Sources of the Constituents of Minnesota Soils. 405 



Application- and Siumnary. The foregoing analyses disclose 

 rocks of a varied composition within the borders of the state. 

 Were they the rock-floor which, directly beneath the workable soils 

 were affording replenishment of the mineral substances of these 

 soils, it would not be difficult to read the characters of the best 

 crops in the tables of chemical constituents. But the work of the 

 glacial period of geologic history must be given recognition. It is 

 not alone that all the foregoing rocks have been covered by glacial 

 drift in places to the depth of hundreds of feet by rock debris, but 

 the very rocks themselves have been broken, torn up and scattered 

 over wide areas. 



What does occur, then, as soil-making material is the frag- 

 ments of these rocks torn from the ledges and scattered broadcast 

 over that glacial plain which the surface of the underlying rock- 

 formations so plainly shows. True, much material derived from 

 the underlying rocks within this state has been carried across the 

 boundary to form the soil-material of neighboring states, while on 

 the other hand no small amount brought from other regions has 

 •been deposited within the borders of this commonwealth. Its 

 present occurrence is in the form of particles fine and coarse, 

 which," by affording a large proportion of surface to bulk are 

 rapidly disintegrating and yielding their chemical elements to be 

 used as the food of growing plants. 



If a further summary of this paper were written it would 

 state : The term soil is defined. Soils are made by the mingling 

 of rock-debris with the remains of organisms, chiefly plants, and 

 its degree of fertility depends upon physical and chemical condi- 

 tions combined. A soil fertile for one crop is not necessarily the 

 best one for another type of plants. The chemical elements con- 

 stituting the essential plant foods are few, yet these must be m 

 such condition that the crops can readily secure them from the 

 multitude of mixtures in which they occur. The rocks of Min- 

 nesota are classified under five groups; i, acid crystallines; 2, 

 basic crystallines ; 3, sandstones and quartzites ; 4, calcareous 

 shales, and, 5, the carbonates. Among these, granitic rocks and 

 basic eruptive, which occupy large areas beneath the drift in the 

 northern and western portions of the state, furnish many impor- 

 tant food elements, particularly alkalies and alkaline earths. 



The sandstones and quartzites among the most barren soil 

 producers have mingled with other substances their beneficent 



