GEOLOGY. 261 



thought, will exceed 1,000 tons. The whole amount of copper 

 annually imported into the United States is about the value of 

 $2,000,000, or about 5,400 tons. But little has been supplied from 

 our own mines. Nine such mines, then, as the Cliff would render 

 us independent of foreign supplies. Present appearances indicate 

 that this amount of copper must be supplied in a very few years, and 

 this metal soon become, as lead already has, one of export instead of 

 import. The recent failures of mining speculations, wildly under- 

 taken, and ignorantly and extravagantly conducted, may for a time 

 check the development of these- mines; but their wonderfully rich 

 character is now beginning to be properly appreciated, as well as the 

 reliance which may be put in the surface-appearance of the veins. 



The silver found associated with the copper has not proved of much 

 importance, perhaps for- the reason that the greater part of it is pur- 

 loined by the miners. The Cliff mine has probably yielded more 

 than $30,000 worth, of which not more than a tenth part has been 

 secured by the proprietors. Proc. of the American Association. 



LAKE SUPERIOR COPPER MIXES. 



A CORRESPONDENT of the Railroad Journal, writing from Mackinaw, 

 November 2d, gives the results of the season's operations in the Lake 

 Superior copper mines, as he obtained them from the directors or 

 agents. The Cliff mine seems to have been by far the most produc- 

 tive, the company having shipped, or had ready to ship, 1,000 tons on 

 November 1st, the average percentage of which is estimated at 63. 

 Six other companies mentioned vary in their products from 57 to 6 

 tons ; the percentage of four is 67 ; of one, 75 ; and of the one which 

 produces only 6 tons, 100. Four of these mines, it is estimated, will, 

 during the year 1850, produce in the aggregate L950 tons. A large 

 number of new companies are being formed, but during the next year 

 they can do little more than clear away for future operations. 



BLACK OXIDE OF COPPER FROM LAKE SUPERIOR. 



AT a meeting of the Boston Natural History Society, Jan. 3d, 

 Mr. J. D. Whitney made some remarks on the remarkable vein of 

 black oxide of copper which was formerly worked at Copper Harbour, 

 Lake Superior. The ore in the vein was 14 inches wide, and for a 

 short time the mine furnished a good supply of copper ore, yielding 

 about 60 or 70 per cent, of rretallic copper. It "was soon exhausted, 

 a bed of fine-grained sandstone cutting off the copper vein, the calc 

 spar only continuing in the sandstone below. It was the only vein of 

 this substance, and perhaps the only locality known in the world, and 

 specimens will be highly prized by the mineralogist hereafter. The 

 substance called copper-black, and sometimes black oxide of copper, 

 which occurs in an earthy, pulverulent form, is not to be confounded 

 with the pure oxide of copper found at Copper Harbour. Copper- 

 black is a mixture of various hydrated oxides, especially of iron, man- 



