THE FORMATION OF SOIL 17 



disintegrated, provided water can gain access 

 to its interior. Such entrance of water is 

 facilitated by the cracks that are formed 

 as a result of the unequal expansion and 

 contraction that is associated with variations 

 of temperature. 



Water also acts powerfully as a disrupting 

 agent through the agency of frost. A vessel 

 may contain water without injury, but a 

 different result will ensue if the water is 

 subjected to a temperature sufficiently low 

 to convert it into ice. During the change 

 the volume of the water is materially in- 

 creased, and so powerful is the pressure thus 

 set up that no ordinary vessel is able to resist 

 it. The result is seen in the bursting of 

 water-pipes, and in similar phenomena. 



Directly water enters a stone to fill up the 

 interstices, the fate of that stone depends 

 upon the occurrence of frost. So long as 

 the water remains in a liquid form its effect 

 is but slow, but whenever it is converted 

 into ice the parts of the stone are pushed 

 asunder, and when a thaw comes, and the 

 ice is reconverted into water, the hardest 

 stone may crumble down into a shapeless 

 mass. This effect of water is undoubtedly 

 one of the most powerful agencies in the 

 formation of soil. 



