Ordovician outcrops are present in the Llano uplift of central Texas and
in the Marathon, Solitario, El Paso, and Van Horn regions of Trans-Pecos
Texas. These are sedimentary rocks and consist largely of sandstones,
cherts, limestones, and dolomites.
Although some of the Ordovician formations are fossiliferous, they are
seldom collected by amateur paleontologists because they are exposed in
relatively inaccessible places and the fossils are usually poorly
preserved. Ordovician fossils reported from Texas include sponges,
corals, brachiopods, gastropods, cephalopods, and trilobites. In
addition, the Marathon formation of the Marathon uplift contains large
numbers of well-preserved graptolites (fig. 24, p. 86).