VIII RIVERS AND. LAKES 287 



near Wallingford, but the escarpment itself 

 is still gradually retreating eastward. 



So, again, the Elbe cuts right across the 

 Erz-Gebirge, the Rhine through the moun- 

 tains between Bingen and Coblenz, the Poto- 

 mac, the Susquehannah, and the Delaware 

 through the Alleghanies. The case of the 

 Dranse will be alluded to further on (p. 292). 

 In these cases the rivers preceded the moun- 

 tains. Indeed as soon as the land rose above 

 the waters, rivers would begin their work, 

 and having done so, unless the rate of eleva- 

 tion of the mountain exceeded the power of 

 erosion of the river, the two would proceed 

 simultaneously, so that the river would not 

 alter its course, but would cut deeper and 

 deeper as the mountain range gradually 

 rose. 



Eivers then are in many cases older than 

 mountains. Moreover, the mountains are 

 passive, the rivers active. Since it seems to 

 be well established that in Switzerland a 

 mass, more than equal to what remains, has 

 been removed ; and that many of the present 

 mountains are not sites which were originally 



