[113] 
Rocks of Pkesidio and Brewstee Counties. 
7 
One of such manifestation, to which, on account of its especially not- 
able character, we gave the name of the Ross ampitheater, occurs near 
Terlingua creek some twelve miles south of the end of the section given 
above. This ampitheater is about half a mile in diameter and approxi- 
mately circular in outline. The enclosing walls are of the massive lime- 
stones of the Fredericksburg which form an almost perpendicular escarp- 
ment around the entire area, the only egress being through two or three 
narrow gorges. The dip of the Fredericksburg seems to be quaquaversal 
and away from the ampitheater. Near the center of the circle there 
rises a small hill of the Exogyra arietina marl capped by the creamy 
limestone of the Yola, its top, however, much lower than that of the 
limestone walls which surround it. 
At no place was this character of faulting more clearly exhibited than 
at the California mine, where the conditions obtain which are shown in 
the following section. 
The faulting here is that of the east-west strike, or that which seems 
to be the earliest disturbance recorded in these beds. As will be seen, 
the throw is not very great. In fact, the greatest throw in the entire 
area, so far as we saw them, was that of the Ross ampitheater which 
brought the Yola somewhat below the top of the Fredericksburg — prob- 
ably not more than 250 feet. The width of the blocks as shown at the 
California mine is also small, being only from 10 to 40 feet. The struc- 
ture is clearly exhibited by the numerous gulches which cut the beds. 
