62 



Conservation Reader 



H. W. Fairbanks 

 Little by little the great rocks break in pieces and crumble finally to form soil. 



away, she raises up new ones somewhere else so that the 

 tearing-down work begins again. 



Let us, in imagination, sit down by the side of a rock, 

 prepared to stay there many years, that we may learn just 

 how Nature makes the soil. It will be a long, long time 

 before we can see any change in the rock. Each bright day 

 the sun warms the cold rock and makes it expand a very 

 little. At night the rock grows cold and shrinks. In this 

 way minute crevices are finally formed between the grains 

 of the different minerals that make up the rock. 



When it rains, water creeps into the tiny crevices. The 

 water carries with it a Uttle carbonic acid which the rain- 

 drops took from the air. This substance aids in dissolving 

 some of the rock materials. If the nights are very cold, 

 the water in the crevices freezes and opens them a little 

 wider, for ice, as you know, takes up a Uttle more room than 

 it did when it was water. 



