298 THE EARTH'S SURFACE AND PLANT LIFE 



is not of the same composition as that of the underlying 

 rock ; it must have been transported. 



Sometimes the end of a glacier remains comparatively 

 stationary over an area for a long time, owing to the fact 

 that the advance of the ice is just about balanced by the 

 melting. In this case the morainic material which has 

 collected on the top of the glacier is deposited, forming 

 irregular heaps of bowlders, gravel, and sand, with inclosed 



BOWLDERS AND SAND LEFT BY A RETREATING GLACIER 



hollows between. When the glacier has retreated, ponds 

 and lakes are formed in the depressions, and streams wander 

 about in the low places between the morainic heaps, receiv- 

 ing the overflow of some of the lakes and ponds. The 

 arrangement of the streams is unsymmetrical and without 

 order. The whole surface is a hodge-podge of glacially 

 dumped material a terminal moraine country. It was 

 this sort of country that made the East Prussian campaign 

 of the World War so difficult for both Russians and Germans, 

 and rendered the final defeat of the Russians so disastrous. 



