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- 
