CHAPTER VI 

 CHEMISTRY. 



General natur 



of the chemical activity. — TliG general results of chemical activity 

 whicli have been observed in the Washoe District can be very briefly 

 stated. Decomposition is widespread, but while in the greater part of the 

 area it has not seriously modified the character of the rock, the alteration 

 within a certain portion of the region is profound, and often wholly obscures 

 lithological distinctions. This area of extreme decomposition is precisely 

 the most important, lying immediately about the Lode.^ The characteristic 

 bisilicates of the eruptive rocks have been replaced by chlontic minerals, 

 epidote, quartz, and calcite; pyrite has. been deposited in the mass of the 

 rock, and the feldspars have in great part undergone degeneration of a 

 complex kind; finally, ore-bearing quartz has been deposited in the Lode. 

 It is the i)urpose of the present chapter to give as rational an account of 

 these changes as I am able to suggest, and to trace their geological rela- 

 tions. Any such account must, in the present state of knowledge as to 

 the constitution of minerals, be largely hypothetical; but, although future 

 investigations will probably greatly modify the present conceptions of the 

 nature of inorganic compounds, the best hypotheses at present are those 

 which put the least strain on well-proved theories. The Washoe District 

 affords, as has been seen, a remarkable opportunity for microscopic exam- 

 ination of the results of decomposition ; not, however, for their chemical 

 investigation, for no occurrences have been met with in which single alter- 

 ation products, excepting pyrite, are concentrated in sufficient masses to fur- 

 nish good material for analysis. Even were this the case, it seems to me that 



1 See Fig. 1. 

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