'J'lic Theory of Copl'cv Dc/'ositloii — Laitc. 305 
In a thorou<;lily cryslali/.cd Ira]), dnU riiic nK'la|)liyrc av diabase 
the porosity is not over i per cent, i'ut in the case of an amyg- 
daloid the amount of vesticular sjjace may have been very 
considerable, and this space must have been filled either with 
the original gases or possibly in the case of submarine flows 
with sea water more or less contaminated with such gases. 
Such an origin would readilv account for the saline character 
of the waters, and it is wortli noting that such saline waters 
attack copper as is shown ))y the fixtures around the salt 
baths of L-ower i\Iichigan. 
Another most weighty argument is the occurrence of cop- 
per native in the iron ores near Crystal Falls.* One can hardly 
imagine this other than produced by descending waters since 
the iron ore is universally allowed to have been formed by 
descending waters. Moreover it occurs in the u])per parts of 
iron ore bodies and is not known to have any connection with 
lower deposits. It may easily be conceived to have Ix-en de- 
rived from an over-lying extension of the Keeweenawan, now 
eroded aw a}'. 
Pumi)elly supposed that the copper may have been orig- 
inallv deposited with the strata, as sulphurets under submarine 
conditions. He was slightly inclined to call the old lavas altered 
(metamorphic) sediments. 
Irving apparently agreed with I'umpelly speaking of the 
copper having been arrested in its descent. The more recent 
writers on ore deposits however seem inclined to refer the 
origin of the copper deposits to the upward rising waters. For 
instance Posepny writes as follows : 
"Some of the attempted explanations assume, in my opin- 
ion correctly, as the cause of the first ore depositions, the action 
of hot springs — in vhii^n comecn'on i< i-^ only to be emphasized 
these thermal effects occurred long after the intrusion of the 
eruptive flows between the sedimentary strata, so the ores were 
brought, not by or in the eruptives themselves, but by the later 
springs, from great depths and perhaps from considerable dis- 
tances. This explanation, applicable to all deposits, suits also 
the exceptional case cited by R. U. Irving, namely, the None- 
• A. E. Sbaman writes that he has native copper in iron ores from the Cliffs 
mine at Iron Mountain, also with ferruRinous chert from the tenth level of the 
Great Western mine. Crystal Kails, also from the Montana mine. Tower, 
Minn., where it occurs in the iron ore. 
