184 Ooi a Specimen of Native Copper. 



Lake Superior copper of not less than half a cubic yard 

 bulk. 



But with this Lake Superior copper, metallic silver is 

 also found, not in alloy, but distributed in isolated patches 

 and crystals through the copper mass ; and I should like to 

 point out that this peculiar relation of the silver to the 

 copper appears to be indicative rather of after changes of 

 an electro-chemical nature, as the origin of these metallic- 

 masses, than of their presence in the original molten silicates 

 when first spumed out. This would certainly apply to the 

 silver, and I beg to lay. stress on the probability of its also 

 applying to the copper, the precipitation of which would 

 certainly result from the percolation of water charged, how- 

 ever feebly, with copper salts, through fissures in which 

 metallic iron (as Andrews has shown it to exist) was originally 

 present. Very similar conditions to those which produce 

 the common haloid compounds of copper — coj)per pyrites 

 for instance — in the veins of the Cornish mines, would 

 in basalts originally charged with metallic iron, produce 

 deposits of metallic copper, and ultimately those also of 

 metallic silver, as found at Lake Superior, silver salts being 

 present in the mine waters. 



But returning to this specimen from Footscray, it may be 

 now asked whether there is any physical proof in the 

 specimen itself connecting it with the facts i^ertairdng to the 

 copper-bearing trap rocks of Lake Superior 1 I confess that 

 when I first handled the specimen I could not resist the temp- 

 tation presented by a small and delicately attached portion of 

 it; a slight pressure of the thumb detached this fragment from 

 the mass. (I maj" mention that Mr. McMeikan was present 

 when this happened.) I examined this detached fragment 

 for silver, but failed to detect the precious metal, so that 

 this correspondence is so far wanting. 1 do not say that 

 silver is altogether absent from the mass, but the point is 

 one which w^ould require a further trespass on Messrs.. 

 McMeikan's indulgence and a more extensive inroad on the 

 specimen for its solution. 



There is, however, another fact, — the hollows of the- 

 specimen contain a portion of the attached but altered 

 matrix. I have taken liberties with this portion, and 

 have ascertained that it is of a steatic nature — a silicate 

 of alumina and magnesia — a composition pointing to a 

 basaltic origin ; in fact, the position in which the specimen 

 was found, the nature of the rocky debris with which it was- 



