308 Our Surroundings 



Soil consists of small particles of rock and organic matter 

 supplied by plants and animals. 



Water is the chief cause of erosion. Other causes are wind, 

 glaciers, ice, air, animals, and plants. 



The principal kinds of soil are clay, sand, and loam. Clay is 

 used for the making of bricks and pottery. 



Glass is made from a mixture of sand, soda, and limestone, 

 usually by heating, blowing, rolling, and pressing. 



Cultivation of the soil prevents weeds, increases the circulation 

 of air in the soil and adds to the soil's capacity to hold moisture. 



Soil exhaustion is caused by the failure to restore to the soil 

 the nutrients which growing plants take from it. 



Soil is kept fertile by adding to it materials to replace those 

 taken from it by growing crops. This is accomplished by the 

 use of fertilizers and by proper crop rotation. 



The importance of some knowledge of the soil is evident when 

 we recall that the continuance of all kinds of life on the earth 

 depends on the fertility of the soil for food production. 



FACT AND THOUGHT QUESTIONS 



1. How are rocks classified as to origin? 



2. Describe ways in which sedimentary rocks are formed? 



3. What are igneous rocks? Give examples. 



4. Complete these statements orally: 



(a) The principal kinds of building rocks are . 



(b) is a rock used in sculpture. 



5. What is cement? How is it made? 



6. What is concrete? Name several uses of concrete. 



7. What are ores? Outline briefly the process of extracting iron from ore. 



8. What is soil? How is it formed? 



9. Name the principal kinds of soil. 



10. Name four agents that aid in soil formation. Tell how each acts. 



11. At the bottom of most stone cliffs are many fragments of stone from 

 the cliff face. What caused them to break off? 



12. How are bricks made? 



13. Describe in brief the process of making common pottery. 



14. Why is soil cultivation necessary? 



15. What is meant by soil exhaustion? 



16. How can soil be kept fertile? 



17. Why is knowledge of the soil important? 



