46 HOW ROCKS AND CLIMATE AFFECT SOILS 



(c) A muck contains much silt and clay. What of its supply of mineral 

 plant-food elements? 



(d) Suppose the mineral matter in a muck is all quartz sand. Would its 

 supply of phosphorus and potassium be the same as that of (c)? Why? 



To Learn to Recognize the Common Rocks. Procedure. Examine with 

 hand lens the different rock specimens provided. Record observations in 

 tabular form headings as follows: Rock group, name of rock, color, texture, 

 structure (dense, fine grained, granular, or laminated), and important min- 

 erals of which composed. 



Questions. (a) What kinds of soil form the following rocks granite, 

 sandstone, limestone, and shale? 



(6) What forms the soil in the weathering of a limestone? 



Field Studies. When practicable, field trips may be made for studying 

 the rock formations of the community. Note relation between the prevailing 

 rocks and the kinds of soil. Note also whether the areas of soil visited are of 

 residual or transported formation. 



QUESTIONS 



1. Name the three large groups or classes of rocks. How do these three groups 



differ from each other as regards origin? Name some of the common 

 rocks belonging to each group. 



2. Tell of the changes that rock undergoes. 



3. What is a rock? 



4. Name some of the common rock-forming minerals. 



5. What is the source of the important mineral elements required by plants? 



6. Why are some sandy soils poor in mineral plant-food elements? 



7. Why are peat soils generally deficient in potassium and phosphorus? 



8. Do muck soils contain more or less mineral elements than peat? Explain. 



9. Name the products of rock weathering. 



10. Distinguish between clay and true clay. 



11. What is carbonate of lime? Name some materials containing much 



lime carbonate. 



12. What kinds of soils are formed from granite? From sandstone? From 



shale? From limestone? 



13. Why is the water of the sea salty? 



14. Explain how sandstone, shale and limestone are formed. 



15. How can a soil form from a limestone? 



16. What are alkali soils? Alkali spots? 



17. Name other differences in soils of arid and humid regions. 



18. In what kind of a climate are acid soils likely to occur? Explain. 



19. Distinguish between "arid," "semi-arid," "sub-humid" and "humid" 



climates. 



20. In which ones of these have you lived? 



