HOW SOILS ARE FORMED 49 



that help the water to soften or dissolve the rocks. Every 

 one has seen rocks covered with lichens and mosses. When 

 these are taken away one can often see where the rocks 

 have been eaten into by the small plants, due to the action 

 described. As this process of growth and decay continues for 

 ages, the soil is gradually improved until it will produce 

 plants useful to man. 



rocks brought by the edges of two moving streams of ice and snow: T, terminus or 

 end of the glacier where the sun melts the snow and leaves the rock and soil. The 

 finest soil is carried by running water to the broad field farther down the valley. 



How Animals Help. Burrowing animals, such as the 

 ground squirrel and the prairie dog, earthworms and insects 

 living in the ground, as well as rabbits, gophers, and wolves, 

 aid in preparing the soil for the growth of plants. They 

 often burrow deep into the ground; the openings aid in free 

 movement of air and water, and roots can enter the soil more 



