22 SILVER LEAD DEPOSITS OF EUREKA, NEVADA. 



peculiar to tlie region of Ruby Hill" and Prospect Mountain, and is due to 

 faults which in many places have followed the contact of the different for- 

 mations. The local non-conformity bears upon the ore bodies only as an 

 indication of structure. 



Relations of the three formations underground. — The subterranean structure of Ruby 

 Hill presents features of unusual interest to the geologist and miner. The 

 underground explorations have been very extensive, but they have not been 

 so complete that it has been possible to trace the contacts of the different 

 rocks in every instance, and in making the maps which accompany this 

 memoir it has often been necessary to calculate the position of points not 

 actually exposed. These calculations have been made with care and due 

 reference to the position which the different formations bear to each other 

 at all exposed points. The main beds of Ruby Hill are an underlying 

 mass of quartzite, a broad zone of mineral limestone, and an overlying 

 belt of shale, all of which have been tilted so that they stand at an angle 

 of about 40° ; this angle being somewhat greater in the upper than in the 

 lower workings of the mines. That these strata should pitch at a smaller 

 angle as they approach the valley is naturally to be expected. Beginning 

 at the Jackson mine, the most southerly location on the mineral zone, the 

 strike of these formations is to the north, but their course is soon deflected 

 toward the west, until, in the Albion mine, the most northerly, they strike 

 nearly east and west. Their course underground resembles in its general 

 outlines that on the surface, though there are many irregularities and fre- 

 quent breaks caused by faults. As far as the deepest workings have pene- 

 trated (namely, to a depth of 1,230 feet in the Richmond shaft), the average 

 dip of the contact of the quartzite and limestone has been found to be 

 about 40°. Near the surface the angle of dip is much less, as the highest 

 point of the quartzite seems to be at the crest of an anticlinal fold. The 

 line of contact between quartzite and limestone on the southwest slope of 

 Ruby Hill would be very near the top of this anticlinal, which can be ob- 



"It should be mentioned that Ruby Hill proper stops at the divide south of the Eureka hoisting 

 •works, and that the Jackson and Phoenix mines are on spurs of Prospect Mountain. The term "Ruby 

 Hill mines," however, will be used in this report as including the Jackson, Phoanix, K. K. (now be- 

 longing to the Eureka Company), Eureka, Richmond, and Albion, the six mines that are situated on 

 that belt of limestone included between the quartzite and shale. 



