COPPER IN WISCONSIN AND MINNESOTA. 429 
amygdaloids carrying copper with interbedded cupriferous conglomerates. 
The region is one which in the early days of mining excitement on Lake 
Superior was so remote and inaccessible that the flood of copper hunters 
which at that time spread west from Keweenaw Point failed to reach it. It 
still lies almost wholly unexplored, while promising more to the copper 
hunter than any other portion of the entire extent of the formation outside 
of the State of Michigan. 
Further north and east from the district last described lies the Copper 
Range of Douglas County, Wisconsin.’ This range has already been fully 
described on a previous page as to its position and structural characters. 
Copper has been found along its course in a number of places, chiefly in 
epidotic altered amygdaloids, and the general structural characters are such 
as to indicate the possibility of the occurrence of copper in quantity along 
this belt. Some little mining has been done at several points, but not 
enough to lead to any satisfactory conclusions. 
On the Minnesota coast of Lake Superior, copper has been met with 
at only two or three points. Of the five subordinate groups into which I 
have divided the rocks of this coast, only two, the Agate Bay and Tem- 
perance River groups, are of such a nature as to encourage the expectation 
that copper might be found in them. The great thickness which makes up 
the other three groups—and the same is true of considerable portions of the 
two groups named—is for the most part composed of very massive compact 
beds such as have never yielded copper on the South Shore. The beds of the 
Agate Bay and Temperance River groups are often thin, much altered, and 
highly amygdaloidal, and might perhaps be found to carry here and 
there workable deposits of copper. The distribution of the rocks of these 
two groups is approximately shown on Plate XXVI of this volume, from 
which it will be seen that the extent of country within which there is any 
likelihood of the discovery of copper in this region in the future is a small 
one, lying for the most part in the immediate vicinity of the lake shore. 
It is also to be observed that the most probable mode of occurrence for 
copper within this restricted area is the amygdaloid belt, the form in which 
occurs the copper of French River, where the metal is associated with 
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1See Chapter VI, p. 250. See also Geol. of Wis., Vol. III, pp. 357, 362. 
