FAULTED LIMESTONE BLOCKS. 129 



the westward the Devonian limestone is exposed in Mountain Valley, the 

 three horizons being determined by characteristic species. 



Lookout Mountain. This isolated mountain stands out prominently from 

 the surrounding country, cut off on three sides by faults. On the east runs 

 the Lookout fault, and along the west base the persistent and profound 

 Pinnacle Peak fault brings up the Nevada limestone against the Eureka 

 quartzite. The mountain is wholly made up of quartzite, inclined eastward 

 at low angles, the beds of which are for the most part darker in color and 

 more ferruginous than those of the same horizon found elsewhere. At the 

 east base of the mountain occurs a small patch of limestone, in part 

 obscured by surface accumulations of Sierra Valley and in part by 

 andesitic lavas. As this limestone lies on the east side of the Lookout 







fault its age can be determined only by its fauna, but fortunately this is 

 sufficiently typical to admit of its reference to the Cambrian. 



Northward of this last exposure and separated from it by only 300 feet 

 of acidic lavas, occurs a larger body of limestone, which forms a narrow 

 ridge, cut by the stream bed which comes down along the north side of 

 Lookout Mountain. The ravine affords a fair exposure of the beds. This 

 second body of limestone presents no structural evidence of its position, 

 the fauna alone determining its age, but fortunately it yielded a small num- 

 ber of fossils. These two groupings are not quite identical, but the beds 

 from which they were obtained can not be wide apart. The outcrop east of 

 Lone Mountain indicates clearly the horizon of the Hamburg limestone, 

 carrying certain species which extend downward into the Prospect Moun- 

 tain beds, mingled with others occurring as high as the middle portion of 

 the Pogonip. The larger exposure at the northeast base of the mountain 

 has been assigned to the Prospect Mountain limestone, without any decided 

 evidence as to the correctness of the reference otherwise than that it belongs 

 to the Cambrian. 



Pinnacle Peak. This summit lies about one and one-quarter miles due 

 south of Lookout Mountain and presents much the same general features 

 in the character of the beds and mode of occurrence, the two mountains 

 being connected by a continuous mass of quartzite. The beds strike 

 invariably north and south and incline eastward at angles si-Mom 

 MON xx 9 



