14 SILVER LEAD DEPOSITS OF_EUREKA, NEVADA. 



935 feet mineral limestone (Prospect Mountain limestone). 



30 feet shale" (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). 

 The tunnel section, Plate II., gives an excellent idea of the formations 

 which compose the east slope of Prospect Mountain and its spurs. It is 

 true that in all probability no other section parallel to this one, and taken 

 at a considerable distance either north or south of it, would closely corre- 

 spond, yet it is safe to assume that there would be enough resemblance be- 

 tween them to permit of this particular one being taken as a type. Mi-. 

 Hague, in his geological map of the district, has placed the mouth of this 

 tunnel in the Hamburg limestone. The first belt of shale encountered is 

 therefore the Secret Canon shale. 



The second belt of shale is probably nothing more than a fragment of 

 the third and widest, and has been brought into its present position in the 

 tunnel by movements of upheaval. If Plate II. is examined it will be seen 

 that the numerous faults which have occurred along the line of the Eureka 

 Tunnel have so displaced the shale beds that it is not possible to determine 

 with any certainty what was their original position. In drawing this sec- 

 tion it has been necessary to depend very much on probabilities in placing 

 the dividing lines between the different formations. The mass of shale 

 marked B, Plate II., does not appear in the tunnel, but it is exposed in the 

 incline winzes of the workings below the tunnel level from a distance 50 

 feet below that level down to the deepest excavations. As these incline 

 winzes are several hundred feet south of the tunnel, and as the strike of the 

 shale is east of north, it would appear in the tunnel section in the position 

 shown in the plate. There is only one boundary of this shale which has 

 been exposed, namely, that which is laid bare in the winzes, and the other 

 boundaries given it in the section must be necessarily of a very indefinite 



"The term " Prospect Mountain limestone" of course refers to a group of beds characterized by tbe 

 presence of certain fossils. Though limestone predominates, the intercalated shales which are charac- 

 teristic of this formation, according to Mr. Hague, are necessarily classified as members of the same 

 group of beds. 



