SUKPRISE PEAK. 131 



Surprise Peak.— Xo nuiuntaiu ill this part of tlu' district affords a more 

 commanding Aaew than Surprise Peak. It is situated between the Sierra 

 fault on the east side and Sierra Valley on the west. It is capped by 

 Eureka quartzite, wliicli is underlain 1)y the Pogouip, the limestone being 

 distinctly seen to pass beneath the quartzite. On the north side of the 

 peak, and on the opposite side of the fault, in beds unconformable with 

 the Prospect Mountain limestone, was found a small but characteristic 

 Pogonip faiuia. Its occurrence here is so important that it is given in full, 

 as follows: 



Keceptaculites niainmillaris. Kaphistoma iiasoui. 



Cystidean plates. Pleurotomaria? 



Orthis perveta. Lei)erditia bivia. 

 Orthis tricenaria. 



Sien-a Valley, along the west base of Surprise Peak, has been the 

 center for the eniption of considerable masses of audesitic pearlites and 

 hornblende andesites, which, in the fonn of small irregular knolls and dikes, 

 have penetrated the limestone on the south side of the peak. Associated 

 with these dikes are others of rhyolite, while still farther southward, where 

 the sedimentary rocks pass beneath the valley, occur large accumulations 

 of pearlites, pumices, and tuffs. Details m regard to these igneous rocks 

 will be found on page 234 et seq. 



Grays Canyon.— The Pinnacle Peak fault lies on tlie west side of the 

 peak of the same name, at the southern end of the mountains. The 

 line of the fault is obscured by broad lava flows, but where these gi\'e out 

 it is easily traceable northward nearly to Prosjiect Peak with the Eureka 

 quartzite on one side and the Nevada limestone on tlie otiier. 



West of the Pinnacle Peak fault the Nevada limestone extends from 

 Mountain Valley southward till the sedimentary lieds pass beiieatli Fish 

 Creek Valley. Through these liiucstoiies Grays Canyon cuts a narrow 

 ravine, which offers a few good exposures, but nowhere exhibits a continu- 

 ous sectioa across any great thickness of lieds. Only the lower jiortions of 

 the Nevada limestone are exposed, and ti\er the greater part of tliis area 

 bedding planes are wanting. The best locality obser\ed for the collection 

 of fossils was found on the low, flat-topped ridge west of Gra\s Canvon 



