HOW SOILS ARE FORMED 49 



ice moving like rivers, carrying quantities of earth and 

 rocks. The results of ancient glacial action are found in 

 many places. Rocks with deep scratches show the wearing 

 and grinding effects of the moving masses of ice. Drift or 

 glacial soil is easily recognized by the presence of rounded 

 rocks or boulders. It is usually fertile because of the variety 

 of mineral substances brought from far and near. Much 

 drift soil is found throughout the northern states and Canada, 

 east of the Rocky Mountains. 



Two other kinds of transported soil should be studied. 

 One, known as colluvial soil, occurs on mountain slopes and 

 steep hillsides, and is the mixed mass of soil and rocks brought 

 down by avalanches and landslides. Such soil is not generally 

 in condition to grow good crops. The other, known as wind- 

 drifted or aeolian soil, is found in arid or semi-arid regions, 

 that is, in places where there is very little rain-fall and the 

 soil is dry, and there is little vegetation to hold the soil. 

 This soil is carried by the winds and is deposited in dunes 

 or drifts like snow. These dunes sometimes cover cultivated 

 fields, forests, and even villages. As this soil is shifting, 

 plants frequently do not have an opportunity to grow and 

 hold it. (Fig. 24.) 



REVIEW. 



1. What is soil ? 



2. From what is soil made ? 



3. Name fom* forces which are making soil. 



4. How does the air help to make soil ? 



5. Tell of the influences of temperature in crumbling rocks. 



6. Tell of the ways in which water helps to crumble rocks. 



7. Tell where and when you have seen running water carrying 

 fine soil or mud. 



8. In what kinds of places is this mud deposited ? 



9. Do plants help to form soil ? How ? 



10. In what ways do animals help to make soil useful ? 



11. What is transported soil? 



12. Describe the several kinds, and tell where they are likely to be 

 found. 



Reference. — U. S. Farmers' Bulletins: 421, Control of Blowing 

 Soils. 

 4 



