MOVEMENT IN CARBONIFEROUS. 203 



Movement in Carboniferous. In the chapter devoted to the Upper Coal- 

 measures descriptions have been given of the coarse conglomerates inter- 

 bedded in the limestone, containing siliceous pebbles and worn fragments 

 of limestone carrying Coal-measure fossils, evidently derived from neigh- 

 boring land areas undergoing denudation. Many of the siliceous pebbles 

 have the appearance of coming from the Weber conglomerate, but this 

 can not be positively stated. The Productus semireticulatus and other 

 species found in these rolled fragments may have been derived from either 

 the Upper or Lower Coal-measures. The change in sediment from lime- 

 stone to conglomerate is abrupt, and no indications of erosion in the under- 

 lying rocks were observed. The evidence of movement rests wholly upon 

 the lithological character of the material forming the conglomerate, which 

 was in turn covered by deposits in every way similar to the limestone 

 below it. It seems evident that fragments of fossil-bearing limestone could 

 not have withstood the disintegrating action of water for any great length 

 of time or have been transported for any great distance. 



Distribution of Upper Silurian and Devonian. Over large areas of the Great 



Basin, Upper Silurian and Devonian sediments are either wanting or have 

 not as yet been recognized. Several longitudinal ranges have been described 

 in their geological structure as tilted blocks formed either exclusively of 

 Carboniferous rocks, or else made up of the Pogonip of the Lower Silu- 

 rian overlain conformably by Coal-measure limestones, the intervening 

 horizons, which at Eureka are known to measure over 12,000 feet in thick- 

 ness, being entirely unrepresented. Sediments of Upper Silurian and 

 Devonian age, while they occupy limited areas, nevertheless play a most 

 important part in the ranges which rib the central portion of Nevada. To 

 the north of the Humboldt River, as already pointed out, the Nevada lime- 

 stones have been recognized in the Tucubit Mountains ; they form the 

 greater part of the Roberts Peak Mountains west of the Pifion Range, 

 where they probably overlie a considerable but unknown thickness of Lone 

 Mountain Silurian, and the writer has traced the Devonian beds all along 

 the Pinon Range, connecting them with the grand exposures of the Eureka 

 district. At Ravens Nest, at the northern end of this latter range, that 

 portion of the Eureka series of beds lying between the Silurian quartzitr 

 and the Coal-measures is strikingly reproduced, the structure being a faulted 



