HUGE MASSES OF NATIVE COPPER. 233 



one place only 6 inches, while in another they are 5 

 feet in thickness. Dr Jackson states that, at the CHff 

 Mine, " one mass of pure copper was extracted, when he 

 was surveying the country, which weighed 80 tons ; and 

 other masses, probably of equal magnitude, were in 

 process of being uncovered." Mr Trowbridge, in his 

 later Report to the Secretary of State, says that, " in 

 proceeding along the fifth level of the same mine, he 

 passed a mass of copper 125 feet in length, and varying 

 from 1 to 2J feet in thickness. Its depth was unknown. 

 At one place Captain Jennings (the mine captain) said, 

 ' Here are 100 tons of pure copper in sight.' On the 

 second level we passed another of the same description, 

 &c." In the Minnesota Mine, Mr Hodge describes a 

 sheet which he saw, having a known length of 150 feet, 

 a height of 8 feet, and a thickness, in some places, of 5 

 feet. What was visible in the overhanging wall of this 

 drift was estimated to contain 250 tons of copper. 

 The poorer part of the vein is blasted out, brought 

 to the surface, heated to redness, quenched in water, 

 stamped, and then washed. By this means the metal- 

 lic copper is separated, and packed in barrels. This 

 and the chiselled copper are the only forms in which 

 the products of the mines have hitherto been sent to 

 market. 



The copper thus obtained, according to Dr Jackson, 

 who first drew the public attention to the value of these 

 deposits of native metal, is pure metallic copper, as 

 dense as the densest hammered copper. It possesses 

 the remarkable peculiarity of being intermixed with 

 variable quantities of metallic silver, not diffused uni- 

 formly through the mass, but forming distinct crys- 

 tals and crystallised masses, scattered through the 

 body of the solid copper. I saw some of these crystals 

 in specimens possessed by Dr Jackson, and he stated to 

 me that some masses are actually porphyritic^ with 



