50 THE BOTTOM OF THE SEA. 



When the interior sea is the bottom of a bo,sin 

 without issue, either the supply of water by means 

 of rains and rivers must equal in volume that which 

 is lost by evaporation, or the sea must gradually dry 

 up. Tiie Caspian and the Dead Seas are both examples 

 in point. The first is surrounded by ealt steppes, 

 where it is easy to discover traces of the lecent exist- 

 ence of the waters. Its level is above 100 feet below 

 that of the Black Sea, and it is constantly decreasing 

 in extent, and is very salt. The Dead Sea is at pre- 

 sent about 1400 feet below the level of the Bed Sea ; 

 yet travellers have recognised between the two seas 

 the dried-up bed of a river, which, through causes not 

 yet ascertained, has ceased to unite them. Since that 

 epoch, the Dead Sea has not received sufficient water 

 from the Jordan to supply the loss ocasioned by eva- 

 poration ; its level has consequently sunk and its salt- 

 ness has proportionately increased, until an equilibrium 

 has been established between the supply and loss. 



There are many salt lakes, both in the Old World 

 and the New, which owe their saltness entirely to the 

 rivers which flow into them. The delivery of water is 

 increased, and the lakes overflow ; it is diminished, the 

 lake retires, and its saltness increases. When the 

 supply of water is quite insufficient to compensate for 

 evaporation, the lake dries up, and in its place is 

 seen a valley covered wath a bed of salt. 



