CHAPTER V 



THE ICE AGE AND ITS WORK 

 II. EROSION OF LAKE BASINS 



Lakes are distributed very unequally over the various 

 parts of the world, and they also differ much in their position 

 in relation to other physical peculiarities of the surface. 

 Most of the great continents have a considerable number 

 of lakes, many of great size and situated on plateaux or in 

 central basins ; while the northern parts of Europe and 

 North America are thickly strewn with lakes of various 

 dimensions, some on the plains, others in subalpine valleys, 

 others again high up among the mountains, these latter 

 being of small size and usually called tarns. The three 

 classes of lakes last mentioned occur in the greatest pro- 

 fusion in glaciated districts, while they are almost absent 

 elsewhere ; and it was this peculiarity of general distribu- 

 tion, together with the observation that all the valley 

 lakes of Switzerland and of our own country occurred in the 

 track of the old glaciers, and in situations where the erosive 

 power of the ice would tend to form rock-closed basins, 

 that appears to have led the late Sir Andrew Ramsay to 

 formulate his theory of ice-erosion to explain them. He 

 was further greatly influenced by the extreme difficulty 

 or complete inadequacy of any possible alternative theory 



a difficulty which we shall see remains as great now as at 



the time he wrote. 



This question of the origin of the lake-basins of the 

 glaciated regions is especially interesting on account of the 

 extreme divergence of opinion that still prevails on the 

 subject. While the general facts of glaciation, the extent 



