viii INTKODUCTION. 



Lakes are also expressive of climatic conditions. In humid regions 

 they usually overflow, are fresh, and varj' but slightl}- in area or in depth, 

 from season to season, and from century to centur3^ In arid lands they 

 are frequently without outlets and consequently alkaline and saline, and 

 fluctuate in sympathy with even the minor changes in their climatic 

 environment. 



The history of a lake begins with the origin of its basin and considers 

 among other subjects the movements of its waters, the changes it pro- 

 duces in the topography of its shores, its relations to climate, its 

 geological functions, its connection with plant and animal life, etc. It is 

 in this general order that the lakes of North America are considered in 

 the present volume. The standpoint from which the subject is treated is 

 that of the geologist and geographer, its relation to man being left to the 

 archaeologist and the historian. 



