122 THE GEOLOGY OF MINNESOTA. 



[Elevations. 



In the midst of this broken tract of the upper Mississippi are flat and 

 sandy areas in the central part of the state, characterized by an abundance 

 of Pinun Batiksiana, which include much of the region from Leech lake to 

 the Crow Wing and Leaf rivers and Otter Tail lake, and on the east of the 

 Mississippi embrace much of Crow Wing and eastern Morrison counties. 

 Similar flat and sandy tracts are found in Carlton and Pine counties, though 

 not so uniformly characterized by the same species of pine. 



In the southeastern portion of the state the surface is broken and hilly, 

 the contour depending immediately on the form of the rocky surface 

 overspread with a sheet of fine loam. This configuration is due to the 

 erosion of deep valleys in the horizontal strata in former ages, without 

 the 'supplementary planing and filling process of the glacial epoch. Hence 

 the changes of level are abrupt, as bench after bench of the rocky 

 substructure is brought to form the surface. The benches are often 

 separated from each other by wide plains of fertile soil, but along the 

 river-courses they are brought into juxtaposition, and furnish instructive 

 opportunities for making out the stratigraphic geology of the Cambrian 

 and Lower Silurian rocks. This topography is most perfectly illustrated 

 in those counties that border on the Mississippi river below St. Paul. 

 It gradually becomes less conspicuous toward the west, on account of 

 the feebler erosive action of drainage at points removed from the main 

 valley, and also because the drift materials begin to be insinuated within 

 and beneath the loam of that region, preventing the rocky substructure 

 from expressing itself in the topography. 



IV. THE RELATIVE ELEVATION OF DIFFERENT TARTS OF THE STATE. 



Lake Superior is 602 feet above the sea; and a narrow tract bordering 

 the shore of that lake, including the valley of the St. Louis river as far as 

 Fond du Lac, is the lowest land in the state. The Mississippi river where 

 it leaves Minnesota is 620 feet above the sea. The valleys of the streams 

 in Houston, Winona, Wabasha and Goodhue counties are but little elevated 

 above that river, and probably should be classed, as a group, next higher. 

 But these valleys are narrow, and the adjoining surface rises rapidly to the 

 hight of about 1000 feet above the sea, sometimes reaching 1200 feet. The 

 Red river of the North leaves the state with an elevation of 767 feet above 



