and its associates on Lake Superior. 353 
was effected, should seem to be limited to silicates, carbonates, 
and sulphates of copper. Probably all of these combina- 
tions took part in the process, but while we may consider the 
translocation of the copper to have been initiated by the sul- 
phate, this salt must have been so soon decomposed by the 
abundant acid carbonate of lime* as well as by the alkaline sili- 
cates, that we cannot readily suppose the sulphatet to have 
generally effected the final concentration of large deposits. It 
18 more probable that this was accomplished by the more per- 
_ manent solutions of carbonate and silicate of copper respectively, . 
as the circumstances favored. e position of the metallic 
~ before those which were formed by the destruction of the 
‘8 a A 
per could not, therefore, take place until the esa had so 
ar disappeared as to leave a relative excess 0: 
pared with the amount of ferrous salts exposed to a higher oxi- 
dation. Throughout its deposits the copper exhibits a decid- 
edly intimate connection pr 
favored by copper. This association is so invaria 
intimate that one is forced to the conclusion that there exists a 
close genetic relation between the metallic state of the copper 
and the ferric condition of the iron oxide in the associated sili- 
cates; that the higher oxidation of the iron was effected 
ugh the reduction of the oxide of copper and at the expense 
of the oxygen of the latter. : 
As regards the green-earth and that variety of chlorite or del- 
€ssite which is intimately associated with the copper, they either 
immediately follow the copper in point of age or are contempo- 
3 very thin sheets of copper from the jointing- 
* A coating of gypsum covering : 
Cracks of the ae we contiguous to the conglomerate, may be due to this 
decomposition, followed by the reduction of the coppe: 
Compare Bischof u, Phys. Geol., I, p. 52, i 
) oi 
and III, p. 716. a 
; The result of this oxidation is seen in the brick-red color of the amygdaloids 
in the brown color and spots of many of the melaphyr beds. 
