70 THE CANADIAN NATURALIST. [Vol. viU. 



chloritic matter, sometimes slickensided — a structure com- 

 mon in Keweenaw. The veinstones are often quartz or caicite, 

 or sometimes bat ite or fluorite. L lumonite in many places is 

 most abundant, as it is on the South Shore. Sulphides, which 

 seem to be almost absent in Keweenaw, are quite common on the 

 Canadian ^ide ; as sulphides of copper, silver, iron, zinc, and 

 lead, besides nickel, cobalt, molybdenum, uranium and arsenic. 



Many other minerals oecur on both sides of the lake, especially 

 in the veins traversing the region under consideration. Besides the 

 Dative copper on both sides of the lake, malachite, chrt/socolla t 

 melaconite and cuprite are found. Some years since a large 

 pocket of melaconite was found at Copper H .rbour, but the 

 workings were abandoned. The cuprite or red oxide of copper 

 usually occurs in small quantities in the sandstones and conglo- 

 merates, and I believe one or two beds of this ore have been found 

 which contain as much as four per cent, of copper. WkitHryite, 

 D<>nifn/kite, besides the v r arious hydrous silic ites mentioned before, 

 as well as the sulphides just referred to, h tve also been found ; 

 silver, gold, and le id in vein form itions hive attracted consider- 

 able attention. Native silver occurs associated with the metallic 

 copper, b ing deposited in a pure state on the latter metd. The 

 two metals are not alloyed, and their contact surfaces are perfectly 

 distinct; the silver, usu.dly in arbore?ceut forms, projects from the 

 copper. 



Recently, there has been considerable excitement over some 

 silver-bearing veins which are situated in the Copper- Bearing 

 Formation in Onton igon County. The prospects of these are 

 said to be encour iging. 



The temperature of the rocks in which the copper mines are 

 situated is low, and at a depth of 1,4-40 feet, it is scarcely higher 

 than at the surface. Mr. Emerson made some experiments on this 

 subject, by taking the temperature of the w T ater which percolates 

 through the rocks, entering the mines at different levels. He found 

 that, the aver g temperature at different p] <ees was not far from 

 60° Fahr. The eau.->e of this low temp ^ra^ure m iy b ttributed 

 to the fact that the region of Lake Superior, which was .-.o long 

 subjected to igneous influences, and to great contortions of the 

 earth's crust, has had very long ages during which it has parted 

 with it* heat, and this has not been raised in recent geological 

 times by the bendiug of the various strata. 



