4 Transactions Texas Academy of Science. [110] 
by a considerable thickness of clays. The basal portion is identical with 
the deposits described as the Val Verde flags,* and carries a rich fauna 
of Eagle Ford species, of which Inocerami appear to be the most numer- 
ous. 
The lime shales have a thickness of 250 feet in the vicinity of Alamo 
de Caesario, while the great thickness of the clays is east of Terlingua 
creek and amounts to several hundred feet. 
Austin Chalk. 
The materials here referred to this horizon, because of the occurrence 
in them of such typical fossils as Radiolites austinensis and the crenu- 
late variety of Exogyra costata, comprise a series of black and yellow 
clays immediately overlying the black clays of the Eagle Ford without 
any marked change in material or conditions of deposition, there being 
seemingly a gradual passage from the deposits with one series of fossils 
(o the beds containing the other. Its thickness is about 100 feet. 
Overlying these yellow or brown clays there are 40 feet of brown sandy 
shale and sandstone containing numbers of a large oyster. Lying upon 
this is a deposit of brown clay with a bed of coal at its base, followed 
by a shale and beds of carbonate of irop. These beds have a thickness 
of 100 feet and are covered by 80 feet of sandy clay shales which carry 
a little lime and gradually pass into sandstone. The entire thickness 
from the base of the materials assigned to the chalk to the sandstone 
cap is 360 to 400 feet. - 
TERTIARY. 
ISTo attempt will be made to subdivide the materials here referred to 
as Tertiary, and later into divisions or series, since nothing was found 
which would form any basis for such a division. 
By far the greater part of these materials are, apparently, of eruptive 
origin, although in places the volcanic conglomerates contain pebbles 
and boulders of limestone and siliceou's rocks. Materials of this kind 
were observed along the entire route from a point a short distance south 
of Marfa to Alamo de Caesario, and they extend for some distance to 
the south and east of that locality. The deposits seem to be composed 
largely of volcanic mud or tuff, but are interbedded with conglomerates, 
agglomerates, and lava beds. The tuffs and agglomerates are usually 
light-colored and frequently porphyritic. They are generally thin bed- 
ded. In the limestone boulders which occur in the conglomerate we 
find fossils of both the Carboniferous and Cretaceous periods. For a 
distance of twenty miles south of Marfa the surface shows a considerable 
quantity of agate and chalcedony which has doubtless been derived from 
*Bul. Geol. Soc. Am., Yol. Ill, p. 221. 
