CHAPTER VIII 



EIVEES AND LAKES 

 ON THE DIKECTIONS OF EIVEBS 



In the last chapter I have aUuded to the 

 wanderings of rivers within the limits of 

 their own valleys; we have now to consider 

 the causes which have determined the direc- 

 tions of the valleys themselves. 



If a tract of country were raised up in 

 the form of a boss or dome, the rain which 

 fell on it would partly sink in, partly run 

 away to the lower ground. The least in- 

 equality in the surface would determine the 

 first directions of the streams, which would 

 carry down any loose material, and thus 

 form little channels, which would be gradu- 

 ally deepened and enlarged. It is as difficult 

 for a river as for a man to get out of a 

 groove. 



279 



