24 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



eral hundred feet in vertical extent, which occurs at about the same depth 

 in all the mines, and which, combined with the undulations along the line 

 of strike, forms large basins of an oval shape. These basins are intimately 

 connected with the ore bodies and will be referred to later. 



The main fault. — The contact surface between the limestone and the shale, 

 like that between the quartzite and limestone, is very irregular, but there 

 seems to be little similarity between them, owing to the presence of a fault. 

 This fault, to which the name Ruby Hill fault has been given, has had a 

 very important bearing upon the structure of the mineral zone as well as 

 upon the ore deposits themselves. Beginning at the southeast, it is first to 

 be observed at the American shaft, which is about 25 feet deep, and is sit- 

 uated a few hundred feet south of the Jackson hoisting works. The course 

 of the fault from this point is a little west of north, and, although not per- 

 ceptible on the surface, passes west of the Jackson hoisting works, and can 

 be seen in the workings of that mine as well as in a tunnel near the Phoenix 

 line. From this shaft it changes its course to the northwest, and were it not 

 for the de'bris could no doubt be seen northeast of the Phoenix shaft. It 

 passes northeast of the Eureka and K. K. shafts, but must be very close to 

 the latter, and is plainly visible near the mouth of a tunnel run southwest- 

 erly to connect with the Bell shaft. The last place where it can be ob- 

 served on the surface is near the Richmond office. Although this fault is 

 not continuously traceable above ground, owing to the de'bris, 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. 



Dip and strike of the main fault. — 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 extremely direct, with 

 the exception of the bend between the Phcenix and Jackson. This fault is 

 marked by the presence of a fissure filled with clay, which is widest in the 

 Jackson and Phoenix mines, where in places it measures as much as 15 feet. 



The miing of the fissure. — The filling or material contained in this fissure is 

 very different at different points along its course, although there is not 

 much change in it where it is followed along its line of dip. 



