146 GEOLOGY OF THE EUKEKA DISTEIOT. 



shale, which on the east side of the Eureka District exposes such an enor- 

 mous thickness. There is but little doubt that these lower beds represent 

 the White Pine horizon, but, as they are so poorly developed as compared 

 with the shales at Newark Mountain and so difficult to trace along any 

 definite horizon, they have been omitted on the geological map. No 

 exposure of these beds was seen more than 100 feet in thickness and in 

 places they are entirely wanting. It would seem that after the deposition of 

 the limestones the conditions here were more favorable for purely siliceous 

 beds than at Newark Mountain, and that the transition was more or less 

 rapid. It must be remembered that the White Pine shale, although of great 

 thickness at White Pine and on the east side of the district, is of local 

 occurrence, never as yet having been recognized in other parts of the 

 Great Basin. The occurrence in the argillites just south of The Gate of a 

 few obscure plant remains and the species Discina minuta is strong evi- 

 dence, taken in connection with their stratigraphical position, that these 

 beds represent the White Pine shale. 



The Diamond Peak beds which overlie the limestones on the north 

 side of The Gate form the great mass of Anchor Peak, showing a greater 

 thickness of strata than the same horizon exposes in the Diamond Range; 

 the explanation being found in the argillites of the White Pine shale giving 

 out and being replaced by a greater development of siliceous material. 

 After the coming in of the siliceous beds north of The Gate the quartzites 

 stretch for nearly a mile beyond the limits of the map. At the west base 

 of Anchor Peak there is a small exposure of Devonian limestones dipping 

 under the quartzites, probably extending northward along the west base 

 of the Pinon Range. 



SILVERADO AND COUNTY PEAK. 



This mountain block is mainly outlined by profound faults, along which 

 igneous rocks of varied composition have burst forth in vast quantities, 

 almost completely isolating it from adjoining sedimentary regions. On the 

 south and east the Quaternary accumulations of Newark and Fish Creek 

 valleys rest against the base of the hills and probably in a large degree 

 conceal eruptive rocks which broke out along the edge of the uplifted 



