136 THE GEOLOGY OF MINNESOTA. 



[Timber distribution. 



state, embracing but 1089 square miles of prairie situated mostly in Free- 

 born and Mower counties. 



Qualities of the natural surface waters in Minnesota. The natural waters 

 of the lakes and streams of the state may be classed in two main divisions, 

 viz., the alkaline and hard waters, and the chalybeate and soft waters. These 

 qualities mix in many streams and lakes, indeed in most of them. The 

 natural waters of the Red river valley may be taken as a type of the 

 former class, and those of the Pigeon river, or of any of the streams that 

 enter lake Superior below Duluth, as types of the second class. What has 

 been said respecting the nature and distribution of the drift and the sub- 

 soils of the state, should be borne in mind in considering the nature of the 

 impurities of surface waters in different parts of the state, since the cause 

 of one is the cause of the other. They both depend on the nature of the 

 underlying till, or, in the absence of till, of the bedded rocks. The chemical 

 peculiarities of the blue, or gray northwestern till are impressed on, and 

 even are made manifest by, the surface waters. Hence we find the alkaline 

 and hard waters occupying the most of the state, but having their chaiac- 

 ters less and less marked in the eastern portion; we find the irony and soft 

 waters draining the surfaces of red till, or, in its absence, of bare rock in 

 the northern part of the state. 



VII. THE NATURE AND DISTRIBUTION OF THE NATIVE FOREST AND ITS 



RELATION TO THE PRAIRIES. 



The state has about 31,800 square miles of prairie, and about 52,200 

 square miles of forest, including in each the water-areas adjacent or embraced 

 within them. In this area of prairie, however, is included a belt of thinly 

 forested country which is interspersed both with prairie and timbered patches, 

 the forest being reckoned to extend only to the limit of large trees and having 

 a continuous margin. Some parts of the prairie portion also embrace isolated 

 patches of heavy timber, as in Fillmore, Houston and Blue Earth counties, 

 as well Olmsted, Winona, Dodge and Wabasha, and along most of the river 

 valleys. At the same time, even within the heavily timbered portions of 

 the state, there are isolated small areas of prairie, or meadow land, but these 

 are in low ground, and their exemption from trees cannot be attributed 

 generally to the same cause or causes as those that have produced the great 



