150 GEOLOGY OF THE EUREKA DISTRICT. 



can be no doubt, the only difference being that the siliceous beds occur 

 here more prominently developed than on the west side of the Hoosac fault 

 with the friable sandstones altered to compact quartzites. Moreover, they 

 are seen to pass into Nevada limestones, except where their continuity is 

 broken by outbursts of basalt. In the region of English Mountain this 

 connection is in no way disturbed by intrusive material and the transition 

 into the Nevada beds maybe readily made out. Nevertheless, there occurs 

 along the Pinto fault one or two exposures of siliceous beds whose geolog- 

 ical position it is difficult to determine. One of these is found east of the 

 Pinto Mill, where a long, narrow ridge, largely made up of quartzites, dips 

 from 25 to 35 to the east. A ravine, which cuts through this ridge, gives 

 a fair idea of the beds, and it is not improbable that they belong to the 

 Eureka horizon. Another instance may be found southeast of Pinto Basin, 

 near the place called The Wells, where a small isolated hill occurs, appar- 

 ently a faulted mass composed of white vitreous quartzite with intercalated 

 bluish gray limestones. Except for these limestones the evidence would 

 point quite as much to the Eureka quartzite as to the overlying Lone Moun- 

 tain beds. English Mountain offers the best locality for a sttidy of these 

 Lone Mountain beds to be found on the east side of the district, as they 

 show a gr.eat thickness of strata dipping uniformly eastward, overlain by 

 the lower beds of the Nevada limestones. The base of English Mountain 

 is formed of quartzites and sandstones, followed by gray limestone, in turn 

 capped by brownish red, vitreous quartzite. The latter is a rough and 

 jagged rock, full of nodules and water-worn cavities. 



On the south side of the Silverado Hills the Silurian rocks rise above 

 the pumices and tuffs that follow the base of the hills and in a large degree 

 conceal the sedimentary beds. Here the limestones have gradually changed 

 their strike and dip and lie inclined to the northward with the great body 

 of Devonian limestone that forms the bold escarpment of Red Ridge resting 

 upon them. Continuing eastward, the limestones gradually swing around 

 until they assume a westerly dip, forming a synclinal fold, with those of 

 English Mountain. This Red Ridge escarpment offers excellent vertical 

 sections of the middle portions of the Nevada limestones, and the variegated 

 red, gray, and brown belts, with the interbedded sandstones, may be traced 



