The Lower Paleozoic Transitional Assemblage represents lithologies deposited within a narrow, depositionally gradational belt, between shallow water shelf Lower Paleozoic Eastern Assemblage carbonates and slope to bathyal cherts, shales, quartzites clastic sediments, and intercalated volcanics and pyroclastics of the Lower Paleozoic Western Siliceous and Volcanic Assemblage. These Cambrian through Devonian lithologies are exposed as local depositional units, in many cases confined to a few outcrops within an individual range. They are present in eastern Lander, western Eureka, Elko, and Nye County in the evaluation area.

The limestones and dolomites exposed in this transitional assemblage are generally more evenly bedded and thinly layered and contain a less abundant shelly fauna than rocks of strata belonging to the eastern carbonate assemblage. Dark siliceous and cherty shales and siltstones as well as coarser clastics are more abundant than the eastern assemblage and much less abundant than strata assigned to the western assemblage.

Although a few units within this assemblage represent lithologies deposited within the upper slope, in essence, many of the transitional units represent a starved outer shelf facies. This makes the differentiation between eastern assemblage and transitional assemblage quite difficult in several cases, and points out the inexact nature of the term "transitional". Still, this writer feels the term has a general utility in bracketing lithologies along the starved outer shelf and uppermost shelf in central Nevada.

The approximately 50 mile wide transitional zone was centered near the longitude of the Roberts Mountains during the Silurian through Devonian, and was probably about 25 to 75 miles farther to the west, at the longitude of the Toquima Range, during the Cambrian and Ordovician (Smith and Ketner, 1975; Johnson and Potter, 1975).