428 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Thus far native copper mining has proved profitable within the limits 
of the State of Michigan only, and it seems to be true also that all or nearly 
all of the producing deposits have been opened on and worked by the 
ancient miners, whose attention was of course attracted by those deposits 
which by the accidents of erosion had been left prominently exposed. It 
is incredible that even in the long-settled districts of Michigan all of the 
workable deposits of copper have been discovered. Thus on Keweenaw 
Point the valley south of the Greenstone Range, in which lie buried 
beneath a surface coating of drift the equivalents of the Portage Lake 
cupriferous beds, has never been explored by trenching or mining opera- 
tions. The same is in a measure true of the Bohemian Range of Keweenaw 
Point. ; 
Without the boundaries of the State of Michigan, the attempts at 
copper mining have been but feeble, and utterly inadequate to prove or 
disprove the existence of workable copper deposits. In Wisconsin native 
copper has been met with all along the course of the southern Keweenawan 
belt from Montreal River to the Saint Croix. Running from the Montreal, 
in Sec. 2, T. 47, R. 1 E., southwest and west, is a belt of distinctly bedded 
and often amygdaloidal diabases in which copper has been seen in greater 
or smaller quantity both in crossing veins and in altered diabase belts, at 
the crossing of each stream, the intervening areas being drift covered At 
the crossing of Montreal and Bad rivers this belt is worthy of further exam- 
ination.’ Beyond Bad River, to the southwestward, float copper is exceed- 
ingly common, and traces of it are here and there met with in the ledges 
themselves. Unfortunately the country is one covered with heavy drift 
accumulations, through which only the harder and more enduring, and 
therefore non-cupriferous, beds ordinarily project. The indications are 
that, but for the overlying sheet of drift, this region would be as productive 
in copper as that of Keweenaw Point. 
Rounding the turn at the western end of the great Keweenawan syn- 
clinal, in the Saint Croix Valley, we find the drift covering lighter, and 
here, in the vicinity of Snake and Kettle Rivers, and thence northeastward 
into Douglas County, in Wisconsin, are found plainly bedded diabases and 
‘See Vol. III, Geol. of Wis., pp. 205, 206. 
