GEOLOGY OF THE MERCURY QUADRANGLE, MCCULLOCH COUNTY, TEXAS GEOLOGY OF THE MERCURY QUADRANGLE MCCULLOCH COUNTY, TEXAS DIDDEEIVnOR Presented to the Faculty of the Graduate ochool of The University of Texas in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By William Adrian Jenkins, Jr., B.S. THE UNIVERSITY OF TsJUS June, 1952 GEOLOGY OF THE MERCURY QUADRANGLE McCULLOCH COUNTY, TEXAS By William Adrian Jenkins, Jr. ABSTRACT k new map showing detailed geology of the Mercury and described quadrangle, and IS detailed, newly measured stratigraphic sections within the quadrangle are the main part of this paper. Lower Ordovician, Mississlpplan, and are Pennsylvanian, Cretaceous, quaternary strata ex­posed. Pennsylvanan beds unconformably overlap older Paleozoic formations, and Cretaceous formations truncate strata. Pennsylvanian and sandstone conglomerate channel deposits, oc­ levels curring at many in the Pennsylvanian sequence, are indicators erosion interpreted as of repeated uplift and of nearby land areas. These irregular deposits complicate accurate correlation of marker beds. Limestone reefs are found in three asoms in the limestone upper Canyon series. Interpretation of these masses as reefs permits clarification of several correlation problems. The development of reefs, one above another along northeast southwest trends, suggests shallow, warm, dear- water conditions of deposition. III The nomenclature of the Canyon series is simpli­fied by elevating former member to formations! rank* names The Corn Creek limestone member of the Placid formation Is the only new name proposed* Lower Paleozoic bed® are folded broadly into the Hall uplift in the southwestern part of the quadrangle* Strewn, Canyon, and Cisco beds, covering 60 of percent the quadrangle, dip northwestward 60 feet per mile, and Cretaceous strata in the southwestern part of the area dip southward 10 feet per mile» IV CONTENTS Page 1 Introduction acknowledgments 7 Physiography Stratigraphy **..« 9 Lower Ordovician 9 • kilenburger £roup. 9 Nomenclature• * 9 Gorman formation. •• 9 • Mssissippian system 13 Ives breccia 13 Garnett shale. •••••«••••••••• 14 Pennsylvanian system. 15 Bend aeries. ••.•••••••• 1? nomenclature* 1? Big balin® formation. . « * 17 bmithwick shale *••••• 19 btrawn series 20 nomenclature. 20 Btr&wn undifferentiated ••«••••• 22 Capps limestone member. 26 • Canyon series «• • 28 Brownwood ahale • • J2 * Str&wn-Canyon boundary. * 38 Adams Branch limestone* *••••*.. 40 Cedarton shale* ••*••*•••»•• 41 Inchell formation* ••••••••. 44 • Placid shale* , 50 . Ranger limestone. $S Colony Creek shale. • . * . 63 Home Creek limestone 64 V Cisco series •••• 83 Bluff Creek shale • * 84 Comanche series Travis Peak formation 86 »•••••«••• 88 Comanche Pe&K limestone ••••«•«•• 90 Edwards limestone •• 90 Walnut formation .«•••• quaternary system » 91 structural Features • 92 * Geologic History «*•••••«..* 94 Introduction. 94 . Pre-6trawn time 97 6trawn epoch, 99 Canyon epoch * 102 Cisco epoch * 103 Post•.CiSCO time • ••««•••*<»«••••••« 104 Appendix A*. 106 List of fossil localities in the Mercury Quadrangle 106 References 11l ••••••«•» • VI ILLUSTRATIONS Figure Page 1. Index showing location of Mercury mapQuadrangle. 3 2. Section of Gorman and Barnett formations 2 miles southwest of Hall, 3an Saba County, Texas. 11 3. Stereogram of Gorman, Ives, Barnett, Big Saline, and Smithwlck formations southwest of Hall, San Saba County, Texas 12 4# History of the correlation of the Bend series, 1889 to 1950.. 16 5. History of the correlation of the Strawn series, 1890 to 1893* * . 21 6. Stereogram of Strawn series and Travis Peak formation (Lower Cretaceous) north of Hall, San Saba County, Texas...... 24 7. section of part of Strawn series ("Indian Creek bed” and "dicker bed”) 1 mile north­ east of Keys Crossing Ford, Brown County, Texas 28 8. Section of part of Strawn series ("Sicker bed" and limestone J north of mouth of Capps Limekiln Creek, Brown County, Texas 29 series 9. Section of part of Strawn ("Ricker bed" and Capps member and Travis Peak for­ mation 4 miles southwest of Placid, McCulloch County, Texas. 30 10. History of the correlation of the Canyon series in the Colorado Elver valley, 1893 to 1952 33 11. Stereogram of Brownwood, adams Branch, Cedar- ton, and Winchell formations near Mercury, McCulloch County,Texas3s 12. Stereogram of ainchell, Placid., E&nger, Colony Creak, and Home Creek formations along Corn Creek, most; of Mercury, McCulloch County, Texas. 46 VII 13* btoreogram showing channel sandstone which replaces limestone Ro. 2 of Wlnchell formation, 2*5 miles northwest of Mercury, McCulloch County, Texas*••••*•••••• 49 14* Reef limestone facies of Placid shale on Tom Dean Creek about 0*25 mile from mouth*********•••*•*••*•«••*•«••••••*••••«•»•»« 55 hammer 15* Close-up of rocks near in Figure 14***«* 56 16* Reef in cherty limestone facies of Placid shale "draping” over beds with steep Initial dip. southward view on Tom Dean Creek, 0*25 mile from mouth* 57 17• Boulders of channel conglomerate above Corn Creek member of Placid shale, showing cross-bedding and chert pebbles**** 59 IB* Section of upper part of strawn series and lower part of Brownwood shale 4000 feet north­ west of Cowboy Cemetery, McCulloch County,Texas 67 19• Section of Brownwood, adams Branch, Cedarton, and wlnchell formations 3*5 miles south-south­east of Placid, McCulloch County, Texas 63 20* Section of Brownwood shale on north bank of Colorado River 2*5 miles east of Winchell, Brown County, Texas*•*•••*••••«»••••****** 69 21* Section of Brownwood shale and Adams Branch limestone 0.5 mile southeast of Mercury, McCulloch County, Texas* 70 22* Section of Brovmwood, adams Branch, Cedarton, and bluebell formations 1 mile east of Placid, McCulloch County, Texas* 71 23* Section of adams Branch, Cedarton, and Win­ch©11 formations at Morgan Mountain, X mile southwest of Wlnchell, McCulloch County,Texas*• 72 24# section of Branch, Cedarton, and win­chell formations I*s miles south-southwest of Mercury, McCulloch County, Texas 73 25. section of «lnchell, Placid, Ranger, Colony Creek, and Home Creek formations west of Mer­cury on W* £• white and Company Ranch, McCulloch County, Texas• ****** 74 VIII 26. section of Winehell, Placid, Hanger, and Home Creek formations Colony Creek, in southeastern Coleman County, Texas.••••*•• 77 27. Section of Winchell, Placid, and Hanger formations on D. B. Humphrey Ranch 3 miles north of Placid, McCulloch County, Texas 7B 28. beetion of Placid and Hanger formations 1.5 miles northwest of Mlaehell, Brown County, Texas...*•••*•«• 79 29. Type section of Corn Creek limestone member of Placid shale at Beef Pasture Tank on W. N. White and Company Ranch, McCulloch County, Texas.BO 30. Beetlon of Placid {cherty limestone). Hanger, Colony Creek, Home Creek, and Bluff Creek formations on Homes Creek 2000 to 3000 feet northwest Coleman of mouth of Boggy Creek, County, Texa5..*...... Si * 31. Composite section of Hanger, Colony Creek, Home Creek, Bluff Creek, and Gunslght formations on Gill Ranch between ranch house and Homes Creek, Coleman County, Texas.•••••• $2 32. Section of Walnut, Comanche Peak, and Ed­wards formations on Parker Pumphrey Ranch, Corn Creak Hills, McCulloch County, Texas*.»• S9 Plate 1. Geologic map of the Mercury quadrangle, Texas* la pocket 2. Structure contour map of the western half of the Mercury quadrangle on the base of the Adams Branch limestone* In pocket 3* Map showing fossil localities in the Mercury quadrangle In pocket table Table 1. Distribution of species in various formations in the Mercuryquadrangle*ln pocket IX INTRODUCTION The Colorado River valley la the vicinity of the Mercury Quadrangle haa been a classic area for the study of Pennsylvanian stratigraphy since the first geological survey of Texas in 1890* The present study contains a detailed map of the Mercury Quadrangle showing all of the traceable stratigraphic units coordinated with carefully measured geologic sections* Particular attention has been given to the mapping of previously neglected Pennsylvanian channels and reefs* Widespread channelling of the upper­ most Strawn limestone sake® it difficult to define the Strawn-Canyon boundary across the quadrangle* The correlation of the basal Canyon conglomerate (Rochelle) with equivalent beds to the north is complicated by channelling and by facies changes* Rapid facies changes associated with limestone reefs in upper Canyon strata are now recognised as part of the problem of questionable and erroneous correlations made in those beds by previous workers• Although nomenclature and correlation problems will continue to be encountered as mapping and faunal studies are made in greater detail, an attempt has been made in this report to simplify the of Pennsylvanian strata nomenclature exposed in the Colorado River valley* 1 about The Mercury quadrangle is in central Texas The 20 miles northeast of the town of Brady (Figure 1). quadrangle is mainly in McCulloch County but it includes portions of San Saba, Brown, and Coleman Counties* Although the only highway crossing the quadrangle is U. Highway 3* 283 between Brady and Brownwood, numerous fans to market roads and ranch roads make the entire area easily accessible. The oldest exposed rocks are in the southeastern ofthe a corner quadrangle and represent small portion of the folded and Strawn and faulted Llano uplift* Canyon beds, dipping gently northwest, are exposed over the greater part of the quadrangle* Cisco rocks crop out in the extreme northwestern corner of the quadrangle. Nearly horizontal Lower Cretaceous beds overlie uncoafonnably the Strawn and Canyon in the southwest and south-central part of the quad­rangle. The first geological work in the Mercury quadrangle was don© by Tarr (1890) in a report on the coal fields of the Colorado Eiver. He classified only the broader divisions of the Pennsylvanian rocks* In the same year, Dumble (1890) classified equivalent rocks outcropping in the Brazos Eiver valley and correlated them with Tarrfs divisions to the south Cummins During the following year, (1891), expanding the work of Tarr and Dumble in both the Colorado and Brazos River valleys, modified the classification of Dumble and applied the Brazos Eiver valley names of Strawn, Canyon, and Cisco 3 - l, Index map showing location of Mercury Quadrangle. to bods of equivalent age In the Colorado River valley* Various writers have since disagreed on the position of the strawn-Canyon boundary and the Cisco-Wolfcamp boundary* (The history of the position of the Strawn-Canyon boundary is summarized under the heading of stratigraphy in this report*} Drake (1593) divided the Btrawn, Canyon, and Cisco of the Colorado River valley into smaller units using the resistant limestone or sandstone beds and the less resistant shale beds as formations* On his map he traced the boundaries between the major divisions and indicated the predominant kind of rock in each division. Plummer and Moore (1922) described and mapped the Pennsylvanian formations of north-central Texas and presented first comprehensive study of the paleontology the of the area. Their map of the Pennsylvanian in the Colorado River valley followed the previously established boundaries of Drake* Hudnail and Pirtle published geologic imps of Coleman (1929) and Brown (1931) Counties including that part of the Mercury quadrangle in these two counties. The next major works in the Mercury area were don© by Bullard and Cuyler (1935) who mapped a narrow strip south of the Colorado River from Mercury westward to the McCulloch County line, and Rickell (1935) who mapped a corresponding area north of the river. Both reports contain detailed measured sections and well defined stratigraphic boundaries. The Coleman County map of 1929 was revised by Plummer ©t al (19>7) but added no additional geologic knowledge to the In- Mercury quadrangle* Cheney (1940) assembled subsurface formation of north-central Texas and proposed changes in the nomenclature of the various stratigraphic units. Plummer’s (1950) posthumous work assembled detailed and reconnaissance data on the Carboniferous of the entire Llano region and included some details of the southern portion of the Mercury Quadrangle. Cheney and Kargle (1951) revised the geologic map of Brown County, which includes the northern part of the Mercury quadrangle. The present work was carried on diiring the summers The of 1948, 1949, and 1950* measuring of the stratigraphic sections and mapping were completed in 1951* The base map waa drawn from the U. 3. Geological Survey 15-minute topographic sheet of the Mercury -Quadrangle (1950), scale 1:24,000* This was supplemented by the use of scale stereographic pairs of vertical aerial photographs, were 1:20,000. Wherever stratigraphic contacts well ex-elevations were determined by means of an altimeter posed, and fixed to the topographic control of the base map* (The limits of error in the use of the altimeter were within plus or minus three feet of the instrument reading.) all geologic sections were measured with a hand level and staff. Descriptive terms for colors of rocks are from the ”Rock-color Chart11 (Goddard, et ai, 1948)• Gjrain-sise terminology of carbonate rocks proposed by DeFord (1946, pp. 1921-192#) arid grain-sise terminology of non-carbonate rocks proposed by Wentworth {1922) are used in the lltho­ *i logic descriptions* ACKNOWLEDGMENTS 1 wish to express my appreciation to the many who have made this dissertation possible: my doctoral committee - B. oamuel F# Elliaon, Jr#, Hal F# Bybee, Ronald K# DeFord, C. Tharp, and Charles Helmsch; the ranchers for their in­ terest and cooperation; and the Stanolind Oil and Gas Company for the scholarship which helped defray field expenses# Dr# Ellison not only gave many helpful suggestions and criticisms during the writing of the manuscript but also for valuable assistance gave freely of his personal time in the field during the mapping of the area# For stimulating discussions of field problems and for use of the large-scale base map, I wish to thank D* Hoye Eargle of the United States Geological Survey. Residence in the field was made much more enjoyable by the generosity of a. L* Finnegan and Parker Pumphrey* Mr. Pumphrey also kindly furnished subsurface information which otherwise would have been unobtainable* Without the continual help and encouragement of my wife, K&rgaret Shirling Jenkins, in the preparation of the manuscript throughout all phases of the work, this and study would have been impossible* 7 PHYSIOGRAPHY The Colorado River meanders across the northern part of the Mercury Quadrangle with apparent disregard for the kind of rock over which it flows* In the western half of the quadrangle, the rock.© are predominantly 'hard limestones and interbedded shale© of the Canyon series. Bore the flood plain of the Colorado is narrow and steep bluffs line its course* In the central area, the Colorado flows through the less resistant Brownwood shale making; a wide In the flood plain. east, the river flows through more resistant Btrawn sandstone faming high bluffs and a narrow flood plain* The physiography of the Mercury quadrangle suggests that the river is superimposed or antecedent for its course la only slightly modified by the hard md soft beds over which it flows* In contrast to the Colorado River, the of courses its tributaries are controlled directly by hardness and softness of the-underlying rooks. The major tributaries such as Deep Creek md Com Creek flow north occupying positions parallel to the strike of the underlying bods* Creek is on the-soft Browmood shale and Corn Creek Deep flows along the soft shale beds of the tfinchell formation* a series of east-facing cuestaa capped by resistant 11m©-. stones Is found east and west of the larger tributaries. The drainage pattern to the east of Deep Creek has become 8 more homogeneous and fine-textured because the sandstones lack definite hard arid soft layers* The cuestas made by these sandstones are low and thoroughly dissected* Richland Springs Creek in the southeast follows the contact between the Big Saline formation and the Btrawn. Drainage patterns around the high, flat-topped Cretaceous hills in the southwest and south-central part of the quadrangle ur« radial* STRATIGRAPHY LOWER ORDOVICIAN ELLENBURGER Group Nomenclature* The of the wGllen~ - Nomenclatureoriginal use name burger limestone91 by Paige (191251) ms redefined by * p* Cloud, .Barnes, and Bridge (1945), and Cloud and Barnes (1948). The redefined Ellenburger group is restricted to the Lower Ordovician and divided, into throe formations, from oldest to youngest: the lanyard, the Borman, and the Honeycut formations* Only rocks of the Qoman formation outcrop in the Mercury Quadrangle* The Honeycut formation is absent west of 98° 55 f longitude because of truncation (Cloud and Barnes, 1948, p. 40 }, - Qojnsjm. formation* formation is exposed in the southeastern part of the quadrangle Gorman Formation The upper part of the Goman In the Hall uplift, an anticline whose axis plunges north­ east under overlapping Strawn beds* The overlying Mississippian system and Bend aeries are also Involved, in the folding of the anticline, but the adjacent Straws beds overlap un­ conformably the fringes of this older structure* Less than 75 feet of the Gorman formation is exposed in the Mercury Quadrangle* The rocks are massive calcareous limestone and cherty limestone, belonging to the upper cal** cltic facie® of the formation* Stromatolites are found in a few layer® near the southwestern limits of the Gorman out­ crop* » typical section of the Gorman formation measured southwest of Hall, Texas, is graphically shown in Figure 2. The reasons for assigning the £llsnburger rock® of the Mercury Quadrangle to the upper calcltic facies of the Gorman formation are the presence of: 1. The gastropod lecanoeplra (restricted to the Gorman in the Llano region); 2. Cryptograined calcitic limestone containing nodular and concretionary porcellaneous chert; 3* Quart*send sparsely scattered throughout the limestone; 4* Stromatolites (characteristic of the upper ¦Gorman ), Differences in vegetation make the contact between the Goman formation and the Barnett shale distinct on atrial photo­ graphs (Figure 3 )* The intervening Ivee breccia supports vegetation similar to the underlying Gorman* Plants growing on the Gorman formation consist of scattered live oaks or - Figure 2, Section of Gorman and Barnett formations 2 miles southwest of Hall, San Saba County, Texas. of - Figure 5. Stereogram Gorman, Ives, Barnett, Big Saline, and Smithwick formations southwest of Hall, ban Saba County, Texas. Oeg indicates Gorman formation; hi, Ives Barnett breccia; ITb, shale; Pbs, Big Saline formation; and Psm, Smithwick shale. live-oak mottos separated by open graft*land* In contrast, the outcrop of the Barnett shale 1© either barren or covered with Mesquite trees* Mississippian System Ives Breccis The Ives breccia first described by Plummer was (Bullard and Plummer, 1939, p* 15) as the basal conglomerate of the Ch&ppel formation* In a later report. Pinaster (1950, pp* 26, 2?) referred to the Ives conglomerate as a member of theChappelformationdesignatingthetypelocality w***along Ives Branch on the Gibbons ranch 2,4 miles southwest of Hall***, San aeba County1* (southeastern Mercury Quadrangle ). Cloud and Barnes (1945, p* 46) raised the unit to formatlonal rank and changed the name to Ives breccia. At the type locality, the Ives breccia la a one-foot cement bed of angular chert phenoelaeta in a sand matrix; the la siliceous, binding the sand and chert so tightly that the rock fractures across the phenoclasts and matrix* The light gray, angular phenoclasts range from less tban a millimeter to B centimeters in diameter, and the light brown matrix con­ sists of rounded to subrounded, asdiute-gralaed* quarts sand. 0 the sand matrix is interstitial between the itt so’se places phanoclasts; at others, the matrix constitutes over 50 percent of the rock. fhe Ives breccia forms a dip slope on its upper sur­ face, cropping out over an area 0.75 *aile long md 0*25 mile wide. It rests unconformably on an old erosions! sur­ face of the Herman formation, the Barnett shale di»conform­ably overlies the Ives breccia. Outcrop® of chert breccias correlated with the Ivea breccia are scattered throughout the llano region# Its out­crop Is lass continuous than that of the Chappel limestone with which it is usually associated# Cloud and Barnes (1945, pp. 4£» 49) stated that the Ives breccia is probably Lower Kieeiesipplen* cm the basis of fossils and field re­ lationships. Conodonte collected at the type locality and their stratigraphic ranges are m follows: Palmatolepia < * Devonian jiothojgaathella (?}•»••« . . Bpp#r Devonian Pifl&coaui&thus* » Kisaissipplan ««.«..»• Osarkod iyia t « Ordovician to Permian * ••»•«**« This assemblage of eondononta 1® interpreted as a mixed assem­blage of Mississippi.*** age. Garnett Shale The Barnett shale was first described by Plunasr and Moore {1921, p. 24) from outcrops at Barnett Spring*, ban Saba County. The Barnett shale of their definition Included all shale and llaaeefeone beds between the Marble Falls limestone and the Ellenburger limestone* Round/, Olrty, and Goldman (1926, p* 2) discovered a limestone (Chappel of Bollards) containing a Lower liississippian fauna between the Barnett and Ellenburger. Bell&rds (1933> p• 92) redefined the Barnett to Include all Misslssippian bed® between the Chappel formation (or older deposits where Is absent) the Chappel and the Falls limestone. This definition is now used by most geologists working in the Llano region* The Barnett shale in the Lercury Quadrangle overlies either the Gorman formation or the Ives breccia# The Chappel limestone Is absent* Outcrops of the Garnett shale in the Mercury Quadrangle are all deeply weathered, forming slopes of thinly laminated yellowish gray shale {unweathered outcrops are typically black or dark brown.) A representative geologic section of the Barnett shale exposed in the quadrangle is shown in Figure 2# The Barnett shale crops out in a narrow band along the axle and on the flanks of the Hall uplift and at the ex* treae southeastern corner of the quadrangle* Most of these less resistant shale outcrops form a barren slope underneath the hard ledges of the Big Saline limestone* The vegetation growing on the Barnett consists of meaquite trees on the lower more gentle slopes whereas the upper steeper slopes are barren or covered with grass. The bottom and top of the formation are easily distinguished on the aerial photographs (Figure }). PENNSYLVANIAN SYSTEM The classification and nomenclature of the Pennsylvania:n the system have been subject of much controversy among geolog* 16 lats who work in different sections of Texas* In this report, the nomenclature of the major divisions of the Pennsylvanian follows Plummer (1950) with some modifications in terminology* A comparison of the nomenclature used herein with the standard section In the midcontinent region, well as with Cheneyfs as (1940, p* 66) divisions, la as follows: Texas Midcontinent Texas (This report) iiegion (After Cheney, 1943) Cisco series Virgil scries Cisco series Canyon series Missouri series Canyon series 3trawn »eriM Strata aerie* Bea Moinea aerie* —­ . mimmmmrnm tmmv mi.uiio ... ...... -­ -i-nmimwT-r-nrrr nr ---mr run inn- Lampasas series Bend series Atoka series Morrow series Morrow series Morrow series Approximately 1200 feet of Pennsylvanian strata be­ longing to the Bend, Btrawn, Canyon, and Cisco series crop out over the greater part of the Mercury quadrangle* Information derived from logs of water wells and oil tests shows that beds also underlie the thin Cretaceous and these quaternary formations which cover a part of the area* The Bend series (gray limestones and black shale) is exposed in the south­ east corner of the quadrangle; the Btrawn series (thick sand- In the east half of the stones and shales), quadrangle; the Canyon series (alternating thin limestones and thick shales), in the west half of the quadrangle; and the Cisco series (alternating thin limestones and thick shales), In the extreme northwest corner of the quadrangle® Bend Series Ko&ionclaure.* of the history of nomenclature and classification of tie Bend scries is shown In figure 4» The classification used In NomenclatureA chronological summary this report follows Plummer (1950 }• Big Saline Formation Tli-a of the - Mz Baling? demotion. oldost rocks B&nd aeries exposed in the Mercury Quadrangle are correlated with the Lemons Bluff limestone member of the Big Ballne formation* The Brook and ayior Bluff members (absent in the Mercury Quadrangle) pinch out towards the Hall uplift and the Richland Springs axis {about 2*5 nils® east of the southeast corner of the Mercury Quadrangle K Hear these up** lifts, the L&aons Bluff member may reei uneonfonsably on the Barnett shale, Llsewhere* according to Pluimor (1950, p. 6B), the Lemons Bluff overlie# uneonfemably older Big Saline rocks. Plummer stated that the hmou& Bluff thins by lose of lower beds over uplift© and reefa la fae Aylor Bluff member* The Lemon© Bluff member consists of eryptograined to meso~ grained, medium gray limestone bed© containing dark gray, nodular, arid bedded chert. The limestone bed© are from 3 Inches to 12 Inches thick and are interboddod with thin 18 19b0. to 1889 Series, Bend the of correlation the of History - 4. Figure 19 «t some places, The limestone weathers into smooth, yellowish gray, angular blocks, A shale bed about 25 feet thick occurs below the more massive Lemons Bluff limestone• Between this shale and the Barnett formation, a, dark gray limestone bed about 3 feet thick is present. It is estimated that the total thickness of the Big Saline formation In this area is from 75 to 100 feet, Plummer (1950, pi* 9) me&lured 65 feet of Lemons Bluff along the Saba County line about 4 miles south of the quadrangle* The Big Saline formation along its northern extent is overlain unconformably by the Strewn series. The unconformity between the Big Saline and Strewn series is definitely angular for the strike of the Strewn is almost at right angles to the strike of the older beds* Along the west side of the Hall up- the lift the Big Saline formation is overlain conformably by Smithwick shale. Vegetation growing on the Big Saline formation is mainly scrubby live oaks on the limestone and taesquites on the shale slopes* Vegatational characteristics as well as are topographic expression Illustrated in aerial photographs {Figure 3)* Smithwickdaithwick shale*shale The soft, dark Smithwlck shale, - in the Mercury Quadrangle only in a mrnll area «eat present of the Hail uplift, is poorly exposed; its extent la-inferred from the vegetation and topographic expression* The estimated 20 thickness exposed in the quadrangle Is from 0 to 75 feet* The Bmithwlck is not exposed north and east of the Hall up-* lift because of overlap by younger .Btrawn beds* It ie known *>¦ in wells to the north and east below the Btrawn* Straw Series - NomenclatureNomenclature* The early history of the classification of the Btrawn series is shown In Figure 5* Subsequent changes In the classification of the Btrawa in the Colorado Elver valley are shown below and in Figure 11. ariter Top of Btrawn Base of Str&wn Plußsnor and Base of Rochelle conglomerate Top of Bend Moore (1922) ———— Hudnail and Base of Palo Pinto limestone Pirtle (1931) Bullard and Base of Rochelle conglomerate Top of Bend Cuyler (19)5) [s*< Hickell, C* 0« Tip of Palo Pinto (?) limestone <—. (193^3 —— Pluiuiier, F* B* Base of Eochelle conglomerate (1950) and Top llmeatone Cheney of Capps Eargle (1950) Cheney (1950) Top of Capps limestone Top of Big Valley beds (?) of Drake Top of Capps limestone or Top of Bend This report (1952) base of Eochelle conglomerate of the correlation of the Strawn TMoure 5 History - 1890 to 1893. Series, Drake (1B93) divided the Strawn sequence of the Colorado River valley into 20 units (Figure 5) using the alternating sandstones and shales as the basis for his classification* Ho have been made major changes in this classification to the present* In this report, no attempt has been made to map the Strawn in detail because of rapid facies changes and beds* lateral discontinuity of individual The classification of Drake ha© been followed wherever his units are recognisable* an estimated 300 feet of Strawn is exposed in the Mercury Quadrangle* The Strawn units mapped by Drake in the Mercury Quadrangle are listed below: JM&a wfgjy yslka mms. M > this report Coral limestone bed Capps limestone Ricker bed (sandstone) Indian Creek bed (shale) Stravm undifferentiated f antelope Creek bed (sandstone) Comanche Creek bed (shale) - Strawn Undifferentiatedundifferentiated * Straw beds below the Capps limestone member are exposed in the western half of the quadrangle* The Travis Peak formation, forming a large out-lier, covers the Strawn in the south~central part of the area* Along the edge of the Llano uplift in the southeast, the Strawn unconformably overlaps the Big Saline and Smith* wick formations* Southwest of the Mercury quadrangle near Rochelle, the Strewn is overlapped by Canyon bed© which rest directly on the Bend series. The ©trike of the Strewn beds 1© about R 20° £, and the dip is northwest* It 1© difficult to determine the amount of northwest dip because of the lenticular ©hap© and discontinuity of beds* Measurement© mad® from well logs and at the surface indicate a dip of about 1° The thick sandstones exposed on the surface thin rapidly • downdip in the subsurface* As a result, btrawn sandstones encountered in wells to the west and northwest are thin* al­ though the Strawn below the Capps limestone has not been sub­ divided, a brief description of the beds in the quadrangle equivalent to Drake 9 © units is given below* The lowest bed of Crake*a classification in tha Mercury Quadrangle ("Comanche Creek bed**) crops out in the broad valley occupied by the heads of Mountain Creek and Wilbarger Creek. The upper grey-shale portion of the "Comanche Creek bed* is exposed along the east aid© of the Cretaceous outlier in the vicinity of xound Mountain* At hound Mountain the shale is more than 100 feat thick. A 10-to 15-foot sandstone underlies the upper shale, faming a ridge which extends from a point 3 miles northeast of Hall to the Colorado diver. Figure 6 shows the vegetation and topographic ex­"Comanche Creek bed" and pression of the the overlying Travis Peak (Cretaceous) formation. Beds » equivalent to Drake9 "Antelope Creek bed" form of Strawn series and Travis Peak - Figure 6. Stereogram formation (Lower Cretaceous) north of Hall, San Saba Texas. Pst indicates Strawn undifferentiated County, "Comanche Creek and Travis Peak (mostly bed"); Kt, formation. high bluffs along the Colorado diver downstream from Keys Crossing Ford* To the south, the upper part of this sandstone merge# with the base of the "dicker bed* 11 The lowest stratum of the Creek bed11 can be traced just below the base of the Travis Peak formation along the Cretaceous escarpment southwest of Holt Church* Thin-bedded, yellowish gray sand­ stone ms well as smsslv#, lenticular, channel~like sandstone w containing plant fossils occurs in the "Antelope Creek be-d* Host of the strata are cross-bedded and contain rippXe-ei&rks* Drake’s "Indian Creek bed* is exposed north of Keys Crossing Ford below the escarpment forced by the overlying .Sticker bed** South of the Colorado liver this shale either changes laterally into sandstone or thins rapialy and dis­ h of a *lndian Creek appears* geologic section part of the bed* Is given in Figure ?* the basal bads of Brake’s flicker bed* form a sand­ stone escarpment which can be traced from a point I*s miles northeast of keys Crossing Ford south along Bustard und Brushy Mountains to the northernmost outcrop of the Cretaceous wdicker bed*is a stale which can be the upper part of the 1 traced south on the east side of Beep Creek* Representative geological suctions of the "kicker bed* are shown in Figures 9* The lower sandstone part of the section contains 7,6, and thick channels, chert conglomerate, and massive lenticular sandstones* The channel, conglomerates are well developed near 26 the mouth of Clear Creek and along Oldham Hollow and .tough Branch (south of Milburn)* Conglomerate bods are found in the upper shale bed south of Milburn* The upper shale inter­ val is overlain, by the Capps limestone or its facies* a limeston conglomerate is present near the base of the shale, cropping out in the bed of the Colorado .liver o*s mile downstream from Beasley Crossing. Hear the measured section (Figure 9) 4 miles southeast of Placid, Plummer (1950, pp* 96, 9B) listed 9 species of fossils, from this shale* He incorrectly placed the shale in the Canyon (Brownwood shale)* The fossils listed by Plummer are included In table 1* Capps Capp%Limestone Th© Capps limestone member - limestoneMember forme isolated outliers in three areas mar the Colorado divert 0.75 mile north of the mouth of Limekiln Creaky west of dim Grove on both aide© of limekiln Creek, ana 0.5 to 2 miles south of Milburn along the ridge wist of Oldham Hollow. The KiOst nearly complete ©action of the Capps exposed in the quadrangle is north of the mouth of limekiln Crmk (Figure 6). elsewhere only the lower beds of the Capps limestone occur on the tops of hills. At the mouth of Clear Creak, th« Capps Is channelled and replaced by sandstone or chert considerate. Between the outcrop north of the Colorado diver and those to the south, the Capps is absent because of channelling or Is covered by alluvium South of Milburn the Capps limestone occurs as discontinuous between channel outcrops deposits. South of Its last outcrop, the Capps changes facias, grading laterally into thin-badded me diuo-grainad sandstone. This sandstone be followed can Creek along the bluff east of beep to a point where it appears to be channelled by the cochelle conglomerate* at other places north of the docholla outcrop, the sandstone facies of the Capps is locally replaced by massive cross-bedded sandstone or chert conglomerate (Figure 16)* This sandstone or conglomerate Brownwood which be- may represent basal channels, or channels gin within the Capps limestone Interval* Fossils are not oosson in the Capps limestone In the Kareury quadrangle* Ghaetetee reefs are present o*s> alie west of £lm Grove and north of the mouth of Limekiln Greek* IWullm Is present in the lower beds of the Capps south of \ ftilburn where the cross-section line AB intersects the west margin of the outlier* series and "Kicker bed”) 1 mile northeast of Keys Crossing Ford, Brown County, Texas. Figure 7. Section of pert of Strawn ("Indian Creek bed’ - 8. Section of Stravm series ("Ricker Bed" and - Figire part of limestone north of mouth of Limekiln Brown Capps Creek, County, Texas. - Figure 9. Section of part of Strawn series ("Ricker Bed" and Capps member) and Travis Peak formation 4 miles southwest of Placid, McCulloch County, Texas. 31 Canyon Series The Canyon series is exposed in tha western half ol covered the Mercury quadrangle except where by Lower Ore­ taccuoua rock or Quaternary alluvium* The thicknesa of the Sanyon measured along the Colorado diver Is about 650 feet* The lower part Is predominantly shale and the upper part is predominantly limestone# Landstone and chert conglomerate channels are found at various levels in the Canyon series# Many of the channels are widespread and occur at particular stratigraphic levels# In addition, to the channel sandstones, mny thin, persistent sandstones occur in the Canyon sequence# these thin sandstones nay grade laterally into channel de­posits# Hoof limestones found in the are upper part of the Canyon in the northwest corner of the quadrangle# Several the 1Umstonea periods of reef growth are interpreted because which thicken at the expense of shales appear to be superimposed The one on top of the other# Canyon overlaps the Strawn along the northwest margin of the .Llano uplift# Louth of koohalla the basal beds of the -Canyon rest on the Big Saline formation# Louth of Brady, the Adams Branch formation overlaps the Brown- wood shale and overlies the Big, Saline formation# This overlap, although known south of the quadrangle, is not so evident on the quadrangle# The strike of the Canyon formations is Hf 20° I; the average dip, 50 to 75 feat .per mile west-northwest (Plate 2). 32 nomenclature used in this report is shown in Figures 5 and 10* I) the elevation Major changes here proposed are; of former member names to formaticmal rank, and 2) the elimination of the Bravos Elver valley names Whitt, Graford, Caddo in Srad, Creek, and Graham, which have little meaning the Colorado Elver valley# Details of other proposed changes can be found under the respective headings which follow. Brownwood-Crake named BrovmwQod Shaleshale* (1593, PP* 3s7* 3®9) the Browietood shale froa exposures Browiwood, Teas* The near history of Its classification is shown In Figure© 5 an 4 IX* In this report the shale includes all bods between the top of the Capps limestone (or its sandstone equivalent) and the lass of the idssis Branch limestone* Sear iiochelle, tasas, the. base of the Brownwood Is placed at the bottcm of the aochelle conglomerate* The toehells conglomerate (Tarr, 1890, p* 205) and laugh Kountaisi conglomerate (Pluamer 1950, p* 95) arc con­sidered as aeabers of the Bremwood shale* The Brownwood shale occupies a I-to 2-mil outcrop of -the band across the quadrangle fro® north to south between Deep Creek and the escarpment formed by the sterns Branch limestone. the The upper part is well exposed on steep slopes below items' Branch limestone; the lower part is covered by alluvium associated with Deep Crack valley* of the alluvium complete measured sections of the BrownwOGd wore cover, no obtained. Data from wells drilled west of the Adams Branch show the following thicknesses of the Brownwood shales escarpment Colorado the in series Canyon the of correlation the of History - in e ¦"'i-ur to 1895 valley, River 34 Edna Location TtalcKneaa of Brawnwooa Sliaju- Blusher Ko* 1 Townsend I mi* 267 ft £ of fcercury « « • • (unknown) B* S. Humphrey I.?> mi. aS* of Her*ary . 20l water well (unknown) B* S* 3 mU n m of Placid . • Pumphrey . 326 water well (unknown.) B* S. Puwahrey I*s mi. MW of Placid 263 ... m.t»r well Buaaell Mo* 1 Paiicor 2 mi. Wof Placid • 260 ... Pximphray Griffith and «o. 1 Tatos 2 mi. BW of Placid .... 329 Horton Sawyer Parker Fuaphrey $.5 mi. S$ of Placid 293 ... Drilling Co. water well Total thicknesees of surface sections obtained by projection of dip in alluvium covered areas are close to the above figures. In the southern part of the quadrangle, however, tha Brownwood shale ha® thinned to about 200 feet, aerial photographs ehowinr typical vegetation and topography developed cm the Brownwood &hale are found In Figure 11. two prominent bed& of chert congloaorate occur in the Browmrood shale, am at the base (Rochelle conglomerate) and am about 120 feet from the top ( lough .Mountain conglomerate). those conglomerates are assigned the mnk of aembera in the Brownwood shale, the a&chelle conglomerate membar has bean doscribed in some detail by Bay (1932, pp. 175**1&U and Pltwaser (1950, p. $3, 94) and the &ough fountain conglomerate member by Flower (1950, p. 95). these eoiutloßeratas are essentially the same of In sinamloglcal composition, consisting of various types angular chert-pebbles in a quart* sand matrix. A listingulahitig Adams - Figure 11, Stereogram of Brownwood, Brandi, Cedarton, and Winchell formations near Heronry, McCulloch County, Texas. Pb indicates Brownwood shale; Pa, Adams Branch limestone; Pc, Cedarton shale; Pw, Minchell formation; and Qal, uaternary alluvium. feature of these as well as other Pennsylvanian chert conglom­erates in the Colored© .Elver valley is the presence of green chert pebbles. The Eochelle conglomerate member can be traced along its outcrop fro® Onion Creek (4il miles southwest of dochelle) to a point 2 miles northwest of Sellman, a distance of about 9 miles* the maximum thickness is IS feet (Plummer, 195C, p* 4 94) south of the Mercury .quadrangle• The thickness of tha member at the southern edge of the quadrangle Is 8 feet, thinning to V the north where it change® laterally into a cross-bedded sand­ stone* The /lough Mountain conglomerate ateaber is exposed along the Rochelle-Oowboy road o*s mile south of the quadrangle for a distance of 2*5 miles north to a tank at %he base of the Adams Bunch escarpment* At its northern outcrop, the member be traced north changes laterally into a sandstone which can a distance of 3*5 miles to the farm road east of Placid. The .tough Mountain conglomerate differs slightly from the doehelle conglomerate because it contains smaller pebble® and fewer groen chert pebbles* The r-axlnum thickness of the conglomerate is 20 ftough Mountain (bench mark 1546 feet at the type locality on feet on Eo4d I*s miles north of south of Mercury Quadrangle ), of the Brownwood shale deprasentat&ve outcrop sections *re given in Figures 18, 19, 20 21,aid 22* The greater part f of tha Brownwood consists of gray to oliv# shale# Although rot a constant feet feature, rad shale about 25 thick is found about-50 feet below the top of the Brownwood* Data from well® drilled west of the Brownwood outcrop Indicate that this red shale Interval Is perhaps more constant than at the outcrop* ftorth of the Colorado Alvar a 25-foot sandstone bed occurs about 70 feet below the top of the Browrwood; it thine rapidly to the south and la either absent or represented by thin beds of sandstone in the vicinity of Mercury* A thin limestone bed {Unit 23 of Figure 20) which has been correlated with a fuaulinid limestone near Brovnwood (Iflckell* 193$# p* 102) is found only north of the river. This limestone contains no fUaullnide In the Mercury quadrangle* A limestone bed containing Triticltea {Unit 7, Figure 21) can be traced north fro& Mercury the into southern Brown County* Ejcpoawea of the lower part of Brovmwood have few distinctive bed* which can be traced very for any distance. The yellow alitatone 40-50 feet above the base of the Brownwood (Unit i # Figure 1$) can be traced west of Deep Creek from the latitude of Placid to Mercury * a wide variety of teegafoaail* including bryoaoans, and brachlopods, erlnoida, corale, trilobitea, pelecypoda, are common at various levels in the Brownwood shale. gastropod® Fuaulinlda have hmrt found only in the limestone 107 feet below the Adams Branch limestone (Unit 7# Figure 21 J* Fossils from the Brownwooa in the Mercury quadrangle are listed in Table i* Strawn-Canyon Boundary To the position - Strawn~Canyon boundary* determine of the dtra*nn-Qanyon boundary across the Mercury quadrangle, one suet solve the stratigraphic relationship between the Capps limestone member and the hocheile conglomerate fiieasber* The Capps limeatone (considered the top member of the Strewn) can be traced far south as as Mercury* In this region the Capps lime scene Is replaced by chert conglomerates interpreted as channel deposits of lower Canyon (Erowswood) or upper btrawn (Capps) age, South of the southernmost limestone outcrop (east of Mercury), the Oapps is represented by a eandatone at the same stratigraphic level* hoar Cowboy Cemetery this sandstone is interpreted to be locally replaced by channel sandstone deposits (Figure !&}• the sandstone equivalent of the Capps can be traced along the elopes below th-v Cretaceous and on isolated hills to the northernmost .i outcrop of the iioehelle conglomerate ramber* At this location, i (2 miles northwest of bellman) the cross-bedded sandstone equivalent of the Hocbelle is interpreted as replacing the sand­stone equivalent of the Capps# The Rochelle conglomerate ;«a&ber da considered a channel deposit of Canyon (Brownwood) age because of its stratigraphic relationships and similarity to other cisAnnei dapoelta higher In the Canyon scriee, although the Rochelle conglomerate la in Its length of outcrop (9 miles 1 downdip in # perhaps unique mter walla at doehalla, turn®, the oon&lo&arata la ratInly ©and­atone (iluaaaar, 1930, p# 94)* Stella drilled 3 miles northwest of the Rochelle outcrop (Com Creek Hill©) did not encounter conglomerate or sandstone at this stratigraphic level* The kochalla Is similar in mineralogy# texture* and thickness to other chert eongloMaratea of the Canyon whose charecteriatlea are hotter known, channels (for example * described under Cedartonf sflnchall, and Flacid foraations }* Thin limestone beds adjacent to channel deposits of the upper Canyon serve as guides for measuring the extent of channelling* In contrast, the Rochelle conglomerate member rests or homo* fenaoes shale making Its relationship to underlying beds less obvious* Flumer (1930# p. ill) reported a Straw* assecsblage of fossils froa the ©hale below the dochalla at a locality 2 of milsa south of the Mercury Quadrangle and 3 alias east £oehelXe, Texas (&ee Table 1 ). kmtmg the fossils found at this locality were Fuatline richsranuis Thompson and eaeolobas (Norwood and Prattan ). The next highest occurrence of fossils is in the Browrwood shale at hugged Mountain (west of hochalX#~Cowfcoy road and 1 mil® north of south edge of Mercury Quadrangle )* The beds in which the fossils occur are estimated to be about 60 feet above the jtoaha.lla conglomerate* The fossils at xuggsd Mountain are lonf-mnging forms and not valuable au indicators» These fosaila are listed in Table 1* age reasons for placing the dtrawn~C&nyon boundary In the Mercury Quadrangle at the top of the Capps {or It© limestone sandstone equivalent) and at the base of the Aochelle con­glomerate are summarised below: I* The Capps limestone is the highest known occurrence of otrown fusullnids. The lowest fusulinida in the Brownwood ©hale {10? feet from top) are of Canyon age. 2. The Capps limestone changes into sandstone southward. This sandstone is replaced by the Aochelle conglom­ erate, interpreted as a channel deposit. 3* The shale below the Rochelle conglomerate is established as strewn because otmwn fossils are present. 4. The .iochelie conglomerate la interpreted as a channel deposit younger than the Capps limestone. This conglomerate is believed to mark the beginning of Canyon sedimentation in the docholle area. -a Adams Branch limestone.Limestone The dams Branch limestone drake on was named by (1893, pp* 38?, 391) from exposures Adftttft Branch west of Brownwood, Texas. a graphic history of its classification is shown in Figure 10. The Adams Branch limestone in is assigned the rank of a formation. this report The Adams Branch limestone is exposed across the central part of the Mercury quadrangle from north to south forming a the width of which rarely exceeds one mile. narrow outcrop Horth of Placid, this formation isakcs a conspicuous escarpment facing Deep Crook volley (Figure 11 ), south of Placid, the os­ carpment is formed by FinchsXl or Cretaceous bed® and the Adam Branch limestone crops out as a lower secondary bench* the thickness of this formation In the Mercury Quadrangle, from 9 to 2? Data from wells ranges feet along its outcrop* drilled in the western part of the Quadrangle indicate a rather uniform 20-to 25-foot thickness of the limestone* The thickest measured section of Adams Branch limestone (2? feet) is located 2 miles south of Mercury* From this point south, the limestone thins to a minimum of 9 feet south of Placid* The average thick­ ness south of Placid is 12 feet* Typical sections of the Adams Branch limestone In the are Mercury quadrangle shown in Figures 19, 21, 22, 23,and 24* the characteristic thin, wavy beds of the formation are apparent $ have been deeply weathered* Wherever the only in exposures which it forma a massive unit in limestone is relatively unweathered, are which bedding planes obscure* Fossils are abundant and varied In the Adam* Branch limestone* Host of the magafosslls can be found in a 4* to 5-foot shale bad below the mssive portion of the limestone and above the 1-foot limestone bed at the base* The top beds of the formation contain fUsulialda* Fossils found in the Adams Branch limestone in the quadrangle are listed in Table X* - The Cedarton shale*Shale type locality of the Coaarton Cedarton shale ( jmke, I£93* PP* 357, 391) is near the village of Cetf*?ton, central Srown County* In the Mercury quadrangle the Gedarton shale interval between the Adams Branch limestone includes the 42 and the basal limestone bed of the Wlnchell formation (kinchell limestone No* 1 of this report ). From Placid to the Colorado diver, the Cedarton shale forms a steep slope below the Winchell euesta and the 1-to 2-mile flat west of the Adams Branch Aerial escarpment# photographs {Figure 11) illustrate the topography and vege­tation normally developed on the Cedarton north of Placid. i>outh of Placid, the Cedarton outcrop is incorporated in the steep slope below the cuesta-fonainr eincheli limestone beds. The Cedar- ton reaches its maximum thickness (60.§ feet) in the quadrangle at outcrops along the Colorado diver, and thins southward to a minimum of 29*3 feet at Placid. South of Placid the shale thickens to 45 feet at the south edge of the quadrangle. Ex- of Cedarton can be found west of its normal posures outcrop as inliers along Com Creek. Sections of the Cedarton shale showing thickness and lithology are given in Figures 19* 22, 23,and24* the greater part of the shale, consistently the formation Is olive but and lower 3-to 6-feet are graying red shales. Thin upper limestone beds and coquinaa occur In the lower 15 feet of the formation. These coquinas contain many well preserved megafoesil© rivaling the rich collections in the Brownwood shale (see Table 1 )• Thick, lenticular, cross-bedded sandstones interpreted 43 &£ channel deposits occur at two horizons in the Cedarton shale* At a locality 3 wiles northeast of Placid on the escarpment feeing Leap Creek, a 20-foot sandstone near the base of the Cedarton completely replaces the Adams Branch limestone* Where the sandstone is thickest the basal beds # are conglomerate, containing the same types of chert pebbles found in the Rochelle and Hough Mountain conglomerates* The Cedarton conglomerate differs from the Rochelle and Hough Mountain conglomerate® in having smaller sized pebbles (average o*s inch) and fewer green chert pebbles. Associated with this occurrence are similar sandstone beds found on top of the Adams Branch limestone at two toilers located o*2 wile west and I*o mile west southwest* This sandstone is in­ terpreted as a part of a narrow channel deposit trending approximately east-west. At the outcrop farthest east, the channel deposits are thicker, contain conglomerate at the base, and replace the underlying Adams Branch limestone, banastone lenses also interpreted as channel deposits occur at a higher level in the Cedarton. At localities 3 to 4 miles south of Placid, massive sandstone lenses are present in the upper part of the Cedarton. The tops of these beds are 10 to 15 feet below the top of the Cedarton and extend downward in the Cedarton shale 10 to 20 feet at places of maximum development* Mo 11neation of these channel deposits can be inferred yet because of the limited number of outcrops* 44 The Ccdarton shale probably contains the widest variety of Canyon fossils in the Mercury Quadrangle# The lower 20 feet of the both in. the shale formation is particu.la.rly rich in fossils, and In the thin limestone beds, A representative but not ex­ haustive list of Cedarton fossils is found in Table 1# Winchell Formation The history of beds in c*IncheIX fomation* classified - this report as the Winehell formation is shown In Figure 11• f ?fickell s definition of the "dinchsll member of the Gr&ford formation* (1936, p# 105) is as follows* A© herein described, the lowest limestone of the member is taken to be that one which caps the escarpment west of 4in­ch© 11, and the top Is taken as the limestone bed that forms the broad bench about 1 mile northwest of tfinchell, on which the United btatee Geological survey bench mark Is set at an altitude of 141? feet* (This altitude is marked **l4Xon on the 1950 edition of the Mercury quadrangle*) In the present report the Tinehell member of Hlckeil is raised to formations! rank* Mlekell numbered the limestone beds of the ainch© 11 1 through 4 In ascending order# The numbering system proposed by Kickall is followed here except that ftiekell’s limestone Mo# 4 i& called Mo# 4 and Mo# 5* houth of the Colorado diver the basal Z feet of Mickell9* limestone Ho# 4 is separated from the top limestone of the a shale by interval which ray be 12 feet thick. The 2-to 2*5-foot lime­ stone below this shale is c&llec limestone Mo* 4 ami the top limestone bed of the Wlnchell above this shale is called limestone Mo. 5* The alternating thin limestone and thick sshaie beds of 45 the ainchell formation make a I-to 3-mile wide outcrop across the quadrangle. At its southern outcrop, the top of the *inch*ll formation is covered by Cretaceous beds, the lower beds east of the Cretaceous being exposed in the escarpment outcrop. Each of the Wlnchell limestone beds my form a cuesta, but limestone Ho. 1 (at the base.) and limestone Ho. 5 (at the top) fora the most conspicuous cueetas of the formation. Live oak trees grow on the limestone beds, in contrast to mesqulte trees or grass on the shale. As a result, each thin limestone makes a line of live oak trees which can be traced in the field or on aerial photographs (Figures 11, 12,5nd13 ). At the type section 0.75 mile north of Wlnehell, the formation is ?2.5 feet thick (Hickeli, 1935, pp« 106, 10?)* Downdip to the west, the Wlnchell formation is thicker due to an expansion of both limestone and shale intervals (Figure 20.)% Kelley, so. 1 Harris-Kcl&niel, an oil test drilled 3 miles west northwest of Winchell, Texas, encountered 105 feet of Wlnchell formation including 57 feet of limestone, eells drilled west of the outcrop of the wlnchell elsewhere in the Mercury Quadrangle show a comparable increase In total thick­ ness and percent of limestone. The Winch*ll formation also thickens southward along the strike to a maximum of about formation 100 feet, west of Mercury* Louth of Mercury the thins rapidly. - Figure 12, Stereogram of V/inchell, Placid, Ranger, Colony Creek, and Home Creek formations along Corn Creek, west of Hercury, McCulloch County, Texas. Pw indicates Rinchell formation with limestones Ho. and 2,3, 4, 5; Placid shale; Ppc, Corn Creek limestone member of Pp, Placid shale; Pr, Ranger limestone; Pcy, Colony Greek shale; and Ph, Home Creek limestone. 47 Uepresent*tlv« section 3 of the winche.il fomition showing types of rock and thicknesses arc shown In Figures 19# 22, 23, 24, 25, 26,and27* Limestone beds of the Winch©ll formation are recognisable by stratigraphic position, thick­ness, peculiarities of weathering, color, and topographic ex­pression* Intervening shale {mostly covered) and sandstone beds are referred stratigraphic*lly to the store prominent limestone beds* Criteria for field Identification of the lime­ stone bed© of the &inshell formation are ao follows: 1* Limestone Ho* X (lower Clear Creek of Bullard and ferns thick ©hale Guylor) truest*; overlies (Gedar­ton); is 5 to 6 feet thick; thickens south of Placid to 9 feet; is aosogralned, yellowieh gray, with to 6-inch beds* 2* Limestone Ho* 2 (upper Clear Creek of Bullard ana Cuyler) la I*s to 3*o feet thick; aesogreined, dark yellowish brown, with X or 2 beds; weathers or moderate yellowish brown; overlain locally replaced by sandstone; most uniform bed of formation; can be traced across entire quadrangle and north of quadrangle 25 miles* 3* Limestone Ho* 3 {Placid Ho* Xof Bullard and 1.0 Cuvier) la to I*s feet thick; mesogralned, light olive my t> pale yellowish brown; car, not be traced with certainty south of a point I*s mile© north of Placid* 4# Limestone Ho. 4 (Placid Ho. 2of Bullard and Cuyler) is 2 to 3 feet thick; meaogralned, light olive gray, with 2-to 6-inch beds; weathers with many large dark yellowish orange splotches (not peculiar to this limestone but splotches are more numerous on this bed); merges into limestone Ho. $ at Colorado sliver. 5. Limestone Ho. 5 (Placid Ho. 3 of Bullard and Cuyler) Is B to 22 feet thick; forms cuesta; meso­ grained, light olive gray, with 3-to 6-Inch beds; has wavy bedding planes; thickens at Colorado Elver. bandstone in this Wlnchell formation Is almost completely confined to the interval between limestone Ho* 2 and No* )• At two places (I*s miles mat of Wlnchell and k miles south of Flaold) sandstone beds have been observed between limestone No* 3 and No* A* The sandstones between limestone Ho* 2 and No* 3 at many places extend downward replacing No* 2 and resting on Ho* 1. These sandstone beds are interpreted as channel sedi­ ments deposited after removal of limestone Ho* 2. No conglomerate has been found in the ilnchell formation* Extensive channel sandstone deposits occur above limestone Ho* 2 near the mouth of Com Creek and at Placid, Texas# Figure 13 shows the outcrop of a part of a system of channel deposits which have replaced limestone Ho# 2* East of Corn Creek there is a well defined east-west lineation of the channel sandstones* West of Corn - Figure 13. Stereogram showing channel sandstone which replaces Finehell limestone No, 2, 2.3 miles northwest of mercury, McCulloch County, Texas. Red dots indicate outcrop of channel sandstone; Pc, Cedarton shale; Pw, FInohe11 formation; Pp, Placid shale; Ppc, Corn Greek member of Placid shale; and Pr, Ranger limestone. Creak, the sandstone is present along the treat bank extending north almost to the Colorado aivar* Megafoasils are rare and fusulinida have not been found A in finchell outcrops in the Mercury quadrangle* coral colony made op of numerous specimens of Caapophyllum occurs at the level of limestone Ho* 5 at a locality I*7 miles northwest of Mercury at the top of an outlier {western peak) of upper Winohell lima©tones* Table 1 lists those fossils which have been found in the iaftnchell formation* Placli m Placid stele*Shale flamed for the town of I lacid, rjj-XL\i-( Texas (southeast Mercury Quadrangle), the Placid stele (Flunmer and Moore, 1922, p* 110) includes beds between the top of the Clear Creek lisas stone {top of limestone Ko* 2 of Wlnchell formation) and the base of the danger limestone* Bullard and Cuyler (1935, p* 20?} closely fallowed the bounder­ les of Plummer and Moore, but numbered the Placid limestone beds I to 5 from oldest to youngest, blcfcell (1938, ill) in- P* cluded the lower part of the Placid stele in the Winetell member and called that portion between the top of the *lnchell and base v of danger the **stele member* Ke placed Drake’s *Cherty lime* stone” {1893, pp* 387, 395) within the unrated stele member* In southern Brown County, Cheney and barbie rapped the lime­ stone occurring about 33 feet below the danger as basal danger (Corn Creek member of this report}, and included the ”Cherty limestone” which occurs above this limestone in the Placid stele* The history of nomenclature and various interpretations of the stratigraphy of the Placid shale are graphically shown in Figure 10, The Placid shale (restricted) of this report applies to beds between the top of the blncheli and the base of the danger f limestone (equals Fickell s "shale member")• The base of the -linger in the Placid area is the base of the limestone capping the outlier about 1 mile northwest of Placid (on top of hill Just west of U. $• Highway 2s3>)> Worth of the Colorado diver the base of tha danger occurs at the bottom of the limestone on top of the highest hill I*s miles northwest of Winchell (Just west of secondary road between Wlncheil and Brookesmith)• The limestone which forms a wide bench about 35 feet below the iianger limestone is herein designated the Corn Creek limestone (new name) member of the Placid shale* The best exposures of the Placid shale are below •>> the .tanger escarpment west of Corn Creek from Beef pasture Tank to Chamberlain Creek* It is suggested that this area be established aa an alternative type area for the Placid shale* lections showing thickness and lithology of the Placid shale can be found In Figures 25, 26, 27, 28, 29, and 30. The Com Creek member (Placid Ho* k end 5 of Bullard and Cuyler) of the Placid shale is named from typical exposures west of Com Creek on the V. F* White and Co* danch* The type section of this member (located at Beef Pasture Tank) i» shown In Flours 30* the Is member typically developed are as follows: Other places where 1. Above Big tank, 1 mile northwest of Beef feature Tank (Figure 26); 2. On the ¥lnch«il-Brookesmith road 0.8 mile north of U. $• Geological Survey bench mark 1416 feet (1.5 mile airline distance northwest of aincheii). Figure 29s 3* I*B mile north of U. S. Geological Survey bench mark 1416 feet on Wlnchell-Brookesmlth road, about 0.1 mile due east of intersection of north-south road and east-west road (just north of Mercury Quadrangle)« In the Mercury Quadrangle the member varies in thickness from 19 to 2? feet* It consists of two limestone beds separated by a 4-to 7-foot shale interval, the member can fee traced fro® the Cretaceous cover southwest of Placid north a dis­ tance of 20 miles to Brookesmlth in southern Brawn County. The limestone thins from the Mercury Quadrangle north, and its northernmost outcrop is terminated abruptly by channel sandstone deposits (Eargle, February 1952, personal commun­ication) • The shale interval below the Corn Greek member is feet thick. West of Wlnchell and in the 37 to 75 vicinity of Big Tank on the W. ff. White and Co. daneh, the lower 10 to 20 feet is red shale. From Beef Pasture tank south to the head of Bull Branch on the D. B. Pumphrey rianch, 1 or 2 thin sandstones are present 10 to 20 feet from the base of the shale. The interval above the Corn Creek member be shale may or limestone. The relationship between these facies has led to much confusion in the correlation of these beds. Drake {1893* pp* 387, 395) called the limestone facies the *Cherty limestone bed.** From his descriptions It appears that he included the overlying danger limestone in the *Cherty lime­ stone bed.* Kickell (1938, pp. ill-114) correctly placed the "Chectf limestone* below the :ianger, stating that it was equivalent to the limestone herein called the Corn Creek member to the north. Cheney (1948) placed the top of the Hanger at the top of the "Cherty limestone* of Mickell. in this report, the "Chatty limestone* is interpreted as a reef facies of the shale between the Com Creek limestone and the danger limestone. The shale facies is exposed over most of the Mercury Quadrangle. It is normally 30 to 40 feet thick, but south of Beef Pasture Tank it thins rapidly to 9 feet at the head of Bull Branch. A persistent sandstone bed is present 6to 10 feet above the Corn Creek member from the Winchell area south to Big Tank. Exposures of the limestone facies of the upper Placid found on Tom Dean Creek 0*25 mile shale are from its mouth. on both sides of the Colorado diver between the mouths of Homes Creek and McDowell Greek, and along Homes Creek from the mouth of Boggy Creek upstream to the mouth of Mukewater Creek (north of the northwest of the Mercury Quad- comer rangle)* Along the Colorado diver, elongate reef-like lime­ stone masses project above the Corn Creek member into the overlying shale* Downdip at the Homes Creek locality the entire interval between the Corn Creek and iianger is cherty limestone# At the locality on Tom Dean Creek, cherty lime­ stone is found below the danger* the lithology of the cherty limestone at Tom Dean Creek is illustrated in Figures 14 and 15* Convincing evidence of the reef-like structure of the cherty limestone facies of the Flacld is shown In Figure 16 where a massive bed "drapes* over the upturned edges of strata the steep east dips of which are interpreted as initial dips associated with underlying reefs* Two miles west of the Mercury Quadrangle, about 2 miles from the mouth of Cedar Creek, the Corn Creek member and the ranger limestone interval between are exposed with the the© composed of cherty limestone. At the mouth of McDowell Creek, the reef limestone a thick cross-bedded chert is locally replaced by conglomerate which rests in places on the Com Creek member. The thickness varies greatly within short distances, reaching a maximum of about 30 feet* The conglomerate forms a narrow outcrop trending 14. Reef limestone facies of Placid shale on Tom Dean - Figure Creek about 0.25 mile from mouth. '“hite rock is chert and rock is limestone. gray - 15. of rooks hammer Figure Close-up near in Figure 14. White rock is chert and gray rock is limestone. 57. with beds over "draping" shale Placid of facies limestone cherty in Reef - 16. Figure mouth. from mile 0.25 Creek, Dean Tom on view Southward dip. initial steep oast-weat# The contact between the reef limestone and the conglomerate Is sharp and can be seen clearly in three dimensions Angular fragments of the underlying Corn Greek member are present in the lower beds of the conglomerate where the two are in contact. This conglomerate has been studied by Bay (1932# p. 182) who stated that it has a composition and texture similar to the iiochelle conglomerate. Figure 17 shows boulders of this conglomerate found near the mouth of McDowell Creek* Because of the narrow east-west lineation of the out­ crop the sharp unconformable contact with the reef limestone, the presence of fragments of the Corn Creek member incorporated the in the base of the conglomerate, composition and grain and the that the con- else, cross-bedding, it is concluded glomerate represents the deposits of a narrow channel which has replaced reef limestone above the Corn Creek member. Ranger limestone -The Hanger limestone was named for ganger limestone* the town of :sanger, Eastland County, Texas* Plummer and Hoorn (1922, 110) applied the name for the first time in the p* Mercury quadrangle to beds which they correlated with Drake fs ”Cherty limestone bed*1 (1693» pp* 367* 395)• Nickell (1936, pp. 106-110) stated that type Home the Creek of Drake Is correlative with the .anger limestone* Cheney (1946) correlated f the danger limestone with Hlckell s Mcherty limestone” and the Home Greek limestone with Nickell 1a Hanger limestone* More recently Cheney and ~argle (1951) mapped the base of the 59 shale, Placid of member Creek Corn above conglomerate pebbles. chert channel and of Moulders cross-bedding - 17. showingFigure .ganger at the base of the Corn Creek member of this report, and the top of the Hanger at the base of the Colony Creek shale. The danger limestone of this report compared with the Interpretations of Drake, Plummer and Moore, Hickell, Cheney, and Cheney and Eargle follows: 1* Drake*» Cls93) top of the Home Creek limestone correlates with the top of the ifengar (this report); his type Home Creak limestone is the base of the danger of this report, A discussion of the correlation of Drake’s Home Creek at the type area can be found in Wlckall (193#, pp, 108-111, 114-118) and under the description of the Home Creek limestone in this report * 2, Plummer and Moore’s (1922) top of tanger is the same as in their base correlates this report; with the present interpretation where the *Cherty limestone* is absent. According to Plummer and Moore, Drake’s *Cherty limestone bed* is equivalent to limestone. The cherty limestone is their ganger now considered to be below the Hanger* 3, #1eke11*a (1938) top and base of the ranger agrees stated with the present interpretation, Nickell that the type Home (Drake) danger Creek is the limestone farther north. Creek limestone 4, Cheney’s (194#) top of the Home his base la the top of the danger of this report; of the Home Creek limestone becomes the base of the hanger in the present interpretation* 5* Cheney and dargl«*s (1951) top of .ranger is the same as described herein; the top of their cherty member (or base of their limestone above Corn Greek member) correlates with the base of the danger cf the present report* A graphic history of the nomenclature and correlation of the iianger is shown in Figure 10* The hanger limestone forms a high escarpment west of U. a* Highway 283 in the western part of the quadrangle* The width of the outcrop averages 2 to 3 miles across the area* The back-slope of the danger (in most places a dip-slope) is dissected by Cedar, Tom dean. Homes, and Boggy creeks which expose younger rocks along their valleys. Aerial photo­graphs showing the outcrop of the danger limestone are shown 12 and in Figures 13* sections showing the thickness and lithology of the Hanger limestone are in Figures 25# 26, 27* 28, 29# 30, and 31. The thickness of the danger in the Mercury quadrangle varies from a maximum of 70 feet on the Colorado diver to a minimum of 25 feet at host (Hickell, 1935, 114) Mountain* The formation thins both to the north and to the of the Colorado diver* Northwest of dlnchell the lowersouth danger contains a 5-foot shale bed near the base. part of the South of the Colorado illver, thin ahala beds are present near the top of the formation. Although nodular and bedded chert is characteristic of the Hangar limestone, the position of the chert within the formation is not constant* At some places it occurs throughout the limestone {Figure 26), at others, it appears near the base (Figures 25, 28,and 29), or, rarely, it Is absent (Figures 3Cand H). The thickened iianger limestone north of Boggy Creek and Creek along Homes Creek upstream from the mouth of Boggy la Interpreted as reefing of the danger limestone* The lithology and the thickness of the danger showing its reef- like facies are illustrated In Figure 30. Plane-table Creek Indicates mapping north of Boggy that the Hanger lime­stone thickens at the expense of the overlying Colony Creek shale and at some places may entirely replace this shale in­terval* dteep dips thought to be initial dips associated with reefs are locally apparent In the hanger along Boggy Greek. The reefing of the danger coincides at least in part with the of the Placid shale (cherty limestone underlying reef facies facies). Fossils are common in the .danger limestone but are not varied. At some places fusullnlds are abundant in the chert nodules. Fossils reported from the Hanger In the quadrangle are listed in Table 1. Colony Creek Shale - shale* Cheney (1948* p. 20) proposed the name "Colony Creek shale 1* for the bade between the Hunger limestone and the Home Creek limestone In order to replace the misapplied "Hog Creek shale** of previous workers* The west Colony Creek shale is named for typical exposures of Hanger in Eastland County, Texas* the history of the nomen­ clature of this formation in the Colorado diver valley is shown in Figure 10* The Colony Creek shale crops out as a narrow band below the Home Create limestone outlier® north and south of the Colorado diver* the maximum thickness of this formation observed in the Mercury Quadrangle was 23 feet at Lost Mountain (west of Mercury). Along Homes and Boggy Creeks in Coleman County, the Colony Creek shale is thin or absent* Thickening of the underlying Hanger limestone at the expense of the shale has reduced the Creek overlying outcrop of the Colony shale to a narrow bench between the Hanger and Home Creek limestones* The bench, which may possibly represent the Colony Greek shale at its thinnest, is covered by talus* Wherever shale reaches a thickness the Colony Creek of approximately 20 feet, a thin sandstone is present near the base* Hear the mouth of Tom Dean Creek, this sandstone Is 5 feet thick: at In the quadrangle it Is 1 to 2 feet thick. other places Vertebrate bones (probably fish remains) were collected from this sandstone at a tank on Tom Dean Greek o*9 mile west of McDowell sell* Fossils other than the vertebrate remains have not been observed in the Colony Creek shale exposed in the Mercury Quadrangle* home - Home Creek limestone*Limestone The type area of the "Home Creek bed" is described by Crake (1693, p* 393) as follows: Along Home Creek, one and a half to two miles above its mouth, the bed is thirty to thirty-five feet thick, the lower twenty-five feet being hard blue rough-surfaced massive limestone. Nickell (1933, pp* 108-111, 114-118) correlated Drake * s type Home Creek with the danger limestone to the north, and stated that Drake used the term "Home Creek" north of the type area for the limestone above the type Home Creek limestone. The present work in the Mercury Quadrangle supports the conclusions of Nickell* The beds described as the "Home Creek bed" by Drake along Homes Creek are mapped as hanger limestone* The thin limestone which occurs above the danger limestone la correlated with the Home Creek limestone in recent geologic boundaries maps of Brown County* Various interpretations of the of the Home Creek limestone are graphically illustrated in figure 10. Outcrops of the Home Creek limestone occur in the Colorado northwestern part of the Mercury Quadrangle along the diver and Homes Creek and on outliers above the danger and Colony Creek outcrops. The Home Creak limestone in the Mercury quadrangle can be divided into two facies: 1* a limestone-shale facies on the outliers north and south of the Colorado diver (Figures 25, 26,and 30); and 2* a reef facies north of the Colorado diver and west of Homes Greek (Figure 31)* Al­ though outcrops of the limestone-shale facies occur as out­liers with no overlying Bluff Creek shale, the thickness of the Home Creek limestone measured west of Winchell (Figure 26) and at Lost Mountain (Figure 25) la thought to be close to the total thickness of the formation* On these outliers the Home Creek is approximately 35 feet thick, and consists of 3 limestones with a 4-foot shale near the base and a 13-to 15-foot shale near the middle of the formation* On Homes Creek (Figure 30) just north of the quadrangle, the thickness of the formation has decreased to 17 feet* The reef facies of the Home Creek limestone (Figure 31) is exposed in high bluffs north of the Colorado diver* The upper surface of the formation is irregular, at places projecting 35 to 40 feet upward into the overlying Bluff Creek shale* One mile northwest of the mouth of Homes Creek the top beds of the Home Creek limestone rise above the dhite tianch limestone; a short distance west, the interval between the White danch limestone and the top of the Home Creek limestone is 35 feet* Dips over these projecting features (here Interpreted as reefs) are steeply quaquaversal * The maximum thickness of the Home Creek limestone observed where feet reefing is present is 50*5 {Figure 31)* The coral Campophyllua is characteristically present in the limestone beds of the Home Creek. Although found above and below this level, the abundance of Camoophyllum is a useful aid in field Identification of the Home Creek limestone* 67 - Figure 18. Section of upper part of Stravm series and lower part of Brownwood shale 4000 feet northwest of CoT.7boy Cemetery, LcCulloch County, Texas. 19. Section of - Figure Brownwood, Adams Branch, Cedarton 3.5 miles south-s inchell formations, or Placid, McCulloch County, Texas. - Figure 20. lection of Brownwood shale on north bank of Colorado River 2.5 miles east of Winchell, Brown County, Texas. and Adams Branch Section of Brownwood shale - Figure 21. 0.5 mile southeast of McCulloch limestone mercury, Texas. County, 22. oection Adams Cedar ton, - Figure of Brownwood, Branch, and Finehell formations 1 mile east of McCulloch Placid, County, Texas. 72 Figure 23. Section of Adams Branca, Cedarton, and Winchell- 1 mile southwest of formaticns at Morgan mountain, ’7lnohe11, McCulloch County, Texas. and 24. Section of Adams Branch, Cedarton, Winohell - Figure formaticns 1.5 miles south-southwest of Mercury, MeCu1loch County, Texas. Section - figure 25, of Rinchell, Placid, Ranger, Colony Creek, "and Homs Creek formations west of mercury on W N, White . and Company Ranch, ReGulloch County, Texas. - Figure 25 (continued). Section of Winch,ell, Placid, Ranger, and Home Creek formations west Colony Creek, of Mercury on W, K. White and Company Ranch, McCulloch County, Texas. 76 - Figure 26. Section of V/inchell, Placid, Ranger, Colony Creek, and Home Creek formations in southeastern Coleman County, Texas . 77 - Figure 26 (continued). Section of ftinchell, Placid, Hanger, Colony Creek, and Home Creek formations in s oitheastern Coleman County, Texas. - Figure 27. Section of V.inohell, Placid, and Ranger formations on D, S. Pumphrey Ranch, 3 miles north of Placid, McCulloch County, Texas. Figure 28. Section of Placid and Ranger formations - miles northwest of inchell, Brown Texas. County, 29. section of Corn Creek limestone member of - Figure Type " Placid shale at Beef Pasture Tank on W. N. White and Company Ranch, RcCulloch County, Texas. Figure 30. Section of Placid (cherty limestone), danger.-Colony Creek, Home Greek, and Bluff Creek formations on Homes Creek 2000 to 3000 feet northwest of mouth of Boggy Coleman Texas. Creek, County, - Figure 31. Composite section of Ranger Colony Creek, Home Creel:, Bluff Greek, and Gunsight formations on Gill Ranch between ranch house and Homes Creek, Coleman County, Texas. Cisco series Cisco series Is in a small area Th« exposed very north of the Colorado iUver in the extreme northwest corner of the Mercury quadrangle* The total thickness of the Cisco in the area is 77 feet. Colorado The Canyon-Cisco boundary in the diver valley Is not marked a by pronounced dlsconformlty as in the Brasos diver valley. In the Mercury quadrangle, it is locally dis­confonaable because of reefing in the underlying Home Creek diaconformable limestone, but the relationship is apparently confined to a small area along the Colorado diver. There is a decided difference between the sedimentary rocks above and below the Home Creek limestone. The sedimentary rocks of the Cisco are more clastic, and contain more shale and sandstone than the upper Canyon. Furthermore, the limestones of the Cisco are thinner and contain more clastic material. Higher in the Cisco, channelling is widespread at many levels* The base of the Cisco in north central Texas is characterised by of ammonites the Uddenltes schucherti assemblage (Plummer and Scott, 1937, pp. 17, 18, 388-390). This cephalopod seme crops out the Gill .ianch about one mile southwest of the north- on west corner of the quadrangle between the Hunger limestone member and the Gunsight limestone. Cisco nomenclature used in this report as well as in- in the terpretations of the stratigraphy by previous workers 84 Colorado River valley la shown in Figure 10. Bluff Shale Drake (1893. 387, 400) - IMI Creek sMle. PP* applied che name "Bluff Creek bed" to the shale and sandstone between the "Home Creek bed" (not type area) and the "Campo­phyllum bed" (Gunsight limestone). The type area for the Bluff Creek shale is on Bluff Creek about 6 miles upstream (south­west) from the place where the Colorado River enters the Mer­ cury Quadrangle. The Bluff Creek shale of the present report contains the Hunger limestone and the White Ranch limestone members. A section of the Bluff Creek shale exposed on the Gill Ranch north of the Colorado Elver and west of Homes Creek is shown in Figure 31* Only beds up to the top of the hunger member are present in the Mercury Quadrangle. Bullard and Cuyler (1935, pp* 221, 222} named the White Ranch limestone member from exposures on the west bank of Cedar Creek (1.5 miles west of Mercury Quadrangle). Outcrops of the Whit© Ranch limestone in the Mercury Quadrangle occur at various strati­ graphic intervals above the Home Creek limestone. Reefing in the shale the Home Creek limestone causes interval between the White Ranch member and Home Creek to vary from 0 to 35 feet. at a locality one mile northwest of the mouth of Hone Creek the reef builds up to a level above the White Ranch member. The Ranch limestone member and interval between the White hunger limestone member is 30 feet in the Mercury Quadrangle. The Bunger limestone member of this report is at about the same stratigraphic position as the hunger limestone at its type locality (Young County, Texas), but exact correlation of the Bunger of the Colorado Elver with the Bunger at the type area has not yet been established* Previous common appli­ cation of the name in McCulloch, Coleman, and Brown counties Justifies its continued use rather than the introduction of a new name* Comanche Series Lower Cretaceous rocks dipping southeastward less than 10 feet per mile unconfomably overlie Pennsylvanian strata in the Mercury quadrangle. Nomenclature of the Comanche series used in this report is as follows: Comanche series Fredericksburg group Awards limestone Comanche Peak limestone Walnut clay Trinity group Paluxy sand (northeastern Llano uplift only) Gian Eose limestone Travis Peak formation Henaell sand Creek limestone Cow Sycamore sand Barnes (1946, pp. 5-8) revised the nomenclature of the Trinity group as follows; Trinity group Jningle Hills formation (new) Glen Rose limestone member Hensell sand member Travis Peak formation (restricted) Cow Creek limestone member dyc&more sand member *ell data and surface measurements show that the total thick­ ness of Comanche strata in the quadrangle is about 240 feet. In the southeast, the walnut, Comanche Peak, and Edwards formations are exposed at the eastern end of the Brady mountains* In the south-central part of the quadrangle, a large outlier of conglomerate and sandstone is exposed as an elongate dissected mesa. The conglomerate and sandstone are tentatively correlated with the Hensell sand member of the Travis Peak formation (Bhingle Hills formation of Barnes) stated below. for reasons - Travis Peak formation the Travis formation formation* Peak consists of2o to 40 feet of sandstone and conglomerate over­ lying Strewn shale and sandstone. a part of the Travis Peak formation is described in Figure 9# *s pointed out by Brake 361), the conglomerate deposits of the Lower Cre­ (I£93# P* are found west of the cuesta-foming limestones of taceous 87 the Canyon series and at a lower elevation than Cretaceous beds to the west* The elevation of the Cretaceous-Pennsylvanian con­tact east of Deep Creek where the Travis Peak formation is present varies from 1550 to 1610 feet, the lowest elevations occurring at the north end of the large outlier* Elevations of the Cretaceous-Permsylvanian contact west of Beep Creek average about 1700 feet, the «alnut formation resting directly on the Pennsylvanian* This difference in elevation of the Pennsyl­vanian-Cretaceous contact is Interpreted to be the result of variations in topography on the pre-Cretaceous erosional sur­face* .-/here the underlying Pennsylvanian contains beds of resistant limestone, the Pennsylvanian-Cretaceous contact is higher than where the underlying beds are composed of less resistant sandstone and shale* The Travis Peak sandstone and the Hensell sand member below the conglomerate may represent Glen Rose limestone. Barnes (1945, P* 8) has shown that a part of the Hensell sand is a shoreward facies of the Glen Eose lime­ stone. Because of the unevenness of the pre-Comanche erosion­al surface, the Glen Rose limestone in the Mercury is absent quadrangle, making the relationship of the conglomerate to over­lying beds obscure. This relationship is further complicated by formations the progressive overlap of younger Comanche south­eastward on the Llano uplift. Damon (in Plummer 1950, pp. 103, 104) has made a de­ 88 two localities tailed study of the Travis Peak conglomerate at in the Mercury quadrangle (one locality Is 2.4 miles north ami 0.5 mile of Hall; another is 2*4 miles north and 2.0 west milea west of Hall), lithologic analyses of the pebbles and cobbles a dominance of rock types in the conglomerate indicate characteristic of the Lllenburger and Marble Falls. The near­ est source for these rock types is the Llano uplift to the south. Directly overlying the Travis Peak conglomerate in some areas Is a deeply weathered of limestone rubble zone which may represent the overlying Glen Rose. *ll observed outcrops contain thick caliche deposits, obscuring the stratigraphic relationship to the underlying conglomerate. These weathered limestone deposits were mapped as part of a the Travis Peak formation, stratigraphic work to the south and west of the quadrangle should solve some of the problems re­ lated to the interval between the Travis Peak conglomerate and the Walnut formation. - walnut formation The walnut outcrop la west of formation* Deep Creek, overlying the alternating limestones and shales of the Canyon aeries* The soft clay of the walnut is ex­ tensively cultivated and fores wide, flat areas with very few outcrops. Consequently, only the top portion of the Walnut is section of the included in the measured Cretaceous (Figure water well drilled in the Corn 32). a Greek Hills on the Parker - 32. Section of '.Valnut, Comanche Peak, and Sdwards Figure formations on Parker Pumphrey Ranch, Corn Creek hills, McCulloch County, Texas. fact of Walnut clay and 19 fo«& Pumphrey Ranch penetrated 82 of Cretaceous red shale, sand, and gravel before entering Pennsylvanian (Hanger?) limestone* This lower 19-foot section may be Glen Rose or Paluxy age. Fossils occur in the Walnut in a thin shell bed at the top of the formation, a list of walnut fossils collected at Fossil Gap (Parker Puaphrey Eanch, I*3 miles east of bench mark 1740 feet located on Brady-Brownwood highway! is as follows: chino idea Heteraster texanus (Roomer) llolecVypua Koemer Felecypoda gyprimeria texana (Eoemer) texana Semer uryphaea giucron&ta Gabb Ammonoidea Metengonocer&a hilli Bohm % - Peak timestone* Immediately above the Walnut Comanche Limestone clay is 60 feet of yellowish gray* nodular limestone which is referred to here as the Comanche Peak limestone (Figure 32). formation makes a wide bench below the This steep-sided out­ liers of Cdwards limestone* Lithologically the Comanche leak limestone is distinct from the underlying Walnut or overlying limestone. ddwards - Awards limestone* the Edwards Edwards limestone limestone forms three flat-topped mesas in the Mercury Quadrangle* The thick­ness of the Bdwards in the Corn Creek Hills is 66 feet (Figure 32)* The Awards of this is characteristically harder area than the Comanche Peak limestone and weathers to large cavernous and honeycombed blocks* Unlike the Edwards farther west in the Brady Mountains, no rudistids or chert xiodules are present* QUATERNARY SYSTEM quaternary deposits mapped in the Mercury quadrangle consist of two units: older terrace gravel adjacent to the Colorado River (probably Pleistocene), and younger flood plain deposits of the Colorado River and its major tributaries (Pleist­ ocene (?) and Recent}* These deposits were mapped only In part. the older terrace gravel is interpreted as a deposit laid down by the Colorado River probably during the Pleistocene The epoch* gravel is composed mainly of rounded chert pebbles and cobbles* Its base occurs 60 to 120 feet above the normal river level, sloping downstream at about the same rate as the River* The present gradient of the Colorado gravel ranges in thickness from 0 to 30 feet, being at places extensive metal* enough to be used as a source of road Gravel, sand, and silt, mapped quaternary alluvium as are present along the Colorado River and its major tributaries* At the mouth of Deep Creek the alluvium consists of 5 to 6 feet of basal sand and gravel overlain by 50 feet of silt* The silt occurs up to 60 feet above the present river level. Where the Colorado Elver the wide outcrop of the Brownwood traverses shale, the silt extends north and south of the river, merging into similar deposits laid down by Conner Branch and Deep Creek. *t higher elevations on Deep Creek, the alluvium grades into slope wash from the valley walls* The thick silt and gravel deposits along the Colorado diver are interpreted as mostly decent age but may be In part Pleistocene* STRUCTURAL FEATURES The structural features can be divided into three divisions, each of which is related in time and type of deformation; I. folded pre-dtrawn strata of the Llano uplift; 2* northwest-dipping otrawn, Canyon, and Cisco strata; and 3. southeast-dipping Lower Cretaceous strata* Pre-dtrawn beds in the southeast dip 3° to 4° north and northwest away from the center of the Llano uplift. These rocks are the west flank of the Richland on ­ Springs axis a that trends northeastward across the Llano broad arch uplift, and can be traced in the subsurface to the north where it baa been called the Bend arch or Bend flexure. A smaller structural feature on the west flank of the Richland Springs axis has been named the Hall uplift* The north end of this plunging anticline is in the Mercury Quadrangle* The axial trace of the anticline trends N 15° I. on Dtps the east and west flanks of the Hall uplift average 8° to 10°, at places reaching a maximum of 15°• South of the quadrangle, the east flank of the anticline is cut by a normal fault whose surface trace trends north­ eastward* Strawn, Canyon, and Cisco strata dip N 70° # at a: average rate of 50 to 75 feet per mile* The structural feature formed by these beds is a homocllne modified locally by faulting or gentle folding* Plate 2 shows the regional dip with minor nosing in the western half of the quadrangle* 'Two faults have been observed in the Mercury Quad­ rangle involving Canyon beds, one south of Mercury, the other along the Colorado River near the northwest corner of the quadrangle. Both faults are oblique, high-angle, normal faults* The fault south of Mercury is downthrown to the southeast and has a maximum observed throw of 32 feet on the old Placid-Mercury road. The throw diminishes to the southwest* Northeast of the old Placid-Mercury road, the fault can not be traced a great distance because of the homogeneity of the Brownwood shale and Quaternary alluvium cover* The fault on the Colorado River is mapped as an In­ ferred fault on the Mercury Quadrangle* This fault has been 94 clearly defined to the southwest on the adjacent Waldrlp Quadrangle. The downthrown side of the fault Is to the northwest and the maximum calculated throw la about 70 fset • Other dips anomalous to the regional dip are present in the form of structural noses and terraces* * comparison of the structure-contour nap (Plate 2) with the areal geo­ logy map (Plate 1) shows that most of the structural noses are reflected In the outcrop pattern. For example, inllers coincide with the minor folds 2 miles northwest of Placid, 2*s miles southwest of Mercury, and 2.5 miles north of Mercury• The attitude of Cretaceous strata in the south­ west is homoclinal; they dip southeast less than 10 feet per mile* These figures are based on the changes In ele­ vation of the fossil bed at the top of the Walnut formation* GEOLOGIC HISTORY INTRODUCTION dtrawn. Canyon, and Cisco strata In the Mercury Quadrangle exhibit many stratigraphic features which are similar to those formed by cyclic sedimentation, but the cyclic repetition of the beds is thought to be interrupted at so many levels that complete cycles are probably absent* The probable reason for the apparent periods of ln~ random terruption In the cyclothems is sporadic uplift of the borderland. More surface and subsurface data are needed before these Interrupted cycles can be fully understood* In the following discussion of the geologic history of the btrawn, Canyon, and Cisco series of the Mer­cury quadrangle, certain conclusions have been reached which apply to the depth of water in which various types of rocks and associated fossils have been deposited* Most of these conclusions are based on previous work of different geo­ logists in other Pennsylvanian and Permian strata that show cyclic sedimentation* as the upper Pennsylvanian formations in the Mercury Quadrangle closely resemble in lithology and type of fossils the Big Blue series in Kansas (Elies, 1937, pp* 403-432), It is believed that the environments of the Upper Pennsyl­ vanian sea in the Colorado River valley correspond closely to the Big Blue environments* Elias (1937, pp* 423, 425) concluded that the maximum depth of the late Paleoaoic sea In Kansas was less than DO feet. This maximum depth might well apply to upper Pennsylvanian sediments in the Mercury Quadrangle. The following list shows an interpretation of the relative depths (from shallow to deep) at which different types of Pennsylvanian sediments in the Mercury Quadrangle were deposited* These depths are inferred in part from 96 stratigraphic relationships involving position in a cyclo­them# and in part on the conclusions reached by Elias* His numerical depths of similar rock in Kansas are given types for comparison* Sandstone and the 1* chert conglomerates croso-bedded, channel-like types sea-level; were deposited above Elias placed Big Blue sandstones above sea level. 2* Eed shale: red shale may be deposited above sea level or very near shore under oxidising condition®; plant fossils are present at some places; at many places {surface and subsurface) red shale overlies sandstone suggesting a close relationship to sub- shale above sea aerial deposits; Elias places red level* 3* Green shale; green shale rarely contains fossils; deposited under reducing conditions; found mixed with red shale, therefore closely related; Elias places green shale from sea level to 30 feet below sea level* 4* Gray shale: may contain crinolds, bryoso&na, br&ch­iopods, peXecypods, gastropods, trilobites, cono­ no donts, ostracodes, and foraminifers, but fusultnids; niay be shallow to deep water? Elias places gray shale from 60 to 160 feet below sea level. $• Limestone without fusulinids: contains brachiopod fauna; Allas places this type 110 to 160 feet be­ low sea level* Limestone limestone 6* containing chert and containing fusulinld©: Ellas places these types 160 to l£o feet below sea level or maximum depth of the sea* PRE-STRAWN TIME The calcitic limestone in the Ellenburger has been likened in origin to the chemical precipitation of aragonite mud on the Bahama Banka at present (Cloud and Barnes, 1945, pp, $9-109)• The fine texture and small amount of terrigen­ ous material found in the calcitic limestone (e. g. Gorman formation) point toward a nerltic environment, probably offshore from a landctasa of low relief (Cloud and Barnes, 1945, pp* $9-109)* Post-Ellenburger truncation, increasing from east to west is demonstrated by the absence of the Honeycut formation (upper Ellenburger) on the west side of the Llano uplift. In the Mercury Quadrangle the Honeycut formation Is absent, Mississippian strata overlying the Gorman formation. Cloud and Barnes (1946, p. 109) have dated this truncation a® pre- Devonian because widespread but isolated Devonian beds over­ lie progressively older Kllenimrger strata from east to west. the fact that Devonian beds have been almost entirely re­ moved from the Llano uplift is indicative of post-Devonian uplift and erosion. The Ives breccia is thought to represent the initial marine invasion in the Llano region of Mlssisaippian seas (Cloud and Barnes, 1946, p. 317)* In the Mercury Quadrangle the Ives breccia rests unconformably on an old erosional surface of the Gorman formation* The of conodonts presence in the sand matrix, the nearby source (Ellenburger chert), and and the uniform angularity of the chert phenoclasts, thickness of the breccia point to a rapid marine invasion over a land of low relief which had been exposed to weather­ ing for a long period of time. Absence of the Chappel lime­ stone above the Ives breccia in the Mercury quadrangle in­ dicates a post-Chappel, pre-Barnett period of uplift and erosion. the next marine invasion is represented by deposits of silt, limestone, and shale of the Barnett formation. sections of the Barnett are thin, the Even though outcrop Barnett sea was extensive, covering a large area in Central Texas. Subsurface data show that the Barnett 1® absent ovsr areas of greatest uplift (Cheney, 1940, p. 71) probably due to pre-Pennsylvanian erosion. Pennsylvanian sedimentation in the Mercury quadrangle was initiated by the deposition of the Lemons Bluff member 99 of the Big Saline formation, which unconformably overlies the Barnett shale, intervening Big baline deposits being absent* according to * lumber (1930, p* 64, 6s) the older Big Baline beds (aylor and Brook members) pinch oat on the flanks of the uplifts and are overlapped by the Lemons Bluff member* If this Is true, the Hail uplift was structurally positive before Big baiine time* Before or during bmith­ wick time renewed uplift in positive areas similar to the Hall uplift is inferred from the thick deposits of omithwick shale to in synclinal areas adjacent the positive areas* The Bmithwick may be thicker west of the Hall uplift for this reason but subsurface data at are insufficient present to support this postulation* STRAWN EPOCH The geologic history of the strewn epoch in the Colorado Hiver valley is essentially a reflection of ero­ genic movements of the inferred Ouachita The foreland sandstone-shale sequence mapped and described by Drake along the Colorado Eiver from Eix, Lampasas County, to Kilburn, McCulloch County, indicates a rhythmical change from littoral and fluvial sand to near-shore marine, perhaps In part lagoonal, silt and clay* at the outcrop, the thick­ ness of the dtravm is more than feet (Plummer and Koore, 100 1922, p* 63). Drilled thicknesses of the dtrawn in the Colorado Elver valley are be considerably leas than might expected. For example, In northeast McCulloch and north­west dan baba Counties where the top of the btrawn is near the surface, wells penetrated about 600 feet of btrawn• These the thin, subsurface Strawa deposit© may represent offshore are facies of the thicker, clastic deposits which exposed at the surface* The alternating sandstone© and shales suggest an oscillating strand line during btrawn time. Periodic up­lifts of the Ouachita Mountain belt to the east accompanied by slight foreland subsidence would have moved the strand line westward allowing sand to accumulate* Fluvial de­ posits (conglomerate and sandstone) filled channels cut by major streams, originating in the highlands* a© the relief of the mountains decreased, the coarser clastic material gave way to near-shore shale and silt, the strand line moving eastward* Eenewed uplift of the mountains would begin a new cycle* The upper part of the Strawn in the Mercury Quad- more marine elements than do the older beds* rangle has hear the top of the “Indian Creek bed,*1 & thin limestone contains marine fossils (Figure 7, Unit ho* 3)« This occurrence of limestone suggests & shallow, offshore, dear-water, marine environments as to the turbid waters which are compared interpreted for the underlying unfossiliferous shales* The Capps limestone, which contains fusulinids and corals, also indicates deposition in marine water* The limestone in the wlndian Creek bed" lies a few feet below chert conglomerate, and the Capps limestone is locally replaced by Chert conglomerate* This conglomerate and associated sandstone are interpreted as the beginning or nonmarine phase of a new sedimentary cycle* During the Ike in which the htrawn was *jeing deposited in the Colorado Elver valley, a period of major faulting occurred along a northeast trend, affecting Strewn and older rocks across the Llano faults uplift. The are normal, high angle, gravity faults, according to Cheney (1940, p. 105) the faulting was caused by tension in an area which was marginal to a stable or rising foreland and which was flankea oy a deeply subsiding geosyncline. Most of these faults lie east and southeast of the Lend Arch or Richland springs axis (east of Mercury quadrangle). ¦fiber® this %om of faulting is exposed In the Llano up­ lift, it consists of narrow, parallel grabens, trending northeast. Cheney (1950, p. 17) states that Drake*s "big Valley beas*1 and older were affected uore Ly the major faulting than younger Ltrawn beds. Thus Cheney would place the age of greatest crustal moveswat along w the faults between “Big Valley" and ßrown Creek** tildes 102 at the close of hia Lampasas (Figure s)# That was a positive area from late the Llano uplift otrawn time to the is demonstrated by the overlap present of Btrawn, Canyon, and Cretaceous strata around the margin of the uplift* CANYON EPOCH Canyon formations represent a change from the near-shore, strand line deposits of the btrawa to a marine, dear-water environment* Canyon seas in the Mercury quad­rangle were shallow but the strand line is thought to have been farther east as compared to Btrawn time* Uplift of the borderland to the east rise probably gave periodically to increased supplies of clastic material to be deposited be­ tween the marine limestones in the foreland seas* Initial Canyon deposition in the Mercury quadrangle is represented by the relatively thick Brownwood shale* The essential difference between the Brownwood shale and under** marine beds lying Btrawn deposits is the presence of more in the Brownwood* Locally the base of the Brownwood is asarked by chert conglomerate, which is interpreted as & channel deposit* The source of the varicolored chert pebbles in the Canyon conglomerates (aa well as otrawn and Cisco conglomerates) is thought to be the folded and uplifted earlier Baleosoic strata of the Ouachita-Maratnon geo­ syncline to the east* 103 Rfter the Brownwood shale was deposited, the Canyon sea became more pogresslvely clearer, for limestone* became numerous and thicker* Periods of channelling occurred throughout the Canyon epoch at different times* Probably the most widespread channelling occurred just after the deposition of limestone ho* 2 of the Winchell formation* From upper Placid time (post-Corn Creek member) to reefs formed the top of the Canyon, were locally in a northeast trending belt along the northwest edge of the Mercury Quadrangle* Superposition of reefs along Homes Creek and the Colorado direr is thought to be the result of reef growth on an old sea-floor shoal area that may have been a structural high* CISCO EPOCH ho evidence ofamajor break In the sedimentary record between the Canyon and Cisco can oe found in the Mercury quadrangle* Locally the Home Creak-Bluff Creek contact is unconform*ole because of reef development in the Home Greek limestone, but this relationship exists at other horizons in the Canyon. When traced laterally away from the reefs, the unconformity ceases to be significant# During lower Cisco time in the Colorado River valley, thin, fusulinld-bearing limestones and thick, intervening shales were deposited. Ripple-marked sandstone and channels 104 filled are with chert conglomerate which widespread in the lower Cisco (Bluff Creek shale) at other places in the Colo­ rado iiiver valley, indicate periods of uplift and erosion. In general, it might be said that during lower Cisco time in the Colorado diver valley, the sea changed rapidly from turbid to clear, fusuiinids flourishing la the clearer water. POST-CISCO TIME after early Cisco and before early Cretaceous time, (probably during the Permian and Triassic periods), region­al tilting of Cisco and older beds to the west and north­west took place In north-central Texas, affecting the Kor­ of eary quadrangle. The Mercury Quadrangle along with most north-central Texas was uplifted before Lower Cretaceous time and subjected to a long period of erosion. The ab­ sence of the Travis Peak formation west of Deep Creek suggests that much of the present topography may have been cut as early as pre-Cretaceous time. The Comanche sea, advancing from southeast to northwest, invaded the Mercury quadrangle, where the maximum relief was more than 100 feet. The oldest con­ glomerates were deposited on the topographically lower and less resistant btrawn sandstone and shale, Cuestas formed by Canyon limestones evidently remained above sea level until «*alnut time. Th« aoseiic© of the Glen Hose limestone In the Mjeroury quadrangle indicates that this region was topograph** tcally high during Glen Hose time* This is true Tor the Llano uplift in general. Luring Walnut, Comanche Peak, and tdwarda was covered time, the Mercury Quadrangle oy the Cretaceous sea* and limestone in- The marl, clay, dicate a near-shore, dear-water, marine environment* The post-Kdwards history of the Mercury quadrangle ia mainly one of erosion* After hdwards time the Comanche sea covered most of north-central Texas, but Cretaceous rocks younger than the Mwards are absent in the Mercury quadrangle* Terrace gravel of Pleistocene (?) age was deposited by the Colorado Elver at topographic levels above the present drainage system, and Recent and Pleistocene (?) silt and gravel are found adjacent to the river and its tributaries* APPENDIX A LIST OF FOSSIL LOCALITIES IN THE MERCURY QUADRANGLE The following list of fossil localities in the Mercury quadrangle includes the localities described by Bullard and Cuyler (1935), williams (1935), and Plummer (19$0), and Early (1951). arbitrary numbers preceded by the initials of the author and the date have been assigned to each locality. These numbers correspond to those found on Table I which shows the distribution of the fossil species, and Plate 3 which shows the fossil localities. Bullard and Cuyler (1935) list fossils in their measured sections* Their localities are as follows: locality Jggk|»er Remarks BC-35-1 Brownwood shale, 20 feet below base of «.dams Branch limestone, o.s mile east of Mercury (Bullard and Cuyler, 1935, p. 201). 30-35-2 Cedarton shale, railroad cut 2.$ miles south of Mercury (Bullard and Cuyler, 1935, p. 203). BC-35-3 Cedarton shale, sandstone bed 10.2 feet below top, Morgan Mountain (Bullard and Cuyler, 1935, p. 204). BG-3s-4 Cedarton shale, 10.7 to 15.8 feet below top, Morgan Mountain (Bullard and Cuyler, 1935, p. 204)• BC-35-5 Cedarton shale, 11*4 to sl*2 feet above base, Morgan Mountain (Bullard and Cuyler, 1935, pp. 204, 20$). 106 107 BC-35-6 Limestone No. 2 of the Winchell formation, near whit© Ranch house (Bullard and Cuyler, 1935, p. 207). BC-35-7 Limestone ho. 1 of the Winchell formation, near white Ranch house (Bullard and Cuyler, 1935, p. 207). BC-35-8 Corn Creek limestone member of the Placid on the White formation. Beef Pasture Tank Ranch (Bullard and Cuyler, 1935, P* 211}* BC-35-9 Limestone No# 5 of the Winchell formation, weet of White Ranch house (Bullard and Cuyler, 1935, p. 212). BC-35-10 Limestone No. 2 of the Winchell formation, 2 miles southwest of Mercury (Bullard and Cuyler, 1935, p. 212). BC-35-11 Limestone No. 1 of the Winchell formation, 2 miles southwest of Mercury (Bullard and Cuyler, 1935, P* 212). BC-35-12 Limestone No. 4 of the Winchell formation, 2 miles northwest of Mercury (Bullard and Cuyler, 1935, p. 213). 8G~35~13 Placid shale, 23 to 35 feet above base, 1 mile north of Beef Pasture Tank on white Ranch (Bullard and Cuyler, 1935, p. 214). Fossil localities listed by Williams (1938) are as follows: Locality dumber Regiarks tf-38-1 Brownwood shale, collection 7506, 3 miles east of &inch*11 (Milliaaa, 1938, p. 153). w-38-2 Browuwood shale, collection 7505# 10 feet above collection 7506, 3 miles east of wlncnell (williams, 1938, p. 153)* Branch limes tor±e, northwest, of bridge over Colorado diver at Winehell, Texas (Williams, 1938, p. 153)* tf-33-4 Limestone No. 2 of the Wincbell formation, 0.5 mile west of Wincbell (Williams, 1933, p. 154). Fossil localities listed by Plummer (1950) are as follows: Locality Number Remarks P-50-1 btrawn, Plummer’s locality 153-T-7# 3 miles northeast of batult, McCulloch County, south of Mercury quadrangle (Plummer, 1950, p. 38). P-50-2 Cedarton shale, Plummer’s locality 153-T-21a, shale above adams Branch limestone, 1.4 miles east of Placid (Plummer, 1950, pp. 96, 93). P-50-3 Brownwood shale, Plummer’s locality 153-T-23, shale below Rough Mountain conglomerate member of the Brownwood shale, south of Rough Mountain (Plummer, 1950, pp. 96# 93). P-50-4 btrawn, Plummer’s locality 153-T-98, 1.0 mile northeast of Rough Mountain (Plummer, 1950, pp. 96, 93). P-50-5 Brownwood shale, Plummer’s locality 153-T-100, 2*5 miles southeast of Placid (Plummer, 1950, pp. 96, 93). p-50-6 Cedarton shale, Plummer’s locality 153~T~113, shale below limestone ho* 1 of the Wincbell formation (Plummer, 1950# pp* 96# 99)* Microfossils have been identified by .aarly (1951) frotu two measured sections of the Brownwood shale (Figures 20 and 21), sample numbers and the units from which the samples were obtained are as follows: Brownwood shale, 2 miles east of Wincbell (Figure 20) Smber Remarks J-51-5 to £•••••••• Unit 14# Figure 20 109 J-51-2, 3 f and J-50-53a, 54 to 58 .Unit 13, Figure 20 J-51-28 to 30 .Unit 9, Figure 20 J-50-48 to 52. . .Unit 11, Figure 20 J-51-23 to 2?. . .Unit 6, Figure 20 J-50-47 and J-51-22. ... .Unit 6, Figure 20 J—so—43 to 45• •Unit 4, Figure 20 • J-50-42#.....Unit 2, Figure 20 Adana Branch limestone o#s mile southeast of Mercury (Figure 21) J-51-32, 33f and B—sl—l .Unit 20, Figure 21 Brownwood shale o#s mile southeast of Mercury (Figure 21) •» £-51-2, 4, 5 .Unit 18, Figure 21 B-51-li • • •# . #Unit 13, Figure 21 hew fossil localities, some of which occur in measured sections, are as follows: ideality dumber remarks ' J-51-1 Cedarton shale. Just west of railroad in small valley on the northwest aide of the hill between U# 3# Highway 283 and the railroad, fossils weather out of shale and yellowish coquina 15-20 feet above base of Cedarton shale# J-51-32,33 adams Branch limes 20, Figure 21# J-51-50 Cedarton shale, about 20 feet from base, south of Mercury in railroad cut o*4 mile northeast of U# 3* G# 3* bench mark 1505 feet# J-51-51 Cedari,on shale, southwest or Mercury in rail­road 100 feet south of U. 3. G. 3. bench cut, mark 1505 feet, 15-20 feet above base of Cedarton# 110 J-51-32 Brownwood shale. Unit 9» Figure 21* J-51-53 Cedarton shale, upper 15 feet of Cedarton o*s mile west of Mercury, just north of road between Kercury and U. S* Highway 2#3» collected by J* L* Wilson* J-50-21 Btrawn (Capps limestone member), road cut on farm road I*o mile east of Deep Creek at top of small hill* J-50-24 Brownwood shale, 0-20 feet below base Hough Mountain conglomerate on west side of old uochelle-Cowboy road, o*l mile north of elevation 1573 feet, same locality as Plummer*a (1930) 153-T-23 or P-50-3. J-50-41 Brownwood shale, Unit 1, Figure 20* J—so—s 4 to 5# Brownwood shale, Unit 13, Figure 20* Barnes, V, E. {1946) Ouachita facies in Central Texas. Bur. hcon* Gao. Kept, of 1nvcstigations rTIo* 2, pp. 1-12 H. X. Bay, U932) a studs, of care,,aln Fermajlvanian son-gl.pmeratea oi Texas, Texas univ. Bull. 3201, pp. 149-213. Bullard, F. M», and Cuyler, E* H* (1935) The upper Pennsylvan­ian and lower Permian section of the Colorado Klver vaTxST: BnTvT^CT.7Trol77^9l3^. * and Plummer, F. B. section of the (1939) Paleozoic Tluno uplift. Guide to geologic excursion sponsoredTy 4e«t Texas' Geol* doc., Fort Portia Ocol# ioc., Texas acad. Gel., and univ. Texas, 20 pp. Cheney, M. G. (1940) Geology of north-central Texas. Asor. *ssoc. Petrol. GeolT SuITT, vol. ”pp 7 . (1948) in Type localities lower Permlan~Upper Pennsylvanian. Guide'book atHone &«dl. toc.Cpringfield TripJune 11-12, 20 pp. , . ___ (1949) in Type localities Canyon-^brawn series rennaylvanian system. ebook aVilene Tieol. 3oc» 1949 Field Tri’p, Kdv. 2-4, 47 pp. * (1950) in Gtravm and older rocks of Pennsylvanian and ttisaissippian ayatsma of~ 'brown'7'San jgbT,' McCulloch7 *4ason.and' Mmhie oouiatlea. Texas, Guidebook Aoilene”" r GSSI7 Goc. K'J'd Sd«rd Yrip, KSvT"2.-4, 44 pp. and Cargle, D. H. (1951) Geologic map of Brown "Sourity, Texas (revised). Texas Univ., bur. aeon. Geoi. (in cooperation with U* 3. Gaol. Purvey). , at &X (1945) Classification of MaslaalPPlan ancT?ennayl7anian rocKS 'of North SerTca. Aster, assoc. Petrol, ieoi. "Soil, vol. 29, pp* li§~Tss. Jr., and V. «. (X9U) Tn» Cloud, l». m...Barnes, -,U.engurf;er croup of central Texas. Texas Univ. Pub. koZX (1946) v7J~pp7 Barnes, V. &*, and Bridge, doslab (1945) strati*­ . #raohy of the -illanburner ,troup in central Texas —• a ~ ogress report, taxaaImlY. Bub. 4301 1{15431, PP• 111 Cummins, If. F. (1891) Report on the geology of northwestern Texas, Texas Geol. Survey, 2n3 ann. Kept. (18?0), PPTTS7-552. DeFord, R. K. (1946) Grain-sige in carbonate rocks, .uner* Assoc. Petrol. Geol. Bull., vol. 35, pp* W2l-1926. Drake, H. F• (1693) Report on the Colorado coal fMd of Texas, Texas Geol. Purvey, XtSTami. Slept. pp. 35T<-CSS* Reprinted; (1917) Texas Univ. Bull. 1755, 75 pp. tumble, £• T. (1690) report of the Etate Geologist for 1669. Texas Geol. Eurvey, Ist Ann, kept. (136§j, pp. xvil-xc. Early, alberta Kuns (1951) of the Browwood shale, McCulloch Count!eaTTexas. unpublished X. a, yo£v• Texas, 9x pp** Eliae, M. K. (1937) Depth of deposition of the 3i£ Blue (late Paleozoic] sediments in nanaa*. Gaol. 3oc. AS. Bull.. » ii mmmmmmn winiiigniiifl W'liii 9 wiii »i«ywy* .<» vol. 46, pp. 403-432. Goddard, E. K*, et al (1946) Rock-color chart, prepared oy the Hock-color~7hart Committee, distributed by sat. Research Council. Hill, E. T. (1689) 2, portion of the geologic story of the Colorado xmer. seoT., ' vol. 3» pp. hudnall, J. E. and Pirtle, G. w* (1929), Geologic ?aap of Coleman County. Iexa a. Texas Univ., BurT^conTveoT, {in cooperation with tear* assoc. Petroleum Geologists). (193D, Geologic wap of drown County* Texas. Texas . Univ., dur. Scon. Seol. tin cooperation with aaer. «s»oc. Petroleum apologises). C. 0. (1936) of the Canyon and Cisco ftickell, groups on Colorado Elver in Brown and CoXeman Counties. TexasT TexiFHnTv7 IuTTT — Sidney (1912) hsscription £f thj Llano and burner .^uadranslea. U. 6. Gaol• Siirve aila» (Folio no. or Folio Field 115 ifeUT# lo pip* no* 163, Edition, pp. Plummer, F. B« (1945) Stratigraphy of the lower Pennsylvanian of^fSxaa."Texas UnlvV Fuß. ' coral~oearlmt strata 44f1l Tnmfpp"­ X (194?) Lower Pennsylvanian tlano strata of the riHon summary o!TclaaslHcatlon.""'dourPaleontology# * voTTTI, pp. 142-145. Plummer, F* B. (1950) |lie iterbonlferoua rocks of the Llano region of cenaralTexas. T.xaTTTnlvTTub. uW.iW^PP. and Koore, &• C* (1922) otratlgrapfty of the Pennsylvanian formations of north-central TexaoTrexas o'niv. 1 ppi . and Lcott, Gayle (1937) Upper Faleosoic ammonites ' In Tei^a. Texas Only* Bull* 3701, 516 pp. . et al (1937) Geologic F:ap of Coleman County* Texas (revisodTTexas Univ. Sur.Icon*SolTTin”cooperation with Ser. assoc* Petroleum Geologists) . Plummer, H* J« (1943) smaller roraainlfera In the Htrble Falls Lowerbtrawn strata' arouiSTThe . LTano uplift in Texas.' BnTv* Yuli* 4tol (19t4l — HoundyF* V*, Girty, G« H., and Goldman, M. I# (1926) ? Kiasisaippian formations of Ban Labe County. Texas. rf U» a* Biol* Survey FroTT Paper 14S, 63nn,pp. Sellards, &• H*, Adkins, %• o*, and Plummer, F. B. (1933) The Geology of Texes, Volume I, Stratigraphy. Texas CfnTvT "Bull* 323rTW32TTSC7 pp.~ Lpivey, K* C. arid Hobarts, X* 0* (1946) Lower Pennsylvanian terminology in central Texas, Amor. assoc• Petrol* 'wCTßir,~oi:^"ppr~i?i-iB6. Tarr, Ralph 3. (1390) Preliminary report on the coal fields of the Colorado River. Texas Qeolv Survey. Ist ann* B»pt7*(IWT7pp7Ty?i2i6. Thompson, M* L* (1947) Ltratigraphy and fußulinlds of pre-Saamoineaian PeimayXv^nTaß'''rocks. Llano upliftTTtexas. Jbiir* Paleontology, voi. Zl, pp. 147-154. wencworch, C. £. (1932) A scale of grade and class terms for clastic sediments. Jour* Geology, vol. Ju, pP« 5T7-39?* Williams, J. 3. (1935) Carboniferous Invertabrace fossils The vita has been removed from the digitized version of this document. GEOLOGIC MAP OF THE MERCURY QUADRANGLE,TEXAS n,miii* * >• A a of the western half of the on Plats 2. Structure contour map Mercury Quadrangle - Branch limestone. the bass of the Adams >r Plate 3. Map showing fossil localities in the Mercury Quadrangle. HBC tf numbers- !f are localities described by Bullard and Cuyler (1935); Wn numbers, illiams Eana J" numbers (1938); ”P ft numbers, Plummer (1950); n ,! numbers, Early (1951); E of localities can be found in new localities (this report). Description 1. and distribution of species, in Table Appendix A, Table I.-Distribution of in various formations in the Mercury Quadrangle. in various rormanons in me I aoie i.-uisinouTion or species mercury wuuurunyie. < UL SIRAWN BROWNWOOD ADAMS BRANCH CEDARTON WINCHELL PLACID / -1 \/ P-50­1 P-50­4 J-50-21 BC-35-1 \ W-38-1 C\J 1 00 PO 1 $ P-50-3 P-50-5 CVJ i in i UJ E -51 -4 E-51-5 E-5I-I4 J -50-24 vf 0 m 1 —> J-50­42 J-50-43 J -50-44 J-50-45 N­o m ¦ ~3 J-50 -48 J-50-49 J-50-50 J-50-51 J-50-52 J-50-53a J-50-54 J-50-55 J-50-56 J-50-57 J-50-58 J-50-54 to 58 (megafossils J-51-2 J-51-3 lO i m i —5 J-51-6 J-51-7 J-51-8 J-51-22 J -51-23 J-51-24 J-51-25 J-51-26 J-51-27 J -51 -28 J-51-29 J-51-30 / CVJ m i m i —> W-38-3 J-51-32 J-51-33 E-5I-I J-5l-32 1 33(megafossils) BC-35-2 BC-35-3 BC-35-4 BC-35-5 P-50-2 P-50-6 1 lO 1 J-51-50 J-5I-5I J-51-53 BC-35-6 — BC-35-7 BC-35-9 BC-35-1 0 BC-35-1 1 CVJ 1 m ro i o CD <*• 1 00 PO i £ BC-35-8 BC­35 -13 BRACHIOPODA Cerurithyris planoconvexa (Shumard) Chonefes granulifer Owen Chonetina flemingi (Norwood and Protten) X X X X X C. C. flemingi var. plebeia Dunbar robust a R. H. King and Condra X X C. rostrata Dunbar and Condra X Chonetes verneuilianus Martin • X Cleiothyridina orbicularis McChesney Composite argentea (Shepard) C. ovata Mather X X X X C. subtilita (Hall) X X X X X X X X X X X X X X X Crania modesta White and St. John X Cryptacanf hi a whitei Dunbar and Condra X Derbyia bennetti Hall and Clarke Derbyia crassa (Meek and Hayden) Derbyia crassa var. su be i r cut a r i s Dunbar and Dictyoclostus americanus Dunbar and Condra D. crassicostatus Dunbar and Condra Condra X X X X X X X X X - D. portlockianus Norwood and D. sp. Echinoconchus semipunctatus (Shepard) Hustedia mormoni Marcou Pratten X X X X X X X X X X X X X X Juesania nebrascensis (Owen) X J. nebrascensis n. var. aff. J. ovalis (Dunbar and Condra) X J. symmetri ca (McChesney) J. sp. Marginifera lasallensis (Worthen) X X X X X X X X M. muricatina Dunbar and Condra X M. M. splendens (Norwood and Pratten) wabashe nsi s (Norwood and Pratten) X X Mesolobus* mesolobus (Norwood and Pratten) X M. Neospirifer N. N. mesolobus var. rochellensis cameratus Morton dun bari R. H. King texanus (Meek) R. H. King X X X X X * X X X X X X X X X X N. triplicates (Hall) Orbiculoidea missouriensis (Shumard) X X Punctospi rife Rhipodomella R. r kent uckyensi s (Shumard) ' carbonaria (Swallow) carbona r i 6 var. subcircular is R. H. King X X X X X X X X X Rhynchopora magni costa Spirifer rocky mont anus Mather Marcou X X Astartella PELECYPODA concent r ica (Conrad) X X X X X Aviculopecten arctisu 1 catus Newell X A. Conocor dium sp. parrishi Wort hen X X Deltopecten texanus? Myalina subquadrat a M. wyoming ensis M. sp. Nucula anodontaides Girty Shumard (Lea) Meek X X X X X X X X X X X X X Nuculana arata (Hall) X PIeurophorus sp. ? Septimyalina perattenuata (Meek and Hayden) X X GASTROPODA Amohiscapha cattiloides (Conrad) Baylea subconstricta (Meek and Worthen) Bel 1 e rophon sp. Bucanopsis meekiana (Swallow) X X X X X X X * . ** X ‘i Euphemites sp. indet. Glabrocingulum grayvillense (Norwood and Pratten) G. cf. G. grayvillense (Norwood and Meekospira peracuta (Meek and Worthen) Orthonemo marvinwelleri ? Pratten) X - 4 X X X X X X X • X X X X X > Pharki donotus percarinot us (Conrad) Phymatopl eura mod os a (Girty) Sphaerodoma primogeni urn (Conrad) Trepospira depressa (Cox) X X X X X X X T. disco idol is Newell X X X Worthenia tabulata (Conrad) X X X X X CEPHALOPODA Liroceras liratum (Girty) Pseudorthoceras knoxense McChesney X X ANTHOZOA Lophophyllum L. profundum radi cosum MHne-Edwords Girty and Haime X X X X X - X X X X X X X X X X X BRYOZOA Fenest el la sp. Fistulipora nodulifera Meek Polypora sp. R horn bopor a lepidodendroidea Tabu 1 ipora sp. Meek X X X X X X X ECHINODERMA Andstrum ludwigi ? Archeocidaris sp. X X X X X C X X Ethelocri nus sp. X Paleoc hi r idot a plummerae Croneis X Platycrinus Plaxocri nus sp. sp. X X Protocaudina kansasensis (Hanna) X X FOR AMIN1FERA Ammobaculites stenomeca Cushman and Waters X X X Ammodi scus se mi con str i ct u s Waters X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Apterinella sp. Calcivertella adherens? Cushman and Waters X X X X X X X X - X Endothyra sp. Endothyranella nitida (Waters) X X X X X Fusulina ri ckerensis Thompson X Fusulina sp. Glomospira diversa Cushman and Waters X X G. reverse Cushman and Waters X X Hyperamminoides H. elegans proteus (Cushman (Cushman and and Waters) Waters) — f X X X X X X X X X X X X X X X X X X Orthovertella protea Cushman and Waters X X X X 0. sellordsi Plummer X X X X X 0. Polytaxis Triticites sp. scutella (Cushman and irregularis (Schellwein Waters) and Staff) • X X X X X X Amphissifes OSTRACODA centronotus (Ulrich and Bossier) X X X X X X A. ciscoensis Harlton X X A. Bairdia girtyi Knight oklahomaensis Harlton « X X *-¦ X X X X Cavellina lintris Coryell and Sample Coryellites Johnsoni (Upson) Cornigella tuberculospinosa Jones and Ectodemites dattonensis (Harlton) Kirkby X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Healdia H. colonyi Coryell and morginata? Harlton Booth X X X H. oklahomaensis Harlton X X X X X X X X X X X X X X X X Hollinella regularis Coryell Kirkbya firma Kellett Knightina ampla Kellett X X X X X X X Macrocypris menardensis Harlton Moorites minutus (Warthin) X X X X X X X X X X X X X X X X X Sonsobe 11 a carbonaria Cooper X X X CONODONTA Cavusgnathus flexa Ellison X X X X X C. C. giganta Gunnell lauta Gunnell X X X X X Y X X X X X X X X X X C. sp. X X X X X Gondella elegantula Stauffer and Plummer X Hibbardella sp. X Hideodel 1 a sp. X X X X X X X X X X X X X Idiognathodus delicatus Gunnell X X X X X X X X Ligonodina Ozarkodina sp. delicatu 1 a Branson and Me)il X X X X X X X X X X Prioniodus sp. X Streptognat hodus S. elegantu 1 us Stauffer and Plummer excelsus Stauffer and Plummer X X X X X X X X X X X X X X X X S. S. gracilis minutus Stauffer dnd (Ellison) Plummer X X X X X X X X X X S. S. Synprioniodina appletus sp. sp. Elli§on X X X X X X X