[Pennsylvanian] rocks are well represented in Texas and are exposed in the Llano uplift, north-central Texas, and Trans-Pecos Texas.
In Trans-Pecos Texas [fossiliferous] rocks crop out in the Hueco and Diablo Mountains. Fossils found in this area are algae, fusulinids, corals, brachiopods, pelecypods, gastropods, cephalopods, and crinoids. There is also a thick section of [Pennsylvanian] rocks in the Marathon uplift, but only one [formation], the Gaptank, is very fossiliferous. It contains many fossils including fusulinids, sponges, corals, bryozoans, brachiopods, gastropods, pelecypods, cephalopods, and crinoids.
Certain [Pennsylvanian] strata in the Llano region are very [fossiliferous], and the material is well preserved. The more abundant forms are fusulinids, corals, brachiopods, gastropods, pelecypods, cephalopods, and crinoids.
Probably the best [Pennsylvanian] collecting areas are to be found in north-central Texas. Here the thick marine limestones and shales contain large numbers of well-preserved invertebrate fossils, and the terrestrial or shallow marine strata have yielded an abundance of plant fossils. Invertebrate fossils are apt to be found along the banks of streams and gullies and in railroad and highway cuts. Many of the limestones bear large numbers of fusulinids or crinoid stems, and the shales may contain many corals, brachiopods, and mollusks. The best collecting will, of course, be found where the rocks have been sufficiently weathered.
Fig. 8. Sketch of typical crinoidal limestone from the [Pennsylvanian] of north Texas.
Typical invertebrate fossils are foraminifera (principally fusulinids), corals (especially the [solitary] or “horn” corals), brachiopods, bryozoans (the lacy and branching types are most common), pelecypods, gastropods (exhibiting a [variety] of coiling), cephalopods (nautiloids and goniatites predominate), and crinoids, which in many areas are found in thick crinoidal limestones ([fig. 8]). Some typical [Pennsylvanian] fossils are illustrated in Plates [14], [15], [17], [18], [19], [20], [21], [24], [32], and [35].
[Permian]
[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 The original shell material of some of the Permian fossils of this area has been replaced by [siliceous] material which is very well preserved.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.