The Devonian-Mississippian transition outcrops of central Texas are here described summarily and assigned to a new stratigraphic unit, the Houy Formation. The beds included are mainly Upper Devonian, but partly Lower Mississippian. Locally a basal fraction may be Middle Devonian. Although the deposits included are diverse and their associations complex, the maximum surface thickness so far known is only about 17 feet.

Pleistocene-age fossil horses of Texas belong to at least three faunal assemblages. The oldest contains Hippotigris (= Plesippus) which disappeared before Yarmouthian time. The second contains Equus scotti and Onager semiplicatus (= Equus (Asinus) calobatus) which disappeared before Sangamon time. Both these groups are found on the High Plains but not on the Coastal Plain or along the central Texas rivers, where a later fauna, probably of Sangamon age, is found which contains remains of Equus, Asinus, and Onager but no Hippotigris.