OUTLINES OF LAKE SUPERIOR. 423 



known under the name of Victoria and Spar Islands, and the other 

 islands continuous Avith Sturgeon Island, in the prolongation of which 

 •we meet the most prominent djkes of Pic Island itself. The whole 

 of Isle Royale lies in that direction, and the numerous promontories 

 of its eastern extremity are particularly remarkable for their agree- 

 ment, both in direction and geological structure, with the Victoria 

 group of islands. The system is particularly rich in copper ores, and 

 presents the most beautiful development of spathic veins. As I have 

 not myself examined Point Keewenaw, I cannot say how far the 

 prominent ridges there agree with those of Isle Royale and the Vic- 

 toria Islands ; but the agreement in the direction of the promon- 

 tory itself is most striking ; and the fact that this is the main centre 

 of copper injections suggests the probability that Point Keewenaw 

 also belongs, in its principal features, to this system ; and I should 

 not be in the least surprised if La Pointe and Whitefish Point de- 

 rive their main features from dykes of the same system, though 

 their solid foundation is concealed by accumulations of sand. The 

 third system in this north-eastern shore runs east north-east near east, 

 and is particularly marked along the southern shore of Thunder 

 Cape peninsula, along which the dykes are nearly east and west, as 

 just mentioned, deviating sufficiently to the north, however, to be 

 clearly distinct from the dykes which form the shores from the Pic to 

 St. Ignace, or from Michipicotin to Otter Head. And the nature of 

 the rock of these dykes differs widely from the last, there being no 

 epidotic injections accompanying them, and the trap being, on the 

 contrary, of a light grayish color, resembling more the system which 

 runs due north and south than any other. 



So we have here six distinct systems of dykes, which contribute 

 mainly to the formation of the northern shore of Lake Superior. 



1. System of Michipicotin, running east and west. (See the 

 annexed chart of the OutUnes of Lake Superior.) 



2. System of the Pic running north 30° west. 



3. System of Neepigon, running due north and south. 



4. System of Black Bay, running north 30° east. 



5. System of Thunder Cape, running east 30° north. 



6. System of Isle Royale, running east 45° north. 



