FAULTED LIMESTONE BLOCKS. 129 



the westward the Devonian limestone is exposed in Mountain Vallev, tlie 

 three honzons bein<>- detennineil 1)\- cliaracteristic speeies. 



Lookout Mountain.— Tliis isolated mountain stands out prominently from 

 the surrounding);- eonntr>, cut off on three sides b\- faults. ( )n the east runs 

 the Lookout fault, and alonjj;- the west l)ase the persistent and profound 

 Pinnaele Peak fault brin<)-s uj) the Nevada limestone against the Kureka 

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

 at low anoles, the beds of which are for the most part darker in color .iiid 

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

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

 obscured by surface nccunuilations of Sierra \'alle\' and in part b\- 

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

 fault its age can be determined only b}' its fauna, but fortunateh' this is 

 sufficiently typical to admit of its reference to the Cambrian. 



Northward of this last exposure and sei)arated from it by onlv 300 feet 

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

 ridge, cut \)\ the stream bed which comes down along the nortli side of 

 Lookout Mountain. The ravine afi'ords a fair exposure of the beds. This 

 second body of limestone presents no structural evidence of its ])osition, 

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

 ber of fossils. These two grou])ings are not (juite identical, l)ut the beds 

 from wliich they were ol)taine(l can n(^t be wide apart. The outcrojt east of 

 Lone Mountiiin indicates clearly the horizon of the Ilandiurg limestone,- 

 carrying certain species which extend downward into the Prospect Moun- 

 tain beds, mingled with others occurring as high as the nii(hlle portion of 

 the Pogonip. 'i'he larger exposure at the northeast base of tlu- mountain 

 has been assigned to the Prospect ^lountain limestone, without any decided 

 e\'idence as to the correctness of the reference otherwise than that it belongs 

 to the Cambrian. 



Pinnacle Peak.— This summit lics aliout oiie 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 moimtains 

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

 invariabl\- north and south and incline eastward at angfles seldom 



MON XX 9 



