234 PRODUCE OF THESE MINES. 



metallic silver scattered through them — without, how- 

 ever, forming an alloy with, or rendering impure, the 

 copper itself. 



As a matter of economical interest to the copper 

 miners of our own country, I may remark that, in all 

 prohabllity, this part of the United States will. In ten 

 years more, be able to supply, not only a sufficient 

 quantity of copper to meet the demands of the Union, 

 but a surplus also for exportation. The quantity of 

 copper hitherto imported into the United States has 

 amounted to about 5400 tons a-year. The Cliff Mine 

 alone, in 1849, has shipped what Is equal to about 560 

 tons of pure copper.* From what is already known of 

 this copper region, it is fair, I think, to presume that in 

 ten years this quantity will be increased ten times, and 

 that the lake region may be seeking foreign markets for 

 its surplus copper, as the upper Mississippi is already 

 doing for its superabundant lead. 



It would be out of place here to discuss the origin of 

 this native copper — the probable mode In w^hlch it has 

 been deposited in the veins. It is very amusing, however, 

 to observe in this, as in so many other cases, how men 

 who look at the same phenomena from different points 

 of view see in them arguments for completely opposite 

 views. Dr Jackson remarks, that the metal bears the 

 imprint of crystals of prehnlte ; that perfect crystals of 

 native copper, sometimes half-a-pound in weight, occur 

 in the prehnlte, datholite, calc, spar, and quartz which 

 form the body of the veins ; and that the melting-point 

 of silver, which is mixed in crystals and large lumps 

 with the copper. Is considerably below that of metallic 

 copper ; and these facts, he justly adds, are objections to 

 the igneous origin of these broad sheets of native 



* 933 tons containing 60 per cent of copper. The quantity of pure 

 copper extracted at the various smelt-works in Great Britain is about 

 25,000 tons, one-half of which is from Cornish ores. 



