182 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



the junction. The face of the quartzite when in contact with the fissure 

 is no longer the original contact of quartzite and limestone, but is the fault 

 face of the southwestern uplifted country. (See Plate IV.) It is evident 

 that if the fissure continues downward with its present dip, at some depth 

 it must enter the quartzite. 



The secondary assure. — At the time of the disturbance which produced the 

 Ruby Hill fault, another and secondary fissure was formed along the con- 

 tact of the quartzite and limestone, and the quartzite was raised higher 

 than the limestone, giving rise to the formation of a wedge of limestone 

 between the quartzite and the main fissure. Up to the present time all the 

 ore of any importance taken from Ruby Hill has been extracted from this 

 wedge of limestone, the crushed condition of which is due to the upward 

 movement of the southwestern country against the hanging wall of the 

 main fissure. Section 7, Plate VIII., is typical of the relations of the 

 two fissures to each other and to the quartzite, limestone, and shale in the 

 mines southeast of the "compromise line." 



The two belts of shaie. — Two belts of shale, only one of which appears on the 

 surface, are known to exist in Ruby Hill. The upper or surface shale can be 

 observed on the map, Plate I. Taking into account the general dip of the 

 surface shale and that of the shale where it is encountered below, it is 

 at once apparent that the two must be distinct masses in all the mines south- 

 east of the compromise line. In the Richmond mine, however, it is dif- 

 ferent. The shale on the surface in which the shaft is sunk is the same 

 body of shale that is encountered below. The manner in which the Rich- 

 mond shale and the lower belt of shale have been brought together in the 

 lower workings of the Richmond and Eureka, and the manner in which 

 this lower shale has been faulted, have been fully explained iu the body of 

 this report. 



influence of the main fissure on the ore formation. — The time and manner of the forma- 

 tion of the Ruby Hill fault and its subsequent filling either with rhyolite 

 or clay are matters of very great importance as regards the mineralization 

 of the limestone between the quartzite and this fissure, and the prospects 

 of finding ore either at a greater depth or by prosecuting developments in 

 the so-called "front limestone." This body of rock lies northeast of the 



