Pre-Mesozoic terrane of northern Mexico consists of a granitic area in eastern Coahuila bordered on the W by Pennsylvanian(?) and Permian rocks, on the E by sedimentary rocks of unknown age and on the SE by Mississippian-Permian rocks in fault contact with pre-Mississippian gneiss and schist. The area was a Paleozoic tectonic land. No direct or simple connection with the Ouachita belt of the United States can be implied, but it may be an extension of an interior zone of the Ouachita system. Alternatively, the Mexican Ouachita may have re- sulted from a younger foredeep on its foreland side. The Ouachita peninsula is probably a Paleozoic structural unit. Oil and gas, if present, should occur NW of the Sierra del Cuervo and Placer de Guadalupe exposures, possibly in northeastern Chihuahua.