Lieut. Ruggles on the Copper Mines of Lake Superior. 71 
portions of the valuable combinations of this metal have been de- 
stroyed and dispersed by subterranean heat in consequence of the 
absence of pressure. 
I will now endeavor to indicate, briefly, the vast region to which 
this question has direct application. 'The general dissemination 
of copper, and indications of its combinations, extending from 
near Grand Island along the southern shore of Lake Superior 
to its head, and several miles inland, as well as abundant indi- 
cations on Isle Royale, near the N. W. coast, is now well estab- 
lished. 'The native copper bowlder, so long known to have lain 
in the Ontonagon, has been very justly regarded as an anomaly 
in the mineral kingdom. ‘There is also an inland trap range 
running some two hundred and thirty miles south of the Kewai- 
wenon bay, and extending inland past ‘“‘ Lac Vieu Desert” towards 
the sources of the Chippewa and Wisconsin rivers. Indications of 
copper and its combinations are said to have been found through- 
out the whole extent. The Indians describe a massive bowlder 
of native copper, surrounded by calcareous spar bowlders, a little 
to the west of ‘‘ Lac Vieu Desert,” so vast that actual examination 
alone would overcome incredulity. I have received authentic ac- 
counts of small fragments of native copper found in sand-rock 
by troops, in 1819, ’20, while quarrying near the junction of the 
Mississippi and St. Peter’s rivers, for building Fort Snelling, 
and where the hand of man could never have placed them. 
Recently ores of copper have been discovered, in the vicinity of 
Prairie du Chien, estimated to yield twenty per centum. Some 
eight or ten years since, a mine, bearing nearly N. and S., con- 
taining earthy oxides associated with the ferruginous sulphuret, 
yielding about fifteen per cent., was opened near Mineral Point, 
and since then other localities have been discovered in its vicinity. 
A large portion of this region, especially that comprised within 
the Mississippi valley, which has come under my personal obser- 
vation, presents clear and abundant traces of submergence during 
a remote period—this, indeed, independent of the incontestable 
evidence indicated every where by organic remains; of these 
waters, the Mississippi appears to have been the final outlet. A 
similar subsidence, though less clearly indicated, probably took 
place contemporaneously in the region of the great lakes, through 
the valley of the St. Lawrence. 
Now it is to be observed, that galena is found geologically 
associated with copper, in strata flanking the trap ranges, and at 
