STRUCTURE OF RUBY HILL. 25 



In the Jackson and Phoenix mines it is rhyolite, which is usually much 

 decomposed, but owing to the mica and smoky quartz which it contains is 

 still easily recognizable. At a place somewhere between the last point at 

 which it is seen in the Phoenix, and the first where it is encountered in the 

 K. K., positive evidences of its rhyolitic character are lost. It is likely that 

 the change is gradual, as there is something over a hundred feet of unex- 

 plored ground between where the rhyolite is last seen on the sixth level of 

 the Phoenix and the first place where it is encountered on the sixth level of 

 the K. K. It is possible, however, that this change may take place sud- 

 denly. Where the fissure is found in the K. K. and Eureka mines, the fill- 

 ing is of a dull yellow, bluish, or occasionally white color, whereas in the 

 before-mentioned localities it was uniformly white, except where stained by 

 its contact with ore. In following the fissure northwest it becomes nar- 

 rower, until in the Richmond mine it is only a few inches wide, although it 

 is a distinct and well-defined seam, with a different character of limestone 

 on either side of it, The clay has here lost its plastic nature and is a calca- 

 reous product of the attrition of the two walls. Underground, as well as 

 on the surface, this fissure takes a northwest course, after leaving the Jack- 

 son, which it retains until it is last seen in the Albion ground. 



General features of the main fissure. — This fissure will hereafter be called the Ruby 

 Hill fault or main fissure, as to its formation are due the most important 

 features of the present structure of Ruby Hill, as well as the relations of 

 the ore bodies to each other. A careful description of its manner of occur- 

 rence and of the phenomena attending it is necessary for a complete under- 

 standing of the deposits of Ruby Hill; and although when examined in one 

 particular locality it does not seem to be of remarkable importance, taken 

 throughout its entire course it is found to be the key to the solution of the 

 structural problem of the mineral zone. A proof of its comparatively recent 

 formation is the fact that it faults all the formations with which it comes in 

 contact, but is itself nowhere faulted or dislocated. At various points in 

 the lower levels of all the mines southeast of the compromise line shale is 

 encountered on the northeast or hanging wall side of this fissure. This body 

 of shale, however, nowhere reaches the surface, as it is cut off by the fault. 

 As the workings in this shale are inconsiderable, it is impossible to tell what 



