Relations of Trap-Rocks with Ores of Copper. 305 



ores normal in depth, but transformed towards the surface 

 in such a manner as completely to change the appearance of 

 the repositories. The sulphurets of iron, by decomposing, 

 have streaked all the gangues, and sometimes the rocks, with 

 ochrey tints producing the characteristic gossan ; the ores of 

 copper are transformed either into the state of oxidules, 

 among which we find the cubic and capillary varieties, or 

 into the state of native copper, of which concentrations in 

 masses have been mentioned of many quintals in dimensions. 



To til is example of copper repositories connected with the 

 trap rocks of Cuba, we may add a second which occurs in 

 North America. 



The region which forms the shores of Lake Superior, on 

 the south-west and north-west, appears to have taken a promi- 

 nent place in the mining of copper ore. This region is form- 

 ed principally of traps, which have upraised and traversed 

 the sand-stones, whose age is still uncertain, and which Mr 

 Jackson has referred to the old red sandstone. Kewena-Point, 

 which forms a very salient cape on the southern shores of 

 the lake, is the part of this still thinly-inhabited region which 

 has been most carefully examined. Mr Jackson, who has 

 studied it, describes the native copper as filling the cavities 

 in an amygdaloidal trap which is arranged in very broad dykes. 



Among the particular characters of the metalliferous trap, 

 Mr Jackson mentions the existence of veins of datholite, 

 which intersect the rock, and contain metallic copper in 

 scales ; also prehnite, which occurs in veins with analcime, 

 laumonite, and calcareous spar. The copper of these traps 

 is argentiferous, and the pure silver is insulated in small 

 veins and crystalline nodules, in a copper containing from 

 tAu to i-^^-^' This locality was visited in 1846 byM.de 

 Verneuil : he found mining operations going actively for- 

 ward, and he brought home interesting specimens, which 

 confirm Mr Jackson's description, and appear to shew that 

 the ore of copper is subordinate to the trappean rocks. 



Here, as at Cuba, the knowledge of the repository was an- 

 terior to European colonisation ; and the savages of Canada 

 had long been in the habit of collecting, among the alluvia 



