104 GEOLOGY OP THE EUKEKA DISTRICT. 



Feet. 



Black crystalline limestone (Hamburg limestone) 85 



Argillaceous shale (Secret Canyon shale) 300 



(Prospect Mountain limestone) : 



Limestone 935 



Calcareous shale 30 



Brecciated limestone 51 



Mountain shale 460 



Stratified limestone 90 



Brecciated limestone 50 



The body of limestone near the entrance to the tunnel belongs to the 

 base of the Hamburg limestone and is a small mass left by erosion 

 upon the west side of Goodwin Canyon, the canyon for the most part having 

 been eroded along the line of contact between the Hamburg limestone and 

 the Secret Canyon shale. Where the tunnel enters the mountain the Secret 

 Canyon shale pinches out to a few hundi-ed feet, and, a short distance to the 

 north, it is entirely cut otf by tlie Prospect Mountain quartzite. At the 

 tunnel the shales are only 300 feet in thickness. Through the Prospect 

 Mountain limestone nearly all signs of stratification and bedding' are want- 

 ing, the rock.>5 everywhere showing evidence of crushing and local faulting. 

 Evidence of movement is seen in the brecciated appearance of the lime- 

 stone, which has been recemented by calcite. Fissures and seams 

 nearly vertical are common, dipping slightly both to the east and 

 west; the larger number of them being inclined toward the east. Dyna- 

 mic action has caused such frequent changes tlu-oughout the limestone 

 that it is difficult to recognize any belt by lithological distinctions. The 

 narrow bed of shale, 30 feet in thickness, is a well defined belt, calcareous, 

 and more or less argillaceous, but of little importance, simply fore- 

 shadowing the coming in of the broad belt of Mountain shale beyond. 

 Whether it would be found to be continuous on further exploration, either 

 to the north or south, is questionable. Beyond this narrow shale band 

 occurs another limestone belt, similar to the main body, in turn followed by 

 the Mountain shale, which, unlike the Secret Canyon shale, is character- 

 ized by intercalated limestone. It resembles the clay shale found on 

 the surface, but is less pure than the Secret Canyon body. It bears a 

 close resemblance to the shale belt found in the Prospect Mountain lime- 

 stone of Ruby Hill, but there is no direct evidence of their ever having 



