16 SILVER LEAD DEPOSITS OF EUREKA, NEVADA. 



This thin band of shale most likely was at some time part of the third and 

 widest mass of shale, which lies to the west, and was separated from it by 

 a series of faults ; at any rate faults are apparent along its contact with the 

 limestone. Alternating beds of shattered limestone and shale seem to be 

 characteristic of this portion of Prospect Mountain. 



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 this rule. The most prominent 

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



Its dip is nearly vertical, 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 occur- 

 rences of the same kind, both in the mountain and in Ruby Hill. Like 

 many others, it has been accompanied by ore, which was found on the north 

 side of the tunnel. The principal ore body yet discovered was found about 

 1 ,200 feet from the mouth of the tunnel, and was also connected with a fissure 

 which runs a little west of south, but pitches westerly. It did not extend 

 any distance above the tunnel level, but it was followed down about 100 

 feet, when a very considerable pipe of ore was encountered running under 

 the tunnel in a northerly direction. Most of these fissures and seams are 

 faults produced by the folding and upheaval of Prospect Mountain. 



Although there have been local subsidences, it is safe to say that the 

 portions of country which lie west of the fissures upon the foot-wall side 

 have as a rule been raised the highest. The strata have reached their great- 

 est relative height just over the axis of fold. The third belt of shale is over- 

 lain by black stratified limestone, which, at its contact with the shale, pitches 

 west at a steep angle until a little distance beyond the summit its stratifica- 

 tion is nearly horizontal. West of the stratified limestone the tunnel is in 

 mineral limestone. 



The following is a list of specimens from the tunnel, and the points at 

 which they were taken: 



430 feet from entrance Black crushed limestone cemented by calcite, friable. 



450 feet from entrance Grayish crushed limestone, compact granular. 



