PREVIOUS INVESTIGATIONS. 2 1 



Wide-spread solfataric action. '^J^llOllf>ll it SeeiHS tllilt tllG CoMSTOCK fissUrG WUS 



the principal tlieater for the emission of steam, and all those })henomena 

 which may be comprised by tlie name of solfataric action, yet the latter left 

 its traces over a wide extent of the adjacent country. The entire belt of 

 rounded hills, extending east of the vein for two miles, to the foot of the 

 trachytic range, shows its effects very conspicuously. It consists of propy- 

 lite, which, however, can scarcely be recognized on account of the complete 

 decomposition it has undergone, and which has transformed it into a clayey 

 rock of red and yellow color, but still showing distin(;tly the inclosed crystals 

 of feldspar and hornblende. It is traversed by numerous crevices from 

 which the decomposition oi-iginated, and shows everywhere evidences of 

 vertically ascending currents which caused it. Whoever has seen active 

 solfataras will be struck by the resemblance of chemical action on the sur- 

 rounding rocks to that displayed in the region east of the Comstock Lode. 

 Near some of the ci-evices the decomposed rock is strongly impregnated with 

 silica, producing the ranges, of red-colored bluffs which accompany the 

 CoMSTOCK vein to the east, and which have been partly located as out- 

 croppings of veins, while at about two miles' distance real metalliferous 

 veins occur, promising in their outcrops, but not yet explored. Besides 

 this belt the former action of solfataras is plainly visible in many parts of 

 the country. The formation of the Comstock vein is but one of its mani- 

 festations. 



Continuity of the Lode in depth. — A.S it lias becu showu that the Vein was filled 

 from a deep-seated source, it is certain that it is continuous in depth. The 

 inclination is not likely to vary considerably, for not only is the west wall 

 remarkably regular, tending to show its continuity, but the previously men- 

 tioned solfataric action to the east is an evidence that the vein underlies the 

 country rock in this direction for a long distance. As for the mean width of 

 the vein in depth no definite prediction can be made. In some places the vein 

 at a distance of 500 feet from the surface forms a channel of 120 feet or more 

 in width; at other points it is contracted. Such places must necessarily occur 

 in an inclined vein of some magnitude, since the hanging wall, during the 

 long periods of the filling of the fissure, required some support. The walls of 

 every true fissure vein are uneven planes. The downward movement of one 



