GEOLOGY OF ECBY UILL. 115 



can be made of the thickness. There are, liowever, only 200 or 300 feet 

 of beds before the horiztui is sliarply cut oH" In' the Iloosac fauh l)ringing- 

 ill the Carboniferous in juxtaposition with it. 



Caribou Hill, separated from McCoy's Ridge by Purple Mountain, stands 

 out as a prominent topographical feature. It is cai)})ed bv the same 

 Eureka quartzite. There are only 200 feet of l)eds and consequently the 

 Lone Mountain limestones are wholly wanting. It is this cap of quartzite 

 which has protected from erosion the underlying limestones. Here, again, 

 in a narrow ra.vine at the west base of the hill, in the underlving limestone 

 immediately beneath the (juartzite, the Rcceptaciilifrs beds occur, with several 

 characteristic species, offering additional proof, if any was needed, as to their 

 geological position. From Caribou Hill northward no outcrops of the 

 Eureka quartzite were recognized. The Pogonip limestones present low, 

 flat-topped ridges inclined northward, gradualh' passing beneath the recent 

 deposits of Diamond Valley. 



RUBY HILL REOION. 



Ruby Hill and Adams Hill together occupy a small but clearl}' defined 

 area which may be considered simply the northern extension of Prospect 

 Ridge. The Jackson fault sharply (Outlines this area on the east side, while 

 the recent accumulations along the line of the Spring Valle}- fault limit it on 

 the west side. The geological importance of the region is mainly derived 

 from the enormous ore deposits found in the limestones of Ruby Hill, whicli 

 had yielded, up to the time of this investigation, over sGO,00(),0()(» in 

 precious metals. In general the orogi-aphic structure is simple, and only in 

 detail in the immediate neighliorhood of Rubv Hill is it in anv wav complex. 



On Plate i will be found a geological map of Rul)y Hill and the adja- 

 cent country, pre[)ared from tlie large atlas sheets for more easy reference 

 to the text. Unfortunately the line between atlas sheets vii and viii runs 

 directly across this area, interfering greatly Avith the clear understanding 

 of the structural relations of the beds of Prospect Ridge with those of 

 the Ruby Hill as well as with those lying east of the Jackson fault. By 

 referring to the maj) it will be readily seen that the Jackson fault cuts off" 

 the Cambrian strata and brings the Pogonip up against the entire series. 



