Recent field studies 4 of the Difunta group in the eastern part of the Parras basin, southeastern Coahuila and western Nuevo Leon, Mexico (Fig. 1), have disclosed the presence of probable Early Tertiary (Paleocene) marine fossils in the youngest strata of this lithic unit which, previously, had been considered to be entirely Late Cretaceous (Gulfian) in age (see, for example, Imlay, 1936, 1937a, 1937b, 1944a, 1944b; Humphrey and Díaz, 1954; and de Cserna, 1956). It should be noted, however, that certain private oil-company reports, which were prepared in the 1930s and are...

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