ORES OF THE DEVONIAN. 297 



4 



much disturbed and faulted and rhyolite has reached the surface only a 

 short distance from the mining property. 



In the Eureka quartzite the only instances known of mineral deposi- 

 tion are those found on Hoosac Mountain, a description of which is given 

 elsewhere. They have been worked extensively and have yielded consider- 

 able ore. Here they are intimately associated with intrusive dikes of both 

 andesite and rhyolite offshoots from the great bodies which forced their 

 way upward along the Hoosac fault. 



Throughout the Eureka Mountains the Lone Mountain horizon has 

 here and there shown evidences of mineral deposits when found in the 

 neighborhood of rhyolite outbursts, but over the greater part of the area 

 they exhibit no surface signs of ore-bearing material. An interesting 

 example of ore in the Lone Mountain horizon may be found at the 

 Seventy-six mine, in hard, flinty limestone on the northwest side of 

 McCoy's Ridge. While it can not be looked upon as remunerative property, 

 from the point of view of the present description it serves as an instructive 

 link in the chain of facts bearing upon the geological position of the 

 Eureka ore bodies. This is the only body of Lone Mountain limestone 

 lying in close proximity to the Hoosac fault, and, in consequence, partially 

 explains the occurrence of ore. 



Ores of the Devonian. Passing upward, without any intervening lithological 

 break, the Nevada limestones are in like manner frequently found to carry 

 oxidized, argentiferous lead ores in fissures and crevices in the regions of 

 profound faults. It by no means follows that rhyolites necessarily accom- 

 pany the ore at the surface, and still less that the latter occurs wherever 

 rhyolite penetrates the Nevada limestone through fissure planes. Instances 

 may be cited in the case of the Reese and Berry mine, just north of the 

 canyon of the same name, and again on the summit of Newark Mountain, 

 both localities indicating disturbances of strata without any .assignable 

 cause on the surface. The dislocation of beds may be due to intrusive 

 rocks which failed to penetrate the surface, the fissuring being filled by 

 mineral matter. 



Along Rescue Canyon, where there is such a continuous and powerful 

 mass of rhyolite under geological conditions similar in many respects to 



