390 GEOLOGY OF THE COMSTOCK LODE. 



strated by the trifling character of the erosion which has since taken place. 

 The water entering at the bottom of the new Yellow Jacket shaft in the win- 

 ter of 1 880-8 1, at a temperature of 170° F., was highly charged with 

 hydrogen sulphide. The Steamboat Springs, only a few miles west of the 

 CoMSTOCK, lie in a north and south line like the Comstock, close to the con- 

 tact of ancient massive rocks and andesites. Some of them are boiling hot, 

 are charged with solfataric gases, and are now depositing cinnabar and silica 

 as at the time of Mr. Phillips's visit many years ago. There is much evi- 

 dence in the structure of the country and in the relations of the fresh rocks to 

 the decomposed masses that alteration was effected by rising waters, and 

 the chemical changes traced are such as could have been effected only by 

 vast quantities of soluble sulphides and carbonic acid, which could hardly 

 have been produced on the necessary scale except by the aid of heat. A 

 deep-seated source of heat, therefore, probably gave rise to the decomposi- 

 tion, and the conditions point to vulcanism as its source. 



Source of the waters. — Thc flood of watcrs Still rcquires explanation, and an 

 hypothesis is suggested to account for it. No meteorological station exists 

 at Virginia City, but the rainfall is so small that the countr}^ is a sage-brush 

 desert, and the precipitation is insufficient to account for the water met with 

 on the Lode. The main influx of water, and especially of hot water, is 

 from the west wall, and when encountered it is found under a head often 

 of several hundred feet. Between the Comstock and the main range of tlie 

 Sierra Nevada, the whole country is covered by massive rocks, principally 

 andesites, with occasional croppings of granite. The general structure of 

 the country, and the exposures of sedimentary rocks in the mines, lead to 

 tlie supposition that the underlying strata dip eastward, and the inference 

 is that the Comstock fissure taps water-ways leading from the crests of the 

 great range. If the heat is conveyed to the Lode b}^ waters from great 

 depths, the variations in temperature are readily explained. The distiibu- 

 tiou of the heated waters would be determined by the presence of cracks, 

 fissures, and clay-seams, and the uniformity of distribution of heat would 

 further be disturbed, even at considerable distances from the surface, by the 

 infiltration of surface water. One published observation, which is impor- 

 tant in this connection, is that a large proportion of the rocks in the Vir 



