286 GEULOGY OF THE COMSTOCK LODE. 



irregularity in the dip of the foot wall prevented the mass broken from the 

 edge of the east country from following the main body of diabase to its 

 final position; while in the Consolidated Virginia and the neighboring mines, 

 at a depth of between 1,000 and 2,()0U feet, a projecting mass upon the foot 

 wall gave rise to a local rent in the hanging wall. Besides these more 

 important openings, numerous clefts formed in the prismatic horse which 

 had been broken off from the hanging wall, and between the horse and 

 the main body of the east country. Large quantities of rock were ground 

 to dust in the course of the faulting, especially at and near the great horse, 

 where the mechanical action was least regular. 



Floods of heated waters now rose from a depth of two or more miles, 

 certainly carrying carbonic and sulphhydric acids, and possibly other active 

 reagents, in solution. The water followed the course of the main fissure as 

 closely as circumstances permitted, but was deflected to a great extent into 

 the fractured mass of the east country, where decomposition resulted. Silica 

 and metallic salts were set free from the mineral constituents of the rock, 

 and were carried into the comparatively open spaces near the main fissure, 

 where they were redeposited. The proportion of silica to ore minerals 

 varied greatly with time and local circumstances, which if they are capable 

 of full explanation certainly have not received it in this report. Some of the 

 causes of the variations, however, can be indicated without difficulty. The 

 lithological character of the rock upon which the waters acted was evidently 

 of prime importance, determining both metallic contents and gangue; so that 

 the deposits of Cedar Hill, those of the Justice mine, and the bonanzas of the 

 main Lode, all show distinctive characters. The duration of the exposure 

 of particular rock masses to solvent action no doubt had much to do with 

 the tenor of the resulting ore. It is likely, for example, that silica under the 

 conditions then prevailing, is more readily soluble than silver com^iounds. 

 If so, the water first passing over a mass of rock would deposit low-grade 

 quartz in the vein, and subsequently, as the supply of soluble silica dimin- 

 ished, a better quality. It seems clear that fresh movements occurred from 

 time to time, and that fresh rock surfaces were thus exposed. This would 

 have brought about alternations in richness, such as have sometimes been 

 noticed in the Lode. Pressure, too, if not temperature, may have varied 



