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.
[Illustration: 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.