148 GEOLOGY OF THE EUREKA DISTRICT. 



steep hill slopes they give way to the Nevada limestones, which continue 

 eastward across the entire width of the mountains till they are lost beneath 

 the lava beds of Basalt Peak. County Peak (8,350 feet) forms the culmi- 

 nating point of this bi-oad, elevated mass of limestones, all the beds of which 

 sti-ike north and south and dip easterly, affording an excellent cross-section 

 over 5,200 feet in thickness, with the Lone Mountain beds at the base. The 

 sequence of rocks shown here may be taken as a typical one of the 

 Nevada epoch and will be found on page 68, in a chapter devoted to the 

 Devonian rocks. The cross-section E-F, atlas sheet xiii, is drawn across the 

 summit of County Peak, and gives at a glance the structure of the moun- 

 tains, which is shown better here than to the south, where it is "diffi- 

 cult to obtain a continuous section for anything like the same distance across 

 the strata at right angles to their strike. Midway on the ridge connecting 

 County and Woodpeckers peaks, about 200 feet below the summit and 3,000 

 feet above the base of the limestone, occurs an important grouping of fos- 

 sils exhibiting the most complete mingling of both upper and lower Devo- 

 nian species yet found in the district. Radiating from County Peak in all 

 directions occur numerous narrow gorges scored deeply into the mountains, 

 frequently exposing 1,000 or 2,000 feet of strata and offering excel- 

 lent opportunities for detailed studies across the middle Devonian strata. 

 These gorges are the source of the two drainage channels that encircle 

 Richmond Mountain, finally running out into Diamond Valley. North of 

 County Peak toward Richmond Mountain, the limestones are characterized 

 by a development of siliceous beds, aggregating a thickness of over 100 feet 

 and rising in bold, rugged outcrops above the otherwise even hill slopes. 

 Nowhere else were similar rocks recognized in the Devonian, the siliceous 

 material apparently increasing in amount toward Richmond Mountain, 

 although the higher horizons maintained their nonnal character. It is only 

 directly west of County Peak that the upper members of the Nevada lime- 

 stone are exposed, the basalts concealing more and more of the beds as they 

 approach Richmond Mountain. In this area north of County Peak, scarcely 

 any fossils were collected, and nowhere any grouping of species ; conse- 

 quently no locality indicating the presence of organic remains is marked 

 upon the map. It is proper to say, however, that very little time was allot- 



