34 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 164. 
Section at Asphalt Falls, Nueces River. 
Feet. 
10. Flint gravel, lower rocks not exposed 8 
9. Coarse-grained, laminated, and cross-bedded yellow sandstone 2 
8. Soft yellow sandstone and clay '25 
7. Oslrea cortex embedded in clay and consolidated to form a firm ledge 2 
6. Laminated, sandy, yellow clays 3g 
5. Soft ledge, composed largely of fragments of oyster shells 1 
4. Soft, laminated, sandy, yellow clays 3 
3. Soft, fine-grained sandstone, frequently beautifully cross-bedded and con- 
taining some asphalt 10 
2. Asphalt-bearing sandstone 5 
1 . Bluish clays to water's edge 2 
10, Pleistocene. 
8-9, Eocene? 
1-7, Cretaceous. 
The area occupied by these sandstones and cla}^s 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 for- 
mations 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. 1 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 cla} r s 
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 mol- 
i Hill and Vaughan : Eighteenth Ann. Rept. U. S. Geol. Survey, Part II, 1898, p. 240. 
