 13,306-09, 13,329-32y 2, 13,332-35, 13,478-81, 13,481-84 (2), 13,478-500, 13,500-03, 13,523-28, 13,552-55, 13,594-97, 13,700-03, 13,730-33, 13,781-84, 13,800±(?), 13,828-31, 13,865-67. — Description of metamorphic rocks. Woods (1957) reported base of Jurassic(?) and top of "basement" at 13,462 feet. Cores m the Bureau of Economic Geology Well Sample Library indicate that the top of the metamorphic sequence is at 13,332 feet, considerably higher than the figure given by Woods; possibly the cores are incorrectly labeled. The metamorphosed section in this wellis overlain by hard red to maroon conglomerate and shale of unknown age; the conglomerate contains — — abundant fragments of metamorphic rocks phyllite, schist, metaquartzite and vein quartz. Petrographic study shows the upper clastic rocks are (1) dark reddish fine-to medium-grained, angular to round, fairly well-sorted to poorly sorted, hematitic calcareous or dolomitic feldspathic micaceous quartz sandstone commonly quartzitic, containing abundant fragments of chert and slatephyllite, commonly veined by calcite, less commonly by fine quartz; (2) dark red, hematitic calcareous conglomerate; and (3) dark red, hematitic quartz siltstone. The conglomerate is composed of low- grade metamorphic rock fragments (slate, phyllite, schist, metaquartzite) which commonly show evidence of strong shearing, chert, sandstone, metasandstone, vein quartz, and feldspar in a matrix of quartz-feldspar silt-sand, micaceous matter, and sparry calcite. The rock fragments appear to have been derived from the Ouachita— structural belt. One sample contains a pebble of cataclastically altered sericitized muscovite granite indicating the presence of pre-deformation granite in the structural belt.Fine-grained siltycalcilutiteispresent inthe 8,600 to8,604-foot interval. Beneath the clastic sequence is interlayered dark sericite-chlorite slate (locally siliceous, hematitic, graphitic) and dark chloritized spilitic basalt or greenstone, locally strongly sheared. Quartz and calcite veins, both pre-and post-deformation, are abundant. The slate, wellfoliated, is apparently — greenstone completely altered by shearing and hydrothermal metamorphism the plagioclase is converted to sericite. The greenstone shows a relictporphyritic-subophitic fabric;where strongly sheared, the plagioclase laths are cataclastically re-oriented and the phenocrysts are shattered. Shearing in the greenstone is clearly shown in the calcite and quartz veins which are stretched and deformed. Meta morphism is weak withstrong shearing and metasomatic elements; structures are foliation,micro folding, contortion. This well penetrated a strongly sheared sequence of volcanic rocks in the interior zone of the Ouachita belt. Similar rocks were encountered to the east in wells that penetrated the black slate belt (Humble No. 1 Wilson, Medina County; General Crude No. 1Rogers Ranch, Bexar County). — X-ray data. None. — References. Personal communication: R. D. Woods, Humble Oil& Refining Company, 1957, 1958. Cores areinBureau ofEconomic Geology WellSample Library. County.— McLennan. — Wellname. DanielOilCompany No.1Elizabeth W. Estes. — Location. Duke Faulkner survey; 1%mi. W ofLorena. —— Elevation. 580 feet. Total depth.—2,671 feet. Completed. 1949. —— Top ofPaleozoic rocks. 1,745 feet. Elevation of Paleozoic rocks. -1,165 feet. Thin section coverage (depth in feet).—bureau of economic geology: 1735, 2400, 2468, 2598 (2), 2650 (2). — Description of Paleozoic rocks. According to a scout report, a core (2,551 to 2,556 feet) recovered quartzitic sandstone withstreaks ofblack limestone. The upper part of the sequence is composed of fine-grained, angular to subround, poorly to fairlywell-sorted, feldspathic quartz sandstone containing a high percentage of garnet in the heavy mineralfraction, fine-grained quartz siltstone with streaks and layers of locally deformed dark shale, and layers of cone-in-cone limestone ;quartz and calcite veins are common. These rocks are Stanley. Inthe 2,598-foot interval there is a very dark argillaceous dolomitic chert or siliceous shale containing dark The Ouachita System organic matter that suggests Bigfork lithology; the 2,650-foot sample is fine-grained dolomitic limestone containing a small amount of dark organic material and also may be Bigfork. This wellpenetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1956; H. A.Sellin, Magnolia Petroleum Company, 1956. Samples are inBureau of Economic Geology Well Sample Library. County.—McLennan. Wellname—-DeltaDrillingCompany (Carpenter and Clements) No.1C.Horstman. Location.— B. C. Walters survey; 2,900 feet FSWL, 3,700 feet FSEL; 1mi. SE of McGregor. Elevation.— 69s feet. Total depth.— 2,2s9 feet. Completed.—l939. — Topof Paleozoic rocks. 1,120 feet. Elevation of Paleozoic rocks.-425 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1130-40, 1195-98 (2), 139196,1620- 35,1785-90, 2247-59. — Description of Paleozoic rocks. The sequence is composed of dark argillaceous dolomitic cryptocrystalline chert containing dark organic material, dark siliceous argillaceous dolomite, and dark argillaceous spiculitic dolomitic limestone; the carbonate rocks are all very finely crystalline. This section is identified as Bigfork chert. In the middle of the Bigfork sequence (1,620 to 1,625 feet) there is a fine-grained angular poorly sorted feldspathic quartz sandstone containing angular slivers of garnet among the heavy minerals; it is a typical Stanley sandstone. The general area is one of structural complexity, and the presence of a slice of Stanley sandstone within a Bigfork sequence can be explained by folding or faulting; an alternative explanation is sample mixing or contamination. This wellpenetrated lower Paleozoic Ouachita facies rocks close to the frontof the Ouachita belt inan area of probable overthrusting. — X-ray data. None. — Personal communication: G.L.Turner, Pure OilCompany, 1957. Samples areinBureau ofEconomic Geology WellSample Library. References. — County. McLennan. — Wellname. Falcon OilCompany No. 1H. Mattlage. Location.—E. C. Woodruff survey; 330 feet FSL, 330 feet FEL; 5 mi. NW of Crawford. —— — Elevation. 767 feet, kelly bushing; 750 feet, ground. Total depth. 7,585 feet. Completed. 1954. Top of Paleozoic rocks.—l,o72 feet. Elevation of Paleozoic rocks. 305 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1100-10, 1200-10 (2), 129000 (3), 2510-20, 3270-80, 3430-40, 3500-10, 4440-50, 4710-20 (2), 5000-10 (2), 6010-20 (2), 6500-10, 6850-60, 6880-90, 6950-60, 7000-10, 7430-40, 7580-90. — Description of Paleozoic rocks. The Paleozoic sequence inthis wellis divided into three units. The upper unit is dark silty shale and fine-to coarse-grained, angular to subround, poorly to fairly well- sorted, commonly calcareous, locallyargillaceous quartz sandstone, some of whichisquartzitic;locally the sandstones and shales contain traces of glauconite. These rocks are probably Atoka although the clay mineralogy is not typically Atoka. Underlying the Atoka (?) is a black calcareous shale contain — ingcalcareous andsiliceousspiculesandpelmatozoan debris;thisisMarbleFalls Barnettlithology. The lower unit, topped at 6,870 feet, is fine-grained equigranular dolomite and limestone of the Ellen — burger group. Because of incomplete sample coverage, the top of Marble Falls Barnett rocks cannot be determined withcertainty. This wellpenetrated foreland rocks a short distance west of the Ouachita belt. X-raydata.—l,2oofeet:I> Ch;10/7<-'1;F=20;SR=3.45 (probablynotAtoka). — References. Personal communication: G. L.Turner, Pure OilCompany, 1957, 1958; and sample log. — County. McLennan. — Well name. Hodges et al. No. 1Lawrence. — Location. B. C. Walters survey;"near" McGregor. — —— Elevation. 438 feet. Totaldepth. ni. Completed. Before 1931. — Top of Paleozoic rocks. 1,313 (?) feet. Elevation of Paleozoic rocks. 875(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 1330-35 (2), 1600. Bureau ofEconomic Geology, The University of Texas Description of Paleozoic rocks.—Descriptions in the Bureau of Economic Geology files report samples 1,313, 1,322, and 1,330 to 1,335 feet are hard black shale with some dolomite fragments, and sample 1,600 feet is chert, green shale, and dolomite, possibly Bigfork; top of Paleozoic is not given; top of Trinity is reported as 985 feet. Sellards (1931b, p. 823) described the sequence as chert and black shale and (p. 827) noted resemblance to Bigfork. Goldstein (1955) reported light-colored slightly calcareous cryptocrystallinecherts, some of which are argillaceous and contain radiolarians. Thin section study shows the samples are green argillaceous cryptocrystalline chert and green to shale and darker — brown siliceous (1330-35) cryptocrystalline dolomitic chert (1600). The lighter colored chert higher inthe hole contains sporadic grains of rhombic "pleochroic" carbonate dolomite or siderite. These rocks are interpreted as pre-Stanley Ouachita facies rocks; the darker cherts lower inthe wellmay be Bigfork. This well penetrated the frontal zone of the Ouachita structural belt near its western boundary, probably inan area of overthrusting. — X-ray data. None. References.— Sellards (1931b, pp. 823, 827). Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. McLennan. Wellname.—Korshoj No.1Simon-Ferguson. Location.—A.R.Valdezsurvey; 520feetFSWL,2,340feetFNWL;2mi.NofAxtell. — — Elevation. 570 feet. Total depth. 4,378 feet. Completed.— l9s4. —— InPaleozoic rocks. 3,200 feet. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth infeet). bureau of economic geology: 3200-10 (2), 3300-10, 340010, 3500-10, 3600-10 (2), 3700-10 (2), 3800-10 (2), 4000-10 (2), 4200-10 (2), 4350-60. — DescriptionofPaleozoic rocks. Thiswellpenetrated atleast 1,150 feetofgraymicaceous dolomitic quartz metasiltstone and gray to silty metashale quartz, black or clay-slate; quartz-chlorite, and quartz-dolomite veins are common. Structures are microfolding, rucking, and shearing. The presence of small blebs of new chlorite and new mica fibers indicates very weak to weak metamorphism. This wellpenetrated weaklymetamorphosed dark clastic rocksofunknown ageintheinteriorpartofthe frontal zone. — X-ray data.—l> Ch; 10/7 0.4-1.5; F=20; SR=9.0. — References. Personal communication: H. J. Morgan, Jr., The Atlantic Refining Company, 1955. — County. McLennan. Wellname.—}.L.Myers&Sons No.1AxtellCityWater Well. — Location. Inthe city ofAxtell. Elevation—-528 feet. Total depth— -2,129 feet. Completed.— l9s9. Top of Paleozoic rocks.—3,069 feet. Elevation of Paleozoic rocks. 2,541 feet. — Thin section coverage (depth infeet). bureau of economic geology: 3040-60, 3060-80, 3080-3100. — Description of Paleozoic rocks. The rocks include dark red and green hematitic rutiliferous sericitechlorite slate, veined with quartz and extensively sheared and sliced, and dark hematitic dolomitic sericitic chloritic metasiltstone veined withquartz. This well penetrated weakly metamorphosed rocks along the boundary of the frontal and interior zones. The highly sheared rutiliferous slate is similar to rocks in the interior zone farther east; the metasiltstone resembles rocks of the dark clastic unit in the eastern part of the frontal zone inthis area. Possibly the rocks have been tectonically mixed. — X-ray data. None. — References. Personal communication :H. D. Holloway, 1959. County.— McLennan. — Wellname. MuthandBerryNo.1Freeman (alsoknownasFreeman andButler). — Location. R. Simpson survey; 2% mi. S of ValleyMills. —— Elevation.—-732 feet. Totaldepth. ni. Completed. 1950. — Top of Paleozoic rocks. 1,120 feet. Elevation of Paleozoic rocks. 388 feet. Thin section coverage (depth in feet).—bureau of economic geology: 1200-10, 1880-90. The Ouachita System — Description of Paleozoic rocks. H. J. Plummer (Bur. Econ. Geol. files) described the following sequence; 1,120 to 1,190 feet, red, red-brown, and gray shale, probably a weathered surface; 1,190 to 1,380 feet, hard dark carbonaceous shale and silty shale; 1,380 to 2,000 feet, hard dark shale and hard gray sandstone or siltstone. Petrographic study of two samples shows dark silty shale and fine-grained, mostly subangular, fairly well-sorted, slightly argillaceous and dolomitic quartz sandstone ;the rocks are cut by dolomite and bitumen-pyrite veinlets. The sandstone contains fragments of metasiltstone and dark siliceous shale rich in organic material (Bigfork?) evidently derived from the Ouachita belt to the east. This wellpenetrated Atoka beds immediately west of the Ouachita belt. X-raydata.—l>ML>Ch>X;10/7 1.2;F=20;SR=1.50. — References. Bureau of Economic Geology files. — County. McLennan. — Well name. F. J. Ossenbeck No. 1Charles Bezdek (Bezdak). — Location. 12mi.NofWaco, 7mi.SW ofWest. —— Elevation. 570 feet (from topographic map). Total depth. —3,200± feet. Completed. 1921. — Top of Paleozoic rocks. 1,540 feet. Elevation of Paleozoic rocks. 970± feet. — Thinsection coverage (depth in feet). None. — Description of Paleozoic rocks. Adkins (1923, pp. 134-136) included a driller'slog and placed top of Pennsylvanian at 1,540 feet. He described the rocks (p. 26) as black shale, slate, and limestone, probably belonging to theBend series. From its location and the sample descriptions, this wellprobably penetrated Stanley shale. — X-ray data. None. References.— Adkins (1923, pp. 26, 134-136) . — County. McLennan. — IFellname. St. Louis OilPool Company No.1EllaV.Stuart (Stewart). — Location. J.L.Johnston survey;NWcorner;2%mi.S,%mi.EofMcGregor. Elevation—722 feet. Total depth.— 3,sl2 feet. Completed.— l92o. — Top of Paleozoic rocks. 1,235± feet. Elevation of Paleozoic rocks. 513± feet. — Thin section coverage (depth in feet). bureau of economic geology: 1940 (2), 2120, 2310, 2340 2660, 2380 (2),2700 (3),3340-3500. Description of Paleozoic rocks.—Descriptions by J. A. Udden of scattered samples between 1,940 and 2,700 feet show black siliceous spiculitic limestone and chert, locally bituminous (Bur. Econ. Geol. files). Adkins (1923, p. 26) described the sequence as black shale, slate, and limestone, probably belonging to the Bend series and included a driller's log and sample descriptions by L. Pace (pp. 142-145). Sellards (1931) reported chert, limestone, and black shale. Goldstein (1955) described two samples: dark brown chert of the Bigfork formation (1,940 feet) and clay shale and glauconitic dolomite (3,348 to 3,500 feet). The upper part of the Paleozoic sequence is dark argillaceous dolomiticcryptocrystalline chert con taining dark organic material, locally spiculitic, of the Bigfork chert. Underlying the chert is dark slightly silty shale and fine-to medium-grained, slightly fossiliferous and pelletiferous, slightly glauconitic argillaceous dolomiticlimestone ofunknown age. This well penetrated pre-Stanley rocks of Ouachita facies close to the western margin of the belt in an area of probable overthrusting. Possibly the carbonate rocks in the bottom part of the wellare foreland rocks beneath a frontal overthrust, but sample coverage is too meager for a reliable identi fication. — X-ray data. None. References.— Adkins (1923, pp. 26, 142-145) ;Sellards (1931b, p. 823). Bureau ofEconomic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, '955. — County. McLennan. Well name.— Waco City Water Works Well. — Location. First and Webster Streets, Waco, Texas. — —— Elevation. ni. Total depth. ni. Completed. 1914(?). — — Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth infeet). bureau of economic geology: 2385. Bureau ofEconomic Geology, The University of Texas — Description of Paleozoic rocks. Adkins (1923, p. 26), reporting on the possibility of Ordovician rocks in an old wellat Waco, quoted E. G. Woodruff from a letter written to J. A. Udden in October 1919:"...Late inthe fallof1914...Ivisited a wellwhich was being drillednear the center of the town [Waco]...Iprocured a sample...from about 2,400 feet. Lithologically this appeared to be older than the Upper Paleozoics. AsIremember the specimen, there were some fragmentary fossils init.... some of the men of the United States Geological Survey...expressed the opinion that it was probably as old as Ordovician...Iconsidered the evidence too imperfect to form a basis for scientific conclusion. ...Personally Iam inclined to think that the specimen came from Lower Paleozoic." Adkins(lettertoJ.A.Udden,1923) referredtoOrdovicianrocks foundintheWacowellatFirst and Webster Streets and discussed the possibility that: (1) a strip of Ordovician rocks forms the pre-Cretaceous subcrop east of Waco and is in fault contact with Pennsylvanian beds to the west of — Waco, or (2) there is an eroded uplift with Pennsylvanian beds stripped off in the area of Waco Pennsylvanian beds thicken to the north (inthe Ossenbeck well) and south (in the Stuart well). A driller's log of this welland Udden's description of the samples (Adkins, 1923, pp. 153-154) extend only to a depth of 2,230 feet. The single sample available for study is composed of fine fragments of light and dark-colored cryptocrystalline microgranular and microspherulitic chert some of which contains abundant red- brown organic material and round siliceous bodies (radiolarian tests?). Cross-cutting veinlets of quartz-bitumen are common. This chert is Bigfork type. The wellpenetrated pre-Stanley Ouachita facies rocks (Bigfork) inthe frontal zone of the Ouachita belt. — X-ray data.-None. References.— Adkins (1923, pp. 25-26, 153-154). Bureau ofEconomic Geology files. — County. McLennan. — Wellname. WacoOiland Refining Company No.1G.H.Harrington. — Location. M.Moore survey; 4% mi.Nof Waco. Elevation.— 4B6 feet. Totaldepth— -3,697 feet. Completed.— Before 1923. Top of Paleozoic r0ck5.—2,215 (?) feet; 2,114(?) feet. Elevation of Paleozoic rocks. 1,729(?) feet; -1,628(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 2600 (2), 2650 (3), 2660, 2670 (2), 2680 (2), 2730 (2), 3060, 3069, 3255, 3300-3495, 3315, 3425, 3435 (2), no depth given (7). — Description of Paleozoic rocks. Adkins (1923, p. 26) reported top of Pennsylvanian (probably Bend) at 2,215 feet and noted that Udden described a sequence of arkosic quartzite, graphitic schist, and other ancient-looking rocks from 2,596 to 3,697 feet which he assigned to the Precambrian; a sample log by Udden and a driller's log are included (pp. 119-129). Sellards (1931b) placed the topof the Paleozoic at 2,600 feet and described the sequence as composed of quartzitic sandstone and black shale, probably of the Stanley-Jackfork formations. Barnes (in Sellards, 1933) described a single sample of quartzite from this well as composed of grains of quartz that have been largely recrystallized and much broken, and concluded that metamorphism is rather advanced. The sequence in this well is fine-grained, angular, poorly sorted, feldspathic quartz sandstone, locally quartzitic, calcareous, argillaceous, micaceous, and dark metashale. The rocks show incipient to very weak metamorphism, and quartz grains in the sandstones are commonly fractured. There is general similarity to Stanley lithology. This wellpenetrated incipiently to very weakly metamorphosed Stanley rocks in the eastern partof the frontal zone of the Ouachita belt. — X-ray data. None. References.— Adkins (1923, pp. 26, 119-129) ;Sellards (1931b, pp. 823, 826; 1933, p. 135). Samples areinBureau ofEconomic Geology WellSample Library. — County. Medina. — Well name. California-Medina Association (also known as California-Medina OilCompany) No. 1 Rothe Estate. — Location. Section 1012, Medina County School Land survey; 940 varas FWL, 1,440 varas FSL; 8 mi. NWofD'Hanis. — —— Elevation. 1,025 feet. Total depth. 3,705 feet. Completed. 1925. Top of Paleozoic rocks.— 2,6l6± feet. Elevation of Paleozoic rocks. 1,591± feet. — Thinsection coverage (depth infeet). bureau ofeconomic geology: 2616. The Ouachita System — Description of Paleozoic rocks. Sellards (1931b) described a core from the interval 3,560-3,565 feet as black shale. Anote in the Bureau of Economic Geology files reports black shale at 3,144 feet. A single sample examined from 2,616 feet is angular tightly packed calcareous quartz siltstone. On the basis of location and lithology, this wellprobably penetrated upper Paleozoic Ouachita facies rocks inthe frontal zone of the Ouachita belt. — X-ray data. None. References— Sellards (1931b, p. 822; 1933, p. 190). Bureau of Economic Geology files. Incomplete samples are inBureau of Economic Geology Well Sample Library. — County. Medina. — Well name. R. E. Fair, Incorporated, No. 1McAnelly. Location.—E.C. Durst survey; 475 feet FWL, 370 feet FEL; 9 mi. W, 3 mi. Nof Devine. —— — Elevation. 717 feet, derrick floor. Total depth. 5,512 feet. Completed. 1946. Top of Paleozoic rocks.—5,427 feet. Elevation of Paleozoic rocks. 4,710 feet. — Thinsection coverage (depth infeet). shell oilcompany: 5425-27. bureau of economic geology: 5425-27, 5438-41. Description of Paleozoic rocks.—Only two samples from this wellwere examined. The rock in the interval 5,425 to 5,427 feet is massive siliceous hematite-calcite vein rock which gives little indication of the nature or facies of the country rock in the area. The 5,438 to 5,441-foot sample is dark-banded calcareous cryptocrystalline chert. On the map (PI. 2) the well falls in the black slate belt of the interior zone. In all probability the well penetrated the Ouachita belt somewhere close to the boundary between the frontal and interior zones. Samples are too meager to permit use of this well for geologic control. X-ray data.—None. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1956. — County. Medina. — Wellname.-HumbleOil&Refining Company No.1E.E. Wilson. Location.—Aß&Msurvey;1,980 feetFSL,1,980 feetFEL;6.4mi.SWofYancey. Elevation—-725 feet, derrick floor. Totaldepth.—l,l6lfeet. Completed— -1949. — Top o/ metamorphic rocks. 6,980 feet. Elevation of metamorphic rocks. 6,255 feet. — Thin section coverage (depth in feet). shell oil company: 7068-70, 7161-62, 7163-66. bureau of economic geology: 7065-68, 7162-63, 7163-66 (2). — Description of metamorphic rocks. According to Masson (1954), the following rock types were logged in this well:7,068 to 7,070 feet, granitic rock; 7,161 to 7,162 feet, dacite or andesite porphyry; 7,162 to 7,166 feet, altered dacite or andesite porphyry. Goldstein (1955) reported top of granite at 6,980 feet withtotal depth 7,167 feet in granite. Thin section study shows that the rock in the 7,065 to 7,068-foot interval is a brecciated and cataclastically altered, medium-grained, biotite granite. Quartz and feldspar grains are fractured and broken apart; the plagioclase is partly sericitized; mica plates are locally bent; chlorite occurs as granular masses in breccia zones and as sheaves (after biotite);calcite is common in the brecciated parts of the rock. The intervals 7,162 to 7,163 and 7,163 to 7,166 feet are composed of fractured and altered andesite or dacite porphyry. The groundmass is a mass of plagioclase, epidote, and chlorite in which the outlines of relict feldspar microlites are visible; plagioclase phenocrysts are partly altered to epidote and chlorite; quartz is present as round embayed . phenocrysts and as veinlets and secondary cavity fillings; prehnite occurs in cavities withquartz and also partly replaces plagioclase. This wellis located within the interior zone of the Ouachita belt. Similar rocks were encountered inthe General Crude No. 1 Rogers Ranch, Bexar County, which also penetrated black slate (p. 224). — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; P. H.Masson, Humble Oil&Refining Company, 1954. — County.-Medina. — Wellname. JohnI.MooreNo.1AlfredJ.Wurzbach. Location.—Juan Delgado survey; 4,500 feet FEL, 3,400 feet FNL; 5 mi. NE of Castroville. Elevation.—l,ollfeet. Totaldepth.— 3,l93 feet. Completed.— l94s. Bureau ofEconomic Geology, The University of Texas Top of Paleozoic r0ck5.—2,864 feet. Elevation of Paleozoic rocks. 1,853 feet. — Thin section coverage (depth in feet). shell oil company: 3160-70 (3), 3191-92 (2).bureau of economic geology: 2874-76, 2879-81, 2886-98, 2950-60 (4), 3000-10 (4), 3050-60, 307080 (2), 3080-90, 3150-60, 3170-80 (2), depth unknown (2). — Description of Paleozoic rocks. Goldstein (1955) reported that below the base of the Cretaceous at 2,852 feet, there are thin beds of hard massive dark gray micaceous shale, sandy shale, and sandstone to a depth of 2,885 feet. From 2,885 to 2,985 feet is a contact zone of sediments intruded and metamorphosed by serpentine-like igneous rock. Gray altered shale and very fine-grained dirtyquartzitic sandstone were penetrated from 2,985 to 3,080 feet. Another mixed zone of altered sediments intruded by dikes and stringers of igneous material extends from 3,080 to 3,193 feet. Thin section study shows a sequence of deformed and brecciated dark sandy and silty micaceous metashale and dark, fine-to medium-grained, mostly angular, poorly sorted, locally slightly glauconitic pyritic calcareous micaceous feldspathic argillaceous quartz sandstone extensively veined bycalcite and quartz. The distinguishing characteristic of this sedimentary sequence is the presence of abundant plates of second-cycle reddish biotite. In the intervals 2,890-2,895, 2,950-2,960, 3,0003,010, 3,080-3,090, 3,150-3,160, and 3,170-3,180 feet the samples contain fragments of cataclasticallyaltered muscovite biotite granodiorite; fractured and broken grains of microperthite and albite are separated by zones of crushed quartz-feldspar-sericite-chlorite-calcite, and veins of sericite-chloritecalcite are common. In the intervals 2,950 to 2,960 and 3,000 to 3,010 feet there are also fragmentsof trachyte porphyry and fragments of dark, fine-grained, locally fossiliferous, calcilutite veined by sparry calcite and quartz. A fragment of muscovite schist occurs at 2,890 to 2,895 feet and in the bottom part of the wellthere are abundant fragments of masses of sericite-chlorite. As an alternative to Goldstein's interpretation of intrusive igneous rock in this section, the writer suggests that the igneous fragments (and limestone fragments) were derived from conglomerate or breccia in the sandstone-shale sequence; itis significant that the red biotite so abundant in the sandstones is also present in the granodiorite, suggesting that both the sandstones and the granodiorite fragments were derived from the same provenance. Metamorphism in the sandstone-shale sequence is incipient, but the rocks are strongly deformed and extensively invaded by quartz and calcite veins. This wellis interpreted as penetrating Ouachita facies rocks of Mississippian-Pennsylvanian age very close to the Luling overthrust front but north of it in the south part of the frontal zone. The fragments of cataclastically altered granodiorite are similar to those which occur in General Crude No. 1Rogers Ranch in Bexar County where they occur as the result of tectonic injection in a more highly sheared black slate. Brecciated and partly mylonitized granitic rock also occurs in Humble No. 1Wilson to the south in Medina County. X-raydata.—l>Ch;10/7^l;F=20(?);SR—1.65. Samples from2,886 and 3,070 feet donot appear to have been metamorphosed. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; J. B. Souther, Pan American Petroleum Corporation, 1953. — County. Medina. — Well name. Roxana Petroleum Company No. 1Rothe. Location.—Medina County School Land survey; 1,200 feet FNL, 250 feet FEL; 9 mi. NW of D'Hanis. — —— Elevation. 1,117 feet. Total depth. ni. Completed. ni. Top of Paleozoic rocks.—3,000 feet. Elevation of Paleozoic rocks. 1,883 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3020-30, 3130-35, 3300-05, 3400-05, 3527-32 (2). — Description of Paleozoic rocks. The rocks are dark silty shale, locally containing carbonaceous fragments or small siliceous lenses, locally brecciated, and fine-to medium-grained, mostly angular (some larger grains round), very poorly sorted, dolomitic to calcareous micaceous feldspathic quartz sandstone or arkose containing abundant fragments of bubbly vein quartz, quartz mosaic, chert, and shale; the rocks are veined by quartz and carbonate. In some samples there is incipient reconstitution of the interstitial micaceous-chloritic material. This sequence is composed of Mississippian-Pennsylvanian beds of Ouachita facies (Stanley- Tesnus) ;the wellpenetrated the frontal zone of the Ouachita belt. X-raydata.—l>Ch>X(?);10/7 1.2;F=20;SR=2.3. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Medina. — Wellname. Switzer et al. (also known as O'Dell, Haught and Bond) No. 1Martin Zerr. Location.—J.J. Casanova survey;2,850feetFNL,10,500feetFWL;5mi.WNWofHondo. —— Elevation. 927 feet. Total depth.— 3,63s feet. Completed. 1924. The Ouachitu System — Top of Paleozoic rocks. 3,340 feet. Elevation of Paleozoic rocks. 2,413 feet. Thin section coverage (depth in feet).—BUREAU OF ECONOMIC GEOLOGY: 3635-45, 3645-55. — Description of Paleozoic rocks. Sellards (1933) described the rock encountered in this well as black shale. Thin section study of two samples shows that the sequence contains very fine-grained slightly calcareous (dolomitic?) chloritic micaceous quartz siltstone veined with quartz and car bonate. This well probably penetrated Ouachita facies rocks of Mississippian-Pennsylvanian age ( Stanley-Tesnus ? ) inthe frontal zone of the Ouachita belt. — X-ray data. None. References— Sellards (1933, p. 190). Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1956. — County.' Milam. — Wellname. JohnB.CoffeeNo.1NelsonDavis. — Location. MiguelDavillaleague; 5mi.WofSharp. — —— Elevation. 506 feet, derrick floor. Total depth. 3,795 feet. Completed. 1955. Top of metamorphic rocks.-—3,745 feet. Elevation of metamorphic rocks. 3,239 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3701-29 (3), 3702, 3722, 3729-59,3744,3759-82 (2),3782-90 (2), 3790-95, 3800. — Description of metamorphic rocks. Pre-Cretaceous rocks are very highly sheared hematitic chloritic sericite phyllite. Structures are foliation, fracture cleavage, micro-thrust faulting, micro-imbricate structure, and sharp crinkling. Cleavage is nearly vertical inthe cores examined. Quartz veins are broken, stretched, and drawn out into augen. Metamorphism is low grade with a very strong shearing element. This wellpenetrated the interior zone of the Ouachita belt. — X-ray data.—l> Ch; 10/7 5; SR = 4.8. — Personal communication: B. P. Journeay, 1955. References. — County. Milam. — Wellname. D.A.McCraryNo.1E.M.andJ.F.Gibson (was G.L.Reasor No.1Gibson). Location.—]. J. Whiteside survey; 3,450 feet FSWL, 4,900 feet FNWL; 19 mi. N of Cameron. — —— Elevation. 391 feet, derrick floor; 387 feet, ground. Total depth. 6,104 feet. Completed. 1955. Top of metamorphic rocks.—6,loo±(?) feet. Elevation of metamorphic rocks. 5,709±(?) feet. — Thinsection coverage (depth infeet). None. — Description of metamorphic rocks. Reported in "schist" at total depth. From its location, this wellpenetrated the interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1958. — County. Milam. Wellname.—Rimrock-Tidelands, Incorporated, No.1W.F.Crawford. Location.—Newson Gwatney survey; 517 feet FNEL, 577 feet FSEL; 2% mi. SE of Clarkson. —— — Elevation. 351 feet, derrick floor; 342 feet, ground. Total depth. 6,995 feet. Completed. 1956. — Top of metamorphic rocks. 6,550 feet. Elevation of metamorphic rocks. 6,199 feet. — Thin section coverage (depth in feet). bureau of economic geology: 6590-00, 6650-60, 6700-10, 6900-10, 7000-03. — Description of metamorphic rocks. Becwar (1957) reported conglomerate containing phyllite pebbles, 6,490 to 6,550 feet;top ofPaleozoic red and green schist, 6,550 to 6,560 feet;top of black slaty shale, phyllite,and schist, 6,590 to 6,600 feet;total depth, 6,995 feet. The sequence is composed mostly of rutiliferous hematitic graphitic chlorite-sericite and sericite muscovite phyllite locally invaded by massive quartz veins and masses of secondary carbonate. Manythin sections are nearly opaque due to graphite, hematite, and a dense mat of rutile needles. Structures are foliation, brecciation, contortion, and, locally, fracture cleavage. Metamorphism is low grade with high shearing and metasomatic elements. The wellpenetrated the interior zone of the Ouachita belt. Bureau ofEconomic Geology, The University of Texas = X-raydata.—l>Ch>X;10/7—'1;F 22;SR=6.4. — References. Personal communication: H.D.Becwar, The Texas Company, 1957. — County. Milam. — Wellname. Texas Gulf Sulphur Company No. 1Baker. Location.— -Jose Lealsurvey; 43,000± feet Sof NE cor., thence 9,100 feet Wtolocation; 3% mi. Wof Milano. — Elevation. 446 feet, kellybushing; 434 feet, ground. Totaldepth.— l2,67o feet. Completed.— l9ss. —— Top of metamorphic rocks. ni. Elevation of metamorphic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic or metamorphic rocks. ni. — X-ray data. None. — References. Personal communication:J. H. Ogg, Texas Gulf Sulphur Company, 1959. — County. Navarro. — Wellname.— FalconDrillingCompany No.IJ.C.Keitt. Location. Sam Benton survey; subdivision 66; 6mi. SE ofDawson. — Elevation.— s2s feet. Totaldepth. —6,455 feet. Completed. 1942. Top of metamorphic rocks. —6,340 feet. Elevation of metamorphic rocks. 5,815 feet. — Thin section coverage (depth in feet). bureau of economic geology: 6330-40, 6400-10, 6440-50 (2). — Description of metamorphic rocks. The sequence in this well is composed of sericitic chloritic metaquartzite and sericite slate. Foliation is well developed and grains are stretched. Metamorphism is lowgrade witha prominent shearing component. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: B. W. Fox, The Atlantic Refining Company, 1956. — County. Navarro. — Wellname. H.L.HuntNo.1E.E. Hamilton. — Location. F.R.Kendallsurvey; 8mi.WofCorsicana. —— — Elevation. 485 feet. Total depth. 6,674 feet. Completed. 1948. — Top of metamorphic rocks. 6,635 feet. Elevation of metamorphic rocks. 6,150 feet. Thin section coverage (depth in feet).—bureau of economic geology: 6630-40, 6660-70 (2). — Description of metamorphic rocks. The rocks penetrated in this wellare fine-grained dolomitic sericitic metaquartzite and sericite slate. Metamorphism is low grade with a pronounced shearing element ;structures are foliation, fracture cleavage, and grain elongation. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. = X-raydata.—Ch>I;10/7 <—0.4;F 20;SR=24. — References. Personal communication:B.W.Fox,The AtlanticRefining Company, 1956. — County. Pecos. Wellname.—Deep Rock OilCorporation No.1Slaughter. Location.—Section 31, block 129, T&STL survey; 660 feet FSL, 660 feet FEL; 20 mi. SE of Fort Stockton. Elevation.—3,s27 feet. Totaldepth—10,031 feet. Completed.—l9s2. — — Topof Paleozoic rocks. 800 feet. Elevation of Paleozoic rocks. +2,727 feet. — Thin section coverage (depth in feet). None. Description of Paleozoic rocks.—According to Galley (1957), top of Wolfcamp is at 800 feet and total depth is 10,031 feet in Wolfcamp(?). According to a note in a West Texas Geological Society Guidebook (Adams and Frenzel et. al., 1952), a core from this well from a depth of 2,680 feet shows dips of 65°. The well penetrated thick lower Permian Wolfcamp clastic rocks north of the Ouachita belt. There is anormal foreland section beneath the Wolfcamp elastics inthisgeneral area (p.136). The Ouachita System — X-ray data. —None. References. Adams and Frenzel et al. (1952, p. 28). Personal communication: J.E. Galley, ShellOilCompany, 1957. — County. Pecos. Wellname.—PhillipsPetroleum Company No.1Elsinore Cattle Company. Location.—Section 53, block D,GC&SF survey; 435 feet FSL, 2,095 feet FWL. —— Elevation.—4,105 feet, derrick floor. Totaldepth. 12,095 feet. Completed. 1946. Top of Paleozoic rocks.41 Elevation of Paleozoic rocks. 1-4,105 feet. — Thinsection coverage (depth infeet). None. Description of Paleozoic rocks.—Young (1952) reported the following sequence in this well: spudded in Leonard, probably 200 feet below the top of the Leonard; 0 to 5,530 feet, Leonard dolomite, limestone, and shale; 5,530 to 10,770 feet, Wolfcamp sandstone and shale with limestone at the base; 10,770 to 12,096 feet, Pennsylvanian (Cisco) mostly dark shale with minor limestone and sandstone. A core from 8,110 feet shows that the steep surface dips of the Sierra Madera structure have given way to gentle dips on the order of 12°. More recent studies indicate that top of Wolfcamp may be as high as 1,430 feet and much or all of the sequence identified as Pennsylvanian (Cisco) may be Wolfcamp. This wellis located north of the Ouachita belt. — X-raydata. None. — References. Addison Young (1952, pp. 72-73). County. —Pecos. — Wellname. Transcontinental Oil Company No. 1Slaughter (Blackwood and Nichols?). Location.—Section 29,block129,T&STLsurvey; 40mi.SEofFortStockton. — —— Elevation. 3,536(?) feet; 3,544(?) feet. Totaldepth. 4,988 feet. Completed. ni. —— Top of Paleozoic rocks. 520 feet. Elevation of Paleozoic rocks. -(-3016 (? ),+3024 (?) feet. — Thin section coverage (depth in feet). None. — Description of Paleozoic rocks. Goldstein (1955) reported top of San Andres, 510 feet; top of "sand zone," 1,575 feet; top of black shale, 2,200 feet; total depth 4,988 feet, in foreland(?) facies. This wellis located north of the Ouachita belt and probably penetrated a section of Wolfcamp beds similartothosefoundinDeepRockOilCorporation No.1Slaughter. — X-ray data. None. — References. Personal communication: J. E. Galley, Shell OilCompany, 1956; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Real. — Well name. Stanolind Oiland Gas Company No. 1Knippa. — Location. G.H. Boone survey. — Elevation. —1,747 feet. Total depth.—8,181 feet. Completed. 1953. —— Top ofPaleozoic rocks. 915 feet. Elevation of Paleozoic rocks. -(-832 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1240-50, 3080-90, 3270-80, 3700-10, 7440, 7640-50, 7720-30. — Description of Paleozoic rocks. According to Montgomery (1957), this well topped Paleozoic shales at 935 feet, lower Atokan fusulinids were found from 7,210 to 7,220 feet, and the top of the Ellenburger was encountered at 7,225 feet. The upper clastic section is composed of fine-grained, angular, slightly feldspathic argillaceous quartz sandstone and dark silty shale, probably Atoka. The lower section is chiefly carbonate and includes calcilutite, fine-grained oolitic pelletiferous limestone, and fine-grained dolomite. This wellpenetrated foreland facies rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957; J. B. Souther, Pan American Petroleum Corporation, 1956. 41Well was spudded inPermian (Leonard) rocks on the Sierra Madera structure. Bureau ofEconomic Geology, The University of Texas — County. Red River. Well name.— Bentley, Shepherd, and Stevens No. 1Southern Pine Lumber Company. Location.—George W. Parks (West) survey; 10,250 feet FSL, 400 feet FWL; 17 mi. N of Clarksville. Elevation—4l4 feet. Total depth.— l,B6Bfeet. Completed—l939. — Top of metamorphic rocks. 1,810 feet. Elevation of metamorphic rocks. 1,396 feet. — Thin section coverage (depth in feet). shell oilcompany: 1841, 1843-45, 1845-47, 1860-68. — Description of metamorphic rocks. The sequence encountered in this wellis composed of sericite phyllite and hornblende metaquartzite ;fracture cleavage is developed in the phyllite. Metamorphism islow grade witha strong shearing element. This wellpenetrated metamorphosed rocks extension of the Broken — in the southwestern subsurface Bow Benton uplift of the Ouachita Mountains. Probably the rocks are lower Paleozoic Ouachita facies. — X-ray data. None. — References. Personal communication: B.W. Fox, The Atlantic Refining Company, 1956. — County. Red River. — Well name. S. M.Brasfield No. 1Eichenberg and Miller. Location.—George S.Parksurvey;330feetFEL,2,850feetFSL;15mi.NEofClarksville. — —— Elevation. 415 feet, derrick floor. Total depth. 1,808 feet. Completed. 1956. — Top of metamorphic rocks. 1,800 feet. Elevation of metamorphic rocks. 1,385 feet. — Thinsection coverage (depth infeet). None. — Description of metamorphic rocks. Love,Kirkland, and Richey (1957) reported top of "Paleozoic schist" at 1,800 feet. This well—encountered metamorphosed rocks in the southwestern subsurface extension of the Broken Bow Benton uplift of the Ouachita Mountains. The rocks are probably lower Paleozoic Ouachita facies. — X-ray data. None. — References. Love,Kirkland,and Richey (1957, p. 1179). Personal communication :B. W. Fox, The Atlantic Refining Company, 1956. County. —Red River. — Well name. Byars No. 1Chapman. — Location. H.B.Shaw survey; 26mi.NEofClarksville. Elevation.—346 feet. Total depth.— 3,323 feet. Completed.— -1954. Top of Paleozoic rocks.—3,162 feet. Elevation of Paleozoic rocks. 2,816 feet. — Thin section coverage (depth infeet). bureau of economic geology: 3000-10, 3250-60, 3270-80. — Description of Paleozoic rocks. The Paleozoic rocks encountered in this well are fine-grained, angular to subround, poorly sorted, calcareous and micaceous quartz sandstone containing varied amounts of feldspar. There is no metamorphism. The lithology is more typically Atoka than Stanley, but on the basis of welllocation the section is identified as Stanley (? ). — This well penetrated rocks of the Ouachita belt southeast of the Broken Bow Benton uplift of the Ouachita Mountains. — X-raydata. None. — References. Personal communication: B. W. Fox, The Atlantic Refining Company, 1956. Samples are in Bureau of Economic Geology WellSample Library. — County. Red River. — Wellname. ConcordOilCompany (Pearsons etal.)No.1Dillahunty. Location.—l.Moore survey; 200 feet FNL,200 feet FWL; 3 mi. FW County line; 6 mi.Sof Red River. —— Elevation.—482 feet. Totaldepth. 2,545 feet. Completed. 1933. — Top of metamorphic rocks. 2,137(?) feet. Elevation of metamorphic rocks. 1,655(?) feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2137 (2). — Description of metamorphic rocks. Sellards (1933, p. 190) reported schistose sandy shale fromdepths of 2,137 and 2,500 feet. Barnes (in Sellards, 1933, p. 135) noted that the core shows almost The Ouachita System horizontal crinkly cleavage and that the rock is composed mostly of chlorite withlesser amounts of sericite and quartz; he remarked that the metamorphism is "rather advanced." Thin section examination shows that the rock is a chlorite slate or phyllite;metamorphism is weak. Foliation was the only structure observed. This wellpenetrated metamorphosed subsurface extension of the Broken — rocks in the southwestern Bow Benton uplift of the Ouachita Mountains. Probably the rocks are lower Paleozoic Ouachita facies. — X-ray data. None. References.— Sellards (1933, pp. 135, 190). Samples are inBureau of Economic Geology WellSample Library. — County. Red River. Wellname.—D. J.Flesh etal.No.1K.M.Bailey. — Location. John Robbins survey;1mi. WofBagwell. Elevation.—446 feet. Totaldepth.—3,377 feet. Completed.—l939. —— Top of Paleozoic or metamorphic rocks. 3,375 feet. Elevation of Paleozoic or metamorphic rocks. -2,929 feet. — Thinsection coverage (depth infeet). shelloilcompany: 3355-65. — Description of Paleozoic or metamorphic rocks. A note inthe Bureau of Economic Geology files describes fragments from the 3,360-foot interval as schistose shale. The single sample examined for this study is rutiliferous argillaceous siliceous rock, possibly a chert. This wellprobably penetrated metamorphosed lower Paleozoic rocks of Ouachita facies in the southwestern subsurface extension — oftheBrokenBow BentonupliftoftheOuachitaMountains. — X-ray data. None. — References.-Bureau of Economic Geology files. Personal communication :B. W. Fox, The Atlantic Refining Company, 1956. — County. Red River. — Wellname. Johnston Petroleum SyndicateNo.1LadyAlice(AntoneandMartin). — Location. Robert T. Gamble survey; 1,067 varas FSL, 215.1 varas FEL; at Silver City, 18 mi. N of Clarksville. Elevation.—-397 feet. Total depth.—4,47o feet. Completed.— Before 1923. — Topofmetamorphic rocks. 1,763 feet. Elevationofmetamorphic rocks. 1,366 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1977-2080 (2). — Description of metamorphic rocks. Sample descriptions infiles of the Bureau of Economic Geology report phyllite, quartzite, sandy marble, graphite schist, vein quartz, and calcite from 1,763 to 2,522 feet, and mostly graphite schist and vein quartz and calcite from 2,522 to 4,491 feet. Sellards, inreexamination of the cuttings, described the rocks below 1,763 feet as mostly hard black shale or phyllite, locally graphitic, with vein quartz and calcite. A note (author unknown) suggests samples from 4,000 to 4,491 feet may be metamorphosed Stanley shale. Miser and Sellards (1931, p. 811) stated that this wellpassed from Lower Cretaceous beds into Paleozoic rocks at a depth of 1,673 feet (note discrepancy above) and remained in Paleozoic rocks to total depth of 4,520 feet (note discrepancy above). They reported that the cuttings consist of shale with some interbedded limestone and sandstone. The shale is bluish black to black, shows shiny surfaces, and has been metamorphosed, some having been changed to slate or phyllite. Much of the shale ispapery andshowscrumpling;thesandstone isgrayandlocallyquartzitic;thelimstoneisgrayand sandy; white quartz and calcite are plentiful in the samples and probably occur as veins. T.L.Bailey described a sample from this well from 1,763 to 1,767 feet as a shiny slate-gray phyllite composed principally of quartz and biotite.Miser and Sellards (1931, p. 812) remarked that the cuttings from the No. 1 Lady Alice are comparable in lithology to the Womble shale, Blakely sandstone, Mazarn shale, Crystal Mountain sandstone, and Collier shale, and they concluded that the sequence in this wellis Cambrian or Ordoyician inage. Thin section examination shows that the rocks are chlorite-sericite slate, locally phyllitic, chloritic, and sericitic metachert or very fine-grained metaquartzite, and fine-grained quartzose dolomiticcalcite marble, locally graphitic. Metamorphism is weak to low grade with a pronounced shearing element; foliationin marbles is expressed in stretched grains and development of parallel shear planes. The sequence is probably composed of metamorphosed lower Paleozoic Ouachita facies rocks similar to — those to the northeast exposed in the Broken Bow Benton uplift of the Ouachita Mountains; the marbles are similar to those penetrated inVal Verde County. — rocks in the subsurface southwestern of the Broken This well penetrated metamorphic extension Bow Benton uplift of the Ouachita Mountains. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. References.— Miser and Sellards (1931, pp. 811-812) ;Sellards (1933, p. 190). Bureau of Economic Geology files. Samples are inBureau ofEconomic Geology WellSample Library. County.— Red River. — Wellname. Magnolia Petroleum Company No.1Henry. Location.—MßP&P survey; 640 feet FWL, 700 feet FNL; 4% mi. NE ofDeport. — — — Elevation. 472 feet. Totaldepth. 4,788 feet. Completed. 1941. — Top of Paleozoic and metamorphic rocks. 4,490 feet. Elevation of Paleozoic and metamorphic rocks. 4,018 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 4225, 4285, 4335, 4565, 4585, 4615, 4760, 4785. shell oilcompany: 4744-47. — Description of Paleozoic and metamorphic rocks. Goldstein (1955) reported base of Cretaceous and probable top of Paleozoic, 4,490 feet; total depth 4,788 feet, in Paleozoic rocks. He noted that at 4,490 feet the drillpenetrated red indurated shales, argillites, and red quartzitic sandstone cut by quartz veins; red and gray quartzites were encountered to 4,770 feet; at 4,780 to 4,790 feet a single sample is contorted quartz-mica phyllite. Thin section studies of samples from 4,560±, 4,565, 4,585, and 4,615 feet show that the rocks are red, fine-grained, angular, mostly poorly sorted, hematitic quartz sandstones and dark red hematitic sandy and siltymicaceous metashale;quartz veins are common. Metamorphism inthis upper section ranges from none to incipient. The lower sequence is composed of metamorphosed rocks: 4,744 to 4,747 feet, hematitic chlorite-sericite phyllite; 4,760 feet, fine-grained, angular, poorly sorted, feldspathic high-rank metasandstone ;4,785 feet, hematitic sericite phyllite. The phyllites are foliated rocks showing microfolding and abundant quartz veins. Metamorphism is weak to low grade with a promiinent shearing component. Goldstein (1955 ) suggested that the upper red-bed sequence is probably deeply weathered Paleozoic sediments of Ouachita facies but pointed out that itcould be a post-Pennsylvanian unit such as Eagle Mills.Inthe writer's opinion the presence of abundant quartz veins and the nature of the sandstones indicate that the red-bed sequence is of Ouachita facies. The change from unmetamorphosed rocks in the upper part of the section to metamorphic rocks in the lower part is very likely due to faulting or folding. This wellpenetrated Ouachita— facies rocks (lower Paleozoic?) in the subsurface southwestern extension of the Broken Bow Benton upliftof the Ouachita Mountains. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Red River. — Well name. Texas Trading Company No. 1Southern Pine Lumber Company. — Location. D.D.Brutonsurvey; 11mi.NofDetroit. —— — Elevation. 407 feet. Total depth. 2,383 feet. Completed. ni. —— Top of Paleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 2370-80, 2382-83. — Description of Paleozoic rocks. Bureau of Economic Geology files report quartzite and mica at 2,382 to 2,383 feet. Petrographic study of two samples available shows the rock is fine-grained, angular to subround, poorly sorted, slightly argillaceous chloritic micaceous feldspathic quartzlow-rank metasandstone containing layers and streaks of dark metashale and extensively veined with quartz; the rock shows partial reconstitution of intergranular material to mica-chlorite and, locally, shearing. One fragment contains grains of sheared chert and vein quartz. The sequence is — identified as very weakly metamorphosed Stanley on the southeast side of the Broken Bow Benton upliftofthe Ouachita Mountains. — X-ray data. —None. References. Bureau of Economic Geology files. — County. Red River. — Wellname. The Texas Company No.1H.0.Solomon. Location—W.E.Edwardssurvey; 3,150 feetFNLofEdwardssurvey, 660 feetFWLofM.Blankston survey; 10mi.SW ofAnnona. The Ouachita System Elevation.—Mlfeet. Totaldepth.—6,152 feet. Completed.—l944. — Top of Paleozoic rocks. 6,045 feet. Elevation of Paleozoic rocks. 5,698 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 5920, 6000, 6060, 6080, 6110, 6125. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Paleozoic of Ouachita facies at 6,045 feet, total depth, 6,150 feet. The rocks from 6,060 to 6,110 feet are fine-grained, angular, poorly sorted, tightly packed, hematitic to quartzitic feldspathic micaceous quartz sandstone containing up to 5 percent metamorphic rock fragments; they show incipient to very weak metamorphism. At 6,125 feet the sample is sericite slate with well-developed foliation. This well penetrated Ouachita— facies rocks (possibly Stanley overlying older Ouachita rocks) southeast of the Broken Bow Benton uplift of the Ouachita Mountains. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Red River. — Wellname. WelchPetroleum Company No.1R.Williams. Location.—Lanson Moore survey; 2,871 feet F most Ely EL, 4,089 feet F most Ely SL; 6 mi. N of Manchester. — —— Elevation. 393 feet, derrick floor. Total depth. 1,168 feet. Completed. 1956. —— Top of Paleozoic or metamorphic rocks. 1,124 feet. Elevation of Paleozoic or metamorphic rocks. -731 feet. — Thin section coverage (depth infeet). None. — Description ofPaleozoic ormetamorphic rocks. ni. X-ray data.—None. References. —Love, Kirkland, and Richey (1957, p. 1179). Personal communication: B.W.Fox,The AtlanticRefining Company, 1957. — County.-Red River. Wellname.—-Joe Whiteetal.No.1KurthLumberCompany. — Location. Elizabeth Smith survey; 3,260 feet S and 600 feet W ofNE cor.; 12 mi. Nof Clarksville. ——— Elevation. 410 feet. Totaldepth. 2,139 feet. Completed. 1940. — TopofPaleozoic rocks. 2,133 feet. ElevationofPaleozoic rocks. 1,723 feet. — Thin section coverage (depth infeet). shell oilcompany: 1965-2090, 2090-2135. — — Description of Paleozoic rocks. The rock is dark microgranular to cryptocrystalline chert probably Bigfork. This wellis located on the southeast margin of the southwestern subsurface ex — tension of the Broken Bow Benton upliftof the Ouachita Mountains. — X-ray data. None. — References. Personal communication :B. W. Fox, The Atlantic Refining Company, 1956. Samples areinBureau ofEconomic Geology WellSample Library. County. —-Terrell. — Wellname. Big Bend No.1Bassett. Location.— Section 156, block D, MK&TE survey; 1,320 feet FNL, 1,320 feet FEL; Sy2 mi. S, 15 mi. WofNWcor.ofValVerde County. Elevation—2,396 feet. Total depth.— 2,669 feet. Completed.— l93l. —— Top of Paleozoic rocks. 1,130 feet. Elevation of Paleozoic rocks. -f-1,266 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Kleihege (1948) noted that this wellpenetrated a pre-Cretaceous section composed of about 1,300 feet of very fine-textured clayey green shale withsubordinate thin beds of brown shale. Woods (1955) remarked that samples from 2,370 to 2,610 feet are all slightly metamorphosed. The wellappears to be close to the Ouachita front (PI. 2);most probably the sequence is com posed of Pennsylvanian or Permian foreland basin rocks. Bureau of Economic Geology, The University of Texas — X-ray data. None. Kleihege (1948, p. 22). Personal communication: R. D. Woods, Humble Oil&Refining Company, 1955. References.— — County. Terrell. — Wellname. BLTCompany No.2M.C.Goldwire. — Location. Section95,block1,TCRRsurvey;7mi.NofSanderson. — —— Elevation. 3,529 feet. Totaldepth. 3,036 feet. Completed. 1952. Top of Paleozoic rocks.— l,ooo±(?) feet. Elevation of Paleozoic rocks. 1-2,529±(?) feet. — Thin section coverage (depth infeet). shell oilcompany: 1950 (2). — Description of Paleozoic rocks. The two thin sections examined are angular to subangular, fairly well-sorted, micaceous chloritic feldspathic quartz siltstone, locally argillaceous; the rock contains both plagioclase and potassium feldspar. No reliable identification can be made from these samples; on the basis of location, this well probably penetrated Tesnus beds inthe frontal zone of the Ouachita belt. — X-raydata. None. — References. Personal communication: J. P. Olson, Shell OilCompany, 1958. — County. Terrell. Well name.— Briggs No. 1Kerr. Location.—Section18,blockD5,HE&WTsurvey; 1,800 feetFWL,790 feetFNL. Elevation.—2,lso feet. Total depth.—3,ooo±(?) feet. Completed—l944. —— Top of Paleozoic rocks. 1,335 (?) feet. Elevation of Paleozoic rocks. —{-815(?) feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic or metamorphic rocks. Information gathered on this wellis conflicting. According to Kleihege (1949), the wellpenetrated well-cemented dolomitic fine-grained buff to tan sandstone containing traces of gypsum (depth 2,735 to 2,868 feet) and moderately crystalline tan dolomite (2,890 to 2,993 feet);he noted that the dolomite is similar to the Ellenburger dolomite encountered in Shell No. 1Honeycutt in Edwards County and suggested that inasmuch as the well is located "south of the belt of metamorphosed rocks," it may have penetrated an overthrust. Galley(1956) said that according to available records, total depth of this wellis 1,265 feet, stillin Trinity beds. No samples of the pre-Cretaceous section were located. From the location of this well (PI. 2),—the pre-Cretaceous rocks should be very weakly metamorphosed Ouachita (Marathon) facies rocks Tesnus and/or pre-Tesnus. Possibly the dolomite observed by Kleihege is Cretaceous dolomite (see p. 285), or possibly there was some confusion in the samples. If Ellenburger (or lower Paleozoic foreland facies carbonate rock) was penetrated in this well, an overthrust and possibly a fenster are indicated. — X-ray data. None. — References. Kleihege (1948, p. 50). Personal communication:J.E.Galley,ShellOilCompany, 1956. — County. Terrell. Well name.— Downie Test Well. — Location. Section 21,blockMM;10mi.NofSanderson. — Elevation. 2,600 feet (from topographic map). Totaldepth.—ni. Completed.—ni. —— Topof Paleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology report gray sandstone and black shale at 720 feet and indicate that the sequence may be Tesnus. The locationofthewelliscompatible withtheidentificationofTesnus. — X-ray data. None. — Bureau of Economic Geology files. References. The Ouachita System — County. Terrell. Wellname.—Dovtme Water Well. — Location. Section 11, block R4, GC&SF survey. —— — Elevation.-ni. Total depth. ni. Completed. ni. —— TopofPaleozoic rocks. ni.ElevationofPaleozoic rocks. ni. — Thin section coverage (depth in feet). None. — Description of Paleozoic rocks. Notes in the files of the Bureau of Economic Geology report black shale from 500 to 1,325 feet. This wellprobably penetrated Ouachita (Marathon) facies rocks, possibly Tesnus beds. — X-raydata. None. — References. Bureau of Economic Geology files. — County. Terrell. — Wellname. Dryden OilCorporation No. 1Bassett Trust Company. — Location. Section 68, block A-2, GH&SA survey; 3% mi. SE of Dryden. Elevation.— 2,l97 feet. Total depth.— l,694 feet. Completed.— l9s6. — Top ofPaleozoic rocks. 1,550± feet. Elevation ofPaleozoic rocks.— -j-647± feet. — Thinsection coverage (depth infeet). shell oilcompany: 1630-90 (3). — Description of Paleozoic rocks. The single sample thin-sectioned for this study is dark brecciated and deformed metashale or clay-slate, dark slightly calcareous microgranular to microspherulitic chert containing dark organic material, and dark slightly silty argillaceous and micaceous siliceous dolo mite containing a few spicules; the rocks are veined with quartz and bituminous material. The wellpenetrated incipiently to very weakly metamorphosed pre-Tesnus Ouachita facies rocks inthe frontal zone of the Ouachita belt. — X-ray data. None. — References. None. — County. Terrell. — Wellname. R.E.Freeman No.1Barksdale. Location.—Section50,blockA-2,GH&SAsurvey; 600feetFNL,1,980feetFEL;7mi.EofDryden. Elevation.— 2,ols feet. Total depth— B,747 feet. Completed.— l9s6. —— TopofPaleozoic rocks. 1,565 feet. ElevationofPaleozoic rocks. +510 feet. Thin section coverage (depth in feet), shell oilcompany: 3380-86 (5), 5576-86 (2), 5670-80, 5715-29, 5729-42, 5775-87 (2), 5787-96 (2), 5796-5809, 5809-20 (2), 5820-32 (2), 5832-45 (2), 5845-54 (2), 5880-92, 5892-5900 (2), 5914-25, 5955-63, 5990-03 (3), 6003-18, 6027-44 (2), 6044-58 (2), 6072-85 (2), 6098-6110 (2), 6230-44, 6273-81, 7985-00, 8540-60 (2), 8560 70,8560-86, 8580-90, (2),8590-00, 8600-20 (2),8620-40 (2),8640-60, 8660-70. — Description of Paleozoic rocks. Kleihege (1949) reported the rocks beneath the Cretaceous as very fine-textured glossy variegated slaty shale. Olson (1958) remarked that the sample log on this wellshows a predominantly shale section. Petrographic study shows that the sequence is composed mainly of: (1) black finely dolomitic and calcareous shale, commonly siliceous, and containing abundant black opaque material that is probably a bitumen; in some intervals the rocks are metashale and clay-slate with incipient foliation and, locally, fracture cleavage; and (2) dark fine-grained dolomitic spiculitic limestone, commonly silty, pyritic, siliceous, and bituminous, locally containing shell fragments, pelmatozoan debris, and authi — genic feldspar;insome intervals the limestone is strongly sheared calcite is deformed, stretched, and extensively twinned. Minor rock types in the sequence include fine-grained dolomite and dark dolomitic argillaceous spiculitic chert. The spicules in the limestones and cherts are, withrare exceptions, calcite. The rocks are cut by—pre-metamorphism veins of calcite, dolomite, and quartz which also show evidence of strong shear calcite is deformed and very extensively twinned;commonly itforms a mosaic with strained quartz. Metamorphism is difficult to assess because of the obscuring effect of the abundant bituminous material in the shales. Itappears to be much more intense in some intervals than in others (zones of shearing) ;probably the highest grade of metamorphism attained is very weak to weak. The well penetrated incipiently to very weakly metamorphosed pre-Tesnus rocks (probably Marathon limestone) in the frontal zone of the Ouachita structural belt. Inoutcrop, the Marathon limestone shows considerable variation in the carbonate/clastic ratio; in the Dagger Flat area, for ex ample,itismostly shale. — X-ray data. None. — Kleihege (1948, p. 26). Personal communication: J. P. Olson, Shell OilCompany, 1958. References. Bureau ofEconomic Geology, The University of Texas County. —Terrell. — Wellname. HumbleOil&RefiningCompany No.1N.D.Blackstone. Location.—Section 58, block B-2, CCSD&RGNG survey. Elevation.—2,67l feet. Total depth— l2,3o3 feet. Completed.— l9s3. — TopofPaleozoic rocks. 840± feet. Elevation ofPaleozoic rocks. 1-1,831± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Hull (1957 a) reported top of Wolfcamp, 5,365 feet; base of Wolf- camp and top of Strawn, 11,220 feet; Canyon and Cisco sections are missing. The Wolfcamp sequence is dark shale, fine-grained quartzitic sandstone, and fragmental limestone. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. References.— Hull (1957a, p. 88). — County. Terrell. — Wellname. Humble Oil&Refining Company No.1J. C.Mitchell. Location.—Section 24, block 128, T&STL survey; 1,700 feet FNL, 2,080 feet FEL; 30 mi. N of Sanderson. Elevation.—3,olo feet. Total depth.—l2,o74 feet. Completed—l949. — Top ofPaleozoic rocks. 600 feet. Elevation of Paleozoic rocks. f-2,410 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1460-70 (2), 1720-30 (3), 3130-40 (2), 3230-40 (2), 3610-20 (3), 4850-60, 5900-10 (3), 5930-40 (2), 6390-00 (3). — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top ofLeonard, 600 feet; base of Leonard fusulines and top of "Wolfcamp fusulines, 3,710 feet; base of Wolfcamp fusulines, 5,930 feet; total depth 12,074 feet, in Pennsylvanian. Galley (1957) reported top ofLeonard, 660 feet.;topofWolfcamp, 3,540 feet;total depthinWolfcamp(?),12,074 feet. This wellpenetrated foreland basin rocks north ofthe Ouachita structural belt. — X-raydata.—l>ML>Ch>X;10/7 '2;F=20;SR=1.3. — Personal communication: J. E. Galley, Shell OilCompany, 1957; August Goldstein, Jr., References. Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. County. —Terrell. — Wellname. HumbleOil&Refining Company No.1University. Location.—Section15,block34,Universitysurvey; 490feetFNL,2,790 feetFEL. Elevation—2,284(?), 2,366(?) feet. Total depth.— 4,47o feet. Completed.— l92B. —— Top of Paleozoic rocks. 615 feet. Elevation of Paleozoic rocks. -J-1669(?), 1751(?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. — References. Bureau ofEconomic Geology files. — County. Terrell. — Wellname. Keck-Pecos Trust (Trans-Pecos Development Company) No. 1Hamilton. — Location.-Section 6, Cedar Springs block D-7, MK&TE survey; 6 mi. N of Rio Grande, 2 mi. W of County line. Elevation.—l,736feet. Totaldepth.—3,l6s feet. Completed.—l92B;1932. Top ofPaleozoic rocks— 2,230 feet. Elevation of Paleozoic rocks. 494 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in Bureau of Economic Geology files report hard black shale, not appreciably altered, in the interval 2,780 to 2,810 feet. Kleihege (1949) described the sequence as follows: base of Trinity, 2,230 feet; 2,280 to 2,450 feet, black dense fine-textured and slightly micaceous shale with a few thin beds of gray very fine-grained well-cemented sandstone; 2,450 to 2,583 feet, predominantly sandstone; 2,715 to 2,830 feet, variegated blocky shale overlying interbedded gray sandstone and black finely arenaceous slate, in turn overlying 50 feet of glossy black slate veined by quartz and calcite;2,860 to 2,920 feet, black arenaceous shale overlyingslaty micaceous The Ouachita System fine-grained sandstone; 2,965 feet, variegated blocky arenaceous shale; below 2,965 feet, finely arenaceous black micaceous shale. These rocks are probably very weakly metamorphosed Tesnus. This wellappears to have penetrated the frontal zone of the Ouachita belt. — X-ray data. None. References.— Kleihege (1948, pp. 39-40). Bureau ofEconomic Geology files. — County. Terrell. — Well name. Magnolia Petroleum Company and Western Natural Gas No. 1Brown and Bassett. Location.—Section 218, block V,TCRR survey; 25 mi.S ofSheffield. —— — Elevation. 2,448 feet. Total depth. 15,556 feet. Completed. 1957. — TopofPaleozoic rocks. 875 feet.Elevation ofPaleozoic rocks.— +1?573 feet. — Thin section coverage (depth in feet). bureau of economic geology: 15,440-45 (2), 15,460-65, 15,480-85, 15,500-05, 15,520-25, 15,540-45, 15,550-55. — Description of Paleozoic rocks. Vinson (1957) reported top of Strawn limestone, 11,435 feet; top of Mississippian limestone, 11,540 feet; top of Woodford, 11,584 feet; top of Devonian, 11,920 feet; top of Simpson, 12,448 feet; top of Ellenburger, 13,755 feet; top of Wilberns, 15,365 feet; top of Precambrian, 15,442 feet; total depth 15,556 feet, inPrecambrian. Thiswellpenetrated averythickforelandbasinsectionnorthoftheOuachitabelt.Itisoneofthe few wells which has encountered Precambrian rocks inthis general area. The Precambrian basement rocks are (1) metavolcanic rock composed of magnetite, calcite, and oligoclase with traces of biotite and hornblende and showing a relict microlitic fabric; (2) leucomicrogranite; and (3) magnetite-quartz-biotite-hornblende-oligoclase gneiss. The rocks are cut by quartz and hornblende veinlets. Metamorphism is medium grade regional metamorphism ;structures are imperfect foliation (gneiss) and fracturing (microgranite). These rocks may be part of the Van Horn orogenic belt (Flawn, 1956). — X-raydata. None. References.— Flawn (1956, pp. 32-36). Personal communicaion:M.C.Vinson,MagnoliaPetroleum Company,1957. Samples are inBureau ofEconomic Geology WellSample Library. — County. Terrell. — Wellname. MilhamOilCorporation No.1Bassett. — Location. Section 76, block V, W. H. Robinson survey; 2,640 feet FEL, 150 feet FNL; 6 mi. W and 7^/2 mi. S of NW cor. of Val Verde County (also reported as section 99). Elevation.—2,2ls feet. Totaldepth.— s,47s feet. Completed—l929. — TopofPaleozoic rocks. 1,215 feet. ElevationofPaleozoic rocks.— -f-1,000 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1275-79, 1304-10, 14981505,1512- 17,1600-08,3565-95. — Description of Paleozoic rocks. Lewis (1941) reported about 2,300 feet of dark calcareous shale overlying several hundred feet of dark sandy shale with graptolites and ostracods resembling the fauna of the Woods Hollow formation throughout several hundred feet of section just below the Cretaceous ;the lower sequence does not resemble the strata below the Woods Hollowinthe Marathon Basin and may be Permian in age. The apparent thickness of the Woods Hollow-type beds suggests steep dips. Goldstein (1955) reported base of Cretaceous and top of Woods Hollow(?), 1,215 feet; topofPennsylvanian (?),3,565 feet; totaldepth 5,300 feet,inPennsylvanian (?);he suggests that Woods Hollow(?) of Marathon facies is thrust over foreland facies Pennsylvanian beds. Kleihege (1949 ) noted the presence of 2,300 feet of fine-textured green shale overlying 1,700 feet of black fine- textured arenaceous shale; he stated that there is a distinct lithologic break between the two units and remarked that the lower black shale sequence is similar to the Pennsylvanian black shales found inwells to the east. Skinner (1958), from a study of the ostracods, noted that the wellpenetrated alternating Mississippian and Pennsylvanian (Morrow) beds below the Cretaceous; he cast some doubt on previous graptolite work. The repetition of Mississippian-Pennsylvanian sequence indicates complex structure. Olson (1958) remarked that on basis of ostracod fragments this well penetrated Silurian thrust over Pennsylvanian ( ? ). Sample coverage available shows that the upper unit is composed of dark commonly dolomitic or sideritic silty shale, locally hematitic, pyritic, and carbonaceous. No sample coverage is available on the deeper parts of this well. Bureau of Economic Geology, The University of Texas This well is close to the northern boundary of the Ouachita belt and may have penetrated lower Paleozoic Marathon facies rocks thrust over Pennsylvanian beds or Mississippian-Pennsylvanian beds ina disturbed zone along the Ouachita front. X-ray data.— Shallow samples: ML>I>X> Ch; 10/7 0.5; F= 20; SR =1.0. Woods Hollow shale from Marathon outcrops also contains abundant mixed-layer clay. References.— Kleihege (1948, p. 22);Lewis (1941, pp. 78-79). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; J. P. Olson, Shell Oil Company, 1958; John Skinner, Humble Oil& Refining Company, 1958; R. D. Woods, Humble Oil& Refining Company, 1955. Incomplete samples are inBureau ofEconomic Geology WellSample Library. — County. Terrell. — Wellname. Perkins and Lierney No.1McCue. — Location. Section 3,block152, GC&SF survey; 1% mi.NofSanderson. —— Elevation.—2,908 feet. Totaldepth. 1,498 feet. Completed. 1947. —— Top of Paleozoic rocks. 775 feet. Elevation of Paleozoic rocks. -|-2,133 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. From its location, this wellprobably penetrated rocks of Ouachita (Marathon) facies inthe frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication :J. P. Olson, Shell OilCompany, 1958. — County. Terrell. Wellname.—Pittsburgh Western Company No.1Downie. — Location. Section 36, block R2, GC&SF survey. —— — Elevation. 3,115 feet. Totaldepth. 1,250 feet. Completed. ni. —— Top ofPaleozoic rocks. ni. Elevation ofPaleozoic rocks. ni. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. From its location, this well probably penetrated very weakly metamorphosed rocks of Ouachita (Marathon) facies in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. — County. Terrell. — Wellname. Sides No.1Rose. Location.—Section15,block148,T&STLsurvey; 440feetFSL, 440feetFWL. — —— Elevation. 2,618 feet. Totaldepth. 1,320 feet. Completed. 1944. — — Topof Paleozoic rocks. 860± feet. Elevation of Paleozoic rocks. -f-1,758-j-(?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. References.— Personal communication :J. P. Olson, Shell OilCompany, 1959. — County. Terrell. — Wellname. SkellyOilCompany No.1Roberts. Localion.—Section190,blockD,MKTsurvey; 660feetFNL,660FEL;45mi.NEofSanderson. Elevation.—-2,77 r4 feet, derrick floor. Totaldepth.— 3,94o feet. Completed.—l942. Top of Paleozoic rocks.—1,180 feet. Elevation ofPaleozoic rocks.—+1,594 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1180-90 (4), 1210-20, 124050,1430- 40,1670-80. — Description of Paleozoic rocks. Goldstein (1955) reported base of Cretaceous and top of Pennsyl vanian(?) of foreland facies(?) at 1,180 feet; total depth 3,940 feet, in Pennsylvanian. The rocks are mostly dark-colored silty carbonaceous shales veined with calcite and, locally, red hematitic shales. There is no evidence of metamorphism. This well appears to be very close to the northern limitof the Ouachita belt; the rocks are probably foreland facies. The Ouachita System X-ray data.—l>ML> X> Ch; 10/7'—' 1.4; SR= 1.6. Ch becomes more abundant than X with depth. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955;R.D. Woods, HumbleOil&RefiningCompany, 1955. Samples are inBureau of Economic Geology Well Sample Library. County.— Terrell. — Wellname. Southwest Texas Oiland Gas Association No.1A.T.Folsom. — Location. Section 148, block D7, ELRRsurvey; 8mi. S ofWatkins. Elevation.—l,7o3(?),l,850(?) feet. Totaldepth.—3,sBo(?),3,650(?) feet. Completed.—l9lB(?); 1921(?). Top of Paleozoic rocks.—l,97o(?) feet. Elevation of Paleozoic rocks. 267(?), -120(?) feet. — Thin section coverage (depth in feet). bureau of ECONOMIC GEOLOGY: 2297, 2654, 2752, 2795-2805, 2800-10 (4), 2819-61, 2880-90, 2948-52, 2952-3001 (2), 3001-27, 3027-70, 3070-80, 3080-3100 (2), 3100-08, 3108-18, 3118-53, 3153-88 (2), 3188-22 (3), 3222-26, 3250, 3266-70 (2), 3270 90,3290-3300,3300-3420,3457-65,3580 (2). — Description of Paleozoic rocks. Sellards (1933) placed approximate top of Paleozoic at 1,970 feet; elevation from topographic map is 1,850 feet; total depth is 3,580 feet; he described the rock as schistose shale. Goldstein (1955) referred to Sellards (1933) but reported an elevation of 1,703 feet; he as Marathon facies showing incipient to very weak metamorphism. identified the section — R. D. Woods (1955) remarked that there are three elevations on record for this well 1,703, 1,850, — and 2,600 feet and that 1,703 feet appears to be correct from the topographic map. Kleihege (1949) noted a total depth of 3,650 feet and described the sequence as follows: 2,115 to 2,690 feet, gray fine- textured sandstones and black fine-textured slates, some of which are phyllitic; from 2,215 to 2,905 feet there is a general decrease in metamorphism ;2,740 to 3,065 feet, dense black fine-textured shale decreasing in metamorphism from slate to shale; 3,070 to 3,185 feet, black dense cherty phyllitic slate permeated by quartz veins; 3,190 to 3,260 feet, black fine-textured slate; 3,315 to 3,580 feet, olive-green glossy phyllitic slate which is a fine-textured matrix of chlorite flakes having cataclastic structure. Kleihege remarked that the alternation of differing grades of metamorphism indicates that folded or thrust-faulted rocks have been penetrated. Thin section study shows that the sequence is composed of dark carbonaceous and micaceous shale, locally silty and sandy, dark siliceous shale and argillaceous chert, fine-grained, angular, poorlysorted, tightly packed, chloritic micaceous argillaceous carbonaceous quartz sandstone and metasandstone, and dark carbonaceous to graphitic sericitic chloritic metashale, clay-slate, and slate, locallysandy, pyritic, and siliceous. Vein material including quartz, dolomite, and chlorite is common in intervals showing higher metamorphism. Metamorphism ranges from incipient to very weak to weak withincipient foliation developed inthe higher grade rocks. Clay-slate and slate are closely associated withshale and metashale. The observed changes in metamorphic grade in this wellmay be explained by (1) folding and faulting (as noted by Kleihege) with metamorphic grade being more advanced along axial planesand faults and/or (2) variations in susceptibility to metamorphism of different rock types in the sequence (p. 15). The sequence penetrated in this wellresembles very weakly metamorphosed Tesnus and is tentatively identified as Tesnus. The wellappears to have encountered Ouachita (Marathon) facies rocks in the frontalzone of the Ouachita belt. — X-ray data. None. References.— Kleihege (1948, p. 38);Sellards (1933, p. 190). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; R. D. Woods, Humble Oil&Refining Company, 1955. Samples are inBureau of Economic Geology Well Sample Library. — County. Terrell. — Wellname. Sun OilCompany No.1Scott. — Location. Section 12,block R,TCRR survey; center ofNE/4. Elevation.—2,442(?) feet (from topographic map.) Total depth.— 4,o2o feet. Completed.—l927. — Top of Paleozoic rocks.—900(?) feet. Elevation of Paleozoic rocks. +1,542(?) feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Cannon and Cannon (1932) stated that the wellentered typical upper Cisco at 3,250 feet. This wellpenetrated upper Paleozoic foreland rocks north of the Ouachita belt. — X-raydata. None. — Cannon and Cannon (1932). References. Bureau ofEconomic Geology, The University of Texas — County. Terrell. — Wellname.-IrvinSvoboda No.1J.L.Bassett. — Location. Section 1, block 149, T&STL survey. Elevation.—2,467 feet. Totaldepth.—2,lBofeet. Completed.—l94B. — Top of Paleozoic rocks. 1,100 to 1,200 feet (estimated). Elevation ofPaleozoic rocks.— +1,267 to +1,367 feet (estimated). — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-raydata. None. — References.-Personal communication: R.D. Woods, Humble Oil&Refining Company, 1956. — County. Terrell. — Wellname.-Texas Consolidated OilCompany No.1Holmes. Location.—Section 14, block A2, GH&SA survey; 467 feet FNL, 467 feet FEL; 5y2 mi. NW of Dryden. — —— Elevation. 2,760 feet. Total depth. 2,015 feet. Completed. 1941. —— -f-l,340(?) Top of Paleozoic rocks. 1,420(?) feet. Elevation of Paleozoic rocks. feet. — Thin section coverage (depth in feet). bureau of economic geology: 1420-30, 1500-10, 1540-44, 1545-50, 1639-45 (2). Description of Paleozoic rocks.—According to Kleihege (1949), the interval 1,420 to 1,700 feet is characterized by a gradual increase in grade of metamorphism from black shale at the top to slate at the bottom;the shales are arenaceous at the top and beds of fine-grained gray well-cemented sandstone are present. There are thin beds of gray quartzite at 1,560 and 1,615 feet. From 1,630 to 1,700 feet the rock is black fine-textured slate. Between 1,800 and 1,870 feet, slate grades to black shale and from 1,875 to 1,935 feet there is another alternation to slate. Kleihege noted that the change in metamorphic grade may indicate folding or thrust-faulting. Goldstein (1959) studied samples from 1,420 to 1,936 feet and considered the sequence to be weakly metamorphosed Tesnus. Limitedthin section coverage shows a sequence of dark sandy and silty shale and metashale, fine- grained, angular, poorly sorted, tightly packed, feldspathic quartz sandstone, locally micaceous, and dark micaceous chloritic clay-slate; the rocks have undergone incipient to weak metamorphism, and quartz veins are common. Incipient foliation is developed in the clay-slate. Alternation in grade of metamorphism is due to structure and/or rock susceptibility (p. 15). This wellpenetrated the Ouachita belt in the interior part of the frontal zone; the sequence is tentatively identified as very weakly metamorphosed Tesnus. X-ray data.—l>Ch; 10/7'—'o.7; F=20; SR= 4.0. Absence of kaolinite and relatively high SR tend to confirm the Tesnus identification. References.— Kleihege (1948, pp. 25-26). Personal communication: August Goldstein, Jr., Bell Oiland Gas Company, 1959; R. D. Woods, Humble Oil&Refining Company, 1955. Samples are in Bureau of Economic Geology WellSample Library. — County. Terrell. — Wellname. Transcontinental OilCompany (Ohio) No.1Goode. Location.— Section 26, block 161, GC&SF survey; 2,152 feet FEL, 330 feet FSL; 26 mi. SE of Sheffield. — Elevation. 2,405 feet. Total depth.—9,140 feet. Completed.—l937. — Top of Paleozoic rocks. 680 feet. Elevation ofPaleozoic rocks. [-1,725 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3005, 3700+, 5470-80. — Description of Paleozoic rocks. Galley (1957) noted top of Leonard, 680 feet; top of Wolfcamp, 3,100 feet; total depth 9,140 feet, in Wolfcamp. Goldstein (1955) described this well as normal fore- land facies. Samples at 3,700-j-and 4,570 to 4,580 feet are dark carbonaceous pyritic silty shale; silicified fossil debris is present at 4,570 to 4,580 feet. The 3,005-foot sample appears to be a contaminant in that itis a sericitic dolomitic metaquartzite showing low-grade metamorphism with a high shearingelement. Such a rock is very unlikely to occur in the No. 1Goode. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data.-None. The Ouachita System — References. Personal communication: J. E. Galley, Shell OilCompany, 1957; August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Terrell. Wellname.—-Williams,Calvert,andBrownNo.1GeorgeM.Snowden (alsoknownasE.T. Williams etal.No.1Cowden, No.1Snowden, orNo.1Robertson). Location.—Section 71, block DlO, TCRR survey; 1,320 feet FNL, 2,640 feet FWL; 7 mi. SE of Sanderson. Elevation.—2,442(?), 2,504(?) feet. Totaldepth.—3,lso(?), 3,145(?) feet. Completed.— -1927. — Top of metamorphic rocks.—1,385 feet. Elevation of metamorphic rocks. -j-1,057( ? ) feet, +1,119(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 1385, 1443, 1485, 1515, 1575, 1670, 2200, 2660, 2725 (3). shell oilcompany: 1295, 1424(?), 1450, 1452, 1648, 1750, 1910, 1670,2200,2325,2400,2560,2650,2735 (3), 2935, 2960 (2), 3142-45 (5). — Description of metamorphic rocks.-Sellards (1933) stated that samples examined from 3,150 feet are schistose shale and that "the log" reports quartz and calcite veins in more or less altered shale from 2,685 feet to bottom of the well; he gave an elevation of 2,430 feet and a total depth of 3,150 feet. Woods (1955) reported top of the Paleozoic rocks near 1,400 feet and said that first samples studied at 1,423 feet are metamorphosed. Goldstein (1955) reported probable base of Cretaceous and top of Paleozoic at 1,440 feet. Kleihege (1949) described the sequence as follows: 1,385 to 1,425 feet, very fine-grained glossy variegated schist or phyllite; 1,430 to 1,800 feet, black calcareous glossy graphitic to carbonaceous phyllite cut by quartz-calcite veinlets; 1,443 feet, carbonaceous slaty limestone and marble; 1,585 feet, recrystallized limestone containing opaque carbonaceous impurities; 1,860 feet, glossy black carbonaceous phyllite; 1,900 and 2,190 feet, glossy black calcareous phyllite; 2,280 feet, glossy black phyllitic slate; 2,315 to 2,600 feet, calcareous black phyllite showing a decrease in metamorphism to fine-textured black slate; 2,630 to 2,640 feet, black phyllitic slate; 2,645 to 2,785 feet, glossy calcareous fine-textured phyllitic slate; 2,725 feet, slaty carbonaceous limestone showing only slight metamorphism. Thin section study shows a sequence of very fine-grained calcareous and dolomitic metaquartzite, commonly graphitic, feldspathic, locally rutiliferous, sericitic, chloritic, with lesser amounts of fine- grained quartzose dolomite and calcite marble; there is abundant vein quartz in the cuttings. Fine grain size suggests these rocks might be metachert, but the presence, locally, of abundant feldspar in the quartz mosaic suggests that the fine grain size is due to crushing of an originally feldspathic rock. Metamorphism is low grade with a strong shearing component and possibly a high metasomaticelement; structures are (1) foliation expressed by stretched quartz and calcite grains and parallelstreaks of graphitic material, (2) suturing of quartz contacts, and (3), locally, microfolding and contortion. This well penetrated sheared metamorphic rocks in the interior zone of the Ouachita belt and marks a salient of the interior zone. — X-ray data. None. References.— Kleihege (1948, pp. 36-37) ;Sellards (1933, p. 190). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; R. D. Woods, Humble Oil &Refining Company, 1955. Samples are inBureau ofEconomic Geology Well Sample Library. — County. Travis. Wellname.— Tom BirdwellWater Well. — Location. West LakeHills,near Austin. —— Elevation. 740 feet. Totaldepth.—1,043 feet. Completed. 1946. TopofPaleozoic rocks.-—1,013 feet.ElevationofPaleozoic rocks. 273feet. — Thin section coverage (depth infeet.) bureau of economic geology: 1023-43. — Description of Paleozoic rocks. H. J. Plummer (Bur. Econ. Geol. files) described this sequence as brown schistose shale and brown sandstone. Thin section study shows dark angular calcareous chloriticsericitic siltstone veined by quartz; metamorphism isincipient. This wellpenetrated dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau of Economic Geology files. Samples are inBureau ofEconomic Geology Well Sample Library. Bureau ofEconomic Geology, The University of Texas — County. Travis. — Well name.-Boy Scout Water Well. — Location. J. Jett survey; 300 feet from side ofBullCreek, near mouth. —— Elevation. 508± feet. Total depth.— Bs2 feet. Completed. Before 1938. Top of Paleozoic rocks.— Bs2 feet. Elevation of Paleozoic rocks.— -344± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. A U. S. Geological Survey sample log shows "Smithwick shale" at the bottom of the hole. From the location, it is probable that this well penetrated incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the Ouachita belt. — X-raydata. None. — References. FilesofU.S.GeologicalSurvey,Ground WaterBranch, Austin,Texas. — County. Travis. — Wellname. Brewster andBartleNo.1Tucker. — Location. W. Wells survey; 2 mi. SSE of Manor. —— Elevation. 608 feet. Totaldepth.—4,506 feet. Completed. ni. — Top of Paleozoic rocks. 3,840 feet. Elevation ofPaleozoic rocks. 3,232 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3869-99, 4024, 4207-38, 4345, 4400, 4500. — Description of Paleozoic rocks. The sequence penetrated in this wellis composed of dark, fine-to coarse-grained, angular, poorly sorted, feldspathic quartz metasandstone (low rank) containing abundant fragments of chert, phyllite, and metaquartzite, dark, angular, micaceous low-rank metasiltstone, and dark metashale. Allof the rocks contain streaks and lumps of opaque matter which appears to be mostly carbonaceous but locally resembles bituminous matter. Quartz, quartz-bitumen, and calcite veinlets are common. The large amount of opaque matter makes itdifficult to assess the degree of metamorphism ;itappears to be incipient to very weak. Reconstituted sericite and chlorite occur in the matrix, and both mica and carbonaceous matter are bent around large quartz grains (incipient augen). The sandstones (graywackes) in this sequence contain abundant metamorphic rock fragments and appear to be a "dumped" tectonic sediment deposited close to an area of tectonism. This well encountered incipiently to very weakly metamorphosed dark clastic rocks inthe interior part of the frontal zone of the Ouachita belt. X-ray data.—l> Ch; 10/7 0.5; F = 20; SR = 6.0. — References. Samples areinBureauofEconomic GeologyWellSampleLibrary. — County. Travis. — Wellname. CityofAustinNo.1BlunnCreek (waterwell). — Location. I.Decker survey; East LiveOak Street and Sunset Lane, Austin, Texas. —— Elevation. 538 feet. Total depth.—2,246 feet. Completed. 1932. — Topof Paleozoic rocks. 2,213± feet. Elevation of Paleozoic rocks. 1,675± feet. — Thin section coverage (depth infeet). bureau ofeconomic geology: 2246. — Description of Paleozoic rocks. Sellards (1933) reported black indurated "much squeezed" shale and black quartzite cut by calcite veins; he stated that top of Paleozoic is 2,200± feet. A single sample from 2,246 feet examined in thin section is siliceous clay-slate containing carbonaceous or graphitic material and extensively veined withquartz; metamorphism is incipient to very weak and the rock shows incipient foliation. This wellpenetrated dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-ray data. None. References.— Sellards (1933, p. 191). Files ofthe U. S. Geological Survey, Ground Water Branch, Austin, Texas. Core fragment from2,246 feet is inBureau of Economic Geology Well Sample Library. — County. Travis. — Wellname. CookeWaterWellNo.J-22(alsoknownasC.R.FranklinNo.1GeorgeCooke;possiblythe same asWaldronetal.No.1TravisCooke). — Location. James M. Tribblesurvey; 0.15 mi. FEL, 0.6 mi.FNL. Elevation—lls± feet. Total depth.— l,B3s feet. Completed.— l93l. The Ouachita System TopofPaleozoic rocks.—1,070 feet. Elevation ofPaleozoic rocks. 295± feet. — Thin section coverage (depth in feet). bureau of economic geology: 1690 (2), 1733, 1785. — Description of Paleozoic rocks. The sequence is described in the Bureau of Economic Geology files as dark gray laminated dense somewhat schistose shale, black hard dense siltstone, and hard medium-grained sandstone. Old logs give conflicting data, e.g., top of Paleozoic, 1,610 feet; total depth, 1,790 feet. The sequence is composed of dark very finely micaceous and chloritic carbonaceous metashale and fine-grained, angular, poorly sorted, micaceous and chloritic feldspathic silty low-rank quartz metasandstone locally containing fragments of slate, chert, and stretched quartz mosaic; dark argil laceous cryptocrystalline chert occurs in the 1,785-foot interval. Metamorphism is very weak; there isincipient foliation. This well penetrated very weakly metamorphosed dark clastic rocks in the interior part of the frontalzone of the Ouachita belt. — X-ray data. None. — References. Files ofU.S. Geological Survey, Ground Water Branch, Austin,Texas. Bureau of Economic Geology files. — County. Travis. — Well name. Cypress Creek Drilling Association No. 1Romberg (also known as Jones No. 1Romberg). — Location. J. M.Millersurvey; 8 mi. N, 25 mi. W of Austin. —— Elevation. 800 feet (from topographic map). Total depth.—1,560 feet. Completed. 1927. — TopofPaleozoic rocks. 300± feet. ElevationofPaleozoic rocks. 1-500± feet. — Thin section coverage (depth infeet). bureau of economic geology: 834, 1340. — Description of Paleozoic rocks. Sellards (1931b) reported black shale at 834 feet. Thin section examination shows angular, tightly packed, fairly well-sorted, quartz siltstone and micaceous silty shale. The rocks show nometamorphism;probably they are Atoka. This well probably penetrated foreland rocks within the frontal boundary of the Ouachita belt (PI.2). — X-raydata. None. References.—-Sellards (1931b, p. 823). Samples areinBureau ofEconomic Geology WellSample Library. — County. Travis. — Wellname. Davenport Ranch Water Well. — Location. 8,000 feet northeast of St. Stephens School, 6 mi. NW of Capitol inAustin. — —— Elevation. 595 feet. Totaldepth. 1,127 feet. Completed. 1951(?). — TopofPaleozoic rocks. 931feet. ElevationofPaleozoic rocks. 336 feet. Thin section coverage (depth infeet).—None. — Description of Paleozoic rocks. Adkins (U. S. Geol. Surv. files) described samples from this well as follows: 862 to—875 feet, sand, sandstone, and Ellenburger-type chert plus weathered brown shale of Paleozoic type probably basal Cretaceous; 914 to 920 feet, angular —sand and chert fragments, quartz, and dolomite; 920 to 922 feet, chalcedonic chert and sandstone possibly Cretaceous conglomerate or Paleozoic; 931-965, 1,000-1,030, 1,030-1,070, 1,070-1,085, 1,095-1,123 feet, all black — hard Paleozoic shale Carboniferous or older; itis harder and more indurated than outcropping Smithwick shale. On the basis of Adkins' description and the location, this wellprobably encountered incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-ray data. None. — References. Files of the U.S. Geological Survey, Ground Water Branch, Austin, Texas. — County. Travis. Wellname.—C. R.FranklinNo.1B.J. Reimers. — Location. J. C. Littlesurvey. —— — Elevation. 1,008 feet. Total depth. 835 feet. Completed. 1932. — Top ofPaleozoic rocks. 469 feet. Elevation of Paleozoic rocks. [-539 feet. Bureau ofEconomic Geology, The University of Texas Thin section coverage (depth in feet).—bureau of economic geology: 525-55, 575-85, 585-90, 620-40, 670-80, 680, 695-710, 715-30, 735, 820, 837, 937. — Description ofPaleozoic rocks. Sample descriptions inthe files of the Bureau of Economic Geology report gray dense metamorphosed shale, dark hard gray siltstone, and gray hard dense quartzitic sandstone. The sequence is composed of very fine-grained, angular to subround, very poorly to poorly sorted, argillaceous silty quartz sandstone, locally calcareous, dark silty shale, and angular, micaceous and chloritic siltstone. Quartz and calcite veins are common and bituminous material is present. These rocks cannot be positively identified. Contortion, microfolding, and incipient to very weak metamorphism indicate that the sequence is within the Ouachita belt. The rocks are tentatively labeled Atoka(?) (see Summerow No.1Reimers, p.316). = X-raydata.—l>Ch>ML>K(?);10/7 1.1;F 20;SR=1.6. — References. Bureau of Economic Geology files. Samples are inBureau ofEconomic Geology WellSample Library. — County. Travis. Wellname.—H. E. GoffNo.1Basdall Gardner (Basdall Gardner No.1OilTest). — Location. Jose A.Ybarbosurvey; 7mi.SofLeander. Elevation.—7Bo±feet. Totaldepth.—73o feet. Completed.— l9s2. — Top of Paleozoic rocks. 710 feet. Elevation ofPaleozoic rocks. )-70 feet. — Thinsection coverage (depth infeet). bureau ofeconomic geology: 725-30. — Description of Paleozoic rocks. The single sample available is very dark brown shale or metashale. No identification can be made. This wellpenetrated the frontal zone of the Ouachita belt (PI. 2). — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. — County. Travis. Wellname—P.S.Griffithsetal.No.1(2?)Evans (SunsetRanch) (alsoknownasP.F.Griffin).42 Location.—-Faubian (?),D&W(?)survey; 9.3mi.SWofLeander. —— Elevation. 1,024 feet (from aneroid barometer). Total depth. 1,500(?), 1,875(?) feet. Completed— l92l. — Topof Paleozoic rocks. 620 feet. Elevation of Paleozoic rocks. |-404± feet. — Thin section coverage (depth in feet). bureau of economic geology: 500-600 (2), 600, 625 (2), 630, 743, 775-800, 815, 828-40 (2),848, 1400-1500 (2). — Description of Paleozoic rocks. Sellards (1931b) reported as follows:"The Evans wellin Travis County entered pre-Cretaceous rocks at or near a depth of 620 feet. Cores were received from this well at a depth of 789-793 feet. The rock at this depth is black non-calcareous shale alternating with gray quartzitic sandstone. The core shows bedding or cleavage planes of different steepness, the maximum being 70 degrees. The shale is much slickensided and inclusions of the shale are found in the sandstone. The rock is cut by calcite veins and by minute faults. This rock, in the opinion of Miser, represents Stanley shales." Barnes (in Sellards, 1933) noted very slight metamorphism. Thin section study shows a sequence of dark, fine-grained, angular, poorly sorted, argillaceoussandstone, dark shale, and calcareous micaceous siltstone, allveined withquartz. Incipient metamorphism (development of metashale) is present in the 828 to 840-foot interval. In the 1,400 to 1,500-foot interval the sandstone contains abundant angular garnet in the heavy mineral fraction and is typical Stanley lithology. This wellpenetrated Stanley inthe frontal zone of the Ouachita belt. = X-ray data.—l> Ch; 10/7 ~>0.7; F 20. References.— Sellards (1930; 1931b, p. 825; 1933, p. 135). Bureau of Economic Geology files. Samples in Bureau ofEconomic Geology Well Samples Library. — County. Travis. — Well name. Insane Asylum Water Well. — Location. Austin,Texas (notplottedonPI.2;seePerrywell,BlunnCreekwell,pp.315,312). * 2 Notes in the files of the Bureau of Economic Geology indicate that there may be two Evans wells, the No. 1drilled to 789 feet and the No. 2,% mi.N,drilled to 1,875 feet. The Ouachita System — — Elevation. 635 feet. Total depth. 1,975 feet. Completed. —Before 1897. Topof Paleozoic rocks.—1,800 feet. Elevation of Paleozoic rocks. 1,165 feet. — Thinsection coverage (depth infeet). None. DescriptionofPaleozoicrocks.—Adriller'slogisgivenbySellards (1930);base ofTravisPeak is determined as 1,800 feet. From its location, this wellprobably penetrated incipiently to weakly metamorphosed dark clastic rocksintheinteriorpartofthefrontalzoneoftheOuachita belt. — X-raydata. None. Hilland Vaughan (1898, pp. 280-286) ;Sellards (1930, p. 53). References.— — County. Travis. — Wellname. Midcoast (B.R. Floyd) No.1E.A.Jones. Location.—o.Bmi.SWofJonestown, 0.3mi.NWofFarmRoad1328. Elevation.—l,ooo± feet. Totaldepth—2,99l feet. Completed.—l9s3. — TopofPaleozoic rocks. 695 feet. Elevation ofPaleozoic rocks. (-305± feet. — Thin section coverage (depth in feet). bureau of economic geology: 630-32, 646-50, 680-86, 695-00, 705-10, 720-25, 866-69, 935-62, 1146-76, 2997. — Description of Paleozoic rocks. The sequence is composed of dark shale and metashale, commonly silty and sandy, some greenish siliceous shale (1146-76), and dark, fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone containing a high percentage of garnet in the heavy mineral fraction. The sample from 2,997 feet is clay-slate showing bedding cleavage at an angle of 60° to the core. The rocks are Stanley shale; the well penetrated the frontal zone of the Ouachita belt. X-ray data.—l>Ch>ML (3,000-foot sample, no ML); 10/7 —2;F=20; SR=1.6 (shallow), 2.3 (deep). — References. Bureau of Economic Geology files. Sample and cores are inBureau ofEconomic Geology WellSample Library. — County. Travis. Well name.—F. B. Perry Water Well. — Location. S. Goocher survey; 0.5 mi. S of State Capitol, next to DriskillHotel, Austin. — — Elevation. 500± feet. Total depth.—2,025 feet. Completed. 1899. Top of Paleozoic rocks.—1,965 feet. Elevation ofPaleozoic rocks. 1,465± feet. Thin section coverage (depth infeet).—None. — Description of Paleozoic or metamorphic rocks.-From the location, this well probably penetrated incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-raydata. None. — References. Files ofU.S. Geological Survey, Ground Water Branch, Austin, Texas. — County. Travis. — Wellname. G.L.Reasor No.1Jesse Ezell. — Location. M.M.Bain survey; 10 mi. SE of Austin. —— — Elevation. -250 feet. Total depth. 3,309 feet. Completed. 1952. — TopofPaleozoic rocks. 3,080 feet. Elevation ofPaleozoic rocks. 2,830 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2790-00, 2890-00, 2990-00, 3090-00,3140-50 (2), 3190-00, 3240-50 (2),3300-10 (2). — Description of Paleozoic rocks. The sequence is mostly dark carbonaceous sericitic clay-slate and dark calcareous carbonaceous micaceous quartz low-rank metasandstone. The degree of metamorphism is difficultto assess because of the abundant opaque matter, but it appears to range from incipient to very weak; incipient foliation and slaty cleavage are present. The cuttings of Paleozoic rocks are mixed with abundant olivine basalt (locally termed "serpentine") which resembles the late Cretaceous- Tertiary intrusive rocks of the Balcones fault zone. Such rock occurs higher in the section also (720 to 890 feet), and the association of basalt and Paleozoic rocks may be only contamination from higher in the well. However, the abundance of basalt cuttings withthe Paleozoic rocks suggests that Bureau ofEconomic Geology, The University of Texas the basalt intrudes Paleozoic rocks inthe boring as wellas Mesozoic rocks higher inthe section. This well penetrated very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. X-raydata.—l>Ch;10/7 1.1;F=20and 24(?);SR=5.9. — Samples inBureau ofEconomic Geology Well Sample Library. References. — County. Travis. — Well name. St. Stephens School Water Well. — AntonioRodriquez survey;0.5mi.FSL,0.3mi.FEL;1mi.NofLoneTree triangulation Location. — station. Elevation—77o± ( ? ) feet. Total depth.— l,oo4 feet. Completed.— l949. Top of Paleozoic rocks.— 9oo (?), 990(?) -220±(?) feet. — feet. Elevation of Paleozoic rocks. 130±(?), Thin section coverage (depth infeet). bureau of economic geology: 990-1004 (2). Description of Paleozoic rocks. H. J. Plummer (Bur. Econ. Geol. files) described this sequence as hard gray sandstone and schistose shale. The single sample examined is composed of very dark shale and fine-grained, angular, poorly sorted, argillaceous micaceous quartz low-rank metasandstone ; the rocks are veined with quartz and calcite. Metamorphism is incipient to very weak. This well penetrated very weakly metamorphosed dark clastic rocks in the interior part of the frontalzone of the Ouachita belt. — X-ray data. None. — Files ofU.S. Geological Survey, Ground Water Branch, Austin, Texas. References. Bureau of Economic Geology files. — County. Travis. — Wellname. E.D.Summerow No.1Reimers. — Location. J. C.Littlesurvey; 23mi.W, 6mi.NofAustin. —— — Elevation. 800 feet (from topographic map). Total depth. 1,274 feet. Completed^ -1926 and 1932. — — Top of Paleozoic rocks. 266 feet. Elevation of Paleozoic rocks. -j-534± feet. Thinsection coverage (depth infeet.).—bureau ofeconomic geology: 1140, 1243. — Description of Paleozoic rocks. Notes in the Bureau of Economic Geology files describe the sequence as dark gray shale and quartzite. Sellards (1931b) reported black shale. Goldstein (1955) reported that the first sample at 650 feet is in Pennsylvanian and the last sample, 1,243 feet, is also in Pennsylvanian ;he tentatively identified the sequence as foreland facies. The two samples available for study are fine-grained chloritic micaceous feldspathic quartz sandstone andsiltymicaceous metashale. Identificationofthissequence isuncertain bothinthiswellandin Franklin No.1Reimers immediately to the south (p.313);the deformation noted inFranklin No.1 Reimers and the incipient metamorphism observed in both wells indicate that they are within the margin of the structural belt. These beds may be either Stanley or Atoka; on the basis of the X-ray determinations they are tentatively identified as Atoka( ? ). — X-raydata. Mixedlayerillite-montmorillonite shale offoreland type. References.— Sellards (1931b, p. 823). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County.--Travis. — Well name. Woodward and Company No. 1Nelson. Location.—P. C. Harrison survey; 3,750 feet FNWL, 5,650 feet FNEL. — —— Elevation. 567 feet, derrick floor. Total depth. 3,771 feet. Completed. 1955. — Top of metamorphic rocks. 3,730 feet. Elevation of metamorphic rocks.— -3,163 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3660-70, 3740-50. — Description of metamorphic rocks. The samples examined are dark, fine-to medium-grained, angular to subround, poorly sorted, carbonaceous micaceous silty quartz metasandstone (graywacke) showing weak metamorphism with a high shearing component. The rocks show incipient foliation, and micaceous minerals are bent around larger grains which form incipient augen. Rock fragments, quartz,andfeldspararesetinafinefoliatedmatrixofsericite, chlorite,andfinequartz. The Ouachita System This wellpenetrated highly sheared weakly metamorphosed rocks of the black slate beltin the in — terior zone of the Ouachita belt. X-ray data.—l> Ch; 10/7 '0.6; F =20; SR =8.5. — References. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1957. — County. Uvalde. — Wellname. Bernard Einstoss No.1Roswell Wardlaw. — Location. R.Middletonsurvey; 1,000 feetSEofNcor.ofJas. Goucher survey,thence 500 feetNE; 10 mi.EofMontell. — Elevation. 1,792 feet. Total depth.— 2,sls feet. Completed.— l94l. —— Top of Paleozoic rocks. 1,735 feet. Elevation ofPaleozoic rocks. +57 feet. — Thin section coverage (depth in feet). bureau of economic geology: 838-44 (2), 1853-57, 204448, 2093-96, 2196-2205. — Description of Paleozoic rocks. Barnes (Bur. Econ. Geol. files) reported slickensided phyllitic rocks inthe interval 1,971 to 1,973 feet. The sequence is composed of (1) fine-to medium-grained, angular, very poorly sorted, calcareous argillaceous micaceous feldspathic quartz sandstone containing abundant rock fragments; (2) fine- grained, angular, micaceous quartz siltstone; and (3) dark silty shale. Quartz, calcite, and bitumen occur in veinlets. Rock fragments include chert, quartz mosaic, shale, slate-phyllite, metaquartzite, metasiltstone, and microgranular feldspathic igneous rock. The feldspar is plagioclase ;mica includes faded biotite;a large part of the quartz is bubbly and strongly undulose. Zircon is the only common heavy mineral. These rocks possess many characteristics of Mississippian-Pennsylvanian rocks of Ouachita facies. The alternative hypothesis is that the rocks are foreland basin rocks, probably of Atoka age, located close to or within the structural belt and derived from an uplift of Ouachita facies rocks immediately to the south. In either case, this well is within or very close to the front of the structural belt. The overall texture and mineralogy and the presence of quartz, calcite, and bitumen veins suggest that these rocks are of Ouachita facies. —= — ¦ X-raydata.I>Ch;10/7 '3;F 20;SR=2.3.Theabsence ofkaolinitesuggests Ouachita facies. — References. Bureau ofEconomic Geology files. Personal communication :R. P. Maner, Shell OilCompany, 1959. — County. Uvalde. — Wellname. HumbleOil&Refining Company No.1R.L.Anderson. Location.—i.J. Guerra survey; 6,000 feet FSWL, 2,850 feet FSEL; 4 mi. Eof Uvalde. —— — Elevation. 961 feet. Totaldepth. 5,015 feet. Completed. 1934. — Top ofPaleozoic rocks. 3,482 feet. Elevation of Paleozoic rocks. 2,521 feet. Thin section coverage (depth in feet).—shell oilcompany: 3470-80, 3480-82, 3628-31, 3675-78, 3787-89, 3819-21, 4094, 4122, 4140-50, 4150-52, 4449-52, 4884, 4886, 4918-21, 4955-57, 6264-73. PAN AMERICAN PETROLEUM CORPORATION: 4680-85, 4918, 5806. BUREAU OF ECONOMIC GEOLOGY: 4075-80, 4100-05, 4995-00. — Description of Paleozoic rocks. Goldstein (1955) reported top of Paleozoic Ouachita fades (Penn sylvanian?), 3,460 feet; last sample, 5,000 feet,inPennsylvanian (?) Ouachita facies. Petrographic study shows a sequence of dark silty shale and fine-grained, angular, poorly sorted, feldspathic quartz sandstone; locally, the rocks are metamorphosed to metashale, clay-slate, and chlorite- sericite slate, and to low-rank metasandstone ;the sandstones are commonly quartzitic and locally contain abundant metamorphic rock fragments;quartz and calcite veins are common. Metamorphism ranges from none to incipient to very weak and weak without any pronounced directional structures. The interval 4,650 to 4,685 feet contains olivine basalt, and there are numerous intrusions cropping out on the surface in the general area. Possibly the variations in degree of metamorphism are the result of local thermal metamorphism by igneous intrusions. The rocks appear to be upper Paleozoic Ouachita facies (Stanley-Tesnus?) ;Hazzard (1958) noted that cores show steeply dippingbeds. This well penetrated the frontal zone of the Ouachita belt. = X-ray data.—l>Ch> X;ML= Tr;10/7 --'2;F 20. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955;R.T.Hazzard, GulfOilCorporation, 1958. Samples areinBureau ofEconomic Geology WellSample Library. Bureau ofEconomic Geology, The University of Texas — County. Uvalde. — Wellname. Phantom OilCompany No.1M.D.Cloudt. FSL,162varasFWL;9mi.FN,2mi.FW County Location.—Section 661, GC&SF survey; 318.9 varas line. Elevation.—l,sllfeet. Totaldepth— -2,710 feet. Completed.— l93o. — Top ofPaleozoic rocks. 1,690 feet. Elevation of Paleozoic rocks. 179 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1696-1700, 1772, 1963-70, 1975-81, 2110-20, 2230-40 (2). — Description of Paleozoic rocks. Getzendaner (1931) described sporadic samples as follows:1,690, 1,938 to 1,945, 1,981 to 1,985 feet, very black shiny slickensided shale; 2,230 to 2,240 feet, gray sandstone, one fragment cut by a calcite veinlet. He concluded that the age is probably Pennsylvanian. Petrographic examination shows that the sequence is composed of dark, fine-grained, angular to subround, poorly to fairly well-sorted, calcareous to argillaceous slightly feldspathic quartz sandstone, angular to subround, poorly to well-sorted, slightly calcareous micaceous sandy siltstone, and dark shale. There isno metamorphism. The rocks are foreland facies (Atoka? ). This wellpenetrated foreland basin rocks north of the Ouachita belt. = X-raydata.—l>Ch>ML;10/7 <—0.7;F 20; SR=1.7. References.— Getzendaner (1931, pp. 95, 104-106). Samples are inBureau of Economic Geology Well Sample Library. — County. Uvalde. — Wellname. The Texas Company No.1Mitchell. Location.—HE&WT survey; 2,298 feet FNL, 262 feet FWL; near Utopia. — Elevation.—l,66B feet. Totaldepth.—6,so3 feet. Completed. 1949. —— TopofPaleozoic rocks. 1,272 feet. ElevationofPaleozoic rocks. -f-396 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1284-1312, 1346-76, 13761407, 1589-1601, 1650-80, 1826-56, 4000-30, 5650-55, 5700-05, 6150-55, 6300-05, 6400-05, 64956500. — Description of Paleozoic rocks. Goldstein (1955 ) reported base of Cretaceous and top of Permian, 1,272 feet; base of Permian and top of Pennsylvanian (? ),1,745 feet; total depth 6,503 feet, in Stanley-Jackfork(?). Hazzard (1958) says that the cores show bedding inclined at about 60°. The sequence in this well is composed of dark silty shale, very micaceous and containing carbonaceous debris in some intervals, fine-grained, angular, argillaceous micaceous quartz siltstone, and fine-to medium-grained, mostly angular, poorly to very poorly sorted, argillaceous and micaceous feldspathic quartz sandstone, locally calcareous and/or dolomitic, locally containing abundant rock fragments (quartz mosaic, chert, shale-slate, phyllite, volcanic rock, granite(?), and vein quartz); some of the samples are graywacke. The sequence is not metamorphosed; veinlets are restricted to a few fine silica veinlets and minor calcite veinlets. One sample from the 1,376 to 1,407-foot interval is a fine-grained bioclastic limestone composed predominantly of calcareous fossil fragments in a fine- grained equigranular matrix of sparry calcite; a fusulinid has been identified by Ellison (1957) as probably Fusulina witha range from Atoka through Strawn. The very poor sorting and abundant rock fragments suggest "dumping" close to a tectonically active source; the provenance of these rocks appears to have been metasedimentary, volcanic, and graniticrocks. Probably the rocks penetrated in this wellwere derived from erosion of the Ouachita belt to the south. They are tentatively considered to be Atoka and/or Strawn. The graywacke sandstones aresimilartoAtokanbeds foundinFishNo.1PostellinKinneyCounty. Thewellpenetrated Atoka- Strawn(?) beds of foreland basin facies close to or withinthe frontal zone of the Ouachita belt. X-raydata.—-I>Ch>X;10/7<—'1.2;F=20;SR=2.1; weakMLandXintheupper sample are absent inthe lower sample. — References. Personal communication: S. P. Ellison, Jr., Department of Geology, The University of Texas, 1957; August Goldstein, Jr., Pan American Petroleum Corporation, 1955; R. T. Hazzard, Gulf OilCorporation, 1958. — 'County. Uvalde. — Wellname. Transcontinental OilCompany (Benedum and Trees) No. 1Patterson. — Location. IsaacR.Henrysurvey;20mi.FE,5mi.FNCountyline;24mi.NofUvalde. Elevation.—l,slofeet. Totaldepth.—4,22o feet. Completed.—l92o. — Top ofPaleozoic rocks. 1,726 feet. Elevation of Paleozoic rocks. 216 feet. Thin section coverage (depth in feet).—bureau of economic geology: 1293, 1700-2450 (2), 2450 (2). The Ouachita System — Description of Paleozoic rocks. Getzendaner (1931, p. 95) described samples from 1,700, 2,400, and 2,450 feet as hard black finely micaceous shale and compared them to Humble No. 1Thompson in Bandera County; he referred them to the Pennsylvanian. Notes in Bureau of Economic Geology files describe the section 1,700 to 2,450 feet as deformed dark to black indurated shale, locally sandy, and not of Ouachita facies. Petrographic examination shows a sequence of dark silty shale and very fine-grained, angular to subround, fairly well-sorted, silty quartz sandstone. These rocks are foreland facies. This well penetrated upper Paleozoic foreland basin rocks north of the Ouachita belt. X-raydata.—l>Ch>ML>X;10/7 1.5;F=20;SR=1.7. — References. Getzendaner (1931, pp. 95, 106-107). Bureau of Economic Geology files. Samples are inBureau of Economic Geology Well Sample Library. — County. Uvalde. — Wellname. UnionOilCompany ofCalifornia No.1Anderson. — Location. Jedediah Peck survey;10mi.SW ofUvalde. —— — Elevation. 825 feet (from topographic map). Total depth. 3,775 feet. Completed. 1911. — TopofPaleozoic rocks. 3,147 feet. ElevationofPaleozoic rocks. 2,322 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Notes in files of Bureau of Economic Geology describe the rock as black shale. No other data are available. — X-ray data. None. — References. Bureau of Economic Geology files. — County. Uvalde. — Wellname. Universal No.1Mountain Eagle Ranch. Location.—M.P. Zoto survey; 1,980 feet FNL,1,980 feet FEL. Elevation.—l,346feet. Totaldepth—2,37ofeet. Completed.—l949. — Top ofPaleozoic rocks.—l,l32 feet. Elevation of Paleozoic rocks. —{—214 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1038-44, 1150-56, 1351-56, 1450-63, 1546-60, 1634-40, 1985-90, 2135-40, 2211-15, 2230-35, 2245-50 (2). Description of Paleozoic rocks.—-The sequence is composed of (1) fine-grained, angular, poorly to very poorly sorted, argillaceous-micaceous feldspathic silty quartz sandstone sporadically calcareous, containing abundant rock fragments (shale, slate-phyllite, fine-grained chlorite schist, quartz mosaic, metaquartzite, metasiltstone, fine-grained feldspathic igneous rock, chert) ;(2) fine-grained, angular, argillaceous-micaceous sandy quartz siltstone, locally very micaceous; and (3) dark shale, locally silty, pyritic. Most of the quartz is strongly undulose; the matrix is clay-mica hash. The rocks are cut by veinlets of quartz, carbonate, and bitumen. One slide (2245-50) suggests incipient metamorphism. This well apparently penetrated Mississippian-Pennsylvanian rocks of Ouachita facies in the frontal zone of the Ouachita belt. -— = X-raydata.—l>Ch;10/7 1.2;F 20;SR=2.3. — References. Personal communication:R.P.Maner, ShellOilCompany, 1959. — County. Val Verde. Wellname.— Caraway No.1Guida Rose. Location.—Section2,GC&SFsurvey;2,310 feetFNL,330feetFEL;3mi.FN,8mi.FECountyline. — —— Elevation. 1,971 feet, derrick floor. Total depth. 11,590 feet. Completed. 1951. — — Top of Paleozoic rocks. 760 feet. Elevation of Paleozoic rocks. +1,211 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Young (1957) reported base of Cretaceous and top of Wolfcamp, 760 feet; top of lower Strawn limestone, 9,890 feet; top of Bend, 10,780 feet; top of Mississippian, 10,885 feet; top of Silurian, 10,940 feet; top of Montoya, 11,110 feet; top of Simpson, 11,160 feet; top of Ellenburger, 11,290 feet. This wellpenetrated foreland basin rocks north of the Ouachita belt. Bureau ofEconomic Geology, The University of Texas — X-ray data. None. — References. Personal communication: Addison Young, Phillips Petroleum Company, 1957. County.—Val Verde. Wellname.—Caraway No.1Whitehead. Location.—Section 8,blockB,C&Msurvey; 467 feet FSL, 725 feet FWL. — — Elevation. 2,088 feet, derrick floor. Total depth.—10,602 feet. Completed. 1956. — Top ofPaleozoic rocks. 900± feet. Elevation of Paleozoic rocks.— +I,lBB±feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. Sellin (1957) reported that top of Pennsylvanian brown shale is between 9,500 and 9,800 feet and top of Ellenburger is at 10,360 feet; he noted that data are poor and not reliable. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: H. A. Sellin, Magnolia Petroleum Company, 1957. — County. Val Verde. — Wellname. Cockburn No. 1Ingram. Location.—Section 42, block LLL,GC&SF survey; 1,980 feet F most Sly NL, 330 feet F most W'ly WL.— — Elevation. 1,622 feet. Total depth. —1,885 feet. Completed. 1943. — Top of Paleozoic rocks. l,700+(?) feet. Elevation of Paleozoic rocks. 78±(?) feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. ni. — X-ray data. None. — References.-Personal communication:J.P.Olson,ShellOilCompany,1959. — County. Val Verde. — Well name. Delta-Gulf (Phillips Petroleum Company) No. 1Wilson. Location.—Section 82,blockE,GC&SFsurvey; 1,980 feetFNL,1,980 feetFEL;56mi.NofDelRio. —— Elevation. 1,894 feet. Total depth. —16,456 feet. Completed. 1952. —— TopofPaleozoic rocks. 930 feet. Elevation ofPaleozoic rocks. +964 feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. The following stratigraphic data are reported: top of Permian, 930 feet; top of lower Strawn limestone, 13,800 feet; top of Mississippian, 14,160 feet; top of Silurian, 14,210 feet; top of Fusselman, 14,340 feet; top of Simpson, 14,520 feet; top of Ellenburger, 14,905 feet;top ofWilberns, 16,400 feet (Young, 1958). Barnes (1958) noted that the Ellenburger sequence in this wellis darker than inwellsto the north and that fractures in the rock are filled withquartz; north of this well the fractures in the Ellen- burger commonly are open. This may reflect Ouachita orogenic movements. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — Barnes (1959, p. 660). Personal communication: V. E. Barnes, Bureau of Economic Geology, 1958; Addison Young, Phillips Petroleum Company, 1958. References. Samples in Bureau of Economic Geology Well Sample Library. — County. Val Verde. — Well name. Douglas OilCompany No. 1J. E. Sellars, Jr. (Sellers) (also known as Benedum and Trees No.2Sellars). Location.—Section 82, block A,I&GNsurvey; 4,182 feet FSL, 4,182 feet FEL. Elevation.—l,2BBfeet. Totaldepth.—4,l92 feet. Completed.—l927. —— TopofPaleozoic rocks. 1,860 feet. Elevation ofPaleozoic rocks.-—572 feet. Thin section coverage (depth in feet).—-shell oilcompany: 1820-40 (6), 1905-15, 1915-25, 194555, 1985-95, 2005-15 (2), 2015-20, 2044-55, 2125-30, 2150-60 (2), 2190-00, 2200-10, 2210-20 The Ouachita System (2), 2220-30, 2240-50, 2310-20, 2550-60 (2), 2600-10, 2620-30, 2630-40, 2660-70 (2), 2740-50, 2770-80, 2780-00, 3175-80 (2), 3227, 3260-64, 3271-78, 3284-94, 3294-03 (2), 3303-15, 3343-53, 3353-67, 3378-82, 3397-3402, 3434-38 (2), 3438-41 (2), 3456-66, 3466-70, 3489-97, 3497-03, 3625-35 (2), 3745-50, 3785-3810 (2), 3835-50, 3885-00, 3915-30, 3950-60, 3990-4000, 4015-25 (2), 4035-45, 4140-45, 4145-50, 4155-60, 4160-65. — Description of Paleozoic rocks. Kleihege (1949) made the following observations on the pre- Cretaceous sequence: 1,860 feet, clear to gray quartzite; 1,900 to 2,320 feet, slates; 3,175 to 3,500 feet, sandstones and shales; 3,800 to 4,192 feet, metamorphosed and unmetamorphosed carbonate rocks. He suggested that the alternation in degree of metamorphism is due to structural conditions but remarked that ifthere is no dislocation the sequence isprobably Cambro-Ordovician. Petrographic studyofcuttings fromthiswell(based onverysmallandfragmentarythinsections) shows the following sequence : 1. Thinsections 1820-40 to 2044-55:Fine-grained quartzose dolomite or dolomitemarble and dark, very fine-grained pyritic dolomitic sericite chlorite-quartz rock, locally feldspathic; there are also fragments ofpyrite-quartz-dolomite veinrock. 2. Thin sections 2125-30 to 2780-00: Very fine-grained opaque black calcareous and dolomitic graphite slate, locally siliceous, and veined by quartz and carbonate; two samples (2620-30, 2630-40) contain rod-like calcite bodies which appear to be spicules. 3. Thin sections 3175-80 to 3497-3503: Fine-grained, angular to round, fairly well-sorted to poorlysorted, tightly packed, quartzitic feldspathic quartz sandstone containing abundant shale fragments and some chert grains, locally calcareous or dolomitic, locally micaceous and argillaceous, and locally (3343-53) fossiliferous (pelmatozoan fragments, ostracod(?) fragments, fusulinids, shell fragments, and spines) ;both plagioclase and potassium feldspar are present and quartz grains commonly show siliceous overgrowths. 4. Thin sections 3625-35 to 4160-65 (last sample) :Very fine-grained dolomitic limestone or calcilutite containing intraclasts of twinned sparry calcite and fine-grained dolomite and calcareous dolomite, commonly sandy. The upper two units appear to be very weakly to weakly metamorphosed, although the degree of alteration is difficultto assess due to extremely fine grain size and obscuring effects of the abundant graphitic material; in some samples in the upper sequence fine fibers of sericite and chlorite occur in a non-oriented mat in an aggregate of quartz and the fabric appears to be crystalloblastic. It is difficult to determine whether or not the dolomite rock is recrystallized. There are no pronounced shearing structures, but the vein rock is commonly severely strained and fractured. The over-all lithology, the presence of what are probably spicules in some of the graphitic rocks, and the presence of very weak or weak metamorphism without strong shearing suggest that these rocks are lower Paleozoic Ouachita facies. Unit (3) above shows no effects of metamorphism; the general lithology and the fossil assemblage noted in the interval 3343-53 suggest a Mississippian-Pennsylvanian age; the degree of sorting suggests foreland facies, but the feldspar content is higher than normal in foreland facies rocks. The carbonate sequence in the bottom of the well is unmetamorphosed except for shearing in the upper part (3745-50 and 3885-3900). These rocks may be lower Paleozoic foreland facies carbonates, but their lithologyis not typically Ellenburger. The following tentative interpretation is offered: The wellpenetrated very weakly metamorphosed lower Paleozoic Ouachita facies rocks thrust over a foreland sequence composed of Mississippian- Pennsylvanian quartzitic feldspathic sandstones and lower Paleozoic carbonate rocks. An alternative hypothesis is that lower Paleozoic Ouachita facies rocks are thrust over upper Paleozoic sandstones ofOuachita facies,whichinturnhaveoverriddenaforeland faciescarbonate sequence. — X-ray data. None. References.— Kleihege (1948, p. 28). Personal communication:E.A.Vogler,ShellOilCompany, 1955. — County. Val Verde. — Well name. East Del Rio OilCompany No. 1Russell and Weatherby (Weatherbee). — Location. J.I.Mitchellsurvey;1mi.EofDelRio. Elevation.—9s3 feet. Total depth.— 3,332 feet. Completed.— l92B. — — Top of Paleozoic or metamorphic rocks. 2,800 feet. Elevation of Paleozoic or metamorphic rocks. -1,847 feet. Thin section coverage (depth in feet).—bureau of economic geology: 2837-42, 2842-51, 2851-57, 2871-83. — Description of Paleozoic or metamorphic rocks. Descriptions of scattered samples between 3,280and 3,310 feet show gray dolomiticlimestone and quartz fragments (Bur. Econ. Geol. files). Kleihege (1949)reportedthatthiswell(hecarrieditasNo.1RussellWithersbee) entered dolomitebelowthe base of the Trinity at 2,790 feet; 2,790 feet, finely crystalline gray to neutral dolomite; 2,845 to 2,950feet, finely crystalline ivory-colored dolomite ;3,025 to 3,180 feet, finely crystalline to medium crystalline light gray dolomite; 3,290 to 3,310 feet, light-colored poorly sorted well-cemented sandstone over Bureau of Economic Geology, The University of Texas lying light gray moderately crystalline dolomite. Kleihege noted that the well lies south of the zone ofmetamorphism but he interpreted the sequence as unmetamorphosed. Petrographic study was difficultbecause of the extreme fineness of the cuttings available; a few cuttings show dolomite and quartz in a granoblastic mosaic and therefore the sequence is interpreted ascomposed ofveryfinelycrystalline dolomitemarble—metamorphism islowgrade. Theoriginofthe abundant magnetite inthe slides isnotclear. This well appears to have penetrated a low-grade metamorphic carbonate (dolomite) sequence in theinterior zone ofthe Ouachita belt. — X-ray data. None. — Kleihege (1948, p. 51). Bureau of Economic Geology files. Samples areinBureau ofEconomic Geology WellSample Library. References. — County. Val Verde. — Well name. Fenslund (Fensland) OilCompany No. 1AbbRose. Location.—Section 56,blockAZ,GC&SF survey;6mi.NofNWcor.ofKinneyCounty; 30mi.N ofDel Rio. — Elevation.—l,B6s( ?) feet. Totaldepth 2,928 feet. Completed— ni. — TopofPaleozoic rocks.—1,810(?), 1,935(?) feet. Elevation ofPaleozoic rocks. {-55(?), 70(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 1827-35, 1880-1935 (3), 1935-55, 1980-2010 (4), 2010-75 (2), 2428-35, 2450-75, 2425-60, 2540-2605, 2686-93, 2775-85 (2), 2810-20, 2900-15, 2915-28. shell oil company: 2681 (2), 2699, 2790, 2800, 2820 (4), 2840 (2), 2850, 2880-85, 2900 (3). — Description of Paleozoic rocks. Udden (Bur. Econ. Geol. files) described the sequence as black shale and dark gray highly indurated sandstone and suggested a correlation with the Tesnus forma tion. Kleihege (1949) noted that this well penetrated a pre-Cretaceous section composed of nearly1,000 feet of black finely arenaceous shale, indurated toward the bottom of the section, with beds of clear to gray quartzite in the bottom one-third of the sequence; he believed that the No. 1 Abb Rose isadjacent to thebeltofmetamorphosed sedimentary rocks. Petrographic study shows that the rocks are mostly dark slightly sandy and silty shale, locallydolomitic, dark dolomitic carbonaceous micaceous siltstone, and dark, very fine-grained, angular to subround, fairlywell-to well-sorted, dolomiticquartz sandstone, commonly feldspathic and micaceous, locally calcareous, carbonaceous (or bituminous?), and locally veined with quartz. The presence of quartz veins and the X-ray data suggest proximity to the Ouachita belt but general lithology indicates that the rocks are foreland facies. This wellis close to the Ouachita front; probably itpenetrated foreland basin rocks north of the Ouachita belt. — '— X-ray data. I>Ch; 10/7 '1; F=20; SR=3.3. Absence of kaolinite and mixed-layer clay suggests these rocks may be Ouachita facies. References.— Kleihege (1948, p. 23). Bureau of Economic Geology files. Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Val Verde. — Wellname. HiawathaOilCompany (BenedumandTrees)No.1Sellars(Sellers). Location.—Section1031,blockA,GC&SFsurvey;1,200 feetFSL,5,800 feetFWL. Elevation—-1,221(?),1,205(?) feet. Totaldepth—3,so2 feet. Completed—l927. — Top of metamorphic rocks. 1,700± feet. Elevation of metamorphic rocks. 479(?), -495 (?) feet. — Thin section coverage (depth in feet). shell oilcompany: 1725 (2), 1725-35 (5), 1750-60 (3), 1815 (4), 1920, 2000, 2050 (2), 2641 (4), 2650, 2708, 2725 (3), 2780, 3009-14, 3035-42 (2), 3070 (5), 3152-58, 3192-00, 3200-04 (2), 3210-15 (6), 3215-22, 3231-40, 3248-55, 3261-70 (2), 3270-78 (2),3284-89, 3433-46, 3476-81, 3503. — Description of metamorphic rocks. Kleihege (1949) reported 700 feet of quartzite overlying 1,000 feet of quartz-chlorite schist. Goldstein (1955) described chlorite phyllite and metaquartzite and noted a similarity in degree of metamorphism to the metasedimentary rocks of the Luling area. The upper sequence penetrated in this well(including samples from1,725 to1,815 feet withskips) is fine-grained dolomite marble, commonly calcareous and quartzose, locally pyritic and sericitic, fine- grained dolomitic calcite marble, and very fine-grained finely micaceous dolomitic metaquartzite or The Ouachita System metachert. Below is a sequence (samples from 1,920 to 2,050 feet) of fine-grained slightly sericitic calcareous metaquartzite and fine-grained dolomitic sericitic quartzose calcite marble; the quartz is severely strained and grain contacts are sutured. Dolomite rhombs in the marbles are extensively twinned and calcite grains are commonly twinned, stretched, and deformed; rude foliation is expressed by stretched grains and oriented sericite fibers. Metamorphism is low grade witha pronounced shearing component, and the rocks are similar to those encountered in many wellsin the interior zone of the Ouachita belt. At1,815 feet the sample is composed of unaltered fine-grained dolomite, and at 2,000 feet there is a fragment of fine-grained calcareous—dolomite. The presence of these unaltered rocks in the sheared sequence is not readily explainable possibly they are cavings. From 2,050 to 2,641 feet there is a sample skip. Samples from 2,641 through 3,433 to 3,446 feet (with skips) are metavolcanic rocks. This lower sequence is composed mainly of foliated microgranular to cryptocrystalline sericite (muscovite)-chlo rite-quartz-alkali feldspar rocks, locally containing epidote, dolomite, biotite, and commonly cut by quartz and calcite veins. Some rocks contain relict albiteoligoclase or microcline phenocrysts and/or coarser lenses of quartz-alkali feldspar inthe fine granular mass. Most of the rocks are metarhyolite but some may be intermediate varieties. Metamorphism — is difficultto assess itappears to be a low grade regional metamorphism witha strong metasomatic element. This metavolcanic sequence is not commonly found in the Ouachita structural belt; to the east in Kinney County metarhyolite is overlain by lower Paleozoic dolomite in Havoline No. 1 Weatherby and is probably Precambrian (p. 284). The sample from 3,503 feet is fine-grained chloriteactinolite- augite-plagioclase rock (not foliated);this altered microgabbro may be part of the Precambrian (?) igneous sequence, or it may be a younger intrusion in the metavolcanic sequence. Probably the upper sheared sequence is part of the Ouachita belt which has been overthrust from the south. The following interpretation is offered: The well passed out of Mesozoic rocks, penetrated allochthonous sheared marbles of the interior zone of the Ouachita structural belt, intersected an over thrust, and bottomed inPrecambrian metavolcanic rocks. — X-ray data. None. References.— Kleihege (1948, p. 44). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; E. A. Vogler, Shell OilCompany, 1955. — County. Val Verde. Wellname.—HumbleOil&RefiningCompany No.1MillsMineralTrust. Location.— Section 128, block 1, I&GNsurvey; 802 feet FSL, 2,174 feet FEL; 2 mi. W of Pandale, 2,000 feet SW ofOwens No.1Mills. Elevation.—l,Bl2feet,derrickfloor.Totaldepth.—l7,s2s feet. Completed.—l9s7. — Top ofPaleozoic rocks. 180 feet. Elevation of Paleozoic rocks.— +1,632 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Woods (1957) reported the following sequence: top of Permian, 180 feet; top of Pennsylvanian, 3,420 feet; top of lower Strawn, 14,165 feet; top of Hunton, 14,715 feet; top of Simpson, 15,180 feet; top of Ellenburger, 16,187 feet. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: R.D. Woods, Humble Oil&Refining Company, 1957. County.—Val Verde. — Wellname. Humble Oil&Refining Company No.1Emma Wardlaw. — Location. Section 53, block D, GC&SF survey; 15 mi. SE of Juno. Elevation.— l,99B feet. Total depth.— ls,29s feet. Completed— l9s6. — — TopofPaleozoic rocks. 1,090 feet.ElevationofPaleozoic rocks. +908 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Bybee (1959) reported the following information: 1,090 to 12,200 feet, dark shale and sandy shale of Permian age; 12,200 to 12,670 feet, hard quartziticsandstone of Permian age; 12,670 to 13,900 feet, dark shale of which the lower part is probablyPennsylvanian ;13,900 to 14,210 feet, Lower Pennsylvanian Strawn or Bend(?) limestone; 14,210 to 14,240 feet, Mississippian rocks; 14,240 to 14,500 feet, Devonian rocks; 14,500 to 14,730 feet, Simpson rocks; 14,730 to 15,295 feet, Ellenburger dolomite. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. P. Olson, Shell Oil Company, 1958; R. W. Bybee, Humble Oil&Refining Company, 1959. Bureau ofEconomic Geology, The University of Texas — County. Val Verde. — Wellname. Hurlbut No. 1BluffCreek Ranch. — Location. Section 3, block 5, I&GNsurvey. — Elevation. —1,198 feet. Total depth. —3,485 feet. Completed. 1954. — Top of Paleozoic and/or metamorphic rocks. 2,490 feet. Elevation of Paleozoic and/or metamorphic rocks. 1,292 feet. Thin section coverage (depth in feet).—shell oil company: 2690-2730, 2930-70, 3310-30, 336080, 3440-60. Description of Paleozoic and/or metamorphic rocks.— Vogler (1955) reported top of Hosston, 2,410 feet; top of Ellenburger, 2,490 feet; top of granite, 3,480 feet. Masson (1955) reported the followingbrief descriptions: 2,720 to 2,730 feet, fine-to medium-grained limestone, no metamorphism; 3,390 to 3,430 feet, medium-to coarse-grained limestone and dolomite, locally weakly sheared, shows slate-zone metamorphism; 3,450 to 3,480 feet, quartzite and siliceous calcphyllite showing phyllite zone metamorphism. Petrographic studies indicate the followinglithologies: 2,690 to 2,730 feet, fine-grained equigranular dolomite showing slight deformation and blurring of grain boundaries, and cut by strained and de formed quartz veinlets; 2,930 to 2,970 feet, fine-grained equigranular quartzose dolomite with both dolomite and calcite veinlets extensively twinned; 3,310 to 3,330 feet, graphitic (?) metamorphosed dolomite with a rude foliation and sericitic dolomitic quartzite; 3,360 to 3,380 feet, pyritic meta morphosed dolomite withsericite developed in shear zones; 3,440 to 3,460 feet, feldspathic dolomitic quartzite showing granulation and crushing along grain boundaries. This well is difficult to interpret. Operating geologists generally consider the dolomite rocks as Ellenburger ;itshould be pointed out, however, that ifthese beds are Ellenburger, they are not normal Ellenburger. The lower part of the "Ellenburger" sequence is metamorphosed and rudelyfoliated; foliation is expressed in orientation of long dimensions of grains and metamorphism is weak to low grade. The samples from 3,310 to 3,330, 3,360 to 3,380, and 3,440 to 3,460 feet are part of the same general sequence. Itis difficultto relate the apparently unmetamorphosed carbonate rocks at 2,690 to 2,730 and 2,930 to 2,970 feet to the underlying metamorphosed carbonate rocks. It was reported that "granite" was encountered between 3,480 and 3,485 feet (total depth) but no samples were located for this interval. Inspection of the map (PL 2) shows that this well lies between the Ouachita front and Havoline No. 1Weatherby (p.284).In this area, rocks south of the Ouachita front are dislocated highly sheared metamorphic rocks of the interior zone. In Havoline No. 1Weatherby, siliceous or quartzose lower Paleozoic dolomite rests on metarhyolite of probable Precambrian age which is part of the Devils — River uplift an area of high-standing Precambrian rocks. The Ouachita belt was crushed against the Devils River uplift and the lower Paleozoic carbonate beds that mantle the buttress were deformed and slightly metamorphosed. Here, then, foreland facies rocks are slightly metamorphosed. The No. 1BluffCreek Ranch wellprobably penetrated deformed and slightly metamorphosed lower Paleozoic foreland facies carbonate rocks in an area of great structural complexity north of the allochthonous interior zone of the Ouachita belt.If"granite" was penetrated inthe bottom of this well, itisprobably Precambrian. — X-ray data. None. References.— Personal communication: P.H.Masson, Humble Oil&Refining Company, 1955; E. A. Vogler, Shell OilCompany, 1955. — County. Val Verde. — Wellname. Husky OilCompany No.1Rose-Robertson. Location.—Section 83, block N, GH&SA survey; 660 feet FSL, 1,980 feet FEL; 1mi. S of Comstock. Elevation.— l,sBo feet. Totaldepth.— -2,426 feet. Completed.— l9sl. — Top of metamorphic rocks. 2,170 feet. Elevation of metamorphic rocks. 590 feet. — Thin section coverage (depth in feet). shell oilcompany: 2330-40 (5), 2400-08. bureau of economic geology: depth unknown. — Description of metamorphic rocks. The samples available are very fine-grained actinolitic chloriteepidote- sericite schist and very fine-grained actinolite-epidote schist, locally chloritic and calcareous. Metamorphism is low grade with a very strong shearing element; structures are foliation, contortion, and fracture cleavage. The original rock may have been basaltic. This wellpenetrated the interior zone of the Ouachita beltand/or Precambrian metavolcanic rocks of the Devils River uplift. — X-ray data. None. — Personal communication: E. A.Vogler, Shell OilCompany, 1955. References. The Ouachita System — County. Val Verde. Well name.—Independent Operator No. 1L.Rust (Whitehead) (also known as W. H. Bowers No. 1BluffCreek Ranch, Huber OilSyndicate No.1Rust, Permian Basin Operators No.1Rust, Permian Basin Operators No.1Whitehead). — Location. Section 30, block 4, I&GNsurvey; 8 mi. E ofDel Rio. Elevation.—l,l77feet,derrickfloor.Totaldepth.—s,43o feet. Completed.— -1924(?). Inmetamorphic rocks at 2,420 feet. Elevation of metamorphic rocks.—< -1,243 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2420, 2530, 2774, 2780, 2836, 3070, 3110, 3150, 3240, 3250. — Description of metamorphic rocks. Kleihege (1949) interpreted the sequence in this well as follows: 2,700 to 2,830 feet, gray to black finely crystalline slaty limestone; 2,830 to 3,080 feet, slightly more metamorphosed than above and composed of white finely crystalline limestone, black slate, and glossy partly marmorized slaty limestone; 3,080 to 3,120 feet, gray shaly limestone with a micro- gastropod fauna as carbonaceous molds; 3,155 to 3,220 feet, finely crystalline slaty dark gray glossy limestone; 3,280 to 3,420 feet, phyllitic marble and black slate; 3,510 to 3,710 feet, gray slaty finely crystalline marble. Petrographic study of very fine cuttings shows that the sequence is made up mostly of fine-grained calcite marble withminor dolomiticcalcite marble and dolomite marble; graphite, commonly associ atedwithpyrite,occursincloudymasses andopaque patches. Metamorphism islowgrade;foliationis expressed in elongate, stretched calcite and quartz grains and long smeared-out streaks of sericite. There is a strong shearing element. Thiswellpenetrated metamorphic rocksintheinteriorzoneoftheOuachitabelt. — X-ray data. None. References.— Kleihege (1948, p. 32). Personal communication :J. R. Sandidge, Magnolia Petroleum Company, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Val Verde. — Wellname. Joiner OilCorporation No. 1Sellars (Sellers) Bros. Ranch. Location.— Section 59, block A,I&GNsurvey; 2,728 feet FEL, 2,340 feet FNL; 22 mi. W of DelRio. Elevation—l,296 feet. Totaldepth.— 2,2s2 feet. Completed.— l94o. — Top of metamorphic rocks. 1,950 feet. Elevation of metamorphic rocks. 654 feet. — Thin setcion coverage (depth in feet). bureau of economic geology: 1940-50 (2), 1950-58 (2), 1958-70 (2), 1970-77, 1977-90, 2023-25, 2032-39, 2047-65, 2065-68, 2068-74, 2074-78, 2078-82. — Description of metamorphic rocks. Hills (1941) remarked that "showings of gas were found in crystalline dolomite, probably Ellenburger, which underlies the Cretaceous in Joiner's Sellers No. 1... This test is probably near the border of the overthrust, as another test 2 miles east passed from the Cretaceous into metamorphic rocks." Kleihege (1949) noted that the Cretaceous rocks are underlainby a clear gray quartzite (1,950 to 1,990 feet) which in turn is underlain by a finely crystalline gray tight dolomite which shows no signs of metamorphism ;he places the wellin the "slate zone" on the basis of location. Goldstein (1955) reported base of Cretaceous and top of Paleozoic is between 1,990and2,060feet,withtotaldepth2,252feetinPaleozoic dolomite. Petrographic study shows a sequence of metaquartzite overlying fine-grained dolomite which is probably dolomite marble. The metaquartzite is a granoblastic-cataclastic rock with sutured and stretched grains; metamorphism is low grade witha strong shearing element. The underlying dolomite does not show evidence of metamorphism in the carbonate mosaic, but small patches of quartz mosaic locally show stretched grains and contain oriented sericite fibers. This well appears to be located very close to the front of the Ouachita belt. Hiawatha No. 1 Sellers immediately to the southeast (p. 322) passed from the Cretaceous into sheared rocks of the Ouachita belt, intersected an overthrust, and bottomed in Precambrian metavolcanic rocks. Douglas No. 1 Sellars to the northeast is interpreted as having passed from Cretaceous rocks into very weakly metamorphosed Ouachita (Marathon) facies rocks thrust over a foreland facies sequence. Joiner No. 1 Sellars appears to have passed from Cretaceous rocks into an overthrust slice of sheared metaquartzite and bottomed in slightly metamorphosed dolomite (lower Paleozoic(?) Ellenburger ( ?) ). — X-ray data. None. References.— Hillset al. (1941, p. 1530);Kleihege (1948, p. 27). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955; E. A. Vogler, Shell OilCompany, 1955. Samples are inBureau ofEconomic Geology WellSample Library. Bureau ofEconomic Geology, The University of Texas — County. Val Verde. — Wellname. KillamNo.1Babb. Location.—Section 104,block2,I&GNsurvey; 3,840 feetFSL,1,500 feetFWL. Elevation.— l,ss9 feet. Totaldepth.—3,o7s feet. Completed.—l949. —— TopofPaleozoic rocks. 800 feet. ElevationofPaleozoic rocks. +759 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Reported as upper Paleozoic clastic rocks of foreland facies. This well is probably located north of the Ouachita front. — X-ray data. None. — References. Personal communication :J. P. Olson, Shell OilCompany, 1959. County.— Val Verde. — Wellname. KillamNo.1Everett. Location.—Section138,block1,I&GNsurvey; 1,800feetFEL,750feetFSL. —— — Elevation. 1,563 feet. Total depth. 3,001 feet. Completed. 1948. —— Top of Paleozoic rocks. 820 feet. Elevation of Paleozoic rocks. +743 feet. — Thin section coverage (depth infeet). None. Description of Paleozoic rocks.—Reported as upper Paleozoic clastic rocks of foreland facies. This wellislocated north of the Ouachita front. — X-ray data.—None. References. Personal communication: J. P. Olson, Shell OilCompany, 1959. — County. Val Verde. — Wellname. KillamNo.1Parker. Location.—Section 489, CCSD&RGNG survey; 467 feet FSL, 481 feet FWL; 8 mi. N of Del Rio. — —— Elevation. 1,185 feet. Total depth. 2,676 feet. Completed. 1949. — Top of metamorphic rocks. 2,390 feet. Elevation of metamorphic rocks. 1,205 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2350-60, 2380-90, 2450-60, 2550-60, 2560-70, 2660-70. — Description of metamorphic rocks. The pre-Cretaceous rocks are fine-grained dolomitic calcite marble locally containing abundant quartz in patches of mosaic (recrystallized chert?) and locally containing sheaves and plates of muscovite. The marble is transected by veinlets of extensively twinned sparry calcite, quartz, and chlorite. Metamorphism is low grade with a high shearing element; foliation is expressed by dimensional orientation of stretched grains and by mica orientation. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — Personal communication :Addison Young, Phillips Petroleum Company, 1957. References. — County. Val Verde. Wellname.— Magnolia Petroleum Company No. 1Morrison. Location.— Section 10, block Q-4, TCRR survey; 990 feet FNL,1,980 feet FWL. — —— Elevation. 2,227 feet, derrick floor; 2,213 feet, ground. Total depth. 15,143 feet. Completed. 1956. —— Topof Paleozoic rocks. 630 feet. Elevation of Paleozoic rocks. -f-1,597 feet. — Thin section coverage (depth in feet). None. Description of Paleozoic rocks.—According to Sellin (1957) the following divisions are recognized in this well: base of Cretaceous and top of Permian, 630 feet; top of Pennsylvanian limestone, 12,180 feet; top of Devonian, 12,480 feet; top of Fusselman, 12,780 feet; top of Sylvan, 12,905 feet; top of Simpson, 13,035 feet; top of Ellenburger, 13,586 feet; top of Wilberns, 15,124 feet. The section from 630 to 12,180 feet is shale and sandstone witha few limestone beds in the basal part; the limestones disappear to the west. General opinion is changing to favor acceptance of a Wolfcamp age for this sequence. According to Barnes (1957), the Ellenburger in this wellis darker than is normal in beds to the north. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication:V.E.Barnes,BureauofEconomicGeology,1957;H.A.Sellin, Magnolia Petroleum Company, 1957. The Ouachita System — County. Val Verde. — Wellname. MagnoliaPetroleum Company No.1W.E.Whitehead. Location.—Section 81,blockD,GC&SF survey; 160 feet FWL,1,600 feetFSL. Elevation.—l,779 feet. Totaldepth.— 6,72s feet. Completed.— l92B. — —— Top of Paleozoic rocks. 960 feet. Elevation ofPaleozoic rocks. |—819 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sandidge (1955 ) reported base of Cretaceous, 960 feet;black shale and gray sandstone to total depth. This sequence was formerly thought to be Pennsylvanian (Cannon and Cannon, 1932), but Galley (1957) suggested that itmight be Wolfcamp. Kleihege (1949) re marked thatthe wellpenetrated 5,600 feetofblack arenaceous shale closelyresembling that foundin Milham No. 1 Bassett. In the files of the Bureau of Economic Geology, a number of different terms including Gaptank(?), Strawn, and Bend have been applied to this sequence, which is described as dark sandy shale, locally bituminous, fine-grained sandstone, and rare limestone beds, locally cri noidal. This wellpenetrated upper Paleozoic foreland basin rocks north of the Ouachita belt. — X-ray data. None. References.— Cannon and Cannon (1932, p. 172);Kleihege (1948, p. 23). Personal communication: J. E. Galley, Shell OilCompany, 1957; J. R. Sandidge, Magnolia Petrol eum Company, 1955. — County. Val Verde. — Wellname. C.A.MaurerNo.1John W.Ingram. Location.—Section 33,blockS2,ELRRsurvey; 730feetFEL,2,030 feetFSL;9mi.N70°EofLang try. Elevation.—l,s64 feet. Total depth.— 2,o3o ( ? ),2,078 (? ) feet. Completed—l947. Top of metamorphic rocks.—1,905(?), 1,950(?) feet. Elevation of metamorphic rocks. 341(?), -386(?) feet. Thinsection coverage (depth infeet).—None. Description of metamorphic rocks.—According to Kleihege (1949), the base of the Trinity is at 1,905 feet and immediately underneath is 5 feet of fine-grained white poorly cemented sandstone (1,905 to 1,910 feet) and 25 feet of variegated and white chert (1,910 to 1,935 feet). From 1,950 — to 2,010 feet there is glossy green and red waxy textured phyllitic slate and vein quartz the phyllite at the top of the section is composed mostly of chlorite withminor sericite and hematite causing the red color. The grade of metamorphism decreases with depth and the rock looks like a gray-green slickensided slaty shale. From 2,010 to 2,073 feet the sequence is composed of a black waxy shale ranging from slate at the top to shale at the bottom. On the basis of location and interpreting Kleihege's descriptions, it appears that this wellpene trated metamorphosed rocks in the interior zone of the Ouachita belt. The chert and sandstone di rectly beneath the Cretaceous are not readily explainable; the chert section suggests equivalence withOrdovician-Devonian beds of the Marathon Basin but no correlation is warranted. Possibly the sandstone is Cretaceous. The structural salient of the interior zone mapped in south-central Val Verde County is based on this well. — X-ray data.-None. — References. Kleihege (1948, p. 41). — County. Val Verde. — Wellname. 0.0.Owens No.1MillsRanch. — Location. Section 128, block 1,I&GNsurvey; NE cor. of section; 4 mi. W of Pandale. Elevation.—l,B6o feet. Total depth.—6,7Bo feet. Completed.—l93l. —— Top ofPaleozoic rocks. 775 feet. Elevation of Paleozoic rocks. +1,085 feet. — Thin section coverage (depth infeet). bureau of economic geology: 2883-88, 3030-53, 4032-38, 4170-78. — Description of Paleozoic rocks. Galley (1957) reported top of Wolfcamp ( ?), 775 feet; total depth 6,780 feet, in Wolfcamp. Samples studied are mostly fine-grained, angular to subround and round, fairly well-sorted, calcareous quartz sandstone commonly containing partly disintegrated shale fragments. There is no metamorphism or veining. This well penetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. Bureau of Economic Geology, The University of Texas — References. Personal communication: J. E. Galley, Shell OilCompany, 1957. Samples areinBureau ofEconomic Geology WellSample Library. — County. Val Verde. — Wellname.-Petrocel No.1Waldrop. Location.—Section 27,block5,I&GNsurvey;1,200feetFSL,2,940 feetFWL. Elevation.—l,263 feet. Total depth.— 2,3B4 feet. Completed— l9s2. — Topof Paleozoic rocks. 1,930± feet. Elevation ofPaleozoic rocks. 667± feet. — Thin section coverage (depth infeet). None. — Description of Paleozoic rocks. From its location and data from Stiles et al. (1955), this well appears tohave penetrated lower Paleozoic carbonate rocks. — X-ray data. None. — References. Stiles et al. (1955). — County. Val Verde. — Wellname. Phantom OilCompany (Bovaird DrillingCompany) No.1Ingram. — Location. Section 44, block DB, ELRR survey; 175 feet FEL, 300 feet FSL; 8 mi. N of Langtry. Elevation.—l,494 feet. Totaldepth.— 3,olo(?), 3,035 ( ?) feet. Completed.— l93o. TopofPaleozoic rocks.—1,605feet.ElevationofPaleozoic rocks. 111feet. — Thin section coverage (depth in feet). bureau of economic geology: 1665-75, 1715-25, 1755-65 (2), 1905-15, 2235-45, 2495-00, 2525-38, 2700-10, 2820-30, 2940-50. — Description of Paleozoic rocks. Notes inBureau of Economic Geology files describe a sequence of black shale "not much altered." Kleihege (1949) described the Paleozoic beds as very fine-textured black shales with some beds of brown to gray fine-grained sandstone; about 90 percent of the sec- tionisshale,commonlyslickensided.Heconcluded thatthewellislocatednorthofthe"slatezone." Petrographic study shows that the sequence is composed of dark shale, locally carbonaceous, micaceous, locally silty, and fine-grained, angular to subround, fairly well-sorted to poorly sorted, slightly calcareous argillaceous quartz sandstone, feldspathic in the deeper part of the well, locally containing bituminous material; the sandstone is cut by calcite veinlets in some intervals. There is no metamorphism ;fabrics are clastic and bedding is the only structure observed. These rocks are tentatively identified as Pennsylvanian or Wolfcamp rocks of foreland facies; the well is probablylocated close to the front of the Ouachita belt. = X-ray data.—l> Ch; 10/7 1.2; F 20; SR =2.1. References.— Kleihege (1948, p. 23). Bureau of Economic Geology files. — County. Val Verde. Well name. —Phillips Petroleum Company No. 1-A Guinn. Location.—Section 2, BS&F survey; 2,030 feet FNL,1,980 feet FEL; 11.4 mi. FN, 27 mi.FW County line. — Elevation. —2,066 feet, derrick floor. Total depth.—15,015 feet. Completed. 1957. —— TopofPaleozoic rocks. 1,185 feet. ElevationofPaleozoic rocks. -j—BBlfeet. — Thin section coverage (depth infeet). None. — Description ofPaleozoic rocks. Young (1957) reported base ofCretaceous and topofWolfcamp, 1,185 feet; top of lower Strawn limestone, 11,960 feet; top of Siluro-Devonian limestone, 12,840± feet; top of Montoya, 13,180 feet; top of Simpson, 13,210 feet; top of Ellenburger, 14,050 feet. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: Addison Young, Phillips Petroleum Company, 1957. — County. Val Verde. — Wellname. Plateau OilCompany No.1B.S. Harrison et al. Location.—Section 14, block 3, I&GNsurvey; 1,280 feet FNL, 660 feet FWL; 9 mi. E, % mi. N of Del Rio. — — Elevation. 1,111 feet. Total depth.— 3,so7 feet. Completed. 1926. The Ouachita System Top of metamorphic rocks.—3,l4B (?), 2,900(?) feet. Elevation of metamorphic rocks. 2,037(?), -1,789 (?) feet. — geology: Thinsection coverage (depth in feet). shell oilcompany: 3100-34. bureau of economic 3215, 3485. — Description of metamorphic rocks. Sample descriptions in the Bureau of Economic Geology files report basal sand and conglomerate of the Trinity from 2,910 to 2,940 feet, gray to red sandstone from 2,940 to 3,000 feet, and gray limestone, chert, and loose sand from 3,000 to 3,148 feet; the first frag ments of metamorphic rock are reported at 3,148 feet. Sellards (1933) placed top of the Paleozoic at 3,148 feet and described the rock as talcose shale. Kleihege (1949) placed the base of the Trinity sand between 2,880 and 2,900 feet and described the succeeding sequence as follows: 2,900 to 3,025 feet, finely crystalline vari-colored limestone containing a 20-foot sandstone bed; 3,045 to 3,100 feet, light gray to orange quartzite, the lower 30 feet very fine-grained and approaching novaculite; 3,120 to 3,130 feet, hematitic quartzite; 3,130 to 3,225 feet, glossy phyllitic marble ranging from gray to green to yellow; 3,270 to 3,400 feet, white granular recrystallized limestone with green schistose chlorite and sericite; 3,475 to 3,505 feet, white marble and glossy black phyllite. Goldstein (1955) called base of Cretaceous and top of Paleozoic at 3,150 feet; he said that the uppermost Paleozoic beds consist of dark gray limy shale, argillaceous limestone, and light green talcose phyllite (3,160 to 3,210 feet), they are succeeded by a series of pink altered limestones and green phyllites, and from 3,240 feet to total depth scattered samples are argillaceous limestones, limy argillites, and sandy lime stones, allsomewhat metamorphosed. Petrographic study indicates a higher grade of metamorphism than that given in the above descrip tions. The sample at 3,215 feet is a fine-grained garnetiferous sericite schist; at 3,485 feet the sample is composed of dolomitic sericite phyllite, dolomite marble, and very fine-grained dolomitic meta- quartzite or metachert. The discrepancy between Kleihege's base of Cretaceous (above) and determinations made by Sel lards and Goldstein is very considerable; sample coverage now available for this well is very scanty, and the writer was not able to make an independent investigation. Inview of the metamorphism seen inthelowerpartofthewell,itisprobable thatitislocatedintheinterior zoneoftheOuachitabelt and the upper unmetamorphosed part of the section is Cretaceous. — X-ray data. None. References.— Kleihege (1948, p. 48);Sellards (1933, p. 191). Bureau of Economic Geology files. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Val Verde. — Wellname. Producers OilCompany No.1Bob Everett. Location—Section 40, block DB, CCSD&RGNG survey; 420 feet FEL, 2,400 feet FSL. Elevation—-1,929 feet. Totaldepth.—2,s3o feet. Completed— -1929. —— Top of Paleozoic rocks. 1,365(?) feet. Elevation of Paleozoic rocks. +564(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 1530, 1575, 1760-65, 19902000. — Description of Paleozoic rocks. Bureau of Economic Geology files report hard sandstone and hard black shale at 2,450 feet. Kleihege (1949) reported 400 feet of dark gray, fine-grained, poorly sorted, sandstone witha few thin-bedded layers of dark gray finely arenaceous shale below Cretaceous beds. Thin section study shows a sequence of dark, fine-grained, angular, poorly sorted, slightly feldspathic dolomitic argillaceous quartz sandstone, locally containing bituminous material, and dark silty shale, locally carbonaceous. These are unmetamorphosed rocks, probably ofWolfcamp orPennsylvanian age. This well penetrated foreland basin rocks north of the Ouachita belt. X-day data.—l> Ch; 10/7 —^3.5; F=20; SR= 2.6. References— Kleihege (1948, p. 24). Bureau ofEconomic Geology files. Samples areinBureau ofEconomic Geology WellSample Library. — County. Val Verde. — Well name. Reclamation OilProducing Syndicate No. 1 J. B. Moore and Whitehead (also known as No.1Mclntyre). Localion.—Section 491,CCSD&RGNG survey;1,432feetFNL,714feetFEL;5mi.dueNofDelRio. Elevation.— l,oso feet. Totaldepth.— 2,sso feet. Completed.—l923. — Top of metamorphic rocks. 2,400dt feet. Elevation of metamorphic rocks. 1,350± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 2420-25. shell oilcompany: 2370,2420-35 (2), 2450. Bureau ofEconomic Geology, The University of Texas — Description of metamorphic rocks. Descriptions in the Bureau of Economic Geology files report top of Paleozoic rocks at 2,170 feet;the sequence is described as gray sandy limestone, dolomite, cal careous sandstone, and limestone conglomerate ;red beds are reported from 2,360 to 3,400 feet. Udden noted that the conglomerate from 2,360 to 2,400 feet does not resemble Permian or Pennsylvanian rocks. Probably the determination of base of Cretaceous at 2,170 feet is in error and the entire section to 2,400± feet is Cretaceous. Samples below 2,400± feet are fine-grained metaquartzite and fine-grained dolomitemarble(?);metamorphism islowgrade withahigh shearing component. Stretched grains show dimensional orientation. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. — Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1955. Samples areinBureau ofEconomic GeologyWellSample Library. References. — County. Val Verde. — Wellname. StanolindOiland Gas Company No.1West. Localion.—Section4,blockCl6,GC&SFsurvey;1,620 feetFWL,330feetFSL. — — Elevation.—1,883 feet, derrick floor. Totaldepth. 15,673 feet. Completed. 1956. —— Topof Paleozoic rocks. 870 feet. Elevation of Paleozoic rocks. -f-1,013 feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Goldstein (1957) reported the following stratigraphic information: top of Strawn, 12,310 feet; top of Atoka, 12,440 feet; top of Devonian, 13,000 feet; top ofFusselman, 13,260 feet; top of Montoya, 13,380 feet; top of Simpson, 13,500 feet; top of Ellenburger, 14,121 feet. Montgomery (1958) noted top of Permian at 870 feet; total depth at 15,673 feet. This wellpenetrated foreland basin rocks north of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1957;Porter Montgomery, Pan American Petroleum Corporation, 1958. — County. Val Verde. — Well name. Transcontinental OilCompany (Ohio) No. 1W. S. Stephenson (Stevenson). Location.—Section8,block4,I&GNsurvey; 300feetFEL,3,250 feetFSL;4mi.NofDelRio. — —— Elevation. 1,065 feet. Totaldepth. 4,412 feet. Completed. 1927. Top of metamorphic r0ck5.— 2,423 feet. Elevation of metamorphic rocks. 1,358 feet. — Thin section coverage (depth in feet). shell oilcompany: 3815, 4050-4150, 4330. pan American petroleum corporation: 2406-08, 2450-55 (2), 2491-95, 2676-82, 2688-95, 2703-15, 2760-68, 2775-82, 2938-46, 2960-70, 2994-3002, 3106-12 (2),3123-31, 3131-39, 3224-32 3262-70, 3328 33, 3338-43, 3373-78, 3845-50, 3950, 4050-4150. rureau of economic geology: 2420-23, 242633 (2), 2455-60, 2472-75, 2521-25, 2532-38, 2592-98, 2670-82, 2675-82, 2702-09, 2715-22, 2729-35 (2), 2733-60, 2782-90, 2833-38 (2), 2846-54, 3232-40, 3317-23, 3390-96 (2), 340410 (2), 3500-08, 3596, 3605 (2), 3695-3725 (3), 3725-75, 4050-4150, 4340-45, 4348-83 (3), 4404-07 (3). Description of metamorphic rocks—Kleihege (1949) placed base of Cretaceous at 2,408 feet and described the sequence as follows: 2,425 to 2,615 feet, metamorphosed shaly limestone grading down ward into glossy slaty marble; 2,615 to 2,642 feet, whitemarble; 2,670 to2,800 feet, partly recrystallizedwhite, pink, and red limestone, locally sericitic; 2,800 to 2,855 feet, alternating white and red glossy marble; 2,855 to 2,890 feet, white and red partly recrystallized marble; 2,890 to 3,300 feet, white, gray, and red marble; 3,380 to 3,405 feet, glossy slaty crystalline limestone showing cataclastic structure; 3,485 to 3,575 feet, white crystalline limestone; 3,575 to 3,835 feet, slaty gray crystalline limestone containing olive-green phyllitic slate beds; 3,650 feet, unmetamorphosed limestone with stringers of slaty shale; 3,730 feet, partly recrystallized limestone showing cataclastic structures; 3,820 feet, slaty limestone; 3,835 to 4,150 feet, black fine-textured slaty shale containing a few white calcite veinlets; 4,160 to 4,415 feet, white marble. Goldstein (1955) reported base ofCretaceous and top ofPaleozoic at 2,430 feet. Petrographic study shows that most of the rocks in the sequence are fine-grained (aphanitic) rudely foliated quartzose dolomitic calcite marble containing streaks and layers of graphitic and/orsericitic rock. Metamorphism is low grade with a very strong shearing element; foliation is expressed in dimensional orientation of stretched grains, oriented sericite fibers, and graphitic streaks. This wellpenetrated metamorphic rocks inthe interior zone of the Ouachita belt. — X-ray data. None. The Ouachita System Kleihege (1948, p. 46). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau of Economic Geology Well Sample Library. References.— — County. Val Verde. — Wellname. D.Henry Werblow and Associates No.1Maude S. Newton. Location.—Section10,block4,I&GNsurvey; 660feetFNL,660feetFWL;4mi.NWofDelRio. —— Elevation.-1,126 feet. Totaldepth.-—-7,337 feet. Completed. 1955. — Top of metamorphic rocks. 2,660 feet. Elevation ofmetamorphic rocks. 1,534 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2600-10, 2700-10, 2800-10, 2900-10, 3000-10, 3100-10, 3200-10, 3300-10, 3400-10, 3500-10, 3600-10, 3700-10, 3800-10, 3900-10, 4000-10, 4100-10, 4200-10, 4300-10, 4400-10, 4500-10, 4600-10, 4700-10, 4800-10 (2), 4900-10, 5000-10, 5100-10, 5200-10, 5300-10, 5400-10, 5500-10, 5600-10, 5700-10, 5800-10, 5900-10, 6000-10, 6100-10, 6200-10, 6290-00, 6390-00, 6490-00, 6590-00 (2), 6690-00, 6790-00, 6890-00, 7000-10, 7090-00, 7190-00, 7290-00, 7295-00. — Description of metamorphic rocks. The pre-Cretaceous sequence in this well is composed of fine- grained calcite marble (grading into dolomiticcalcite marble and dolomite marble toward the bottom of the well), fine-grained metaquartzite, and sericite phyllite; the major rock types grade into each other; for example, the metaquartzite is commonly calcareous and sericitic, the marble contains sericite, and the phyllite is calcareous and quartzose. Graphite and hematite are commonly present in streaks or layers or as finely disseminated particles; some of the marbles contain small amounts of albite. The metaquartzite is uniformly very fine-grained and originally may have been chert. Metamorphism is low grade with a very high shearing element. Calcite marble is extensively twinned and the grains are stretched and deformed; metaquartzite grains are stretched; phyllite is excessively sheared and mica is "drawn out." Foliation is expressed in orientation of mica, stretched calcite, and quartz grains. The similarity of lithology over an interval of more than 4,500 feet suggests that the wellmay have penetrated steeply dipping beds; this is confirmed by the excessive hole deviation which occurred during drilling. The sequence in this well has been called Ellenburger by some geologists (Stiles et al., 1955), probably because of the electric log characteristics of the dolomite marble section. The rocks are completely metamorphosed and are inno sense Ellenburger as the term is normally used. The well penetrated metamorphic rocks in the interior zone of the Ouachita belt. The section is very similar to that penetrated inTranscontinental No.1Stephenson. = X-raydata.—l>>X;10/7 <—12;F24?;SR=6.4 (range from4to12). References.— Stiles et al. (1955). Personal communication: J. R. Sandidge, Magnolia Petroleum Company, 1955; W. N. Tindell, Mayfair Minerals, Incorporated, 1955. — County. Val Verde. — Well name. Western Natural Gas No. 1Bassett. Location.—Section 5,block 195, TCRR survey; 660 feetFNL,467 feetFEL. — Elevation.—l,BB3feet. Totaldepth.—4,Bl9feet. Completed. 1953. — — TopofPaleozoic rocks. 990 feet. Elevation ofPaleozoic rocks. +893 feet. — Thinsection coverage (depth infeet). None. Description of Paleozoic rocks.—Reported as upper Paleozoic limestone and clastic rocks of fore- land facies. This wellis north ofthe Ouachita front. — X-ray data. None. — References. Personal communication :J. P. Olson, Shell OilCompany, 1959. — County. Val Verde. Well name.—E. T. WilliamsDrillingCompany No.1W. T. 0.Holman et al. Location.—Section 5,blockN,GH&SAsurvey; 200feetFNL,500 feetFWL;10mi.Wand11mi.N of Del Rio. Elevation.—l,293 feet. Totaldepth.—3,oos feet. Completed.—l92l(?);1927(?). — Top of metamorphic rocks. 2,110 (?) feet. Elevation of metamorphic rocks. 817(?) feet. — Thin section coverage (depth infeet). bureau of economic geology: 3005. Description of metamorphic rocks.— Sellards (1933) noted hard black shale and calcite. The drill er's login the Bureau of Economic Geology files reports metamorphism from 2,520 to 2,935 feet. The Bureau ofEconomic Geology, The University of Texas base of Cretaceous in this wellis in doubt. Kleihege (1949) presented the following description: 2,110 to 2,115 feet, soft gray blocky shales and alternating beds of sandstone; 2,215 to 2,355 feet, mostlylimestone; 2,350 to 2,410 feet, slightly indurated black shale; 2,600 feet, black slate containing traces ofmilkyquartzandwhitecalcite;2,945 feet,blackphylliticslate withwhitecalciteveinlets. The single sample available for petrographic study is fine-grained graphitic quartzose dolomitic calcite marble. Metamorphism is low grade with a high shearing element; structures are twinning, grain stretching, and deformation. At least the lower part of the well penetrated metamorphic rocks in the interior zone of the Ouachita belt. The section from 2,110 to 2,600 feet described by Kleihege is apparently unmetamorphosed, andits relation to themetamorphic rocks isnot clear. — X-ray data. None. References.— Kleihege (1948, p. 42) ;Sellards (1933, p. 191). Bureau of Economic Geology files. Personal communication :E. A. Vogler, Shell OilCompany, 1955. Samples are inBureau of Economic Geology Well Sample Library. — County. Williamson. — Wellname. Anderson No.1Teichelman. Location.—A.Jettsurvey; 700feetFNL,150feetFWL;6mi.NofTaylor. Elevation.— 622 feet. Total depth.— 3,49B feet. Completed.— l93B. — Top of Paleozoic rocks. 2,848 feet. Elevation of Paleozoic rocks. 2,226 feet. — Thin section coverage (depth in feet). bureau of economic geology: 3030-40, 3130-40, 3310-20, 3456-66, 3486-98. — Description of Paleozoic rocks. Goldstein (1955) reported base of Travis Peak and top of Paleo — zoic (Pennsylvanian ) at 2,848 feet; total depth 3,498 feet, in Pennsylvanian Ouachita facies. Petrographic study shows a sequence of dark dolomitic micaceous low-rank metasiltstone and sericite-chlorite clay-slate; the rocks are veined withquartz and bituminous material. Metamorphism isveryweak;structures areincipientfoliationandslaty cleavage. This well penetrated incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-ray data. None. References.— Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County. Williamson. — Wellname. Burnette No.1D.C. Reed. — Location. E. Leichtle League; 5,450 feet FSEL, 1,500 feet FSWL; 5 mi. SE of Bertram on County line. — — Elevation.—1,158 feet. Totaldepth. 1,155 feet. Completed. 1939. — Top of Paleozoic rocks.—ni. Elevation of Paleozoic rocks.-ni. — Thin section coverage (depth in feet). bureau of economic geology: 860, 930, 1000 (2). — Description of Paleozoic rocks. According to Goldstein (1955), this well was in Paleozoic rocks at 780 feet and the last sample at 1,040 feet was also in Paleozoic rocks; he interpreted the sequence as probably foreland facies. The rocks are brown silty shale, olive-green shale veined with fine silica, argillaceous micaceous siltstone, and fine-grained, subangular to subround, poorly sorted, argillaceous calcareous quartz sandstone. The quartz appears to be mixed foreland and structural belt type. This wellis tentatively considered to have penetrated foreland rocks (probably Atoka beds) very close toorwithinthemarginofthestructuralbelt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. — County.-Williamson. — Wellname. S.L.Carpenter No.1S.J.Seward. — Location. James Roebuck survey; 340 feet FSEL, 100 feet FNEL; 5^ mi. W of Schwertner. Elevation.— B93 feet. Total depth—l,Bl6(?), 2,023 (? ) feet. Completed.— l94B. Top of Paleozoic rocks.—1,630 feet. Elevation of Paleozoic rocks. 737 feet. The Ouachita System — Thin section coverage (depth in feet). bureau of economic geology: 1670-80 (2), 1790-96, 180305 (2), 1888-90 (2), 1897-00 (2), 1908-12, 1920-22, 1935-38, 1966-68 (2), 2006-08 (2). — Description of Paleozoic rocks. Goldstein (1958) from a study of the above suite of thin sections made the following tentative identifications: 1,670 to 1,796 feet, Stanley; 1,803 to 1,922 feet, Arkansas novaculite; 1,966 to 2,008 feet, Missouri Mountain and/or Blaylock formations. The sequence penetrated in this well consists of (1) dark gray-green clay-slate, locally pyritic, commonly brecciated and deformed, and dark angular carbonaceous chloritic micaceous low-rank quartz metasiltstone, locally slightly dolomitic; (2) light to dark microgranular to cryptocrystalline to chalcedonic chert, sparsely dolomitic, locally with streaks and patches of dark organic material, locally containing scattered spicules, commonly brecciated, and dark spore-bearing siliceous shale containing dark organic matter; and (3) fine-grained, angular, low-rank quartz metasiltstone, locally pyritic, and dark deformed and brecciated chloritic and pyritic clay-slate. The rocks are cut by veinlets of quartz, carbonate, chlorite, and bituminous material. Metamorphism is very weak. These rocks are Ouachita facies rocks of lower Paleozoic age, possibly overlain by very weakly metamorphosed Stanley beds. The wellmarks the easternmost occurrence of the pre-Stanley chert sequence in the central Texas area, and the cherts are associated with dark carbonaceous micaceous chloritic dolomitic metasiltstone and dark clay-slate similar to that found to the east in the belt ofdarkclasticrocks(PI.2).Possiblythiswellpenetrated atransition zoneandthedarkclasticrocks are a nearer-source facies of the lower Paleozoic Ouachita facies known inoutcrops. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Bell Oil and Gas Company, 1958; Porter Montgomery, Pan American Petroleum Corporation, 1957. — County. Williamson. — Well name. Carr (Hewitt and Dougherty) No. 1Maggie Mather. Location.—N. Campbell survey; 660 feet FSEL, 3,500 feet FNEL; 6 mi. Nof Liberty Hill. —— — Elevation. 993 feet. Total depth. 7,545 feet. Completed. 1951. —— Top of Paleozoic rocks.-780 feet. Elevation of Paleozoic rocks. -j-213 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1100-10, 2316-17, 4880-90 (2), 6980-90 (2), 7530-40. — Description of Paleozoic rocks. This well penetrated a sequence of dark shale, locally sandy and silty, and fine-grained, angular to subround, poorly sorted, argillaceous feldspathic quartz sandstone; the sandstones commonly contain abundant angular garnet inthe heavy mineral fraction. Calcite veins are common;finesiliceous veinlets are present insome ofthe shales. This sequence is Stanley shale. The wellpenetrated the frontal zone of the Ouachita structural belt near the northwestern margin. —= X-raydata.—l> Ch>ML>X;10/7 v0.5;F 20;SR=1.65. — Samples References. are inBureau ofEconomic Geology WellSample Library. — County. Williamson. Wellname.—Donnellyetal.No.2Conway (alsoknownasNo.1Conway). — Location.-Burleson survey; 7 mi. SW of Liberty Hill(also given as Burleson League at Hopewell, 1mi. E of Burnet County line, 7 mi. SW of Liberty Hill). — — Elevation. 950 feet (from topographic map). Total depth.—1,133 feet. Completed. Before 1930. — — Top ofPaleozoic rocks. 695 feet. Elevation ofPaleozoic rocks. -{-255 feet. — Thin section coverage (depth in feet). bureau of economic geology: 695, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 867, 880, 890 (3), 900, 920 (2), 930, 940, 950, 970 (2), 980, 962-1000 (3), 990, 1000 (2), 1010 (3), 1020, 1030 (2), 1040, 1050, 1060, 1070 (2), 1080. — Description of Paleozoic rocks. Sellards (1931b) reported siliceous limestone and black shale and quoted Miser as having identified the rocks as Bigfork chert. Goldstein (1955) noted Paleozoic rocks of probable Ouachita facies from 700 to 1,080 feet (last sample) ;he remarked that the sediments differfromOuachita Mountainlithology,buttheyarebrecciated andveinedwithquartz. Petrographic study shows fine-grained calcareous argillaceous silty dolomite and dolomitic limestone with lesser amounts of dolomitic chert and glauconitic spiculitic limestone; beds of sandy and silty shale, and fine-grained, angular to subround, fairly well-sorted, argillaceous slightly feldspathic quartz sandstone are more common toward the bottom of the section. Quartz and calcite veinlets are common; garnet is present inthe heavy mineral suite of the sandstone. This sequence seems to have no counterpart either in foreland rocks or in Ouachita facies beds within the structural belt. The presence of extensive veining and the deformed and brecciated condition of some of the rocks indicate that the sequence is probably within the structural belt. The Bureau of Economic Geology, The University of Texas wellis located near other wells interpreted to have penetrated foreland basin rocks close to or within themarginofthestructural belt.IfMiseriscorrectinhisidentificationofBigfork,itisprobable that there is frontal thrusting in this area; the writer believes that these rocks are of foreland or transitional facies, possibly Atoka or older. — X-ray data. None. References.— Sellards (1930a, p. 83; 1931b, p. 827). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Williamson. Wellname.—Georgetown City Water Well. — Location. City of Georgetown Tract; near I&GNdepot. —— Elevation. 750± feet. Total depth. 1,820 feet. Completed.— l9l4. — TopofPaleozoic rocks. 1,260± feet. ElevationofPaleozoic rocks. 510± feet. — Thinsection coverage (depth infeet). bureau of economic geology: 1700, 1820 (3). — Description of Paleozoic rocks. Udden (1919) discussed this well and made a number of observations: 1,280 feet, red shale or slate cut by quartz veins; 1,340 feet, dark gray indurated micaceous slaty shale; between 1,300 and 1,800 feet, black schistose shale. Udden remarked that six samples taken between 1,280 and 1,820 feet are highly fissured material bordering between schist and shale, slickensided, and cut by quartz veins; he concluded that the rocks are Precambrian. Sellards (1931b) described the rock as schistose shale. Two samples studied are chloritic micaceous low-rank metasiltstone, slaty, low-rank to high- rank metasandstone, and silty metashale; the rocks are invaded by quartz-chlorite-dolomite veins. The variabilityofmetamorphism (rangingfromincipienttoweak)suggests thattherockshave beenlocally altered by metasomatic-hydrothermal effects of the vein-forming solutions. This wellpenetrated dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. X-raydata.—l> Ch;10/7 5;F=20;SR — 4.2. References— Sellards (1930a,p.86;1931b, p. 823);Udden (1919, pp.125-126). Samples are inBureau of Economic Geology Well Sample Library. — County. Williamson. — Well name. W. E. Green (Reeves) No. 1Lehman. — Location. Elisha Davis survey;W/% mi.NofJarrell. — —— Elevation. 786 feet. Totaldepth. 3,064 feet. Completed. 1950. — Top of Paleozoic rocks. 1,350±(?) feet. Elevation of Paleozoic rocks. 564±(?) feet. — Thin section coverage (depth in feet). bureau of economic geology: 1450-60, 1650-60, 2050-60, 2470-80, 2680-90, 2750-60, 2980-90 (2). — Description of Paleozoic rocks. The Paleozoic sequence is composed of fine-grained, mostly angular to subround, poorly sorted, micaceous-chloritic-argillaceous feldspathic quartz sandstone containing abundant angular garnet in the heavy mineral fraction (Stanley lithology) overlying a sequence of dark gray-green, pyritic, variably siliceous sporadically radiolarian-bearing shale, and dark argillaceous chert and siliceous shale rich in dark organic matter, commonly veined with quartz, calcite, and/or bituminous material (pre-Stanley Ouachita facies, probably Arkansas novaculite or Bigfork). There is no metamorphism ;structures are fracturing, brecciation, and veining. This well penetrated Stanley and pre-Stanley Ouachita facies rocks in the frontal zone of the Ouachita belt. — X-ray data. None. — Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. References. Samples are inBureau ofEconomic Geology WellSample Library. — County. Williamson. — Wellname. LoisHenna etal.No.1(2?) Alsabrook (Alsterbrook?). — Location. D.Curry survey; 2mi.NofRound Rock. Elevation.— -759 feet. Total depth.— 2,333 feet. Completed.— l94B. — Top of Paleozoic rocks. 1,520 feet. Elevation ofPaleozoic rocks. 761 feet. Thin section coverage (depth in feet).—bureau of economic geology: 1790-1800, 2300-2330, depth unknown (2). The Ouachita System — Description of Paleozoic rocks. H. J. Plummer (Bur. Econ. Geol. files) reported dark fissile shale — and black finely crystalline limestone Marble Falls(?). The samples examined are very dark carbonaceous silty metashale and clay-slate veined by quartz and quartz-bitumen. Metamorphism is incipient to very weak. This wellpenetrated incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — X-ray data. None. — References. Bureau ofEconomic Geology files. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. Samples are inBureau of Economic Geology Well Sample Library. — County. Williamson. — Wellname. Hewittand Dougherty No.1Pearson. Location—W.H.McGillsurvey; 1,400 feetFmostSlySEL,1,980 feetFSWL;5mi.NofLibertyHill. Elevation.—l,oB7 feet. Totaldepth.— 9,lo4 feet. Completed.— l9s4 (?). —— -{-232 feet. TopofPaleozoic rocks. 855feet. ElevationofPaleozoic rocks. — Thin section coverage (depth in feet). bureau of economic geology: 970-80 (2), 1170-80 (2), 2500-10,4100-10 (2), 5900-10 (2), 8200-10. — Description of Paleozoic rocks. The sequence is composed of dark, fine-grained, subangular to sub- round, poorly sorted, argillaceous feldspathic quartz sandstone, locally calcareous and locally con taining angular garnet, and dark gray locally sandy and silty shale. The shales are brecciated. The sandstones show some resemblance to Stanley sandstones, but they are locally calcareous andappear tobebetterrounded.Thesequence iseitherStanleyorAtoka. Thewelliswithinthenorthwestboundary ofthestructuralbelt. X-ray data.—l>Ch>ML>X; 10/7 1.6; Fr=2o; SR=2.1. Presence of kaolinite suggests Atoka. — References. Samples areinBureau ofEconomic Geology WellSample Library. — County. Williamson. Wellname.— W. M.Jarrell No. IC.N. Avery, Jr. — Location. E.Ryan survey;2mi.EofHutto. —— — Elevation. 646 feet. Total depth. 2,953 feet. Completed. 1950. — Topof Paleozoic rocks. 2,680 feet. Elevation of Paleozoic rocks. 2,034 feet. — Thin section coverage (depth in feet). bureau of economic geology: 2700-10, 2800-10, 2900 10 (2). — Description of Paleozoic rocks. The pre-Cretaceous sequence is composed of dark, fine-grained, angular, dolomite carbonaceous micaceous chloritic quartz metasiltstone (mostly lowrank) and black carbonaceous or graphitic metashale or clay-slate; the rocks are veined with quartz-chlorite. Meta morphism ranges from incipient to weak; shales show incipient foliation, but there is no strong shearing element. This wellpenetrated incipiently to weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. — = X-ray data.—l> Ch; 10/7 0.7; F 20. — References. Samples are inBureau ofEconomic Geology Well Sample Library. — County. Williamson. — Wellname. SolKopelNo.1Ragsdale (Saver). — Location. T.W.Medcalfsurvey;6%mi.NEofLibertyHill. — — Elevation. 960 feet, derrick floor; 959 feet, ground. Total depth.—1,620 feet. Completed. 1951. InPaleozoic rocks at 850 feet. Elevation ofPaleozoic rocks.— > +110 feet. — Thin section coverage (depth in feet). bureau of economic geology: 850-65, 928-86, 998-1004, 1049-53, 1126-35, 1200-06. — Description of Paleozoic rocks. The Paleozoic sequence in this wellis composed of dark locally pyritic siliceous (?) shale or metashale containing dark organic material and extensively veined with quartz, calcite, and bituminous material (less commonly veined with chlorite), overlying fine-grained, mostly angular, poorly sorted, argillaceous micaceous feldspathic quartz sandstone which locally con Bureau of Economic Geology, The University of Texas tains angular garnet inthe heavy mineral fraction and which also is veined by quartz and calcite. Metamorphism ranges fromnone to incipient;shales show localbrecciation. The first two samples (above) are altered (sericitized and chloritized) olivine gabbro similar to Balcones Cretaceous-Tertiary intrusive igneous rocks; possibly these gabbroic rocks are emplaced in the overlying Cretaceous section but possibly they also intrude Paleozoic rocks in this well. There may be localcontact metamorphism. The upper dark siliceous(?) shale section is probably part of the Stanley; the sandstones below are typical Stanley. This well penetrated Stanley shale in the frontal zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Porter Montgomery, Pan American Petroleum Corporation, 1957. Samples are inBureau ofEconomic Geology WellSample Library. — County. Williamson. Wellname.—R.C. Millerand R.V.MayfieldNo. 1Miller(Fee). — Location. Malone survey;3mi.EofLibertyHill. — — Elevation. 1,000 feet (from topographic map). Total depth.—1,910 feet. Completed. 1926. — — Topof Paleozoic rocks. 858 feet. Elevation of Paleozoic rocks. +142 feet. — Thin section coverage (depth in feet). bureau of economic geology: 867-72, 908-16, 967-1000, 1830 (3), depth unknown (5). — Description of Paleozoic rocks. Sellards (1931b) reported top of Paleozoic black shale at 696± feet and concluded that itis probably Stanley-Jackfork. Barnes (in Sellards, 1933) noted that "metamorphism is very slight" and said that the rock is "littlemore than a shale." Goldstein (1955) — reported top of Paleozoic at 858 feet and identified the rocks as Pennsylvanian Ouachita facies(?). Petrographic study shows that the sequence is composed of dark sandy and silty shale, micaceous feldspathic siltstone, and fine-grained, mostly angular, poorly sorted, argillaceous, micaceous, and chloritic feldspathic quartz sandstone; profuse veinlets of quartz, calcite, and bituminous material transect the rocks, and plant fragments are abundant. Locally the presence of new chlorite indicates incipient metamorphism. Most of the quartz and feldspar grains are very angular, but there are occasional round grains (foreland source?).Garnet and authigenic tourmaline are present inthe heavy mineral fraction of the sandstones. The sequence is Stanley shale. This wellpenetrated the frontalzone of the Ouachita belt. — — X-raydata.I>Ch]>ML;10/7' .0.6;F=20.Thesamplefrom1,830feetshowsasmallamount of mixed-layer illite-montmorillonite, which indicates foreland tendencies. References.— Sellards (1931b, pp. 823, 826; 1933, p. 135). Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples areinBureau ofEconomic Geology WellSample Library. — County. Williamson. — Wellname. PalmValleyOilCompany (RoundRockOilCompany?) No.1Walsh. — Location. Dillardsurvey; 5% mi. W of Round Rock. —— Elevation.— B39 feet (by aneroid barometer). Total depth. 1,230 feet. Completed. 1915. — Top of Paleozoic rocks. 1,230± feet. Elevation of Paleozoic rocks. 391± feet. — Thinsection coverage (depth infeet). None. — Description of Paleozoic rocks. Sellards (1931b) described the Paleozoic rock as "novaculite." Thelocationofthiswellandrockspenetrated innearby wellssuggest thatitpenetrated incipientlyto very weakly metamorphosed dark clastic rocks, but Sellards' lithologic description indicates that it encountered pre-Stanley rocks ofOuachita facies (PI.2).No samples orother published orunpublished descriptions areavailable.Possibly thesituationissimilartothatinNo.1Sewardtothenortheast (p. 332) which may have penetrated a transitional zone between siliceous rocks and dark clastic rocks. — X-ray data. None. References.— Sellards (1931b, p. 823; 1933, p. 192). — County. Williamson. — Well name. OrvilleH.Parker (Parker Petroleum Company, Incorporated) No. 1-A Pearson. — Location. J. Shelton survey ;4>l/2 mi. Wof Round Rock. —— Elevation. 900 ± feet. Total depth. 6,510 feet. Completed.—1956. The Ouachita System — Top of Paleozoic rocks. 1,430 feet. Elevation of Paleozoic rocks. 530 feet. — Thin section coverage (depth in feet). bureau of economic geology: 1440-50, 1450-60 (2), 2090-3000 (3), 3000-10 (3), 3170, 3650-60 (3), 4090-4100 (3), 4565-75 (3), 5990-6000 (3), 6490-6500 (2). — Description of Paleozoic rocks. The sequence is composed of: (1) dark, locally silty, metashale or clay-slate which in some intervals is pyritic and/or dolomitic; contortion and brecciation are com mon and quartz veins are abundant; (2) fine-grained pyritic micaceous low-rank metasiltstone veined withquartz, commonly sandy; and (3) fine-grained, angular, poorly sorted, silty micaceous feldspathic quartz low-rank metasandstone (locally graywacke) veined with quartz; rock fragments, mostly phyllite and metaquartzite, are abundant in some intervals. Dark fine-grained pyritic dolomite occurs in the 4,090 to 4,100-foot interval. Metamorphism is incipient to very weak; structures are incipient foliation, brecciation, and contortion. This well penetrated incipiently to very weakly metamorphosed dark clastic rocks in the interior part of the frontal zone of the Ouachita belt. X-ray data.—l>Ch; 10/7-^1.8; F=20; SR=2.6. Shales are composed of well-crystallized illite-chloriteof Ouachita type. — References. Personal communication: M.W. Eddleman, Parker Petroleum Company, Incorporated, 1956; A.P.Werner, 1956. — County. Williamson. — Wellname. Jesse Russell No.1A.B.McGill. Location.—T.F.Gray survey; 4,445 feetFEL,6,775 feet FSL. —— Elevation. 1,118 feet, derrick floor. Total depth. —4,331 feet. Completed. ni. — — Top ofPaleozoic rocks. 695 feet. Elevation ofPaleozoic rocks. +423 feet. — Thin section coverage felepth infeet). bureau of economic geology: 713-20 (2), 828-35, 1238-44, 1406-15, 1816-25 (2),2431-40, 2440-45, 2651-60, 3500-10, 4300-05. — Description of Paleozoic rocks. Goldstein (1955) reported first sample in Pennsylvanian at 1,472 feet; top of Smithwick, 2,400(?) feet; total depth 4,331 feet, in Smithwick. The sequence is composed of dark silty shale, argillaceous micaceous siltstone, and fine-to coarse- grained, mostly fairly well-sorted, slightly argillaceous and micaceous calcareous to dolomitic quartzsandstone, locally slightly feldspathic; rock fragments (chert, shale, siltstone, stretched quartzmosaic, and phyllite) are present in the sandstones in some intervals. There is no metamorphism. The sequence is Atoka. This wellpenetrated foreland rocks close to and possibly within the margin of the Ouachita belt. — X-ray data. None. — References. Personal communication: August Goldstein, Jr., Pan American Petroleum Corporation, 1955. Samples are inBureau ofEconomic Geology WellSample Library. — County. Williamson. — Wellname. ShellOilCompany (and SinclairOiland Gas Company) No.1Purcell. Location—lff.H.McGillsurvey; 1,196 feetFWLofMcGillsurvey,1,196 feetFSLofPurcell Tract; 18mi.NWof Georgetown. —— — Elevation. 1,074 feet, derrick floor; 1,060 feet, ground. Total depth. 9,485 feet. Completed. 1954. — — TopofPaleozoic rocks. 720 feet. ElevationofPaleozoic rocks. +354 feet. — Thinsection coverage (depthinfeet). bureau ofeconomic geology: 820-30, 1320-30, 2050-60 (2), 2380-90, 3300-10, 5500-10, 6320-30, 6490-00, 6530-40, 6760-70 (2), 6920-30, 9387-97. shell oilcompany: 8237, 9389-90, 9396-97, 9475-79 (2). — Description of Paleozoic rocks. The following stratigraphic data are reported for this well: top of Atoka, 720 feet; top of Marble Falls—Barnett, 6,900 ± feet; top of Ellenburger (Honeycut), 6,940 feet; top of Gorman, 7,775 feet; top of Tanyard, 8,290 feet; top of glauconite-bearing rocks, 8,810 feet; top of San Saba, 8,960 feet; top of Point Peak, 9,380 feet; top of Morgan Creek, 9,400 feet; top of granite gneiss, 9,470 feet. Identifications from top of Ellenburger to total depth are by Barnes (1956), who noted that the Ordovician beds are normal foreland shelf facies. The Precambrian granite gneiss in this well resembles the Town Mountain granite of the Llano uplift area; this wellis the farthest southeast penetration of the Precambrian basement of the Texas craton (Flawn, 1956). The Atoka sequence is dark silty shale, locally micaceous, and/or carbonaceous, and fine-grained mostly subangular, poorly to fairly well-sorted, slightly argillaceous to slightly calcareous quartz Bureau ofEconomic Geology, The University of Texas — sandstone, locally slightly feldspathic. There is no metamorphism. Marble Falls Barnett rocks are dark calcareous shales containing abundant siliceous and calcareous spicules. This wellpenetrated foreland rocks close to or withinthe margin of the Ouachita belt. X-raydata.—l>Ch>ML>K(?);10/7 1.0;F=20; SR=1.9. References.— Barnes (1959, p. 674);Flawn (1956, pp. 30, 202-203). Personal communication:V.E.Barnes,BureauofEconomicGeology,1956;R.P.Maner,ShellOil Company, 1958. Samples are inBureau of Economic Geology Well Sample Library. — County. Wilson. — Wellname. Quintana Petroleum Corporation No.1-AA.L.Moore. Location.-—D. O. Warren League; 1,100 feet FNWL, 1,200 feet FSWL; 4 mi. SW of Dewville. — —— Elevation. 432 feet. Total depth. 9,177 feet. Completed. 1945. — Top of metamorphic rocks. 9,168 feet. Elevation of metamorphic rocks. 8,736 feet. — Thinsection coverage (idepth infeet). bureau ofeconomic geology: 7172-76, 9168-72. — Description of metamorphic rocks. The samples are hematitic chlorite-sericite phyllite and phyllitic metaquartzite containing small garnet crystals and larger octahedral non-magnetic porphyroblasts of brookite(?),octahedrite(?);quartz veins are common. Metamorphism is low to medium grade; foliation is welldeveloped. This well penetrated metamorphic rocks in the interior zone of the Ouachita belt. It provides the southernmost control point formapping. X-ray data.—None. References.— Goldstein and Reno (1952, p. 2289). — County. Zavala. — Well name. Park and Phillips No. 1Flowers and Ward Ranch. Location.—Section 20, block1,I&GNsurvey; 660feetFNL,1,980 feetFEL;16mi.SWofUvalde. —— Elevation. 826 feet. Total depth.—7,290 feet. Completed. 1955. — Topof metamorphic rocks. 7,240 feet. Elevation of metamorphic rocks. 6,414 feet. — Thinsection coverage (depth infeet). shell oilcompany: 7256. — Description of metamorphic rocks. The single sample examined is very fine-grained amphiboleepidote schist. Metamorphism is low grade with a high shearing element; structures are foliation and microfaulting. The original rock may have been a basaltic igneous rock. This wellpenetrated metamorphic rocks in the interior zone of the Ouachita belt and is one of the southernmost control points for mapping. — X-ray data. None. — References. Bureau ofEconomic Geology files. Part 2. Summary Reports on Selected Wells Penetrating Rocks of the Ouachita Belt and Adjacent Foreland in Oklahoma and Mexico August Goldstein, Jr., and Peter T. Flawn Information on the following wells was compiled from many different sources. The bulk of the basic well data and stratigraphic data are from files of operating companies and State orFederal agencies. The petrographic data are original;allpetrographic determinations made on samples from Oklahoma wells are by August Goldstein, Jr. X-ray determinations weremade byC.E.Weaver. The symbol nimeans that no information was available. OKLAHOMA — County. Bryan. Wellname.— Atlantic Refining Company No. 1Brown. Location.—Section 16, township BS, range 8E; NW/4, NW/4, SE/4. —— — Elevation. 661 feet. Total depth. 6,676 feet. Completed. 1950. — Top ofPaleozoic rocks. 1,590 feet. Elevation of Paleozoic rocks. 929 feet. — Thin section coverage (depth in feet). pan American petroleum corporation: 1600, 1610, 1735, 1815, 2055, 2272-77, 2294-2300, 2345, 2595, 2870, 2915, 3195, 3235, 3345, 3575, 3655, 3745, 4095, 4155, 4165, 4195, 4215, 4275, 4305, 4485, 4692, 4745, 4785, 4850, 4880, 4995, 5045, 5145, 5200, 5375, 5470, 5635, 5710, 5825. — Description of Paleozoic rocks. Top of Stanley was encountered at 1,590 feet and the wellbottomed in Stanley at 6,676 feet. The sequence is composed of (1) fine-grained, angular to round (mostly angular), poorly to very poorly sorted, argillaceous chloritic micaceous feldspathic quartz sandstone (and siltstone), commonly containing fragments of chert and quartz mosaic, locally calcareous, carbonaceous, or siliceous, locally containing abundant detrital garnet; the feldspar includes both plagioclase and potassium feldspar; (2) dark silty shale and metashale (locally clay-slate), locallychloritic, calcareous, carbonaceous, and pyritic; (3) between the intervals 3,195 and 4,215 feet, the samples contain fragments of fine-grained argillaceous tuff, partly to completely devitrified, locally chloritic; and (4) locally the sequence contains carbonate rock, fine-grained pelletiferous limestone in the interval 2,294 to 2,300 feet, and glauconitic silty limestone and cone-in-cone carbonate in the interval 5,145 feet. Dark bituminous graptolitic chert and dolomitic spiculitic chert in the interval 5,635 feet may be caved material. Stanley sandstones appear to be unusually calcareous in this area. Locally the rocks show incipient to very weak metamorphism. This wellpenetrated Stanley beds in the frontal zone of the Ouachita belt southwest of the buried Arbuckle element. — X-ray data. None. — References. None. — County. Bryan. — Wellname. AtlanticRefining Company No.1State. Location.—Section 36, township 7S, range 8E; SE/4, SW/4, SW/4. —— Elevation. 664 feet. Total depth. —6,647 feet. Completed. 1945. — Top of Paleozoic rocks. 1,570 feet. Elevation of Paleozoic rocks. 906 feet. — Thin section coverage (depth infeet). pan American petroleum corporation: 1720, 1724, 1727, 1730, 1978, 2218, 2298, 2330, 2390, 2660, 2700, 2721, 2890, 2926, 3040, 3240, 3422, 3727, 3790, 3910, 4180, 4455, 4700, 4825, 4830. 4835, 4855, 4865, 4870, 4875, 4885, 4920, 5020-30, 5045, 5055, 5075, 5190-5200, 5196, 5200-10, 5210-20, 5220-30, 5230-40, 5240-50, 5270-80, 5280-90, 5290-5300, 5300, 5360-70, 5390, 5740. Description of Paleozoic rocks.—The stratigraphic sequence encountered in this well is: base of Cretaceous and top of Stanley, 1,507 feet; top of Arkansas novaculite, 4,740 feet; top of Polk Creek, 5,160 feet; top of Bigfork, 5,175 feet; top of Womble, 5,680 feet; total depth, 6,647 feet in Womble. Bureau ofEconomic Geology, The University of Texas The Stanley is composed of (1) dark silty shale and metashale, locally micaceous, chloritic, carbonaceous, siliceous, and pyritic and (2) fine-grained angular to subround, poorly sorted, argillaceous chloritic micaceous feldspathic quartz sandstone (and siltstone) commonly containingabundant fragments of chert and quartz mosaic, locally calcareous, pyritic. The Stanley appears to be unusually calcareous in this area; both potassium feldspar and plagioclase are present. Calcite and bitumen veinlets transect the rock. The Arkansas novaculite is composed of light and dark crypto crystalline to microgranular chert and siliceous shale, commonly containing radiolarians and spicules, locally silty,dolomitic, pyritic,and withabundant organic material. Veinlets ofbitumen are common. Possibly Missouri Mountain beds are present at the base of the sequence. The Polk Creek is black carbonaceous shale which grades downward into the siliceous shale and chert of the Bigfork.Bigfork rocks are (1) dark cryptocrystalline to microgranular chert and siliceous shale, commonly containingradiolarians, spicules, and graptolite fragments, commonly calcareous and dolomitic, pyritic, argillaceous, and rich in organic material; (2) dark argillaceous siliceous dolomitic limestone, commonly containing spicules, graptolites, locally bituminous, glauconitic, or pyritic. Veinlets of carbonate and bituminous material are common. The underlying Womble is composed of dark pyritic bituminous chloritic shale or metashale containing graptolites and conodonts. Locally the rocks show incipient to very weak metamorphism. This well penetrated a normal Ouachita facies sequence in the frontal zone of the Ouachita belt southwest of the buried Arbuckle element. — X-ray data. None. — References. None. — County. Bryan. — Well name. Carter OilCompany No. 1Jewel Loyd. — Location. Section 21, township 7S, range 10E; C,NW/4; 8mi. SE Durant. Elevation.— 664 feet, derrick floor. Total depth.—7,023 feet. Completed.— l9s9. —— Top ofPaleozoic rocks. ni. Elevation of Paleozoic rocks. ni. — Thin section coverage (depth in feet). bureau of economic geology: 2180-87, 2600-10, 3010-20, 3430-40, 3510-20, 3600-10, 3649, 3750-60, 3900-10, 3940-50, 3990-4000, 4040-50, 4190-4200, 4300-10, 4750-60, 4800-10, 5100-10, 5350-60, 5370-80, 5520-30, 5570-80, 5650-60, 5680-90, 6000-10, 6200-10, 6750-60, 6900-10. — Description of Paleozoic rocks. The following stratigraphic information is reported: top of Ouachita facies, 3,395 feet; top of Arkansas novaculite, 3,428 feet; top of Missouri Mountain, 3,876 feet; top of Polk Creek, 3,940 feet; top of Bigfork, 3,976 feet; top of Womble, 4,772 feet; thrust fault and top of Arkansas novaculite, 5,190 feet; top of Missouri Mountain, 5,468 feet; top ofPolk Creek, 5,556 feet; top of Bigfork, 5,590 feet; top of Womble, 6,038 feet; total depth, 7,023 feet, in Womble. Petrographic study shows the followinglithologic units (from top to bottom) :(1) very fine-grained, subangular, poorly sorted, argillaceous feldspathic quartz sandstone (graywacke) containing fragments of chert and metamorphic rocks and dark silty shale; this unit includes thin sections 2180-87 to 3010-20 and indicates that the well penetrated Ouachita facies rocks considerably higher than the "top of Ouachita facies" reported above; lithology is typical Stanley; (2) microgranular to cryptocrystalline chert, locally pyritic, bituminous, dolomitic, spiculitic, and radiolarian-bearing, commonly cut by veinlets of quartz-bitumen and calcite, and dark spiculitic siliceous shale or argillaceous chert; this unit includes thin sections 3430-40 to 3750-60; lithology is typical of the Arkansas novaculite; (3) the thin section from 3649 feet is fine-grained, sharply angular, very poorly sorted, argillaceous feldspathic quartz sandstone (graywacke) containing large grains of feldspar and fragments of granite; the matrix appears to be tuffaceous; this sample is probably caved material from overlying Stanley beds; (4) red (hematitic) and green (pyritic) silty clay-slate; the single thin section is from the interval 3900-10; the rock is identified as (5) pyritic bituminous Missouri Mountain; — argillaceous dolomitic limestone (marlstone) ;the single thin section is from the interval 3940-50 from general stratigraphic position the rock is probably Polk Creek but itcontains much more carbonate than exposed Polk Creek rocks; (6) thisunit includes thin sections 3990-4000 to 4800-10 and is composed of pyritic bituminous calcareous dolomitic cryptocrystalline to microgranular chert containing spicules, graptolite debris, and fragments of ostracod carapaces, dark bituminuous, pyritic, calcareous shale ormetashale containing spores, radiolarians, graptolites, and spicules, locallypyritized, and fossiliferous limestone, locally siliceous, bituminous, pyritic, commonly containing spicules, ostracods, and graptolites; calcite and quartz-bitumen veinlets are common, and calcite inveinlets is commonly twinned; these rocks are Bigfork; (7) a thrust or reverse fault occurs between the 4800-10 — and 5100-10-foot intervals the 5100-10 sample is fine-grained, subangular, very poorly sorted, quartz sandstone and dark shale or metashale; the lithology is characteristic of upper Paleozoic rocks (Stanley?) rather than Womble, as was reported ;(8) thin sections below 5100-10, including intervals 5350-60 to 6200-10, show a repetition of the above sequence and include Arkansas novaculite, Missouri Mountain, Polk Creek, and Bigfork lithologies; (9) thin sections from the 6750-60 and 6900-10 intervals are fine-grained, fairly well-sorted, quartz sandstone and coarse siltstone, locally micaceous, The Ouachita System and dark metashale or clay-slate;the heavy mineral suite is largely zircon, tourmaline, and leucoxene — and indicates a pre-Missouri Mountain age these rocks are probably Womble. Most of the rocks are unmetamorphosed but locally there is incipient to very weak metamorphism. The siliceous rocks are commonly fractured. Veins are most common in pre-Stanley rocks and include quartz-bitumen and calcite veins. The wellpenetrated a sequence of Ouachita facies rocks repeated by faulting in the frontal zone of the Ouachita beltimmediately southwest ofthe buried Arbuckle element. — X-ray data. None. — References. Scout report on formation tops. — County. Marshall. — Well name. Capitol HillOilCompany No. 1Williams. Location.—Section 20, township 6S, range 6E; SW/4, SW/4, NW/4. Elevation.— 77s feet. Total depth.— 7,ol3 feet. Completed.— l9s3. — TopofPaleozoicrocks. 840feet.ElevationofPaleozoicrocks. 65feet. — Thinsection coverage (depth infeet). bureau of economic geology: 960-70 (2),1400-10, 1950-60, 1980-90, 2000-10 (2), 2120-30, 2200-10, 2290-2300, 2370-80, 2440-50, 2450-60, 2490-2500, 2530-50, 2550-60, 2620-10, 2640-60, 2670-80, 2730-50, 2790-2810, 2820-30 (2), 2830-40 (2), 2850-55, 2855-60 (2), 2880-90 (3), 2915-20, 3590-95, 3630-35, 3650-85, 3725-30, 3750-55, 3900-05, 3915-20, 4340-50, 4840-90, 5070-80, 5090-5100, 5140-50, 5150-60 (2), 5170-80, 5230 40, 5240-70, 5340-50 (3), 5360-70, 5400-20, 5470-5510, 5550-60, 5600-10, 5750-60, 6390-6410, 6800-10, 7010-13. — Description of Paleozoic rocks. According to the log of Mr.Clement A. Weintz, this wellpenetrated a section of gray, finely micaceous to glassy very fine-grained sandstone and dark gray shale from about 1,095 to 2,380 feet. From 2,810 to 2,895 feet, there is a zone of dark brown chert and siliceous shale with abundant brown spores. From 2,895 to 3,000 feet, there is a zone of variable lithology, dominated by blue-green to olive-green smooth shale and argillaceous dolomite. This material passes gradationally into waxy and flaky green to dark green shale with occasional brown streaks and a few sand grains. This shale zone extends from 3,000 to 3,585 feet. At 3,585 feet the well penetrated a zone of sooty black slickensided shale underlain by dark brown brittle hard siliceous shale. This zone extends to approximately 3,750 feet. From 3,750 to 3,990 feet there are alternations of brown shale and green smooth flaky shale with a thin zone of dark brown chert at 3,900 to 3,920 feet. The well was diamond-cored from 3,990 to 4,335 feet and no samples are available. At 4,335 feet there is some dark brown siliceous shale which grades into green splintery to waxy shale with graptolites. This zone extends from 4,335 to 4,840 feet. From 4,840 to about 5,040 feet, there is another zone of dark brown siliceous shale and chert. Underlying this zone and ex tending to 5,205 feet is a group of sediments of variable lithologic character, including light-coloredcherts, dolomite, green shale, and siltstone. From 5,205 to 5,335 feet, the rocks consist of dark brown siliceous shale and chert. From 5,335 to 5,575 feet, the rocks are predominantly light-colored mottled cherts, dolomitic at places. This zone passes gradationally into dark brown siliceous shale, and chert from 5,575 to 5,700 feet. From 5,700 feet to total depth of 7,013 feet, the wellpenetrated, green to dark green waxy shales with a few sandy streaks and graptolite debris. Petrographic data are summarized as follows: The Atoka(?) formation was encountered immediately beneath the Cretaceous and extends to 2,810 feet.Itmaybedividedintotwomembers orzonesinthiswell:(1)anupper zoneoftight,micaceous, very fine-grained sandstone, siltstone, and gray shale and (2) a lower zone of dark gray shale and siliceous shale. The sandstones and shales of the upper zone are apparently unmetamor phosed and cannot be positively identified as of either "normal" facies or "frontal zone Ouachita" facies. The spiculitic siliceous shales with abundant pyrite in the lower zone are similar to siliceous shales in the Stanley-Jackfork-Atoka sequence of the Ouachita Mountains. Insofar as known to the writer, this unusual lithologic type has not been reported from Pennsylvanian sediments of the Ar- buckle Mountains. No rocks which are lithogenetic equivalents of the Wapanucka-Chickachoc (Morrow) horizon or Mississippian Caney are present in this wellunless they are represented by argillaceous sediments in thelowerpartoftheAtoka(?)from2,380 to2,810 feet. Outcrop samples of both the Bigfork and Woodford-Arkansas novaculite horizons contain dark brown, sapropelic, pyritic cherts which are lithologically similar. However, abundant graptolite debris is widespread in and typical of the Bigfork chert (Ordovician) at Black Knob Ridge. Ithas not been found in thin sections of rocks from the Woodford-Arkansas novaculite horizon (Devonian-Mississip pian). On the other hand, thin sections of the latter typically contain well-preserved spores and radiolarians. The Bigfork chert contains some radiolarians and some questionable spores, but the preservation and general appearance of the fossils is markedly different from that in the younger formations. Consequently, it is considered practicable to separate the similar cherts and siliceous shales on the basis of their microflora and microfauna, even though generic and specific identifications cannot be made. This approach was followedherein. Bureau of Economic Geology, The University of Texas The chert and siliceous shale zone from 2,810 to 2,895 feet contains abundant spores and radiolarians. Itcontains no graptolites and more closely resembles Woodford than Arkansas novaculite on the basis of lithology. The light-colored argillaceous chert and siliceous shale at 2,880 feet may represent the lithogenetic equivalent of the Pinetop chert horizon. The zone of mixed lithology from 2,895 to 3,000 feet cannot be correlated at this time, but it probably contains equivalents of some or all of the Hunton group and Sylvan of the Arbuckle MountainsortheMissouriMountainandPolkCreekoftheOuachita Mountains. The waxy to flaky green shale zone from 3,000 to 3,585 feet more closely resembles sediments of the Womble rather than Simpson ingeneral lithology. No identifiable microfossils were found in the siliceous shale zone from 3,585 to 3,750 feet. The peculiar "yellow bodies" observable in thin sections at this depth are also found in the Woodford, but this may not be significant. This zone is tentatively termed Woodford(?) on the basis of lithologic appearance alone. At 3,900 to 3,920 feet some of the cherts contain fragmentary graptolites, and itis probable that the wellisinOrdovician(?) sediments at that depth. Below the diamond cores there are graptolites in the green shales. The general appearance of this section also suggests that the rocks are closely allied to the Womble sediments. The chert and siliceous shale zone from 4,840 to 5,040 feet contains Woodford-type spores and radiolarians and are referred to that formation. The mixed group of sediments from 5,040 to 5,205 feet contains probable Silurian— and Upper Ordovician sediments tentatively referred to the Hunton-Sylvan and Missouri Mountain Polk Creek. The siliceous shale and chert zone from 5,205 to 5,335 feet contains fragmentary graptolites. Itis the lithogenetic equivalent of the Upper Bigfork at Black Knob Ridge. The chert, dolomiticchert, and siliceous dolomite zone from5,335 to 5,575 feetis probably equivalent to the lower part ofthe Bigfork at Black Knob Ridge. The green shale section from 5,700 to 7,013 feet more closely resembles Womble than Simpson. Capitol HillOil Company No. 1 Williams was drilled in a faulted area in which slices of sedi mentary rock are piled upon one another in varying thickness and at various angles of dip. The most nearly complete sedimentary sequence is that from 4,840 feet to total depth of 7,013 feet in which the various formations from Woodford (Devonian-Mississippian) to Womble (Ordovician) are apparently present innormal sequence and inmore or less normal thickness. The lithology and petrographic character of these rocks from this well are neither strictly of normal facies nor strictly of Ouachita facies. It must be presumed that the sediments encountered were laid down in the frontal zone of the Ouachita Mountains distal to the axis of the downwarping, between the geosyncline and the foreland. Inthe Black Knob Ridge area itmay be that sedimentary rocks equivalent to those in Capitol HillNo. 1Williams are in the faulted zone between the Ti Valley and Choctaw faults, although those rocks which are older than Middle Devonian do not crop out. — X-ray data. None. — References. None. — County. Marshall. — Wellname. GulfOilCorporation No.1Berniece (also known as No.1NPFP). — Location. Section 25, township SS, range SE; NW/4, NE/4, NE/4,North Madillpool. —— — Elevation. 758 feet, derrick floor. Totaldepth. 7,250 feet. Completed. 1957. —— TopofPaleozoic rocks. ni.ElevationofPaleozoic rocks ni. — Thin section coverage (depth in feet). bureau of economic geology: 3900-10, 4150-60, 4600-10, 4800-10, 4990-5000, 5050-60, 5100-10, 5300-10, 5425-30, 5460-65, 5700-05, 5760-65, 5950-60, 6500-05, 6550-60, 6775-80, 6900-05, 7000-05, 7245-50. — Description of Paleozoic rocks. The following stratigraphic information is reported: top of Springer or Goddard, 3,140 feet; top of Caney, 4,660 feet; top of Sycamore, 4,890 feet; top of Wood- ford, 5,050 feet; top of Hunton detrital, 5,425 feet; top of Sylvan, 5,444 feet; top of Viola, 5,739 feet; top ofBromide, 6,400 feet; top ofTulip Creek, 6,770 feet; top ofMcLish, 7,125 feet. Petrographically, the upper part of the sequence is pyritic carbonaceous micaceous chloritic siltyshale, locally calcareous, bituminous, and siliceous, and pyritic argillaceous bituminous silty limestone, locally glauconitic and fossiliferous. Beneath the shale and limestone section are typical Wood- ford rocks, including red-brown pyritic bituminous calcareous spore-bearing siliceous shale and chert. The Woodford rests on a lower Paleozoic foreland sequence of fossiliferous argillaceous bituminous clastic limestone, limy shale, pyritic bituminous shale and silty shale, and fine-to medium-grained, rounded, well-sorted calcareous quartz sandstone, locally quartzitic. This wellpenetrated foreland rocks west of the Ouachita structural belt. — X-ray data. None. — References. Personal communication :W. R. Johnson, The Texas Company, 1958. The Ouachita System — County. Marshall. — Well name. Magnolia Petroleum Company No. 1Beard. Location.—Section 7, township 7S, range 6E; SE/4, SE/4, NW/4. — —— Elevation. 635 feet. Totaldepth. 2,010 feet. Completed. ni. — Top of Paleozoic rocks. 740 feet. Elevation ofPaleozoic rocks. 105 feet. — Thin section coverage (depth in feet). bureau of economic geology: 730-40, 1000-1100, 1320-30, 1410-15, 1750-60, 2000-10. — Description of Paleozoic rocks. The following stratigraphic data are reported: base of Trinity, 740feet;topofunweathered Stanley,880feet;totaldepth,2,010feet,inStanley The sequence is composed of (1) fine-grained, subangular to subround, poorly sorted, argillaceous feldspathic quartz sandstone (graywacke) containing detrital mica, abundant rock fragments, and witha "mud" matrix partly reconstituted into new chlorite and sericite and (2) dark silty and sandy metashale or clay-slate, locally siliceous, bituminous, and pyritic. Metamorphism is very weak. This well penetrated the Stanley shale in a disturbed zone close to the western margin of the Ouachita belt. — X-ray data. None. — References. Personal communication: J. Eric Bucher, Magnolia Petroleum Company, 1959. — County. Marshall. — Wellname. Shell OilCompany No. 1Keystone. Location—Section 10, township BS, range SE; SE/4, SW/4, NW/4. —— — Elevation. 654 feet, derrick floor. Totaldepth. 10,043 feet. Completed. 1957. — Top ofPaleozoic rocks. 663 feet. Elevation ofPaleozoic rocks. 9 feet. — Thin section coverage (depth in feet). bureau of economic geology: 750-60, 950-60, 2350-60, 2800-10, 3250-60, 8785-90, 8850-55, 9050-55, 9300-05. — Description of Paleozoic rocks. This wellis reported to have encountered Pennsylvanian (Morrow) rocks at 633 feet and bottomed in Pennsylvanian (Morrow) beds at 10,043 feet. The main rock types are (1) silty and sandy clastic limestone (calcarenite), locally fossiliferous, containing fine-to medium-grained, subangular to subround quartz sand, chert, glauconite, phosphaticmaterial, bituminous material, and clay; fossil fragments include spicules, ostracods, bryozoans, crinoids, and foraminifers of Millerella type; (2) fine-grained, subangular to subround, well-sorted, calcareous quartz sandstone containing detrital calcite, chert, glauconite, fossil fragments, and phos phatic material with a calcareous, and less commonly argillaceous-micaceous or siliceous, matrix. Locally there are fine-grained compact limestones without appreciable sand or silt, some of which are pelletiferous and some of which are composed largely of fossil fragments. Sandstones and limestones grade into each other with limestone generally more abundant, particularly toward the bottom of the well. This well penetrated foreland facies Pennsylvanian rocks of Morrow age west of the Ouachita belt;the abnormal thickness of the sequence indicates faulting or folding. — X-ray data. None. — References. Personal communication: Carl Branson, Oklahoma Geological Survey, 1958. — County. Pittsburg. — Well name. Southwest Exploration Company No. 1Hoehman. Location.—Section 16, township 2N, range 14E; SE/4, NE/4, SE/4. — —— Elevation. 775 feet. Total depth. 8,758 feet. Completed. 1954. Top of Paleozoic rocks.* 3 Elevation of Paleozoic rocks. [-775 feet. — Thin section coverage (depth infeet). bureau of economic geology: 80-90, 750-60, 1440-50, 2500-10, 3480-90, 3500-10, 5450-60, 6800-10, 8650-60, 8730-40. — Description of Paleozoic rocks. The sequence is composed of (1) dark micaceous silty shale or metashale, locally carbonaceous or containing dark red-brown organic material; (2) fine-to medium- grained, mostly subangular, fairly well-sorted to poorly sorted, calcareous quartz sandstone; (3) coarse-grained, subangular, fairly well-sorted, carbonaceous micaceous quartz siltstone, and fine- grained quartz sandstone, locally argillaceous or siliceous; and (4) fine-grained, subangular, well- sorted, calcareous to siliceous quartz sandstone. The sandstones contain minor feldspar and rock fragments and detritalmica. The entire sequence is Atoka. The wellis located in the frontal part of the Ouachita Mountains, between the Pine Mountain and Ti Valley faults. 43 Well was spudded inAtoka. Bureau of Economic Geology, The University of Texas — X-ray data. None. — References. None. — County. Pushmataha. — Wellname. ErieHalliburtonNo.1Bagwell. Location.—Section 30, township 3S, range 15E; SW/4, SW/4, NE/4,NE/4. —— — Elevation. 585 feet. Total depth. 6,010 feet. Completed. ni. — Top of Paleozoic rocks. 900± (? ) feet. Elevation of Paleozoic rocks. 315± ( ? ) feet. — Thin section coverage (depth in feet). bureau of economic geology: 930-35, 1150-55, 1250-55, 1500-10, 2150-60, 2900-10, 3690-3700, 4250-60, 4350-60, 4400-10, 5150-60, 5990-6000. Description of Paleozoic rocks.—This well penetrated a sequence of Stanley shale under a thin Cretaceous cover and bottomed inStanley. The sequence is composed of (1) fine-to medium-grained, subangular to subround, poorly sorted, argillaceous feldspathic quartz sandstone (graywacke), locally micaceous, chloritic, pyritic, commonly containing abundant rock fragments, and with a partly reconstituted "mud" matrix; (2) angular siliceous and calcareous micaceous quartz siltstone; and (3) dark chloritic micaceous meta- shale or clay-slate, locally pyritic and bituminous. Argillaceous sandy tuff and dark siliceous shale containing spicules and radiolarians occur in the 5,990 to 6,000-foot interval. The rocks are veined byquartz and calcite;metamorphism isincipient tovery weak. This sequence is typical of the Stanley formation in the frontal zone of the Ouachita belt. X-ray data.—None. — References. None. — County. Pushmataha. — Well name. Southwest Exploration Company No. 1Denton Perrin. — Location. Section 9, township 2S, range 15E; C, SE/4, SW/4. —— Elevation. 562 feet,kellybushing. Totaldepth.—ll,32B feet. Completed. ni. Top of Paleozoic rocks.4iElevation of Paleozoic rocks.-1—562 feet. — Thin section coverage (depth in feet). bureau of economic geology: 100-120, 600-605, 980-985, 1250-55, 1995-2000, 3500-05, 4000-05, 6300-05, 6545-50, 6690-6700, 6900-05, 6980-85, 7075-80, 7300-05, 7500-05, 7600-05, 7850-55, 8050-55, 8600-05, 9095-9100, 9500-05, 9700-05 (2), 9985-90, 10,022-24, 10,150-55, 10,972-11,000. — Description of Paleozoic rocks. Two interpretations of the stratigraphic sequence encountered are as follows: (1) Spudded in Stanley; Hatton tuff zone in Stanley, 5,047 to 5,080 feet; Arkansas novaculite, 6,460 feet; Missouri Mountain shale, 6,956 feet; Polk Creek shale, 7,066 feet; Bigfork chert, 7,456 feet; fault and Stanley, 9,020 feet; Hatton tuff zone in Stanley, 9,984 to 10,020 feet; Arkansas novaculite, 10,972 feet. (2) Spudded in Stanley; upper Hatton tuff, 5,044 feet; lower Hatton tuff, 5,312 feet; Arkansas novaculite, 6,490 feet; Missouri Mountain shale, 6,955 feet; Polk Creek shale, 7,155 feet; Bigforkchert, 7,465 feet; Womble shale, 9,014 feet; reverse fault and Mississippian(? ),10,770 feet; total depth, 11,328 feet, invaricolored chert. The thin sections studied fallinto five groups. Group 1, including sections 100-120 through 4000-05, is composed of fine-grained, subangular to subround, poorly sorted, argillaceous feldspathic quartz sandstone containing abundant chert and shale fragments, argillaceous quartz siltstone, and dark silty shale ormetashale, locally pyritic, carbonaceous, orbituminous;these rocks are Stanley. Group 2, including sections 6300-05 through 6900-05, is mostly chert and siliceous shale. The chert ranges from dark red-brown pyritic bituminous dolomitic cryptocrystalline to microgranular chert containing spores and radiolarians to light-colored spiculitic chert, locally chalcedonic; quartz, carbonate, and bitumen veinlets are common. The sequence includes dark dolomiticshale or metashale and dark bituminous siliceous shale. This interval includes the Arkansas novaculite and possibly older beds as well.Group 3, including sections 6980-85 through 7300-05, is made up of dark pyritic bituminous calcareous and dolomiticsilty shale and metashale and fine-grained siltstone, locally containing radiolarian remains; this sequence was not identified but is lithologically similar to the lower Paleozoic Ouachita facies. Group 4, including sections 7500-05 through 8600-05, is composed of dark red- brown pyritic bituminous dolomitic spiculitic chert and fragmental fossiliferous bituminous clasticlimestone, inpart dolomiticand siliceous; fossils include spicules, ostracods, pelmatozoan fragments, and graptolitic (?) debris. Quartz, carbonate, and bitumen veinlets are common. These rocks are Bigfork. Group 5, including sections 9095-9100 through 10,150-55, is made up mostly of sandstone and shale. In the upper part are dark bituminous calcareous silty shale and fine-grained, sub ** Well was spudded in Stanley. The Ouachita System angular to subround, poorly sorted, calcareous quartz sandstone with abundant fragments of chert, shale, quartzite, phyllite, limestone, and mica; below, chloritic calcareous tuff occurs in the sand- stone-shale sequence. The tuff is typical of the Hatton tuff lentil of the Stanley, so that the sand- stone-shale sequence above is probably Stanley. The single section below Group 5 (10,972-11,000 interval) is a siliceous shale, possibly from the top of the Arkansas novaculite. This well penetrated a typical and fairly complete sequence of Ouachita facies in the frontal zone of the Ouachita belt sequence. The sequence is repeated by faulting. The petrographic data support stratigraphic interpretation (1). — X-ray data. None. — Personal communication:G.H.Thompson, ShellOilCompany, 1958. References. MEXICO — Estado. Coahuila. — Wellname. Peyotes No. 2-A. Location.—Approximately 82.5 km.S 22° WfromEagle Pass, Texas. — Elevation.—692.3 meters. Total depth.—1,812 meters. Completed. 1956. Top of metamorphic rocks.—1,761 meters. Elevation of metamorphic rocks. 1,068.7 meters. — Thin section coverage (depth in meters). bureau of economic geology: 1762.8-65.0, 1786.1-86.7, 1810.3-12.0. — Description of metamorphic rocks. Goldstein (1958) described a core fragment from the 1762.8 to 1765.0-meter interval as a very fine-grained micaceous metaquartzite showing stretched quartz grains; he compared the rock to those found in the interior zone of the Ouachita structural belt in Caldwell County, Texas. Masson (Dfaz G., 1958) called samples from 1,786 and 1,810 meters quartz schist and quartz mica schist, respectively; he noted the presence of biotite as wellas muscovite and referred the rock to the biotite zone of regional metamorphism. Rocks studied are fine-grained muscovite-albite-quartz schist and fine-grained sericitic to muscovitic — feldspathic metaquartzite. Metamorphism is low grade with a strong shearing component structures are foliation, crush zones, and sharp microfolding. A trace of very pale biotite occurs within masses of sericite, but the amount is very small and appears to have no great significance as far as grade of metamorphism is concerned. On the basis of location, lithology, and type of metamorphism itis probable that this wellpenetrated the interior zone of the Ouachita belt. — X-ray data. None. — References. Personal communication: Teodoro Diaz G., Petroleos Mexicanos, 1958; August Goldstein, Jr., BellOiland Gas Company, 1958. — Estado. Nuevo Leon. — Wellname. Chapa No. 101. — Location. 11,750 meters S 77°09' E of the town of Cerralvo. — —— Elevation. 189 meters, kelly bushing. Total depth. 3,280 meters. Completed. 1958. — Top of metamorphic rocks. 3,182(?) meters. Elevation of metamorphic rocks. 2,993(?) meters. — Thinsection coverage (depth inmeters). bureau of economic geology: 3188.3-3192.8, 3192.8-3199.3 — Description of metamorphic rocks. The sequence is composed of dark gray-green sericite-chloriteslate, locally carbonaceous, commonly containing abundant leucoxene, and dark green, fine-to medium- grained, angular, poorly sorted, chloritic micaceous feldspathic high-rank quartz metasandstone, locally dolomitic, carbonaceous, pyritic, and locally containing abundant rock fragments (slatephyllite, chert, quartz mosaic). Some samples are metagraywackes. Foliation is well developed, and locally the slates show incipient fracture cleavage; in the metasandstones new sericite is commonlyoriented at a high angle— to original bedding as indicated by plates of second-cycle mica-chlorite. Metamorphism is weak quartz and feldspar have not recrystallized but reconstitution of mica-chlo rite appears to be complete. The general lithology is of orogenic facies. This well is located far from other wells that penetrate pre-Mesozoic rocks. The lithology and typeof metamorphism are similar to those which occur in the interior zone of the Ouachita belt in the black slate beltofTravis,Bastrop, and Hays counties, Texas. — X-ray data. None. References.— Personal communication: D. C. Buzzo, Edwin W. Pauley, Northeast Mexico Division, 1958;Teodoro Dfaz G., Petroleos Mexicanos, 1959. Part 3. Summary Reports on Selected Wells Penetrating Paleozoic Rocks in the Southeastern States Philip B. King The following list gives significant data on Triassic (? ),Paleozoic, and older rocks in selected wells in the southeastern states. These data indicate the basis for the features shown on the geologic map (PI. 3) and for interpretations made in the text. The list includes only records of wells incritical areas, mainly toward the south; for records of wells farther north, see publications in the bibliography. In critical areas most wells which are known tohave entered Paleozoic or older rocks are listed, although for some of them little information is available as to the nature of the rocks penetrated. Wells are grouped according to the subcrop map units in which they occur. Publications referred to are given in the bibliography. Citations based on unpublished communications are italicized. Some informants have requested that their names be withheld, so that some of the data given are not documented. UnitPenetrated Triassic(?) (1)45 J\[elson Exploration Company No. 1Smith Lumber Company Alabama, Crenshaw County; Sec. 26, T. 8 N., R. 16 E. Elev. 396 ft.; T. D. 10,830 ft.; completed 1948. — Triassicf?) rocks. Red micaceous shale and other red clastic rocks from 3,156 feet to total depth, of which 4,285 feet have been assigned to the Triassic(?) (McKee and others, 1959). According to Applin, some geologists have suggested a Paleozoic age for the lower part of the red clastic rocks. Higher red strata probably include equivalents of Jurassic (Cotton Valley) and Lower Cretaceous. References— Applin, 1951, p. 28, table 5, well90; McKee and others, 1959, pi.4. (2) W. B. Hinton No. 1 J. S. Creel Alabama, Barbour County; Sec. 14, T. 9 N., R. 26 E. Elev. 504 ft.;T. D. 5,546 ft.;completed 1939. — Triassicf?) rocks. According to driller's log, from 3,000 feet to total depth penetrated dark red shales and sandstones of Early Cretaceous age or older; overlain by Tuscaloosa formation. Of these, 1,085 feet have been ascribed to the Triassic (?). At 5,342 to 5,372 and 5,491 to 5,522 feet they contain diabase sills or—dikes. References. Bowles, 1941, pp. 252-256; Applin, 1951, p. 26, table 4, well79; McKee and others, 1959, pi. 4. (3) H. A. Stebinger No. 1Alice S. Robertson Alabama, Barbour County; Sec. 19, T. 10 N., R. 26 E. Elev.554ft.;T.D.5,215ft.;completed 1939. Triassicf?) rocks. —-According to driller's log, penetrated shale, sandy shale, and sand, mostly red, below 4,135 feet. Diabase dikes or sills at 4,135 to 4,152, 4,202 to 4,208, and 4,273 to 4,274 feet. References.— Bowles, 1941, pp. 256-260; Applin,1951, p. 26, table 4, well80. (4) Messergill & Williams (R. G. Hauser) No. 1T. R. Grubles Alabama, Barbour County; Sec. 9, T.11N., R. 26 E. Elev. 649 ft.; T. D. 3,384 ft.; completed 1948. — Triassicf?) rocks. Sample of bottom hole core at 3,378 feet reported by Charles Milton to be "probably Triassic" (P. L. Applin, 1960). (5) Robert York Trustee No. 1S. V. Dismuke Alabama, Barbour County; Sec. 16, T. 12 N., R. 27 E. Elev. 272 ft.;T. D. 2,727 ft.;completed 1948. — Triassicf?) rocks. Core at total depth and a little above reported by Charles Miltonto "resemble Triassic sediments" (P.L.Applin, 1960). (6) Renwar Oil Corporation No. 1 H. D. GranberryAlabama,Henry County; Sec.6,T.4N.,R.29E. T. D. 6,610 ft.;completed 1956. Elev. 193 ft.; 46 These numbers refer also to well numbers on Plate 3. Bureau ofEconomic Geology, The University of Texas — Triassicf?) rocks. Top at 5,980 feet. Core at 6,326 feet is of Triassic(?) aspect. Top of Paleozoic is reported at 6,528 feet from electric log. Samples are currently being studied by E. R. Applin. (P. L. Applin,1960). (7) Sowega Minerals Exploration Company No. 1J. W. West Georgia, Calhoun County;Lot328, LandDist.4. Elev. 345 ft.; T. D. 5,265 ft.; completed 1950. — Triassicf?) rocks. Penetrated 1,340 feet of Triassic(?) rocks; diabase from 5,190 feet to total depth. Overlain byLower Cretaceous (? ). — References. Applin,1951, p. 26, table 4, well85; McKee and others, 1959, pi.4. (8) Stanolind Oil&Gas Company No.1J.H.Pullen Georgia, MitchellCounty; Lot133, Land Dist. 10. Elev.338ft.;T.D.7,487ft.;completed 1944. — Triassicf?) rocks.-At 7,350 to 7,470 feet, diabase sills or dikes in clastic rocks of Triassic(?) age; other igneous rocks at 6,550 to 6,620 and 7,070 to 7,090 feet. Reference.— Applin,1951, p. 27, table 4, well 87. (9) Pan-American Petroleum Corporation No. 1 J. R. Scaly Florida,WaltonCounty; Sec.9,T.1S.,R.18W. Elev. 99ft; T.D.11,947 ft.; completed 1958. — Triassicf?) rocks. Rocks of Early Cretaceous age were penetrated at about 5,060 feet, but in the unfossiliferous clastic rocks below this depth Lower Cretaceous and older stratigraphic units have not been clearly differentiated. Red shale and red sand are major constituents of the cuttings beginning at about 7,650 feet and probably are at least in part of Triassic(?) age. Igneous rock occurs in cuttings from 11,910 feet to total depth (P.L.Applin,1960). (10) Humble Oil&Refining Company No.1G.H.Hughes Florida, Taylor County; Sec. 12, T. 5 S., R. 6 E. Elev. 36 ft.; T. D. 6,254 ft.; completed 1948. — Triassicf?) rocks. Clastic rocks at about 5,960 to 6,153 feet, overlying basaltic rock at 6,153 to 6,165 feet, and diabase gabbro at 6,165 to 6,254 feet. References.— Applin,1951, p.26, table 4, well83; 1957, p.1489, table 4, well21. (11) Gulf OilCorporation No. 1Brooks-Scanlon Inc., Block 33 Florida,TaylorCounty; Sec.18,T.4S.,R.9E. Elev. 96 ft.; T. D. 5,243 ft.; completed 1950. — Triassic(?) rocks. Clastic rocks of Triassic(?) age at about 5,140 feet, underlain from 5,200 feet to total depth by diabase gabbro. Reference.— Applin,1951, p. 26, table 4, well81. Besides the wells listed, other wells in the same parts of Alabama, Georgia, and Florida drilled through Triassic (? ) rocks into Paleozoic or older rocks. See wells 57, 58, 62, 63, 64, 65, and 80, listed below. Permian (? ) Representative wells which have been drilled into the Eagle Mills formation of Permian (?) age in southern Arkansas prior to 1945 are listed by Hazzard and others (1947, p. 485).No further compilation of well data on this formation has been made by the writer. Pennsylvanian (12) Lion OilCompany No. 1Nally Arkansas, White County, Sec. 33, T. 8 N., R. 7 W. Elev. 425 ft.; T. D.—6,397 ft.; completed 1945. Paleozoic rocks. Published log (Maher and Lantz, 1953) shows Atoka formation at surface; Morrow group at 890 feet; Jackfork sandstone at 1,510 feet; Stanley shale at 2,570 feet; underlain by Penters chert(?) (Devonian) at 5,545 feet, and by Ordovician formations, with Everton formation at total depth. The wellis near the edge of the Mississippi embayment, inthe Arkansas basin about 30 miles north of the structural front of the Ouachita Mountains. Well log correlation indicates that the units assigned to the Stanley and Jackfork thin westward across the Arkansas basin, the first changing into the Mississippian formations of the Ozark Mountains sequence, and the second wedging out entirely. References.— Maher and Lantz, 1953, well 10; Caplan, 1954, pp. 15-17; Sheldon, 1954, pp. 199-204. The Ouachita System (13) W. W. Martin&J.H.CokerNo.1W.H.Stewart Arkansas, Prairie County, Sec. 3, T. 3 N., R. 5 "W. Elev.210 ft.;T.D.3,163 ft.;completed 1946. Paleozoic rocks.—Top at 1,878 feet. Driller'slog shows alternating thin units of sand, sandy shale, shale, black shale, and lime. These rocks are probably Atoka formation, which crops out about 25 miles along the strike to the west. Overlain by basal sand ofUpper Cretaceous. Reference.— Renfroe, 1949, pp. 128-129. (14) Panhandle Eastern Pipeline Company No. 1-22 Ives Arkansas, PrairieCounty; Sec. 22,T.1S.,R.4W. Elev. 207 ft.; T.D. 11,950 ft.;completed 1958. Paleozoic rocks.—Top at 3,303 feet. Sample log shows a monotonous sequence of shale and sandstone to total depth. Some of the shales are micaceous, others lustrous, others black; most of the sandstone is fine grained. Samples contain vein quartz fragments and pyrite. The welllies outside the Ouachita structural front as projected, but the nature of the samples suggests deformation and weak metamorphism. Probably much or allof the sequence is Atoka formation. Overlain by basal sand ofUpper Cretaceous. Reference.-—Sample log from Arkansas Geological and Conservation Commission, 1960. (15) David J. Flesh No. 1 Rosencrantz et al. Arkansas, Arkansas County; Sec. 2,T.3S.,R.6W. Elev. 219 ft.; T.D. 3,635 ft.; completed 1947. — Paleozoic rocks. Top at 3,464 feet. Driller's log records very hard shale, brittle splintery shale, hard quartzitic sand, and lime to total depth. Sidewall cores at 3,470 and 3,518 feet are hard, tightly cemented, dense, micaceous quartzite, the second core pyritic; sidewall core at 3,583 feet is hard black shale with some quartzite and micaceous material. Assigned to Atoka formation in log; wellis close to Ouachita structural front as projected, and the record suggests deformation and weak meta morphism. Overlain by pre-Nacatoch sand of Upper Cretaceous. Reference.— Renfroe, 1949, pp. 17-18. (16) Ryan Consolidated Petroleum Corporation No.1Roy McCollum Arkansas, Arkansas County; Sec. 24, T.2 S., R. 5 W. Elev.215ft.;T.D.3,731ft.;completed 1947. Paleozoic rocks.—Top at 3,530 feet. Driller's log records "hard shale flint and novaculite at top; bottom of hole inAtoka." Overlain by sand correlated withOzan formation (Upper Cretaceous) . References— Renfroe, 1949, pp. 18-19; Caplan, 1954, pi. 5, well5. (17) BlackwellOil&Gas Company (C. W.Robinson) No.1E.P. Fox Arkansas, Arkansas County; Sec. 23, T. 5 S., R. 3 W. Elev. 190 ft.; T.D. 4,372 ft.; completed 1941. Paleozoic rocks.—Top at 4,337 feet. Driller's log records alternating shale and chert; the "chert" may actually be novaculite or very fine-grained quartzitic sandstone. "The Fox well is assumed to have been abandoned in the Atoka since the presence of chert or novaculite has not been determined withassurance" (Caplan, 1954).The wellis close to the Ouachita structural front as projected. Overlain by sand correlated withOzan formation (Upper Cretaceous) . Reference.— Caplan, 1954, p. 13; pi. 5, well6; pi.8, well7. (18) Continental OilCompany No. 1DeWitt Bank &Trust CompanyArkansas, Arkansas County; Sec. 32, T. 5 S., R. 2 W. Elev. 186 ft.; T. D. 4,520 ft.; completed 1954. — Paleozoic rocks. Top at 4,500(?) feet. Cuttings are black, pyritic, blocky shale; chert fragments {W. M. Caplan, 1960). Correlation of these rocks is uncertain; the well is close to the Ouachita structural frontas projected. Overlain bybasal sand ofUpper Cretaceous. (19) /.L.Youngblood No. 1 J. B. West Arkansas, Arkansas County; Sec. 24, T. 4 S., R. 2 W. Elev. 183 ft.; T. D. 4,183 ft.; completed 1949. — Paleozoic rocks. Top at 4,160(?) feet. Driller's log records dark gray to black quartzitic sandstone, assigned to Atoka formation; circulation sample at total depth described as black, very fine- grained quartzitic sandstone or novaculite, black brittle shale, and black micaceous shale. Caplan (1954) interpreted the former as novaculite but suggested it forms detrital fragments in the Atoka formation. Overlain by Ozan (?) formation (Upper Cretaceous). Reference.— Caplan, 1954, pp.13-14; well6,pi.8. Bureau ofEconomic Geology, The University of Texas (20) Plymouth OilCompany No. 1BushArkansas, Phillips County; Sec. 2, T. 6 S., R. 1E. Elev. 155 ft.; T. D. 4,595 ft.; completed 1956. Paleozoic rocks.—Top at 4,575 feet. Sidewall cores at 4,583 feet are reported to be gray limy shale {W.M.Caplan, 1960). Overlain by Ozan formation or older Upper Cretaceous. (21) McAlester Fuel Company &H.M.Cox No. 1E.M. Welch Arkansas, Phillips County; Sec. 24,T.4S.,R.2E. Elev. 174 ft.; T. D. 4,939 ft.; completed 1948. — Paleozoic rocks. Top at 4,522 feet. Driller's log records "anhydrite and lime" from 4,522 feet to total depth; sidewall cores at 4,700 and 4,891 feet are "bituminous coal." The anhydrite and lime of the driller's log are inexplicable ifthe rock is Paleozoic, but the coal of the sidewall cores is compatible withAtoka formation. Overlain by Ozan formation or older Upper Cretaceous. Reference.— Renfroe, 1949, pp. 101-103. (22) McAlester Fuel Company No. A-lHome Lumber Company Arkansas, Phillips County; Sec. 27, T.3 S.,R.2E. Elev. 171 ft.; T.D. 4,576 ft.; completed 1948. Paleozoic rocks.—Top at 4,461(?) feet. Consists of quartzitic sandstone and dark gray to black shale. Sidewall core at 4,523 feet reported to be dark brown lignitic shale. "Top of Paleozoic may be at base of the green shale" ( W.M.Caplan, 1960).Rocks below green shale suggest Atoka formation. Overlain by Upper Cretaceous (? ). (23) Union Producing Company No. 1-A Tensas Delta Louisiana,Morehouse Parish; Sec.8,T.22N.,R.4E. Elev. 71 ft.; T. D. 10,475 ft.; completed 1940. Paleozoic rocks.-—Top at 9,285 feet. The Paleozoic rocks, termed the Morehouse formation, have been penetrated to a thickness of 1,190 feet. They are mainly gray, brownish-gray, and black shales and siltstones, withminor gray sandy shales, gray sandy limestones, and red shales. The shales are carbonaceous, siliceous, or finely micaceous, and are less commonly dolomitic or calcareous. Some beds contain carbonized or pyritized plant remains. There is no apparent dip in the cores, and the rocks are not metamorphosed. Cores at various levels contain a sponge, a scaphopod, 9 genera of pelecypods, and the bellerophontid gastropod Patellostium. The pelecypods resemble those in Pennsylvanian and Permian faunas elsewhere, and the gastropod resembles Pennsylvanian species (Imlay and Williams, 1952). A core at 10,243 to 10,253 feet contains plant spores of the genera Illinites, Florinites, and Puncti-sporites whichindicateaMiddleorLatePennsylvanian age(HoffmeisterandStaplin,1954). Overlain unconformably by Werner formation and Louann salt (Hazzard and others, 1947), of Jurassic (?) age. The structure and history of the Paleozoic rocks in this famous wellhave been much discussed, but no final interpretations are possible, as rocks like these have not been reached by drilling in surrounding areas. The Paleozoic rocks might be earlier than the Ouachita orogeny but have escaped deformation because they were on the axis of a fold, or in a stable mass that resisted deformation (Imlay and Williams, 1942), or they may have been deposited after the orogeny (H. J. Morgan, 1952). They are notincontact withthe Eagle Millsformation, penetrated inwellstothe north,but they are generally believed to be older (McKee and others, 1956);however, ithas been suggested that they might be younger (Hazzard and others, 1947). — References. Imlay, 1940a, pp. 7-8; Imlay and Williams, 1942, pp. 1672-1673; Hazzard and others, 1947, p. 486; H. J. Morgan, 1952, pp. 2269-2271; Hoffmeister and Staplin, 1954, pp. 158-159; McKee and others, 1956, p. 1. (24) PhillipsPetroleum Company No.1Knowlton&Perthshire Mississippi,BolivarCounty; Sec. 2,T.24N.,R.7W. Elev. 164 ft.; T. D. 6,009 ft;completed 1937. Paleozoic rocks.— Top at 4,700(?) feet. Reported to be shale and limy shale, probably equivalent to the Atoka formation. "A core fragment from 5,677 to 5,683 feet is sheared, silty and sandy, bituminous, pyritic dolomite; black opaque bituminous material occurs in irregular streaks and fracture fillings. The rock is more characteristic of the foreland facies than of the Ouachita facies. It is not metamorphosed, but itis sheared and fractured, suggesting proximity to the Ouachita belt" (P.T.F1awn,1959). Overlain by pre-Tokio strata (Lower Cretaceous) . — Reference. Caplan,1954,pi.5,well8;BeikmanandDrakoulis,1958a,p.14. The following additional wellsin Bolivar County are reported to have been drilled in to the Paleozoic, but no information is available as to the nature of the rocks penetrated (Beikman and Drakoulis,1958a,p.14):Central OilCompany No.1Tuminello; HuntOilCompany No.1Raymer. See also well70 (p.358). The Ouachita System (25) Roeser &Pendleton No. 1 Young & Ogilvie Mississippi, Tallahatchie County; Sec. 32, T. 25 N., R. 2 E. Elev. 160 ft.;T.D.3,970 ft.;completed 1940. Paleozoic rocks.—Top at 3,750 feet. Reported to have entered igneous rock and altered shale. Rocks areof"Ouachita"facies(H.J.Morgan,Jr.,1958).Asthiswellisconsiderably northoftheOuachita structural front as projected, the rocks penetrated are here interpreted as being Pennsylvanian, altered either by deformation or igneous intrusion. Overlain by—Tuscaloosa formation (Upper Cretaceous) . Reference. Beikman and Drakoulis, 1958 a, p. 55. (26) H.M.Ogg&H.A.ClarkNo.1G.Burkhalter Mississippi, Tallahatchee County; Sec. 27, T. 26 N., R. 3 E. Elev. 357 ft.;T.D. 4,725 ft.;completed 1945. — Paleozoic rocks. Top at 3,275 feet. A sample log by Mellen shows that rocks are depositionally and technically like the Ouachita facies and are intruded by felsic microgranites and rarer mafic sillsand dikes (F.F.Mellen,1960). Overlain by—Tuscaloosa formation (Upper Cretaceous). Reference. Beikman and Drakoulis, 1958a, p. 55. The following additional wells in Tallahatchie County, are reported to have been drilled into the Paleozoic, but no information is available as to the nature of the rocks penetrated (Beikman andDrakoulis,1958a,p.55):Louisiana-Mississippi OilCompany No.1C.E.Shores; H.M.Ogg&H.A.ClarkNo.1D.G.Bardwell. Also,the following wells are reported tohave been drilledinto the Paleozoic inLeflore County to the south (Beikman and Drakoulis, 1958b; P. L. Applin, 1960) :J. W. Hughes No. 1 Board of Supervisors and No.1McLemore. (27) W. L.Stewart et al. No. 1 W. W. Wood Mississippi, Grenada County; Sec. 19, T. 22 N., R. 5 E. Elev. 213 ft.;T.D. 4,600 ft.;completed 1935. Paleozoic rocks. —Top at 3,995 feet. Pennsylvanian (?) (Beikman and Drakoulis, 1958 a). Rocks are of "Ouachita" facies (H. J. Morgan, Jr., 1958). As this well is considerably northeast of the Ouachita structural front as projected, the rocks penetrated are here interpreted as being deformed Pennsylvanian. Overlain by Tuscaloosa (?) formation (Upper Cretaceous). — Reference.-Beikman andDrakoulis,1958a,p.24. (28) /.R.Lockhart No.1Guy Fite Mississippi,Grenada County; Sec. 25,T.22N.,R.6E. Elev. 322 ft.; T. D. 4,545 ft.; completed 1946. — Paleozoic rocks. Top at 3,620 feet. Pennsylvanian (Beikman and Drakoulis, 1958 a). A sequence of dark siliceous shale and siltstone with a few crinoid impressions and other fossil traces which suggest a Pennsylvanian age. Cores show steep dips (F. F. Mellen, 1960). See comment on well27. Overlain by—Tuscaloosa formation (Upper Cretaceous). Reference. Beikman and Drakoulis, 1958a, p. 24. (29) BillupsBros.&SerioNo.1N.H.Heath Mississippi,CarrollCounty; Sec. 29,T.21N.,R.4E. Elev. 270 ft.;T.D.4,696 ft.;completed 1952. — ). Paleozoic rocks. Top at 4,564 feet. Pennsylvanian (Beikman and Drakoulis, 1958a The nature of the rocks penetrated is not recorded, but the welllies near the Ouachita structural front as projected. The rocks are here interpreted as Pennsylvanian in the deformed belt bordering the structural front. Overlain by Lower(?) Cretaceous. — Beikman and Drakoulis, 1958a, p. 14. Reference. (30) Billups Bros. No. 1C. A. Townsend Mississippi,Montgomery County;Sec. 20,T.19N.,R.7E. Elev. 450 ft.;T. D. 4,564 ft.;completed 1952. Paleozoic rocks.—Top at 4,545 feet. Pennsylvanian (Beikman and Drakoulis, 1958a ). See comment on well31. — Reference. Beikman and Drakoulis, 1958a, p. 45. (31) Gulf Refining Company No. 1F. W.Parker Mississippi, Montgomery County; Sec. 22,T.19N.,R.7E. Elev. 394 ft.;T.D.5,303 ft.;completed 1940. Bureau ofEconomic Geology, The University of Texas — Paleozoic rocks. Top at 4,480 feet. Pennsylvanian (Beikman and Drakoulis, 1958 a). Of "Ouachita facies" (H. J. Morgan, Jr., 1958). A core from 4,637 to 4,652 x/2x/2 feet contains pelecypods and is a dark gray silty argillite, with stratification dipping about 15°. "Thin-section examination of the sample shows that the argillite is composed of a mass of dark clay and sericite containing fine quartz- feldspar silt, shreds of second-cycle muscovite, carbonaceous fragments, sporadic grains of pyrite, and spots of cryptocrystalline silica. The sericite forms a network of braided fibers, locally with two directions of orientation at a high angle. Possibly the oriented sericite indicates an incipient metamorphism" (P. T. Flawn, 1960). "The pelecypods are Sanguinolites sp. and Nucula or Paleonucula sp., neither of which is specifically determinable. Both genera range at least from Silurian through Permian. There is nothing about these specimens either to confirm or refute the Pennsylvanian age which has been ascribed to the beds" (E. L. Yochelson, 1960).Presumably the well is in the belt of deformed Pennsylvanian rocks northeast of the Ouachita structural front. Overlain by Lower Cretaceous. The well is on the Kilmichael dome, a cryptovolcanic structure; Tertiary and Cretaceous beds are disturbed, but the top of the Paleozoic is at normal level. — References. Priddy andMcCutcheon, 1943,pp.42-43;Beikman andDrakoulis, 1958a,p.45. The followingadditional wellinMontgomery County is reported to have been drilled into the Paleozoic, but no information is available as to the nature of the rocks penetrated (Priddy and McCutcheon, 1943, p. 42; Beikman and Drakoulis, 1958a, p. 45) :Henderson OilCompany No. 1Columbia Mutual Life. (32) Union Producing Company No. 1J. N. Henderson Mississippi, Clay County; Sec. 22, T.15 S., R. 4 E. Elev. 437 ft.;T. D.10,551 ft.; completed 1953. Paleozoic rocks.—Top at 1,750 feet. Pennsylvanian to 9,763 feet, underlain by Mississippian (Chester series) to total depth. Samples indicate 54 coal zones in the Pennsylvanian, mainly thin, and electric log suggests possible presence of 93 zones. Twenty of these zones have yielded spores (Cropp, 1960, p. 362). Spores of the highest zone, at 1,950 feet, indicate a correlation with the upper Tradewater formation of Illinoisand the upper Pottsville or basal Allegheny of the northern Appalachian area; spores of the lowest zone at 8,950 feet include only Pennsylvanian genera and no Mississippian genera. Allthe 8,013 feet of Pennsylvanian rocks in the wellare clearly correlative withthePottsville formation of the outcrops inAlabama to the east. This well,and well33, are near the center of the Black Warrior basin, far northeast from the disturbed belt along the Ouachita structural front, yet south of the belt of shallow-lying Mississippian rocks of the northern part of the basin.NorthofthewellthePennsylvanian thinsrapidlyto1,000feetinlessthan20miles. Overlain by—Tuscaloosa formation (Upper Cretaceous). BeikmanandDrakoulis,1958a,p.17;Cropp,1960,pp.361-366, fig.3. References. (33) Atlantic OilCompany No.1R. G. Dunning Mississippi, Clay County; Sec. 12, T. 19 N., R. 16 E. Elev. 184 ft.;T.D.9,243 ft.;completed 1947. — Paleozoic rocks. Top at 1,390 feet. Pottsville formation (Pennsylvanian) to 8,120 feet; Park- wood(?) formation to 8,610 feet; Chester series (Mississippian) to total depth. Published log (Dott and Murray, cd., 1954) indicates that the Pottsville is shale, sandstone that is conglomeratic in the lower 1,000 feet, and minor coal; the underlying Parkwood(?) is sandy shale. Thin sections were studied of cuttings at depths of 1,630, 1,650, 3,010, 3,170, 3,590, 3,700, 4,410, 7,490, and 8,170 feet (August Goldstein, Jr., 1960). The rocks are carbonaceous and micaceous shale, silty shale, and siltstone; and fine-to medium-grained sandstone (protoquartzite), wellsorted, wellwashed, contain ing grains of quartz, metamorphic rocks (metaquartzite, phyllite, and mica schist), and detrital muscovite. Clearly, the rocks were derived from a metamorphic terrane, but they have not themselves been metamorphosed. See comments on well32. Overlain by—Tuscaloosa formation (Upper Cretaceous) . DottandMurray,cd.,1954, sheet1,well6;BeikmanandDrakoulis, 1958a,p.17. References. (34) N. W. Shiarella No. 1I.L. Murphy Mississippi, Oktibbeha County; Sec. 28, T.17 N., R. 12 E. Elev. 450 ft.; T.D. 4,024 ft.; completed 1940. — Paleozoic rocks. Top at 3,640 feet. Pottsville formation (Pennsylvanian) to total depth. Published log (Dott and Murray, cd., 1954) indicates that Pottsville is shale and sandy shale. Overlain by—Lower Cretaceous. References. DottandMurray,cd.,1954,sheet1,well5;BeikmanandDrakoulis,1958a,p.47. The following additional wells in Oktibbeha County are reported to have been drilled into the Pennsylvanian, but no information is available as to the nature of the rocks penetrated (Beikman and Drakoulis,1958a,p.47):John AllenNo.IW.C.Howell; McAlester Fuel Company No. 1-A Sudduth. Also, the following are reported to have been drilled into the Pennsylvanian in Choctaw County to the west (Beikman and The Ouachita System Drakoulis,1958a,p.15):Henson &RifeNo.IW.J.&T.W.Green and No.1Stafford, Copeland & Stafford. (35) Shell Oil Company No. 1H. H. Wheeles Mississippi, Attala County; Sec. 5, T. 14 N., R. 9 E Elev. 511 ft.; T. D.6,217 ft.; completed 1945. Paleozoic rocks— Top at 5,504 feet. Pottsville formation (Pennsylvanian) to total depth (Dottand Murray, cd., 1954; Beikman and Drakoulis, 1958 a). Classed by some geologists as of "Ouachita" facies. Published log shows that the Pennsylvanian is shale and sandy shale. Thin sections were studied of cuttings and cores from depths of 5,635, 5,847, 5,950, 6,010, 6,080, and 6,160 feet (August Goldstein, Jr., 1960; P. T. Flawn, 1959). Most of the rocks are dark carbonaceous shale, largely silty, partly calcareous. Inone specimen (6,080 feet) laminae of quartzose feldspathic siltstone alter nate with laminae of silty carbonaceous shale. Part of the clay in the shales is unaltered, but as much as half or more has been recrystallized to chlorite and minor sericite. One specimen (5,635 feet) is dark, laminated, sublithographic limestone, veined by quartz. Allthe specimens show incipient to verylowgrade metamorphism. "Finely divided and disseminated organic matter reduces the apparent metamorphic grade of the rock. Without this, these rocks might have been equal in metamorphic grade to those inStanolind No.1Steed farther west in the county" (Goldstein). The rocks are com parable inmetamorphic grade to many of those in the Ouachita belt, but they are interpreted here as part of the belt of deformed Pennsylvanian rocks close to the structural front. Overlain by 1,780 feet of Lower Cretaceous. References.— Dott and Murray, cd., 1954, sheet 1, well4; Beikman and Drakoulis, 1958a, p. 13. (6b) Continental Oil Company No. 1H. O. Fortenberry Mississippi, Neshoba County; Sec. 13, T. 12 N., R. 10 E. Elev. 453 ft.; T. D. 5,915 ft.; completed 1952. Paleozoic rocks.—Top at 5,740 feet. Reported to be Pennsylvanian black shale of "Ouachita" facies. As this welllies a short distance northeast of the belt of older Paleozoic carbonate rocks, its rocks are here interpreted as Pennsylvanian that has been deformed along the edge of this belt and not as part of the main Ouachita belt. Overlain by—Lower Cretaceous (? ). Reference. Beikman and Drakoulis, 1958 a, p. 46. (37)H.IV.Elliottetal.No.1Mrs.Laura Eakes Mississippi, Neshoba County; Sec. 36, T. 11 N., R. 13 E. Elev.503ft.;T.D.5,427ft.;completed 1950. Paleozoic rocks.—Top at 5,364 feet. Pennsylvanian (Beikman and Drakoulis, 1958a). Reported to be of "Ouachita" facies. See comment on well36. Overlain by—Lower Cretaceous. Reference. Beikman and Drakoulis, 1958a, p. 46. (38) Magnolia Petroleum Corporation No.1C. Culpepper Mississippi, Lauderdale County; Sec. 4, T. 8 N., R. 14 E. Elev.426ft.;T.D.6,256 ft.;completed 1941. Paleozoic rocks.—Top at 6,060 feet. Undifferentiated Paleozoic (Beikman and Drakoulis, 1958a). Reported to be Pennsylvanian of "Ouachita" facies. See comment on well 36. Overlain by—Lower Cretaceous. Reference. Beikman and Drakoulis, 1958a, p. 39. In addition to these, the following wells are reported to have been drilled into the Paleozoic inKemper County to the east, but no information is available as to the nature oftherockspenetrated (BeikmanandDrakoulis,1958a,p.37):R.A. Lamb&S.G. GaitNo.1PhillipsEstate;E.B.LaßueNo.1Edmund Longshore. (39) C.H.Murphy,Jr.,No.1R.E.Eaton Alabama, Pickens County; Sec. 34, T. 19 S., R. 16 W. Elev. 315 ft.; T. D. 5,503 ft.; completed 1946. — Paleozoic rocks. Top at 940 feet. Pottsville formation (Pennsylvanian) to total depth. Sample log shows a monotonous sequence of gray and black micaceous or sandy shale, with some beds of sandstone, occasional coal beds, and one bed of crinoidal limestone. Overlain by Tuscaloosa formation (Upper Cretaceous). References.— Mellen, 1947, fig. 8, p. 1813; Applin, 1951, p. 22, table 3, well 35; McGlamery, 1955, pp. 369-379. (40) L.M.Glasco No. 1J. A. Norwood Alabama, Greene County; Sec. 17, T. 23 N., R.1W. Elev. 211 ft.; T. D. 5,510 ft.; completed 1957. Bureau ofEconomic Geology, The University of Texas — Paleozoic rocks. Top at 1,865 feet. Reported to have drilledin Pennsylvanian to total depth, but littleinformationis available (P.L.Applin,1960). Overlain by Lower Cretaceous (? ). (41) Stanolind Oil&Gas Company No.1G.B.SandelAlabama, Tuscaloosa County; Sec. 2, T. 18 S., R. 9 W. Elev. 600 ft.; T.D. 5,410 ft.; completed 1943. — Paleozoic rocks. Paleozoic at surface. Pottsville formation (Pennsylvanian) to 2,985 feet; shale and sandstone, with some coal beds and marine fossiliferous layers. Underlain to total depth by limestone and sandy limestone, with traces of fossils. Driller's log reports these underlying strata to be Bangor limestone (Mississippian) (Toulmin, 1945), but sample examination indicates that they areprobably Ordovician (McGlamery, 1955). Thewellisinthe WileyorFriedman dome, whichhas about 300 feet of closure in the Pennsylvanian; superposition of Pennsylvanian on Ordovician sug gests a periodic upliftof this feature before the finaldoming. References.— Toulmin, 1945, pp. 133-135; McGlamery, 1955, pp. 380-389; Jones, 1960, pp. 89-90. Mississippian and Pennsylvanian ( ? ) (42) A.Gutowsky et al.No.1Ada Mills Arkansas, LittleRiver County; Sec. 18, T.12 S.,R. 29 W. Elev. 328 ft.; T. D.—about 4,300 ft.; completed before 1943. Paleozoic rocks. Top at about 2,700 feet. "Folded Paleozoics of Ouachita facies"; no data are given as to their character. Overlain by Hosston formation (Lower Cretaceous). Published section shows a thin intervening wedge of Eagle Millsformation. — Reference. Hazzard and others, 1947, section A-A'. (43) Boettcher No. 1State Life Insurance CompanyArkansas, Howard County; Sec. 28, T. 11 S., R. 27 W. Elev. 292 ft.; T. D. 2,936 ft.; completed 1937. — Paleozoic rocks.-Penetrated 750 feet of hard tight sand, with streaks of carbonaceous shale. Lithologically, the sandstone suggests Jackfork formation, but the black shale streaks may indicate Atoka formation. Overlain by Hosston formation (Lower Cretaceous), withbasal chert conglomerate. References.— Weeks, 1938, p. 962; Swain, 1944, p. 589, fig. 7. (44) S. S. Alexander No. 1 Smythe Arkansas, Calhoun County; Sec.7,T.11S.,R.14W. Elev.263ft.;T.D.about 4,000ft.;completed 1938. — Paleozoic rocks. Top at about 2,500 feet. "Folded Paleozoics of Ouachita fades"; no data are given as to their character. Overlain by Ozan and Tokio formations ofLate Cretaceous (Austin) age. — Reference. Hazzard and others, 1947, section B-B'. Besides these wells,Weeks (1938,p.962) mentions oneinSec. 25,T.9S.,R.19W., Clark County, which penetrated 610 feet of black carbonaceous shale, with streaks of tight fine sand and some gray and brown limestone, probably Atoka formation; and another in Sec. 36, T.10 S., R. 11 W., Cleveland County, that penetrated 100 feet of tightsandandblackshale,probablyEarlyPennsylvanian orMississippian. Imlay(1940a, sectionC-C)indicates thatOhioOilCompanyNo.1Taylor,Sec. 27,T.9S.,R.17W., Dallas County, entered "folded Paleozoics" at a depth of 1,698 feet but does not show their character. Spooner (1935, p. 334) states that in Grant County to the north, the Paleozoic rocks penetrated inthe half-dozen wells drilled prior to 1935 "consists chiefly of light-colored to gray quartzitic sandstone and dark gray slaty shale." Although records for the wells classed as "Mississippian and Pennsylvanian (?)" are incomplete, some or all of them probably penetrated Stanley shale and Jackfork sandstone of Mississippian age, and perhaps also Atoka formation of Pennsylvanian age. Devonian to Cambrian of Appalachian System (45) Carter OilCompany No. 1Denkman Mississippi,Leake County; Sec. 31,T.11N.,R.7E. Elev. 449 ft.; T.D.9,408 ft.; completed 1952. The Ouachita System — Paleozoic rocks. Top at 8,728 feet. Apparently most of the sequence is carbonate rocks. Poorly preserved brachiopods occur ina core at 9,356 to 9,379 feet, whichare Coelospira sp. and Stricklandia sp., of Silurian age (G. A. Cooper, 1952, letter to Rizer Everett). No information is available as to whether Paleozoic formations of other ages overlie or underlie the Silurian strata. Overlain by Cotton Valley group (Jurassic) . — Reference. Beikman and Drakoulis, 1958a, p. 40. (46) Southeastern Drilling Company No. 1 L.D. Eley et al. Mississippi, Scott County; Sec. 19,R.8 N.,T.8E. Elev. 383 ft.; T.D. 9,814 ft.;completed 1952. Paleozoic rocks.—Top at 9,458 feet. Cambro-Ordovician (Beikman and Drakoulis, 1958a). Red calcareous dolomitic chert, much like that in well 45 from which Cooper identified Silurian fossils; probably not Cambro-Ordovician (F. F. Mellen, 1960). Overlain by Cotton Valley group (Jurassic) . — Beikman and Drakoulis, 1958a, p. 51. Reference. (47) SlickOilCompany &Plains Producing Company No.1J.D.Breazeale Mississippi, Neshoba County; Sec. 28, T. 12 N., R.10 E. Elev.398ft.;T.D.6,132ft.;completed 1947. — Paleozoic rocks. Top at 5,825 feet. Cambro-Ordovician cherty dolomite to total depth. Overlain by—Lower Cretaceous. Dott and Murray, cd., 1954, sheet 1, well3;Beikman and Drakoulis, 1958a, p. 46. References. (48) Pure OilCompany No. 1J. D. Jones Mississippi, Neshoba County; Sec. 19, T. 11 N., R. 13 E. Elev. 493 ft.;T.D.—5,610 ft.;completed 1951. Paleozoic rocks. Top at 5,381 feet. Reported to be Ordovician dolomite. Overlain by—Lower Cretaceous ( ? ). Reference. Beikman and Drakoulis, 1958a,p. 46. (49) Pure OilCompany No. 1A. S. Rea Mississippi, Neshoba County; Sec. 36, T. 11 N., R. 12 E. Elev. 527 ft.; T. D. 5,519 ft.; completed 1950. Paleozoic rocks.—Top at 5,510 feet.Reported tobe Ordovician dolomite. Overlain by—Lower Cretaceous ( ? ). Reference. Beikman and Drakoulis, 1958a, p. 46. (50) Southern Natural Gas Company No.1J. W.Smith Mississippi, Neshoba County; Sec. 1, T. 9 N., R. 11E. Elev. 557 ft.; T. D. 6,876 ft.; completed 1943. — Paleozoic rocks. Top at 6,450 feet. Cambro-Ordovician limestone, sandy limestone, and dolomite to total depth. Overlain by—Lower Cretaceous. References. DottandMurray,cd.,1954,sheet1,well2;BeikmanandDrakoulis,1958a,p.46. (51)SunOilCompany No.1CitizensNationalBank Mississippi, Newton County; Sec. 23, T. 5 N., R. 13 E. Elev. 389 ft.; T.D.8,340 ft.; completed 1945. — Paleozoic rocks. Top at 8,300? feet. Ordovician dolomite to total depth. Samples from 8,300 and 8,306 feet are red, fine-grained, calcareous dolomite and fine-grained dolomite of lower Paleozoic type (P.T.Flawn,1959).Samples arereported tosuggest faultingorfolding. Overlain by Cotton Valley group (Jurassic) . — Reference. Beikman and Drakoulis, 1958 a, p. 46. (52)SunOilCompany No.1HilmaWall Mississippi, Newton County; Sec. 28, T. 5 N., R. 13 E. Elev. 406 ft.; T.D.10,117 ft.; completed 1943. Paleozoic rocks. —Top at 8,761 feet. Cambro-Ordovician limestone with some dolomite and sandy dolomite inlowest 300 feet. Overlain by Cotton Valley group (Jurassic) . — References. Dott and Murray, cd., 1954, sheet 1, well1; Beikman and Drakoulis, 1958a, p. 46. (53) Marott No. 1Larkin Alabama, Sumter County; Sec. 34,T.20N.,R.2W. Elev. 204 ft.; T.D. 4,590 ft.; completed 1955. Paleozoic rocks.—Top at 3,082 feet. Knox dolomite (Cambro-Ordovician) reported to total depth. (54) Johnson &Hawkins Company No.1Willis Alabama, Greene County; Sec. 11, T. 20 N.,R.1E. Elev. 130 ft.; T. D. 2,616 ft.; completed 1940. Paleozoic rocks.— Top at 2,350 feet. Driller's log records "hard lime" and "hard sandy lime" to total depth. At first reported to be Mississippian, including Fort Payne (Bowles, 1941) but later Bureau ofEconomic Geology, The University of Texas assigned to the Ordovician(?) (Shreveport Geol. Soc, 1947). The assignment of the rocks to the Ordovician(?) is more compatible withthe regional relations. Overlain by Lower Cretaceous. References.— Bowles, 1941, pp. 151-152; Shreveport Geological Society, 1947, pi. 3; Applin, 1951, p. 22, table 3, well29. (55) E. C. Johnston No. 1H. D. Peteet Alabama, Marengo County; Sec. 3,T.16N.,R.2E. Elev. 247 ft.;T. D.4,523 ft.;completed 1944. — Paleozoic rocks. Top at 3,872 feet.Driller'slogrecords "lime"and "hard gray lime"to total depth, with cores at 3,927, 4,209, 4,291, and 4,523 feet. Cores contain fossils of high Black River or of Trenton age (G. A.Cooper, 1944, letter toAlabama Geological Survey). Overlain by Lower Cretaceous. References.—Toulmin,1945,pp.114-116; ApplinandApplin,1947,sheet2,fig.10,well26;sheet 3, text; Applin, 1951, p. 22, table 3, well34. System Devonian toCambrian of Ouachita (56) A.L.Kitselman, No. 2 Fee Arkansas, Pulaski County; Sec. 2, T.1S., R. 13 W. Elev. 250 ft.; T. D.4,080 ft.; completed 1938. — Paleozoic rocks. Paleozoic at 250 feet. Driller's log and sample examinations by W. B. Weeks are available. "The rocks are greatly deformed and metamorphosed; descriptions of cuttings show they contain much vein quartz and are cut by several dikes of igneous rocks. Apparently the drillpassed through the Arkansas novaculite from 792-1,132 feet, possibly the Missouri Mountain slate in the next 200 feet, possibly the Polk Creek shale from 1,400-1,700 or 1,800 feet, possibly the Bigfork chert to 3,600 feet or beyond" (H.D. Miser, 1938, letter to Arkansas Geological Survey). This wellis only a few miles from outcrops of Devonian and older rocks at the east end of the Ouachita Mountains. Overlain by—Midway(?) formation. References. Caplan, 1954, p. 12; log and sample report from Arkansas Geological and Conserva tion Commission, 1960. Devonian to Cambrian of Suwanee Basin (57) Union Producing Company No. 1E. P. Kirkland Alabama, Houston County; Sec. 20,T.7N.,R.11W. Elev. 140 ft.; T.D. 8,100 ft.; completed 1949. Paleozoic rocks.—Top at 7,556 feet. Quartzitic gray sandstone and black micaceous shale to total depth, containing graptolites of Early Ordovician (Canadian) age. The rocks in this well are the only ones in which graptolites have been found inthe Suwanee basin (Jean Berdan, 1960). Overlain by 566 feet of Triassic (?) clastic rocks. References.— Applin, 1951, p. 22, table 3, well 30; Bridge and Berdan, 1951, 1952; McKee and others, 1959, pi. 4. (58)Mont Warren et al.No.1A.C.Chandler Georgia, Early County; Lot 406, Land Dist. 26. Elev. 181 ft.; T.D.7,320 ft.; completed 1943. — Paleozoic rocks. Top at 6,600 to 6,607 feet is a weathered zone composed of dullbrick-red, finely sandy, somewhat micaceous shale containing molds and impressions of small bivalves. First black shale fragments occur in cuttings at about 6,780 feet. Quartzitic sandstone was penetrated from 7,240 feet to total depth. Black shale at 6,995 to 7,015 feet contains Chevroleperditia chevronalis, a new genus and species of ostracode, originally interpreted from its stage of evolution to be of Late Ordovician or Early Silurian age (Swartz, 1949). Subsequently, J. M. Schopf has determined plant spores from the same horizon as not older than Middle Devonian, and the ostracodes are compatible withthis age. No fossils have been recovered from the lower part of the black shale or the sandstone beneath it. Overlain by 930 feet of Triassic (? ) clastic rocks. References.— Applinand Applin,1947, sheet 1,fig.2,well61; Swartz, 1949, p. 320; Applin,1951, p. 25, table 3, well73; Bridge and Berdan, 1951, 1952; McKee and others, 1959, pi. 4; revisions by P. L.Applin and Jean Berdan, 1960. (59) Humble Oil&Refining Company No.1Bennett &Langsdale Georgia, Echols County;Lot146, LandDist. 12. Elev.181ft.;T.D.4,185ft;completed 1949. Paleozoic rocks.—Top at 4,120 feet; weathered? shale. Paleozoic rocks are intruded by one or more sillsof diabase of Triassic (?) age from 4,125 to 4,150 feet, withshale beneath to total depth. The shale is tentatively correlated with micaceous shale and quartzitic sandstone which have yielded Early Ordovician (Canadian) fossils in well57 (Bridge and Berdan, 1951, 1952). The Ouachita System Overlain by Lower Cretaceous ( ? ). References.— Applin, 1951, p. 16, p. 25, table 3, p. 27, table 4, well74; Bridge and Berdan, 1951, 1952. (60) Hunt OilCompany No. 4 Superior Pine Products Company Georgia, Echols County; Lot 219, Land Dist. 13. Elev. 156 ft.; T.D. 3,916 ft.; completed 1948. Paleozoic rocks.—Top at 3,911 feet. Red micaceous silty shale, probably in a weathered zone, containing linguloid brachiopods of Middle Ordovician age. Overlain byLower Cretaceous ( ?). References.— Applin,1951, p. 25, table 3, well78; Bridge and Berdan, 1951, 1952. (61) Hunt OilCompany No. 1Superior Pine Products Company Georgia, Echols County; Lot 364, Land Dist. 13. Paleozoic rocks.—Top at 3,782 feet. Black or dark gray shale with some reddish streaks, containing fragments of the inarticulate brachiopod Trematis, identified by Bridge and Cooper; this genus ranges fromMiddletoLateOrdovicianinage (Jean Berdan, 1960). OverlainbyLower Cretaceous (?). References— Applin, 1951, p. 25, table 3, well75; Bridge and Berdan, 1951, 1952. (62) Humble Oil &Refining Company No. 1 C. W. Tindel Florida, Jackson County; Sec. 8, T. 5 N., R. 11 W. Elev. 128 ft.;T. D.9,245 ft.;completed 1949. Paleozoic rocks.— Top at 8,440 feet. Red, brown, and gray, cross-bedded sandstone and shale to total depth, probably of fresh-water or continental origin, from which plant fragments and spores of probable Middle Devonian age have been identified by Serge Mamay and J. M. Schopf (Jean Berdan, 1960).Two basalt sills occur in the Paleozoic rocks at depths of 8,890 to 8,932 and 8,970 to 8,983 feet. Overlain by about 220 feet of Triassic( ? ) clastic rocks. References.— Applin, 1951, p. 23, table 3, p. 26, table 4, well53; Bridge and Berdan, 1951, 1952; McKee and others, 1959, pi.4. (63) Coastal Petroleum Company No. 1E. P. Larsh Florida,Jefferson County; Sec.1,T.2S.,R.3E. Elev. 51 ft.; T. D.—7,913 ft.; completed 1949. Paleozoic rocks. Top at 7,909 feet. White quartzitic sandstone without fossils but possibly of Early Ordovician age. Overlain by 810 feet of clastic rocks of Triassic(?) age, with diabase sills or dikes at 7,763 to 7,792 and 7,850 to 7,890 feet. References.— Applin, 1951, p. 23, table 3, p. 26, table 4, well54; Bridge and Berdan, 1951, 1952; McKee and others, 1959, pi. 4. (64) Hunt OilCompany No. 2 J. W. Gibson Florida,Madison County; Sec. 6,T.1S.,R.10E. Elev. 107 ft.; T. D. 5,385 ft.; completed 1944. — Paleozoic rocks. Top at 4,628 feet. Black shale to total depth, containing a trilobite and some linguloidbrachiopods ofprobable earlyMiddleOrdovician (Chazyan) age. Overlain by diabase from 4,589 to 4,628 feet, and this by Lower Cretaceous or older Mesozoic rocks. Applin, 1951, p. 24, table 3, p. 26, table 4, well62; Bridge and Berdan, 1951, 1952; References.— Whittington, 1953. (65) Hunt OilCompany No. 4 J. W.Gibson Florida,MadisonCounty;Sec. 5,T.2S.,R.11E. Elev. 73 ft.;T.D.4,096 ft.;completed 1945. — Paleozoic rocks. Top at 4,060 feet. Black quartzitic sandstone with worm borings, and shale, probably of Early Ordovician ( Canadian ) age. Overlain by diabase from 4,044 to 4,060 feet, and this by Lower Cretaceous or older Mesozoic rocks. Applin, 1951, p. 24, table 3, p. 26, table 4, well63; Bridge and Berdan, 1951, 1952. References.— (66) Humble Oil&Refining Company No.1R. L.Henderson Florida, Lafayette County; Sec. 20, T. 4 S., R. 11E. Elev. 52 ft.;T. D. 4,235 ft.;completed 1948. — Paleozoic rocks. Top at 4,192 feet, with weathered zone to 4,205 feet. Penetrated a boulder zone containing red and yellow quartzite pebbles and ended in hard white to gray unfossiliferous quartzite of uncertain but probable early Paleozoic age. Overlain by Lower Cretaceous (? ). References.— Applin, 1951, p. 24, table 3, well57; Bridge and Berdan, 1951, 1952. (67) Gulf OilCorporation No.1Brooks-Scanlon, Inc.,Block 49 Florida, Lafayette County; Sec. 36, T. 5 S., R. 10 E. Elev. 87 ft.; T.D. 4,512 ft.;completed 1949. Bureau of Economic Geology, The University of Texas — Paleozoic rocks. Top at 4,505(?) feet. Quartzitic sandstone to total depth. May be pebbles or boulders of early Paleozoic rock incorporated in Cretaceous or earlier Mesozoic conglomerate, or may be a Paleozoic formation. There is no information either way, as maximum penetration of the quartzite was only 7 feet. Overlain by Lower Cretaceous (?) References.— Applin,1951,p.23,table3,well56;BridgeandBerdan,1951,1952. (68) Sun OilCompany No. 1P. C. Crapps Florida, Lafayette County; Sec. 25, T. 6 S., R. 12 E. Elev. 70 ft.; T.D.—4,133 ft.; completed 1946. Paleozoic rocks. Top at 3,993; weathered zone to 4,030 feet. Unfossiliferous quartzitic sandstone and shale, probably of Early Ordovician (Canadian) age. Overlain by Lower Cretaceous ( ? ). References. —Applin,1951, table 3, well58;Bridge and Berdan, 1951, 1952. For wells which entered Paleozoic rocks in the Suwanee basin south and east of the map area, inFlorida and Georgia, see Applin (1951) and Bridge and Berdan (1951, 1952). Weakly Metamorphosed Rocks (69) Fohs-Loffland Bros. No. 1Louis Miller Arkansas, Arkansas County; Sec. 33, T. 5 S., R. 4 W. Elev. 190 ft.; T. D. 4,560 ft.; completed 1940. — Paleozoicf?) rocks. Top at 4,518 feet. Driller's log records "gray slaty schist" to total depth. Core at 4,550 to 4,560 feet is described as "gray slate and schist, graphitic in spots." The degree of metamorphism implied by the driller's record suggests that the rocks may be of Ouachita facies (Caplan, 1954). Overlain by "Eutaw" (Tokio formation) (Upper Cretaceous). References.— Renfroe, 1949, pp. 20-21;Caplan, 1954, p. 13. (70) Holman&RussellNo.1E.K.Thomas Mississippi, Bolivar County; Sec. 18, T. 24 N., R. 7 W. Elev.159ft.;T.D.4,659ft.;completed 1941. — Paleozoicf ?) rocks. Top at 4,587 feet. Rocks are of "Ouachita" facies (H. J. Morgan, Jr., 1958). This wellis close to the Ouachita structural front as projected and only a few miles southwest of No.1Knowlton&Perthshire (well24) which is here interpreted as of foreland facies. The rocks intheThomas—wellarehere placedinthemetamorphic unit,butwithdoubt. Reference. Beikman and Drakoulis, 1958a,p. 14. (71) The Texas Company No. 1E. G. Whitehead et al. Mississippi, CarrollCounty; Sec. 22,T.18 N.,R.5E. Elev.342ft.;T.D.5,283 ft.;completed 1948. — Paleozoicf?) rocks. Top at 5,215 feet. Undifferentiated Paleozoic (Beikman and Drakoulis, 1958a ). Reported to be "metamorphic schist." This welllies close to the Ouachita structural front as projected, and the "schist" is compatible withthe weakly metamorphosed rocks penetrated in Attala County to the south (wells 72 and 73). According to C. E. Weaver (fig.7, p. 148) the clays from this wellhave a "sharpness ratio"of more than 5.0, the highest recorded inMississippi, and comparable to clays of the interior zone of the Ouachita beltinTexas. Overlain by—Lower Cretaceous ( ? ). Beikman and Drakoulis, 1958a, p. 14. Reference. (72) StanolindOil&Gas Company No.1C.E.Steed Mississippi,AttalaCounty;Sec. 4,T.13N.,R.6E. Elev.329 ft.;T.D.7,108 ft.;completed 1947. Paleozoicf?) rocks.—Top at 6,724 feet. Thin sections were studied from depths of 6,700, 6,705, 6,805, 6,815, 6,886, 6,905, 6,995, 7,075, and 7,085 feet (August Goldstein, Jr., 1960). Most of the specimens are chert, cherty clay-slate, and clay-slate, but there is one specimen (6,805 feet) of siliceous limestone and another of metaquartzite (6,905 feet). The cherts are variably argillaceous, dolomitic, and calcareous, and grade into cherty or siliceous slate. The whole suite was probably a high-silica shale before metamorphism, but half or more of the clay has been recrystallized to chlorite and sericite; metamorphism is weak to low grade (muscovite-chlorite subfacies of green schist facies). In some of the cherts are monaxon sponge spicules that have been recrystallized and partly resorbed, but noother fossils are visible. "These cuttings are comparable inmetamorphic grade torocks ofOuachita facies along the Balcones fault zone " to assign them to a definite in central Texas. It is not possible formation, but their general aspect is Ordovician ( ? ) ( Goldstein) . Overlain by—Lower Cretaceous. Reference. Beikman and Drakoulis, 1958a, p. 13. The Ouachita System (73) Continental OilCompany No.1MillardSudduth Mississippi,AttalaCounty; Sec. 28,T.13N.,R.6E. Elev.342ft.;T.D.8,018—ft.;completed 1952. Paleozoicf?) rocks. Top at 7,249 feet. Rocks are weakly metamorphosed but strongly sheared black slate. Cores were examined from depths of 7,080, 7,601, 7,798, and 7,970 feet (Josiah Bridge, 1953; P. T. Flawn, 1959). They are carbonaceous or graphitic clay-slate, containing abundant mica and chlorite, well foliated and in places with incipient fracture cleavage or microfaults. Foliation crosses bedding at angles of 20° to 40°. Inone core (7,970 feet) thin layers of black graphitic slate alternate with thin layers of fine-grained dolomite, in which the carbonate grains are stretched and twinned. Quartz veinlets, dolomite veinlets, and pyrite are common; one core (7,798 feet) is a breccia of angular vein quartz fragments, cemented by limestone and shale. Metamorphism is weak but with a strong shearing element. The cores were searched for fossils without result, but the general aspect of the rocks would seem to be like that of the older Paleozoic formations of Ouachita facies. Overlain between 7,018 and 7,249 feet by altered porphyry, in which feldspar laths are changed to clay; flowage structure in the groundmass suggests that the rock was extrusive. The porphyry is overlain in turn by Lower Cretaceous. — Reference. Beikman and Drakoulis, 1958a, p.13. (74) Gulf Refining Company No. 49 Louis Werner SawmillCompany Arkansas, Union County; Sec. 5, T. 16 S., R. 16 W. Elev. 128 ft.; T.D.—7,973 ft.; completed 1935. Paleozoic rocks. Top at 7,600 feet. "Mudstone" or "hornfels"; hard, dense, silicified, reddish to purplish, dipping 15° to 20°, intruded by diabase. From the available record itseems likely that much or all of the metamorphism is related to the igneous intrusion. Overlain with basal conglomerate by Werner formation, of which this is its type section. The well is on the Louann dome inthe Smackover oilfield. — References. Imlay,1940, p. 10;Hazzard and others, 1947, pp. 486-487, section B-B'. (75) Phillips Petroleum Company No. 1J. T. Arnold Arkansas, Ouachita County; Sec. 27, T. 15 S., R. 15 W. Elev. 208 ft.;T.D.about 7,000 ft.; completed 1936. — Paleozoic rocks.--Top at about 6,700 feet, with igneous rocks near total depth; no data are given as to nature of the Paleozoic rocks, but they may resemble the rocks in well74. Overlain by Werner formation. The wellis inthe Smackover oilfield. Reference. —Imlay,1940, section E-E'. Farther northeast in Cleveland County, Spooner (1935, pp. 392-394) reports that Arkansas Natural Gas Company No. 1 Tate, Sec. 4, T.9 S., R 11 W., penetrated altered pre-Mesozoic rocks at 3,310 feet which, according to C. S. Ross, are shale, limestone, and possibly chert, intruded and contact-metamorphosed by peridotite. The description suggests the older Paleozoic rocks of the Ouachita Mountains. Metamorphic and Plutonic Rocks (76) Gulf Refining Company No. 1C. C. Sellers Alabama, Wilcox County; Sec. 13, T.11 N., R. 7 E. Elev.182ft.;T.D.7,575 ft.;completed 1952. Metamorphic rocks.—Top at 7,422 feet. Reported to be "schist." Overlain by pre-Smackover Jurassic rocks. (77) Seaboard Oil Company No. 1S. M.McConnico Alabama, WilcoxCounty; Sec. 32,T.12N.,R.10E. Elev.186ft.;T.D.5,780ft.;completed 1945. — Metamorphic rocks. Top at 5,518 feet. Granite gneiss to total depth. Overlain byLower Cretaceous or older Mesozoic rocks. Reference. —Applin, 1951, p. 19, table 1, well 4. (78) Seaboard OilCompany No. 1J. T. Rollins Alabama,WilcoxCounty; Sec.16,T.12N.,R.10E. Elev.152ft.;T.D.5,449—ft.;completed 1958. Metamorphic rocks.--Top at 5,220 feet. Weathered schist to 5,313 feet, schist to total depth (P. L. Applin,1960). Overlain by Cotton Valley group (?) and Lower Cretaceous. (79) Montgomery OilCompany No. 1Snowdown Alabama, Montgomery County; Sec. 29 or 30, T. 15 N., R. 18 E. Elev. 222 ft.; T.D. 2,007 ft.; completed 1922. Bureau of Economic Geology, The University of Texas Metamorphic rocks.— Top at 1,995 feet. Crystalline rock to total depth. Overlain by Tuscaloosa formation (Upper Cretaceous) . References.— Bowles, 1941, pp. 158-159; Applin,1951, p. 19, table 1, well3. (80) Gulf Refining Company No. 1 D. A. Hendrix Alabama, ButlerCounty; Sec. 26,T.7N.,R.13E. Elev. 440 ft.; T. D. 9,480 ft.; completed 1952. — Metamorphic rocks. Top at 9,460 feet. Logged as "diorite schist" (P.L.Applin, 1960). Cores from 9,460 to 9,480 feet were examined (Charles Milton,1952; P. T. Flawn, 1960). Miltonidentified the rock as rhyolite tuff and rhyolite porphyry tuff. According to Flawn, "The sample is an altered volcanic rock composed largely of sericite, calcite, chlorite, and epidote, with corroded remnants of plagioclase phenocrysts, and sporadic smaller quartz phenocrysts. The sericite fibers which compose most of the groundmass may be inherited from a pre-existing flow structure or they may form a foliation imposed by regional metamorphism. Well developed smooth planar surfaces make an angle of about 45° with the core wall." The felsic nature of this igneous rock distinguishes itfrom the mafic igneous rocks of Triassic (?) age in the same area, and itis here interpreted as part of the basement complex of the Piedmont. The rock may be comparable to felsic volcanic rocks penetratedby wells insoutheastern Georgia (well88, below, and Applin,1951, pp. 8-11). Overlain by about 781 feet of red conglomerate, sandstone, and shale, with basalt at top, probably Triassic(?), and this by Lower Cretaceous. Core at 8,679 to 8,688 feet is olivinebasalt, core at 8,727 to 8,737 feet is coarse arkosic conglomerate (Charles Milton,1952; P. T.Flawn, 1960). (81) Alabama OilDevelopment Company No. 1 Jacob Hill Alabama, Pike County; Sec. 35, T. 8 N., R. 19 E. Elev. 438 ft.; T. D.2,691 ft.; completed 1928. — Metamorphic rocks. Top at 2,665 feet. Logged as "graphitic mica schist." This reported penetration of metamorphic rocks requires verification, as itis at surprisingly shallow depth, compared with sequences in wells 1and 80 adjacent to the west, where thick bodies of Triassic (?) rocks underlie the Cretaceous. Overlain by Tuscaloosa formation. Reference.— Bowles, 1941, pp. 245-247. (82) CapitolOil&Gas Company No.1EthelB.Gholston Alabama, Bullock County; Sec. 18, T. 14 N., R. 22 E. Elev. 270ft.;T.D.1,714ft.;completed 1945. — Metamorphic rocks. Top at 1,703 feet. Logged as "granite gneiss" but termed "dioritegneiss" by Applin (1951). Overlain by Lower Cretaceous. References. —Toulmin, 1945, pp. 19-20; Applin and Applin, 1947, sheet 1, fig. 6, well3; Applin, 1951, p. 5, p. 19, table 1, well1. (83) CapitolOil&Gas Company No.1FredPickett Alabama,BullockCounty; Sec. 22,T.13N.,R.21E. Elev. 430 ft.; T.D.2,523 ft.; completed 1945. Metamorphic rocks.—Top at 2,502 feet. Metamorphic rock, probably gneiss, to total depth;no cores taken. Overlain byLower Cretaceous. — References. Toulmin, 1945, pp. 21-23; Applin and Applin, 1947, sheet 1, fig. 6, well4; Applin, 1951, p. 19, table 1, well2. (84) Southeastern Operator's Committee No.1Mrs.Beatrice Gamble &0.A.Gamble Alabama, HenryCounty; Sec.13,T.4N.,R.28E. Elev. 304 ft.;T. D. 6,395 ft.;completed 1952. — Metamorphic (?') rocks. Core at 6,391 to 6,394 feet is granophyre, which might be a marginal phase of either a granite batholith or of a large body of diabase or gabbro (Charles Milton, 1952). Information is not available as to the nature of the overlying rocks. Considerable thicknesses of Triassic(?) clastic rocks and mafic igneous rocks are penetrated in nearby wells. The granophyre might be an unusual differentiate of one of the mafic igneous bodies, but its depth is comparable to that ofpre-Mesozoic rocks inthe vicinity. (85) Tricon Minerals, Inc., No. 1J. D. Duke Georgia, Houston County; Lot44, Land Dist. 14. Elev. 419 ft.; T. D.1,494 ft.; completed 1949. — Metamorphic rocks. Top at 1,490 feet. Biotite gneiss to total depth. Overlain by Tuscaloosa (?) formation (Upper Cretaceous) . Reference.— Applin, 1951, p. 5, 19, table 1, well9. (86) TriconMinerals, Inc.,No.1H.B.Gilbert Georgia, Houston County; Lot 266, Land Dist. 13. Elev.367ft.;T.D.1,698ft.;completed 1949. — Metamorphic rocks. Top at 1,685 feet. Biotite gneiss to total depth. The Ouachita System Overlain by Tuscaloosa( ?) formation (Upper Cretaceous). — Reference. Applin, 1951, pp. 5, 19, table 1, well 10. (87) MiddleGeorgia Oil&Gas Company Georgia, Washington County; 12 miles northwest of Sandersville. Elev. 300 ft.; T. D. 400 feet; completed 1920. — Metamorphic rocks. Incrystalline rock to total depth. Overlain by Tuscaloosa formation (Upper Cretaceous). This well is only a few miles south of outcrops of metamorphic rocks inthe Piedmont province. References.— Richards, 1945, p. 926; Applin, 1951, p. 20, table 1, well 28. (88) Sun OilCompany No. 1Doster-Ladson Georgia, Atkinson County; Lot71,Land Dist.7. Elev. 222 ft.;T.D.4,296 ft.; completed 1945. Metamorphic rocks.—Top at 4,220 feet. Volcanic tuff or agglomerate composed of hydrothermally altered rhyolite. Overlain by Lower Cretaceous. Similar rhyolitic volcanic rocks were penetrated in a well in Camden County, Georgia, to the east, suggesting the existence of a belt of these rocks along the northeast edge of the Suwanee basin of Paleozoic rocks. Reference.— Applin,1951, pp. 9, 21, table 2, well 27. For additional wells which entered metamorphic and plutonic rocks in Georgia east of the map area, see Applin (1951, pp. 19-21, tables 1-2). Plates 5-15 Bureau of Economic Geology, The University of Texas Plate 5 Photomicrographs of lower Paleozoic Ouachita facies rocks from the frontal zone of the Ouachita belt A. Bituminous dolomitic spiculitic chert (Bigfork chert, Stringtown quarry, Atoka County, Oklahoma). x63 B. Bituminous dolomitic spiculitic chert (Bigfork chert, Sun Oil Company No. 1 Tucker, Fannin County, Texas, 3,820 to 3,830 feet, p. 256). x63 C. Dolomitic chert (lower Paleozoic Ouachita facies, Mellon Oil Company No. 1 Noah Bailey, Bell County, Texas, 3,575 to 3,580 feet, p. 218). x9l D. Bituminous radiolarian-bearing chert (lower Paleozoic Ouachita facies rocks, Roland Blumberg No. ID.C. Knibbe, Comal County, Texas, 1,535 to 1,540 feet, p. 243). xB2 Bureau ofEconomic Geology, The University of Texas Plate 6 Photomicrographs of sandstone from the Stanley shale in the frontal zone of the Ouachita belt A. Fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone (Ouachita Mountains, 32-IS-12E, NW/4, NW/4, Atoka County. Oklahoma) . x56 B. Fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone (Texas Minerals No. 1Snowden, Fannin County, Texas, 3,395 to 3,425 feet, p. 256). x49 C. Fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone (Shell Oil Company No.IC.E.Massie, BellCounty, Texas, 850to860 feet, p.221). x56 D. Fine-grained, angular, poorly sorted, argillaceous feldspathic quartz sandstone (Midcoast (B. R. Floyd)No.IE.A.Jones, TravisCounty,Texas.695to700feet,p.315). x49 = g garnet 368 Bureau of Economic Geology, The University of Texas Plate 7 Photomicrographs of Mississippian-Pennsylvanian sandstone (including sandstone from the Tesnus formation) from the frontal zone of the Ouachita belt A. Fine- to medium-grained, angular to subround, poorly sorted, argillaceous feldspathic quartz sandstone (Tesnus formation, Persimmon Gap, Brewster County, Texas) . x49 B. Fine-to medium-grained, mostly angular, poorly sorted, calcareous argillaceous feldspathic quartz sandstone containing abundant rock fragments (Bernard Einstoss No. 1 Roswell Wardlaw, Uvalde County, Texas, 1,853 to 1,857 feet, p. 317). x49 C. Fine-grained, angular, poorly sorted, argillaceous micaceous feldspathic quartz sandstone veined by quartz (General Crude Oil Company No. 1 J. H. Talley, Bexar County, Texas, 2,615 to 2,622 feet, p. 225). x56 1). Fine-grained, subangular to subround poorly sorted, feldspathic argillaceous quartz sandstone (Roland Blumberg No. 1 D. C. Knibbe, Comal County, Texas, 2,930 feet, p. 243). x56 Bureau of Economic Geology, The University of Texas Plate 8 Photomicrographs of rocks from the frontal zone of the Ouachita belt A. Radiolarian tests and spicules in shale (Jackfork sandstone, Cox Drilling Corporation No. 1 S. F Leslie, Fannin County, Texas, 4,100 to 4,110 feet, p. 254). x63 B. Cone-in-cone limestone (Stanley shale, Peter Oil and Gas Co., Inc., No. 1Butcher, Grayson CountyTexas, 3,340 feet, p. 262). x24 C. Radiolarian ( ?) tests in chert (lower Paleozoic Ouachita facies rock, General Crude Oil CompanyNo. 1Earnest Day, Coryell County, Texas, 6,870 to 6,880 feet, p. 246). xlO5 D. Sheared calcite marble (metamorphosed lower Paleozoic Ouachita facies rocks, Johnston Petroleum Syndicate No. 1 Lady Alice, Red River County, Texas, 4,000 to 4,033 feet, p. 301). x42, crossed nicols sc=stretched calcite Bureau of Economic Geology, The University of Texas Plate 9 Photomicrographs of rocks from the frontal and interior zones of the Ouachita belt close to the Luling front clay-slate extensively veined with quartz (dark clastic unit in the interior part of the frontal zone, City of Austin No. 1 Blunn Creek, Travis County, Texas, 2,246 feet, p. 312). xl4, crossed nicols A. Carbonaceous B. Strongly deformed black graphitic slate containing broken quartz veins (interior zone, General Crude OilCompany No.1Rogers Ranch, Bexar County, Texas, 2,676 feet, p. 224). x49 C. Strongly deformed graphitic black slate containing augen of broken quartz veins and slate fragments (interior zone, Woodward No. 1 Schubert, Hays County, Texas, 3,333 to 3,338 feet, p. 272). xlB D. Strongly deformed black graphitic slate containing broken quartz veins (interior zone, Stanolind Oiland Gas Company No. 1Schmidt, Guadalupe County, Texas, Core No. 38, p. 269). x49 Bureau ofEconomic Geology, The University of Texas Plate 10 Photomicrographs oflow-grade metamorphic rocks from theinterior zone ofthe Ouachita belt A. Chloritic sericite phyllite veined with quartz (John B. Coffee No. 1 Nelson Davis, Milam County, Texas, 3,729 to 3,759 feet, p. 297). x2B, crossed nicols B. Sheared graphitic sericite-chlorite phyllite (Skelly Oil Company and Sunray Midcontinent Oil Company No. 1Cornell, Lee County, Texas, 6,745 to 6,750 feet, p. 288). x2B C. Fracture cleavage in sericite phyllite (United North and South Development Company No. 8 W. H. Tabor, Caldwell County, Texas, 4,831 feet, p. 240). x46 D. Graphitic calcite marble (Plumber and Schwab No. 1Bud Roark, Brewster County, Texas, 2,804 feet, p. 235). x49, crossed nicols < B > — Bedding sc =stretched calcite Bureau of Economic Geology, The University of Texas Plate 11 Photomicrographs of metamorphosed rocks from the Ouachita belt A. Metaquartzite or metachert (interior zone, Joiner Oil Corporation No. 1 Sellars (Sellers) Bros. Ranch, Val Verde County, Texas, 1,950 to 1,955 feet, p. 325). xBO, crossed nicols B. Calcite marble (interior zone, D. Henry Werblow and Associates No. 1 Maude S. Newton, Val Verde County, Texas, 5,300 to 5,310 feet, p. 331). x5B, crossed nicols. C. Fine-grained chlorite-mica-albite schist (Sierra del Carmen, Coahuila, Mexico, p. 99). x35, crossed nicols D. Chlorite-sericite slate (Tesnus? frontal zone. Southwest Texas Oil and Gas Association No. 1 A.T.Folsom, Terrell County, Texas, 3,580 feet, p. 309). x42,crossed nicols 378 Bureau of Economic Geology, The University of Texas Plate 12 Photomicrographs of igneous rocks from the interior zone of the Ouachita belt A. Cataclastically altered biotite granite (Humble Oil & Refining Company No. 1 E. E. Wilson, Medina County, Texas, 7,065 to 7,068 feet, p. 295). xls, crossed nicols B. Cataclastically-altered granodiorite from an augen in black slate (General Crude Oil Company No.1Rogers Ranch, Bexar County, Texas, 5,713 feet, p. 224). x49, crossed nicols C. Altered andesite porphyry (Humble Oil & Refining Company No. 1 E. E. Wilson, Medina County, Texas, 7,161 to 7,166 feet, p. 295). xls, crossed nicols D. Spilitic basalt porphyry (Humble Oil & Refining Company No. 1 Bandera County School Land, Maverick County, Texas, 13,523 to 13,528 feet, p. 290). x46,crossed nicols Bureau, of Economic Geology, The University of Texas Plate 13 Cores of strongly deformed black slate from the interior zone of the Ouachita belt immediately south oftheLulingfront.General CrudeOilCompanyNo.1RogersRanch,BexarCounty,Texas (pp. 224-225) (All% natural size) A. Black slate containing broken and contorted quartz veins (3,160 feet). B. Black slate and dark slaty metasiltstone (3,263 feet). C. Dark slaty metasiltstone containing augen of altered granodiorite at top (5,713 to 5,723 feet). Bureau of Economic Geology, The University of Texas Plate 14 Cores of strongly deformed black slate from the interior zone of the Ouachita belt immediately south of the Luling front (All% natural size) A. Black slate containing broken and contorted quartz veins (Stanolind Oil and Gas Company No. 1Schmidt, Guadalupe County, Texas, Core No. 38, p. 269). B. Black slate (same as A, p. 269). C. Dark slaty metasiltstone (Woodward No. 1Schubert, Hays County, Texas, 3,297 to 3,305 feet, p. 272). Bureau of Economic Geology, The University of Texas Plate 15 Core of chloritic sericite phyllite from the interior zone of the Ouachita belt (John B. Coffee No. 1 Nelson Davis, MilamCounty, Texas, 3,729 to 3,759 feet, p. 297).Natural size. Index Abercrombie and Harrison Oil Company No. 1 Lena Kunz and Joe Nickel: 157, 277 Acadian orogenies: 180 Adams &LylesNo.1Leeders: 229 Adams No. 1, Cosden Petroleum Company: 287 age determinations: 81, 94, 124, 154, 175, 176, 186 age of deformation: 44 Alabama OilDevelopment Company No. 1 Jacob Hill:360 Alexander Brothers No. 1, Mark Alexander et al.: 288 Alexander et al. No. 1 Alexander Brothers: '288 Alexander No.1Smythe: 354 Allison No.1, Hunt Oil Company: 250 Alpine geosyncline: 181 Alsabrook (Alsterbrook?) No. 1 (2?), Lois Henna et al.: 334 Alsate shale: 50,60, 154 Alvarado Oil Company No. 1 M. S. Richardson: 277 Amerada Petroleum Corporation No. 1Strick land: 115 American Liberty OilCompany No. 1 Clanton: 230 No. 1R. T. Greenwade :231 No. 1McClain:2sl No. 1 McNatt: 276 No. 1 Reichert: 231 Anderson No. 1, General Crude Oil Company: 211 Humble Oil & Refining Company: 123, 276, 317 Union Oil Company of California: 319 Anderson-Prichard Oil Corporation No. 1E. H. Yturri: 127, 223 Antibus et al. No. 1J. Howe: 270 Antler orogenic belt: 182 Apache group: 176 Appalachian clay minerals: 157 Appalachian system: 85, 89, 91-92, 97, 175, 177, 186, 189 Aramberri area: 102 — Arbuckle element: 166, 171 group: 130, 162 Mountains: 25, 130, 176, 177, 183, 189 uplift: 73,95,141, 146 Ardmore basin: 142 Arkansas: 26 Ashley County: 125 basin: 85, 87, 88, 89, 183, 186 County: 122 well data: 349, 358 Little Rock: 95, 190 novaculite: 33, 34, 42, 67, 89, 90, 157, 179, 180, 182 Arkansas Fuel Oil Company No. 1 George Burk hardt: 79, 223 Arkoma basin: 87, 130 Armstrong No. 1, Continental Oil Company: 259 Arnold No. 1, Phillips Petroleum Company: 359 Ashley County, Arkansas: 125 Askey No. 1, Seaboard Oil and Gas Company: 280 asphaltite: 192 veins: 117 asphaltum :17 Athens plateau: 21 Atkinson County, Georgia: 94 well data: 361 Atlantic Coastal Plain:85, 95 Atlantic OilCompany No. 1R. G. Dunning: 352 Atlantic province fauna: 50 Atlantic Refining Company No. 1Brown: 339 No. 1State: 339 Atoka: 41, 42, 135, 136, 157 County, Oklahoma: 192, 364, 366 formation: 38, 40, 73, 87, 89, 130, 133, 182, 183, 184, 186 sandstone: 18 shales: 154, 156 Attala County, Mississippi: 92 well data :353, 358-359 Austral Oil Exploration Company, Inc., No. 1-A Wardlaw-Whitehead Estate: 283 Avery No. 1, W. M. Jarrell: 335 Axtell City Water Well No. 1, J. L. Myers & Sons: 292 Babb No. 1, Killam: 326 Bacon No. 1,Nolan Bell Oil Company: 219 No. 2, Nolan Bell OilCompany: 20, 219 Bagwell No. 1, Erie Halliburton: 344 Bailey Development Company No. 1 Alex Ford: 286 Bailey No. 1, D. J. Flesh et al.:301 MellonOilCompany: 218, 264 Baker No. 1, Magnolia Petroleum Company: 269 Texas Gulf Sulphur Company: 157, 298 Balcones fault zone: 9, 111, 190 Bandera County: 67, 75, 76 School Land No. 1, Humble Oil & Refining Company: 105, 110, 115, 290, 378 well data: 211-214, 347 Barksdale No. 1, R. E. Freeman: 66, 68, 305 Barnett shale: 136 Barril Viejo,No.1:103, 105 basin, starved depositional: 31, 32 Bassett No. 1, Big Bend: 303 IrvinSvoboda: 310 Milham OilCorporation: 20, 307 Western Natural Gas: 331 Bassett Trust Company No. 1, Dryden OilCorporation: 305 Bastrop County, well data: 214 Baugh No. 1, Shambeck and Casey: 220 Beard No. 1, Magnolia Petroleum Company: 343 Bechner (Dallas Oil Company, United Petroleum Company) No. 1 Howard Garvin: 252 Beekmantown age, graptolite zone: 26 Behr No. 1, Dixon OilCo., Inc.; 278 Beidler No. 1,Josey, Incorporated: 284 Belanger No.1NellaT.Evans: 238 Bell County: 20, 68, 111, 134, 364, 366 OilCompany No.1T.R.Holcomb: 215 well data: 215-223 Bell Williams Oil Company No. 3 John Kolls: 215 No.18. F. Warrick:2ls Below No. 1, Magnolia Petroleum Company: 68, 136, 278 Bureau of Economic Geology, The University of Texas Belt series: 176 Bend arch: 156 Benedum and Trees No.1Patterson: 318 No. 2 Sellars: 320 Bennett & Langsdale No. 1, Humble Oil & Refining Company: 356 Bentley, Shepherd, and Stevens No. 1 Southern Pine Lumber Company: 66, 300 Bernice (No.1NPFP) No.1,GulfOilCorporation: 342 Bertram City Well No.1:238 Bexar County: 75, 76, 79, 110, 125, 157, 169, 368, 372, 378, 380 well data: 223-228 Bezdek (Bezdak) No. 1, F. J. Ossenbeck: 293 Bibbs No. 1, Diamond Half Oil Company: 268 Big Bend No. 1 Bassett: 303 — Bigfork chert: 27, 28, 29, 67, 135, 179, 364 formation: 31, 179 shale: 157 Billups Bros. No. 1C. A.Townsend: 351 and Serio No.1N.H. Heath: 351 Birdwell water well: 311 Birmingham, Alabama: 87, 89 bitumen: 17, 118 Black Knob Ridge: 27, 28, 29, 31, 32, 33, 35, 36, 40, 166 Blackman No. 1, J. K. Wadley: 233 Blackstone No. 1, Humble Oil & Refining Company: 306 Black Warrior basin: 84, 85, 87, 88, 89, 97, 129, 159 clay minerals: 157 Blackwell Oil & Gas Company (C. W. Robinson) No. 1E. P. Fox: 349 Blackwood and Nichols? No. 1 Slaughter: 299 Blakely formation: 31, 32 sandstone: 26, 180 Blanco County: 75, 76 well data: 228-230 Blankenship No. 1, Starr Oil Company, Incorporated: 266 Blaylock sandstone: 28, 29, 32, 68, 180 Bloomer No.1,U.S.Army:222 BLTCompany No.2M.C. Goldwire:304 Blue Ridge structural province: 81, 85, 91, 93, 94, 163, 175 Bluff Creek Ranch No. 1, Hurlbut: 324 W. H. Bowers: 325 Blum No. 1, H. A. Pagenkopf: 78, 125, 226 Blumberg No. 1 D. C. Knibbe: 67, 243, 364, 368 No. 1Wagner: 228 Blunn Creek (water well) No. 1, City of Austin: 312, 372 Boettcher No. 1 State Life Insurance Company: 354 Boerne City Well: 278 Boggy shale: 44 Boktukola fault: 46,48 Bolivar County, Mississippi: 92 welldata: 350, 358 Bone Spring quadrangle: 62 Boquillas, Coahuila: 99 Bosque County, well data: 230-232 Boston Mountains: 130, 132 boulder beds: 38, 44, 53, 54, 58, 105, 108, 110, 180, Bovaird Drilling Company No. 1 Ingram: 328 Bowie County, well data: 232-233 Bowers No.1Bluff Creek Ranch:325 Bowles No. 1, Permian Oil Company: 281 Boy Scout Water Well:312 Brasfield No.1Eichenberg and Miller: 300Brazos River Electric No. 1, Meyers & Sons: 222 Breazeale No. 1, Slick Oil Company & Plains Producing Company: 355 Brevard belt :93, 94 Brewster and Bartle No. 1Tucker: 312 Brewster County: 8, 20, 49, 54, 62, 80, 81, 123, 145, 368, 374 well data: 233-237 Brewster No. 1Fee: 233 Briggs No. 1—Kerr: 304 Broken Bow Benton anticlinorium: 69, 122, 123, 166, 167, 171 uplift: 32, 34, 36, 37, 46, 117, 166 Brooks-Scanlon, Inc., Block 33 No. 1, Gulf Oil Corporation : 348 Block 49 No. 1, Gulf Oil Corporation: 357 Brown No. 1, Atlantic Refining Company: 339 Shell OilCompany: 264 Brown and Bassett No. 1, Magnolia Petroleum Company: 110, 137, 138 and Western Natural Gas: 307 Bruckner No. 1, Winan &Forbes: 229 Bryan County, Oklahoma: 73, 75 well data: 339-340 Bryant No. 1, H. W. Snowden: 265 Buckeye and Mid-Tex Oil Company (Mid-Kansas?) No.1G. A.Strickland: 244 Bucklin No. 1A.K. Eisner: 270 Bullock County, Alabama, well data: 360 Bur-Kan Petroleum Company and Stanolind Oil and Gas Company No. 1Lee Hubbard: 79, 223 Burkhalter No.1,H.M.Ogg &H.A.Clark:351 Burkhardt No. 1 Arkansas Fuel Oil Company: 79, 223 Burnet County: 59 well data: 238-239 Burnette No.1D.C. Reed: 332 Burns No.1,Telegram OilCompany: 232 Burton et al. (Burton Syndicate, Zee-Tex Oil Company) No.1Cannon: 258 Bush No.1,Plymouth OilCompany: 350 Butcher No. 1, Peter Oil and Gas, Inc.: 72, 262, 370 Butler County, Alabama, well data: 360 Butting Ram sandstone: 92 Buttrill Ranch member: 49 Byars No. 1 Chapman: 300 Bybee No. 1, Caldwell &Lanier: 244 Caballeros canyon:102 Caballos formation: 60 novaculite: 50, 51, 62, 63, 67, 135, 170, 179, 180, 182 Caddo Gap quadrangle: 21, 27, 28 Caldwell County: 9, 374 welldata: 239-241 Caldwell & Lanier No. 1 T. J. Bybee: 244 Calhoun County, Arkansas, welldata: 354 Calhoun County, Georgia, well data: 348 California-Medina Association No. 1 Rothe Estate: 294 California-Texas Oil Company No. 1 Mastin (Maston) :272 Calvert et al. No. 1, Cecil Hagen: 268 Camden County: 94 Subject Index, The Ouachita System Camp No. 1, Sun Oil Company: 91 Campbell No. 1, Sinclair-Prairie Oil and Gas Company: 156 Camp Bullis Water Well No. 1, U. S. Government: 227 Canadian Shield: 175 Caney shale: 34, 37, 44, 152, 154 cannibalization:30 Cannon No. 1, Burton et al.: 258 Canyon group: 134 Caopas-Rodeo area: 101-102 Capitol Hill Oil Company No. 1 Williams 341 Capitol Oil &Gas Company No. 1Ethel B. Gholston: 360 No. 1Fred Pickett: 360 Caraway No.1Guida Rose: 319 No. 1Whitehead: 320 carbonaceous material :17 carbon ratios: 88, 193 "Carolina gneiss" :93 slate belt: 93, 94 Carpenter No.15. .). Seward: 332 Carr (Hewitt and Dougherty) No. 1 MaggieMather: 333 Carroll County, Mississippi:93 well data: 351,358 Carroll No. 1, Humble Oil &Refining Company: 253 Carson No. 1-A, Phillips Petroleum Company: 136, 251 Carter No. 1, A.G.Hill:260 Carter OilCompany No.1Denkman: 354 No. LLoyd: 73,75,340Cartersville fault: 91 Cartersville, Georgia: 92 Casey No. 1, W. W. Connell, Inc.: 244 Catoctin greenstone: 175 Cd. Victoria area: 102, 104, 105 Central Basin Platform: 143, 146, 156 Central Stable Region:85, 175, 177 Chaffin No. 1, Damon Oil Company: 255 Chandler No. 1, Mont Warren et al.: 356 Chapa No. 101, Petroleos Mexicanos: 103, 105, 345 Chapman No. 1, Byars: 300 Chautauqua arch: 140 Cheaha sandstone: 92 Check Ranch No. 1, Clarence Newton: 76, 157, 280 Chester series: 88 shales: 158 Chewacla marble: 93 Chickachoc chert: 38, 39, 40, 184 limestone: 44 Chihuahua: 99, 104, 139 Chilhowee group: 89 chlorite: 118, 149, 150 Choctaw anticline: 46 fault: 34, 38,42,47, 171 Christie et al.No.1N.Peikoff:277 Chupadero No. 1, Petroleos Mexicanos: 105, 345 Cincinnati dome: 94 Cisco: 134 Citizens National Bank No. 1, Sun Oil Company: 355 City of Austin No. 1 Blunn Creek (water well): 312 372 City of Dallas No. 40, Texas Water Wells, Inc.: 250 No. 41, Texas Water Wells, Inc.: 250 No. 42, Texas Water Wells, Inc.:250 No. 45 Water Well: 248 No. 46 Water Well: 248 City of Temple No. 3, Layne-Texas: 222 Clanton No. 1, American Liberty Oil Company: 230 Clark and Ogg No. 1Smiley: 287 Clark No. 1, Keystone Texas OilCompany: 247 Westmont Drilling Company: 277 clastic wedges: 182, 186 Clay County, Mississippi, welldata: 352 clay facies: 156 mineral zones: 161 minerals: 154 Clayton No. 1, Wood Texas OilCompany: 214 Cleveland County: 89 Cloudt No.1, Phantom Oil Company: 318 Coahuila: 99, 101, 102, 104, 169 Boquillas: 99 Mexico, well data: 345 peninsula: 104, 105 Coal County, Oklahoma: 132 Coastal Petroleum Company No. 1 E. P. Larsh: 357 Cockburn No.1Ingram: 320 Kearny: 245 Coffee No.1Nelson Davis: 297, 374, 384 Coleman and Wasson Oil Company No. 1 R. M. Cox: 231 Collier formation: 30 shale: 25,26,68,177 Collin County: 116, 172 well data: 241-243 Collins No. 1, Humble Oil &Refining Company: 250 Columbia Texas Oil Company No. 1 W. L. Sadler: 248 Comal County: 67, 75, 364, 368 well data: 243-244 Conasauga formation: 89 Concho arch: 143 Concord Oil Company (Pearsons et al.) No. 1 Dillahunty: 300 Coombs No. 1, Gulf Oil Corporation: 20, 57, 188, 234 Fred Turner, Jr.: 51,177,237 Connell, Inc., No.1 Casey: 244 Continental OilCompany No.1B.F. Armstrong: 259 No. 1 DeWitt Bank & Trust Company: 349 No. 1H. O. Fortenberry: 353 No. 1 Millard Sudduth: 359 Cooke County: 132 Cooke Water Well No. .1-22 (George Cooke No. 1, C. R. Franklin):312 Cordilleran system: 175, 177, 186, 189 core area, of McCurtain County: 26 Cornell No. 1, Skelly Oil Company and Sunray Midcontinent Oil Company: 288, 374 Coryell County: 20, 75, 370 well data: 244-247 Coryell County OilCorporation No. 1J. Q. Davidson: 245 Cosden Petroleum Company No. 1 W. T. Adams: 287 Cowden No. 1, E. T. Williams et al.: 311 Cox Drilling Corporation No. 1S. F. Leslie: 254, 370 Cox No. 1, Coleman and Wasson Oil Company: 231 Bureau of Economic Geology, The University of Texas Crapps No. 1, Sun OilCompany: 358 Crawford No. 1, Rimrock-Tidelands, Inc.: 157, 297 Creel No. 1, W. B.Hinton: 347 Crenshaw County, Alabama, well data: 347 Crist No. 3, E. L.Nixon: 230 Cromwell sandstones: 132 Crossett Lumber Company No. 1-E, Union Producing Company: 125 Cross Mountains anticline: 46 Crystal Mountain: 31 formation: 32 sandstone: 25,26,68, 177 Crystal Mountains: 26 Culpepper No. 1, Magnolia Petroleum Corporation: 353 Cumberland block: 193 Plateau: 85, 87 Curb-Fee No. 1, B.F. Gilchrist: 217 Cypress Creek: 59 Drilling Association (Jones) No. 1 Romberg: 136, 313 Dagger Flat: 108 anticlinorium: 50, 56, 69, 165, 177 formation:25, 49, 154 sandstone: 51, 60, 177 Dallas County: 133 well data: 248-250 Damon Oil Company No. 1Chaffin: 255 Daniel Oil Company No. 1 Elizabeth W. Estes: 72, 290 Davenport Ranch Water Well: 313 Davidson No. 1, Coryell County OilCorporation: 245 Davidson et al. No. 2 Warrick: 215 Davis et al. No. 2, Snuggs and Cox: 265 Davis No. 1, John B. Coffee: 297, 374, 384 Day No. 1, E. A. Dunham and Hensman Drilling Company: 238 General Crude Oil Company: 20, 75, 167, 246, 370 Decie et al. No.l, Woods Oiland Gas Company: 237 No. 1-47: 54,56,58 Decie ranch area: 137 Decie-Sinclair No. 1, Slick-Urschel Oil Company: 187, 188, 237 Deepkill graptolite zone: 26 Deep Rock OilCorporation No.1W.M.Sherley: 241 No. 1Slaughter: 298 Deese formation:133 Delaware basin: 155 Del Rio uplift: 144 Delta Drilling Company (Carpenter and Clements) No.1C.Horstman: 291 Delta-Gulf (Phillips Petroleum Company) No. 1 Wilson: 320 Denkman No. 1, Carter OilCompany: 354 Demon County: 132, 133, 134 DeQueen quadrangle: 21, 27, 28 Devils River uplift: 144, 145, 167, 172, 176, 194 Devonian: 89-90 DeWitt Bank and Trust Company No. 1, Continental Oil Company: 349 Diablo Platform: 57,145,166 uplift: 145 Diamond Half Oil Company No. 1 Bibbs: 268 Dillahunty No. 1, Concord Oil Company (Pear- sons et al.):300 Dimple formation:74, 155 limestone: 53, 54, 184, 187 Dismuke No. 1, Robert YorkTrustee: 347 Dixon Oil Company, Inc., No. 1Ottmer Behr: 278 Dodson (Hinton) No. 1 Texas American Syndicate: 234 Dog Canyon area: 62 Donnelly et al. No. 2 (1?) Conway: 333 Dornick Hillsformation: 133 Doster-Ladson No. 1, Sun Oil Company: 361 Douglas Oil Company No. 1 J. E. Sellars, Jr. (Benedum and Trees No. 2 Sellars) :320 Dove Mountain : 51 Downie No. 1. Pittsburgh: 308 Downie Test Well: 304 Water Well: 305 Downs, Perry, and Hughes No. 4 John Kolls: 216 Doyle and Jondreau No. 1 Joe Horn (Martin): 288 Dryden Oil Corporation No.1Bassett Trust Company: 305 Dugout Creek overthrust: 54, 56, 57, 138, 165, 188 Duke No.1, Tricon Minerals, Inc.: 360 Dumas Company et al. No. 1 M. E. (Mollie) Williams: 259 Dunham No. 1J. E. Hunt: 216 No. ITienert: 245 Dunham and Hensman Drilling Company No. 1W. F.Day: 238 Dunning No. 1, Atlantic Oil Company: 352 Duval County: 76 Eagle Millsformation: 86, 89, 189, 190 salt: 125 Eakes No.1,H.W.Elliottetal:353 Early County, Georgia, well data: 356 East Del Rio Oil Company No. 1 Russell and Weatherby: 321 Easton (Peter Oil and Gas Company, Inc., No. 2 Easton) No. 1, Westover et al. (Westover Oil Company) :267 Eaton No. 1, C. H. Murphey, Jr.: 353. Echols County, Georgia, well data: 356-357 Eclipse OilCompany No. 2 Slayden: 216 Eddy County, New Mexico: 155 Edwards County, well data: 250-251 Eichenberg and Miller No. 1, S. M. Brasfield: 300 Einstoss No.1Roswell Wardlaw: 368 Eley et al. No.l, Southeastern Drilling Company: 355 Elkay Oil and Gas Company No. 1Wilson Lane: 255 Ellenburger: 136, 157 group: 132 Elliottet al. No.1Mrs. Laura Eakes: 353 Elliott well: 248 Ellis arch: 140 Ellis County, well data: 251-253 El Paso-Ellenburger: 162 Elsinore Cattle Company No.1:137 Phillips Petroleum Company: 299 Eisner No. 1, E. A.Burklin:270 Englemann No. 2, Security Drilling Company: 227 epidote: 118 Epperson Underwriting Company No. 1-A W. L.Helton: 257 Subject Index, The Ouachita System Erin shale: 87 slate: 92 Estes No.1,DanielOilCompany: 72,290 eugeosynclinal belts: 177 euxinic facies: 30 Evans No. 1, AlBelanger: 238 G. L. Rowsey: 214 No. 2 Love: 282 Evans (Sunset Ranch) No. 1 (2?), P. F. Griffin (P. S. Griffiths) : 314 Everett No.1,Killam:326 Producers OilCompany: 329 EwertNo.1,Hickok &Reynolds: 225 Exstein No. 1, Gace Milling Company: 260 EzellNo.1, G.L.Reasor: 315 facies, euxinic: 30 flysch: 14, 30, 43, 53, 54, 72, 100, 102, 104, 139, 182 molasse: 14, 30, 53, 54, 182, 186 Fair and Woodward No. 1 Pauline Lyro: 224 Fair,Inc., No.1McAnelly:295 Falcon Drilling Company No. 1 J. C. Keitt: 298 Falcon OilCompany No. 1 H. Mattlage: 291 Falls County, well data: 253-254 Fannin County: 72, 73, 168, 364, 366, 370 well data: 254-257 Farrell Drilling Company No. 1 J. R. Gillam: 289 Federal Land Bank No. 1, A. T. Walter et al.: 288 Federal-Wiggs No. 1, Humble Oil & Refining Company: 155 Fee No. 1, Brewster: 233 H. L.Mcßride: 211 G. L. Rowsey: 213 Fee No. 2, A.K.Kitselman: 356 G. L. Rowsey: 213 Fee No. 5, G. L.Rowsey: 214 feldspar: 162 Fenslund (Fensland) Oil Company No. 1 Abb Rose: 322 Ferguson No. 1, J. E. Winans &Forbes: 222 Finley No. 1, Pine Oil Company: 242 Fish Production Corporation No. 1 Roy Henderson: 283 No. 1Postell: 116,283 FiteNo. 1, J. R. Lockhart:3sl Flesh et al. No.1K.M.Bailey: 301 No. 1Rosencrantz et al.: 349 Flowers and Ward Ranch No. 1, Park and Phillips: 79, 338 Floyd shale: 88, 89, 158 flysch: 14, 30, 43, 53, 54, 72, 100, 102, 104, 139, 182 Fohs-Loffland Bros. No. 1 Louis Miller:358 Folsom No. 1, Southwest Texas Oil and Gas Association: 309, 376 Ford No. 1, Bailey Development Company: 286 Fortenberry No. 1, Continental Oil Company: 353 Fort Pefia formation:50, 51, 60, 154, 179 Fort Stockton high: 137, 143, 146 uplift: 145 Fort Worth basin: 73, 133, 135, 156, 194 fossils :20 Foster Drilling Company No. 1 G. W. Tyler Est.: 222 Fox No. 1, Blackwell Oil &Gas Company (C. W. Robinson) :349 Franciscan formation: 180, 183, 184 Franklin No.1George Cooke: 312 No. IReimers: 136,313 Freeman No.1Barksdale: 66, 68, 305 Muth and Berry: 292 Freestone County: 80, 115 well data: 257 Frio County: 79,80, 123,125 well data: 258 frontal zone: 164, 165, 166, 167 Gace MillingCompany No. 1Exstein: 260 Gage No.1,King&Franklin: 235 Galeana area:102 Gamble and Gamble No. 1, Southeastern Operator's Committee: 360 Gaptank formation: 53, 54, 187 Gardner No. 1, H.E. Goff:314 Garland City Water Well (J. L. Myers & Sons, Federal Works Agency Docket) :248 Garland County, Arkansas: 69, 165 Garrison No. 1, Plateau Oil Company: 67, 212 Garvin No. 1, Bechner (Dallas Oil Company, United Petroleum Company) :252 Garza No. 1, Petroleos Mexicanos: 105, 115, 345 Gas Ridge Syndicate (Clark OilCompany) No. 1Pepper: 224 General Crude Oil Company No. 1Anderson: 211 No. 1Earnest Day: 20, 75, 167, 246, 370 No. 1 Rogers Ranch: 110, 169, 224, 372, 378, 380 No.1J. H.Talley: 225,368 geophysical data: 94-96 Georgetown City Water Well: 334 Georgia, Cartersville: 92 geosynclinal cycle: 30 Gholston No. 1, Capitol Oil & Gas Company: 360 Gibson No. 1, D. A. McCrary (G. L. Reasor) : 297 No. 2, Hunt Oil Company: 357 No. 4, Hunt Oil Company: 357 Gideon No. 1, United North and South Development Company: 240 Gilbert No. 1,Tricon Minerals, Inc.: 360 Gilchrist No. 1Curb-Fee: 217 Gillam No. 1, Farrell Drilling Company: 289 Glasco No. IJ.A.Norwood :353 Glasscock No. 1, Johnson (R. A. Rodson et al.): 229 Glass Mountains: 189 GoffNo.1Bassett Gardner (Basdall Gardner No. 1OilTest) :314 Goldwire No. 2, BLT Company: 304 Goode field: 138 Goode No. 1, Transcontinental Oil Company (Ohio) :310 Goodenough No. 1, Rossman (Stan-Ross) :213 Gonzales County, well data: 258 Gotcher No. 1, New York Syndicate: 247 Granberry No. 1, Renwar Oil Corporation: 347 Grand Canyon series: 176 Grant County: 89 Grants Gap: 154 graphite: 17 graptolites, Normanskill type: 27 graptolite zone, Deepkill: 26 Grasdorf No. 1, Trans-Pecos Oil and Gas Company: 234 Bureau of Economic Geology, The University of Texas GravisNo. 1Weyel: 268 gravity maps: 94, 170 Grayson County: 20, 68, 72, 126, 132, 134, 172, 370 well data: 258-268 graywacke: 15, 17, 30 Great Basin: 186 Great Smoky fault: 91 Green (Reeves) No. 1Lehman: 334 Greene County, Alabama: 90 well data: 353, 355 Greenwade No. 1, American Liberty Oil Company (Southland OilCompany) :231 Grenada County, Mississippi, well data: 351 GriffithNo. 1, Sherman Drilling Company (Clarence Houseman et al.):275 Griffiths et al. No. 1 (2?) Evans (Sunset Ranch) :314 Grubles No. 1, Messergill & Williams (R. G. Hauser) :347 Guadalupe County: 169, 372, 382 well data: 28-269 Guinn No. 1-A,Phillips Petroleum Company: 328 Gulf Coast Drilling Company No. 1Schawe: 239 Gulf Coastal Plain: 21, 85, 89, 95, 98, 189, 190 Gulf of Mexico: 190 Gulf Oil Corporation No. 1 Berniece (NPFP): 342 No. 1 Brooks-Scanlon, Inc., Block 33: 348 Block 49: 357 No. 1 D. S. C. Coombs: 20, 57, 188, 234 Gulf Refining Company No. 1 D. A. Hendrix: 360 No. 1F. W. Parker: 351 No. 49 Louis Werner Sawmill Company: 359 No. ICC.Sellars: 359 Gutowsky et al. No. 1Ada Mills:354 Hagen No.1Henry Calvert et al.: 268 Hair No. 1, Rio Grande OilCompany: 220 Hale No. 1, Triangle Corporation: 253 Halliburton No.1Bagwell: 344 Hamilton No. 1, H. L. Hunt: 298 Keck-Pecos Trust (Trans-Pecos Development Company) :306 Hamilton-Powell Drilling Company No.1Losche: 255 Hardeman No. 1, Magnolia Petroleum Company: 239 Harley and Whittington No. 1 Heidenreich: 271 Harrington No. 1, Waco Oil and Refining Company: 294 Harrison et al. No. 1, Plateau OilCompany: 79, 328 No. 1C. Weatherby: 273 Hartman No.1B. F. Warrick: 217, 218 Hartshorne sandstone: 87, 132 Harwell No. 1, Shell Oil Company: 136, 271 Hatton tufflentil:36, 43, 75 Havoline Oil Company No. 1 Weatherby: 109, 144, 284 Haymond boulder beds: 57 formation: 53, 54, 74, 108, 155, 182, 183, 184, 187 Hays County: 75, 76, 136, 372 382 well data: 270-272 Heath No. 1, Billups Bros. &Serio: 351 heavy minerals: 32, 43, 63, 72, 74, 75, 155 Heidenreich No. 1, Harley and Whittington: 271 Heidrick No. 2, Yates: 244 Hells Half Acre overthrust: 56 Helton No. 1-A, U. S. Epperson Underwriting Company: 257 Henderson No. 1, Fish Production Corporation: 283 Humble Oil&Refining Company: 357 Union Producing Company: 352 Hendrix No. 1, Gulf Refining Company: 360 Henna et al. No. 1 (2?) Alsabrook (Alsterbrook?) :334 Henry County, Alabama, well data: 360 Henry No. 1, Magnolia Petroleum Company: 67, 302 profit: 232 Hewitt and Dougherty No. 1Pearson: 335 Hiawatha Oil Company (Benedum and Trees) No.1 Sellars: 109, 144,322 Hickey and White No. 2 Medford: 252 Hickok &Reynolds No.1Ewert: 225 Hicks No. 1Albert Specht: 157, 228 Hillabee sill: 92 HillCounty: 75, 157 well data: 272-275 HillNo. 1, Alabama Oil Development Company: 360 lone Carter: 20 Hillsboro City Wells No. 1, No. 2, No. 3: 272, 273 Hill-Texas OilCompany (B. H. Harrison et al.) No. 1C. Weatherby: 75,273 HintonNo. U.S. Creel: 347 Hodges et al. No.1Lawrence: 291 Hoehman No. 1, Southwest Exploration Company: 343 Hohenberger No. 2, E. L.Nixon:230 Holcomb No. 1, Bell County Oil Company: 215 Holderman No. 1, Humble Oil &Refining Company: 157, 273 Hollis quartzite: 93 Holman & Russell No. 1 E. K. Thomas: 358 Holman et al. No. 1, E, T. Williams Drilling Company: 331 Holmes No. 1, Texas Consolidated OilCompany: 310 Honeycutt No. 1, Shell Oil Company: 251 Horn (Martin) No. 1, Doyle and Jondreau : 288 Horstman No. 1, Delta Drilling Company (Carpenter and Clements) :291 Hot Springs sandstone: 34, 43, 89, 182 Houseman et al.No. 1J. F. Griffith: 275 Houston County, Alabama, well data: 356 Georgia, well data: 360 Howard County, Arkansas, well data: 354 Howard No. 1, A. B. Johnson :218 Howe No. 1, Bob Antibus et al.: 270 Hubbard No. 1, Bur-Ken Petroleum Company and Stanolind Oil and Gas Company: 79, 223 Huber Oil Syndicate No. 1Rust :325 Hueco Mountains: 155 Hughes No.1,Humble Oil&Refining Company: 348 Humble Oil & Refining Company No. 1E. M. Anderson :276 No.1R. L. Anderson: 123,317No. 1 Bandera County School Land: 105, 110, 115, 290, 378 No.1Bennett &Langsdale: 356 No.1N.D.Blackstone: 306 No. 1 Carroll: 253 No.1Collins: 250 Subject Index, The Ouachita System No. 1Federal-Wiggs: 155 No. 1R.L.Henderson: 357 No.1M.Holderman: 157, 273 No.1G.H.Hughes: 348 No.1Marberry: 115,257 No.IH.C. Miller:116,242 No.1MillsMineral Trust: 323 No. 1J.C.Mitchell: 306 No.1Norman: 75,276 No. 1Pucek: 254 No. 1 Rutherford :75, 276 No. 1Thompson: 211 No. 1C. W. Tindel: 357 No. 1 University: 306 No. 1 Emma Wardlaw: 223 No.1E.E. Wilson: 110, 295, 378 Humphrey No.1J. E. Osborne: 274 Hunt County: 75 well data: 276-277 Hunt No. 1, E. A. Dunham: 216 Hunt No.1E. E. Hamilton: 298 Hunt Oil Company No. 1Allison: 250 No. 2 J.W.Gibson: 357 No. 4 J.W.Gibson: 357 No. 1 Superior Pine Products Company: 357 No. 4 Superior Pine Products Company: 357 No.1E.W.Wright: 274 Hunton anticline: 141 arch: 130, 140 limestone: 132 uplift: 186 Hurlbut No. 1BluffCreek Ranch: 324 Husky Oil Company No. 1 Rose-Robertson: 79, 109, 324 igneous rocks: 107 illite:149 illite-montmorillonite:149 Independent Operator No. 1 Rust (Whitehead) : 325 Ingram No. 1, Cockburn: 320 C. A. Maurer: 327 Phantom Oil Company (Bovaird DrillingCompany) :328 Insane Asylum Water Well: 314 interior zone: 165, 169 iron ores: 89 Ives No. 1-22, Panhandle Eastern Pipeline Company: 349 Jackfork formation:43, 74, 157 sandstone: 18, 34, 36, 37, 73, 88, 89, 168, 182, 183 shales: 154 Jackson County: 91 Florida, well data: 357 Jackson, Mississippi: 95 Jackson No. 1 Peter Oil and Gas Company, Inc.: 263 Jarrell No.1C.N.Avery,Jr.: 335 U. S. Army: 222 Javelina Canyon: 50 Jefferson County, Florida, well data :357 Jemison chert: 92 Johnson & Hawkins Company No. 1 Willis: 355 Johnson City Oil Company No. 1Waller (Winan &Forbes No. 1 Bruckner, water well):229 Johnson County, well data: 277 Johnson No. 1F. C. Howard: 218 Johnson No. 1, J. K. Wadley: 233 Johnson (R. A.Rodson et al.) No. 1Glasscock: 229 Johnston No.1H.D.Peteet: 356 Johnston Petroleum Syndicate No.1Lady Alice: 66, 67, 68, 301, 370 Johns Valley shale: 34, 37, 38, 44, 175, 183 Joiner OilCorporation No.1Sellars Bros. Ranch: 325, 376 Jones No. 1, Midcoast (B. R. Floyd):315, 366 Pure OilCompany: 355 Romberg: 313 Jones Ranch area: 60, 63, 165 Josey, Inc., No.1A.F.Beidler: 284 Kansas City Syndicate No. 2 Thomas Young: 246 kaolinite: 147, 148, 149 Kasten (Kaston) No. 1, A. S. Mowinkle: 279 Katy Club fault: 38, 39, 41, 42, 47 Kearny No. 1, Cockburn: 245 Keck-Pecos Trust (Trans-Pecos Development Company) No. 1 Hamilton: 306 Keeling No. 1, The Texas Company: 289 KeittNo. 1, Falcon DrillingCompany: 298 Kelly No. 1, United North and South Development Company: 240 Kendall County: 67, 75, 76, 136, 157 well data: 277-281 Kendricks No. 16-T, Pure Oil Company: 289 Kerr basin: 135, 136, 194 Kerr County, well data: 282 Kerr No. 1, Briggs: 304 Keystone No. 1, Shell OilCompany: 343 Keystone Texas Oil Company No. 1J. S. Clark: 247 Kiamichi Mountains: 36 KillamNo. IBabb: 326 No. 1Everett: 326 No. 1Parker: 326 Killeen-Bell Oil Company No. 1 Swope: 222 Kinderhook formation: 33 King&Franklin No.1A.S. Gage: 235 KingNo. 1, J. S. Woodward, Inc.: 241 Kinney County: 20, 76, 80, 81, 99, 109, 111, 116, 123, 144, 172 well data :283-286 Kirkland No. 1, Union Producing Company: 356 Kitselman No. 2 Fee: 356 Klamath Mountains: 175 Knibbe No. 1, Roland Blumberg: 67, 243, 364, 368 Knippa No. 1, Stanolind Oiland Gas Company: 299 Knowlton &Perthshire No. 1, Phillips Petroleum Company: 350 Knox group: 89, 90, 157, 160 Knoxville formation: 183 Kolls No. 1, Petoskey Oil Company: 220 No.3,BellWilliamsOilCompany: 215 No. 4, Downs, Perry, and Hughes: 216 KopelNo.1Ragsdale (Saver):325 KorshojNo.1Simon-Ferguson: 159, 292 Kunz and Joe Nickel No. 1, J. S. Abercrombie and Harrison OilCompany: 157, 277 Kurth Lumber Company No. 1 Joe White et al.: 303 La Boca canyon :102 Lacey and Guiberson No. 1 Meyers (Moyer?): 248 Lady Alice No. 1, Johnston Petroleum Syndicate: 66, 67, 68, 301, 370 Bureau of Economic Geology, The University of Texas Lafayette County, Florida, well data: 357-358 Lake Travis: 59 Lamar County: 65 well data: 286-288 Lampasas County, well data: 288 Lampkin No. 1, Quintana Petroleum Corporation: 78, 258 Lane No. 1, Elkay Oil and Gas Company: 255 La Presa canyon: 102 Laramide orogeny :186 LarkinNo. 1, Marott: 355 Larsh No. 1, Coastal Petroleum Company: 357 Las Delicias-Acatita area, Coahuila, Mexico: 101, 104, 105, 107, 188 Lauderdale County, Mississippi, well data: 353 Lawrence No. 1, Hodges et al.:291 Layne-Texas No. 3 City of Temple: 222 Leake County, Mississippi: 90 well data: 354 Lee County, well data: 288, 374 Leeder No. 1, Lile and Adams: 229 Lehman No. 1, W. E. Green (Reeves) :334 Leonard series: 53, 187 Leon Springs Water Well No. 1, U. S. Government: 227 "leptogeosynclinal" deposits: 181 Lesage (water well) No. 1, Lesco: 252 Lesco No. 1Lesage (water well):252 Leslie No. 1, Cox Drilling Corporation: 254, 370 Light No. 1, Pure OilCompany: 243 Lileand Adams No.1Leeder: 229 Limestone County, well data: 289 Linder No. 1, Fred Turner, Jr., et al.: 67, 281 Linson Creek syncline: 46 LionOilCompany No. 1Nally:348 LittleRock, Arkansas: 95, 190 LittleNo. 1, Snuggs.and Neal: 265 Little River County, Arkansas, well data: 354 — Llano buttress: 194 recess: 166 region: 156 uplift: 57, 59, 67, 73, 122, 133, 142, 145, 176 Llanoria: 30, 181 structural belt: 13 LockhartNo.1Guy File:351 Losche No. 1, Hamilton-Powell Drilling Company: 255 Louannsalt: 86, 125, 190 LoveNo.2,Evanset al.:282 Loyd No. 1, Carter Oil Company: 73, 75, 340 Ludwick No. 2, W. S. Stanfield: 222 Lukfata sandstone: 25, 30, 32, 177 Luling-Mexia-Talco fault system: 19 Luling overthrust front: 75, 77, 78, 118, 123, 169 Lynchburg gneiss: 175 Lyro No. 1, Fair and Woodward: 224 McAlester basin :21, 72, 87, 88, 130, 186 formation: 187 McAlester Fuel Company & H. M. Cox No. 1E. M.Welch: 350 McAnelly No. 1, R. E. Fair, Inc.: 295 McßrideNo. 1Fee: 211 McClain No. 1, American Liberty Oil Company: 251 McCloskey Hospital Water Well No. 1, U. S. Army: 221 McCollum No. 1, Ryan Consolidated Petroleum Corporation : 349 McConnico No. 1, Seaboard Oil Company: 359 McCracklin No. 1, P. B. Sterling et al.: 281 McCrary No. 1 E. M. and .1. F. Gibson (G. L. Reasor No.1Gibson):297 McCue No. 1, Perkins and Lierney: 308 McCurtain County, Oklahoma: 25, 26, 29, 34, 36, 41, 46, 69, 107, 165 McElroy No. 1, Sun Oil Company: 145, 236 McGillNo. 1,Jesse Russell: 337 Mclntyre No. 1, Moore and Whitehead: 329 McLean No. 1, Union Producing Company: 227 McKinley No. 1, Magnolia Petroleum Company: 79, 125, 258 McLennan County: 72, 122, 159 well data: 290-294 McNatt No. 1, American Liberty Oil Company: 276 McNeil &Matthews No. 1 W. W. Seaton: 249 Mackay No. 1, Seitz, Comegys and Seitz: 264 Madison County, Florida, well data: 357 Magnet Cove: 115 — Magnolia Petroleum Company No. 1 Frances Baker: 269 No. 1 Beard: 343 No. 1Ed Below: 68,136,278 No. 1 Brown and Bassett: 110, 137, 138, 307 No. 1C. Culpepper: 353 No. 1 Hardeman (salt-water disposal well): 239 No.1Henry: 67, 302 No. 1McKinley: 79, 125,258 No. 40 Alf Mercer: 239 No.1Morrison: 326 No.1Murphy Pfulman: 269 No.1Trigg: 249 No.1C. B. Wardlaw:2Bs No.1W.E. Whitehead: 327 Mann No. 1Reeder: 271 — Marathon anticlinorium: 56, 69, 165 area, stratigraphy: 49-54 structures: 56 Basin: 49 dome: 189, 19a foldbelt: 13 formation :50, 51, 60, 99, 108 limestone: 49, 68, 154, 177, 179 orogenic epoch: 58 region: 154,177,178,179,187 salient: 13,57, 165,168 uplift: 25 Maravillas chert: 50, 51, 60, 62, 67, 179, 180 formation: 179 Marberry No. 1, Humble Oil & Refining Company: 115, 257 Marble Falls limestone: 59, 136, 156 Marengo County, Alabama: 90 well data: 356 Marietta basin: 132 syncline: 132 Marietta-Sherman basin: 132 Marion County: 91 Maritime Provinces: 189 Market Square Well (Hillsboro City Well No. 3):273 MarottNo. 1Larkin: 355 Marshall County, Oklahoma, welldata:341-343 Marshall No. 1, The Texas Company: 267 Martin & J. H. Coker No. 1 W. H. Stewart: 349 Subject Index, The Ouachita System Massie No. 1, Shell Oil Company: 221, 366 Mastin No.1, California-Texas OilCompany: 272 Mather No. 1, Carr (Hewitt and Dougherty) : 333 Mattlage No. 1, Falcon Oil Company: 291 Mauch Chunk shale: 158 Maurer No. 1John W. Ingram: 327 Maverick County: 80, 105, 110, 115, 378 well data: 290 Mazarn shale :25, 26, 31, 68, 177 Medford No. 2, Hickey and White: 252 Medina County: 72, 75, 78, 110, 123, 378 welldata: 294-296 Meeks No. 1E. W. Walker: 230 Mellon Oil Company No. 1 Noah Bailey: 218, 364 Mercer No. 1, Magnolia Petroleum Company: 239 MerrittNo.1Henry Nors: 274 Messergill &Williams (R.G.Hauser) No.1T.R. Grubles: 347 metamorphic zones: 122, 123 metamorphism : 121 Mexico: 99-106 Meyers & Sons No. 1Brazos River Electric: 222 No. 1 Sanderford: 223 Meyers (Moyer?) No. 1, Lacey and Guiberson: 248 Midcoast (B. R. Floyd) No. 1E. A. Jones: 315, 366 Middle Georgia Oil & Gas Company: 361 Mid-Tex Production Company No. 1 C. C. Walker: 226 Milam County: 157, 374, 384 well data: 297-298 Milham Oil Corporation No. 1 Bassett: 20, 307 Miller and R. V. Mayfield No. Miller (Fee) :336 MillerNo. 1, Fohs-Loffland Bros.: 358 Humble Oil &Refining Company: 116, 242 MillsMineral Trust No. 1, Humble Oil &Refin ing Company: 323 MillsNo. 1,A. Gutowsky et al.:354 MillsRanch No. 1, O. O. Owens: 327 MiktonNo. 1Stelzer: 212 miogeosynclinal belts: 177 Miquihuana area: 102 Mississippi embayment: 83, 85, 89, 95 Mississippi, Jackson: 95 Mississippian: 88-89 Missouri Mountain shale: 29, 32, 68, 157 Mitchell County, Georgia, well data: 348 Mitchell No. 1, Humble Oil &Refining Company: 306 J. L. Rush: 252 Standard Oil Company of Texas: 266 The Texas Company: 318 molasse: 14, 30, 53, 54, 182, 186 Monograptus: 28 Monroe County: 89 Montgomery County, Arkansas: 69, 165 Mississippi, well data: 351 Montgomery Oil Company No. 1Snowdown: 359 Montoya limestone: 162, 179 montmorillonite: 149 Monument Spring dolomite member: 50, 51, 177, 179 Moore and Whitehead No. 1, Reclamation Oil Producing Syndicate: 329 Moore No. 1-A, Quintana Petroleum Corporation: 338 MooreNo.1AlfredJ.Wurzbach: 110,295 Morehouse formation :86, 125 Morehouse Parish, Louisiana: 125 well data: 350 Morgan No.1,E. V.Parsons (George L.Pace?) : 256 Morris No. 1, Mark Raley: 249 Morrison field: 138 Morrison No. 1, Magnolia Petroleum Company: 326 Morrow fauna: 20, 36 Moser No. 1, Starr Oil Company, Inc.: 267 Mountain Eagle Ranch No. 1, Universal: 319 MowinkleNo.1J.Kasten: 279 Movers siliceous shale: 35 Mud Creek Oil and Gas Company No. 1 J. O. Taylor: 285 Muenster arch: 73, 142, 146 uplift:132, 134, 145 Munson No. 1, Peter Oiland Gas Company, Inc.: 263 Murphy belt: 92 Murphy, Jr.,No.1R.E.Eaton: 353 Murphy No. 1, N. W. Shiarella: 352 muscovite-type structure (2M):149 Muth and Berry No. 1 Freeman (Freeman and Butler):292 Myers &Sons No. 1AxtellCity Water Well:292 Myrick No. 1, Telegram Oil Company: 232 Nally No. 1, Lion OilCompany: 348 Nashville dome: 85, 87. 88, 94 Navarro County: 80, 123 well data: 298 Nelson Exploration Company No. 1 Smith Lumber Company: 347 Nelson No. 1, Woodward and Company: 316 Neshoba County, Mississippi: 90 well data: 353, 355 Nevadan orogeny: 186 Newark group: 86, 126, 189 NewkirkNo.1,A.M.Sutton: 232 Newton No.1Check Ranch:76, 157, 280 Newton County, Mississippi: 90 well data: 355 Newton No. 1, D. Henry Werblow and Associates: 331, 376 New York Syndicate No. 1 Charles Gotcher: 247 Nixon No. 2 Hohenberger: 230 No. 3C. E.Crist: 230 Nolan Bell Oil Company No. 1 William Bacon: 219 No. 2 William Bacon:20, 219 Norman No. 1, Humble Oil &Refining Company: 75, 276 Normanskill-type graptolites: 27 Norphlet formation: 86 Nors No. 1, A.P. Merritt: 274 North American fauna: 50 NorwoodNo.1,L.M.Glasco: 353 Novillo canyon: 102 NowlinNo.1and No.2,G.L,Rowsey: 282 Nuevo Leon, Mexico: 99, 102, 115 well data: 345 Oblate Fathers Water Well :244 Ocoee belt: 91, 92, 93 series: 93, 175, 184 O'Dell No. 1, Peter and Johnson (McCarty Company) : 262 U. S. Army: 222 Bureau of Economic Geology, The University of Texas Ogg and J. A. Clark No. 1 G. Burkhalter: 351 O'Hanlon No. 1, Standard OilCompany of Texas: 266 Ohio Oil Company No. 1 J. H. Soul (Saul?): 282 OilCreek :133 oil seeps: 192 Oklahoma, Atoka County: 192 clay suite: 152 McCurtain County: 25, 26 Redden County: 192 Oktibbeha County, Mississippi, well data: 325 Olson Drilling Company No. 1Southwestern Life Insurance Company: 20, 260 No. 1 Utiger: 261 orthoquartzites: 30 Osage formation: 33 Osborne No. 1, J. H. Humphrey: 274 Ossenbeck—No.1Charles Bezdek: 293 Ouachita Arbuckle junction: 171 belt, clays: 157 County, Arkansas, well data: 359 facies: 13,88,93 foldbelt: 13 front: 163,172 geosyncline: 176, 181 Marathon belt: 13 mobile belt:13 Mountains: 21, 89, 95, 165, 168, 179, 189, 366 frontal belt: 47 salient: 73, 74, 122 stratigraphy: 25-45 structure: 46-48 peneplain: 190 structural belt: 13 system: 13, 90, 92-93, 97, 175, 176, 177, 178, 186, 189 Owens No.1MillsRanch: 327 Ozark dome: 85 uplift: 73, 86, 87, 130, 140, 145, 183, 186 Pagenkopf No.1MaxBlum: 78,125, 226 Pahrump series: 176 Paleozoic rocks, post-orogenic: 125 Palm Valley Oil Company (Round Rock Oil Company?) No. 1Walsh: 336 Pan-American Petroleum Corporation No.1J. R. Sealy: 348 Pan American Production Company No. 1 J. Umphress: 261 Pandale field: 138 Panhandle Prairie Pipeline Company No. 1-22 Ives: 349 Park and Phillips No. 1 Flowers and Ward Ranch: 79, 338 Parker County: 133 Parker No. 1, Gulf Refining Company: 351 Killam: 326 Parker Petroleum Company, Inc. No. 1-A Pearson: 336 Parkwood formation:88, 89 shale: 158 Parsons (George L.Pace?) No.1R.E. Morgan: 256 Paskenta formation:183 Patterson No. 1, Transcontinental OilCompany (Benedum and Trees) :318 Pearson No.1,Hewittand Dougherty: 335 No. 1-A,Orville H. Parker: 336 Pecosarch: 137, 142 Pecos County: 137 well data: 298-299 PeikofT No.1Christie et al:277 Pefia Colorada synclinorium: 56, 165 Peninsular arch: 85 Pennington shale: 158 Penters formation :33 Pepper No. 1, Gas Ridge Syndicate (Clark Oil Company) :224 Peregrina (La Presa) canyon: 102,104 Perkins and Lierney No.1McCue: 308 Permian Basin Operators No. 1 Rust (White head) :325 Permian Oil Company No. 1Bowles: 280 Perrin No. 1, Southwest Exploration Company: 344 Perry Water Well :315 Persimmon Gap: 165, 368 area: 62, 165 shale: 50 Peteet No.1,E. C.Johnston: 356 Peter and Johnson (McCarty Oil Company) No. 1J. A. O'Dell: 262 Peter Oil and Gas Company, Inc., No. 1 Butcher: 72, 262, 370 No. 2 Easton: 267 No. 1Jackson: 263 No. 1Munson: 263 Petoskey Oil Company No. 1 John Kolls: 220 Petrocel No. 1Waldrop: 328 Petroleos Mexicanos: 103, 105 No. 101 Chapa :103, 105, 345 No.1Chupadero: 105,345 No.1Garza: 115,345 No. 2-APeyotes: 103,345 No.1Trevino:105,345 No. 1Zambrano: 105, 345 petroliferous provinces: 191 Peyotes No. 2-A, Petroleos Mexicanos: 103, 345 Pfulman No. 1, Magnolia Petroleum Company: 269 Phantom Oil Company No.1 M.D.Cloudt: 318 No. 1Ingram: 328 Phillips County, Arkansas, well data: 349 Phillips Petroleum Company No. 1 J. T. Arnold: 359 No. 1-A Carson: 136,251 No. 1 Elsinore Cattle Company: 299' No. 1-A Guinn: 328 No. 1Knowlton &Perthshire: 350 No. 1-A Posey: 275 No. 1-EE University: 137 No. 1 Wilson: 137 (and Garrett) No. 1J. R. Rose: 275 Pickens County, Alabama, well data: 353 Pickett No. 1, Capitol Oil& Gas Company: 360 Piedmont province: 85, 90, 91, 93, 94, 163 Pike County, Alabama, well data: 360 Pine Mountain fault: 33, 38, 41, 47 Pinetop chert: 33, 178 Pittsborg County, Oklahoma, well data: 343 Pittsburgh Western Company No. 1Downie: 308 Placer de Guadalupe, Chihuahua, Mexico: 101, 104,108 Plateau Oil Company No. 1 R. D. Garrison: 67, 212 No.1B.S. Harrison et al.: 79, 328 Plumber and Schwab No. 1 Bud Roark: 81, 235, 374 Subject Index, The Ouachita System Plymouth Oil Company No. 1Bush: 350 Polk Creek shale: 28, 29, 32, 68, 157 Pontotoc group: 189 Pool Drilling Company No. 1 E. L. Rainey: 213 Posey No. 1-A,Phillips Petroleum Company: 275 Postell No. 1, Fish Production Corporation: 116, 283 post-orogenic Paleozoic rocks: 125 Potash Sulphur Springs, Arkansas: 115 Potato Hills:32, 35, 40, 166 anticlinorium: 47 Potrero de La Mula area, Coahuila, Mexico: 102, 105, 108 Pottsville formation: 87, 89 Prairie County, Arkansas, well data: 349 Preston No. 1, Peter Oil and Gas Company, Inc.: 263 Proctor No. 1Wardlaw-Whitehead: 286 Producers Oil Company No. 1Bob Everett: 329 Profit No. 1Henry: 232 Pseudoschwagerina :188 Pucek No. 1, Humble Oil & Refining Company: 254 Pulaski County, Arkansas, well data: 356 Pullen No. 1, Stanolind Oil &Gas Company: 348 Purcell No. 1, Shell Oil Company: 109, 136, 337 Purcell series: 176 Pure Oil Company No. 1Finley: 242 No. 1J.D.Jones: 355 No. 16-T W. H. Kendricks: 289 No. 1Light: 243 No. 1A. S. Rea:3ss No. 1Massie West: 145, 236 Pushmataha County, Oklahoma, well data: 344 Quintana Petroleum Corporation No. 1Lampkin: 78, 258 No. 1-A A.L.Moore: 338 Ragsdale (Saver) No. 1. Sol Kopel: 325 Rainey No. 1, Ray Pool Drilling Company: 213 Raley No. 1Morris. 249 Ray No. 1, Skelly Oil Company and Sunray Mid- continent Oil Company: 214 Ray Pool Drilling Company No. 1 E. L. Rainey: 213 Rea No. 1, Pure Oil Company: 355 Reagan formation:25 sandstone: 177 Real County, well data: 299 Reasor No. 1Jesse Ezell: 315 No. 1Gibson:297 Reclamation OilProducing Syndicate No.1J. B. Moore and Whitehead (No. 1 Mclntyre): 329 Reed No. 1,Burnette: 332 Reenlee Oil Corporation No. 1 A. Theis: 226 Red River County: 65, 66, 67, 68, 81, 370 well data: 300-303 Red River uplift: 133, 142 Redden County, Oklahoma: 192 Reeder No. 1, Mann: 271 regional distribution of clay mineral suites: 160 Reichert No. 1, American Liberty Oil Company: 231 Reimers No. 1, Franklin: 136, 313 Summerow: 136, 316 Reneau No. 1, Sinclair: 47 Renwar Oil Corporation No. 1 H. D. Granberry: 347 Richardson No. 1, Alvarado Oil Company: 277 Richardson Oil Company No. 1Martin Rose: 20, 109, 144, 286 Rimrock-Tidelands, Inc., No. 1 W. F. Crawford: 157, 297 Rio Grande Oil Company No. 1 D. W. Hair: 220 Roark No. 1, Plumber and Schwab: 81, 235, 374 Roberts No.1,Skelly OilCompany: 308 Roberts Ranch member: 49 Robertson No.1,H.A.Stebinger: 347 Williams etal.: 311 Rocky Mountains: 186 Rodriguez Tank sandstone: 80, 180 Roeser &Pendleton No. 1 Young & Ogilvie: 351 Rogers Ranch No. 1, General Crude Oil Com pany: 110, 169, 224, 372, 378, 380 Rollins No. 1, Seaboard OilCompany: 359 Romberg No. 1 (Jones No. 1Romberg), Cypress Creek Association: 136, 313 Rome formation: 89 Rose No. 1, Caraway: 319 Fenslund Oil Company: 322 Phillips Petroleum Company and Garrett: 275 Richardson Oil Company: 20, 109, 144, 286 Sides: 308 Rose-Robertson No. 1, Husky Oil Company: 79, 109, 324 Rosencrantz et al. No. 1, David J. Flesh: 349 Rossman (Stan-Ross) No. 1Goodenough: 213 Rothe Estate No. 1, California-Medina Associa tion:294 Roxana Petroleum Company: 296 Rowsey No.1and No.2Fee: 213 No. 5 Fee: 214 No. 1Gus Evans: 214 No.1and No.2R.B.Nowlin:282 Roxana Petroleum Company No. 1 Rothe: 296 Rush No. 1, John Mitchell: 252 Russell and Weatherby No. 1, East Del Rio Oil Company: 321 Russell No. 1A.B. McGill: 337 Rust (Whitehead) No. 1, Independent Operator: 325 Rutherford No. 1, Humble Oil &Refining Company: 75, 276 Rutledge No. 1M.E. (Mollie) Williams: 263 Ryan Consolidated Petroleum Corporation No. 1 Roy McCollum: 349 Sadler No. 1, Columbia Texas Oil Company: 248 Safely No.1,U.S. Army:222 St. Louis Oil Pool Company No. 1Ella V. Stuart (Stewart) :167, 293 St. Stephens School Water Well: 316 Saline County, Arkansas: 69, 165 Sallisaw formation: 33 Sandel No. 1, Stanolind Oil&Gas Company: 354 Sanderford No. 1, Meyers &Sons: 223 sandstone dikes: 35 San Luis Potosi: 99,102 Santiago formation: 51, 62 sapropel: 17 Savanna formation: 187 Schawe No. 1, Gulf Coast DrillingCompany: 239 Schmidt No. 1, Stanolind Oil and Gas Company: 169, 269, 372, 382 Schubert No. 1, Woodward: 169, 272, 372, 382 Scott County, Mississippi: 90', 131 well data: 355 Bureau of Economic Geology, The University of Texas Scott No. 1, Sun Oil Company: 309 Seaboard Oil and Gas Company No. 1W. H. As- key: 280 Seaboard Oil Company No. 1 S. M. McConnico: 359 No. 1J.T.Rollins: 359 Scaly No. 1, Pan-American Petroleum Corpora tion: 348 Seaton No. 1 McNeil &Matthews: 249 Security DrillingCompany No. 2 Englemann: 227 Seiderman (New Braunfels Oil Company) No. 1 Alvina Seidermann: 28 Seitz, Comegys and Seitz No. 1 W. P. Mackey: 264 Sellars (Sellers) Bros. Ranch No. 1, Joiner Oil Corporation: 325, 376 Sellars No. 1, Douglas Oil Company (Benedum and Trees No. 2 Sellars) :320 Gulf Refining Company: 359 Hiawatha Oil Company: 109, 144, 322 Seminole uplift: 132 Sequatchie anticline: 87 Seward No. 1, S. L.Carpenter: 332 Shambeck and Casey No. 1 Sudie Baugh: 220 sharpness ratio: 147, 148, 149, 150, 159 Sheffield channel: 136 Shelby County: 115 — Shell Oil Company No.1R. O. Brown: 264 No.1Harwell: 136,271 No.1Honeycutt: 251 No.1 Keystone: 343 No.1C.E.Massie: 221,366 No. lPurcell: 136,337 No. 1University: 137 No.IH.H. Wheeles:3s3 Sherley No. 1, Deep Rock Oil Corporation: 241 Sherman anticline: 133 Sherman City Well:264 Sherman Drilling Company (Clarence Houseman etal.) No. 1J. F.Griffith:275 Shiarella No. 1L.L.Murphy: 352 Sides No. 1 Rose: 308 Sierra de Catorce, Mexico: 102 Sierra del Carmen, Mexico: 79, 80, 81, 99, 105, 169, 376 Sierra del Cuervo, Mexico: 99, 104, 108 Sierra Diablo: 145 Sierra Madera: 137 Sierra Madre Oriental: 102 Simon-Ferguson No.1,Korshoj:159, 292 Simpson-Fells Oil Company No. 1 G. W. Wall: 20, 264 Simpson group: 132, 162 Sinclair No. 1 Reneau :47 Sinclair Oil and Gas Company No. 1A.M.White: 232 No.°l Campbell: 156 No. 1 Purcell: 337 Skelly Oil Company No. 1Roberts: 308 and Sunray Mid-Continent Oil Company No. 1 Cornell:288, 374 No. 1 Itha Ray: 214 Slaughter No. 1, Deep Rock Oil Corporation: 298 Transcontinental Oil Company: 299 Slayden No. 2, Eclipse Oil Company: 216 Slick OilCompany &Plains Producing Com pany No.1J. D. Breazeale: 355 Slick-Urschel No. 1 Decie: 187, 237 Smackover oil field: 93 Smiley No. 1, Clark and Ogg: 287 Smith Lumber Company No. 1, Nelson Exploration Company: 347 Smith No. 1, J. B. Stoddard: 253 Southern Natural Gas Company: 355 Smilhwick shale: 59 Smythe No. 1,S. S. Alexander: 354 Snowden et al. No.1A.M.Bryant: 265 Snowden No. 1, Texas Minerals: 72, 256, 366 Williams, Calvert, and Brown: 311 Snowden No. 1, Montgomery Oil Company: 359 Snuggs and Cox No.1Q.Little:265 No. 2 M. M.Davis et al.: 265 Solitario: 51 area: 59-61, 165 thrust: 60, 61 Solomon No. 1, The Texas Company: 67, 302 Soul (Saul?) No. 1, Ohio OilCompany: 282 Southeastern DrillingCompany No.1L.D.Eley et al.: 355 Southeastern Operator's Committee No. 1 Mrs. Beatrice Gamble &0. A.Gamble: 360 Southern Natural Gas Company No. 1 J. W. Smith: 355 Southern Pine Lumber Company No. 1, Bentley, Shepherd, and Stevens: 66, 300 Texas Trading Company: 302 Southland Oil Company (American Liberty Oil Company) No. 1 R. T. Greenwade: 231 Southwest. Exploration Company No. 1Hoehman: 343 No.1Denton Perrin: 344 Southwest Texas Oil and Gas Association No. 1 A. T. Folsom: 309, 376 Southwestern Life Insurance Company No. 1, Olson Drilling Company: 20, 260 Sowega Minerals Exploration Company No. 1 J. W. West: 348 Specht No. 1, Theodore Hicks: 157, 229 Springer formation: 37, 38, 44 Standard Oil Company of Texas No. 1Mitchell: 266 No. 1 O'Hanlon: 266 Stanfield No. 2 Ludwick: 222 Stanley formation: 74, 75, 78, 108, 152, 154 sandstone: 18 shale: 34, 35, 36, 43, 72-73, 88, 89, 157, 182, 366 — Stanolind Oil and Gas Company No. 1Knippa: 299 No. 1 J. H. Pullen: 348 No.1G. B.Sandel: 354 No.1Schmidt: 169, 269, 372, 382 No. 1 C. E. Steed: 358 No. 1 West: 330 Starr Oil Company, Inc., No. 1Blankenship: 266 No.1W. A.Moser: 267 starved depositional basin: 31, 32 State Life Insurance Company No. 1, Boettcher: 354 State No. 1, Atlantic Refining Company: 339 Stebinger No.1 Alice S. Robertson: 347 Steed No. 1, Stanolind Oil & Gas Company: 358 Stelzer No. 1, Mikton: 212 Stephenson (Stevenson) No. 1, Transcontinental Oil Company (Ohio): 330 Sterling et al. No. 1McCracklin: 281 Sterling No. 1 Werner: 281 Stewart et al.No.1W.W.Wood:351 Stewart No. 1, W. W. Martin &J. H. Coker: 349 Subject Index, The Ouachita System Stoddard No.1W. E. Smith: 253 Stones River formation: 160 Strawn formation: 133, 134 Strickland No. 1, Amerada Petroleum Corporation: 115 Buckeye and Mid-Tex Oil Company (Mid-Kansas) :244 Stringtown shale: 68 Stuart (Stewart) No. 1, St. Louis OilPool Company: 167, 293 subgraywacke: 30 subsurface lithologic units: 65 Sudduth No. 1, Continental Oil Company: 359 sulfide minerals: 117 Summerow No.1Reimers: 136, 316 Sumter County, Alabama: 90 well data: 355 — Sun Oil Company No.1H.N.Camp: 91 No. 1 Citizens National Bank: 355 No.1P. C.Crapps: 357 No. 1 Doster-Ladson :361 No. 1 Hilma Wall: 355 No. 1 McElroy: 145, 236 No. 1Scott: 309 No.1Tucker: 256, 364 Sunray Midcontinent Oil Company No. 1 Ray: 214 Superior Pine Products Company No. 1 and No. 4, Hunt Oil Company: 357 Sutton No. 1J. G. Newkirk: 232 Suwanee basin :85, 90, 94, 95 River basin : 138 Svoboda No. 1J. L,Bassett: 310 Switzer et al. (O'Dell, Haught and Bond) No. 1 Martin Zerr: 296 Swope No. 1, Killeen-Bell Oil Company: 222 Sycamore limestone: 34 Tabor No. 1, United North and South Development Company: 240, 374 Taconian orogenies: 180 Talladega belt: 87, 91, 92 Tallahatchie County, Mississippi, well data: 351 Talley No. 1, General Crude Oil Company: 225, 368 Tamaulipas: 99, 102 Cd. Victoria: 104 Taylor County, Florida, well data: 348 Taylor No. 1, Mud Creek Oil and Gas Company: 285 Twin Cities Oiland Gas Company: 239 J. S. Woodward, Inc.: 241 Telegram Oil Company No. 1 J. W. Burns: 232 No.1M.B.Myrick: 232 Tennessee Gas Transmission Company No. 1 Washburn :133, 267 Tensas Delta No. 1, Union Producing Company: 350 No. 1-A: 125 Terrell County: 9, 20, 66, 68, 80, 99, 109, 110, 123, 137, 138, 165, 376 well data: 303-311 Tesnus formation: 53, 54, 60, 62, 72-73, 76, 108, 155, 182, 184, 368 Texas American Syndicate No. 1, Dodson (Hinton): 234 Texas arch: 133, 143 Texas Consolidated Oil Company No. 1 Holmes: 310 Texas craton: 57 Texas Gulf Sulphur Company No. 1 Baker: 157, 298 Texas Minerals No. 1Snowden: 72, 256, 366 Texas No. 1Mitchell: 126 Texas Trading Company No. 1 Southern Pine Lumber Company: 302 Texas Water Wells, Inc., No. 40, No. 41, and No. 42 City of Dallas: 250 Theis No. 1, Reenlee Oil Corporation: 226 The Texas Company No.1Keeling: 289 No.1John Marshall: 267 No. 1 Mitchell: 318 No. 1 Solomon: 67, 302 No.1Whitehead: 159,358 Thomas No. 1, Holman &Russell: 358 Thompson No. 1, Humble Oil & Refining Company: 211 Thurman sandstone: 44 Tienert No. 1, E. A. Dunham (New York Syndicate) :245 Tiller No. 2, United North and South Development Company: 240 Timberlake No. 1,J. M.West: 228 Tindel No. 1, Humble Oil &Refining Company: 357 Ti Valley: 33, 34 fault: 33, 34, 38, 40, 44, 47, 166, 178 Town Mountain granite: 136 Townsend No. 1, Billups Bros.: 351 Transcontinental Oil Company (Benedum and Trees) No.1 Patterson: 318 (Blackwood and Nichols) No. 1 Slaughter: 299 (Ohio) No. 1 Goode: 310 No. 1W. S. Stephenson: 330 Trans-Pecos Development Company No. 1Hamilton: 306 Trans-Pecos Oil and Gas Company No. 1, John C. Grasdorf (Grostorf) :234 Travis County: 59, 72, 75, 122, 136, 366, 372 well data: 311-316 Trevino No. 1, Petroleos Mexicanos: 105, 345 Triangle Corporation No.1Hale: 253 Tricon Minerals, Inc., No. 1 J. D. Duke: 360 No. 1H.B.Gilbert: 360 Trigg No. 1, Magnolia Petroleum Company: 249 Twin Cities Oil and Gas Company No. 1 Taylor: 239 Tucker No. 1, Brewster and Bartle: 312 Sun Oil Company: 256, 364 Tuff beds: 154 turbidity currents: 184 Turkey Bend area of Lake Travis: 59, 165 Turner No. 1 D.S.C. Coombs et al.: 51, 177, 237 No. 1 R. Linder: 67,281 Tuscaloosa County, Alabama, well data: 354 Tyler Est. No. 1, C. J. Foster Drilling Company: 222 Uinta Mountain group: 176 Umphress No. 1, Pan American Production Company: 261 Union County, Arkansas, well data: 359 Union Oil Company of California No. 1 Anderson: 319 — Union Producing Company No. 1-E Crossett Lumber Company: 125 No.1J. N. Henderson: 352 No. 1E. P. Kirkland: 356 Bureau of Economic Geology, The University of Texas No. 1L. S. McKean: 227 No. 1-A Tensas Delta: 125, 350 United North and South Development Company No. 1 Gideon: 240 No. 1-A T. C. Gideon: 239 No.1 George Kelly: 240 No. 8 W.H. Tabor: 240, 374 No. 2, Tiller: 240 Universal No. 1 Mountain Eagle Ranch: 319 University No. 1, Humble Oil & Refining Company: 306 Shell Oil Company (Humphries) :137 No. 1-EE Phillips Petroleum Company: 137 — U. S. Army No. 1 Bloomer: 222 No. 1 Jarrell: 222 No. 1McCloskey Hospital Water Well: 221 No. 1 Odell: 222 No. 1Safely: 222 Water Wells No. 1, 2, 3, 6, 7, 10, 11, 12: 247, 248 No. 2 Wilson: 222 U. S. Government No. 1 Camp Bullis Water Well: 227 No. 1Leon Springs Water Well: 227 Utiger No. 1, Olson Drilling Company: 261 Uvalde County: 75, 76, 111, 123, 172, 368 well data: 317-319 Valley and Ridge province: 85, 87, 88, 90, 91, 94, 97, 163 Val Verde basin: 136, 188, 194 Val Verde County: 9, 68, 79, 80, 81, 99, 109, 123, 144, 376 well data: 319-331 Van Horn mobile belt: 57, 109 oroeenic belt: 176 Van Horn sandstone: 145 vein material:117 Vinegarone field: 138 Viola formation: 162 limestone: 27, 132, 179 volcanic rocks: 104 volcanism: 31, 43 Waco City Water Works Well: 293 Waco Oil and Refining Company No. 1 G. H. Harrington: 294 Wacoochee belt: 93 Wadley No. 1E. Blackman: 233 No. 1Bentley Johnson: 233 Wagner No. 1, Roland K.Blumberg: 228 Waldrop No.1, Petrocel: 328 Waldron et al. No.1Travis Cooke: 312 Waldron quadrangle: 131 Walker et al.No. 1Federal Land Bank: 288 Walker No. 1,D.J. Meeks: 230 Mid-Tex Production Company: 226 Wall No. 1, Simpson-Fells Oil Company: 20, 264 Sun Oil Company: 355 Waller No. 1 Bruckner (Winan & Forbes) :229 Walsh No. 1, Palm Valley OilCompany (RoundRock Oil Company?) :336 Walton County, Florida, welldata: 348 Wapanucka limestone: 38, 39, 44, 154 Wardlaw No. 1, Bernard Einstoss: 368 Humble Oil&Refining Company: 323 Magnolia Petroleum Company: 285 Wardlaw-Whitehead Estate No. 1-A, Austral Oil Exploration Company, Inc.: 283 Wardlaw-Whitehead No. 1, George Proctor: 286 Warner uplift: 130 Warren et al.No.1A.C. Chandler: 356 Warrick No.1, J. B. Hartman: 217 Bell Williams Oil Company: 215 Warrick No. 2, Davidson et al.: 215 J. B. Hartman: 218 Washbiirn No. 1, Tennessee Gas Transmission Company: 133,267 Washington County, Georgia, well data: 361 Water Wells Nos. 45 and 46, City of Dallas: 248 Weatherby No. 1, Havoline Oil Company: 109, 144, 284 Hill-Texas Oil Company: 75, 273 Weisner formation: 89 Welch No. 1, McAlester Fuel Company &H. M. Cox: 350 Welch Petroleum Company No. 1 R. Williams: 303 Wells Creek formation: 160 Werblow and Associates No.1Maude S.Newton: 331, 376 Werner formation: 86, 93, 190 Werner No. 1, P. B. Sterling: 281 Werner Sawmill Company No. 49, Gulf Refining Company: 359 West No. 1. Pure Oil Company: 145, 236 Sowega Minerals Exploration Company: 348 Stanolind Oil and Gas Company: 330 Timberlake: 228 J. L. Youngblood: 349 West Texas basin: 179, 188 Western Natural Gas No.1Bassett: 331 Westmont Drilling Company No. 1 Clark: 277 Westover et al. No. 1Easton: 267 Weyel No. 1, Frank Gravis: 268 Wheeles No. 1, Shell OilCompany: 353 White and Green Drilling Company (Hillsboro City Well No. 2):272 White County, Arkansas, well data: 348 White et al. No. 1 Kurth Lumber Company: 303 White No. 1, Sinclair Oil and Gas: 232 Whitehead et al. No. 1, The Texas Company: 358 Whitehead No. 1, Caraway: 320 Magnolia Petroleum Company: 326 Permian Basin Operators: 325 The Texas Company: 159 Whitestone fault: 91 Wichita- Mountains: 176, 177, 189 paleoplain: 19, 189, 190 system: 178, 189 uplift: 95 Wilcox County, Alabama, well data: 359 "wildflysch": 44 Williams Oil Company No. 3 John Kolls: 215 No. 1B. F. Warrick: 215 Williams, Calvert, and Brown No. 1 George M. Snowden (No. 1 Robertson) :311 Williams Drilling Company No. 1 W. T. 0. Holman et al.:331 Williams No. 1, Capitol HillOil Company: 341 Verne Dumas Company et al.:259 W. J. Rutledge: 263 Welch Petroleum Company: 303 Williamson County: 67, 109, 111, 136 well data: 332-337 Willis No. 1, Johnson & Hawkins Company: 355 Wilson County, well data: 338 Wilson No. 1, Delta-Gulf (Phillips Petroleum Company) :320 Subject Index, The Ouachita System Humble Oil & Refining Company: 110, 295, 378 Phillips Petroleum Company: 137 No. 2, U.S. Army: 222 Winans &Forbes No. 1Bruckner: 229 No.1Ferguson: 222 Windermere series: 176 Windingstair fault: 44, 47 Winkler County: 156 Wise County: 134 Wolfcamp formation: 53, 137, 187, 188 Hills: 137 Womble formation :31, 32, 67, 68, 134 schistose sandstone: 27 shale: 27,68, 135 Wood No. 1, W. L.Stewart et al.:351 Wood Texas Oil Company No. 1 A.E. Clayton: 214 Woodford chert: 33, 179 formation: 44, 132 Woods Hollow shale: 50, 57, 60, 154 Woods Oil and Gas Company No. 1-47 Mary Decieetal.: 54,56,58,237 Woodward and Company No. 1 Nelson: 316 Woodward, Inc., No. 1P. S. King: 241 No.1Schubert: 169, 272,372, 382 No. 1Taylor: 241 Wright No. 1, Hunt OilCompany: 274 Wurzbach No.1, John I.Moore: 110, 295 X-ray patterns: 150 studies of shales: 147 Yates No. 2 Heidrick: 244 YorkTrustee No.1S. V.Dismuke: 347 Young & Ogilvie No. 1, Roeser &Pendleton: 351 Young No. 2, Kansas City Syndicate: 246 Youngblood No.1J.B.West: 349 YturriNo. 1,Anderson-Prichard OilCorporation: 157, 223 Zacatecas: 99, 101 Zambrano No. 1, Petroleos Mexicanos: 105, 345 Zavala County: 79, 80,123 well data: 338 Zerr No. 1, Switzer et al. (O'Dell, Haught and Bond) :296