178 SILVER-LEAD DEPOSITS OF EUEEKA, NEVADA. 



The following are the different formations encountered, in the order of 

 their succession from the mouth of the tunnel: 



85 feet mineral limestone " Hamburg limestone. 



290 feet shale ... Secret Canon shale. 



935 feet mineral limestone Prospect Mountain limestone. 



30 feet shale l Prospect Mountain limestone. 



51 feet mineral limestone Prospect Mountain limestone. 



460 feet shale Prospect Mountain limestone. 



90 feet stratified limestone Prospect Mountain limestone. 



50 feet mineral limestone Prospect Mountain limestone. 



At various points along its course the tunnel cuts through seams and 

 fissures, which generally cross it at right angles. Their usual pitch is east- 

 erly, though there are many exceptions to the rule. The msot prominent 

 one of these fissures is at a point 840 feet from the mouth of the tunnel. 

 It dips nearly vertically, perhaps a little inclined to the east. It is open in 

 places and filled with sediment, bowlders, etc., which have been washed in 

 from above. At the point where it is encountered it is about 350 feet below 

 the surface, and it is a characteristic example of numerous occurrences of 

 the same kind both in the mountain and in Ruby Hill. Like many others, 

 it has been accompanied by ore which was formed on the west side of the 

 tunnel. Faulting has occurred on most of these fissures, and it is safe to 

 say that the portions of country which lie west of the fissures or upon the 

 foot-wall side have as a rule been relatively raised, and the strata have 

 reached their greatest relative elevation just over the axis of fold. 



The stratified limestone in the end of the tunnel pitches west at a 

 steep angle where first encountered, but gradually becomes flatter until a 

 little distance west of the summit its stratification is nearly horizontal. 



Section of Prospect Mountain through Prospect Mountain tunnel. The Pl'OSpeCt Mountain. 



tunnel, starting at a point about 2,700 feet west of the summit, nearly op- 

 posite the Eureka tunnel and several hundred feet below it, has been driven 

 over 2,350 feet into the mountain. For the first 1,400 feet it passes through 

 a hard, compact, white limestone, which in places resembles marble. This 



""Miueral limestone" is the term employed in the district to designate the broken and meta- 

 morphosed rock almost invariably connected with ore. 



6 Tho term "Prospect Mountain limestone," of course, refers to a group of beds characterized by 

 the presence of certaiu fossils. Though limestones predominate, the intercalated shales are uecessarily 

 classified as members of the same group of beds. 



