STREAMS AND THETR WORK 185 



9. What is a flood plain? Give examples of flood 

 plains. 



10. Describe some of the accidents which occur to 

 rivers during their life history. 



11. What is meant by a drowned river valley ? Give 

 examples of rivers having such valleys. 



12. How do you account for the fact that so many 

 of our large cities are located on rivers? 



13. Why are streams not of so much importance as 

 a means of travel as they formerly were ? 



14. How can you account for the fact that rail- 

 roads have so frequently been built along water 

 courses ? 



15. Can you think of any objections to having rail- 

 roads along water courses ? 



16. About how many acres of land are now being 

 irrigated in the United States? 



17. If possible, ascertain the value of the crops 

 grown upon this irrigated land. 



18. To what extent is water power used in the 

 United States for manufacturing purposes? 



