210 



CASPIAN SEA. 



rounded shingle and beds of sand filled with the 

 peculiar shells of this sea. From these accumula- 

 tions we may infer that the water over this area 

 had a former level higher by a hundred feet at 

 least than it has at present. The difference of level 

 between the Black Sea and the Caspian has been 

 put as high as about eighty feet, and as low as only 

 forty j but whichever may be the correct measure, 

 accumulation of water within the Aralo-Caspian 

 depression of such an amount would again unite 

 the seas, and that without the intervention of any 

 local depression of the land — a course somewhat 

 too often invoked by the geologist to explain such 

 changes. 



The Caspian, having no outlet, should present 

 indications of a gradual increase in the depth and 

 extent, in consequence of the vast volumes of water 

 which annually flow into it. So far, however, from 

 this being the case, its mean level is constant, and 

 apparently has continued so for a considerable 

 period, as the accession from all its tributary rivers 

 is counterbalanced by the enormous evaporation of 

 that region. 



Evaporation alone is the agent engaged in re- 

 ducing the level of certain internal seas below that of 

 the adjacent ocean. But for its communication with 

 the Atlantic the Mediterranean could not maintain 

 its level, and this consideration leads to an inference 

 that the change which has taken place between 

 the present time and that at wilich the Caspian 



