io8 Physical Geography. 



phorus, it might be converted into a fresh lake, if the 

 supply of river water were sufficient to overbalance 

 evaporation and secure an overflow. At present a great 

 body of salt water is constantly being poured out through 

 the Bosphorus, and its place taken by the fresh water 

 of rivers. Owing, however, to the uncongenial quality 

 of the freshening water, some of the Black Sea shells 

 are strangely distorted, as shown by Edward Forbes. 



Or if we take the Caspian alone as an example, we 

 have an inland brackish sheet of water, with a present 

 area of 178,866 square miles, the surface of which is 

 83 feet below the level of the Black Sea. This, accord- 

 ing to accepted zoological and physical views, was 

 once united by a narrow strait with the North Sea. 

 Changes in physical geography have taken place of such 

 a kind that the Caspian is now disunited from the 

 ocean, while its waters are still inhabited by a poor and 

 dwarfed marine molluscan fauna, and by seals. If by 

 increase of rainfall the Caspian became freshened, the 

 loss of water by evaporation not being equal to supply, 

 it would by-and-by, after reaching the point of overflow, 

 be converted into a great fresh-water lake, larger in 

 extent than the whole area now occupied by the British 

 Islands and the Irish Sea. It is even conceivable that 

 the great area of inland drainage of Central Asia, now 

 holding many salt lakes, might in the same manner be 

 so changed that all its lakes would become fresh and 

 widened in extent, thus occupying areas larger than all 

 the Old Ked Sandstone of Europe. Under these cir- 

 cumstances, in the Caspian area we should have a 

 passage more or less gradual from imperfect marine to 

 perfectly fresh- water conditions, such as I conceive to 

 have marked the advent of the Old Eed Sandstone. 

 When the whole area was fairly separated from the sea, 



