SILVER AND GOLD, CONTINUED. 



233 



2.11.19. Comstock Lode. A great fissure vein, four miles 

 long, forked into two branches above, along a line of faulting in 

 eruptive rocks of the Tertiary age and chiefly andesites. In the 

 central part of the vein the displacement has been about 3000 

 feet, shading out, however, at the ends. The ores are high-grade 

 silver ores in quartz, and occur in great bodies, called " bonanzas," 

 along the east vein. Over $325,000,000 in gold and silver has 

 been extracted, in the ratio of two of the former to three of the 



TiahX of 

 M* Davidso 



FIG. 57. Section of Comstock Lode on line of Sutro Tunnel. After G. F. 



Becker, Monograph TIL, U. S. Geol. Survey. The colors of the 



original are h-'re indicated by line-work. 



latter. The vein lies on the easterly slope of a northeasterly spur 

 of the Sierras. West of it is Mount Davidson. The outcroppings 

 lie on the flank of the latter, about 6500 feet above the sea and 

 1500 feet below, the summit. The general strike of the vein is 

 east of south and it dips east. Views regarding the geology of 

 the Comstock have changed in the course of years, as they have 

 been influenced by the successive writings of Von Richthofen, 

 King, Church, Becker, and Hague and Iddings, the points in es- 

 pecial controversy being the determinations of the rock species. 

 2.11.20. It may be remarked that the whole scheme of the 



