Publications of the University of Texas Publications Committee: F. w. GRAFF R.H. GRIFFITH G. C. BUTTE J. L..HENDERSON D. B. CASTEEL E. J. MATl!EWi FREDERIC DUNC-ALF C. E. Rowm The University publishes bulletins six times a month, so num­bered that the first two digits of the number show the year of issue, the last two the position in the yearly series. (For ex­ample, No. 1701 is the first bulletin of the year 1917.) These comprise the official publications of the University, publications on hUillJlnistic and scientific subjects, bulletins prepared by the Department of Extension and by the B-!lreau of Government Re­ ' search, and other bulletins of general educational interest. With the exception of special numbers, any bulletin will be sent to a citizen of Texas free on request. All communications about Uni­versity publications should be addressed to the Chairman o! the Pabliaa.tions Committee, University of Texas, Austin. B 214-620-3m-L University of Texas Bulletin No. 1857: October 10, 1918 Geology and Mineral Resources of Crockett County With Notes on the Stratigraphy, Structure, and Oil Prospects of the Central Pecos Valley By R. A. LIDDLE AND T. M. PRETTYMAN BVBEAV OF EOOllOXIC GEOLOGY .oUl'D TECJDl'OLOGT DIVISION OF ECONOMIC GEOLOGY J. A. VDDEll Director of the Bureau and :e:ead of the Division PUBLISHED BY THE UNIVERSITY SIX TIMES A MONTH. AND ENTERED AS SECOND-CLASS MATTER AT THE POSTOFFICE AT AUSTIN, TEXAS, UNDER THE ACT OF. AUGUST 24, 1912 The benefits of education and of a!leful knowledge, generally dJJrused through a ·community, are essential to the preservation of a free govern• ment. Sam Houston Cultivated mind is the guardian genius of democracy. • • • It Is the only dictator that freemen acknowl· edge and the only security that free­men desire. Mirabeau B. Lamar CONTENTS Page. · Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 7 Location and Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . . . . . 7 Geography and Physiography.................·. . . . . . . . . . . . . . . . . . . 8 Relief . . ......... ........ ....• ..... . .......... .... ..... . ... . · 9 Climate and Rainfall...-.. ............................... : . . . . . 12 Drainage . . . . ...... _. .•............. , .............. , . . . . . . . . . . 12 Soils .......·............................ , .....•.......: . . . . . . 12 Top lands . . . . . .........,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Bottom lands . . . . . . .. ........................ .•. ....., . . 13 Flora and Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . . . . . . . 14 ~tratigraphic geology . . . . ..........·.·...·. . . . . . . . . . . . . . . . . . . . . . . 17 Nature and purpose of Investigation...'......................... 17 Control . . .......•. .. : . ........................ ~............ 18 Synopsis of formations from Pandale to Texas-New Mexico line.. 18 Strata exposed on Pecos River in Crockett County. . . . . . . •. . . . . . 18 Review of literature on the Pecos Valley. . ... . . . . . . . . . . . . . . . . . . . 20 Description and areal Distribution of formations in Pecos Valley 33 Permian ..............-. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Rustler formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Red Beds . . . . ...............-...... .. ......•.. .... ... , . •. 34 Triassic .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . 34 1Dockum beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '37 Comanchean Cretaceous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Trinity· Division . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . . . . . 42 Trinity conglomerate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Basement sands . . . . ......... : ........-. . . . . . . . . . . . . . . 43 Fredericksburg Division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Walnut clay ..................................·. . . . . . 44 Comanche Peak limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Edwards limestone . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . 45 Pleistocene and Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Structural Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Pre.Comanchean Movements .............. : . . . . . . . . . . . . . . . . . . 47 Post-Comanchean Movements . . . . .............. ; . . ••. . . . . . ••. 49 Igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Description of Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Section No. 1, Pandale section........................... 52 Section No. 3, Chandler section.......................... 52 Sectfon No. 3, 14 mile point section...................... 53 Section No. 4, 9 mile point section............... . ....... 53 Section No. 5, 3 mile point section........................ 54 Section No. 6, Camp section.............................. 54 University of Texas Bulletin Page. Section No. 7, 7 mile point section..... . . . ............... 56 Section No. 8, Crossing section........................ . .. 57 Section No. 9, Round point section....................... 57 Section No. 10, White Point section....................... 57 Section No. 11, W + 1.................................... 58 Section No. 12, W + 2............ .. .-.. .. .. .. .. .. .. . . .. .. . 5·8 Section No. 13, W + 3.................... .• . . . . . .. . . . . .. . 58 Section No. 14, W + 4........... . ........................ 59 Section No. 15, Diamond Y Draw. . . . . . . . . . . . . . . . . . . . . . . . . . 59 Section No. 16, Girvin Highway .Bridge Section............ 59· Saline solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . .. 60 Sheffield Terrace . : . . .......................... ; . . . . . . . . . . . . . . 66 Structural features of the Pecos Valley in their relation to PetToleum Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . 67 Economic Notes .... ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Roads .. . , . .......... ~ ................................... 73 Gravel . . . . . ...................... :. . . . . . . . . . . . . . . . . . . . . 75 Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 76 Building stones . . . . .................. , . . . . . . . . . . . . . . . . . . 78 Clay ...........·............ •. . . . . . . . . . . . . . . . . .. . . . . . . . . 80 Lime and Calcareous Cements. ............................ 82 Salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Gypsum and anhydrite .................·....... . .. . .. .. . . 83 Calcite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Glass sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Flint or chert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Oil Possibilities on University lands.. .. .. .. ..................... . 85 · Location and Area . . . . . ...... . ................. : . . . . . . . . 85 Topography and drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . 85 Geology . . . . . ....... .................... .............. ; . 86 LIST OF ILLUSTRATIONS Plate 1. Areal geologic map of Pecos Valley. Pocket. Plate 2. Horizontal and vertical sections along the Pecos River. From Pandale to Barstow. Pocket. Plate 3. Land map showing location of Sheffield Terrace. Pocket. Plate 4. Geological map of Ccrokett County, showing location of Uni­ versity Lands. Pocket. Page Figure 1. Geologic column showing the formations exposed on Pecos River between Pandale and Barstow . . . . . . 19 Figure 2. Correlation .of Comanchean Cretaceous in Pecos Valley with San Angelo and north-central Texas sections.. 61 Figure 3. Diagrams showing conditions encountered in obtain­ing water from the Edwards limestone.. . . . . . . . . . . . . 77 Figure 4. Structural reconnaissance map of the Sheffield tract of University lands......... , . . . . . . . . . . . . . . . . . . . . . 91 Figure 5. Structural reconnaissance map of the Barnhart tract of University lands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Figure 6. Structural reconnaissance map of the Big Lake tract -Of University lands... . .. .... ...... .. ... . . . .. . ... . . 93 THE GEOLOGY AND MINERAL RESOURCES OF CROCKETT COUNTY BY R. A. LIDDLE AND T. M. PRETTYMAN 1 INTRODUCTION LOCATION AND AREA Crockett County, containing 3004 square miles, is situated in the southwestern part of the Edwards Plateau, east of the Trans-Pecos Plains, and southeast of Toyah Basin. The Pecos River, flowing to the southeast along the boundary between Crockett County and P ecos and Terrell counties, on the southwest and west respectively, also forms the demarcation between the Edwards Plateau and the Trans-Pecos Plains. The extreme northwestern corner of Crockett County lies within Toyah Basin. To the north of the county are the southern boundaries of Crane, Upton, Reagan, and Irion counties, ap­proximately along the 31st parallel north. To the east, Schleicher and Sutton counties bound Crockett County approxi­ _mately along the lOlst meridian west. Immediately to the south is Val Verde County. Ozona, the 'County-seat and the only town in the county, is in the east-central part. It has a population of about 430, and. is the location of the only school in the county. The school build­ing, together with a number of other public and private insti­tutions, is constructed of undressed native Edwards limestone.. This is a very durable material, works readily, and on aC'Count of its hardness and homo-geneous nature, weathers slowly and eveniy. When :first quarried, it is a very bright gray, but later turns to a pale straw color, due to a partial oxidation of the ferrous elements. Ozona has no manufacturing industries, except a saddlery 'Manuscript submitted October, 1919. Published December, 1920. University -0f Texas Bulletin and a blacksmith shop. Its distance from a railroad makes any industry necessitating more than local transportation unprofita­ble. The Kansas City, Mexico and Orient Railroad runs east ·and west through the southern part of Irion, Reagan and Upton counties, parallel to the northern boundary of Crockett County and about 30 miles north of Ozona. Barnhart, in Irion County, is the nearest railroad station. All transportation within the county is by means of auto-truck lines or mule teams. The principal roads, being in good condition, materially assist in transportation to the interior. The Government Military Highway from San Antonio to El Paso runs east and west across the north-central part of the county. From this, secondary roads lead to the interior. GEOGRAPHY AND PHYSIOGRAPHY The Pecos River, forming the west and ·southwest boundaries of Crockett County, and flowing southeast along ihe dip of strata, affords an excellent opportunity for studying the Comanchean-Cretaceous series. By extending the line of inves­tigation along the river into the adjoiniJ1g counties, a complete section of the Comanchean-Cretaceous can be obtained. The· bluffs on either side of the river make desirable vertical sections. Howard's Draw and Live Oak Creek are the two main drain­age features of the county. The former is an intermittent stream and is dry the greater part of the time. Live Oak Creek, the only flowing stream in the county, is fresh water, and fed from springs in the Edwards limestone. Both of these drain into .the Pecos River, which empties into the Rio Grande. ' F'or a considerable time after each rain, the Pecos has a red, muddy appearance, due to the material being transported. As 'it flows for some distance through the :ij,ed · Beds of the Permian, the Triassic, and the red sands and sandy clay of the lowest Comanchean-Cretaceous, the material which it and its t:ributaries have eroded colors the ·water to a deep red. The· alkali in solution renders the river water unfit for do­mestic use, but it is not present in sufficient quantities to be hariri.fUl to stock. Geology and Mineral Resources of Crockett County RELIEF The chief topographic features of the Comanchean-Cretaceous, as developed in Crockett County, consist of deep, narrow, steep­walled canyons, high plateaus, and :flat-topped hills in the river district. This area constitutes the greatest relief in the county. The boldness of the river district topography is ma­terially modified as the distance from the river increases. At the river banks, it begins in precipitous bluffs and cliffs, carved out of the massive · Bdwards limestone, and grades back un­noticeably until it terminates in the broad expanse of the Ed­wards Plateau. These vertical bluffs of great height along the river are formed by the erosive agencies undercutting the softer clays and sands directly beneath the resistant Edwards lime­stone. Such a nature of erosion also renders it practically. ini.­possible to judge accurately the dip of the strata along the river, except over oonsidera:ble dista~ces, and then allowance for slumping is necessary. All of the prominent relief in the county, such as hills, draws, canyons, ridges, peaks, and plateaus, is due to differential erosion. The harder strata, being more resistant, have remained in places, and have been little affected; while the softer material has been carried away. The cliffs along the Pecos gradually give way to low~r hills and ridges and less sharply defined canyons, the greater the distance is from the river, until at the northern boundary of the county the canyoru; have become broad valleys, and the steep banks and canyon walls have changed to grassy slopes. Farther to the north these become high plains, the cap-rock of which is the top of the third division of the Edwards limestone. The relief of this plateau is confined to very local slopes toward drainage channels, which are broad, shallow depression.~ when at some distance from the edge of the plateau. At the edge of the pla­ teau, however, the drainage consists of short, narrow, steep­ walled gullies, leading to the intermittent streams in the valleys. The stratigraphy of the county, as well as the agents of erosion, has had a great influence upon its relief. As the whole area of Crockett County, with the exception of the lower walls of the Pecos, is covered to a great thickness by the resistant homo­ University of Texas Bulletin geneous Edwards limestone, and since i.n the area examined the Edwards has only a very slight dip to the southeast, the result has been a dip slope of very low degree, to the southeast. Transit examinations of extended areas, such as . the Uni­ versity tracts, show a S 60°-70° E dip of from 0 minutes to 5 minutes. This slight departure from the horizontal is only ob­ tained by very accurate measurements. The agencies of erolilion, of which rainfall, chemical action of ground and underground water, daily range of temperature, and the difference between day and night temperatures are the prin­cipal forces, also have a great modifying influence upon the appearance of the earth. The rainfall, coming as it does in cloudbursts which continue for only a very short time, and falling upon the sparsely vegetated soil, has dissected the Ed­wards limestone in this region to such an extent that for :fifteen or twenty miles back from the river the topography is a con­tinuous series of drainage channels, whose walls become steeper and steeper toward the river, where they :finally terminate in high bluffs. The isolated buttes, mesas, and small conical peaks are the remnants of the Edwards Plateau. The change of temperature between day and night is considerabl~, and also assists the rainfall in dissecting the strata. . Masses of rock as her~ exposed, being subjected to a rapid change of tempera­ture amountfog to as much as from 30° to 40°, are irresistibly expanded and contracted, and as expansion and contraction are not uniform, internal and external stresses are produced, thus exfoliating the outer surface. The material thus exfoliated is carried away, leaving the bed rock exposed at practically all times. The chemical and physical actions of underground water are as important as are the mechanical factors. Numerous caves of all kinds have been dissolved out of the Edwards limestone, from cavities a few inches in diameter to great caves with . miles of widening passages. This undermining of.the rocks tend<: to break down the resistant cap, and gives thf we_athedng aw~nt better access. _About five ~iles south of Barnha;t, on the Barnhart-Ozona road, an old sink-hole can. be seen, where the solvent action of­ Geology and Mineral Resources of Crockett County 11 .the water has eroded a hole four hundred feet in diameter, and fifteen feet deep. What remains of the high plains .is called the Edwards Plateau, from the top of which the horizon of the surrounding country is almost level. 'This is due to the absence of any noticeable dip in the Edwards formation, in the region. This very resistant and uniform limestone forms a hard level cap which protects the Walnut clays and Basement sand::i, four to iive hundred feet below. The Basement sands are only exposed for some forty or fifty feet in the·river banks, along the south and southeast part of the Pecos, forming the west and southwe.st boundary of Crockett County, and in a great many places where only a few feet ·are exposed, ibs covered by the Edwards limestone, which has under­ cut and slumped to the"stream bed. However, farther up the river, beginning about twenty miles north of Sheffield, and continuing to the nort~west corner of the county, since there is some two or three hundred feet of these sands exposed, it has a marked effect upon the topography of the county. This is noticeable in the contour of the hills and valleys adjacent to the river. · The base of the Edwards limestone in the vicinity of the 102nd meridian crossing is about half-way up the slopes of the hills, and from this base · there is a gradual gradient to the allu­ vial plain or the water-level. The valleys of both primary and secondary streams are low, wide, and rounded, as the debris has formed large talus slopes. The hills recede farther from the river, and strongly contrast the vertical bluffs farther toward the river mouth. The tops of the hills are flat plateaus, mesas, and buttes, and the escarpments are formed by the Edwards limestone being much more resistant than the underlying Basem.ent sands. F'rom the southeas+. to the northwest corners of the county, along the river valley, there is a gradual transition from the severe topog­ raphy of the true Edwards region to the ffiQre modified well­ rounded valleys, capped by·the lower part of the :first division of the Edwards limestone. This is due to the southeastern dip of the Comanchean-Cretaceous strat.a., which reveals a proportion­ ately greater amount of Basement sands, and less amount of Ed­ wards limestone from southeast to northwest. University of TexM Bulletin CLIM;ATE AND RAINFALL Typical of the region embracing the western portion of the Edwards Plateau and the Trans-Pecos Plains, CrockettCounty has a climate that is semi-arid, quite warm, and very uniform. Wea th er reports from Fort Stockton in adjacent Pecos County to the west, and from Eagle Pass to the south, indicate an ave~·­age anpual rainfall of about 16 inches in the northwest portiol} of the county, and from 17 to 18' inches in the southeast part; the humidity increasing in this direction. The moderate eleva­tion of 2000 feet, latitude of 30 degrees north, and a low humid­ity, cause relatively high temperatures to prevail during the day, which fall much lower at night. The county lies wholly without the pathway of storms and other meteorological disturbances, thus giving a uniformity of climatic co'nditions. Precipitation occurs most often during the late spring and middle fall. Sudden torrential rains of short duration are characteristic of the region, though long periods of drought are not uncommon. The wind is usually of moderate velocity and from the west or southwest, except during the infrequent rains which usually come from the southeast, and at the time of the "northers", at which time it is from the north or northwest. DRAINAGE The drainage of Crockett County is toward the south and southeast, principally through Live Oak Creek, and Howard's Draw, into the Pecos River. Live Oak Creek and its tributaries drain the northwestern part of the county, while Howard's Draw, which flows across the entire county from northeast to southwest, drains the remainder; except for a number of dry creeks along the south, southwest and west, which drain directiy into the Pecos. All of the drainage features ultimately find an outlet in the Pecos and Devil's Rivers. SOILS The topographic features of the . county make it desirable to divide a discussion of soils into two parts: (1) top lands and (2) bottom lands. Geology and Mineral Resources of Crockett County 13 Under top lands is classed the sgil upon the plateaus, mesas, buttes, and that along the steeper slopes. Under the head of bot~om lands are classed those soils which have accumulated on the more gentle slopes of the valleys and in the valley and river bottoms. On the uplands there is little soil in: any place, and in a great majority of instances there is nothing but the gray Edwards limestone, with a few broken fragments of the same material scattered about. The intermittent rainfall followed by periods of extreme drought is anything but conducive to soil accumulation upon the hiithlands. The little calcareous soil in situ which has been de­ <.iomposed from the underlying resistant Edwards limestone is quickly washed away by the deluge before it has had time to ac­ cumulate to any depth, or.gain a protection of vegetable matter, which would increa.Se both the depth of the soil andits productiv­ ity by adding carboniferous matter. Thus when present upon the plateaus and steeper slopes, the soil i.s poor and thin. On the bottom lands, although the same forces are at work, there is considerable soil accumulation, due to the fact that the . slopes are considerably less, and als.o to the dual source of the material. Because of the nature of the grac;Ies, the residual soil has a mqch better chance to accumulate than on the uplands, and the soil carried down from above is either deposited in the valleys or river bottoms. River overflows also add to this ma­ terial. Vegetable matter which has had an opportunity to grow and corlect holds the soil in place, adds to the amount, and en­ riches the soil to a great extent, so that in the bottom lands good soil for agricultural purposes can be found. The principal ingredients, silica, lime, and vegetable matter in such forms and proportioJ!S as exist in these valleys and alluvial flats, form a c.lay loam, which is especially adapted to plant life. From southeast to northwest in the Pecos valley, there is a gradual increase in the amount of sand in the soil, and a deepen­ ing of the reddish color, due to the increase in amount and area of the red Basement sands. Univ,ersity of Texas Bulletin FLORA 'AND FAUNA Vegetation upon (1) top lands and (2) bottom lands, though individual and characteristic of each, is nevertheless typical of the semi-arid climate of the county. 'Two of the most important factors determining such a vege­tation as here exists are the supply of moisture and the relative length of ti.Ine in which it is available for plant life after each rain. IJying almost at the center of the semi-arid southwest, over three hundred miles from the Gulf of Mexico, with the broad, high Edwards Plateau reaching fo the Llano Estacado on •he · north, the dry mountains of northern Mexico on the south and the southern extension of the Great American Desert ter• minating in the foothills of the Cordilleras to the west, the vegetation of necessity must adapt itself to such an environment. The prevailing winds, being froin the west and southwest, are wrung dry of all their moisture in passing over the mountainous regions, after which they cross the arid country to_ the west and south before reaching the Central Zon.e. :ffilre they not only supply no moisture, but, being hot and dry, carry away from the soil· and plant surfac.es practically all the moisture brought from the southeast and east. The absence of clouds and vapor in the air over nearly all months of the year increases the intensity of the sunlight, and the white calcareous rock and soil reflect it with practically no absorption; so that the great daily extremes of temperature demand an adjustment of plant life to . extreme conditions. As a result of these combined environmental factors, to­gether with the nature of the soil upon the uplands, there is a_ meagre vegetation. The rainfall from the southeast not only is very small, but in the uplands it is i)racti:eally all run-off, thus giving even a less supply of moisture than in the bottom­lands. The ability of scrub-cedar, mesquite, scrub-oak, cacti species, sotol, lechugilla, chaparral, Spanish dagger, greasewood, and yucca to withstand the severity of these .conditions makes them practically the only vegetation upon the uplands. The past season, however, has been one of extreme precipitation over Geology and Mineral Resources of Crockett County 15 the county, and there is a good supply of grass and a great . number of wildflowers in addition to the plant life mentioned as the normal vegetation of the uplands. As these lands are in excess, the vegetation upon them has also a great economic value, as this area because of its mild win­ters is available for the pasturing of stock throughout the entire year, and the capacity of the county has practically no stock limits except the supply of food and water. The long drought which lasted until the beginning of the recent rainy season has reduced to a minimum the goats, sheep, and cattle. The bottom lands, receiving in addition to their soil in situ t.he wash from the uplands, and because of their better water storage facilities, support a more luxuriant vegetation, which in turn supplies humus to the soil. . Over the gr.eater part of these bottom lands there is a good covering of grass, except in extremely dry seasons. Upon the alluvial flats are found live-oaks, a few cottonwoods, a great. amount of mesquite, some willows, and hackberries. Some of these alluvial flats are cultivated, the supply of water being in some cases artificial, and in others natural. The Bru:iement sands are expqsed only in the Pecos Valley in Crockett County, in the central and southern part of the county on the river banks. Here they are in the form of vertical walls, and are undercut and carried away for some distance under the Edwards limestone, which has faH.en to the stream bed. There is practically no opportunity for vegetation to exist. Far­ther up the river, however, where some 200 or 300 feet are ex­posed in the river valley, the lower part of the bluffs and hills along and near the river has smooth gradual slopes to the river. These gradients in the stream .and river valleys are in marked contrast to the vertical walls in the southern part of the county, and support a flora which is more typical of a sandy soil. The high porosity of the soil also permits. quick, deep penetration of surface waters, and a similar rate of drying thr:ough the atmosphere. These conditions, and also the abrasive effect of wind-blown particles, make it possible for only the hardier plants to exist. In places, a cQmbination of this sand, silt, from the river, and kaolin from the Edwards limestone above, forms a very productive sandy loam. University of Texas Bulletin Animal life, typical of the southwest, is plentiful in all parts .of Crockett County. An abundance of food, easy protection from their enemies, and freedom from long-continued severe climatic conditions permit of a varied fauna. Several species of wolves are so plentiful as to necessitate great vigilance among the sheep ranchmen to protect their flocks from these marauders. · Occasionally a panther or bob-cat is found, but only at rare intervals is such a large carnivorous animal encountered. Jackrabbits, cottontails, prairie dogs and ground squirrels are especially numerous and may be seen in great numbers in an hour's .drive in any direction. Deer, foxes, ­ gophers, coons, ·opossums, weasels and other wary creatures, make their homes in the more· wooded and less frequented · sections. Along the sides of the numerous steep-walled canyons, the Edwards limestone usually weathers cavernom, making suitabl~ caves where the animal life may be sheltered. The thorny nature of the vegetation as well as the many crevasses among the rocks offer protection from their enemies when pursued. The bird life too includes a few species some of which have adapted their habits to the almost treeless region, building their nests among the rocks instead of in the branches of trees. Swal­ lows make clay houses along the cliffs. Owls, hawks, and bats have their habitat in holes of the precipitous rock ledges. Pheasants, quail, paisano, larks, killdees, mockingbirds, blackbirds, scissor­ tails, redbirds and sparrows are more or less common on the shrub-covered lowlands. Reptile life during the warm weather is plentiful. Rattle­ snakes, bull snakes, moccasins, and prairie runners are the most common. Chameleons, horned toads, lizards, scorpions, taran-· tulas, spiders and numerous insects are in abundance. In the Pecos River and the lower reaches of Live . Oak and Howard's creeks,. several kinds of fish are found, but in this dry, semi-arid country with few streams, water fauna is compara­ tively insignificant. Geology and Mineral Resources of Crockett County STRATIGRAPHIC GEOLOGY NATURE AND PURPOSE OF THE INVESTIGATION In an investigation recently made by Dr. Udden in the Glass · Mountains district of Brewster County, the trend of the Mara­thon Mountains was observed to extend from the Solitario Uplift on the Brewster-Presidio County line toward the nortneast. The general direction and appearance of the fold suggested the possibility of its extending farther to the northeast and in­fluencing the local or regional stratigraphy of .the Edwards . Plateau or Toyah Basin.1 In the present survey a section along the Pecos River from Pandale Crossing to the ;Texas and Pacific Railway crossing near Barstow was given a detailed examination before any of the land in the valley was examined in recon­naissance for structure. Althoqgh Permo-ca:rboniferous structure antedating Coman" chean'-Cretaceous deposition may underlie the P~cos Valley, it is only through a subsurface examination that it can be detected, since folding which terminated at the md of the Carboniferous or Permian would not be reflected in the overlying strata. Following the stratigraphic work, the three University tracts in Crockett . County, namely, the Sheffield, Barnhart, and Big Lake tracts, were carefully examined in reconnaissance, as. condi­tions did not permit a stadia survey of the entire areas. All ob­servations for structure were taken with a transit. Any movement later than the Paleozoic, which would influ­ence the geology of the counties containing University land along the Pecos River would be evident in a section between Pandale and Barstow. As the purpose of the survey is to begin a series­of county geologic reports on the southwest, including detailed structural examinations of University lands, it is not necessary · to carry the stratigraphic work beyond the limits where it influences the area under examination. Later, if desirable, it can be continued the entire length of the Pecos Valley.' The Balcones fault on the southeast and the Rustler Hills on the nort.hwest make it necessary to give those localities ex­tremely careful study, and the time available and the nature of the work did not warrant an investigation of these two areas. Representative collections of fossils have been made at various 1The first known suggestion of the northeast extension of the Mara­thon Mountains was made by.R. T. Hill in U. S. G. S. Folio 3. Physical Geography of the Texas Region, p. 4. Washington 1900. University of Texas Bulleti?l localities. Only such identifications were made m the field as were found necessary for correlation. CONTROL As the time did not permit the developme?-t of a triangula-· tion system, and as no topographic work has been done in the county, it was necessary to establish control for both the strati­graphic and .structural work. _At the point of observation 1,4 mile north of the steel bridge across the Pecos River, three miles east of Sheffield on the Ozona­Sheffield road, the latitude is 30° -43'-45" N. ; longitude 101 °-54'­30"_W; magnetic declination 11 ° E. This control, from which traverses were run, was u8ed for .all th"e work along -the Pecos River and on the Sheffield tract. Since the majority of the connties -containing University land border on the Texas portion . of the Pecos Valley, throughout practically it\ entire length, and as the river affords the ·best opportunity for a geologic study of the region, a careful examin­ation of the valley from Pandale to the Texas-New Mexko boun­dary was made, .and horizontal and vertical sections were taken from Pandale to Barstow. The following geologic column shows that formations ranging from the Triassic through the Comanchean and including Pleis­tocene and Recent deposits are exposed. SYNOPSIS OF FORMATIONS FROM PANDALE TO THE TEXAS-NEW M•EXICO LINE P!eistocene and Recent Alluvium and Conglomerate Edwatds limestone Fredericksburg Comanche Peak limestone { Comanchean Walnut clay Cretaceous rBasement sands Trinity ~ Trinity Co~glomerale orl equivalent Trias!lic Dockum Upper Trujillo Permian Rustler, Red Beds STRATA EXPOSED ON PECOS RIVER IN CROCKETT COUNTY In Crockett County, only formations from the Basement sands through the Edwards· limestone, including some Pleistocene Geology and Mineral Resources of Crockett County AGE SYSIEM DIVISION FORMATION GEOLOGIC COLUMN SHOW[NG FORMATIONS EXPOSED ON PECOS RIVER BETWEEN PANDALE AND BARSTOW F ig. 1. ,. University of Te3!as Bulletin and Recent alluvium and conglomerates, are exposed. On the geological map of Croc~ett County the areal distribution of the geologic formations outcropping within the county is shown. REVIEW OF LITERATURE ON THE PECOS VALLEY During the years 1855-1856 the first geological exploration of •the Pecos Valley was made. An expedition commanded by Captain John Pope, of the Corps of Topographical Engineers of the United States Army, under orders of the War Department, left Indianola on the Gulf of Mexico, in 1855, and in 1856 com­pleted an investigation of a large portion of the plains of Texas · and New Mexico for artesi;ni water. "To ascertain the practi­cability of building the Southern Pa'Ci'fic Railroad .was also an especial object to this Expedition".1 1 To this expedition, in the capacity of paleontologist and geolo­gist as well as surgeon, was attached Prof. Geo. G. Shumard: The results of this exploration were published ill 1886 under the · title ·of "A Partial Report of the Geology of Western Texas", by the State of. Texas. On the 4th of April, 1855, the expedition left Indianola and proceeded northwest, reaching ~an Antonio on the 11th of April. After a short stay in San Antonio the party continued north­west and on the 12th of May reached the lower Emigrant Cross­ing of the Rio Pecos. This crossing is 3 miles northwest of Fort Lancaster, and about 3;6 miles southeast cif Sheffield, in Pecos County, just north of the highway bridge over the Pecos on the Sheffield-Ozona Road. No better digest can be given of the geology noted on this expedition than Prof. Shumard 's own notes covering the area included in the Pecos Survey, from his Journal· of Geological Observations, entries from May 9-21, 1855. May 9.-Leaving Howard's .Springs we continued to wind our way through the canyon, which varied from a few hundred yards to several miles in width, exhibiting an uneven floor, and in many places a mod· erately fertile soil. About eight miles from the springs we again reached the summit of the table land, over which we traveled the remainder of the day. ·1Introduction, p. vii, Geol. Western Texas, by B. F. Shumard. Austin, 1886. Geology and Mineral. Resources of Crockett County As before, the surface of the table land or plateau is here covered with coarse fragments of limestone, and is traversed by immense rocky canyons, some of them many miles in length. This feature, together with the almost entire absence of soil, imparts to the face of tha country a remarkably sterile and forbidding aspect. Distance, 15! miles. 'The route travelled from May 9-llth lies approximately be­tween Pandale, the southernmost point reached on the present survey, and Live Oak Creek, near old Fort Lancaster. The canyon by Howard's Spring is one of the intermittent stream beds which empty into "the Pecos, and the tableland over which they travelled is the Edwards Plateau, the top of the third di­vision of the Edwards limestone., May lp.-After a travel of about sev.en miles we entere.d another canyon, similar iii all respects to the last. . The strata of this canyon present a slight dip E. S. E. and assume a variety of colors-white, gray, yellow, brown, red, and black. In some places they are highly ferruginous,. and contain nodules of flint in great abundance; at several points thin seams of selenite were observed traversing the limestone. The principal fossils seen to-day are Arcopagia Texana, Gryphaea Pitcheri, Janira quadricostata, 'dardium muztistriatum, Ammonites acuto-carinatus, and Pterodonta (Eulima) subfusiformis. · Late in the da'y we came to Live Oak Creek, a beautiful stream of clear water, flowing over a rough, rocky bed. The temperature of this stream was found to be 70 degrees F. ·The soil, during the greater portion of the day's march, was barren, being composed princip.ally of disintegrated limestone; but in · the vicinity of Live Oak Creek it is moderately fertile, and supports a sparse .growth of oak trees. Distance, 11 miles. As previously mentioned, the Edwards Plateau generally supports a scanty vegetation, while that of. the valleys is more luxuriant. May 11.-Beyond Live Oak Creek our route lay over a broken, rocky region; characterized on all sides by rough hills and cliffs of thin-bedded Cretaceous Limestone, some of which attain a height of more than five hundred feet. As we progressed through the canyon it widened rapidly, and 1'1.nally opened into the broad valley of the Rio Pecos, which here pursues a tortuous course between rough hills and picturesque cliffs from four to six hundred feet high. University of Texas Bulletin The water of this stream is of a deep red color, and contains some · muriate of sodium. Its average width is about seventy-five feet: Tem­ perature 70 de.grees F. The valley possesses a red clayey soil, which -appears to be moder­ ately fertile. Near the bed of the river I observed a layer, a few feet thick, or coarse breccia, made up of fragments of limestone, loosely cemented with a calcareo-ferruginous paste. Distance, 7i miles. Live Oak Creek is the only permanent stream in Crockett County. The coarse breccia mentioned by Prof. Shumard was identified in situ, near the mouth of Liv.e Oak Creek at the Pecos River, to b~ a recently cemented conglomerate, containing a great variety of material ·both igneous and sedimentary, deposited by the river and cemented as Shumard mentioned, with a 'Calcareo­ferruginous paste . •'IIay 12.-The greater portion of this day was spent in exploring the hills and cliffs in the vicinity of our camp on the Rio Pecos. The thick­.ness of the Cretaceous Limestone here was estimated·.at not less than a thousand feet. In its lithologicat character it varies considerably from that previously encountered, consisting for the most part of hard, compact rock, often crystalline, and usually of a light bluish color. The greater .portion .of the mass is .almost ·entirely destitute of organic remains, but near the summit of the highest hills I discovered a band of soft earth; limestone, of a bright yellow color, highly charged with elegantly preserved fossils, which have been determined by my brother, Dr. B. F. Shumard, to belong chiefly to the following species: · Ammonites acuto-carinatus (Shum.), Oeratites (Ammonites) Pedernalis ( Roem. sp.), Ptei·odOnta subfusiformis (Shum.), Scalaria vertebroidesr (Mart. sp.), Nattca (Globi concha) tumida (Shum.), Arcopagia Tex­ana (Roem.), Panopora T exana (Shum.),. Janira quadricostata (Sow. sp.), Exogyra T exana (Roe~), Grypha~a Pitcheri (Mcirt.), Homomya alta (Roem.), Oardium multistriatum (Shuri:i..), Hotectypus planatus; (Roem.) , and Toxaster T exanus (Roem.). In addition to these we found a number of species not yet described. After leaving the Pecos crossing we wound our way amid rough hills and cliffs of the same geological constitution as those just described. Everywhere we found a barren soil, composed almost entirely of pul­verized limestone. Distance, 5~ miles. The area referred t~ under this date is in the vicinity of the Sheffield-Ozona highway bridge, and the formations exposed Geology and Mineral Resources of Crockett County · 23 are described in de'tail under Camp Section (Pl. 2). The soft, bright yellow, earthy limestone from which Shumard obtained a good collection of fossils also .afforded the present survey a fine collection. It is described as I Yellow Peak horizon from asmall conical peak 4 miles east of the Sheffield-Ozona highway bridge, at which the majority of the collection was made. It is· at the bottom of the second division of the Edwards Hmestone. Ma,y 13.-During the entire day we traveled through the valley of the Rio Pecos. For the first six miles the rocks do not differ in general appearance from those observed yester!lay. Beyond this the hills as­sume a more regular outline and the cliffs are less -rugged in their aspect. The former are generally smooth, of a conical form with . truncated apices. At first they are closely aggregated, but as we ptQgress ·they become widely separated by smooth and g_ently undulat­ing praide. Their height is from ·five to eight hundred feet, and they present every indication of having once formed; a portion of the ele­vated table land, now several miles distant, and from which they have 'been separated by denudation. The different strata composing them are found to agree in every particular w,ith those composing the table land. Near the summits of the highest of them the strata are very prolific in well · preserved organic remains. The following are the prevailing forms:. Ammonites vespertinus, Ammonites Marcyana, Pteroctonta subfusiformis, Terebratuza Wacoensis, Janira Texana, Lima Wacoensis, Oardium Sanci-Sabae, Trigonia (undt.), Gr'Jiphaea Pitcheri, and Hemi­aster ~Zegans. · With these I also found examples of Gryphaea which are not to be distinguished from.those figured by Mr. Marcou under the names of G. Marshii and G. Tucumcarii. Near the base of o~e of the hills I observed layers of soft, thin-bedded, quartzose sandstone, about twenty feet in thickness. This rock is fine ·grained, of a light yellow color, and is conformable with the limestone. Thin seams of white gypsum and selenite were observed to occur at i;1everal points. Th~ surface of the valley is for the most part thickly strewn.with coarse angular fragments of li~estone, which are not infrequently firmly cemented into calcareous brecchr. .Near .the base of some of the hills this breccia often presents athickness of twenty or thirty fe~t. and is of such extreme hardness as te> be broken only with great difficulty. Soil and sub-soil highly calcareous and barren. Distance,' 13 miles. The quartzose sandstone is a local coarse deposit of the Base-. ment sands. May 14.-Contlnued our way thrO'Ugh the valley of the Pecos; en­ " . University ut several miles from the parent mass. The strata present a slight but uniform dip to the E. S. E., and every­where appear to be rapidly yielding to the influence of the weather. In the lower fossiliferous band I collected the following fossils: Am­monites vespertinus, Scalaria vertebroides?, Turritella cp.?, G'T'yphaea .Pitcheri, Ostrea crenulimargo, Janira Texana, Lima Wacoensis, Trig­·onia crenulataf, Terebratula Wacoensis, and Pygaster, Fuaus, Opis, and Oardium of undescribed species. Toward the latter portion of the day we found nearly horizontal layers of red and blue indurated m3.ilY clay beneath the limestone. This day agrees ,Iithologically in all respects, save in color, with that ob­served in the vicinity of San Antonio, and is in several places crowded with an angulated variety of G'T'yphaea Picheri. The valley as observed during th.e day varies from twenty to twenty­ ftve .miles in width, and the surface is in many places rough and broken. Soll marly and fertile; sub-soil calcareo-arglllaceous, in a few places arenaceous. Distance, 151 miles. University of Texas Bulletfr1 May 18.-After traveling a few miles from our camp of last evening the valley through which we have been passing for so many days widens rapid~y, and soon terminates in a broad, open, and gently un­"dulating plain. Here the Cretaceous Limestone, while still preserving a nearly horizontal position, terminates abruptly to the west and .northwest in bold, rugged precipices, from four to six hundred feet in height.* These are to be traced, stretching somewhat irregularly north and southwest, a!l far as Vision extends, marking the edges Of the table land and serving to indicate the great extent to which the strata. of this region have been removed by denudation. . The surface now assumes a deep red color, and is everywhere marked by small hills and ridges of .indurated red marly clay, which are. for the most part gently rounded and from ten to forty feet high. .The summits of the highest of them are thinly Cjlpped with nearly hori­ zontal layers of Cretaceous Limestone, generally soft, of light grayish and yellowish colors, and with imperfect fossils of the same character as those of the cliffs. • . The Rio Pecos as observed during the day has a. width ..,a.rying from sixty to eighty feet, and still continues to flow between low bluff banks of red clay. The water is highly charged with deep red sediment, and still contains a small percentage of saline matter. On either side of the ·stream there extends a chain of small, shallow, saline lakes, and the adjacent ground is often covered with an efilorescence of chloride of sodium, usually about a fourth of an inch in thickness. Soil moderately fertile; sub-soil calcareo-argillaceous, occasionally arenaceous. Distance, .16 miles. The area referred to under this ·entry begins in the vicinity of Girvin, on. the Pecos River southwest of the Castle Mountains. May 19.-0ur way still leads over rolling and gently ascending prairie, its surface often whitened. with saline efilorescences, and pre­senting here·and there small patches of Cretaceous Limestone and de­tritus. The former is usually soft, white or of a light grayish color, and resembles very closely the. pulverulent limestone observed in the· vicinity of San Antonio. From the harder varieties a few imperfect . characteristic cretaceous fossils were obtained. The prevailing forma-· tion consists for the most part of l'hdurated red and blue marly clay, with intercalations of soft yellow and pinkish fine grained quartzose sandstone. The sandstone does not anywhere 'exceed two or three feet. in thickness. It ii! usually thinly laminated, and traverses the clay in *.These cliffs are laid dowp. on some of the maps as the "Castle Moun­tains." It is hardly necessary to state that no mountainliJ occur in this. portion of Texas, the so-called Castle Mountains being nothing more than the abrupt borders of the Table Land. Geology and llfineral Resources of Crockett County 27 nearly horizontal ~ands. During the day sections of sixty or eighty feet of these strata were exposed, and near the base of one of them the sandstone Was found to <:ontain small rounded pebbl~s Of eruptive rocks. The Pecos still pursues a tortuous course, and lakes of highly saline water abound· in its vicinity. The ground is also frequently coated with ~hite saline effiorescences. Soil marly, in some places arenaceous; sub-soil calcareo-argillaceous and argillo-arenaceous. Distance, 16! miles. May 20.:--In general appearance and structure the country traversed . today differs but slightly from that of yesterday. As we advance the soft pulverulent iimestone is better developed, and presents often a thickness of ten oi: fifteen feet. Its stratigraphical position is im.med­iately. over the m.arly clay. At the distance of twelve miles ·we arrived at the rapids of the Pecos. Here the water descends impeteou~ly for a distance of about twenty feet over coarse quartzose sandstone and conglomerate. The total amount of fall is ab.out ten feet. On either side are high bluff banks of red marly clay, coarse quartzose sandstone, and pulverent limestone, in nearly horizontal strata. The sandstone is soft, friable, and of red ·and gray' colors. Near the base it passes into a conglomerate of welf rounded pebbles of quartz, red porphyry, granite, and other varieties of eruptive rocks. Soil and sub-soil the same as before. Distance, 21i miles. The rapids of the Pecos River were identified just north of the highway bridge near Grand Falls and the conglomerate de­scribed was referred to the Trinity· conglomerate or its equiva­lent. May 21.-General formation the same as before. After a travel of three miles, over a nearly fla~ and moderately fertile district, we ar­rived at a range of low hills, composed of red and blue clay, sandstone, and conglomerate, surmounted by about ten feet of hard grayish lime­stone, the ·latter containing a few imperfect fossils, of which the most common species is Janira quadricostata. Dip 2 degrees E. S. E. Tb.ese hills constitute the remains of a once continuO'lls plain, the borders of which, by denuding agencies, have been made to recede, gradually, many miles to the east, where, as we have already seen, they are abruptly defined by lofty and nearly vertical precipices. As we progressed the .surface b.ecame much more uneven, and some­times covered ·with ·coarse drift deposits, consisting of quartz, jasper, chalCedony, and granite, often loosely cemented with calcareo-ferrugin­ous paste, and with an average thickness of about three feet. The red clay formation was . seen in several places exposed to the '28 University of Texas Bulletin height of nearly a hundred feet. South of our road, and at a distance .of perhaps sixty miles, are seen the bold rugged·chain of the Limpea Mountains, whose lofty peaks and sharp outline denote, even at this distance, their igneous character. During our day's travel the ·pulverulent limestone frequently pre­.sented itself on the surface, but nowhere exceeded five or six feet in thickness. The accompanying section, taken from · a deep depression in the prairie, shows the character of the strata observed _during the day. Soil and sub-soil calcareous and. calcareo-argillaceous. Distance, 12! miles. The igneous pebbles covering the surface of the ground north of ·Grand Falls are fragments of the conglomerate which forms the falls. Its dip is slightly greater than the river gradient; sufficient to place it at the surface in this area. In the Pecos Valley, Shumard referred all formations en­ countered in the present survey to the Cretaceous System, which then was assigned to,the "Secondary period". This system he divided into the Lower Cretaceous, or Marly Clay Group, and the Upper Creta·ceous, or Calcareous Group. As he included some sandstone in the Upper Cretaceous it is impossible to estab­ lish the contact between his two groups. It is very p'robable, however, that the base of the Upp.er Cretaceous was ·approxi­ mately at the base of .the Walnut Clay, at the contact with the Basement sands, as the sands ·which he relegated to the upper group were not true sands but siliceous phases of the lime above. In the lower or Marly Clay Group were placed all the remain­ ing beds south of the Rustler Hills. Shumard thus included under the Upper Cretaceous or Calcareous Group the Edwards ·. limestone, the Comanche Peak limestone, and the Walnut clay; and under the Lower Cretaceous or Marly Clay Group, at least all the Basement s;mds and Triassic sandstone south of the Rus.tler Hlills. In his opinion there was not sufficient evidence to even indicate other than a Cretaceous age of all formations described. At this time, Prof. Jules Marcou advocated the Triassic and Jurassic age of sandstones underlying the limestones of the Pecos Valley. His conclusions were based mainly upon the finding of fossil wood in the Marly Clay Group. This, however, is not Geology and Mineral Resources of Crockett County 29­ conclusive, as fossil wood is also recognized in unquestioned Cretaceous strata in Texas. The 'Jura.ssic age of some of the Marly Clay Group ~as ad­vocated by Marcou upon the presence of Ostrea Marshii, which he concludes to be typical of American Jurassic. However, Shumard finds this fossil in the Upper limestone at Fort Washita, associated with such characteristic Cretaceous fossils. as Gryphaea pitcheri, H emiaster elegans, H olaster simplex, and Ammonites vespertinus. Maroou to a great extent fixed the Trias­sac age of these strata upon their lithologic character and though this is not conclusive evidence, it is not without value. The Ju­rassic age of some of the strata, determined by paleontology alone, seems to .be entirely refuted by Shumard. There probably is little to be said in defense of their Jurassic age. Again in 1891 the formations of the Pecos Valley became the subject of investigation. W. F . Cummins explored the Pecos. Valley from New Mexico as far south as Horsehead Crossing. The results of his inyestigation are embodied in the Third An­nual Report of the Geological Survey of Texas, for the year 1891, under the ti~le "Report on the Geography, Topography, and Geology of the Llano Estacado, or Staked Plains". Be­ginning at Pecos City, the county-seat of Reeves County, his. notes on the geology of the country southeast to the Castle Mountains are as follows: "We crossed to the east side of the Pecos river at Pecos City, and camped about fourteen miles below, where we found Permian beds of red clay and gypsum, with the bed of Quaternary drift on top of the red clay. This camp is about south of Quito station. "Continuing down the river, at about three miles, we came to the massive be.ds of red sandstone that is being so extensively quarried west of Quito. I think this sandstone is Triassic. It is underlaid by red clay with selenite. "We continued down the river to the falls. The valley on the east side is about one mile wide and widens to three or more on the south, and then closes in again at the falls to one-half mile. The escarpment on the east is not more_than thirty feet high; and is always capped by the white conglomeritic· limestone so characteristic of the Blanco beds. This rock here contains .sand, siliceous pebbles, and pieces of red sand­stone, and is from three to five feet thick. "There are two falls in the river at this place, in a distance of about one hundred yards. The upper fall is about three and a half feet and 30 University of Teias Bulletin the lower abuut five and a half feet. The stone making the falls Is a coarse conglomerate composed of carboniferous, porphyritic, and , ·siliceous rocks with a .light sand matrix sligqtly ferruginous. · "We continued down the river thirty-ei:ght miles to Horsehead Cr-oss­ing, tra'Veling along on the flat valley of the river. The low escarpment facing the valley was red marly gypseous clay overlaid unconformably by ten feet of red slightly arglllaceous sand, and this was overlaid by ten feet of the white conglomeritic limestone· so characteristic of 'the upper,beds of. the Staked Plains. · "We here left the river and took the road to Castle Gap, camping ten miles farther on, ;i.nd seven miles beyond passed through Castle Gap. The strata seen between Castle Gap and the Pecos River w:ere the upper 0 limestone of the Staked Plains anC. the deep sand beds that had formed above lt. The following is a section of Castle Mountain: Section 25. 1. Limestone, hard......................... ; 6. feet 2. Clay and limestone.......................15 feet 3. Limestone . . ............... : ...........20 feet 4. Limestone . . .. .. ........................30 feet 5. Clay, yellowish ...........................lZ feet 6. Limestone . . . ........... : ...............60 feet 7. Clay, yellowish white............... ,; ....20 feet 8. Limestone, rotten.................... ' .. . 5 fe~t 9. Limestone . . ........ .,..................80 feet 10. Sand, compact . . . ..........·.............50 feet 11. Calcareous sandstone . ....................90 feet 12 .. Conglomeritic sandstone.................30 feet 418 teet :•No. 1 Of this section is fl.rm, eve~ly weathering, white limestone, that ·would make very good building stone. The layers are about two to three feet thick. "No. 2 is alternating clay and argillaceous limestone layers, contain­ing alarge number of DiQ,dema, Toxaster texanus, .Pecten texanus, some Arca, several species of gasteropods, and a .small Gryphaea pitcheri. "No. 3 is a white crumbling 'limestone, forming a prominent horizon that stands out beyond the rock below and above, as it resists the atmospheric influences better than they. "No. 4 is a crumbling wqite argillaceous limestone, somewhat similar to the one above. "No. 5 is a clay containing a great number of Gryphaea pitcheri and a few Exogyra texana. "No, 6 white crumbling limestone containing a few fossils. "No. 7 is an argillaceous bed containing Arcopagia, Lima wacoensis, Toxaster texamis, Arca, Ammonites, Diadema, Pecten texana. Geology and Mineral Resources of Crockett County 31 '.'No. 8 is a slightly ferruginous limestone containing many small Gryphaea pitcheri. "No. 9 is a nearly uniform friable white limestone, though it has some layers of marly material that weathers more rapidly. The most common fossils are Arca, Toxaster texanus, Diadema, Pecten and small Gryphaeci pitcheri. "No. 10 is a white compact sand containing a few siliceous pebbles and calcareous pink sandstone near the top, which is slightly fossili­ferous. This stratum shows a graduation into the one beiow. "No; 11 is a ·massive calcareous sandstone. It has much white sand, but the weathered surface of the rock is always brown. The rock varies in· its proportion of lime, but this never becomes the principal ingredient of the stone, except in streaks. False-bedding occurs in places, and a few siliceous pebbles are found in the bed at some Of the localitie~. The stone is generally firm and weathers into large boulders, yet there are one or two layers of friable stone in the middle of ·the bed. "No. 12 is a red friable conglomeritic sandstone, very much resem­ bling the characteristic Triassic bed at Dockum. Hardened small pieces of calCareous ciay and sand, of yellowish and brown colors, and pieces of red sandstone and calcite make up the mass of rock. At the center and top of this stratum, as seen here, the rock is a shaly micaceous red sandstone and red marly clay." The red clay beds at Pecos City were examined and found to be true clays. Part of the material evidently has been eroded from the Permian red clays of New Mexico and deposited here by the riyer as alluvium associated with Triassic clays formed by the' dec6mposition of the feldspars which are present in great quantities in the Triassic sands. The falls which Cummins observed are the same ones mentioned liy Shumard and the coarse conglomerate has been referred, in the present survey, to the Trinity conglt>merate or its equivalent. The section of Castle Mountain is about four miles from the section at Red Point given in the following report. The basal 20 feet o{ Cummins' bed No. 9 is Comanche Peak limestone and Walnut clay. The fossiliferous band mentioned under N6. 10 is the key horizon, at the top of the Basement sands, As the Trinity conglomerate or its equivalent was identified at Grand Falls, all the sands here exposed are described in this report as Basement sands. They greatly resemble the Triassic sands, from ·which they undoubtedly were in part derived . . Again in 1891,. E. T. Dumble, assisted by N. °F. Drake, studied the · formations of the Pecos Valley and the results of their in­ University of Texas Bulletin vestigations were published by Drake, in the Third Annual Re" port of the Geological Survey of Texas for 1891, under the title ."Stratigraphy of the Triassic Formation of Northwest Texas". Page 232 of his report describes the strata from Pecos City to the Ca!'ermian. The following characteristics of the Triassic strata also serve to sep­arate them from those of the Permian (1) The Triassic sand­stones are. gray and brown in color; (2) the lower Triassic shales are variegated, with maroon, wine, white, lavender, and yellow colors predominating, while the upper Permian shales are bright brick red; (3) the Triassic strata exhibit an extensive develop­ment of cross-bedding and local u:riconformities. '' In differentiating these two formations in the Pecos .Valley, Baker's .characteristics readily distinguish them.; the difficulty, however, lies in placing the line of demarcation between the Triassic and the Basement sands of the Lower Cretaceous. From their most southern exposure :five miles above Chandler in Terrell County, tb Red Point in the Castle Mountains, at every section there is a perfect gradation from the Walnut clay into the Basement sands below. These in turn, without the slightest arigular unconformity, continue into the sandstones of the Triassic. The lowest and'heaviest conglomerate, about seven feet thick, is first seen in the beds of the river at Grand Falls and in the bottom of the irrigation canals, north of the Pecos River bridge. In the vicinity of Pyote it comes to the surface, and more clearly shows the igneous origin of the greater part of the pebbles which form it. There are in ·addition a few flints and some w_ater-formed chalcedony. Above this conglomerate are found numerous others at various elevations. These lie in perfect conformity with the sandstones above and below them, and some massive sandstone ledges contain layers of these peb­bles, while in others the pebbles are interspersed throughout the stratum. Mica is also ~ound in the sandstone, above and below the heavy conglomerate. Its highest occurrence is about 150 feet below the base of the Edwards limestone, while the pebbles con­tinue to within :fifty feet of the Walnut clays. As, the conglomerate at Grand Falls is the lowest one exposed in the Pecos Valley, and since its composition is the same as the Trinity conglomerate observed in other parts of 'Texas, it has been called the Trinity conglomerate or its equivalent, and placed as the base of the Cretaceous in the Pecos Valley. The Goology and Mineral Resources of Crockett County 39 ·conglomerate containing mica or pebbles is probably to a great extent a re-worked product of the underlying Triassic. In the Pecos Valley, there was almost continuous deposition from the Triassic through the Jurassic and lower Cretaceous. Whatever break in sedimentation occurred is represented by the heavy conglomerate. Both below and above this conglom­erate, the strata are similar in composition and are conformable with each other. Thus Shumard, working from the southeast, could see no ground for making any division :of the red beds of the Pecos Valley, but placed all in the lower Cretaceous or Marly Clay Group. Dllillible and Drake, working from the opposite di­rection and finding the upper conglomerates and pebbles, placed all of the red beds west of the Castle Mountains in the Triassic. Cummins agrees with Dumble and Drake in that the Triassic extends with a few minor breaks to the Castle Mountains, but he is inclined to consider as Permian the red sand and clay in the immediate Pecos Valley below Pecos City. The presence of this heavy basal conglomerate at Grand Falls, which is the 'lowest introduction of foreign igneous pebbles, records a break in sedimentation-a parallel erosional uncon­formity-and makes the contact of the Triassic and the lower Cretaceous sands. The rugged topography of the lower Pecos Valley, with its numerous steep-walled canyons and precipitous cliffs, gives abundant exposures of all horizons near the surface. From about eighteen miles above Girvin, at the kansas City, Mexico and Orient Railroad crossing of the Pecos, to the New exico line, exposures are rare in the immediate vicinity of the river, because of the covering of Quaternary alluvium, and the majority of the work done was at widely separated exposures at some distance from the river. The Edwards limestone cap, . which has preserved a varied topography along the lower Pecos, on account of its southeast dip, has here exposed so much of the Basement sands and underlying Triassic that erosion has been extremely rapid, undercutting the Edwards limestone, which has ·been carried away, and leav­ing a broad flat valley with little relief. The re-worked Baseme:O:t . and Triassic strata :form the red alluvium which conceals the underlying rocks. University of 1'exas Bulletin All the strata are persistent over large areas, and lie in normal sequence from the Permian formation, near the Texas-New Mex­ico line, up through the column to the upper Edwards limestone. Above the Permian Red Beds and immediately underlying the Trinity conglomerate or its equivalent, and having no angular unconformity, are the beds of the Upper Triassic. Since the time was so limited, these beds were not correlated ·in the. field, but it is highly probable that they are the equivalents of Drake's Upper Dockum bed and Gould's Trujillo formation, which under­lie the Comanchean-Oretaceo~, form the hase of the northern and eastern escarpment of the Llano Estacado, and extend west­ward into New Mexico. They first come to the surface immediately under the 'Trinity conglomerate :fifteen miles above Grand Falls, and· as their south­east dip is a little greater than the gradient of the river, they ·rise to a sufficient elevation in Loving County and along the Pecos Valley in southeastern New Mexico to form the base of the southwestern Llano escarpment. Without·further study it is impossible to say how much the upper part of this sandstone has been eroded, but it is probable that very little has · been carried away from the exposed surface, since the deposition and erosion of the Cretaceous. The same grayish-red, cross-bedded ledge is found. at about the same elevation and distance below the surface of the ground four miles below Barstow, where little post-Comanchean erosion· has taken place, and at the Texas-New Mexico line. Also over this area, unless there has been extreme lateral variation, there probably has been no more erosion in the 'rriassic--Comanchean interval than over. the other parts of the Llano, as the variegated shales of the Tecovas formation are not exposed, and almost the entire thickness of the Trujillo is present. The beds of the Upper Triassic exposed in the Pecos Valley of northwestern Texas, and southeastern New Mexico, are light red in color on freshly exposed surfaces, but readily weather to a very deep red, due to a more complete oxidation of the iron and its redistribution when the feldspar and silica decompose to clay. 'They ·vary both laterally and vertically from hard, massive, ~venly-bedded ·sandstone, to thin, cross-bedded, shaly sands. However, over the top of the entire area a hard, thickly-bedded, Geology and Mineral Resources of Crockett County 41 homogeneous, deep red sandstone prevails. This can best be seen in the quarry four miles southeast 0£ Barstow where a focal vertical section of some seventy-five feet .does not show the entire thickness. The general thickness of this cap, however, is only about ten or fifteen feet. The texture does not show an extreme range, though in places it is rather coarse sandstone, but generally the grains are of medium size and well cemented. In all localities both muscovite and biotite were found, but they have no regularity of occur­rence. Ip. some places . they cannot be identified with a lens, perhaps being too minute, or probably being absent; in · others flakes from microscopic size to those 1 inch in diameter are · present in great quantities. The individual grains· a~e mostly feldspar and quartz and are firmly held together with a highly calcareous cement. Upon weathering, the feldspar, which is a silicate of aluminum, potas­sium, sodium, and calcium, decomposes and forms the greater part of the clay found in the area. The additional kaolin prob­ably comes from the underlying Permian clays farther to the north. The remaining alkaline bases form the oxides which in turn change to the hydroxides, on presence of water; and furnish at . least a . part of the strong basic alkali, so characteristic of the region. A part of these surface alkalies in the region probably also has fill origin in the underlying Permian. The angle of sharpness in the welj.thering process of the sand~ stone cap is above the ordinary; in the lower sandstones it is about normal. Two types of weathering are present: (1) a: mechanical dis­integration-a breaking down of the calcareous ce.ment and lib­eration of the sand grains, forming the lo-0se red sand ; (2) a chemical decomposition, forming clays. The thickness of the Triassic region is not known, as nowhere is the base exposed, but over a hundred feet are visible. The areal distribution of the Triassic is shown on the ac­companying map (Pl. 1). To the northwest of Barstow out­liers of Comanchean limestones have been found overlying the older formations, but their relation has not been described in detail. University of Texas Bulletin COMANCHEAN-CRETACEOUS The Comanchean-Cretaceous System' of that portion of the Pecos Valley included in the present survey has two compo­nents, a part of the Trinity and the overlying Fredericksburg divisions. No strata of the Washita Division have been identified within these limits. The aggregate thickness of the two divisions is about 850 feet. TRINITY DIVISION 'The Trinity Division of the CGmanchean Cretaceous embraces all the strata in the Pecos Valley overlying the Triassic and underlying the Walnut clay. This division in the Pecos Valley incl~des the Trinity conglomerate which forms its base, and the Basement sands, which are the stratigraphic equivalent, although presumably not the entire time equivalent, of the Paluxy sands, Glen Rose, Travis Peak and Basement sands of east and central Texas. Jn the absence of organic life to furnish paleontological defi­nition and the lack of · persistent lithologic features in every­horizon, it was not found practicable to subdivide the Trinity division except to recogn.ize the Trinity conglomerate, the re­mainder being referred to as the Basement sands. · 'l'he Trinity conglomerate or its equivalent, lying at the base of the Trinity division of the Comanchean-Cretaceous, owing to the rapidity with which its cementing material breaks down, does not outcrop intact at any point in the Pecos Valley, but may be best studied in the vicinity of Grand Falls. Here in the river bed just above the steel highway bridge over the Pecos River and in the irrigation canals, are found the recently cemented components of the conglomerate. This material also is scattered over a considerable area extending northward· many miles, where the beds, with a thickness of some seven feet and a southeast dip only slightly greater than the slope of the ground, come to the surface. In the Castle Mountains the re-worked products of this con­glomerate are found in the overlying Basement .sands to within fifty feet of the Walnut clay. The nature of the material of which these fragments are com­ Geology a;nd Mineral Resources of Crockett Co·unty 43 posed varies greatly. Igneous quartz, water-formed chalcedony and flint constitute about one-half of the material. The remain­der consists of rhyolites and trachytes with their corresponding porphyries, and coarse-grained equivalents, granite and syenite, some of the more basic types of basalt and dolerite, and some few which have been so changed by weathering processes as to prevent classification. . The individual pebbles of this heterogeneous collection vary much in form, color, composition and texture. The well rounded shape of the greater part of them indicates the great distance they · have been transported. The difference in texture between the almost glassy rhyolites and the coarse-grained granites and syenites shows all degrees of depth at which the cooling magma must have solidified. The highly acidic granites had their origin in a much different rock from the more basic dolerites and basalts. Water-formed strata contributed the chalcedony and flint, while igneous intrusions and extrusions furnished the other i:)'.l.aterial. The source of this material cannot be ascribed to any one local­ity or formation, but the Wichita-Arbuckle Mountains of Okla­homa are generally conceded to have furnished the greater part of the igneous fragm.enbi. The Basement sands, with a thickness of about 250 feet, which overlie the Trinity conglo;rnerate of Toyah Basin, first appear in situ ·about eighteen miles north of Girvin. They undoubtedly once covered the greater part of Toyah Basin, but becarnie of their elevation north of this point and the argillaceous nature of the overlying Edwards in this region, they have been eroded. They for¥1 the greater part of Red P.oint, one of the prominent topographic features making up a semi-circular range of hills which constitute the most northwestern exposure of the Edwards in Toyah Basin. Overlying these sands at Red Poin.t are the Walnut clay, the Comanche Peak limestone, and about twenty­five feet of the base of the Edwards limestone which forms the cap of the escarpment and protects the underlying strata. The most • southern exposure of the sands is five miles north of Chandler in Terrell County, where they dip under the water level. The ac­companying map shows their distribution. (Pl. 4). The Basement sands ar.e conspicuously variegated in color, University of Texas Bulietin and vary extremely in·hardness, texture, and composition. A<;l­jacent zones of unequal oxidation and hydratio~ of the 'iron, manganese and other bases give a range of colors an~ shades from light yellow through the browns, reds and purples. This variation is both lateral and vertical and also both abrupt and by gradual transition. The . presence of an effective siliceous cement has locally produced a sandstone of such a quartzitic nature that fracture is through rather than around the grains, but by far the greater part is pulverulerit, even between the fingers, when in small pieces. At no point w.as there observed any metamorphic action of the superimposed strata sufficiently great to produce even the slightest induration. This of course was to be expected in. consideration of the relative youth of the Coinanchean-Cretaceous and the absence of movements capable of producing intense pressures. In many places the sandstone is composed of pure silica grains while in others it contains m1;1.ch kaolin and could more correctly be called an arenaceous clay. The proportion of sand to clay varies between these wide limits, but as a whole the sandy nature predominates. The individual grains are small, of uniform size, and well rounded. Scattered pebbles and thin layers of reworked Trinity conglomerate are found at various elevations to Within some .fifty feet of the base of the Walnut clay. At the top of the Basement san!'ls immediately below the walnut clay is a hard, dark brown, evenly bedded sandstone. Because of its wide distribution, fossil content, and uniform thickness of about 2 feet, it is readily identified wherever exposed and has been selected as .a key horizon. FREDERICKSBURG DIVISION The Fredericksburg Division of the Pecos Valley included in tlie present survey .is composed of the calcareous members, namely, Walnut clay, Comanche Peak limestone, and Edwards limestone. In ascending order, as given, they increase in amount of lime and in hardness, and decrease in clay content. Their total thickriess is about 575 feet. · Walnut Olay and Comanche Peak Limestone. Lying on the Basement sands is the Walnut clay, conformwble and somewhat blended, but generally with visible definition. its areal distribu­ Geology and Mineral Resources of Crockett County tion is equal to that of the Basement sands, for in the absence of a protective cap of the Edwards limestone they both disintegrate rapidly. Its lower beds contain an appreciable amount of sand which decreases upward with an addition of calcareous matter, passing imperceptibly into the nodular Cmnanehe Peak with a slight loss in yellow color. The contact between these formations . cannot be detected. Their aggregate· thickness is from 2 to 24 feet ; the ibeds of the northernmost exposures being thinner than those farther south. The Comanche Peak limestone in turn changes vertically from the argillaceous limestone with a loss in kaolin and an increase in lime and nodular texture into the true Comanche Peak, gray in color, with practically·po sand, slightly argillaceous, moderately hard and distinctly nodular. its areal distribution is the same as that of the Walnut clay. The Edwards Limestone. Approaching the top of the Coman­ . che Peak, the same gradual nature of change, so characteristic of the formations under observation, takes place. Without a break the nodular texture disappears and with practically no change in color the small amount of remainin~ sand and koalin is no longer present and the massive ledges of the Edwards lime­stone are at hand. Its hundreds of feet of unbroken. sequence contribute much to make the Comanchean-Cretaceous no mean rival of the Ordovician as a producer of limesto:o,e. As indicated by the map, the Edwards limestone covers the lower half of the Pecos Valley. Only in small areas is it oovered by later formations. From here it extends northeast into north­central Texas and southwest to, and in so~e places beyond, the Marathon region in Brewster County. It is the chemical and physical .properties of the Edwards which . determine the surface contour of the area which it covers. Occasionally heavy ledges of hard, pure limestone, being slow to weather and intersected by fewer jointing and bedding planes, stand out as :bold precipices or as cap rook for the :flat­topped hills. Softer and more argillaceous beds are quickly disintegrated, giving gradual slopes and benches upon which the debris from above collects and in most cases, unless the erosive agencies are extremely active, covers the underlying rocks ill place. Ledges of varying thickness from a few inches to twenty University of Texas .Bulletin feet are found and this factor greatly influences the rate of disintegration. Over the southern Pecos Valley the Edwards generally weathers to one of three benches which are referred to in as­cending order as :first, second and third div~sions of the Edwards limestone. In places other less definitely marked benches overlie the third. The cap of the third division forms the top of the Ed­wards Plateau which is the largest and most marked topographic feature of the loyv-er Pecos Valley. These divisions of the Ed­wards are lithologic entirely but are. useful in reference becia:t;ise of the great thickness which the limestone reaches. The lowest or first division is approximately 160 feet thiek and is characterized by horizons of chert occurring as nodules in the fo'rm of concretions, or as sills by replacement. This division also supports a more luxuriant vegetation because of its more gentle slopes and deeper accumulation of soil. The second di­vision is about 105 feet thick and more thinly bedded. Upon weathering it develops a netlike channeled surface resembling mud cracks which are not found to any extent in either of the other two divisions. The third division, about 180 feet in thickness, is more massively bedded than the others and its tex­ture is more highly crystalline. It is filled with small calcite crystals and concretions. PLEISTOCENE AND RECENT Over the greater part of the Pecos Valley, especially in the lower lands, there are considerable depositions of Pleistocene and Recent age. The ;material . eroded from( the older rocks is re­deposited by the weathering agents in various forms. Only very locally are these deposits well stratified; deposits only a short distance from .each other having practieally no resemblance. Laterally and vertically they overlap and grade into one another. A:. sand, pure in one locality, will grade imperceptibly or abruptly into a gravel and boulder bed or a clay deposit. Practically all the alluvial deposits are lenticular and exhibit cross~bedding, In the valleys of the tributaries of the Pecos, over the Edwards Plateau region, the deposition is principally talus from the lime­stone. This is chiefly fragmental and the particles are often re­ Geology and Mineral Resources of Crockett County 47 • cemented by calcium carbonate which has gone into solution when some of the limestone has decomposed, or it is folmd mi\}-gled with clay in places where the limestone has had a greater kaolin content. · Along; the lower Pecos flood plains the deposition is more heterogeneous, for to the native material is added the wash from the older beds nearer the source of the river. · In the upper valley where the Edwards has been eroded for a considerable time, the limestone fragments are in a minority, as their only source is the Rustler formation. The assortment consists chiefly of sand and gravel from the Triassic and lower Comanchean sands and conglomerates, and, in addition, clay de-. composed from the feldspar in the Triassic sandstone and some carried by the river from the Permian Red Beds of New Mexico. The deposits of the upper Pecos Valley in Texas are more homo­ geneous and regular. Layers of assorted pebbles are frequently found and the sands and clays are le~s frequently intermingled. Here also are wind-blown deposits of fine sand and nnconsoli­ dated fragments of igneous origin. At the beginning of the Llano escarpment, a new accumula­ tion in the form of ''caliche'' is e~countered. This deposit im­ mediately overlies the Triassic sandstone in the northern Pecos Valley. It is first noticed as a white pulverulent coating of the older limestones and sandstones in the valley, but at the Staked Plains it has cemented the soil material to a depth of ten or fif­. teen feet and forms the cap rock of the Llano Estacado. The cementing m'atter is a precipitate of calcium carbonate brougp.t to the surface by capillary attraction and re-.deposited as a cement which binds the surface particles together. STRUCTURAL GEl()LOGY Dynamic geology of the Pecos Valley is separable into two parts: (1) Pre-Comanchean movements and (2) post~Coman­chean movements. (1) Any folding antedating the deposition of the Lower Cretaceous system would not be reflected in the overlying strata but a structural and erosional unconfori:nity would exist, with magnitude depending upon the amount and rate of disturbance, University of Texa8 Bulleti11 the period of exposure to weathering agencies before the de­positi9n of the overlying strata, the resistance of the beds, and th-e power of the decomposing elements. Dr: Udden has given the following discussion of the possibili· ties of structural geology in the Pecos Valley :1 "Looking at the ancient Marathon Mountain structure as a whole, it does not appear unreasonable to regard it as suggesting fhe possibility of the existence of buried structures in which oil mal have accumu· lated, farther to the northeast. If .we take into consideration. all that is known concerning the trend of this structure of the ancient Marathon Mountains, all the· way from the Solitario on the Brewster-Presidio County line to the· norf;heast, the general trend of this structure, as near as it can be made out, is north 40° east. At the last exposure of the Pennsylvanian to .the northeast, at a point near the Purington Ranch, where the Dimple Formation occurs, it·has a trend in the di: rection of north 600 east. There can be no doubt that this structure extends a considerable distance northeast under the overlying Comiin· chean limestones. The last exposure. seen shows the Carboniferous strata in an almost vertical position. There is no intimation ·in·this or in any other expostirelf that the . mountain structure developed in these old formations has undergone any modification except that it.may have b.eeti cut d.own to a .lower level in this direction. The same, we may say, is suggested also by the isolated. uplift coming up through the Comanchean in the Madera Mountains, which suggests also that there is a narrowing of the folded region in this direction. From my ob­ . servations on all· parts of the Glass Mountains it appears that the for~ mations from the Vidrio up are much less tilted. and folded than the Gaptank and other formations of probable Pennsylvanian age. It would seem, therefore, that most of the folding of the Marathon Mountain&. antedated the deposition of the latest Perm~arboniferous sediments. I believe that the red beds exposed within the Pecos Valley overlie. the Tessey formation. These and the overlying Com.anchean, therefore, probably have been very little disturbed by the Marathon uplift. So that there should exist, under the Comanchean. and under the Red Beds, so~e· places northeast of the Marathon uplift where the Pennsylvanian and. probably some of the Pernio-carboniferouil lie folded \l.nder the relatively undisturbed red beds and the Comanchean limestones. The red beds are entirely impervious and would make an excellent cover for an oil pool. How far such covered places of tilted petroliferous formations of the Pennsylvanian may be found away from the exposures in the Marathon .country', no one could say, but it would be no surpri8e · to fl.rid them at a distance of at least fifty (lr a hundred miles beyond 'Notes on the Geology of the Glass Mountains; J. A. Udden'; Bulletin Univ. of Texas No. 1753, pp. 56-58. · Austin, 1917. Geology and Mineral Res0urces. of Crockett County 49 . the Brewster-Pecos Caunty boundary. The trend of the Marathon Mountains would run through the southeast part of Pecos County into IJ'pton and Reagan counties, or even farther east than this. "It will be remembered that on the west fiank of the Glass Moun­tains the Comanchean limestones have . been slightly tilted and that outliers of this formation occupy some of the highest points on the mountains, . This cannot be altogether due to an overlap. It.eertainly represents a slight uplift in post-Oomanchean times. From what is generally known of the geologic history of the mountain-building forces, It is quite reasonable tO suppose that the post.Comanchean disturbances . should have ·taken place over more thii.n one part of a buried mountain aystem, such as the Marathon uplift. It ought for this reason to be. · practicable to find out how far in a northeast direction this uplift prO]?jl­bly extends, for it can be expected to be marked by at least some Blight elevation in the ·later Comanchea:n sediments. We have here a geologic problem, the solution of which may be of decided economic signiftcance. In the distribution of the Comanchean along the North Conc:i>.o .and the Colorado rivers, there is nothing to especially . wggest such an upiift. The conditio~s in the country to the northeast of the Glass Mountains, along the Pecos River, are singulp.rly favorable for the test~ Ing of such a theory. The Comanchean Umestones contain several shai'ply marked horizons that can be followed for long distances, in the southwest part of Pecos County, and in most of· Upton, Reaga~· anlf Crockett counties. Quite accurate measurements of any structure present can certainly be made. It is, however, · a r~on where very little work has yet been done, and· in the absence of any accurate knowledge of the conditions involved, further speculations seem tm­profitable. We can only see that in the buried unconformity which certainly must exist between the· lower folded series and the overlying merely gently folded or quite undisturbed sediments·there are natural chances for finding accumulations of gas as well as oil · Drilling shauld not be un:dertake.n, however, before a thorough geologic exam.­_ination has been made whereby the exceedingly small chance of making the right · location for a test may be materially increased." Professor Haker and Mr. Bowi:$n1 also have foUn.d ' evidenee of folding in the Glass Mountains region which is later'than the Permo-carboniferous and earlier than the Comanchean~Creta­ceons. They place it iri the Lower Triassic, probably about the time the Llano Estacado geosyncline was formed. (2) Subsequ.e~t folding during the deposition. of the Cre­taceous and more recent formations would not only show struc­tural features in these beds, but would at the same time be indie­ 'Geologic Exploration of the Southeastern Front Range of Trans­Pecos Texas. Univ.1 Tex. Bull. No. 1753, p. ~U. Austin, 1917. University of Texas Bulletin tive of folding beneath. Whether or not the conditions in the lower beds have been and are favotll!ble for the accumulation of petroleum depends upon many factors, and will be discussed later. Again Professor Baker has observed Cretaceoui and post­C'retaceouS movement in :the Pecos Valley.2 "Near the close of the Cretaceous, the Rocky Mountains were first uplifted and the entire Texas region, with the exception of the western Trans­Pecos country, was gently tilted in a southeastwardly direction ·toward the present Gulf of Mexico.'' Undoubtedly there is both pre-and post-Cretaceous folding in the Pecos Valley. The former, however, cannot be discussed to any great extent because the lower formations do not give suf'fWient exposure within the present survey and a few isolated well logs furnish practically the only data for the subsurface work. As the accompanying sections from Pandale to Barstow in­. dicaJte, the C'omanchep.n-Cretaceous over this area lies almost horizontal. The slight departure from the normal rate of dip, together with the gentle tilting of the whole formation to the southeast, are the only indications of Cretaceous or post~Cre­taceous folding. That there have been only slight disturbances in the Pecos Valley after the deposition of the Permo-carbonifer­ous, in contrast .with the extreme ~ctivity·of the Paleozoic, is in accord with the observation of U dden, Baker, and Bowman, in the Glass Mountain region and in the southeastern Front Range of Trans-Pecos Texas . . Even in the vicinity of the Marathon region and the Davis and Barilla Mountains, Comanchean strata lie practically hori­.zontal upon the beveled edges of Paleozoic formations. Igneous Activity. Though there has been little folding or tilt­ing later than the Permo-carboniferous, igneous activity has been by no means absent. Great intrusive flows to the north­east and northwest from -the Davis and Barilla Mountains are evinced by the rhyolite · boulders and gravei which cover the lower part of the Comanchean to the west and northwest of Fort Stockton. About eighteen miles froII1; Fort Stockton on the !Fort -· -·-. 'Review of the· Geology of Texas, J. A. Udden, c. L. Baker, Emu BoBe. Univ. Tex. Bull. No. 44, 1916. Geology and Mineral Resources of Crockett County 51 Stockton-Pecos road, the residual material from the intrusive . first appears, as the Quaternary covering of the lower part of the Edwards formation. Although isolated outliers of the Comanchean limestone are found occupying greater · elevations than the igneous, at no place was the limestone found to overlie the igneous, thus pointing to a late Cretaceous or subsequent flow. In the Marathon region fossil plants in, associated tuffs prove them to ·be late Cretaceous or early Eocene.1 The nature of the rock itself shows it _to be intrusive rather than extrusive. The absence of acidic obsidian, cellular glassy rhyolite and surface lavas, and the presence of rhyolite porphyry, indicate an intru· sion of moderate depth and an intermediate rate of cooling ; since surface or shallow depth cooling would have produced the lighter textured crusts and lavas, and deep intrusions with a slow rate of cooling would have resulted in heavier textured sills with greater crystallization. The igneous activity was evi­dently a quiet intrusion, since little disturbance over any part affected has been observed, and it has been no greater in strata close to the source of activity than in those one or two hundred . miles removed, and also as there is a noticeable absence of dikes and vertical intrusions. No contact metamorphism ~ the Ed­wards was noted, indicating that the flow was formerly in strata at a considerably greater elevation than it occupies at present. Because of its texture and hardness it has come down more or . . less intact as the underlying older, but less resistant, formations have been eroded. Only in relatively recent times has it broken up to its present condition, for it is spread evenly over the area occupied and its limits are well defined. Greater lapse of time since decomposition to its present state would have resulted in deep accumulations in some places and total absence of flow in others. Its boundaries also would be irregular from transporta­tion. The present eastern boundary of the intrusion is re­markably even and lies in a northeasterly direction. DESCRIPTION OF VERTICAL SECTIONS Two sections, Camp Section and Red Point, have been de­ 1Review of the Geology of Texas, by Udden, Baker and Bose. Bull. Univ. ot Texas No. 44, p. 100. Austin, l916. 52 Uni'Versity of Texas Bulletin scribed in detail, as the strata there exposed give practically the entire geologic column from Pandale to the most western ex­posure of the Edwa~ds limestone and Basement sands in the. Pecos Valley. As there is no greater variation in the strata between sections than within the sections themselves, a repetition of descriptions is unnecessary. When nece·ssary, descriptions of additional strata are given in their respective sections. The variation referretl to is chiefly one of color and appearance of the 'Basement sands. None other than a divisional description of the Edwards lime­stone is practical, as the divisions remain quite uniform, and the strata divide and unite very irregularly. In all other sections the different formations are identified for correlation and their thicknesses given. SE<7I'ION NO. 1 The Pandale Section located on the south bank of the Pecos River at randale Crossing, 3 miles due west of Pandale, in Val Verde County. Feet Edwards limestone: Third Division-Represents entire ~hird .division plus some excess over the normal. Requienia· sp. ·Cyprimeria texana (Roemer) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264+ Second Division-Limestone. Lima sp., Protocardia texana Conrad, Gryhaea navia Hall, Requienia sp ..........:.... 116 . First Division-Not all exposed. Ex.tends below river level. Requienia sp., Lima sp...........................·. . . . . . . .. 138 SEOTION NO. ~. The Chandler Section · at the junction of Independence Creek with the Pecos River at Chandler, in Terrell County, on .the east or Crockett County side of the riveJ.'. Tb.e &liffs afforded the following section: Edwards limestone: Third ·Division-Limesto-qe plus exceBIS. Lima wacoensis Roemer, Requienia sp., Gryphaea navia Hall............ 362+ .second Division-Edwards limestone. Requienia sp., Lima sp. 106 First Division-Edwards limestone. Protocardia texana Conrad ....._.... .. . . .. . . .. . . . . . . . . . . .. . . .. .. ... .. .. .. . . . 164 Comanche Peak: Nodular limestone. Exogyra texana Roemer and Lunatia . pedernalis Roemer very common.................. ; . . . . . 12 AZluvium: Red and yellow clay alluvium from water level to No. 2 cm the river conceals all outcrops at river banks, making further sections impossible. Vertical sections of the Triassic are not given, as the thickness of the forma­tion could not be determined and the distance below the Comanchean could not be measured. Red Point being farther removed from the river ·has not been affected by the slumping and the position of the strata in this section shows the position of the same formations along the river northwest of section 16 before the slumping occurred. Feet Basement sands: Key horizon, very fossiliferous. No .fossils below key horizon. Vari-colored sand, white, gray, brown, drab, purple, vermillion, blue, extremely variegated, some cross-bedding. The glass sand horizon and the equivalent of the top 50 ft. of sand at the crossing section ..................·................ 42 Conglomerate of igneous pebbles and·sandy matrix........... 2 Heavily bedded sandstone, cross-bedded in places, some igneous pebbles, gray, brown .......................·.............. 116 Igneous pebbles with sand and siliceous cement............... 2 Sandstone varying extremely from· thin evenly bedded laye~s to massive cross-bedded ledges, moderately hard, color grayish-brown weathering red, some mica fiakes. . . . . . . . . . 142 Grayish-brown cross-bedded sandstone, weathering deep red, containing inneo.us pebbles and considerable mica. . . . . . . . 10 Conglomerate of igneous pebbles cemented into siliceous sand­ . stone, light brown and gray in color. . . . . . . . . . . . . . . . . . . . . 2 Red alluvium and brown sandstone weathering to a deep red, contains mica flakes and scattered ignMus pebbles....... 18 SALINE SOLUTION Beginning at Round Point section, (Pl. 2) three and a half miles up the river from 102nd west meridian crossing and ex-. tending five miles beyond the highway bl'idge over the Pecos at Girvin, at which point the Quaternary alluvium renders explo­ Geology and Mineral Resources of Crockett County 61 · ration in the immediate vicinity of the river impossible, there is · slumping of various sizes 'and degrees, from some scarcely noticeable to a maximum of some fifty square miles just north :>-­ z 1-i-l IJ) ' g -l z 1:1 .. ~ g -l 0 _, D! ~ t= .. i c (.) 2... w ~ (/):c " .. " 0 U) 0: (.) g Cf) 0 w ~ 2 D-. ~ w z r V) -l '.::J < 0 D:::: w f- u z w tsw u 0::: ·:C 0 f--< p::: z 0 < w z :r:: Q u z ~ < 0 0 0 -l ti.. w 0 ~ zz o < ~z r < ... < U) z L-] 0.. w :r: "' 0::: "'~"' f­ r 0::: 0 3: u of the steel highway bridge. In fact, there is no pla'Ce imme­diately on the river above the 102nd W. longitude crossing where the strata are in place. At the Crossing section, the top of the key horizon, the upper fossiliferous four inches of a hard brown .. llil r;; University of Texas Bulletin sandstone two feet thick at the top of the Basement sands and immediately below the Walnut clay, is 210 feet above the river, This el~vation increases normally to the 102nd West meridian crossing. At the next station, three and a half miles up the river, the Edwards limestone extends below the surface oj. the · river, thus indicating a vertical displacement of over 250 feet in 31h miles. How far below the river level the key horizon lies can­not be determined, but it probably lies at no great depth, for at a hundred yar.ds distance it is some twenty feet above water. The strata here are also slightly inclined toward the northwest. At White Point, a little over a mile above Round Point, the key horizon is 100 feet above the river and in less than a mile upstream the top of the Basement sands is found 30 feet above the river and remains at about this distance above the water to the Kansas City, Mexico and Orient Railroad crossing at Girvin. At the steel highway bridge over the Pecos at Girvin, alluvium _conceals the Walnut clay-Baseinent sands contact, but 15 feet above the river the Edwards lies nearly horizontal, and in the .river bed at the southwest pier of the bridge the sands are ex­posed. Thus somewhere between these two elevations lies the key horizon. Five miles e11:st of Girvin in the escarpments on either side of the highway and railroad, the strata are in place and continue so1• to and beyond Rankin, as far as observed in Upton County. To the west of Girvin on the south side of the railroad, about two miles· from the town, the strata are again in place and con­tinue as far as the investigation was carried to the southwest,, west, and north of Fort Stockton. During its history the Pecos has meandered sufficiently to form the present river valley. The river itself is responsible for .the erosion of the entire river valley here as no streams empty into it near the area, and also as pot-holes are found at different elevations in the walls of the bluffs facing the river, showing that the river at some of its stages occupied these di!-· ferent positions. Farther down the stream where the base of the Edwards dips under the water, the river valley narrows to a steep-walled canyon,. as the limestones aff~rd less opportunity for lateral migration than the Basement sands. To the northwest of Girvin, Geology and Mineral Resources of Crockett County 63 the valley again broadens in proportion to the amouµt of sand exposed. . The meandering of the river over this great area, thus pro­ducing the equivalent of an intermittent lake and standing water, is responsible for the gigantic slumping west of the 102nd meridian. The erosion of the Basement sands underlying the Edwards limestone and causing it to be depressed ·is responsible only for the minor slumping, and that, too, along the edge of the present river course. Slumpi!lg of this nature can be identified from the other in that the latter occurs only in numerous short distance slumps and the strata are never horizontal; while the former extend over vast areas occupying the entire valley and the strata are usually horizontal or practically so. In numero1111 instances there is a combination of both forms. In well logs outside the limit of that portion of the river valley which at some time has been the channel of the river itself, there are recorded strata of almost pure rock salt interbedded with red Permian clays. The highest of these beds, some one hundred to one hundred and fifty feet thick, lies about four hundred feet below the present river level. Above it are only a few layers of Per.r.nian clays and limestone overlaid by the porous Triassic and Basement sands. Lying at such a short distance below the surface of the river valley, and with very little impervious covering, the water from the river, at the various horizontal and vertical positions which it has assumed during its history, has had little difficulty in penetrating in con­siderable quantities to a sufficient depth to dissolve at least the greater part of the upper stratum of salt. 'The present position of. the strata over this area was not reached at once, lbut by a gradual settling as the salt was taken in-, to solution. Such a process would keep the strata practically hori­zontal at all times, and upon the complete solution of a part or the whole of the salt layer, the overlying strata would come to a position about one hundred and fifty feet lower than was form­erly occupied, as is· now the case. As far as known, no other salt layers lie close beneath. This thickness probably represents the amount 0£ vertical displacement which has taken place. Alcmg the present river eourse where the slumping has occurred, the Base­ment sands are practically all present except for a few feet which University of Texas Bulletin have been undercut; and this woul~ not be the case if they were accountable for the great settling. Conditions similar to this are known to exist in .the salines of the Gulf Coastal Plains. Harris, Veatch, Udden, Deussen, Dumble, and others in various publications on the salines of Louisiana and Texas have discussed the theory and process. Underground waters have carrie.d away in solution great amounts of salt from the top of 'the salines, causing a slump in the overlying strata. Later this has become filled with water, forming the lakes and ponds characteristic of the salt dome . country. · The strata overlying ·the salt in the Pecos Valley are even more pervious than those covering the masses of salt in the Gulf Coast region, ·and both surface and underground waters would have greater access to the salt stratum. Ten miles above the 102nd West longitude crossing and one mile southwest of the present river channel. is a sink hole at the edge of the escarpment. The west side of the hole is cut vertically down in the ·edge of the bluff for 135 feet; the east wall, being on the river plain, is only 2o feet high. The diam­eter of this circular hole is 150 feet. Only a few feet away from the sink are a :q.umber of potholes, showing that the river was once at this position, and undoubtedly it has been the greatest factor in forming the hole. . The Edwards limestone which is exposed abOve and.in the walls of the sink is very argillaceous, and therefore would not go into solution read­ily; and it would also tend to fill the pores in the sand below and render it impervious. It is highly improbable that this great hole was eroded by the river, or the material from the hole trans­ported underground either mechanic?lly or in solution. The more probable theory is the solution of a' great thickness of un-· derlying Permian salt, thus permitting a sinking of the overlying bed. Wash has so filled the bottom of the pit that it is inipos­sible to determine if this is the case. 'To the north, northeast, and northw~t of Fort Stocktcm, as far as the Edwards limestone is visible, about twenty miles, a careful examination of the strata showed them 'to be in place and to hav~ the slight southeast dip of the normal Comanchetm. As the strata over this area are in place and show no evidence ·of fold­ Geology and Mineral Resources of Crockett Co'l!-nty 65 ing, it is impossible that any movement from the Glass Mountain region or the.Davis and Barilla Mountains could have influenced this displacement. Since there is no sign of block faulting and much evidence of slumping from solution, it is quite evident that a dissolving of the underlying Permian salt has caused a settling on this gigantic scale. Unfortunately no wells in this area are of suf­ ficient depth to record the presence -0r ·absence of the salt. . Seven Mile Mesa, near the southwestern extremity of the last main Cretaceous escarpment which forms the northern boundary of the Trans-Pecos Plains portion of the E.dwards Plateau, is placed in the Edwards instead of the Georgetown, to which it has previously been referred1 A paleontologic examination of • this mesa would at first give the .impression that the formation· is Georgetown, but a more detailed study of the Comanchean fauna has shown that the fossils have a greater vertical range ·than was anticipated. Fossils considered characteristic of the Georgetown strata in this region, such as Terebratula wacoensis Roem., Lima wacoensis Roem., Pholodomya texana Con., Gry­phaea pitcheri Mort.; Vola, (J aneria) wrightii Shum., have been found throughout the Edwards also. · Shumard too, in his Journal of Geological Observations2 has identified Terebratula wacoensis Roem., Lima wacoensis Roem., and Gryphaea pitcheri Mort. in undoubted Edwards limestone along the Pecos in the vicinity of Sheffield. Stratigraphically the top of Seven Mile Mesa has been traced east and southeast where it forms the cap of th~ Edwards Plateau, which is the top of the third division of the Edwards. However, in the present survey, a number of Georgetown fossils were identified from the upper part of Seven Mile Mesa, associated with fossils· which · evidently are · of Edwards age. The establishment of the boundary between the Edwards and Georgetown dimions can only· come through a thorough and detailed study of both the paleontolQgic and lithologic characters of each. ~ careful com, parison of the section at Seven Mile Mesa, and the area to the _ 'Geologic Exploration of the Southeastern Front Range of Trans­ Pecos Texas. C. L: Baker,_W .. F. Bowman, Univ. Tex. Bull. 1733, p. 115. 'A Partial Report of the Geology of Western Texas, by G. G. Shu­ mard, Austin, 1886. University of Texas Bulletin .south, with the original sections, would not be without benefit. Horizontal sections from areas where the demarcation between the. two formations is known, if possible parallel to the shore line at the time these strata were deposited, would give the least amount of lateral variation, and perhaps simplify the problem materially. The general section at Seven Mile Mesa afforded the species listed below : Cyprimeria texana (Roemer) Epiaster cf. ·aguilerae? Boese Lunatia pedernalis Roemer · Enallaster cf. mexicanus Cotteau Hemiaster sp. Pyrina sp. Holeyctypus sp. Pecten cf. occidentalis (Conrad) Nerinea sp. Turritella sp. Pleurotomaria c!. Austinensis Shumard Gryphaea navia Hall Grypha'Ela marcoui Hill and Vaughan Gryphaea sp. Schloenbachia belknapi (Marcou) Exogyra texana Roemer Schloenbachia sp. ·PI'otocardia texana Conrad Codiopsis sp. aff. texana Whitney Pyrina sp. aff. inaudita Boese Lima sp. Lima wacoensis Roemer Pecten ·subalpina Boese Peete!' texanus Roemer SHEFFIELD TERRACE In the Pecos Valley, Comancheanand post-Comanchean move­ . ments hav.e only to a slight extent influenced the structural features ofthe area. The greater part of this "disturban.ce proba­bly occurred at about the time the Rocky Mountains were first uplifted, during late Cretaceous or early Tertiary time. Then the sediments of .the entire valley were tilted toward the south-. east to their present position, and any deviation from the normal southeast dip also probably occurred. Geology and Mineral Resources of Crockett County .67 AB the accompanying sections (Plate 2) indicate, there is a slight flattening in the dip of the surface formations near Shef­field, between Seven Mile Point and Nine Mile Point. At the 102nd west longitude crossing the strata increase above the nor­mal in rate of dip toward the southeast until they reach Seven Mile Point; thence to Nine Mile Point they lie practically hori­zontal. Below Nine Mile Point for about four miles the dip again increases above the normal till below Fourteen Mile Point, when again it reverts to the normal dip' as found west of the 102nd west longitude crossing. The longer axis of this terrace extends northeast and south­west, showing that the diastrophic movements were from the southeast toward the northwest. Had the forces acted from the southwest, the longer axis would have been at right angles, thus placing it northwest and southeast. Pressure exerted from the northwest would have placed the longer. axis of the terrace in its present position,.but all deviations in dip would have been in ex:cess of the normal, and this is not the case. The shorter axis of the terrace is about eleven miles long and lies northwest and southeast between Seven and Nin'3 Mile points. The longer axis, ·at right angles to the former, extends at least for some fifteen miles to the east of the river and passes immediately northwest of the northwestern half of Block 29 of the Sheffield tract of University land, as observations on this tract have shown. Its extent into Pecos County on the west has not been traced as far as is possible, though it has been observed to continue for six miles. · Plate 3 shows the location of the . Sheffield terrace and the bearing of its axes. STRUCTURAL FEATURES OF THE PECO,S VALLEY IN THEIR RELATION TO PETROLEUM ACCUMULATION The economic significance of surface structure in the Pecos Valley to a great extent lies in the relationship existing between surface and subsurface formations., In that portion of the Pecos Valley covered by the Permian Red Beds, Upper Triassic, and Comanchean, there is little value in surface structure as a concentrator and container of indige­ nous petroleum, since in the Comanchean and underlying Upper University of Texas Bullet~n Tri~ssic there are no petroliferous horizons. Below the Upper Triassic, Baker records an unconformity/ but this probably does not modify to any great extent, in the lower horizons, any struc­ture present in the overlying strata. Row great an unconformity there may 1be between the Permian Red Beds .of the Pecos Valley and the overlying Triassic is not known, but in the Llano Estacado region, Baker finds tJ:iat there 'is no great amount of angular unconformity between these two sys­tems, and this is probably true in the Pecos Valley, as the geo­logic history of. both areas has undoubtedly been very similar. This being true, the period through which the Permian Red Beds were subject to erosion and the amount of material which was carried away from their exposed surfaces has no effect upon their structul'al value except as it influences the depth at which . lower horizons are placed. ·If Professor Baker ~s observations in the Llano Estacado region also hold in the Pecos Valley, as there is every reason to believe that they do, surface structure in the latter Will remain practi-· ·c:ally the same through the Permi~n Red Beds to the Tessey for-. mation which is the uppermost of the Permo-carboniferous for­mations, and is believed to underlie the Permian Red Beds of the Pecos Valley., Although unconformities exist above the Tessey formation and some undoubtedly record great breaks in sedimentation and e.i­tensive erosion, they do not show any angular unconformities w'hich would either increase or de.crease the value of surface structure. ~elow the Upper Triassic, which is the lowest horizon exposed in the Pecos Valley iri.cluded in the present survey, and the Tes­sey formation, there are even less possibilities of petroliferous strata than in the Upper . Triassic or Comanchean. The occur­rence of thick cross-bedded, va.ri-colored sandstones, conglomer-· ates, red, yellow and purple arenaceous clays, gypsum, and mas­sive layers of rock salt, is ~icative of subaerial conditions and deposition mainly by rivers, which are very Uiifavora.ble for the formation of oil and gas, as such a complete oxidation of organic •Review of the Geology of Texas. Bull. Univ. Texas No. 44, 1916. Gwlogy and Mineral Resources of Crockett County matter would ensue as to cause its complete dissemination and consequent escape. As surface structure in the Pecos Vialley continues with little increase or decrease to the upper Permo-carboniferous strata, and since the underlying beds are steeply inclined, a structure at the surface would concentrate any hydrocarbons migrating along the inclined strata within the limits of the folding. There are no surface disturbances in the Pecos Valley which are suf­ficiently great to have any noticeable effect upon ;underlying strata that are not angularly conformable with those abr,ve or nearly so. Again, since there are relatively small exposure,;; of the lower Permo-carboniferous .and upper Pennsylvanian strata in the Glass Mountain region where it is possible to study them, and also as these places are so near the center of igneous activity, they. afford little opportunity for determining the exact nature and position of the strata. It is impossible to say what relation the lower beds bear to the upper Permo-carboniferous and overlying strata at any distance from the outcrop. The amount of their disturbance lmdoubtedly decreases as the distance from the Marathon region increases, if that disturbanee was entirely accountable for their folding, which Dr. Udden has found to be intense and extended over a considerable area. In the older formations the disturbance is much greater and decreas.es up­ward till at the surface the Triassic and Comanchean show prac­tically none. If more were known concerning the attitude and relationship of the lower layers t-0 each other, ithe structural geology of the Pecos Valley would be much simplified. There are, however, a few general conditions revealed in the development of the some­what similar geologic field of north-central Texas which are un­doubtedly applicable in the Pecos Valley. There an angular unconformity of unknown magnitude separates the lower an· thracolitic series from the upper, so that there, as here, it is im­possible to determine from surface structures the nature and at­titude of the strata below the unconformity. A folding in the . M:rata at the surface in both fields only indicates in,ovenient later than the deposition of the yc,angest beds which are affected. Of what value it has been in forming favorable structure below depends upon the amount ·of angular unconformity between the University of Texas ]Julletin different formations. In nor'th Texas, it is only necessary to allow for one angular unconformity, but in the Pecos Valley there are several, some of which are of unknown angular size. Th<>~h little is known of the exact relations between the Bend .ind Strawn formations in north Texas, the vast amount of data obtained from well logs indicates a large plunging anti­cline extending northward from the Central Mineral Region, which. is a large igneous intrusion and which has folded the younger formations in a manner similar to the Marathon region. Along the axis of this fold are located numerous small inclined · terraces and. plunging arrested anticlines whose presence is due to the last slight movements in the region. These have taken place along the axis of the fold which, as it has been subjected to the most severe bending, has weakened and become the line of least resistance. • In the Pecos Valley, though it is geologically more complicated and more steeply folded in the lower formations, similar con­ditions exist. From the Marathon Mountain region there extend one or ruore folds whose lower formations are much disturbed and this disturbance relatively decreases toward the surface till, in the Triassic or Comanchean, the course of the extreme folding be~ neath is merely indicated by a slight terracing or :flattening of the dip due to a line of weakness being formed in the direction of the excess folding in underlying strata before later deposition. These terraces may have been form,ed previous to or subsequent to the tilting of the formations of the Pecos Valley to the south­east, but tt is more probable. that they occurred contemporane­ously with it. As in the north Texas field, nothing can be definitely stated concerning we exact attitude of the strata ~low the uppermost angular unconformity, without a great amount of data from well logs which at present are not available. Prospective testing of the PecOl!I Valley for petroleum should at first be confined to the surface structures, however slight they may be, for they may either form the impervious coveting for hydrocarbons which have migrateLF ~LIME STON E Fig. 3. Diagrams showing conditions encountered in obtaining water from the Edwards Limestone. through the more impervious layer is afforded. Thus there are no definite and uniform water-bearing horizons, and no uni­formity in production of wells, as is the case where a definite water sand can be relied upon. University of Texas Bulleti1l Plate 7, the diagrams, contrasts the two general conditions: In the lower diagram a definite water-bearing 0 horizon can be de­pended upon and tlie depth at which th.e water will be found can be computed from the depth at a known point, the <;liP, of the horizon, and the difference in th~ surface elevations. In. such a case the water-bearing horizon is generally quite uniform, and both depth and amount of available water can be quite accurate­ly estimated. In.the upper diagram the reverse is true. No per­sistent water horizon is present and the irregularity of the chan­neling in size, depth, and direction makes it impossible to reach definite conclusions as to depth and amount of proouction. A well only one location from a producer of certain rate may vary to any extent from a large well to a dry hole. Wells drilled in the Edwards limestone in Crockett Couny encounter this situa.tion . • As jointing and bedding in the Edwards limestone follow no regular system, little geological assistance can be rendered. In case of a small well or dry hole, shooting may materially increase . the production, as cracks and fissures can be established which may reach to the water-bearing channels. BUILDING-STONES The factors which determine the value of building stones, other than the properties of the stones themselves, are: the cost of procuring and fitting the material for use, traru;portation, and, in more recent years, the change of fashion of using certain stones for constructive and decorative purposes. The properties of stones themselves, however, to a great extent fix their value. Of primary importance in stones desired for masonry con­struction . is durability, which is dependent upon strength to compressive and transverse forces; hardness, texture, chemical content and color. For buildings and for decorative purposes, color assumes a great importance. In Crockett County the Edwards limestone furnishes the en­tire supply of building stone. The Basement sands are generally too soft and variable to be of any use, and moreover, their surface distribution is confined to the i:mm.ediate valley of the Pecos River. In some places ledges from two to fifteen feet thick are extremely hard and could be used for construction, but they are Geology «-nd .¥ineral Resources of Crockett County 79 of no value in comparison with the Edwards limestone, which. has a surface distribution over the entire county and is practicable for nearly all purposes. The durability of the Edwards limestone, both dressed and rough, is attested by its state of preservation in some of the oldest ranch houses in the county. Though no data on strength are available, the normal crushing strength of about 3000 lbs. per square inch is probably preserved throughout the Edwards, with the exception of the soft argillaceous, fossiliferous layers. 'l'he grains are moderately small, firmly cemented, and practi­cally unmixed with weakening minerals. Because of its tough­ness the Edwards possesses sufficient transverse strength to withstand the normal tr:ansveise pressure of ordinary build­ings. The hardness of the lime varies widely. In some places it is exceedingly clayey and soft, but generally the grains are so !fir~nly cemented with lime that the rock has a sub-c~ystalline appearance and it is difficult to break it with a hammer. Its resistance to both mechanical and chemical weathering is above the average, while its homogeneity causes it to wear evenly. The density of texture also adds to the value of t4e Edwards for building purposes. Its texture is moderately fine and even, eausing it to split and dress well, and its density i3 sufficient to lower the ratio of absorption to the surface exposed below that of the ordinary limestone. 'l'he color of the Ed'>rnrds limestone is remarkably uniform and eonstant, except near the surface arid along joint planes, when ·it is stained by ferruginous or carboniferous matter. Like most other limestones it weathers lighter on exposure. This change is not particularly noticeable for it is a light gray when freshly quarried and weathers to a pale straw color. The absence of minerals other than a great amount of calcite crystals in places and local occurrences of ferruginous and carbonaceous matter in others, eliminates the streaked and blotchy appearance that some stones assume on weathering. The chemical composition of the Edwards shows that it is not dolomitic. The cost of quarrying building stone depends upon the acces­sibility of the rock and its structural features. The accessibility of the Edwards is at the maximum, for it lies practically hori­ ., University .of Texas Bu·zietin zontal and at the surface over the entire county with the excep­ tion of the immediate Pecos Valley, and affords an unlimited supply. Its resistance to weather in situ makes it unnecessary to strip more than a few feet of the surface, and its uniformity and homogeneity eliminate the expense of quarrying waste layers to uncover good stone below. If good judgment is used in locating s quarry, practically the entire content can be used for buildin~ purposes. Jointing and bedding planes also influence the cost of quarry­ ing. If they are moderately regular and not too numerous they greatly facilitate extracting the stone. If too frequent the blocks . will be too small to be of v\lue a:r:d if the ledges are too thick and joints few, the expense of quarrying is much greater. In · the Edwards limestone the bedding is generally from one to four · or five· feet thick, th(!ugh· sometimes it is as nluch as twen'ty to thirty feet. The jointing varies from four to eight or ten feet. There seems to be no system or regularity of either jointing or bedding. In the Edwards limestone, Crockett County has a material of wide distribution and .great accessibility, requiring a mini­ mum expense for quarrying and transportation, and posses8ing properties that make it valuable for practically any building. or decorative purpose: Its distribution makes it available with practically no transportation and its use both for private dwell­ ings and public institutions shows . it to be a desirable material. There is not, however, sufficient building within the county to warrant the expenditure necessary for opening and maintaining a working quarry, as there is no means of more than very local transportation of the stone. It is less expensive to open a new quari·y when stone is needed than it. is to haul the material any distanoe. CLAYS 'The clays of Crockett County are both residual and trans­ported. R esidual is used in the restrictive sense ·and applied only to t.he mantle covering the native rock as it has decomposed in situ. Transported clays are residual clays which have been carried from their place of origin and deposited elsewhere. The transporting agent is chiefly running water, though much wind­ Geology and Mineral Resources of Crockett Oownt'JI Bl blown material settles in the form of clayey· deposit• kno~ $8 aeolian clays. Residual material, however transported, when permitted to settle and accumulate in water is called sedimentary clay. The source of the residual clay in Crockett County is confined to the Comanchean limestone, sand, and clay. The greater part is supplied by the liberation of kaolin as the Edwards limestone decomposes. The Comanche Peak limestone and the Walnut clay supply a proportionately greater amount of clay in comparison to their mass, as there is present in them a greater amount of kaolinite and less of silica. In the Basement sands there is very little clayey material present. Although varying considerably in composition, these sands are high in silica, low in alumina. However, in localities · some of the grains are feldspathic, being chiefly orthoclase feld­spar reworked from the Triassic; and ihe.uld also indicate that the fold extends farther to the northeast than was possible to trace it in reconna..issance. . · '!'here is, then, in Crockett County, a large fold in the buried Carboniferous strata some 2000 feet below the surface, entering the county at about the highway bridge over the Pecos River, ' University of Te;r,as Bulletin three and -a half miles east of Sheffield, and bearing approxi­mately N 50° E. It passes immediately to the northwest of the Sheffield tract of University land and although it could not be located farther in reconnaissance, because of the lack of expo­sures, it probably extends across the entire county, diagonally from southwest to northeast through the Barnhart tract of Uni­versity land and into the adjoining counties to the north. Near its point of origin, in the Marathon Mountains, the lower forma­tions have been observed to be strongly in:clined and this fol<\ing decreases in the upper strata, so that at the surface the trend of this Pennsylvanian fold is marked by slight departures from the normal in rate of dip of the surface formations. · The value of this fold as a concentrator of petroleum cannot be estimated as there is no sub-surface data for a basis. How­ever, the evidence supplied from the development of a si~ilar geological fold in north.-central Texas is positive. It is possible to state that if petroleum is present in any of the formations underlying the Pecos Valley, the most desirable area for testing is along the axis of this fold. As the fold is undoubtedly ir­regular in the lower formations, as is indicated by the surface strata, all locations along the fold will not be of equal value, but it is impossible to :rrtake more definite statements. The few tests under operation in the region record shows of oil in the Carbon­iferous strata, but no completions have been made, nor has pe­troleum in commercial quantities been reported. As has been mentioned, the lower formations of the Marathon fold are not regularly flexed, but plunge to the northeast, from the Marathon region, in a series of plunging, arrested anticlines, or "noses", and synclines. These "noses" along the trei;i.d of the general fold very probably have a definite relationship to the terrace areas of the surface formations. Between the surface terraces, the lower formations are probably relatively lower. Thus the exploration of the Pen~sylvanian strata in the Marathon fold should at first be confined to the surface disturbances. The formations underlying; the Sheffield Terrace, at its dis­tance from the steeply folded strata of the Marathon region, should ·be more gently inclined and favorable for the concen­tration of petroleum. · A testing of the University lar:ids in Crockett, Schleicher, Geology and Mineral Resources of Crockett . County . ... -. Irion, Reagan, Upton, and Terrell counties should first be begun in the northwestern half of Block 29 of the Sheffield tract of University land, as this is the most promising area. Next in order of value are the Barnhart tract in Crockett County, ex­tending into Schleicher, Irion and Reagan counties; and the two tracts in Terrell County. Although no structural maps were made of the University lands in Terrell County, observations upon the University lands and the area to the northeast show definite disturbances in the surface formations. These two tracts undoubtedly lie on the Marathon fold and further investigations may show them to be favorable areas. The Big Lake tract in Crockett County extends into Reagan and Upton counties on the north. The reconn11issance of the area within Crockett County afforded little information, be­cause of lack of outcrops. A more careful survey should be made before being reported upon in detail. From what is known, it would appear that the southeastern part of the tract is the most favorable, as it lies nearest the Marathon fold. In testing the Sheffield tract of University land, the locations ·should be made preferably on the northwestern half of Block 29, as the axis of the fold passes nearest this area, as is indicated by the general trend of the fold from the southwest and the ter­racing of the surface formations in the northwestern half of the block. More definite information cannot be given till the geology of the individual a.reas is outlined by sub-surface data from well logs. It will then be possible to determine the stroctural fea> tures of the fold more closely. . The la.ck of surface exposures on the Barnhart and Big Lake tracts makes it impossible from a reconnaissance to define closely the most favorable area. However, from the reported terrace to the southeast of the Barnhart tract and the general trend of the axis of the fold, it would seem advisable to make detailed stadia surveys for the location of this fold from southwest to northeast across the Barnhart tract, as this is the normal course, if the fold continues across the county. The uniformly _slight dips to the southeast on both the Barn­hart and Big Lake tracts, observed at widely separated points, indicate that the surface formations in general are normal. How­ever, departures from the normal rate of dip may exist between University of Texas-Bulletin points of observation in reconnaissance, and this can be deter­mined only by detailed surveys. The accompanying structural reconnaissance maps (Figs. 4, 5, 6) indicate the results of the investigations upon the University lands in Crockett County. No more than an approximate depth to which a test should be carried can be given, as insufficient drilling data are available. However, the information afforded by a few deep tests near Sheffield and San·Angelo indicates that in the vicinity of the Sheffield terrace, and in general along the axis of the Marathon fold, a test should be carried 4000 feet. This depth, in most instances, should carry the hole well down into or through the Carboniferous. l f I z;i, '\,f 41 _ if' 1 f 1;;# 1 I f t' \11 -if~~ i ~ 2/ \ . \-. _" t ) f ;L .;~"\~ 4L f ;J ~ 4f ~ i 6Ji o ./~T r "2 -6 1 /~INDE~~ . r 6J i1 ,.;1'AL ~ uv . ~RANCH ,if"--'n ..;L ( ,, ; ptLDRESS RANCH) ~ r4/ ­ I 7 1 fi '~ 1P r ---;~L(f;rf;?J f 1 ~~~ ~ :· ,:' .~ f f I221 f l f )./' f// Jf 5f ~ ~ _ 1 s' 11 1-1 f ;f ___;t~~­ STRUCTUR/\L RECONNAISSANCE j :fQ ~ ,;/. j ,,;~'!;/::~--~~---:1-~~r? -0> j/ 4/ UNIVERSITY L/\NDS ; 2rEw> J r r o -~-·-,~-, r ;-r J ~ r 1 5HEFflELD TRRCT /./ / 1.L ~ •HEND~l?SON ~hi! 4/ !L 4 RANC H r;. i-II f~ i jr ---. . . --. . -· 'LEGEND NOTE: LARGE FIG URES REFER TO BLOCK NUMBERS ON COUNTY . MAPS [ZJ~~~~[EJ Fig, 4. Structural Reconnaissance Map of the STRATA TRAILS ROADS WINDMl_LLS RANCHES DIRECTION AND AMOUNT QF' QIP Sheffiield Tract of University. Lands. HORIZONTAL JN MIN\JTf;S ~ // I \ ~~ ~ LEGE ND " \"" ""' ' G2I B 0 EJ ~ - f\ . \ 31 ...., ... ., "~·-~ .....-......-···-· --·· ···-···-···----·­ ~---~·­ :--. I'\ 55 " \ \ \ '\ " \ f IC!. ¥ L jf "f Fig. 5. Structural Reconnaissance Map of the Barnhart Tract of University Lands. LEGEND STRUCTUR.IL RECONNAISSANCE NOTE: LJ\RGE FIGURES REPER TO BLOCK NUMBERS UNIVERSITY LANDS BI G LAKE TRACT ON COUNTY MA.PS G::J B rn 8 CKJ IBAlLS ROADS WINDMILLS RJ\NCHES DIRECTION AND AMOUNT Of DIP I!'J MINUTES Fig. 6. Structural Reconnaissance Map of the Big Lake Tract of University Lands. UNIVERSITY OF TEXAS BUREAU OF ECONOMIC GEOLCOY AND TECHNOLOG Y J. A. UDDEN, DIRECTOR BULLETIN No. 1857 PLATE 2 104° 103° NEW ---.--*/""·------.-·-­ / I I GARDEN CITY i I~~ ·GLAs~cocKi I Cen ! Kc i ____i_____ I . ______________J I j I I . REAGAN ©STILES 1 .I I I I I OR1~NT AREAL GEOL<)GIOAL MAP OF PECOS VALLEY ADAPTED FROM GEOLOGICAL MAP OF TEXAS ACCOMPANYING --+--------­ UNIVERSITY OF TEXAS BULLETIN NO. 44 BY r-­ R. A. LIDDLE AND T. M. PRETTYMAN 1 1919 1. Scale 0""""""'"""~10==~==2~0.....""""""3~0======40,,,,,....,,,,.,....soNfiles _J LEGEND 0 ~ E] G 0 B w LATER CENOZOIC QUATERNARY UPPER CRETACEOUS COMANCHEAN CRETACEOUS TRIASSIC PERMIAN PENNSYLVANIAN UNDIFFERENTIATED IGNEOUS ~ ~SOLID LINES: KNOWN AXIS ANO LIMITS OF FOLD t::::::::__j RELIEF ~BROKEN LINES: PROBABLE EXTENSIONS OF FOLD PLATE 2, Bulletin 1'umber 1857, University of Texa.a. t.-~ /, I LEGEND ~ Pl ltl!T AHi> 'Tli•RO ·01visl0Ns E:OW•.,D$ .~ llCOHOl 01v1 o iO"' ·".llowAff0.5 .~ CONl l'IH'H ' Pt,< •• WALH UT CL,l\Y' K•Y Ho•1z.0tt - , -..UC•NT SllHOf ~.~?~.rJ~~~~ CCUI IC.OM f fll' ,,rt ;.~~~?4 ,\u."VlllM !~~\ :\:;~:/ \ . ' \ ~~ ' ' ' ......... (Bl Fic.1 f• • ...• ' • • Ito,..,.._.,,, Pc.tu Fxo. 2. .... .. .. . ...... J:w~·:<..<~: (6) SECTIONS ALONG THE PECOS FROM PANDALE TO ­ ,.., BARSTOW ,. ' 'i I F/6 l VERTICAL ~ECT/ON.S SCALE ~ FIG Z STRIJCTUR.AL PROFILE ELEVATIONS BA SED ON KEY HORIZON V£R SCALE HOR. SCALE PLATE ';?_ Bulletin Number 1857, University of Texas. ~ ~ LAND MAP S HOWING L.OCAT ION or SHE:f'Ff£LD TERRACE ~ -" " £. '-l& i R R R .. " · &fl, k <1' . " .. Co -/ / I "'9rrbe,... I~ovn?­..5c;hool f.-cnd ./[/ . "[ ." " JI / "I I - .. &A Nore. KNOY.IN AXIS ANO LIMITS OF" SHEF"fl£LD Tt:RRACE:' INOICATCO SY S OL ID OBLIQUE LINES. B ROKEN L1N£.S S HOW Po.s.s18LE EXTCNSJO NS OF 01STUR8(D AREA·. PLATE 4. Bulletin Number 1857, University of Texas. REAGAN COUNTY UPTON COU NTY --.----------:----·-------­ .'!•r'.,.:'.\>.,. ........ f GEOLOGICAL MAP OF CROCKETT COUNTY SHOWING LOCATION Of UNIVERSITY LANDS . ~ s 4 s ' 1 SCALE LEGEND !.,.,.,,) TRAILS k2J ROADS l/j INTERMITTENT STREEMS RECENT J.::;~:l;j ALLUVl UM D EDwARDs LIMESTONE COMANCHEAN § COMANCHE PEAK LS. I CRETACEOUS I 1RION CO UNTY --1--:--­ 8152 1 I I ~ ,_______,.........f----.;.I f-· z ;::=:) 0 u O:'.:'. w I u w ._j :r:: u V) ,-. -:----­ • 8 AG ET T ~ RANCH (5 ~. BASEMENT SANDS 1i __ -------~----_ __ J__ _ BY VA LVERDE COUJ\JTY R A LIDDLE ,AND T M. l'lfETTYMAN INDEX Page Ammonites. . . . . . . . . . . . . . . . . . 30 acuto-carinatus........ ...2'1; 22 marcyana. . . . . . . . . . . . . . . . . . . 23 vespertinus.. . ........23, 25, 29 Anhydrite. . . . . .\ .. ............ 83 Animal life .............. ...... 16 Arca................ . .. .. .. 30, 31 Arcopagia texana..... . .. . 21, 2·2, 3 0 Baker, C. L .......37, 38, 49, 50, 68 Balcones fault. . . . . . . . . . . . . . . . . 17 Barllla Mountains .. .. .. .. . . . 50, 65 Barnhart. ......... .. . ·-. 8, 10, 17 Barnhart-Ozona road. . . . . ..... 10 Barnhart tract.. . . . ..85, 86, 87, 89 Barstow. . . . . ....17, 18, 32, 33, 50 Basement sands . ..... . .... . ... . .. . . . ... . . 11, 1·3, 15, 23,, 28, 31, 33" 35, 37, 38, 39, 42, 44, 52, 62, 63 Bend formation . • , .. .... .. ...... 70 Big Lake .... ....... ..... . . ... . 17 Big I.Jake tract...... .....85, 86, 89 Bird Jife... . . .. .. .. .. .i.... .... 16 Black River . . . . ... . , ....... . ...· 32 Blanco beds ... , . . . . . . . . . . . . . . . . ·29 Bottom lands . . · . .. . . .. ...12, 13, 14 Bowman, W. F ......... ...... 49, 50 Brewster County .......... . ..17, 45 Br'ewster-Presldio County line .. . . ..... . ..... . ..... 1••• • 17, 48, 49 Build'ing stones... . . . . . . . . . . . . . 78 Calcareous group, Shumard's .. 1 .... .... ............. ·'• 28, 34, 35 Calcite....................... 84 Camp section . .. ..... .. ... 23, 51, 54 Canadian River .. · . .... ...... ... 37 Carboniferous . . . . .. .. .17, 48, 88, 90 Cardlum. . . ....... ............ 25 multlstrlatum. . . . ........•21, 22 sancti-sabae. . . . . . . . . . . . . . . . 23 Castle Gap...... ...... ..... . 30, 59 Castle Mountains .. . . . . ... . .. 26, 29, 30, 31, 32, 33, 35, 36, 38, 39, 42 Cave~. In Edwards limestone.... 10 Central Mineral Region . ... .. .. 70 Central Zone ........ ..... ; .. . . . 14 Ceratltes pedernalls . . ... . .... .. 22 Cerlthium bosquense.. ...... .... 55 Chandler. . . . . .1•••••.• 38, 43, 52, 53 Ch·andler section. . . . . . . . . . . . . . . 5·2 Ohert... .... ........... . .... 84 Clays. .. . ....·.......... ..... . 80 residual. .. . . .... .. .. .. ..... 80 transported. . . . . . . . . . . . . . . . 8 0 Clear Fork formation .. ....1.•••• 82 Climate... . . . ................ 12 Codiop,sis sp. aff. texana........ 66 Coleman County . . .. . . ... .56, 58, 84 Comanchean-Cretace<>us 8, 9, 11, 17, 33, 40, 42, 44, 45, 47, 48, 49, 71 Comanche Peak limestone .. .. . . . ..... ... .... . 25, 28, 31, 43, 44, 45 Comstock . ... .. .. ~ ..... .... .. 73 Control. .......... . ..... ... .. 18 CordiHeras......... .. .... ... . 14 PageCrane ·county.: . ...... ..·... . . . . . 7 Cretaceous. . . ..... . . 37, 38, 50, 51 Cretaceous system.. .........28, 34 Crockett County. .. 7, 8, 9, 1'5, 49, 88 larea of....... .. .. ;... . . . . . .. 7 boundaries..... .... . .. .....7, 8 Crossing section. . . . . . . . . .... ... 57 Cucullea.... .. .... ........ .... 55 Cummins, W. F . ..... ...... ... . ... . ....... 29, 31, . 32·, 33, 36, 39 Oyprimeria texana.... .... . . . .. . .. . . .. ....52, 54, 55, 57, 58, 60, 66 Davis Mountains ........ ... . . so, 65 Delaware Creek... . . . . .......... 35 Description of formations . . . . . . 33 Deu,ssen, .A;lexander. . . . . . . . . . . . 64 Devil's River...... .... ... ...... 12 Diadema. . . .....•.. ......... 30, 31 Diamond Y Draw... , . . . . . . . . . . . 59 Diam.ond Y Draw section ....... 59 Dimple formation. . . . . . . . . . . . . 48 Dip.......... .... . . . ........... 10 Dip slope . .. ... . ; .. .... . . ...... 10 Distribution of formations . . .... 33 Dockum.. . . ..18, 19, 32, 36, 37, 40 Double Mountain formation .. .. . 82 Drake, N. F ... . 31; 32, 33, 36, 39, 40 Dumble, E. T ...•.... .31, 33, 36, 39 Eagle Pass. . . . . . . . . . . . . . . . . . . . . 12 Edwards limestone . . .... . . . . .. . .. .... .. ·'· .. 7, 8, 9, ·21, 25, 28, 34, 38, 39, i3. 44, 45, 52, 62, 76, 78 Edwards Plateau . . ... .. .. ... .. . ... . 7, 8, 10, 11, 12, 14, 17\ 21, 46 Elevation. . . . . ........ · ......... 12 El Paso ............. ... .. ·I··.. 8 Emie"rant Crossing. . . . . . . . . . . . . 20 Enallaster cf. bravoensis. . . . . . . 55 cf. mexl.canus .... ... ·'· ........ 66 texanus. ... . ....... .. 55, 57, 58 Engonoceras. . . . • . . . . . . . . . . . . 55 Eocene. .. ..... .. .. . .. . ...... . 51 Epiaster cf. aguilerae.....· . .... . 66 Exo.gyra. . . . . . . . . . . . . . . . . . . . . . 55 texana.. ........ ... 22, 30, 52, 53, 54, 55, 56, 57, 58, 59, 60, 66 Fauna.. .. . ... .. .. . ... ..... .. 14 Flint... . . .. .... . .... .. .. .. ... 89 Flora............... .......... 14 Fort Lancaster. . . . . . . . . . . . . . . . . 21 Fort Stockton .. . . ....1•2. 50, 62, 64 Fort Stockton-Pecos road.. .. ... 51 Fort Washita........ .......... 29 Fourteen Mile point section . . 53, 67 Fredericksburg. . . . . . 18, 19, 42, 44 Front Range .. ....... .... ...... 50 Fusus... . .... ....... , ........ 25 Gapt.ank. . . ........ ............ 48 Georgetown. . . . . . . . . . . . . . . . . . . 65 Geog-raphy of Crockett County. . 8 Girvin... ........ 26, 391 43, 60, 62 Girvin Highway Bridge.. ....... 59 University of Texas Bulletin Page · Page Girvin Highway Bridge Election. 59 Glass M;ountains ... ..... . ~ .. •.. . • : ..........17, 48, 50, 65, 69, 71 Glass .sand..........•.......... 84 Glenrose formation ..........••. 42 Gould, C. N . . ........• ......•.. 40 Government Military highway. . 8 Grand Falls.. 2'7, 28, 31, 38, 39, 40, 42 Gravel. ....................... 75 Great American desert.. ....... 14 Gryphoo. .marcoui. ... ..... ...57, 66 marshii..................... 23 navia........... .. 52, 53, 57, 66 pitcher!. . . ... . ......... ... : . . . . 21, 22, 23, 25, . 29, 30, 31, 65 tucumcari!. . . . . ............ ·23 Gulf Coastal plains. . . . . . . . . . . . 64 Gulf of Mexico .......... . 14, 20, 50 Gypsum. ... ..... • .. ..... . •. . 83 Harris, G. D ... .. .·............. 64 Hemiaster.....•.............. 66 elegans.. ..... ....,.......23, ·29 Hill, R. T ..... ..... .... ........ 17 Holaster simplex .........·• . 1•••• 29· Holeyctypus. . . . . ............. 66 planatus. . . . . . . . . . . . . . . . . . . . 22 Homomya.......... .. .. 55, 57, 60 alta. .................... . .. 22 Horsehead crossing... 29, 30·, 35, 36 Howard's Draw....... .8, 12, rn, 75 Humidity. ... •. ..... .... ...... 12 Ichthyosarcol!tes.. ........... 57 Independence Creek ............ 52 Indianola. . . . . . . . . . . . . . . . . . . . . 20 Inferior division, Shumard's . . . . 34 Irion County . ..... . ...... .. ... 7, 89 Janeria quadricostata .. ...·21, 22, 27 texana...................23, 25 wrighti!. .................... 65 Journal of Geological Observa­tions. . . . . ..... . .... 20, 35, 65 Juras.sic........... ... ...28, 29, 39 Kansas City, Mexico and Orient railroad. . . . . .. .... . 8, 39, 62, 85 Latitude. . . . . ..............12', 18 Lima... . . ......52, 53, 56, 60, 66 Wacaensis. . . . . .......... 23, 25, 30, 54, 55, 57, 58, 59, 60, 65, 66 Lime........ . : .. ... ...... .... 82 Live Oak Creek .............. . . ....8, 12, 16, 21, ·22, 54, 75, 76, 86 Llano Estacado .14, 34, 40, 47, 49, 68 Lon.~itude. . . . . . . . . ... . . . . . . . . . 18 Louisiana. . . . . . . . . . . . . . . . . . • . 64 Loving County. : . ... . ....... .. . 40 Lower Oretaceous............28, 34 Lunatia pedernalis . ..,..... . ... . . . . . . . . . . . . . . 52, 54, 55, 56, 58, 66 Madera Mountains .............. 48 Magnetic declination. . . . . . . . . . . 18 Marathon fold . .....·. . .... . .. 88, 90 Marathon Mountains . ..... . ... . ............._.1'7, 45, 48, 70, 71', 88 Marcou, Jules ....... . . ·'· . .... . . . .......... ..... 28, 29, 35, 36, 37 Marly clay group, Shumard's.. •................•..28, 34, 35, 39 Meridian Crossing, 102nd•.... . . ............. "'" 11, 57, 60, 62, 64 Mexico................•....•.•• 14 Nat!ca tumida. • . . . . • . . . . . . . . • . • 22 Nerineii.......... .•. ........ .. 66 New Mexico . ....•..•. ..... •• 40, 47 Nine Mlle point...•.........53, 67 Oklahoma. . . . . . . . . . . . • . . . .. . . . 42 Opis................ .' . •• ..... . 25 Ordovician. . . . . . . . . . . . . • . . . • . 45 Ostrea crenul!margo .•.. .•... ... 25 marsh!!. .••... •.. .. ••.. ..... 29 Ozona................•.•..7, 8, 7·3 . population of. . . . . . . . . . . . . . . 7 Ozona-S'heffield road ..•.•18, ·20, 86 Paleozoic. . . . ...... . , ...•.•.17, 5 0 Paluxy sands.................. 42 Pandale.........17, 18, 21, 50, 52 Pancl'a.le. crossing..... .......... 111 section..... .......... .. .... 52 Panopora texana .............. . 22 Pecos City ... ... ..29, 31, 32, 36, 39 Pecos County ...7, 12, 49, 54, 57, 71 Pecos River............7, 8, 17, 42 Pecos Valley... . ....15, 17, 28, 34, 37, 38, 39, 40, 46, 48, 50, 67 petroleum accumulation in. . . 67 Pecten. . . . . ............... . 53. 54 irregularis. . . . . ~ ....... .. 5 5,' 56 cf. occidental!s; . . . . ......55, 66 !tratigraphic . ~eology . . . • . . . . . . 17 Strawn format10n . . . . : ... ..... . 70 Structural geology. . . . . . . . . . . . . 4 7 S'utton County .. . .... .. . . . .•.. 7, 73 Synopsis of formations ...... .... 18 No. 2. No. 3. No. 4. No. 5. No. 6. No. 7. No. 8. N'o. 9. No. 10. No. 11. No. 12. No. 13. No. 14. No. 15. No. 16.