Devonian rocks are best developed in Trans-Pecos Texas, especially in
the Marathon, El Paso, and Van Horn regions. In addition to the
Trans-Pecos exposures, there are minor outcrops of Devonian rocks in the
Llano uplift of central Texas.
Fossils are rare and fragmental in the Trans-Pecos exposures and consist
primarily of radiolarians and brachiopods. The Devonian rocks of central
Texas are predominantly calcareous and, although the material is usually
poorly preserved, many fossils have been collected from them. These
include bryozoans, corals, brachiopods, gastropods, and trilobites.
Conodonts and fragments of primitive armored fishes (Pl. 37) have also
been reported.