Vol. 4] 



Reid. — The Comstock Lode. 



193 



the Virginia City portion of the lode from that of Gold Hill, are 

 filled largely or wholly with caleite gangne. The same mineral 

 acts as vein-filling in the Silver City lode. Becker * favors the 

 view that the difference in gangue mineral between the Silver 

 City lode and the main vein, is due to differences of country rock. 

 But as the caleite veins exist in the augite andesite east of Bul- 

 lion Ravine, this idea cannot hold. On the fact, however, that 

 the two lodes are due to different faults, a more probable conclu- 

 sion is that the deposits are of different age. The proof of this 

 lies in the examination of the point where these two lodes inter- 

 sect, which is not now possible. Published reports and maps are 

 insufficient as a basis for judgment. 



A further fact of importance regarding the lode, in the Vir- 

 ginia City portion especially, is that the width of the vein is 

 often little or nothing in the lower levels. Moreover, the west 

 wall is not well defined in all places, because of a complexity of 

 slips in the west country. This portion of the ground in all the 

 lower levels has not been thoroughly prospected, in spite of the 

 many thousand feet of mine workings. 



ROCKS OF HALE AND NORCROSS TUNNEL SECTION. 



A full report of this section is not yet ready, nor would it be 

 proper at this time before the tunnel is complete. A full set of 

 rock specimens, taken every fifty feet, and oftener over impor- 

 tant places, is now being collected for the writer. However, the 

 importance of the main facts concerning the rocks within Mt. 

 Davidson is too great to allow their complete reservation at this 

 time. These facts are briefly as follows : 



1. The Hale and Norcross tunnel (see figure 2) strikes the 

 lode footwall at 1,080 feet in from its mouth. The first wall rock 

 encountered in the foot is the well known "black dyke," of de- 

 composed basalt, f a few feet in width. Beyond this, in to a dis- 

 tance of 1,270 feet, is a fine-grained, dark rock looking much 

 like a fresh augite andesite. In the Mexican ground, in the cross- 

 cut tunnel mentioned above (page 3), the same rock occurs 

 east of the lode, shading into diorite to the west. Under the mi- 



* G. F. Becker, op. cit., p. 220. 



t Hague and ladings, Bull. No. 17, U.S.G.S. 



