SUMMARY. 181 



has been called the Ruby Hill fault, though not perceptible in many places 

 on the surface, passes west of the Jackson hoisting works, its course veering 

 toward the west, and is visible in a tunnel near the Phoenix line. It passes 

 northeast of the Phoenix, Lawton, and K. K. shafts, but must be very close 

 to the latter. It can next be seen near the mouth of a tunnel run to con- 

 nect with the Bell shaft. The last place where it can be observed on the 

 surface is near the Richmond office. Although this fault is not continuously 

 traceable above ground owing to the debris, its existence is fully established 

 by the fact that it is encountered at numerous points in the underground 

 workings of all the mines of Ruby Hill. The average dip of the plane of 

 this fault is about 70° northeasterly, and it is of remarkable uniformity, 

 scarcely ever varying 5° one way or the other. Its course, also, is ex- 

 tremely direct, with the exception of the bend between the Phoenix and 

 Jackson. This Ruby Hill fault is marked by the presence of a fissure filled 

 with rhyolite and clay which is widest in the Jackson and Phoenix, where 

 in places it measures as much as 15 feet. In these two mines it is filled 

 with rhyolite, which, although much decomposed, is still easily recogniz- 

 able. In following the fissure west the clay is found to be more calcareous, 

 and in the K. K. and Eureka positive proofs of rhyolitic character are lost. 

 In the Richmond mine the fissure is narrow, and although a distinct and well- 

 defined seam is only a few inches wide. 



The main fissure. — This fault fissure has been called the main fissure, as to 

 its formation are due the most important features of the present structure 

 of Ruby Hill. A proof of its comparative recent formation is the fact that 

 it faults all the formations with which it comes in contact, but is itself 

 nowhere faulted. It is evident that the country southwest or on the foot- 

 wall side of this fault has been raised many hundred feet above its hanging 

 wall. The distance has apparently been greatest in the Eureka, where it 

 has certainly exceeded 1,400 feet. (See Plate VIII.) 



The dip of the quartzite and limestone contact does not greatly exceed 

 40°, while the dip of the main fissure is about 70°. The two surfaces of 

 motion therefore approach each other, and the line of junction is exposed 

 at various depths in the lower workings of all the mines except the Rich- 

 mond and Albion. In these mines the lowest workings have not yet reached 



