34 LIFE ON THE FARM. 



so much colder, and a consequent slower plant 

 growth results. - 



CHEMICAL COMPOSITION AND KINDS OF SOIL. 



Geologists inform us that the present crust of 

 the earth has been a long time in the process of 

 formation. Early rock-formations have been 

 broken up and decomposed by later actions. 

 Water, cold, heat, and glacial movements have 

 been the great causes in breaking up the surface 

 rocks and leaving them in a fit condition for the 

 growth of plants. 



Soil, in order to yield its ingredients quickly as 

 food for plants, must have its grains so fine 

 that a great amount of surface is exposed for the 

 combined action of roots and water. A cubic foot 

 of solid stone might contain all the necessary food 

 for plant growth, yet so little of its surface is 

 exposed that only a small per cent, of it could be 

 dissolved for a season's growth. By a very simple 

 mathematical law, it can easily be found that the 

 same cubic foot of stone, when broken into small 

 pieces, will present, instead of six square feet of 

 surface, several hundred; and, if reduced to parti- 

 cles fine enough, such as that of most soils, several 

 thousand square feet. 



This not only allows the roots to penetrate more 

 easily, but the surface tension of the particles gives 

 soil a greater water-holding capacity, one of its 

 most valuable properties, The fineness and coarse- 



