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BULLETIN OF THE 



and the conditions to which they were subjected at the time of con- 

 solidation, must have possessed a vast amount of glassy material. 

 Hence they were most liable to decomposition and alterationj which 

 might or might not result in induration. At Copper Fails no general 

 induration exists, except, for instance, where quartz has been deposited, 

 but at the Atlantic the induration is general. We have seen, tliat the 

 action of hot waters on the sandstone at Torch Lake gave rise to the 

 reverse of induration, as its action was that of removal, and not of 



deposition. 



The last form of copper deposit in the district visited by ns is that 

 of the conglomerate mines. The beds of conglomerate are composed, 

 as before said, of rhyolitic, trachytic, and basaltic pebbles and detritus. 

 In some of these conglomerates, as the Calumet and Ilccla, the cement 

 has been removed, and its place, or the original interspaces, filled with 

 copper. In some cases mclaphyr pebbles have been largely removed, 

 and their places filled with copper, giving rise to boulderdike forms 

 (471). These conglomerates, then, are simply old sea-beach deposits, 

 and, like the amygdaloids and ash-beds, are not veins, and cannot prop- 

 erly be so called. They must of necessity partake of the characteristics 

 of their origin, the same as veins do of theirs. 



The copper has been found throughout the district underlying heavy 

 beds of trap or a series of smaller ones; in fact, in the parts visited by 

 us, experience has shown that copper in abundance was only found 

 ■where trap in large amounts overlaid the vein or bed. The copper was 

 found filling, at the Calumet and Hecla mine, the joints of the overly- 

 ing trap, and extending as a continuous sheet through fissures at right 

 angles to one another. At Copper Falls spikes of copper extend down- 

 wards out of the overhanging trap into the ash-bed. Tliese are generally 

 large at the upper end, and pointed at the lower. Like them are the 

 secondary depositions of calcite, in this trap, in long, spike-like forms, 

 that here and elsewhere have been taken for fossils. These features 

 prove that the copper came from above downwards, and that it was de- 

 posited after the jointing of the trap. In fact, the evidence is strong 

 that all the alteration and Assuring of the rocks, and the deposition of 

 the copper and associated minerals, took place after the western sand- 

 stone had been deposited. The above facts indicate that the copper was 

 derived from finely disseminated copper distributed throughout the lava, 

 as modern lavas have been known to contain it. If it was derived from 

 the sandstone, as advocated by Bauerman and later by Pumpelly, it 

 should be found in connection with the sandstone; but such is not the 



