POOLS AND LAKES 323 



Switzerland has had its narrow eastern end filled, for a 

 distance of fifteen or more miles, with the coarse sediment 

 brought down by the Rhone. The whole basin of the 

 lake has been covered to an unknown depth by the finer 

 sediment. The outlet to a lake tends to wear away its 

 bed, but it does this slowly, as it has little sediment with 



SUNSET ON GREAT SALT LAKE. 



which to scour. Thus lakes are being constantly both 

 filled and drained, and so are comparatively short-lived 

 features of the earth. Rivers which have lakes along their 

 courses must be young as otherwise they would have filled 

 or drained the lakes. 



Lakes are very important features to man. They filter 

 river water so that rivers emerging from lakes are clear. 

 Where the Rhone enters Lake Geneva, it is turbid and 



