PALEOZOIC SHORELINE. 177 



mulations of volcanic material. Ranges situated eastward of the supposed 

 shore-line expose above flows of rliyolite long- ridges of quartzite whicli 

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

 unlike the rocks of the region to tlie west. In a study of the geological histor}- 

 of continental development it is important to kno^\- tliat it was along this 

 ancient shore-line that volcanic activity has disphned its g-reatest energ}- 

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

 mous thickness of Paleozoic strata witli no rocks 5^ounger 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 \>-ell up into central Nevada. Tliis old coast line is a region 

 of great interest and one which would well repay careful investigation 

 and yield valuable geological results. 



If this inter[)retation 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 aiid mechanical sediments derived 

 from the neighboring land areas attest the fact that this detrital matei'ial 

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

 tance. Along the shore the conglomerates form heavj^ masses of material, 

 indicating littoral deposits, but to the east these same formations gradualK- 

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

 uniform in character. Exceptional occurrences of coarse and ra}iidly 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- 

 Cambi-ian 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. 

 MON XX 12 



