108 GEOLOGY OF THE EUREKA DISTRICT. 



say. The relation of this granite to the Prospect Mountain uplift will be 

 more fully considered in discussing the geology of Ruby Hill. 



South of Prospect Peak the limestone maintains a fairly persistent 

 north and south strike and easterly dip, the angle of which seldom falls 

 below 60. These highly inclined beds occur for a long distance north of 

 the Geddes and Bertrand mine. In the Irish Ambassador the beds lie 

 inclined at 40. In general, lines of bedding have been obliterated, but 

 are found in sufficient number of instances to establish the structure, while 

 a meager fauna affords ample evidence of the age of the beds. Near the 

 Geddes and Bertraud mine in a compact limestone, the upper horizons of 

 the Prospect Mountain limestone are identified by the occurrence of several 

 species found also in the Richmond Mine on Ruby Hill, as well as by other 

 forms found in the same belt just below the Secret Canyon shale. These 

 beds yielded Kutorgina whitfieldi, Plychoparia oweni, and Agnostus bidcns. 

 Lenticular beds of argillaceous shale are by no means as broadly developed 

 as to the northward, but are of frequent occurrence and indicate the same 

 alternating conditions of deposition. On the other hand cherty beds and 

 highly siliceous dark limestones are very characteristic of the region. 

 Occasionally thin siliceous beds, from their superior hardness, withstanding 

 erosion better than the purer beds, rise like walls above the surrounding 

 hill slopes. This latter feature frequently gives the limestone body quite a 

 different aspect from that observed to the north and at the same tune aids 

 in determining the strike of the beds. 



As already mentioned the Eureka quartzite on the west side of the 

 Sierra fault" lies unconformably against the Prospect Mountain limestone 

 from Prospect Peak nearly to Surprise Peak. At this latter locality a body 

 of Pogonip limestone abuts against the Cambrian limestone; the fault line, 

 which has maintained a persistent direction, swerves suddenly eastward and 

 then again turns and with a north and south course strikes across an easterly 

 spur of Surprise Peak. On a broad shoulder of this spur the Prospect 

 Mountain limestone again comes in contact with the Eureka quartzite of 

 Surprise Peak, the line of faulting passing about 200 feet below the summit. 

 Structurally the position of the Pogonip limestone is shown by its passing 

 conformably beneath the Eureka quartzite. Paleontological evidence con- 



