CHAPTER III. 

 CAMBRIAN AND SILURIAN ROCKS. 



CAMBRIAN ROCKS. 



Rocks of the Cambrian period, with the exception of two small expos- 

 ures, are confined to Prospect Ridge, forming all the more elevated por- 

 tions and the steep slopes of both sidels. Indeed, the ridge is almost 

 wholly made up of Cambrian sedimentary beds. Silurian rocks perfectly 

 conformable with the upper beds of the Cambrian come in only along the 

 outlying spurs and foothills to the east and north. All along the east slope 

 of the ridge these beds exhibit a nearly uniform thickness, but attain their 

 greatest development in the region of Prospect Peak, where the lowest 

 members of the group are best exposed. Here the Cambrian rocks measure 

 about 7,700 feet from base to summit. They have been divided into five 

 epochs, designated by local names, as follows: Prospect Mountain quartzite, 

 Prospect Mountain limestone, Secret Canyon shale, Hamburg limestone, 

 and Hamburg shale. The varied physical differences in the composition of 

 the sediments cause them to fall readily into these five epochs, each char- 

 acterized by its own distinctive geological and topographical features. 

 The fauna also agrees with geological divisions and adds its own evidence 

 to strengthen them. So far as known, nowhere else in the state of Nevada 

 do the Cambrian rocks afford as fine geological sections as at Eureka ; nor 

 have they elsewhere been subjected to as careful a survey. The great 

 thickness of the group, the simplicity of structure in the region of Prospect 

 Peak, the slight rnetamorphism of the strata, and the uniformity of dip 

 over wide areas and across many thousand feet render a study of the sedi- 

 ments a comparatively simple matter and far easier than most Cambrian 

 areas in other regions of the world. 



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