PALEOZOIC SHORE-LINE. 177 



mulations of volcanic material. Ranges situated eastward of the supposed 

 shore-line expose above flows of rhyolite long ridges of quartzite which 

 have been referred to the Paleozoic age. They are at all events quite 

 unlike the rocks of the region to the west. In a study of the geological history 

 of continental development it is important to know that it was along this 

 ancient shore-line that volcanic activity has displayed its greatest energy 

 in Nevada. Upon one side of these accumulated lavas is found an enor- 

 mous thickness of Paleozoic strata with no rocks younger than the Upper 

 Coal-measures, and on the opposite side a great development of alpine 

 Trias and Jura is seen with an absence of the Paleozoic beneath it. These 

 facts furnish strong evidence for belief in the existence of a continental 

 area in western Nevada during Paleozoic time. To the south the shore- 

 line probably ran out toward the California boundary; to the northward it 

 may be traced well up into central Nevada. This old coast line is a region 

 of great interest and one which would well repay careful investigation 

 and yield valuable geological results. 



If this interpretation of observed facts is correct, the degradation of the 

 land surface during Paleozoic time should have supplied an enormous mass 

 of detrital matter to the ocean to the east. Now, by a study of the Eureka 

 Paleozoic strata, this is precisely what is found to be the condition of things. 

 Along this coast line coarse conglomerates aud mechanical sediments derived 

 from the neighboring land areas attest the fact that this detrital material 

 must have come not only from the west, but from a land area at no great dis- 

 tance. Along the shore the conglomerates form heavy masses of material, 

 indicating littoral deposits, but to the east these same formations gradually 

 pass into fine grained sandstones, the beds in general becoming more 

 uniform in character. Exceptional occurrences of coarse and rapidly chang- 

 ing material can be found in eastern Nevada, but for the most part they 

 occupy restricted areas, and may be accounted for by their nearness to pre- 

 Cambrian islands. All evidence goes to show that Eureka was situated not 

 far from this western boundary, and its geological record affords ample 

 proof of elevation and depression throughout Paleozoic time, with inter- 

 vals of shallow water and nearness of land areas between periods of rel- 

 atively deeper seas. 

 MOW xx 12 



