Permian rocks are found in widely separated areas in Texas. The best
exposed section of marine Permian rocks is found in the Glass Mountains
of Brewester County, and many of these rocks are very fossiliferous. The
original shell material of some of the Permian fossils of this area has
been replaced by siliceous material which is very well preserved. These
silicified fossils are removed from the limestone by solution in acid,
and some most remarkable specimens have been recovered in this manner
(Pl. 3). Brachiopods are the most common fossils, but corals, bryozoans,
and mollusks have also been recovered.
Extensive Permian exposures occur also in the central part of the
North-Central Plains region. These rocks were formed from sediments of
both marine and continental origin and some of them are fossiliferous.
The marine rocks contain a variety of invertebrate fossils including
brachiopods, pelecypods, gastropods, and ammonoids. Those rocks
representing terrestrial deposits contain vertebrate remains at many
localities, and numerous amphibians and primitive reptiles (Pl. 40) have
been collected from them.