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A sequence of Paleozoic sedimentary rocks, ranging in age from Cambrian to Carboniferous, was deposited in a transitional zone between the mio- and eugeosynclinal belts and now is exposed in a large area of the central Toiyabe Range south of Austin, Nevada. A maximum of 3,250 ft of quartzite, graywacke, and some limestone constitutes the Gold Hill Formation. Archaeocyathids (Archaeocyathus atlanticus Billings and Ethmophyllum whitneyi Meek), locally abundant at the top of the lower Gold Hill Formation, indicate an Early Cambrian age. The Cambro-Ordovician Broad Canyon Formation (new name), consisting of intensely deformed limestone, argillaceous siltstone, and phyllite, is about 2,000 ft thick. Antelope Valley Limestone, up to 800 ft thick, contains the Palliseria assembl ge (Middle Ordovician) near the top in two areas. Remnants of the Silurian Masket Shale (Roberts Mountains Formation) overlie the Antelope Valley with regional disconformity. Devonian corals are present in a massively bedded limestone overlying the Masket in one locality. A Tertiary conglomerate preserves boulders of coralline limestone and chert pebbles of the Carboniferous Wildcat Peak Formation.
An allochthonous sequence lies tectonically above and next to the transitional succession which is considered to be autochthonous. It consists mainly of Paleozoic chert and argillite about 10,000 ft thick, and, in one small area, of volcanic rocks, chert, and siltstone, perhaps of the Charcoal Canyon Formation. Only poorly preserved radiolarians have been found in these rocks.
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