No. 2.] SPENCER — COPPER-BEARING ROCKS. 69 



are enclosed. Much of the vein fillings is green earth, cnlcite, 

 often much laumonitt; datolite, &c. In these the copper usually 

 occurs both distributed in small grains, and in masses sometimes 

 weighing many tons. One solid mass of copper was obtained in 

 the old Minnesota Mine, which weighed about 450 tons, being 47 

 feet long, 18 broad, and 9 J in thickness, requiring 14 months ira 

 order that it could be cut into portable pieces. This formerly 

 profitable mine is in a vein belonging to the third system, but the 

 more successful mines are in the veins belonging to the first sys- 

 tem, Often between the large masses there is much poor rock, 

 and although often richer than the beds, the percentage in long 

 workings is less, as the deposits are more uncertain. 



Though many beds and veins are known to contain copper, it 

 is generally limited to certain portions, where valuable deposits 

 are found, and veins often side by side, or in continuation, and of 

 the same age, are found not to be of equal value. Mines averaging 

 only one and a half per cent, of copper of all the rock taken out 

 can be made to pay well ; even from the celebrated Calumet and 

 Hecla mines, the ingots of copper only amount to one twenty-fifth 

 of the rock treated. As the profitable mines are scattered so 

 widely, and also the great veins and cupriferous beds occurring on 

 Keweenaw Peninsula, it is doubtless that time will reveal an in- 

 exhaustible supply of the metal. When a large amount of capital 

 will have been expended in researches on the Canadian side, pro- 

 bably no inferior results will be obtained, but at the present little 

 more than the wide existence of cupriferous rocks is known. 



However, the structure on the Canadian side of the Lake is 

 not quite like that on the south side, and as remarked by Bell, 

 the mettlliferous beds are confined mostly to the Upper Groups 

 of the Series. Throughout the amygdaloids on the Canadian 

 side of the lake there are intrusive masses of traps in the Upper 

 Group. The dykes are of gr< en stone, porphyry or syenite, and 

 these often stand in relief, being weathered with more difficulty 

 than the country rocks. Numerous fissure veins also occur of 

 more recent origin than the dykes. Of both, there are two sys- 

 tems, the one coinciding with the range of the rocks, while the 

 other set is at right angles to the first ; and the series of cracks 

 seems to be constant even throughout considerable areas. The 

 transverse veins, on Thunder Bay, are north-west and south-east- 

 ward. As on the South Shore, the Upper Group has many amygda- 

 loidal veins with fragments of the country rock and dark greeui 



