Ch. VI.] ORIGIN OF MINERAL VEINS. 99 



and nowhere showing any trace of regular deposition on 

 the sides. The gold also found in auriferous lodes is 

 never pure, but forms various alloys of gold, silver, 

 copper, lead, iron, and bismuth ; and no way is known 

 of producing these alloys except by fusion. 



It is true that mineral veins contain many minerals 

 that could not exist together undecomposed with even a 

 moderate degree of heat ; but it is only here contended 

 that the original filling of the lodes was an igneous in- 

 jection, not that the present arrangement and composi- 

 tion of all the minerals is due to the same action. Since 

 the lodes were first filled, they have been subjected to 

 every variety of hydro-thermal and aqueous influence ; 

 for the cooling of the heated rocks must have been a slow 

 process, and undoubtedly the veins have often been the 

 channels both for the passage of hot water and steam 

 from the interior, and of cold water charged with carbonic 

 acid and carbonate of lime from the surface, and many 

 changes must have taken place. Auriferous quartz veins 

 have resisted these influences better than others, because 

 neither the veinstone nor the metal is easily altered, and 

 such veins therefore form better guides for the study of 

 the origin of mineral lodes than fissures filled with calc 

 spar and ores of the baser metal, all readily dissolved and re- 

 formed by hydro-thermal agencies. Our mineralogical 

 museums are filled with beautiful specimens of crystals 

 of quartz, fiuor spar, and various ores deposited one on 

 the other ; and the student who confines his attention to 

 these is naturally led to believe that he sees before him 

 the process by which mineral veins have been filled. But 

 the miner, working far underground, knows that such 

 crystals are only found in cavities and fissures, and that 



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