STRUCTURE OF RUBY HILL. 39 



•and eighth levels of the Richmond, it is almost certain that this bend in the 

 shale is not due to twisting and distortion, but was caused by a vertical 

 fault which followed very nearly the course of the compromise line. When 

 the country was raised up, the portion of it lying northwest of the compro- 

 mise line fault was not raised to the same height as the portion of country 

 lying on the southeast side of it. In other words, the block of ground just 

 described subsided either absolutely or relatively. It is almost certain that 

 in this manner the northwest end of the underground or lower body of shale 

 was brought in contact with the surface or upper belt of shale along this 

 compromise line fault. The position of the two bodies of shale southeast 

 of the compromise line favors this belief. Similar cross-faults noticed in 

 the quartzite in the Richmond mine also tend to prove the fact of a 

 frequent cross-faulting of the formations in this part of the hill. This being 

 the case, the lower belt of shale must underlie the stratified limestone in the 

 Richmond mine, and it will be encountered at greater depth. At this lower 

 level the ground must have very much the same appearance as the country 

 on the northeast side of the main fissure in the cross-cut to the Locan shaft. 

 The fissure, however, at the point where it cuts this lower belt of .-hale 

 might or might not be in contact with the quartzite. A calculation made 

 on the basis of the displacement of the shale on the surface would bring 

 the lower belt of shale in contact with the fissure at a point about 1,700 feet 

 below the top of the Richmond shaft, or about 500 feet below the present 

 lowest workings. Another proof that the lower belt of shale has been 

 brought into contact with the surface shale near the compromise line is fur- 

 nished by the fact that the surface or upper bed of shale is always under- 

 lain by distinctly stratified limestone whereas the lower shale is not. This 

 stratified limestone is not to be seen southeast of the compromise line or 

 fault, where the lower shale makes its appearance. It will be noticed that 

 this cross-fault does not in any way affect the course of the Ruby Hill 

 fault; it was, therefore, formed at the same time or prior to it. 



Illustration of the manner of faulting. — FigUlCS 1, 2, 31ld 3, Plate XV.. represent the 



manner in which the two belts of shale were dislocated by the cross-fault 

 and the main fault. A B, Fig. 1, represents the upper or larger belt of 

 shale, and a b the lowtr, there being limestone between and on either side 



