Vol. 4] 



Reid.—The ComstocJc Lode. 



187 



is the same rock which forms the hanging wall of the Comstock 

 lode, the diabase of Becker. This rock continues to the face 

 (given above), and no doubt shades into augite andesite farther 

 west, just as in the east country. Thus the diorite of Mt. David- 

 son is terminated east and west by identical structures. No 

 doubt tunnels north and south would develop the same conditions 

 on the other two sides, as indicated by the surface structures. 

 4. West of this west fault just noted, the prevailing slips are per- 

 pendicular to the tunnel and dip to the west, in contradistinction 

 to the eastward clipping slips near the Comstock. 



The west diabase, as it will be called, now shown in the tunnel, 

 is much fractured and filled with veinlets of pyrite. Some films 

 of galena and sphalerite up to one-eighth of an inch in thickness 

 also occur fifteen feet west of the fault. These gave some values 

 by assay. 



DEEP ORES AND WATERS. 



The ores are doubly interesting from that fact that their 

 deposition still continues, due to faulting opening up new fissures 

 and fractures, and from the fact that the mine waters are, for 

 such waters, rich solutions yielding very positive results to fire 

 assay methods. The ores are moving in two ways : upward and 

 downward. 



That the ores have moved upward at more than one time has 

 been noted best by Becker.* He writes (page 219) : "In the 

 great California and Virginia bonanza several streaks or veins of 

 very rich black silver ores, said to be largely stephanite, occurred. 

 These were separated from the surrounding quartz very sharply, 

 as if of later origin." Again (page 221) he writes: "AVhat I 

 have seen * * * leads to the belief that these rich concentra- 

 tions were of later origin than the rest of the ore. The quartz 

 in the C. & C. was almost everywhere a crushed powdery mass, 

 while the thin and persistent veins of black ore running through 

 it were very solid. A somewhat similar relation seems to have 

 existed near the eroppings, and it is not impossible that these 

 ores were formed at the expense of others of the more usual 

 kind at a later date, and that they occupy spaces opened in the 

 ore masses by faulting action." 



* G. F. Becker, op. cit. 



