ABSTRACT
Limestone containing lower Ordovician cephalopods and gastropods occurs in most of the exposed sections of early Paleozoic rocks east of Sulphur Spring Valley, Arizona. Both the fauna and the lithologic character of this limestone identify it with the El Paso limestone of southwestern New Mexico. It grades downward into upper Cambrian sandy dolomite and dolomitic quartz sandstone which, in turn, overlie Abrigo limestone in the northern Swisshelm Mountains and at Black Gap (Bisbee District), Arizona. These relationships and the regional correlations suggested by them indicate that the Bolsa quartzite and Abrigo limestone in Arizona and the Bliss sandstone and El Paso limestone, respectively, in New Mexico should no longer be regarded as lithogenetic equivalents.
