8 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



Ruby-Duuderburg mine, which is in the Hamburg limestone, might be mis- 

 taken for that of Prospect Mountain. It is only through its connection 

 with the well-established belt of Hamburg limestone that its relative age 

 can be decided. It is hard to say what the properties of the limestone in 

 the Hamburg mine are which make it easy to recognize the difference be- 

 tween it and the Prospect Mountain limestone, but they are characteristic 

 enough to render it evident even to the casual observer that it is a different 

 limestone. It breaks with a sharper fracture, which is probably due to the 

 larger quantity of silica that it contains; and one or two varieties resemble 

 quartzite in texture. The Hamburg shale differs in no essential respects 

 from the Secret Canon shale. 



Pogonip limestone. — The Pogonip limestone forms a nearly continuous belt 

 on the eastern slope of Prospect Mountain, and on the north and east sides 

 of Adams Hill where that elevation merges in the valley. In this lime- 

 stone the first discoveries in the district were made in New York Canon. In 

 it are also situated the Bullwhacker, Williamsburg, and other mines. In 

 color this limestone does not differ much from the two limestones before de- 

 scribed, except that it is of a brownish tinge, but it is softer, shows fewer 

 signs of metamorphic action, and is almost everywhere distinctly stratified. 



Eureka quartzite. — The Eureka quartzite composes Hoosac Peak and the en- 

 tire eastern half of the mountain of that name. It also occurs as a narrow 

 band on the west side of New York Canon and east of the main canon 

 where it enters Fish Creek Valley. Its color is white, reddish, or bluish, 

 and it is very hard and compact. In texture it is granular, and it is rarely 

 found stratified. It is apparently nearly pure silica. 



Massive rocks. — The only massive rocks which make their appearance in 

 the metalliferous zone which is occupied by Prospect Mountain and its off- 

 shoots are granite, quartz-porphyry, and rhyolite, but hornblende-andesite 

 is found in its neighborhood, and basalt within three miles. 



Granite. — The granite crops out at Mineral Hill at the north end of Pros- 

 pect Mountain, covering an area of but a few acres; and this is its only 

 occurrence in the district. It appears between the limestone and the quartz- 

 ite. It is coarse-grained, grayish in color, and very much weathered at the 



