532 THE FEESH-WATEE LOCHS OF SCOTLAND 
of the Caspian Sea, according to Knipovitsch,^ are found nowhere 
else in the world. In its general character the fauna recalls that of 
a fresh- water lake rather than that of a true sea. Fresh-water fish, 
Crustacea, and many plankton organisms met with in lakes and rivers 
are found ; but there are also many typical marine organisms, which 
are not new arrivals but old inhabitants.- G. O. Sars believes that 
the Caspian may be considered as a centre of creation for plankton 
Crustacea, and thinks that this evolution is still going on.^ Seals 
and sturgeons are among the vertebrates represented ; they are relics 
of the time when the Caspian Sea was united with the Black Sea, 
and probably also with the Sea of Aral, to form an immense sea, which 
had obtained its fauna from the ocean at a still more ancient time. 
The character of the fauna of the Caspian Sea changed in accordance 
with the lesser degree of salinity and the almost complete isolation 
of the basin. It became more and more peculiar, although 24'5 per 
cent, of the species are still met with in the Black Sea.* What is 
especially interesting is that the species common to the two seas are just 
those species which characterise the fauna of the shallow waters of the 
Black Sea ; but as the water of the Caspian is comparatively fresh, 
and is not exposed to the invasion of foreign species from the 
Mediterranean, these forms are not limited to the estuaries of 
rivers, as in the Black Sea, but are found everywhere in the upper 
waters. The fauna of the Caspian Sea may be regarded as an ancient 
fauna relatively only slightly modified since remote times, the con- 
ditions of existence in the basin remaining nearly uniform since 
prehistoric epochs. The northern portion of the Caspian, which 
experiences severe frosts and is too shallow to store up large amounts 
of heat in the summer, freezes for three or four months along the 
shores, but in the middle portion ice appears only when it is brought 
down by northerly winds. 
Lake Elton (or Yelton) is situated in the northern part of the 
Caspian depression, between the Volga and the Ural, a steppe region, 
studded with salt lakes, and so largely encrusted with salt that the 
rivers emptying themselves into these lakes are in some cases strongly 
saline. It is fed by the river Charysacha, which has 5 per cent, of 
saline constituents in its waters — that is, nearly a half more than the 
waters of the ocean — and is estimated to contribute nearly 22,000 
tons of salt every year to the lake. From Lake Elton and the 
' See Schokalsky and Schmidt, J.jjerew sur les Exijlorations scientijiques des Mers 
et des Eaux douces de l'Em2)irerusse, Section scientifique, Expos. Maritime Internat., 
Bordeaux, 1907, p. 34. 
2 See p. 358. 
3 "On the Polyphemidse of the Caspian Sea," A7in. Mus. Zool. St. Petersh., 
t. vii. p. 31, 1902. 
^ See Schokalsky and Schmidt, oj). cit, p. 35. 
