LAKES. 



627 



Lakes arc derived from river-drainage and springs. Some are very 

 salt, owing to evaporation carrying away so much water, and leaving the 

 accumulated mineral salts. These very salt lakes are likely to dry up, as 

 the supply of water is not equal to the demands of evaporation. Floating 

 islands appear and disappear on many lakes. Derwentwater is one instance. 

 On the uses of lakes and rivers it would be superfluous to dwell. We are 

 more concerned to examine their influence on climate, and in this sense 

 we must also consider mountains. But we will now group all the pheno- 

 mena of the air and water, and their effect upon climate, under "Meteorology" 

 in the chapters next following. 



