CHAPTER IV. 
FORMATIONS OF THE INTERIOR OF WISCONSIN AND MINNESOTA. 
SECTION IL. 
THEIR LITHOLOGICAL CHARACTER. 
EXTENSIVE deposits of drift prevail throughout the interior of the Chippewa Land 
District. These fill up the inequalities of the surface, and give, for long distances, 
a greater degree of flatness and uniformity of contour than one would expect to 
encounter in a country near the sources of so many large streams. 
Between the western tributaries of the Chippewa River and the heads of the 
eastern branches of the St. Croix and Rum River, this drift seems to rest chiefly on 
the northern extension of the Lower Protozoic Sandstones of Wisconsin, heretofore 
treated of in Chapter I.; which formation appears to be invaded only at a few 
points by intrusive rocks of igneous origin. The drift of this part of Wisconsin, 
which, in a great measure, conceals these underlying formations, is chiefly of a 
light, sandy, and gravelly nature; supporting locally, multitudes of boulders, many 
of which do not appear to be far removed from the parent rock. Where valleys 
have been excavated by streams, these boulders, undermined and rolling from the 
higher grounds, have accumulated on the banks and in the beds of the rivers, 
causing frequent obstructions in the channel, or covering it as with an artificial 
pavement. 
Northeast of the Chippewa, towards the Michigan boundary, the drift reposes 
chiefly upon Metamorphic Schists and Granitic Rocks; and the same is true of the 
extreme northern portion of the District, and of a belt of country, some forty or 
fifty miles in width, ranging north-northeast and south-southwest, from Millelacs, 
through the Rapids of the Mississippi and St. Peter's Rivers, between longitude 
94° and 95°. In these latter regions, besides the coarse boulder drift, sand, and 
gravel, a deposit of finer materials, more marly and argillaceous, and of an ash-gray 
colour, prevails over considerable areas. 
