Permian Formation of Texas. 113 
numerous casts of a species of Pleurophorus. This being a charac- 
teristic genus among Permian molluscan faunas and a prevailing 
form in the Permian strata beneath the gypsum bearing beds, the 
question is suggested whether the latter ought not to be regarded 
as constituting an upper portion of the Permian. If these beds 
are not separable from the Permian, it seems to be doubtful wheth- 
er the Trias has any representation in Texas. 
It will be seen from the foregoing remarks that in the part of 
northern Texas to which special reference has been made, there is 
a great conformable series of strata having a slight general dip to 
the westward, its base being covered from view by mesozoic and 
later formations. The estimated thickness of this older series, so 
far as it is exposed to view, is 3050 feet. The lower 1800 feet, to- 
gether with an unknown thickness beneath, is referred to the Coal- 
measures. The next overlying 1000 feet of strata are designated as 
Permian ; and the upper 250 feet of the series is doubtfully refer- 
red to the Trias, although as already intimated there seem to be 
reasons for regarding the latter beds as constituting the upper part 
of the Permian. Cretaceous strata rest unconformably, and with a 
contrary dip, upon the earlier eastern portion of this series ; while 
upon the later western portion they rest with apparent conformity ; 
although their real conformity there may be properly questioned 
because the Jura seems to be entirely wanting, and at most the 
Trias is only slightly developed. 
As already stated, the Cretaceous strata appear to rest conforma- 
bly upon the gypsum-bearing beds; and the latter beds lie quite 
conformably with the Permian and Coal-measures beneath, all hav- 
ing a westward dip. On the contrary, all the beds from the Dino- 
saur Sands, which are regarded as the lowermost Cretaceous forma- 
tion in Texas, to the Tertiary inclusive, have an easterly dip and 
seem to lie unconformably with the Coal-measures and Permian. 
It is not certain, however, that the Carboniferous and older strata do 
not dip to the eastward beneath the Cretaceous strata, forming an 
anticlinal axis. Having thus shown the stratigraphical relation of the 
Texas Permian with the other formations, the following remarks 
will he confined to the Permian alone. 
The following descriptive section of the Texas Permian is tak- 
en from Mr. Cummins' field notes, but it has been in large part 
verified by my own personal observation. The different members 
of this section, which are indicated by consecutive numbers, are not 
