SOILS. 



189 



vegetable accumulations to such an extent that the resulting humus 

 forms the main constituent of the soil, and the mineral ingredients 

 are entirely subordinate in amount and function, thus forming a soil 

 of vegetable origin. 



With this exception, the leading elements of our soils are derived 

 directly or indirectly from the rocks, either through their powdering 

 by mechanical means, or disintegration by chemical agencies. The 

 chief mechanical agent in pulverizing the rocJ<;s has been water in its 

 various states, especially in the form of glacial ice. When the great 

 glacier plowed over this region, it broke fragments from every forma- 

 tion over which it passed, ground them to various stages of commin- 

 ution, and left the commingled mass spread over the face of the coun- 

 try, forming a most excellent foundation for our soils. Subsequently, 

 water in the form of lakes and rivers washed out and redeposited a 

 portion of this material, giving rise to sandy beach lines and lacus- 

 trine and fluviatile deposits of clay. 



But this material was still too crude to constitute a fertile soil, and 

 besides, over many small areas, these agencies left the rock entirely 

 bare. Then followed a process of disintegration, of a chemical or 

 chemico-physical nature, popularly spoken of as the action of the ele- 

 ments, by which the surface of this material, and the rock surface, 

 where exposed, was reduced to the condition of soil, which in the pro- 

 gress of ages enriched itself by its own vegetation. It appears, then, 

 that (1) a portion of our soils were derived directly from the glacial 

 accumulations, and are properly called drift soils ; that (2) a portion 

 were derived from the same kind of material, but after it had been 

 washed and redeposited by lake and river action, forming soils of 

 lacustrine and fluviatile origin; and (3) that another portion had their 

 origin in the direct decomposition of the undisturbed rock formations. 

 It will now be clear that the character of a soil will depend upon (1) 

 the nature of the rock from which it was derived; (2) the manner and 

 degree of its reduction ; (3) the amount lost by leaching and other- 

 wise; and (4) the amount gained by vegetation from above or capil- 

 lary action from beneath. Or, to put the matter much more simply, 

 a soil depends chiefly upon (1) the chemical nature of the material, 

 and (2) its physical state or the degree of fineness to which it is re- 

 duced. These elements will receive prominent attention in the de- 

 scriptions of soil that follow. 



To fully understand the nature of the material, all the rock forma- 

 tions of the region and those that lie to the north and east,whence 

 the glacier came, should be studied, since they have all made contri- 

 butions to our highly composite soils, and herein the strictly geologir 



