26 GEOLOGY OF THE EUEEKA DISTRICT. 



upper portions of the Nevada limestone. At tlie exti'eme northeast corner 

 tlie Eureka quartzites occupy a small area, but are of no special importance 

 themselves except in determining the basal rocks of this elevated mass and 

 the position of the overlying strata. Numerous narrow gorges with mural- 

 like faces cut deeply into the limestones, affording excellent comparative 

 sections across the strata, datum points being readily established by the 

 brown, red and gray beds of the middle Devonian. Represented in this 

 uplifted mass occur between 6,000 and 8,000 feet of limestones. That the 

 upper beds of the Nevada epoch are represented here is shown just to the 

 east of Sugar Loaf and Island Mountain wliere the White Pine shales lie 

 conformably upon the uppermost beds of limestone. 



Diamond Mountains.— Tliis range is oue of the best defined mountain up- 

 lifts on the Nevada plateau, extending 40 miles along the east side of Dia- 

 mond Valley. Only the southern end of it, however, in the northeast corner 

 of the map, c<imes within the limits of this survey, as the range properly 

 terminates with Newark Mountain. Its immediate proximity to the County 

 Peak limestones, from which it is separated only by an ovei-flow of igneous 

 rocks, relates it in the closest possible manner with the Eureka Mountains. 

 Diamond Peak (10,637 feet), the highest and broadest in the range, lies 

 within the limit (^f this survey, and the geological structure and continuity 

 of l)eds exposed upon the flanks of lioth Diamond Peak and Newark Moun- 

 tain, ad<l gi-eatl}- to our knowledge of the sequence of Paleozoic sediments. 

 For the greater part of its length Carboniferous rocl^s flank both sides of the 

 Diamond Range, and, as is so often the case throughout Nevada, no beds 

 immediately iinderlying them had previously been recognized toward the 

 north. Here, however, Newark Mountain consists exclusively of Devonian 

 rocks pa.ssing beneath the east liase of Diamond Peak, where they are con 

 fonnably overlain by an inunense thickness of Carboniferous beds. New- 

 ark Mountain rises abruptly out of the plain and offers a typical example, 

 so common in the Great Basin, of an anticlinal ridge with one side of the 

 fold dropped down along the lino of the axial plane. In this instance the 

 downthrow lies (in tlie east side and the mountain presents along the summit 

 a bold escarpment 1,000 feet in height, facing Newark Valley. At the base 

 of tlie escarpment easterly dipping beds come in, and dark lilue massive lime- 



