va u.han.] DESCRIPTIVE GEOLOGY. 37 
TERTIARY. 
EOCENE. 
Near India ranch, about 26 miles, in a straight line, below Eagle Pass, 
the lithe-logic 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 12f 
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 Am- 
brosia and San Lorenzo creeks, as there is no covering of more recent 
deposits, loose sands, derived from 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 un weathered the sandstone is gray, but upon dis- 
integration it forms coarse, loose, brown crystalline sands. Its thick- 
ness, so far as ascertained, is 150 feet. (See fig. 5, p. 53.) It is under- 
lain by clays, and is a well-defined lithologic horizon, apparently what 
Owen designated the Carrizo sands. 1 
At Chupadero ranch a well sunk into this sandstone yields a perma- 
nent 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 plcmicosta Lam. 
were found in a piece of sandstone from this locality, and a specimen 
of Ostrea ermulwia/rginata ( rabb was picked up near by. These would 
indicate that the horizon of the beds here exposed is Midwavan Eocene. 
i l-'ir-i Rept; of Progress of Texas Geol. Survey, L889, i>i>. 70-7:3. 
