428 LAKE SUPERIOR. 



innumerable minute fissures, and thus presented a comparatively 

 large surface of contact with the surrounding rocks, there the most 

 diversified combinations could be formed, and thus the various ores 

 appear in this characteristic distribution. The relations which these 

 ores bear to the rocks in which they are contained, sustain fully this 

 view, and even the circumstance that the black oxide is found in the 

 vicinity of the main masses, when the sulphurets and carbonates 

 occur at greater distances from them, would show that this ore is the 

 result of the oxidation of some portion of the large metallic masses 

 exposed more directly to the influence of oxygen in the process of 

 cooling. Indeed, the phenomena respecting the distribution of the 

 copper about Lake Superior, in all their natural relations, answer so 

 fully to this view, that the whole process might easily be reproduced 

 artificially on a small scale ; and it appears strange to me that so 

 many doubts can still be expressed respecting the origin of the cop- 

 per about Lake Superior, and that this great feature of the distribu- 

 tion of its various ores should have been so totally overlooked. 



