
Parr Il. Sucr. ii §4] SALT LAKES. — B97 
between the two seas, with salt lakes, marshes, and other evidences 
to prove that the Caspian was once joined to the Black Sea, and had 
thus communication with the main ocean. In this case also there are 
proofs of considerable changes of water level. At present the surface 
of the Caspian is eighty-five and a half feet below that of the Black 
Sea. The Sea of Aral, also a salt basin, and once probably united 
with the Caspian, now rests at a level of 242-7 feet above that sheet 
of water. The steppes of South-eastern Russia are a vast depression 
with numerous salt lakes and abundant saline and alkaline deposits. 
It has been supposed that this depression continued far to the north, 
and that a great firth, running up between Europe and Asia, stretched 
completely across what are now the steppes and plains of the Tundras 
till it merged into the Arctic Sea. Seals of a species (Phoca caspica) 
which may be only a variety of the common northern form (Ph. foetida) 
abound in the Caspian, which is the scene of one of the chief seal- 
fisheries of the world.’ On the west side of the Ural chain, even at 
present, by means of canals connecting the rivers Volga and Dwina, 
vessels can pass from the Caspian into the White Sea.? 
The cause of the isolation of the Caspian and the other saline 
basins of that region, is to be sought in underground movements 
which, according to Helmersen, are still in progress, but partly, and, 
in the case of the smaller basis, probably chiefly, in a general 
diminution of the water supply all over Central Asia and the neigh- 
bouring regions. The rivers that flow from the north towards Lake 
Balkash, and that once doubtless emptied into it, now lose them- 
selves in the wastes and are evaporated before reaching that sheet 
of water, which is fed only from the mountains to the south. The 
channels of the Amur Darya, Sir Darya, and other streams bear witness" 
also to the same general desiccation.* The change, however, must 
be extremely gradual. At present the amount of water supplied 
by rivers to the Caspian appears just to balance that removed by 
evaporation, though there are slight yearly or seasonal fluctuations. 
Owing to the enormous volume of fresh water poured into it by 
these rivers, the Caspian is not as a whole so salt as the main ocean, 
and still less so than the Mediterranean. Nevertheless the inevitable 
result of evaporation is there manifested. Along the shallow pools 
which border this sea a constant deposition of salt is taking place, 
forming sometimes a pan or layer of rose-coloured crystals on the 
bottom, or gradually getting dry, and covered with drift sand. This 
concentration of the water is particularly marked in the great offshoot 
1 Another variety or species of seal inhabits Lake Baikal. For an account of the 
structures and distribution of seals see an interesting monograph by J. A. Allen in 
Miscellaneous Publications of U.S, Geological and Geographical Survey of the Territories. 
Washington, 1880. 
2 Count von Helmersen, however, has recently stated his belief that for this extreme 
northern prolongation of the Aralo-Caspian Sea there is no evidence. The shells, on 
the presence of which over the Tundras the opinion was chiefly based, are, according 
to him, all freshwater species, and there are no marine shells of living species to be met 
with in the plains at the foot of the Ural Mountains. 
3 Bull. Acad. Imp. St. Petersbourg, xxv. p. 535 (1879). 
