SOIL AND SUBSOIL 71 



QUESTIONS 



1. What are the moat obvious differences between the surface stratum and 



others? 



2. What agencies have been instrumental in producing these? 



3. What are the upper and lower limits of the subsurface stratum? 



4. Under what conditions might the subsurface be absent? 



5. What differences between it and the surface? 



6. Why is the subsoil of much importance? 



7. Upon what do the differences in subsoils largely depend? 



8. What is the origin of the tight clay stratum? 



9. Where are they found? 



10. Does limestone aid or prevent their formation? 



11. What are some objections to tight clay? 



12. What are the methods of improvement? 



13. How is hardpan formed? 



14. How may hardpan be destroyed? 



15. Give differences in subsoils of humid and arid regions. 



16. What is meant by "raw" soil material? 



17. What effect does weathering have on subsoil? 



18. How do humid and arid soils differ in color? Why? 



19. How is a plow sole formed? 



20. What are the remedies for it? 



