[109J Rocks of Presidio and Brewster Counties. 
3 
any of the later beds. The difference between these heavy bedded, dark- 
colored and highly corraded rocks and the light-colored, red-banded, thin 
or irregularly bedded limestone of the Washita with Ammonites leonensis 
is well shown between the California mine and the hill one and one-half 
miles to the northwest. 
Washita. 
The principal difference noted in the Washita from that usually pre- 
sented by it was in its thickness. The limestone is of its usual light 
yellowish color and has the biscuity weathering seen at other places. 
Its thickness, however, does not appear to exceed 100 feet, and at the 
California mine it is not more than 60 feet in thickness. Here, however, 
metamorphism has altered it in places, giving colors from gray to white, 
with ferruginous bandings and sharp angular fractures. The stress to 
which it has been subjected and the infiltration of ferruginous material 
have given it a curious concentric banding of yellow lines as described 
by Prof. Blake. In many places geodes of oxide of iron form the centers 
of the banded blocks. Where still farther metamorphosed, as at Bishop 
and McGuirk’s prospect, the Washita is 'a granular limestone with nests 
and pockets of black calcite. The mercury occurs here in connection 
with these pockets of calcite. 
Arietina. 
The principal peculiarity of this bed is the scarcity of its characteristic 
fossil, the Exogya arietina. The fossils which characterize it here are 
those of its culminating horizon, such as Nodosaria texana , Con., Gry- 
phcea pitcheri f Arietina variety, E. drahei, Cragin, Pectens, Echinoderms, 
etc. 
At the California mine the rocks comprise clayey and siliceous shales, 
dark at the base and containing pyrites and gypsum in abundance. 
Higher up they are more siliceous and carry quantities of the foraminifer 
Nodasaria texana. They culminate in a band of clay carrying Exogya 
drahei and other forms mentioned. Portions of the beds are highly 
ferruginated and present an ochreous appearance. Numerous small 
openings have been made on these as prospect holes for precious metals. 
Vola. 
This limestone has a variable thickness, ranging from fifty to one 
hundred feet, and over a large area it forms a distinct bench above the 
Arietina clay. It is easily recognizable from its peculiar evenness of 
fracture and its creamy color. 
Eagle Ford. 
This division presents a basal series of lime shales and flags, succeeded 
