SUMMARY. 475 



Origin of the ore. — Tlicve IS tliG strongcst evideiice for tlie supposition tliat 

 tlie ciiinabai-, pyrite, and gold of the quicksilver mines of the Pacific slope 

 reached their present positions in hot solutions of double sulphides. Either 

 the metals must have been leached from the granite or they were derived from 

 an infragranitic source, for examination of the conditions of occnrrence shows 

 it utterl)' improbable that they were extracted from any volcanic rock at or 

 near the surface, while the sedimentary strata of the region are composed 

 of granitic detritus. No one fact or locality absolutely demonstrates whether 

 the metals were originally components of the granite or came from beneath 

 it, but the tendency of the evidence at all points is to the supposition that 

 the granite yielded the metals to solvents produced by volcanic agencies, 

 and when all the evidence is considered together it is found that this 

 hypothesis explains all the known circumstances very simply, while the 

 supposition of an infragrnnitic origin leads to numerous difficulties. Though 

 no one of these may be in itself inexplicable, when taken as a whole they 

 appear to me to be so. Had solutions of quicksilver been formed in com- 

 pany with other products at the foci of volcanic activity, cinnabar would 

 often be met with in craters. Though it is often found associated with 

 volcanic effects, it perhaps never occurs in craters. Were the solutions 

 formed below the granite, ore deposition would also almost certainly take 

 place in part within the granite, and most ore deposits would continue 

 down into that rock, probably growing richer with increasing depth. On 

 the other hand, the distribution of the deposits relatively to volcanic vents 

 is such as would be anticipated if the ore were known to be leached from 

 the granite by hot waters of volcanic origin. The varying richness of the 

 different deposits also corresponds to the irregularity in the composition of 

 the granite and in the extent of surfece exposed along the underground 

 passages through which the waters must have reached the surface. Finally, 

 at Steamboat Springs, at least, the composition of the granite answers to 

 that of the deposits of springs which are still depositing small quantities of 

 quicksilver. It thus seems fairly certain that the quicksilver and gold are 

 derived from the granite. I enterttiin little doubt that many of the gold 

 veins of California have a similar origin, while others have probably been 

 produced by the action of cold surface waters. 



