Quaternary deposits of Pleistocene age (geologic time scale, Pl. 1) are
found in many parts of Texas and consist of sands, clays, and gravels.
These rocks are distributed along the Gulf Coast in a belt from 50 to
100 miles wide. They occur also as stream terraces in the Edwards
Plateau and North-Central Plains regions. In addition, Quaternary sands
and gravels are widely distributed over the surface of much of
Trans-Pecos Texas. There are also fossiliferous Pleistocene strata in
the High Plains region.
Invertebrate fossils are rare in Pleistocene rocks, but some fresh-water
and terrestrial mollusks occur. Vertebrate remains, however, are
abundant in many localities, and large numbers of horses, camels,
mammoths, and other mammals (Pls. 46-49) have been collected. Fossil
bones and teeth (figs. 25, 26, p. 104) are commonly found in the gravels
and sands of many of the river terraces of the State.