Cambrian

Rocks of late Cambrian age are exposed in the Llano, Marathon, and

Solitario uplifts, and the Franklin Mountains near El Paso. These are

sedimentary rocks consisting of conglomerates, sandstones, shales,

limestones, and some dolomites.

Some of these formations are relatively fossiliferous, but the specimens

are commonly fragmental and very poorly preserved. Fossils that are apt

to be found in the Cambrian rocks of the Llano uplift include

brachiopods, gastropods, trilobites, and small rounded objects believed

to have been formed by algae (primitive one-celled plants). In other

parts of the State, Cambrian rocks are sparsely fossiliferous and the

fossils consist primarily of fragmental brachiopods, trilobites, and

algae.