Ill 



the Mississippi River. This range of trap dykes is nearly par- 

 allel with the great trappean ranges, forming the north mountains 

 of Nova Scotia, and skirting the coast of the Bay of Fundy with 

 their mural escarpments, and, like them, include, in the amyg- 

 daloidal portions especially, masses and disseminated globules of 

 native copper which fill the cavities. In Nova Scotia, however, 

 the metallic copper is, more frequently, found in the trap tuff or 

 breccia, and regular veins of the metal are not found ; while, on 

 Kewenaw Point, on the south shore of Lake Superior, the 

 copper veins are more regular, and follow, very frequently, the 

 Prehnite veins, which run N. 32° W. and S. 32° E., the crevice 

 filled with Prehnite being, probably, the line of fracture through 

 which the metallic copper was sublimed or injected. That this 

 was sometimes the case, is obvious from the fact that the metallic 

 copper takes the imprint of the crystals of Prehnite which line 

 the sides of one of the leading veins on Eagle River. The 

 disseminated copper in the amygdaloid appears to be coeval in 

 origin with the trap rocks. He had formerly supposed it might 

 have been reduced from copper ores preexistent in the sandstone, 

 the amygdaloid being regarded by him as a product of the inter- 

 fusion of the sandstone and trap. This idea he does not think 

 can be sustained by the facts noticed in the Lake Superior rocks ; 

 for the copper should be found only along the line of junction of 

 the trap and sandstone, if such was its origin, and the copper 

 ores ought to be found more frequently in the adjacent sandstone. 

 The north-western course of the veins, being nearly at right angles 

 with the direction or strike of the dykes, militates against that 

 theory. 



Among the interesting discoveries, which he made while ex- 

 ploring the Lake Superior mines, in 1844, was the occurrence of 

 perfectly pure native silver, attached, by a firm metallic union, to 

 native copper, without any blending or alloying beyond the line 

 of contact, and patches and veins of native silver in masses of 

 pure copper. The silver, being pure and quite soft, had been 

 previously mistaken for metallic tin, an idea obviously arising 

 from the known associations of tin and copper ores in Cornwall. 

 While at Lake Superior, he proved to those who had any doubts 

 that the metal referred to was pure silver, by subjecting it to 

 chemical experiments. 



