VIII RIVERS AND LAKES 323 



watercourse made by last night's rains up to 

 the greatest valleys of all. 



These considerations, however, do not of 

 course apply to such depressions as those 

 of the great oceans. These were probably 

 formed when the surface of the globe began 

 to solidify, and, though with many modifica- 

 tions, have maintained their main features 

 ever since. 



ON THE CONFIGURATION OF VALLEYS 



The conditions thus briefly described repeat 

 themselves in river after river, valley after 

 valley, and it adds, I think, very much to the 

 interest with which we regard them if, by 

 studying the general causes to which they are 

 due, we can explain their origin, and thus to 

 some extent understand the story they have 

 to tell us, and the history they record. 



What, then, has that history been ? The 

 same valley may be of a very different char- 

 acter, and due to very different causes, in dif- 

 ferent parts of its course. Some valleys are 

 due to folds (see Fig. 41) caused by subterra- 



