12 GEOLOGY OP THE EUREKA DISTRICT. 



at. the map which shows liow tlie sedimentary strata have been broken up 

 into separate mountain blocks, each made iip of a ])ortion of the entire 

 thickness of beds. 



In the four grand periods of Paleozoic time represented at Eureka, 14 

 epochs liave been recognized : 5 in the Cambrian, 3 in the Silurian, 2 in the 

 Devonian, and 4 in the Carboniferous, 



With a single exception local geographical names have been employed 

 to designate the different epochs into which the Cambrian, Silurian, and 

 Devonian have been divided. Heretofore, throughout the Great Basin the 

 division of the larger periods into epochs has not been deemed necessary, 

 the individual horizons not having been studied sufficiently in detail to 

 require it. The exception is made in favor of the Pogonip limestone, a 

 name first applied by the Geological Exploration of the Fortieth Partdlel to 

 the belt of limestone whicli forms the base of the Silurian. In the Carbon- 

 iferous period a large quartzite body at the base of the series has been 

 designated the Diamond Peak quartzite, but for the remaining epochs the 

 Avell known names Lower Coal-measures, Weber conglomerates, and Upper 

 Coal-measures are retained, notwithstanding some serious objection to the 

 use of the term Coal-measures in this region. 



Each of the six blocks expose several thousand feet of strata, and 

 while they frequently overlap each other no two of them represent precisely 

 the same horizons, although the Diamond Range includes within its strata 

 the beds whicli make up the Carbon Ridge and Spring Hill blocks. The 

 six blocks essentially correspond to the following periods : 



Prospect Ridge: Cambrian and Silurian. 



Fish Creek Mountains: Silurian. 



Silverado and County Peak : Silurian and Devonian. 



Mahogany Hills: Devonian. 



Diamond Mountain: Devonian and Carboniferous. 



Carbon Ridge and Spring Hill: Carboniferous. 



In the subjoined section, which may be best designated as the Eui'eka 

 section, the relative thickness and general lithological characters are given 

 for all the geological divisions which have been made of the sedimentary 

 rocks. A plane of unconformity in the Silurian is indicated by double 

 dividing lines lietween the Eureka quartzite and Lone Mountain limestone. 



