180 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



before erosion, and it is merely the continuation of the long belt of lime- 

 stone of which the greater part of Prospect Mountain is composed. 



The main beds of Ruby Hill are a mass of quartzite, which is probably 

 underlain by the granite of Mineral Hill; a broad zone of mineral limestone 

 and an overlying belt of shale. All of these beds have been tilted so that 

 they stand at an angle of about 40°, though nowhere ou Ruby Hill does 

 the dip of the stratification of any of the beds conform to the dip of their 

 planes of contact. This lack of parallelism is characteristic of the region 

 of Ruby Hill, and is due to a succession of faulting movements. There 

 are two systems of fault-fissures on Ruby Hill. The first consists of those 

 which are approximately parallel to the strike of the formations, and which 

 were produced entirely by the main folding and upheaval, and the second 

 made up of those which were caused by the same forces supplemented by 

 strong lateral pressure. 



That there has been lateral pressure exerted from a northeasterly direc- 

 tion at some time is shown by the direction of the striation marks observ- 

 able on these latter faults, which have been called cross-faults. Beginning 

 at the Jackson mine at the southeast, the strike of the formations is to the 

 north, but it is soon deflected to the west until in the Albion mine it is 

 nearly due west. 



The quaruite and limestone contact. — The line of the contact of the quartzite and 

 limestone on the surface of Ruby Hill represents very nearly the crest of 

 the anticlinal fold. Underground, this contact is extremely irregular. 

 Besides smaller irregularities in the quartzite there are three large protru- 

 sions along the course of this contact, which occur respectively in the 

 Phoenix, K. K., and Richmond mines. Along the line of dip of the quartzite 

 and limestone contact there is a great depression several hundred feet in 

 vertical extent, which occurs at about the same depth in all the mines, and 

 which combined with undulations along the line of strike forms large basins. 

 These basins are intimately connected with the ore bodies and will be re- 

 ferred to later. 



The main fault. — The most important structural feature of Ruby Hill is a 

 fault which at the southeastern end of the mineral zone is first to be seen 

 at the American shaft. (See Plate III.) From this point, this fault, which 



