240 GEOLOGY OF THE COMSTOCK LODE. 



as greater depths were reached. If, subsequent to the decomposition, erosion 

 had taken place, the rocks at lower elevations would be found fresher than 

 those on the hills. The reverse is the case. But if decomposition was pro- 

 duced by waters rising from great depths, the area of alteration would 

 depend on the structure of the rock, on the existence of fissures through 

 which they could reach the surface, and from which they could act upon 

 the material bounded by these fissures; which accords with the observations. 

 Moreover, the resemblance of the products of decomposition in this Dis- 

 trict to those occurring in solfataric regions is very sti'ong, and their 

 dissimilarity to those produced by ordinary surface action equally great. 



These considerations appear to me conclusive that the decomposition 

 was effected by aqueous currents rising from lower depths, and that these 

 currents carried in solution reagents capable of producing the effects familiar 

 in solfataras. 



Nature of the reagents. — Tlierc Is some posltlve evideucc as to what these 

 reagents were, for the water struck in the Yellow Jacket at 3,080 feet from 

 the surface was so strongly charged with hydrogen sulphide as seriously to 

 inconvenience the miners, and evidence is given in the chapter on chemistry 

 that hydrosulplmric acid must have played an important part in the rock 

 decomposition. The Steamboat Springs, which lie on a fissure parallel to the 

 CoMSTOCK, and on the opposite side of the Virginia range, are also charged 

 with solfataric gases. 



Origin of the reagents volcanic. — Thcrc Is no couceivable rcactiou between water 

 and the components of the eruptive rocks, which would have produced 

 hydrogen sulphide, and the other solfataric gases. Their origin must, there- 

 fore, be sought outside of and below these eruptive rocks. It would cer- 

 tainly be permissible to argue immediately from the agency of solfataric 

 gases to volcanic action, but it may also be suggested that the vast quantity 

 of hydrosuljjhuric and carbonic acids which have been consumed could not 

 have been produced at low temperatures, and that, when formed at unknown 

 but certainly great de^jths, they could have been brought to the surface or 

 the mines only by convection curreuts, which were stimulated by heat. 

 These considerations force me to the belief that below the Comstock, per- 

 haps at a depth of three or more miles, there is a large body of highly 



