234 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Srction V.—NORTHWESTERN WISCONSIN AND THE ADJOINING PART 
OF MINNESOTA. 
This region was examined in considerable detail for the Wisconsin 
Geological Survey in the years between 1873 and 1879, by Messrs. Sweet, 
Strong and Chamberlin. The results of their work are given in Vol. III 
of the Geology of Wisconsin, which volume also contains brief descriptions 
by Pumpelly of a number of the specimens collected. A special trip was 
also made for this work by Mr. R. McKinlay under my directions, in the 
valleys of the Snake and Kettle rivers of Minnesota, with especial refer- 
ence to determining the manner in which the Keweenawan rocks and the 
Lake Superior basin terminate westwardly. From the data collected by 
these several investigators I compile the following brief account of the 
region, adding some conclusions of my own. 
This region includes two distinct belts of the Keweenawan rocks. One 
of these is a continuation of the belt we have been following all along from 
Keweenaw Point, with the dip as usual to the north and west, while the 
other is a parallel belt made up of strata presenting a southerly or south- 
easterly dip, and forming the northern side of a synclinal trough, which 
extends entirely across Wisconsin to the Minnesota line. The axis of this 
synclinal, where it first strikes the lake shore near the Montreal River, 
trends about southwest; beyond Bad River for some 35 miles it runs nearly 
due west. Turning then again, it follows a southwesterly course for about 
80 miles, when it changes to a nearly due south course in the valley of the 
Saint Croix River, where the north and south belts finally unite, under- 
neath the newer Cambrian sandstone of the Mississippi Valley. In this 
region the two main divisions of the series are plainly recognizable. It 
thus follows that the Upper Division, with its great thickness of soft sand- 
rock, occupies the middle of the synclinal, while the ridges on each side are 
composed of the resistant crystalline rocks of the Lower Division. 
The Southern Belt; Numakagon Lake to the Saint Croix “River—In the 
southern belt, including the northward-dipping rocks, with the one excep- 
tion of the conglomerate at the base of the Upper Division, the only expos- 
