174 The American Geologist. March, 1892 
the rapidity being indicated both by the character of the strata 
and the fact that at points four or five hundred feet above one 
another the same stratum is found. The encroachment being 
from west to east, as it proceeded, abedof varying character and 
thickness was formed according as topography and amount and 
character of supply varied. Such being the case it follows that 
at a distance from the elevated Silurian land the soils upon the 
comparatively level and rather soft Permian rocks furnished red 
sands, and, upon the Carboniferous, 2 yellow sand; but near and 
on the Silurian the stream beds supplied the waves with coarse 
material. This conglomerate hurriedly worked over and not 
much altered, soon came beneath the reach of wave action, as 
the subsidence of the land continued, and there became mixed 
with and covered by the finer deposits washed from the succeed- 
ing shore lines. In the quite rapid subsidence it is possible that 
some protected river deposits may have escaped destruction, but 
I know of no instances which can definitely be stated to be of 
this origin. 
Above these beds everywhere are found deposits of great uni- 
formity free from conglomerates, and usually free from sandy 
material. Certain of these beds are stated by Prof. Hill to be of 
truly deep sea origin, indicating a subsidence of several thousand 
feet. The remarkable extension of certain thin beds over hun- 
dreds of square miles proves great uniformity of conditions at- 
tending their deposition. A great thickness of true chalk is also 
proved by him. The aggregate thickness of these deposits is 
several thousand feet. 
If | understand Dr. Comstock aright he conceives the Silurian 
to have been an island in this sea, for there can be no doubt that 
the Cretaceous extended well up to the present limits of the area, 
since the Cretaceous still exists there either in remnants or as an 
escarpment to the main Cretaceous area. This Paleozoic island 
at present seldom reaches much above 2,000 feet, and is usually 
much less. At an elevation of 1,900 feet southwest of Brady, 
us already stated, I have found Trinity beds with distinctive 
Trinity fossils as identified by Prof. Hill, and at present in the 
collections of the Texas geological survey. With the present 
topography this would submerge the greater part of the older 
Paleozoic beneath the Trinity sea. That still greater subsidence 
went on in the main Cretaceous is proved by the accumulation of 
