Double Mountain Section. —Dumble and Cummins. 349 
z | 4, Shaly clay, underlaid by red or terra-cotta _ 
aS BAU StOME ater |, c/n save Staye.e: sinera ve 105 feet. 
2 HOM PEE GyPSUMIAWAS A etic i saeerne  “onece ss OO * 
= HomNt dlr Gry MSW SUS eis ate teicieietave,si0=t2 «ences we. horas 
= lt WUNVeR GW OBUNEE DEUS. tattle aae ss eases sss 135 “* 
CRETACEOUS. 
1. Caprina Limestone. 
The Caprina limestone which caps the mountains has a total 
thickness of forty feet. It is deeply fissured in places, and the 
rapid erosion of the softer underlying materials has scattered its 
debris down all sides of the mountain. In structure, it presents 
the usual characteristics of this limestone and on the surface often 
shows a ferruginous weathering of the Caprina so common in 
western Texas. The rock inthis locality contains many Hippurites 
of large size,and tbe Caprina forms found in it are varied and some 
of them heretofore unknown. ‘They have, however, since been 
found in rocks of the same horizon, in an exposure on Barton 
ereek near Austin, and also at other localities in Western Texas. 
2. Comanche Peak Serivs. 
The rocks of the Comanche series are here separable apparently 
into three distinct divisions, the upper of which is a series of im- 
pure argillaceous limestones having an entire thickness of twenty 
feet, the top being much more shaly than the bottom. The fossils 
are very numerous and well preserved, but diligent search failed 
to show a single Grypha pitcheri in it. The second division is 
somewhat similar in composition but more indurated and is of 
a yellow color. Some of the fossils in this bed had been altered 
into calcite. In it we found very few specimens of Gryphuwa 
pitchert. The third division consists of a shaly limestone con- 
taining a great abundance of very small fossils overlying a marly 
limestone, which is in turn underlaid by the Gryphea conglom- 
erate, which here as elsewhere is almost a solid mass of individ- 
uals of this species. The fossils throughout are abundant and 
well preserved, and correspond in the main with those of typical 
sections farther east. 
3. Trinity Beds. 
Immediately underlying the Gryphwa conglomerate is a bed of 
yellow sand about ten feet in thickness, which at the time of 
making the section was considered as the upper portion of the 
