DEPARTMENT OF THE INTERIOR
BULLETIN
OF THE
UNITED STATES
GEOLOGICAL SURVEY
No. 164

WASHINGTON
GOVERNMENT PRINTING OFFICE 1900

 

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UNITED STATES GEOLOGICAL SURVEY
CHARLES D. WALCOTT, DIRECTOR
RECONNAISSANCE
IN THE
RIO GRANDE COAL FIELDS OF TEXAS

BY

THOMAS WAYLAND VAUGHAN

INCLUDING A REPORT ON IGNEOUS ROCKS FROM THE SAN CARLOS COAL FIELD,

BY E. C. E. LORD

WASHINGTON
GOVERNMENT PRINTING OFFICE 1900

 

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CONTENTS.

 

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ILLUSTRATIONS.

 

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LETTER OF TRANSMITTAL.

DEPARTMENT OF THE INTERIOR,
UNITED STATES GEOLOGICAL SURVEY, Washington, D. C., May 14, 1899.

SIR:

I submit herewith for publication a manuscript by Mr. T. Wayland Vaughan, entitled Reconnaissance in the Rio Grande Coal Fields of Texas. This paper treats of two areas, both of which, in addition to the economic considerations, are of scientific interest, inasmuch as they give interesting types of the geology of the localities studied.

The first of the areas embraces that portion of the Lower Rio Grande region lying between Del Rio and Laredo, and treats of a section of the Cretaceous and Tertiary formations and of the relations of the one to the other. This section has been an object of interest for many years, and, as shown in the literature cited by Mr. Vaughan, has been visited by many geologists. As the region is a transition ground between the phases of these formations hitherto considered peculiar to the Rocky Mountain and the Atlantic Coastal plains, respectively, such a section must necessarily throw some light upon the relations of the formations, including the age position of those hitherto ascribed to the Laramie epoch. Mr. Vaughan could hardly be expected to solve completely all the problems of the region in the short period of time during which he was permitted to examine it, but his paper will be a valuable contribution to a progressive series of researches which have been made in that territory.

The second paper treats of the San Carlos coal field in Trans-Pecos Texas. This paper, too, is of great scientific interest, inasmuch as it gives a detailed section of the Cretaceous beds of the Vieja Mountains of the Trans-Pecos region, and also throws light upon the occurrence of interesting volcanic rocks.

Mr. Vaughan has treated the, economic features more briefly than he would have done if the determination of the stratigraphic position of these coals had not been the principal object of these preliminary reconnaissances.

Very respectfully,

ROBT. T. HILL, Geologist.

Hon. CHARLES D. WALCOTT, Director United State Geological Survey.

 

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RECONNAISSANCE IN THE RIO GRANDE COAL FIELDS OF TEXAS.

By THOMAS WAYLAND VAUGHAN.

INTRODUCTION.

One of the most important economic questions with which Texas has to deal is that of coal supply. Although it embraces 250,000 square miles of territory, and is by far the largest State in the Union, in 1897 it stood nineteenth in the scale of coal producers. For manufacturing enterprises and railroads coal is one of the first requisites; therefore in the following paper an attempt has been made to state all that is known of the coal fields of the Rio Grande region. Two reconnaissance trips made jointly with Mr. T. W. Stanton, under instructions received front Mr. R. T. Hill, during the field season of 1895; a reconnaissance made in 1898 in company with Prof. William L. Bray, of the University of Texas, who was studying the flora of western Texas; and a certain portion of the notes accumulated while mapping the geology of the Brackett quadrangle, as assistant to Mr. R. T. Hill, and later while mapping the geology of the Uvalde quadrangle, serve as a basis for this report, but all available information has been utilized. The fact that this report is, as a whole, the result of reconnaissance work and that it is not based upon a detailed study of the coal fields herein treated, should be emphasized.

Mr. Stanton has determined all of the Cretaceous fossils discovered, except a few Foraminifera, and has contributed his conclusions concerning the age of the beds. The Eocene fossils were determined by the writer.

The general plan of the discussion followed is:

• (1) The general geology of the coal fields and adjoining areas;
• (2) the distribution of the coal and the present condition of mining; and
• (3) the physical and chemical characters of the coal.

Several coal-bearing areas have been recognized in the region adjacent to the valley of the Rio Grande in New Mexico and Texas. The "

---

Coal fields of Colorado, by R. C. Hills: Mineral Resources U. S. 1892, pp. 319 et seq. New Mexico, Its Resources, etc., New Mexico Bureau of Immigration, Santa Fe,1884. The Cerillos coal field, by John J. Stevenson: Trans. New York Acad. Sci., Jan., 1890, pp. 105-122. Mr. T. W. Stanton has made an examination of they White Oaks mine, and informs the writer that the coal there is probably Laramie.

 

first of these includes a number of isolated or limited districts in New Mexico, to which belong the Cerillos, Bernalillos, and Fort Bayard fields, which are probably of the same age as the so-called " Laramie" coals of Colorado, viz, uppermost Cretaceous and transitional Cretaceo-Tertiary. The second area is situated in the Vieja Mountains, the vicinity of San Carlos, Texas. These coal beds are of Pierre age. The third area occupies the interior portion of the Rio Grande Plain, and extends from the Santa Rosa Mountains of Mexico to beyond Eagle Pass, Texas. Mines are worked in it near Eagle Pass, Texas, and near San Felipe, Sabinas, Fuente, and Porfirio Diaz, in Mexico. The coal of this area is of Fox Hills age. Associated with it is a fossil plant, Geonomites tenuirachis Lx., which also occurs in the "Laramie" coal of New Mexico. The marine fauna is equivalent to that of the Ripley and Navarro beds of the Gulf region and to that of the Fox Hills beds of the Rocky Mountain section. The fourth area is the, coal field adjacent to Santo Tomas, Texas. These coals are usually lignites of Eocene age.

In addition to the districts mentioned adjacent to the valley of the Rio Grande, allied beds are found in the Trinidad-Raton district of Colorado and New Mexico and in the White Oaks district of the Sacramento Mountain region of New Mexico.

 

 

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I.—EAGLE PASS AND EOCENE COAL FIELDS OF THE MIDDLERIO GRANDE REGION OF TEXAS.

DEFINITION OF THE AREA.

This part of this report is based upon a reconnaissance, made in 1895, of the Rio Grande region from Del Rio, in Valverde County, to Santo Tomas, in Webb County, thence to Uvalde, in Uvalde County; and upon a second reconnaissance, made in 1898, from Cline, Uvalde County, to Eagle Pass, thence up the Rio Grande to Upson, across to Paloma, hack to Eagle Pass, and from the last-mentioned place to Carrizo Springs, thence to the Rio Grande at the Webb-Maverick county line. After returning to Carrizo Springs the return journey to Uvalde County was made along the Nueces River. Besides the data accumulated on these reconnaissance trips some data obtained while studying the geology of the Brackett and Uvalde quadrangles have been utilized.

The area is approximately a right-angled triangle, the apex being at Santo Tomas; the hypothenuse, the Rio Grande; the base, a line from Del Rio to Uvalde, and the third side a line front Uvalde to Santo Tomas. It embraces portions of Kinney, Valverde, Maverick, Webb, Zavalla, and Uvalde counties. (Pl. I.)

GENERAL PHYSICAL FEATURES.

These coal fields lie within the geographic province of the Texas region denominated the Rio Grande Plain. This plain is a local modification of the southwestern attenuation of the coastal plain of the Gulf and Atlantic States, comprising a western prolongation of the same up the Rio Grande, included in the angle formed by the convergence of the Balcones escarpment line and the eastern front of the Cordilleran region in Coahuila.

The Texas side of the region is a vast plain, slightly inclined to the southeast, sloping front an elevation of 1,082 feet at Johnstone, Valverde County, to about 600 feet opposite Santo Tomas, or at the rate of about 3 feet to a mile. The streams have cut their beds in this plain and now lie considerably below its former level. The larger of these stream valleys are accompanied by series of terraces. The structure of the Texas portion of the plain throughout the greater part of its extent is that of a gently southeasterly dipping monocline. In the "

---

Hill and Vaughan, Eighteenth Ann. Rept, U. S. Geol. Survey, Part II, 1898, p..202.

 

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vicinity of Santo Tomas there is a local exception to the usually uniform direction of dip of the strata. Here the dip, instead of being to the southeast, is to the northeast, according to information, furnished by Mr. D. D. Davis, superintendent of the Cannel Coal Company's mine. This disturbance is, without doubt, genetically connected with the uplift of the Sierra Santa Rosa of Mexico.

The northern limit of this plain is a great southward-facing escarpment, several hundred feet in height, which has been described under the name "Balcones escarpment." Along its foot is a strip of country

from 6 to 15 miles wide, which is broken by faults and in which there has been considerable volcanic disturbance. This scarp is the southern edge of the vast Edwards Plateau. It is composed of practically horizontal limestone strata, and attains an altitude of some 2,500 feet.

The vegetation consists of grasses, which at the time of our visit were mostly dead and dry, and of a variety of prickly plants belonging "

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R. T. Hill: Am. Geologist, Vol.V, No.1, Jan., 1890, pp. 17-18: Am. Jour. Sci., 3d series, 1887,Vol. XXXIV, pp. 291 et seq.

The geographic features of the region are more fully described in a paper by Mr. Hill and the writer entitled The Geology of the Edwards Plateau and Rio Grande Plain: Eighteenth Ann. Rept. U. S. Geol. Survey, Part II, 1898, pp. 193-323.

 

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to the Leguminosas, Rhamnacaæ, and Cactacæ, constituting the chaparral of the Mexicans. There are enormous orchards of Opuntia rafinesquei, the common prickly pear or nopal of the Mexicans, and tasajillo, Opuntia leptocaulis, is often extremely abundant. Of the Leguminosæ, the mesquite and several species of acaciæ are the most common. Lignum vita also is a common and characteristic plant. Except along the creeks, where occasionally live oaks grow, there are no trees, unless the mesquite reaches a size sufficient to entitle it to that name. Professor Bray, of the University of Texas, is making a careful study of the flora of western Texas with reference to climatic and other natural conditions. Rains are very infrequent, and the country is not capable of supporting a dense population.

The following table gives the average annual rainfall at some of the more important places, as determined by observations extending through several years:

The mean annual temperature is as follows:

January is the coldest month, but the average temperature for that month at any place is rarely as low as 45°. August and July are the hottest months, but the average for these months is rarely as high as 90°. In the summer, in the middle of the day the heat is intense, but at night there is always a refreshing breeze.

DESCRIPTIVE GEOLOGY

The region as a whole is underlain by a series of rock sheets belonging to the Cretaceous and Tertiary periods, which are covered to a considerable extent by surficial deposits of silt and gravel. The beds will now be described in ascending order.

CRETACEOUS.

RIO GRANDE SECTION.

The Cretaceous strata of the Texas region have been divided into two great subgroups or series, an upper and a lower. These series have been further divided into formations, which are still further subdivisible into individual strata; but for purposes of general discussion the formations are the units of the system of classification.

"

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Climatic conditions of Texas, by Gen, A. W. Greely: Senate Ex. Doe. No. 5, Fifty-second Congress, first session.

 

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LOWER CRETACEOUS (COMANCHE SERIES).

EDWARDS LIMESTONE

At Del Rio the lowest rocks exposed belong to the Fort Worth limestone, but a short distance above Del Rio, before reaching the mouth of Devils River, exposures of the Edwards (Caprina) limestone are seen. The canyons of the Rio Grande and Devils rivers in this vicinity are cut through it. It is a whitish limestone and occurs in thick ledges.

FORT WORTH LIMESTONE.

Within the breaks of the Rio Grande, on both sides of the railroad where it crosses San Felipe Creek and in the valley of the creek to the north of the railroad, are good exposures of this limestone. Macroscopically it is rather soft, chalky, and argillaceous, and possesses a minutely granular or subflocculent texture. Its color when freshly broken is white or whitish, with a yellowish tinge, due to the presence of ferruginous matter. It weathers to a grayish or yellowish color. The fossils which it contains are frequently ferruginous replacements. Microscopically the limestone is composed of minutely crystalline calcite and much flocculent (argillaceous) Material. Foraminifera belonging to the Globigerina and Nodosaria types are present in very great numbers.

Exposures aggregating a thickness of about 40 feet were seen. In its upper part the limestone becomes very argillaceous and passes into a whitish clay which lies at the base of the Del Rio ( Exogyra arietina) clay.

The Valverde County court-house and jail are built of this limestone. Through it the San Felipe Springs burst forth. the water coming up along a system of joint planes.

The following fossils were obtained near the San Felipe Springs (locality No. 269):

"

---

Mr. W J McGee defines break as follows: "The 'break' is the head of a small retrogressive ravine, a minor water course gradually eating its way back into the upland." Twelfth Ann. Rept. U. S. Geol. Survey, p. 434. What is here called "the breaks" is a much-indented escarpment that constitutes the outer boundary of the Rio Grande Valley, in a restricted sense, and up to which the general level of the Rio Grande Plain extends. The indentation of the escarpment is due to the head-water erosion of numerous small streams which are cutting it away.

 

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DEL RIO CLAYS.

The top of the breaks of the Rio Grande to the northeast, east, and southeast of Del Rio is formed of the Buda limestone, to be discussed later. The slope is composed of the Del Rio clays. Within the breaks near Del Rio, to the southeast, is a conical-shaped butte, called Lone Hill, also composed of these clays, and they are exposed 20 miles west of Brackett, on the road to Del Rio, where they are overlain by the Buda limestone.

The following is a section exposed at the old ocher mine 2 miles north of east of the Del Rio court-house:

In the lowest stratum are thin, sandy flags containing Equisetum? and Nodosaria texana. Exogyra arietina is very abundant throughout the section. No. 4 is the bed from which the red ocher has been mined. This ocher is usually a vermilion-colored clay.

The section above described illustrates the lithologic characters of the beds. At the base, along the contact with the Fort Worth limestone, there is a white calcareous clay. Above this bed the clays are usually greenish before weathering. When subjected to atmospheric action they become yellowish. Beds of red clay occur hear the top. Frequently the Exogyra arietina is cemented into slabs by a sandy ferruginous matrix. The thickness, as determined by the aneroid barometer, is 100 feet.

Although fossils are numerous in these clays, there are but few species. The following are the species collected and the localities whence they were obtained:

 

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BUDA LIMESTONE.

Above the Del Rio clays occurs a limestone, which both in its stratigraphic position and its lithologic characters corresponds to the Buda limestone of the Colorado River section at Austin. Macroscopically this limestone is hard, and whitish or yellowish in color when freshly fractured. The fracture is conchoidal or splintery. It is frequently traversed by minute veins of calcite. Upon weathering it becomes yellowish or pinkish; occasionally, on account of the great amount of iron contained, weathered specimens may be incrusted by hematite. Numerous small red or pink blotches characterize the limestone. Microscopically it consists of minute veins and patches of transparent calcite, between which are patches of minutely crystalline granular calcite of dark-gray or brownish color, in which angular transparent pieces of calcite are embedded. The calcite veins are sometimes clouded in appearance, but are lighter in color than the bulk of the rock. No well-preserved Foraminifera were observed, but there are grayish masses of minutely crystalline calcite that show the structure of Foraminifera of the Globigerina type.

Outcrops of this limestone are to be seen northeast, east, and southeast of Del Rio, where it occurs above the Del Rio clays. It is also exposed at numerous places on the road from Brackett to Del Rio, between Sycamore Creek and the latter place.

Measurements of the thickness of the limestone at Del Rio were not obtained, but near Brackett it is about 100 feet thick-a little more than twice the thickness at Austin.

UPPER CRETACEOUS.

DAKOTA DIVISION.

(Absent.)

EAGLE FORD FORMATION.

The Buda limestone is overlain by a series of flaggy, argillaceous limestones, between the beds of which calcareous shaly layers are frequently found. These beds occupy precisely the same stratigraphic position with reference to the Buda limestone below and the Austin chalk above as do the Eagle Ford shales in central and northeastern Texas. The stratigraphic continuity of the beds has been traced from Del Rio, by way of San Antonio and Austin, to Red River, east of Sherman.

As has been shown, these beds thin from Waco southward toward the Rio Grande; the more unctuous and darker-colored shales of the lower portion of the north Texas section disappear, and only the "

---

In accordance with a suggestion of Mr. R. T. Hill, the name Shoal Creek limestone is here changed to Buda limestone, as the former name is preoccupied.

Robt. T. Hill: Am. Jour. Sci., Vol. XXXIV, Oct., 1887, pp. 291 et seq.; Bull. No. 4, Geol. Survey of Texas, Austin, 1889, p. xxvii; Artesian and other underground waters in Texas, New Mexico, in Indian Territory, Final Rept. of the artesian and underflow investigation of the U. S. Dept. Agriculture, 1892, p. 124.

 

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upper or more calcareous, sometimes arenaceous, horizons (called "fish beds" by Shumard, Hill, and others) persist, becoming more accentuated.

The local name "Valverde flags" has been proposed for these beds along the Rio Grande, but there is not sufficient lithologic difference to warrant the use of a separate designation, and the equivalence of the Valverde flags and the Eagle Ford beds has, as stated, been established by actually tracing the beds across the area intervening between the areas to which the two names were originally applied.

Outcroppings of the Eagle Ford flags were seen along the road from Del Rio to Eagle Pass, from a point 3 miles southeast of the former place until the valley of Sycamore Creek was reached, where they were obscured by the debris in the valley. The distance across the area of exposures is about 8 miles.

No estimate was obtained of the thickness of this formation in the vicinity of Del Rio. Dumble has estimated that it is 600 feet thick. Near Brackett it is about 250 feet thick, by actual measurement, so that it would seem that the foregoing estimate is probably too great.

AUSTIN CHALK.

This formation is a soft, chalky, argillaceous, white limestone, containing a little ferruginous matter in the shape of pyritiferous lumps or nodules of marcasite. Sometimes there are alternations of chalky layers and calcareous clays. It presents exactly the same lithologic; and paleontologic characters in the middle Rio Grande region that it does in the Colorado River region. A microscopic examination of a specimen of the chalk collected 15 miles from Del Rio, on the road to Eagle Pass, showed its foraminiferal nature; Globigerina, Textularia, and Orbulina were present in very great numbers.

The first exposure was seen about 15 miles from Del Rio, on the road to Eagle Pass. Other exposures were seen as far as Tulio Creek (Las Moras Creek), about 33 miles from Del Rio. Pinto, Cow, and Tulio (Las Moras) creeks flow over the chalk where the Eagle Pass Del Rio road crosses the streams. On the road from Brackett to Del Rio exposures were seen as far as the first crossing over the Southern Pacific Railroad.

At the crossing over Cow Creek there is an excellent exposure in a bluff, about 25 feet high, composed of layers of chalk, 1 foot or more in thickness, alternating with beds of yellow clay. From this place the following fossils were obtained (locality No. 271):

"

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E. T. Dumble: Bull. Geol. Soc. America, Vol. 111, 1892, p. 221.

Op. cit., p. 229.

Dumble has used the name "Pinto" for these beds in this region (Bull. Geol. Soc. America, Vol. III, 1892, p. 222), but, as is here shown, there is no occasion for applying a new designation to them.

 

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"This is a typical Austin chalk fauna. The species of Inoceramus and Baculites occur also in the contemporaneous Niobrara limestone of the Western interior region." (Stanton.)

From an exposure in Tulío (Las Moras) Creek Inoceramus digitalus Sowerby vas collected.

No estimate of the thickness of these beds was made. Unfortunately, for some distance below Tullo Creek no exposures of the bed rock were seen, the road being on the wide alluvial terrace flanking the Rio Grande. Dumble estimates that the beds are 1,500 feet thick, basing his estimate upon a dip of 100 feet to the mile.

UPSON CLAYS.

As shown by Dumble the Austin chalk is overlain by a series of stiff clays, which he calls the Upson clays. The actual contact between the two formations was not observed. The following is Dumble's original characterization of the formation:

About 2 ½ miles above Lehmann's house (Upson post-office), near the water level on the Texas side of the Rio Grande, is an exposure only a few feet in thickness.

The bluffs on the Mexican side of the river, as could be seen with field glasses, are composed of dark greenish-yellow clays. In places there appear to be indurated layers, but no limestones reminding one of the Anacacho beds.

Lehmann states that a well, bored to a depth of 45 feet, near a Slough just south of his house, has its bottom in a stiff, dark-blue clay which "

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Bull. Geol. Soc. America, Vol. III, 1892, p. 229.

Op. cit., p. 224.

 

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contains many fossils. Unfortunately none of the fossils were preserved.

An examination of the bluffs of the escarpment bounding the Rio Grande Valley east of Upson was made, but no exposure of the strata beneath the gravel was found. Along the draws was stiff clay, indicating that the gravels rest on a clay foundation.

These observations show that there is no Anacacho limestone along the Rio Grande, but that the equivalent beds have again assumed the character of the Taylor marls of central Texas.

Assuming the dip of these clays to be 100 feet to the mile (the dip of the beds in the vicinity of Eagle Pass) the thickness would be about 700 feet-the estimate made by Durable (op. cit.).

EAGLE PASS FORMATION.

The name "Eagle Pass beds" was first proposed by Dr. C. A. White, in 1891, in discussing the Cretaceous of the Texas region. Dr. White does not define, the formation, but considers it equivalent to the "Ripley" (Navarro of Hill) of eastern Texas, and places it above the Taylor (Exogyra ponderosa) marls. Therefore, according to White, the base of the Eagle Pass formation would rest on the top of the Taylor marls, and the equivalent to these marls, the Upson clays, would be excluded from it. Dumble (op. cit.) amplifies the name "Eagle Pass beds" by the substitution of the word series, and assigns to this series all of the beds from the Austin to the base of the Eocene. It is better. in the opinion of the writer, to use the name as White first employed it, viz, for those beds extending from the Taylor (Upson) marls or clays to the Eocene. The three subdivisions of Dumble are, however, recognized, but with the reservation that future study may very much modify the nomenclature. As yet no detailed study of the area as a whole has been made, and the present attempt is only to give an idea of the section along the Rio Grande proper, with approximate estimates of the thickness of the formation and a general idea of its variations in the area under discussion.

Sam Miguel beds.

-The following is Dumble's original description of these beds: Resting on the clay shales which form the upper member of the Upson clays, there is a deposit of sandstone, thin to heavy bedded, separated by bands of clay, and containing seams of glauconitic material with many fossils, as well as occasional heavy beds of clay, especially toward the top. * * * In the Rio Grande section it first occurs in the hills north of Carter's ranch, where the hills show exposures of it from 75 to 100 feet in height. The exposures are excellent for several miles south of this point, and a very rich fauna which is now being studied was secured. In the upper portion I found Exogyra ponderosa and great numbers of other shells not yet determined. Above this the sandstone becomes more calcareous, and in places is compacted and contains calcareous nodules. Three miles south of the Carter ranch we "

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Bull. U. S. Geol. Survey No. 82, 1891, pp. 116 et seq.

 

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found the teeth and bones of a saurian in the concretions. The materials overlying this become more clayey, as will be seen by the following section made some 10 miles north of Eagle Pass:

Above this there are sands, with lime and greensand, containing many casts of fossils-Inoceramus and other bivalves, together with numerous gastropods. This continues to a point about 8 miles north of Eagle Pass, below which these strata are soon covered by the next newer series of deposits.

Coming up from the creek valley, about halfway between the ranches of Messrs. Lehmann and Burr, 11 miles north of Paloma siding, on the Southern Pacific Railroad, one finds sandstone, underlain by clay, exposed in the eastern bluff. The section is similar to that next described, which is seen in corning up from the Rio Grande flat, on the way front the Lehmann ranch to Eagle Pass.

Twelve and a half miles from Eagle Pass, as the road from Upson passes from the silt terrace of the Rio Grande to the plain above the breaks of the river, the following section was observed:

"The above species all occur in the typical Ripley fauna of Mississippi and Alabama. The horizon is about the same as that of the lower marl bed (Navesink formation) of New Jersey." (Stanton.)

Coal series.

This name has been utilized by Dumble (op. cit.) to designate that portion of the Eagle Pass formation which contains the coal beds in the vicinity of Eagle Pass. The following sections will give an idea of the character of the beds.

"

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Durable, Bull. Geol. Soc. America, Vol. III, 1892, pp. 224,225.

 

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Section in the Maverick County Coal Company's mine, near Eagle Pass, as given by Mr. George Bregg, former manager of the mine.

Section of hill on east side of Elm Creek, 1 mile above the bridge at the crossing of the Del Rio and Eagle Pass road.

Above, the clay apparently the whole section is composed of sandstone like that at the surface in the shaft of the Maverick County Coal Company's mine.

Along Elm Creek, above the bridge, irregularly stratified sandstones and clays containing ferruginous concretions and silicified wood are exposed. There is no constancy in the small beds of sand and clay; they are simply interlocking lenses.

At the old Hartz mine the coal is about 6 feet thick and is both overlain and underlain by clays. From the clays above the coal a specimen of the palm Geonmites tenuirachis Lx. determined by Prof. F. H. Knowlton to be a Laramie species, as it occurs in the coal-bearing Laramie of New Mexico-was collected.

 

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Near this mine a conglomerate, composed of calcareous pebbles and calcareous cement, covers the surface between the arroyos.

 

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About 100 feet north of Burr's ranch, 1½ miles northwest of Paloma siding, is an exposure of brownish or greenish-yellow fossiliferous sandstone underlain by clays. The section is of somewhat doubtful stratigraphic position, but it would seem to belong in the Coal series, and probably below the coal horizon. The following fossils have been determined by Mr. Stanton from the collection made here:

"

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Report on artesian waters, etc., for Texas west of ninety-seventh degree of longitude, by Frank E. Roessler, 1890, Senate Ex. Doc. No. 222, Fifty-first Congress, first session, p.266.

 

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This fauna seems very closely related to that found 2 miles north of Eagle Pass on the Uvalde road, -but Sphenodiscus pleurisepta, which usually characterizes the upper beds, is absent. The stratigraphic position of the exposure near the Burr ranch has not been definitely determined, but it would seem to be considerably below the fossiliferous horizons in the bluffs east of Eagle Pass.

From Paloma to Thomson's siding sands and clays outcrop in the draws, and gravel usually caps the hills.

Escondido beds.

-Dumble (op. cit.) has proposed the name "Escondido beds" for the sandstones and clays occurring above the Coal series. The following sections and notes describe them. (Pl. II.)

Just east of the railroad, on the eastern side of Eagle Pass, is an escarpment about 90 feet high, the rocks having a strike due north-south magnetic, and a dip 3° E. This escarpment is composed at the top of a few feet of soft, yellowish sandstone, underlain by ledges of hard, brownish, ripple-marked sandstone, which is followed by a slope composed of some clays, but chiefly of soft, yellowish sandstone. The fossils collected on the Uvalde-Eagle Pass road, 2 miles above Eagle Pass, belong in the lower part of the slope of this section (see p. 30). The detail of the section is as follows:

From No. 2 the following fossils were obtained (locality No. 273):

The only species identified in this lot is widely distributed in the Ripley and Montana formations." (Stanton.)

This bed contains an oyster ledge and is the base of Dumble's Escondido beds.

"

---

Bull. Geol. Soc. America, Vol. III, 1892, p. 228.

 

 

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According to Mr. Stanton, there is in the National Museum a small collection of fossils obtained in the neighborhood of Eagle Pass by Mr. J. Owen. He collected Exogyra costata at localities 1 mile southeast and 4 miles east of Eagle Pass. At the first locality he also collected a species of Volutomorpha and other Ripley forms.

Beds composed of brownish sandstone, with occasional beds of fossils, were found along the road to Laredo until about 30 miles from Eagle Pass (about 26 miles in a straight line). The following is a list of the fossils collected, with their localities:

"The collection evidently belongs to the same subfauna which is more closely related to the Ripley than to any other. The facts that it is in beds that overlie those containing typical Ripley fossils, and that a considerable proportion of the species are peculiar to these beds, are strong indications that we may, have here more recent Cretaceous beds than the latest Ripley beds of Mississippi, Alabama, and other portions of the Gulf Coast region." This idea has already been advanced by Mr. Dumble. (Stanton.)

Bull. Geol. Soe. America, Vol. III, 1892, pp. 219-230.

 

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RECONNAISSANCE FROM CLINE, UVALDE COUNTY, TO EAGLE PASS.

The road from Cline leads across the Anacacho Mountains to the Beasley ranch, some 10 miles to the south; thence southward to the crossing of the main Eagle Pass-Uvalde road over Chacon Creek. From this point the journey was made along the main public road to Eagle Pass.

The Anacacho formation will receive detailed consideration later. It suffices to say here that in the creek just south of Beasley's house this limestone has dipped beneath clays which initiate the Eagle Pass series.

The whole distance from the first crossing over Mula Creek, south of the Beasley ranch, to the third crossing over the same stream is a silt and gravel flat, with absolutely no bed-rock exposure. The gravel is chiefly flints. The vegetation consists of low, scraggly mesquite bushes, lignum vita, and sonic cats-claw, occasional junco, and sonic tasajillo (Opuntia leptocaulis), with very little grass. The surface of the ground is glazed and checkered by small cracks.

From this crossing over Mula Creek to Chacon Creek the surface is composed entirely of silt and gravel. At the crossing over Chacon Creek the main Uvalde-Eagle Pass road is reached. On the southwest side of the road there is an outcrop, from beneath the silt and gravel, of brownish sandstone, in which is an agglomerate of Ostrea cortex Conrad.

Between Chacon Creek and Salado Creek the surface is covered by gravel and silt. About one-fourth of a mile north of Salado Creek is an outcrop of coarse-grained brown sandstone. The following section was observed on the north side of the creek at the ford:

 

29

There is an oyster, probably 0. cortex, besides which Mr. Stanton has identified the following fossils front the collection made at this place:

These indicate, according to Stanton, the fauna of the Ripley and Navarro beds.

For about a mile after passing Salado Creek the surface is composed of residual sands, with occasional outcrops of yellowish sandstones. For the next half mile there are sands with some gravel embedded in them. For the next 5 miles the soil is usually argillaceous, or a mixture of sand and clay, and there is a considerable amount of gravel scattered over the surface. In ascending a small hill 5½ miles beyond the Salado crossing many fossils were found in a hard layer of greenish sands, which overlies soft yellowish and greenish sands and clays. Mr. Stanton identified the following species from a collection made at this locality:

Mr. Stanton remarks: "The fossils from this locality and those from 11½ miles north of Eagle Pass, near Burr's ranch, and 2 miles north of Eagle Pass are nearly all either identical with or closely related to species that occur in the Ripley fauna of Mississippi and Alabama and in the uppermost Cretaceous beds of Navarro and Kaufman counties, Texas. This fauna has a vertical range of ,several hundred feet in Alabama."

Six and a half miles below the Salado crossing the foundation of the soil is a yellowish-brown clay. Gravel is scattered over the surface. It is chiefly flint, hut there is also a considerable admixture of porphyry, showing that the gravel has been brought down by the Rio Grande.

Although there is not a continuous coating of gravel over the hills from this point (11 miles front the Eagle Pass court-house) to Eagle Pass, gravel occurs, in more or less disconnected patches, the whole distance. The rocks consist of alternations of yellowish flaggy sandstones and clays. From about 11½ to 11 miles north of Eagle Pass Exogyra costata was found in considerable abundance in yellowish clays. These clays are both overlain and underlain by soft yellow sandstone. This clay bed, by aneroid barometer measurement, is 50 feet thick. The road runs approximately along the strike

 

30

of the rocks, and the stratigraphic position of the Exogyra costata clays and their associated sand beds seems to coincide with that of the sands and clays forming the top of the escarpment overlooking the Rio Grande Valley, 61 miles north of Eagle Pass, i. e., the base of the Escondido formation. These beds occur considerably above the coalbearing horizons. About 2 miles from the court-house is a fossiliferous horizon in clays, a section of which gives the following;

Mr. Stanton has determined the following from a collection of fossils made at this locality:

• Cardium eufalense Conrad?
• Mactra sp. Cf. Mactra formosa M. and H.
• Dentalium sp.
• Natica sp. Occurs at Kaufman, Texas.
• Turritella winchelli Shumard. Occurs at Corsicana, Texas.
• Strepsidura ripleyana Conrad.
• Undetermined volutoid? Cf. Ancilla cretacensis Conrad.
• Volutomorpha sp. Cf. V. gabbi Whitefield.
• Sphenodiscus pleurisepta (Conrad).

The conclusion to be drawn from these notes is that the whole of the rocks exposed from the crossing over Chacon Creek to Eagle Pass belong above the Eagle Pass coal and correspond approximately to the base of the Escondido formation.

RECONNAISSANCE FROM EAGLE PASS TO CARRIZO SPRINGS.

From Eagle Pass to Robert Thomson's house, 20 miles east of the city, the bed rock presents the same character that it exhibited in going down the Rio Grande to Santo Tomas. It consists of sandstone and clays; for the last 8 miles before reaching Thomson's ranch clays prevail. The tops of the hills are generally capped by gravels, the sandstone and clays being exposed in the creek valleys and along the slopes.

Four miles east of Thomson's, on the road to Carrizo Springs, a specimen of Sphenodiscus pleurisepta was found in yellow clays.

To within 9 miles east of the Thomson place dirty, dark ocher-colored clays form for the most part the surface of the ground; there is some sand in the draws, and gravels occur on the high ridges. No sharp line between the Cretaceous and Eocene was discovered, and no fossils were found in the transition beds.

At about 9 miles east of Thomson's ranch and 16 miles west of Carrizo Springs, a change of geological formation was noticed. The clays above

 

31

described are here succeeded by fine-grained sandstones containing some mica. There are bands of red iron ore and many bits of hematite. The flora consists mostly of Opuntia, lignum vitae, some guajillo, some rhamnaceous shrubs, and mesquite. There was no grass, the ground between the cactus and the shrubs being barren.

Although it can not be affirmed with certainty, it is quite probable that this change in the character of the rocks marks the boundary between the Cretaceous and the Eocene.

STUDIES ALONG TURKEY CREEK AND THE NUECES RIVER, THE FRIO AND SABINAL RIVERS, BRACKETT AND UVALDE QUADRANGLES (EASTERN KINNEY COUNTY AND UVALDE COUNTY).

The sections along these streams are described in the discussions of the formations.

ANACACHO FORMATION.

This formation was defined by Hill and Vaughan in the Geology of the Edwards Plateau and Rio Grande Plain, etc. It is the stratigraphic equivalent of the Upson clays of the Rio Grande section, and of the Taylor (Exogyra ponderosa marls of central Texas. It overlies the Austin chalk, and is in turn overlain by sandy limestones, sandstones, and clays. Its component rocks are either hard or soft yellowish limestones or yellow marls, the calcareous constituents being in excess of the argillaceous.

The following section is taken from the report cited above:

"

---

Eighteenth Aim. Rept. U. S. Geol. Survey, Part II, 1898, pp. 240, 241.

 

32

The measurements were wade with an aneroid barometer and must be regarded as only approximately correct. The deposit of asphalt at the Lithocarbon Rubber Company's mine is in the Anacacho limestone. The asphalt-bearing horizon corresponds with the upper part of No. 6, above.

The following is a compilation from a large number of sections made along Turkey Creek, beginning at Cline Mountain, in the Brackett quadrangle, and extending to Wagon Top Butte, in the Uvalde quadrangle. Compilation of sections along Turkey Creek.

 

33

The foregoing section must be regarded as only an approximation. Evidently there is considerable variation in the lithologic characters of the sections, frequently making it difficult to correlate from one section to another. The sections were, for the most part, measured with an aneroid barometer, and although it was attempted to check them by the height of the hills as given on the topographic maps, absolute exactness could not be expected.

A carefully measured section along the Sabinal River was not obtained, but from a study from several bluffs, and from several well borings, the general characters of the equivalent beds were discovered, and an estimate of thickness was made. The beds here are intermediate in character between the typically developed Anacacho formation and the Taylor marls. There are beds of limestone showing the same characters as the typical Anacacho, and also rather thick beds of yellow clay of the sane character as the Taylor marls. There is more clay than in the vicinity of the Anacacho Mountains, and more limestone than in the central Texas region. These beds near Sabinal are considerably over 300 feet in thickness, probably 400 or more feet.

EAGLE PASS FORMATION IN BRACKETT AND UVALDE QUADRANGLES.

In the Uvalde quadrangle, between Turkey Creek and the Nueces River, the Anacacho limestone is overlain by a brown arenaceous limestone which grades into brown sandstones.

 

34

The area occupied by these sandstones and clays up to the supposed base of the Eocene is very small being only a mile or two wide, and the writer doubts that their maximum thickness exceeds 100 feet. Along the Frio River they are exposed from place to place from 1 to 2 miles below Engelmann's ranch. About 2 miles, measured in a straight line, below that ranch they dip beneath the Eocene sandstones and clays.

VARIATIONS IN CHARACTER OF THE FORMATIONS IN THE DIFFERENT SECTIONS.

There is very little variation in the formation below the Upson clays-Anacacho formation. The Lower Cretaceous is practically the same in the Uvalde and Brackett quadrangles and westward to Del Rio. This is also true of the Eagle Ford formation and the Austin chalk, but above the latter the variation is great.

Anacacho formation and Upson clays.

-The equivalent of these formations in central Texas is, as already stated, the Taylor marls. In the vicinity of Austin these marls are calcareous clays, blue when fresh, but oxidizing yellow, and are about 540 feet thick. In the vicinity of Sabinal clays resembling the Taylor marls and containing the same fossils are exposed along Sabinal River above the town, and have been penetrated by well borings. Here there are numerous thick beds of yellowish limestone interstratified with the clays. When the Anacacho Mountains in the Brackett quadrangle are reached, the clay beds have either entirely disappeared or become very insignificant. Along the Rio Grande the equivalent Upson clays contain, so far as known, no limestone beds, but are composed entirely of greenish or bluish clays which oxidize yellow. These data show that the Anacacho limestone is a purely local development. It is principally an organic limestone, produced by a great luxuriance of testaceous organisms, chiefly mollucks. "

---

Hill and Vaughan: Eighteenth Ann. Rept. U. S. Geol. Survey, Part II, 1898, p. 240.

 

35

The causes that have brought about the conditions favorable, for their growth are not known to the writer.

Eagle Pass formation.

-These beds have been shown to possess a total thickness of over 4,000 feet along the Rio Grande. They thin very rapidly to the north, so that the total thickness exposed along the Nueces River, in the Uvalde quadrangle, is only 100 or 200 feet. How much of the formation is buried by the Eocene overlap can not at present be determined, but the decrease in thickness is enormous, as is shown by the fact that the thickness below the lowest Ostrea cortex horizon, near Eagle Pass, is some 1,700 feet, while below the same horizon on the Nueces it is probably not more than 100 feet.

These beds are known to be thicker farther to the north than they are along the Nueces River, but how much they are influenced by the Eocene overlap is unknown. These facts reveal an extremely interesting problem-the effect of the Eocene overlap, in regard to which much more data are needed before the problem can be satisfactorily solved.

RELATION OF THE CRETACEOUS TO THE EOCENE.

In order to avoid repetition the details of the basal Eocene will not be described here. They are discussed further on, in the description of the Eocene sections.

Here general statements only will be made.

Rio Grande section.

-As has been pointed out by White, Penrose, and bumble, there is no sharp lithologic line between the Cretaceous and the Eocene. The contact between the two series has not been discovered. The principal result of the writer's work on the Rio Grande was in proving the existence of Eocene fossils some 3 or 4 miles above the Wrebb-Maverick county line, 6 or 7 miles above where Penrose and Durable first found such fossils. The fossils obtained here are typical Lower Eocene, and there has been discovered in this region no greater indication of the commingling of faunas than has been found in Alabama or other States, where it has been distinctly shown that an erosion interval occurred between the two series. Because of these faunal relations, it is the writer's opinion that the Cretaceous and Eocene series here were separated by an erosion interval, as is known to be the case elsewhere, and it is quite probable that more extended investigations will subsequently establish the exact contact, though this may not be possible because of the limited number of fossils obtainable and the lack of good exposures.

Between Eagle Pass and Carrizo Springs.

-The probable contact between the Eagle Pass formation and the Eocene has already been described (see p. 30). No actual contact was observed. The probable contact is 9 miles east of the Robert Thomson ranch, where the Upper "

---

Harris: Bull, Am. Pal., No. 4, 1896, p. 28.

 

36

Cretaceous clays end and sandstones of the Carrizo Springs type are first initiated.

Along the Nueces River.

-Here, again, there is indefiniteness, due to the similar lithologic character of the rocks and the dearth of fossils. A detailed section across the contact is given on p. 34 in the discussion of the Eagle Pass formation. The base of the Eocene is placed provisionally at the top of the Ostrea cortex ledge, because,

• (1) on the Frio River, 19 miles farther east, a ledge of these oysters is undoubtedly the summit of the Cretaceous;
• (2) a short distance below the exposure of this ledge on the river, and stratigraphically above it, a few plant remains were found which Professor Knowlton considers probably Eocene;
• (3) the strata above this oyster ledge on the Nueces are very similar to strata on the Frio River, known with certainty to be Eocene, or are lithologically identical with those strata.

The proof that the writer has located exactly the Eocene-Cretaceous contact on the Nueces is not absolute, but the evidence in favor of the location is strong, and it is doubtful whether the contact will be determined with greater exactness, unless it subsequently becomes possible to make more extended use of the plant remains, which are few and imperfectly preserved.

Along the Frio River.

-About 2 miles, in a straight line, below the Engelmann ranch and about a half mile above Myrick's lower apiary, a definite clear-cut contact is revealed. The section exposed is described in detail on p. 51. Evidence of erosion exists in the pebbles of the basal Eocene, but this evidence is not very strong, because of the general lithologic constitution of the rocks (shallow-water sandstones and clays), and because local erosion unconformities or pebble beds might exist almost anywhere. The faunal break is as sharp as a knife's edge. As the Eocene rests on a ledge of the Cretaceous Ostrea cortex, to be sure some Eocene fossils are mixed with the oysters along the basal contact, but no Eocene species was found below that ledge, and no Cretaceous species was found above the basal contact. These data prove absolutely that there must have been a break in the sequence of sedimentation long enough to permit a complete faunal revolution.

Although fragmentary, these data sustain the conclusion that there are in the Rio Grande region of, Texas no transition beds between the Cretaceous and the Eocene. The respective faunas are absolutely distinct, with as complete a break between them as is known anywhere. The difficulty in differentiating Cretaceous and Eocene rocks lies in the similar lithologic constitution of the two series.

 

37

TERTIARY.

EOCENE.

Near India ranch, about 26 miles, in a straight line, below Eagle Pass, the lithologic character of the rocks changes to a coarsely crystalline sandstone of a yellowish or brownish color. The best exposures of this sandstone are seen near Moro ranch well, at Chupadero ranch, and 124 miles south of Uvalde on the road to Batesville. The grains are small quartz crystals, which are often cemented together by iron oxide.

RIO GRANDE SECTION.

In the arroyo immediately east of India ranch is a clay containing calcareous concretions. This clay lies below the sandstone to be next described.

From India ranch to San Ambrosia Creek the road to Laredo passes over numerous exposures of ripple-marked brown sandstone, which disintegrates rapidly and forms very poor roads. Between San Ambrosia and San Lorenzo creeks, as there is no covering of more recent deposits, loose sands, derived front the disintegration of the sandstone, constitute the surface. The best exposures of this sandstone are at Chupadero ranch. Here it contains numerous fantastically shaped concretions, and peculiar sandstone pillars are formed by erosion and weathering. When unweathered the sandstone is gray, but upon disintegration it forms coarse, loose, brown crystalline sands. Its thickness, so far as ascertained, is 150 feet. (See fig. 5, p. 53.) It is underlain by clays, and is a well-defined lithologic horizon, apparently what Owen designated the Carrizo sands.

At Chupadero ranch a well sunk into this sandstone yields a permanent supply of water, which is, however, never more than a few feet in depth.

Between Chupadero Creek and San Ambrosia Creek flint gravel forms the capping of the divide.

West of San Ambrosia Creek, going down to the Rio Grande from the divide, dirty, dark-brownish or yellow clays are seen. These pass beneath the sandstone exposed around Chupadero ranch. The bluff on Rio Grande 1 mile above the mouth of San Ambrosia Creek is 40 to 50 feet high and is capped by sandstone; the base is of laminated sands and clay. Three and one-half miles above the mouth of this creek the banks of the river are composed of sandstone and thinly bedded lignitic sands. Specimens of Venericardia plainicosta Lain. were found in a piece of sandstone from this locality, and a Specimen of Ostrea crenulimarginata Gabb was picked up nearby. These would indicate that the horizon of the beds here exposed is Midwayan Eocene.

"

---

First Rept. of Progress of Texas Geol. Survey, 1889, pp. 70-73.

 

38

Four and one-half miles above the mouth of San Ambrosia Creek the following section was observed:

There is a considerable amount of soft, very pure sand rock along this part of the river. In No. 4 of the foregoing section the ledges sometimes change to thinly laminated sands along the face of a single exposure, as was observed in one instance.

No. 1 of the section is quite thick, changing toward the base into clays of purplish color, due to the presence of carbonaceous matter. These beds are identical, in external appearance, with the lignitiferous Claiborne beds of Louisiana. They are probably 100 feet thick.

It is at about the point where the foregoing section was made that the southern fence of the India ranch pasture is reached. This fence is, according to the statements of a colored cowboy, between three-fourths of a mile and a mile above the Webb-Maverick county line. Just beyond this fence, within the India ranch pasture, hematitic concretions containing Venericardia alticostata Conrad and a species of Glycymeris (Pectunculus) of the type of G. staminea (Conrad), were found in the clays. A little farther up the river was a large mass of sandstone resting on the clays and containing beautiful specimens of Turritella mortoni. The sandstone was so hard that no attempt was made to get the, shells out.

From 1½ to 2 miles above the fence referred to the thinly bedded sands and clays are seen to be underlain by thinly bedded sands, passing downward into thin ledges of soft sandstone.

This has carried the Eocene to a point at least 2 to 3 miles above the Webb-Maverick county line. The horizon of the Eocene is Midwayan. The following five species of fossils were collected:

• Turritella mortoni Conrad.
• Ostrea crenulimarginata Gabb.
• Glycymeris (Pectunculus) sp. indet.
• Venericardia planicosta Lam.
• Venericardia alticostata Conrad.

Harris has identified, from the Dumble-Penrose collection made 3 miles below the Webb-Maverick county line, fossils that are probably Midwayan, Lower Eocene, but the writer has been unable to obtain a "

---

Dumble: Jour. of Geol., Vol. II, No. 6, 1894, p. 550; Harris: Bull. Am. Pal., Vol. I, 1896, p. 127 (No. 4,13).

 

39

list of the species found there. Harris (op. cit., loc. cit.) says: "we should note the peculiar fauna, Midway, in part, at least, found by Dr. White 18 miles southeast of Eagle Pass. It consists of Cucullœa macrodonta (perhaps saffordi ), Pectunculus, Venericardia [pl. 5, fig. 3]. 'The Shelly matter of these species is completely crystallized.' 'The matrix was evidently a calcareous light sand or sandstone.' Harris, Ann. Rept. Geol. Surv. Ark., 1892, Vol. II."

The actual Cretaceous-Eocene contact has not been located along the Rio Grande.

It has been reported that many fossil oysters occur on the high divide between the Chupadero and India ranches, west of San Ambrosia Creek. The writer was unable to make a search for the locality, and did not learn of anyone who had collected specimens from there. He is of the opinion that the section referred to is a bed of Ostrea crenulimarginata Gabb, as this species occurs at several places in the basal Eocene of Texas.

The following section of Webb bluff, on the Rio Grande, 3 miles below the north line of Webb County and southeast of India ranch, is from Penrose:

Dumble subsequently published the same section and stated that it is capped by gravel. Beds Nos. 2 and 3 are the same as the Webb bluff beds of the section by Durable.

The coarse-grained sandstone seen around Chupadero ranch is overlain near there by a finer-grained laminated sandstone. At Guajolote ranch the coarse-grained sandstone has disappeared, and we have the following section:

First Ann. Rept. Geol. Survey of Texas, 1890, p, 41.

Bull. Geol. Soc. America, Vol III, 1892, p. 228; also, Dumble's Report on brown coal and lignite of Texas, Geol. Survey of Texas, 1892, p. 137. In the latter report it is stated that the lowest stratum is Cretaceous.

 

40

On the hilltops to the southeast of the Guajolote ranch clays occur above the micaceous sandstones. Ten miles, by road, southeast of this ranch, the following section was observed:

From No. 2 several specimens of leaf impressions were obtained and submitted to Professor Knowlton for determination. He makes the following notes on them: There is one fine leaf in this lot, but it unfortunately appears to be new. It is a fine, narrow, toothed Celastrus. There is also a small fragment of a palm leaf, but it lacks both apex and point of attachment, and is thus deprived of all characters. There are two or three other fragments of leaves and a large number of stems, possibly of monocotyledons. The new species of Celastrus appears to resemble most closely a species (C. rectinervis Ward) from the Fort Union (Eocene) of Montana. The palm has some resemblance to a Denver species, but as it lacks the essential characters it is impossible to identify it.

One and an eighth mile from the foregoing locality the first outcrop of the Eocene lignite was seen. The rocks in the vicinity consist of micaceous sandstones and clay shales. The dip is about 1° south of east.

From the last-mentioned locality to Santo Tomas the lithologic characters of the rocks are about the same, i. e., they consist of interbedded micaceous sandstones, which vary much in hardness and in color. and of clays or clay shales.

About 8 miles before reaching Palafox poor remains of marine fossils were collected in a micaceous sandstone.

Two and a half miles northeast of Palafox there is an exposure of lignite.

The following are records of two prospect drills kindly furnished by Mr. D. D. Davis, superintendent of the Cannel Coal Company, which has its mines near Santo Tomas.

 

41

Prospect drill No. 2, by Cannel Coal Company, northeast of Carbon, about 3 miles southeastof Santo Tomas.

 

42

Prospect drill No. 2, by Cannel Coal Company, northeast of Carbon, about 3 miles southeast of Santo Tomas-Continued.

Mr. Davis states that the lower sandstones were not very coarse nor were they crystalline. The elevation at the surface, where this drill was sunk, is about 530 feet.

Prospect drill No. 6, at Pilot ranch, 25 miles west of north from Santo Tomas, and 3 1-2 miles from the Rio Grande.

 

43

Prospect drill No. 6, at Pilot ranch, 25 miles west of north from Santo Tomas, and 3 1-2miles from the Rio Grande-Continued.

 

44

Section at the Santo Tomas coal mine (Rio Grande Coal and Irrigation Company).

The Cannel Coal Company's mine is about 3 miles below Santo Tomas. Through the courtesy of Mr. D. D. Davis, the manager, the writer was enabled to make the following section:

In this mine there is a small fault, and along the plane of the faulting there is a small sandstone dike.

From prospect drill No. 2, between 83 and 90 feet, Mr. D. D. Davis had obtained and preserved some fossil mollusks, which he presented to the Survey. They were referred to Prof. G. D. Harris for determination. He says they belong to an undescribed fuana, and has not yet furnished any identifications.

Mr. D. J. Roy, manager of this mine, rendered much assistance and showed us many courtesies while we were in Santo Tomas. It was through his kindness that we were enabled to examine the mine.

 

45

Dr. C. A. White has collected some fossils near Santo Tomas, but they have not been determined. These specimens, also those from the coal shaft, are poorly preserved.

The dip at Santo Tomas, according to information furnished by Mr. Davis and based upon mine workings, is 2° N. 40° E.

From the sandstone which immediately overlies the coal Mr. Davis had collected several fossil leaves, which he presented to us. Professor Knowlton has examined them, and finds a new species of Juglans, and another species which could not be determined.

From the clays just above the coal (locality No. 280) Mr. Stanton collected some leaves and a Unio. The leaves were too poor for identification. Professor Knowlton states that one looks like a Ficus; he is also of the opinion that the plants from Santo Tomas have a Laramie facies, but does not feel justified in expressing an opinion as to whether they are from the upper or the lower Laramie.

The following is a résumé of the section of the Eocene based on observations and the data accumulated:

The fossils reported by Penrose from Webb bluff probably occur below the Carrizo sandstone.

It is evident that the coarse sandstone seen at and near Chupadero ranch has not been reached in the prospect drill at Carbon, near Santo Tomas. It is difficult to correlate the records of the drill at Pilot ranch with the Santo Tomas section. Lithologically the section resembles very much the coal-bearing portion of the Santo Tomas section. In the Pilot ranch drill hole the lower sandstone has not been reached.

The disturbance in the dip at Santo Tomas, together with the extreme similarity in lithologic character of the beds, introduces such complications that reliable estimates of the thickness of the beds and the determination of the number and relative position of the coal seams can not be made until the area has been studied in detail.

The following is taken from Penrose's description of the section along the Rio Grande from Webb bluff to Laredo. The section of Webb bluff has already been given.

First Ann. Rept. Geol. Survey of Texas, 1890, p. 41.

First Ann. Rept. Geol. Survey of Texas, pp. 42 and 43; see also Dumble's Report on the brown coal and lignite of Texas: Geol. Surv. of Texas, 1892, pp. 137-139.

 

46

A quarter of a mile below (i. e., Webb bluff) is a bluff 50 feet high of indurated sandy clay, containing mica and ferruginous scales between the strata. Dip 1° south. One mile and a half below are seen similar deposits, but with no fossils, and containing numerous gray calcareous concretions, with veins of brown crystalline calcite. Two miles beyond this, on the Mexican side, is a bluff a quarter of a mile long and 75 feet high, of interlaminated gray sands and chocolate clays, with sulphur and gypsum in places, and occasional ferruginous spots. Hard gray clay-ironstones with leaf impressions are also found. The sand beds are from 1 to 5 feet thick, and the clay is in thin laminae. Dip undulating from 1 to 5° southeast. The mica and black specks in the sand, the laminae of chocolate clay, the presence of sulphur and gypsum crystals, all show a strong resemblance to the Tertiary of east Texas. From here to Hardin Ferry, and thence to the mouth of Cavezeras River, are seen similar strata, frequently causing rapids where they cross the Rio Grande. In one place the indurated bluffs encroach on the river until it narrows down to 30 yards. Here the waters have cut a deep channel and rush through at a great velocity. Frequently interbedded glassy ferruginous layers, 1 or 2 inches thick, are found in the sandstone. Three miles below " the Hardin" is a bluff 60 feet high composed of friable sandstones, the harder and softer layers blending into each other and occasionally showing ferruginous patches. Dip 1¹ south. For 19 miles below this point we pass over identically similar strata, frequently containing calcareous concretions 1 to 3 inches in diameter. These contain seams of crystalline calcite and are of a gray color, weathering brown or red in concentric layers.

Similar strata are seen from here to the San Tomas coal mines. These are situated on the Texas side of the river and at the mouth of San Tomas Creek, about 25 miles by river above Laredo.

For 3 miles below this are seen indurated greenish clays with leaf impressions, broken sterns, and specks of lignite. Occasionally seams of chocolate clay and calcareous nodules are found. As usual, the bluffs are capped with pebbles or sand, and dip 2° southeast. Fifteen miles above Laredo is a bluff reaching a maximum height of 40 feet and about 1 mile long. It is composed of interbedded coarse sand, with calcareous nodules, and sandy clay with gypsum and sulphur. The sand grains are red, yellow, white, and gray, and the whole bluff has a greenish appearance, spotted in places by ferruginous matter. Many similar outcrops are seen for 7 miles below, and as the did is often horizontal, or nearly so, the exposures show simply different parts of the same bed. Eight miles above Laredo is a bluff about 80 feet high and half a mile long, composed of semi-indurated buff sands, with an undulating dip. Similar exposures are seen down the river to Laredo, and in fact that town is built partly on the same beds, which are here succeeded by those of the next division of the Eocene.

This section appears to be quite different from that observed a few miles inland from the river. The very sharply defined Carrizo sandstone appears to be absent, at least its presence was not noted.

RECONNAISSANCE BETWEEN EAGLE PASS AND CARRIZO SPRINGS AND SOUTHWEST OF CARRIZO SPRINGS.

The change from the Upper Cretaceous clays to what is probably the basal Eocene has already been described on page 30.

About 15 miles from Carrizo Springs the sandstone is rather fine grained, of a brown ocher color, and the grains are distinctly crystalline.

 

47

Fourteen miles from Carrizo the surface of the ground is formed of deep red sands derived from the disintegration of a hard sandstone. At this locality a very few poorly preserved oysters were found firmly embedded in the sandstone. No specimens good enough for specific determination were obtained.

From here to Carrizo Springs deep, red sands extend the whole distance; the deepest sands are about 8 miles west of the town. There are occasionally more argillaceous beds. The rock whence the sands are derived is, before disintegration, a soft whitish or yellowish sandstone with occasional harder ledges. These are Owen's "Carrizo sands." They are the northward continuation of the sand seam around Chupadero ranch, and are the source whence the water of the artesian wells of the Carrizo Springs vicinity is obtained.

RECONNAISSANCE FROM CARRIZO SPRINGS TO SAN LORENZO CREEK.

From Carrizo Springs to the Richardson ranch, 6 miles east of south of the town, the deep sands are continuous. About opposite the house on the ranch the soil becomes firmer, apparently containing clay enough to make it compact. The tank in Ainsworth's pasture, on the southwest side of the Richardson ranch, has been excavated in clays. Gravel occurs on the summit of the hill near the tank. From this ranch to San Lorenzo Creek clays and compact sandstone are found along the draws, and gravel cappings usually occur on the hills.

NUECES RIVER SECTION.

On the east side of the river, above the coal shaft and just below the Pulliamn ranch, at the northern line of Zavalla County, there is exposed a soft, friable sandstone, bluish when fresh, oxidizing yellow, very often possessing a shaly appearance and containing black specks. This sandstone resembles very closely the basal Eocene along the Frio River. A half mile below the Pulliam ranch it passes below the coal seam and possesses a thickness of some 40 feet.

Section through coal seam.

Professor Knowlton remarks that the leaves from No. 4 are probably Eocene.

 

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