534 THE FRESH-WATER LOCHS OF SCOTLAND 
increased rapidly till 1895, and it has remained high with small 
variations since that year, the highest five-year average (to the end 
of 1906) being 1902-1906. 
In general, the thermal stratification of the deep layers is similar 
to that in fresh- water lakes. Owing to its small depth (less than 
rS per cent, of the lake-floor is covered by more than 100 feet of 
water), the surface temperature of Lake Aral varies considerably with 
the seasons, and in summer is much higher than that of the bottom. 
In winter the conditions are reversed, and consequently twice each 
year, in spring and autumn, the whole mass of water must be uniform 
in temperature. 
The fauna of the Aral Sea is but slightly affected by the degree of 
salinity of the water ; the same organisms can live in the open water, 
with a specific gravity of 1*0110, and in the bays, where the water is 
quite fresh. The fauna is related to that of the Caspian, but is 
characterised by a great poverty of species, on account of the difficulty 
of sustaining life in a comparatively salt shallow basin subject to 
great changes in temperature. The fish all belong to fresh-water 
species, and so do almost all the plankton organisms. 
Lake Balkash, in Akmolinsk, Western Siberia, lies 780 feet above 
sea-level, and is merely a relict of a former much more extensive sheet 
of water, of which Sassy k-kul and Ala-kul are also remaining parts. 
It is 340 miles in length, 50 miles in maximum breadth, with an 
area of about 7000 square miles, but it is only about 33 feet deep,^ 
and has a flat bottom. It was examined in 1903 by a Russian ex- 
pedition under Berg,^ and the temperature at the surface was found 
to be 76^*5 Fahr. (24" "7 C.) in July, while the bottom temperature 
varied very little. From the biological point of view it is as barren 
as the surrounding territories ; there are only four kinds of fish, and no 
benthonic molluscs or other invertebrates were found. The plankton 
of the lake is abundant, and similar to that of ponds. One can only 
conclude that the lake is very young, and has not had time to people 
itself The waters of Lake Balkash are quite fresh and fit for drink- 
ing, though the lake has no visible outlet, and lies in the middle of a 
steppe, where the evaporation is very great in summer, and the pre- 
cipitation very insignificant ; whereas Issik-kul, far more favourably 
situated, contains water that is much too salt to drink Berg accounts 
for this by supposing the lake to have been entirely dried up, the bed 
covered with sand, and then filled again. The lake has been rising in 
level since 1890. 
Ala-kul (called also Kurghi-Nor or Alakt-Ugul-Nor), a lake of 
Russian Central Asia, in the province of Semirietchenisk, is 40 miles 
^ See Scliokalskv and Schmidt, op. cit.,-p. 53 ; the maximum depth is given in 
E/icyd. Brit.^ 10th ed. as 135 feet. 
