Permian Fonnaiion of Texas. Ill 
The strata of the Texas Permian consist of materials which 
are somewhat difficult to describe, but they may be stated in a 
general way to consist mainly of sandstones and sandy and cla)-- 
ey shales, which are sometimes calcareous, with a few layers of im- 
pure limestone, besides one somewhat important limestone horizon. 
A common characteristic of many of the layers is the presence of 
an abundance of small, hard, rough concretions, which usually be- 
come separated and accumulate upon weathered surfaces as the im- 
bedding clayey material is removed by erosion. But what strong- 
ly impresses the general observer is the prevailing reddish color of 
the formation, which is due to the prevalence of red oxide of iron 
in most of its component materials. During the rainy season the waters 
of the streams which traverse the formation are reddened by the 
abundant ferruginous, clayey sediment, which they obtain by ero- 
The stratification is generally more or less regular, but in the 
district here especially referred to it contains comparatively few com- 
pact, evenly-bedded strata. Therefore the formation having been, 
in this district, only slightly disturbed since its deposition, few strik- 
ing features in the landscape occur. That is, the district is a com- 
paratively plain country, the surface of which, in the, general ab- 
sence of forests, is diversified only by shallow valleys of erosion 
and low hills of circumdenudation, with here and there a hill or 
bluff of like origin which reaches a height of one or two hundred 
feet above the general level. From the top of these higher eleva- 
tions extended views are to be obtained, which are of much advan- 
tage in the study of geological structure in that region. 
Because of the slight disturbance which the Permian strata have 
suffered in the district referred to, and the general absence of bold 
escarpments, it is difficult to arrive at an accurate measurement of its 
thickness, but it is approximately estimated at i,ooo feet. By dis- 
tant view from the hills before mentioned, a general, gentle dip to 
the westward of the whole formation is plainly discernable. It is 
from a succession of such observations of the dip, together with 
measurements of the thickness of exposed strata and estimates of 
that of the unexposed, that the foregoing estimate of the full thick- 
ness of the formation has been made. 
A list of all the species of invertebrate fossils that have been dis- 
covered in the Permian of Texas is given on a following page. 
Prof. Cope's list of vertebraie species, already referred to, shows 
