SUKPK1SE PEAK. 131 



Surprise Peak.-No mountain in this part of the district affords a more 

 commanding view 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, which is underlain by the Pogonip, 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 fauna. Its occurrence here is so important that it is given in full, 

 as follows: 



Keceptaculites mainmillaris. Kaphistoma nasoni. 



Cystidean plates. Pleurotomaria? 



Orthis perveta. Leperditia bivia. 

 Orthis tricenaria. 



Sierra Valley, along the west base of Surprise Peak, has been the 

 center for the eruption of considerable masses of andesitic pearlites and 

 hornblende audesites, which, in the form 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 in regard to these igneous rocks 

 will be found on page 234 et seq. 



Grays Canyon. The Pinnacle Peak fault lies on the 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 give out 

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

 quartzite on one side and the Nevada limestone on the other. 



West of the Pinnacle Peak fault the Nevada limestone extends from 

 Mountain Valley southward till the sedimentary beds pass beneath Fish 

 Creek Valley. Through these limestones Grays Canyon cuts a narrow 

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

 ous sectioa across any great thickness of beds. Only the lower portions of 

 the Nevada limestone are exposed, and over the greater part of this area 

 bedding planes are wanting. The best locality observed tor the collection 

 of fossils was found on the low, flat-topped ridge west of (ir;iys Canyon 



