GENERAL PHYSICAL FEATURES. 127 



Soils and subsoils.] 



strongly. Such soils are naturally supplied with abundance of soda, lime, 

 magnesia and potash, and they constitute by far the largest part of the 

 immediate surface of the state. With the exception of the soils based on the 

 lacustrine clays of the Red river of the North, and those in the southeastern 

 part of the state based on the loess-loam, the entire prairie part of the state is 

 characterized by such soils. In addition to this, the same blue till underlies 

 much of the timbered area of the state, in most places extending to the east 

 of the Mississippi river, and including Scott and Le Sueur counties east 

 of the lower Minnesota. Still the characteristic qualities of the blue till 

 of the prairie regions become less and less marked toward the east, and in 

 the timbered areas generally the soils would not correctly be denominated 







alkaline. 



Subsoils of red till differ from those of blue till in containing a high 

 percentage of iron -oxide, and little or none of the salts of the alkalies. 

 They are generally calcareous, but less calcareous than those of the blue 

 till. They are found distributed from Pigeon river, on the international 

 boundary, southwestward, coincident with the strike of the Cupriferous 

 or Potsdam formation. They form the surface as far as St. Paul, and 

 eastern Hennepin county; and further southwest they are covered by the 

 blue till. Toward the south and southeast from St. Paul they gradually 

 blend with the eastern outrunning limit of the blue-till subsoils on the 

 west and with the clay -loam subsoils of the "driftless area" on the east. 

 Thus it will be seen that the blue and red tills give the dominant characters 

 to the soils of the largest pail of the state, and that of these the blue 

 till is the most important. 



Subsoils of gravel, or of sand, result from the superficial modification 

 of the till of the region. They are always underlain, at a less or greater 

 depth, by a till sheet, and if wells penetrate them they obtain the charac- 

 teristic water. These subsoils give little effect to the chemical nature of 

 the soils based on them, but on their successful cultivation they have a 

 powerful influence, since they are quickly susceptible to the changes of 

 climate, and the variations of local drainage. In certain seasons they 

 are moi'e productive than the soils based on a clay subsoil, and in others 

 they are nearly sterile. Such subsoils prevail in the higher areas of modi- 

 fied drift along the principal water-courses, accompanied, in the proper 



