40 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



of them, which, however, for sake of clearness, is omitted in the diagrams. 

 The point of view is in the Richmond ground looking towards the Eureka, 

 and the two bodies of shale dip easterly at an angle of 40°. The plane 

 M N O P, Fig. 1, represents the direction of the cross-fault, which was the 

 first one to occur. This fault takes place nearly on the compromise line, 

 and has a nearly vertical dip. When the faulting occurred the blocks B 

 and b, representing portions of the two shale belts, slipped down until they 

 occupied the positions relative to the blocks A and a shown in Fig. 2. The 

 plane Q RST shows the direction of the main fault, and after it occurred 

 the pieces a' b' and B' were raised above the present surface of the ground, 

 and have been removed by erosion. The piece a' corresponds to the shale 

 which was cut off from below the ninth level of the Eureka; the piece V 

 is the corresponding portion of the lower belt of shale, supposed to exist 

 below the present workings of the Richmond, and B' is the part of the 

 larger mass of shale, which was removed by the main fault. The face a, 

 Fig. 3, represents the shale as it now exists in the Eureka, and the face B 

 represents the shale in the Richmond. The irregular lines on the tops of 

 blocks A and B represent the surfaces of erosion as nearly as possible as 

 they exist at present. If the line e f g h is taken as representing the Rich- 

 mond seventh and the Eureka tenth levels, it will be seen that conditions 

 exist in these ideal beds of shale similar to those which actually occur in 

 the two mines. In the Richmond the contact between shale and limestone 

 is continuous to the surface, and it can also be traced in to the Eureka 

 ground along the tenth level of that mine, but cannot there be followed to 

 the surface. 



Plate XVI. represents a projection of the different formations that are 

 found on the hanging wall of the main fissure upon a vertical plane par- 

 allel to its course. The point of view is from the mineral zone. The various 

 beds of shale are lettered to correspond with those in Fig. 3, Plate XV. As 

 the strata of shale and limestone were not only very much crumpled and 

 disturbed before the faulting took place, but during that dislocation as well, 

 the structure of this country is very complicated, and it is a matter of great 

 difficulty to trace the movements that have taken place. 



