396 Sources of the Constituents of Minnesota Soils. 



has been overwhelmed by g^lacial ice and its soil and subsoil con- 

 ditions completely altered. The material torn up and comminu- 

 ted has been transported and redeposited in other localities, some 

 near and some far. Thus the rocks have been brought into even 

 closer relations to the processes of soil-making than could exist 

 were the surface of the state that of a non-glaciated region. The 

 intermingling of material affords soil material of remarkable ver- 

 satility and strength ; versatility because of the intermingling inci- 

 dent to glacial transportation, and strength because of the mix- 

 ture of partially decomposed and fresh materials, insuring a slow 

 and continuous decomposition of mineral matters and a facility 

 for the extended growth of roots and underground stems and 

 thereby the ceaseless forming of soil to an unusual depth. That 

 there are many rock species in the constitution of the glacial drift 

 the following tables will show\ 



The rocks that form Minnesota soils. — The underlying rocks 

 of the state are : — 



1. The acid crystalline rocks, — largely granitic and rich in 

 silica. 



2. The basic crystalline rocks, — diorites, diabases, gabbros, 

 etc., or those usually poor in silica. 



3. Sandstones and quartzites, consisting mostly of silica. 



4. Calcareous shales, partly carbonates of lime and mag- 

 nesia, partly silica and partly alumina, as leading constituents. 



5. Carbonates, — rocks chiefly of organic origin and chiefl} 

 carbonates of lime, magnesia and iron. 



The first group of rocks includes granites, gneisses and the 

 so-called crystalline schists. All are very hard to break down 

 into the condition of soil. It takes time and chemical action. 

 The chemical substances in these rocks are silica, alumina, potash, 

 soda, lime, magnesia, and the compounds of iron. Quartz and 

 the feldspars are their chief constituents, followed by hornblende, 

 biotite, etc. 



Th'ey are the chief storehouses of the elements furnished to 

 the soil by these rocks, and in their degradation, the chief result- 

 ant products are quartz, sand and kaolin, with chloritic minerals 

 in proportion to the biotite present. The granitic rocks, when 

 broken down on level tracts, make a very sterile and barren soil ; 

 where erosion can collect them into valleys, the soil becomes rich 

 — when not too heavy. But then, the cost! Hundreds of acres 



