172 The American Geologist. March, 1892 
hard rocks of that formation resisted the base-leveling process 
long after the softer rocks of the Carboniferous had been reduced 
to it. The Harper knobs west of the San Saba consist of Trinity 
conglomerate resting on Carboniferous at an elevation of 1,400 
feet. Within five miles in a southeast direction there is Silurian, 
at present 1,650 feet high without any Cretaceous covering. 
Within seven miles in nearly the same direction, there is a Silu- 
rian hill without Cretaceous, at an elevation of 1,850 feet. That 
is, in seven miles, there is a rise of 450 feet at /east in the pre- 
Cretaceous topography. There are many other places where the 
Silurian rises to this elevation without any sign of ever having 
had any Cretaceous covering; but, southwest of Brady, Cretaceous 
is found resting on both Carboniferous and Silurian at an eleva- 
tion of 1,900 feet. Here the Trinity rests at an elevation of 150 
feet above the nearest Cretaceous on the Upper Carboniferous, 
10 miles northeast. The significance of this, with relation to the 
chief point under consideration, will be referred to later on. 
From the above it will be seen that when the Cretaceous period 
began, in Texas, it found a low-lying land of Carboniferous strata 
undulating and nearly base-leveled, and an older Palaeozoic high- 
land district considerably diversified, but probably not strikingly 
mountainous. Upon this area the encroaching sea commenced 
the deposition of the Trinity sands and conglomerates, then, with 
more complete submergence, followed the higher beds of deeper 
water origin. A few words upon this peculiar formation will 
help us in the proper presentation of this argument. 
The basal beds of the Cretaceous are revealed in the Palzeozoic 
region along the base of the retreating scarp from beneath which 
the Carboniferous and other beds are being uncovered, and also 
along the base of the buttes and patches of Cretaceous which. re- 
main as uneroded remnants on this area. Being nearly horizon- 
tal they are revealed over a great area by this means. Along the 
eastern margin in the Colorado river escarpment the beds are con- 
glomerate, in the main, and vary in thickness from twenty feet 
or less to one hundred feet. Farther to the west the basal beds 
are sands instead of conglomerates, and there are also shales and 
impure limestones. Over the Permian these beds are red in color 
from the color of the underlying rocks. 
In lithologic character the conglomerate is quite remarkable, 
being often composed of large pebbles with a chalky cement. 
