98 THE SOIL AND ITS IMPROVEMENT 



result as the hammer or the road crusher. These forces, 

 however, act more silently, and their operation is fre- 

 quently unnoticed. When the earth was young, there 

 was no soil upon it, but only a hard, rocky crust, like 

 that which often appears on hillsides where the soil has 

 been removed. Silently and slowly, through long periods, 



DISINTEGRATION. 

 A limestone ledge breaking up and forming soil. 



nature crushed and refined the outer surface of these 

 rocks by means of two different processes : namely, disin- 

 tegration and decomposition. 



a. Disintegration is a physical process. That is, by it 

 rock particles are pulled apart without their nature being 

 changed. You have perhaps noticed a bottle of water left 

 standing outdoors for a few days during a cold part of the 

 winter. The water froze and broke the bottle. A tre- 

 mendous force must have been exerted in breaking the 

 bottle. When the temperature of water drops from four 

 degrees centigrade to zero, or the freezing point, it 



