234 FIRST YEAR COURSE IN GENERAL SCIENCE 



In the course of time the earth became covered with an 

 accumulation of rock fragments; this covering is called 

 mantle rock. By the process of decay, a thin covering 

 capable of supporting plant life was formed. 



FIG. 122. WEATHERED ROCK 



1. What evidence do you see of the work of air, water, and changes of 

 temperature on this rock? 2. How do you account for the fine material 

 around the base? 



254. Soil. Decayed rock material containing animal or 

 vegetable matter is called soil. Some forms of plants can 

 secure all the material they need to make food from air, 

 water, and rock waste, especially if the rock waste is of 

 volcanic origin. Such plants would be the first' to flourish 

 on new land; their remains would contribute to soil and their 

 roots would assist in the process of weathering. Earthworms 

 and burrowing animals also are agents of weathering and 

 assist in making soil. Even now, after millions of years, 



