24 AGRICULTURE 



of miles, are intermixed with finer material, 

 such as clay and grit. When the ice-sheet 

 melted, and this boulder-clay became ex- 

 posed to the weather, its upper layers under- 

 went the weathering changes that have just 

 been described, the result being the soil that 

 we till on many of our fields, which rests on a 

 subsoil of glacial material in much the same 

 condition as the glaciers left it thousands of 

 years ago. 



CHAPTER II 



THE PROPERTIES OF SOIL 



HAVING briefly considered the formation of 

 soil, we may now conveniently turn to certain 

 physical and chemical properties that it pos- 

 sesses, which are of much importance in their 

 bearings on the nutrition of plants and the 

 cultivation of farm crops. 



One property that soil has is simply the 

 power possessed by the particles of sticking 

 together, or, as it is called, the property of 

 cohesion. At one end of the scale we have 

 dry sand, which is practically destitute of 

 cohesiveness ; while the other extreme is 

 occupied by plastic clay, which exhibits so 



