STRUCTURE OF RUBY HILL. 35 



some places the cross-sections show that the dip has again become slightly 

 flatter in the deepest workings, but this is probably not a permanent change. 

 two belts of shaie exist. — It has already been mentioned that two belts of shale, 

 only one of which appears at the surface, exist on Ruby Hill. If the 

 geological map of the district (Plate I.) is examined, it will be noticed that 

 the shale and limestone contact on the surface lies at a considerable distance 

 northeast from the Jackson, Phoenix, K. K., and Eureka mines. Taking into 

 account the general clip of the Secret Canon shale on the surface and that of 

 the shale where it is encountered below, it is at once apparent that the two 

 must be distinct masses. On the third and fourth levels of the Jackson 

 mine, in the cross-cut to the old shaft, a body of shale upwards of 100 feet 

 thick is encountered, which lies on the east side of the main fissure and dips 

 away from it. 



Lower belt of shale in the American and Jackson. This loWd' shale haS been faulted by 



the fissure, and the western portion has been raised up and can be seen in 

 the American shaft cross-cut, described on page 28. Here it occupies the 

 position where it was to be expected, namely, on the west side of the Ruby 

 Hill fault. This is the only known place where this underground or lower 

 belt of shale is to be found on the surface, the faulted portion having been 

 removed by erosion at all other points aboveground. 



In the cross-cut on the third level of the Jackson it is about f>0 feet 

 east of the main fissure and on the fourth it is in contact with it. It is 

 upwards of 100 feet thick on the third level and widens out somewhat as 

 depth is attained, so that in the cross-cut on the fourth it is 145 feet wide. 

 The dip of the contact of the shale with the limestone on the third and the 

 rhyolite on the fourth is 70° toward the northeast. The dip of the stratifi- 

 cation, at its contact with the limestone or rhyolite, is very nearly the same 

 as that of the contact itself, but in proceeding toward the old shaft the 

 planes of bedding of the shale become flatter, though they again dip off 

 more sharply as a fault plane is approached, which separates the shale 

 from the black stratified limestone in which the old shaft was sunk. The 

 stratified limestone northeast of this fault plane exhibits the same phe- 

 nomena as regards dip as did the shale at its contact with the limestone or 

 the rhyolite. The dip of this fault plane is about 70° northeasterly, and it 



