324 FIRST TEAE SCIENCE 



full of silt, but when it emerges, it is clear and without 

 sediment. Lakes also act as reservoirs for the water that 

 pours into them at the time of freshets. Rivers emerging 

 from lakes of considerable size vary little in the height of 

 their water at different seasons of the year. They are 

 without floods. The St. Lawrence illustrates this. On 

 the other hand the Ohio with its frequent and terribly de- 

 structive floods shows the effect of unrestrained run-off. 



THE DEAD SEA. - ,-- 



Lakes often form most valuable internal waterways, as 

 in the case of the Great Lakes and the Caspian Sea. 

 Lakes are also most beautiful objects on the landscape 

 and their rippling waters give joy and pleasure to thou- 

 sands. 



In some regions the rainfall is so small that the depres- 

 sions never fill up sufficiently to overflow their rims. The 

 water is evaporated from the surface as fast as it runs 

 into the lake. Thus all the salt and other soluble sub- 



