PALEOZOIC SECTION. 11 



accompanied by profound longitudinal faults, several of which extend the 

 entire length of the mountains, and have played a most important part in 

 bringing about the present orographic conditions. 



Although these mountain masses stand so intimately related to each 

 other that it is frequently difficult to draw sharp topographical lines between 

 them, the Eureka Mountains may be divided into six blocks with well 

 marked structural and geological differences. These blocks may be desig- 

 nated as follows: 



Prospect liidge. 



Fish Creek Mountains. 



Silverado and County Peak group. 



Mahogany Hills. 



Diamond Mountain. 



Carbon Ridge and Spring Hill group. 



Paleozoic Section. As already mentioned, the Eureka Mountains lie just 

 eastward of the old shore line. In this and the following chapters the 

 evidence is presented, derived from the history of the rocks themselves, to 

 show the close proximity of a land area when the beds were laid down. 

 The nature of these off-shore deposits near the western border of an old 

 Paleozoic sea form one of the principal objects of this investigation. Much 

 of the material, such as the coarser conglomerates, must necessarily have been 

 off-shore deposits The sedimentary rocks which make up the mountains 

 present a great development of limestones, quartzites, sandstones, and shales, 

 comprising many thousands of feet of Cambrian, Silurian, Devonian, and 

 Carboniferous beds. From the lowest exposed members of Cambrian strata 

 to the top of the Coal-measures there are represented a series of sedimentary 

 deposits 30,000 feet in thickness. Nowhere within the limits of the Eureka 

 district can there be found any one exposure which shows the beds with- 

 out a break in their continuity, the longest unbroken section representing 

 about one-third of the entire sequence of strata, yet the region offers in so 

 many instances such continuous exposures of beds and so many in which 

 the series of strata overlap each other with such a constant repetition of 

 beds, that the reconstruction of the entire section is easily made out when 

 the individual parts are carefully compared and studied. The reason why 

 there is no one unbroken section may be readily understood by a glance 



