344 



FIRST YEAR SCIENCE 



away and so deposited on their valley floors. When the 

 supply ceased, they eroded their valleys, leaving terraces 

 along the sides. 



The region in which a river is situated may be elevated, 

 thus affecting its normal development and beginning a 

 new cycle in its history. The elevating may take place 

 over its whole drainage area or only over a part of it. 



RIVER TERRACES. 

 The river is now cutting down its former plain, leaving terraces. 



If the whole region is elevated, the energy of the entire 

 river is revived, and the river may be called a revived 

 river. 



The elevation may take place at any time during the 

 history of the river. If it takes place after the river has 

 become old and is meandering on its flood plain, the river 

 will begin afresh to cut down its valley. But as its mean- 

 dering course has been established, the trench that it now 

 cuts is not like that of a young river, but is a meandering 



