WATER, AND ITS USES 51 



4. How much is included within the limits of a valley? 

 How many slopes has it? Explain the absence of streams 

 in so many of the smaller valleys ? What various names are 

 given to very small valleys ? Why have these valleys never 

 become larger? Account for the existence of valleys in 

 general. How may hills have been formed? Where hills 

 of considerable height exist what is likely to be true of the 

 nature of the material of which they are made? 



5. Where flowing water makes cuts in the earth, (a) 

 upon what factors does the rate of cutting depend; (6) 

 which parts of the surface are most readily carried away? 

 What significance is there in the muddiness of some surface 

 waters ? Under what conditions will this muddy water be- 

 come clear ? Why is it that streams made up of the surface 

 waters from the hillsides in some parts of the country are 

 clear, and quite free from sediment? What is the relation 

 of this to the fertility of those hillsides? What becomes of 

 much of the soil washed off into streams ? What is the in- 

 evitable result of the continuance of this action upon (a) the 

 fertility of farm lands ; (6) the surface level of the country ? 



