The San Miguel formation of Maverick County, Texas, has generally been correlated with the Navarro formation of central Texas, except by F. M. Getzendaner and the writer. The formation contains many long-ranging species which occur elsewhere in beds of both Taylor and Navarro age, but it also contains species of restricted range, which indicate its upper Taylor age. The formation contains a varietal form of Exogyra costata Say, but lacks the true costata and also lacks other diagnostic Navarro species.

There is an important faunal hiatus between the San Miguel formation and the Escondido, the next higher formation which carries a marine fauna; this break is only partly filled by the Olmos ("Coal series"), an essentially non-marine formation.

The hiatus which exists in the outcropping section may be partly or wholly filled down the dip, under cover, by marine beds representing the lower part of the typical Navarro formation of central Texas.