42 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



by the presence of the lower belt of shale. The shale in general is unfavor- 

 able to the passage of solutions of any kind, as well as to the deposition of 

 ore, and in this particular instance (see Plate VIII.) it acted as a barrier to 

 confine the metalliferous solutions to the wedge of crushed limestone above 

 it, between the main and secondary fissures. 



Front limestone in the Eureka. The explorations ill the frOllt HmeStOlie COllsist of 



a few cross-cuts from the different levels of the K. K. and Eureka mines. 

 The principal of these cross-cuts is the one connecting the twelfth level of 

 the Eureka with the Locan shaft. This cross-cut is 508 feet long and is 

 driven from its junction with the twelfth level, near the station of the main 

 incline, in a northeasterly direction, through the upper belt of Prospect 

 Mountain limestone lying between the upper and lower belts of shale. The 

 rock through which it passes does not differ in any material respect from 

 the limestone which is found above between the quartzite and main fissure; 

 but it is harder and more compact, and does not show evidences of having 

 been crushed and disturbed to the same extent as the latter, except in the 

 immediate neighborhood of the fissure. It is dark colored, and shows some 

 slight signs of stratification. 



Front limestone in the k. k. — The cross-cut on the sixth level of the K. K. (see 

 horizontal section No. 2, Plate XIII.) lays bare another portion of the front 

 limestone. This drift is over 300 feet long, and although the limestone is 

 different in color and texture from that in the cross-cut just described, there 

 is no greater difference than can be observed in varieties of limestone in 

 the mass between the quartzite and fissure. Samples for assay were taken 

 every 30 feet in this drift, and the results obtained will be discussed in the 

 chapter on assays. No signs of stratification were observed in this lime- 

 stone, and it was of a grayish-white color. It is harder and more compact 

 the farther it is removed from the contact with the fissure, and it is highly 

 crystalline in texture. It is considerably broken near this contact, and por- 

 tions of it are crushed and mixed with the clay. The limestone between 

 the fissure and this quartzite is crushed to a powder in many places, and 

 forms a narrow belt scarcely a foot wide, which is often stained with iron. 

 In another cross-cut, some 30 feet long, farther to the southeast, the lime- 

 stone is of a blackish color, and breaks in sharp angular pieces. Similar 



