542 THE FRESH-WATER LOCHS OF SCOTLAND 
Persian Lake Urmi (or Ummia) is situated on the plateau of LTrmi, the 
plateau. water-partiiig between the rivers flowing into the Caspian Sea and 
those flowing into the Persian Gulf, about 4100 feet above sea-level, 
and covers an area of 1750 square miles. Lord Curzon ^ has estimated 
its length at about 85 miles, its breadth at 20 or 30 miles, and its 
circumference at nearly 300 miles. Its greatest depth probably 
does not exceed 40 feet, and its average depth appears to be not 
more than 15 feet, but it varies in size with the season of the year, and 
is also subject to fluctuations occurring in longer and less regular 
cycles. Much of the rainfall of the region is lost by evaporation 
from the plains surrounding the lake, and the mountain torrents are 
redistributed among irrigation canals. 
In 1898 Giinther made a special study of the lake,^ including 
observations on the temperature, specific gravity, refractive index, 
etc. The temperature of the waters varied from 78° to 82° Fahr. 
(25°'5 to 27°*7 C.) in August, according to the direction of the wind. 
The average temperature at the surface was about 80"^ Fahr., and at 
the bottom, in 25 feet of water, some 2° lower. Owing to the great 
seasonal variation in the level of the water, the composition and specific 
gravity undergo considerable alteration during the change from the dry 
season level to that of the wet season. The salinity of a sample of 
water obtained on 16th September 1898, was 14 "85 per cent, (about 
four times as salt as the open ocean). The specific gravity of the 
water, measured on the spot with an ordinary hydrometer, was 1*11 
at the surface and also at the bottom, so that, remote from the 
mouths of fresh-water streams, the lake-water was of fairly uniform 
density. This may have been due to the thorough mixing of the 
waters bv the strong south-easterly winds which prevailed at the time 
the experiments were made. 
The water of the lake is far too salt to permit of the existence of 
any of the fresh- water fish from the inflowing rivers that may happen 
to swim out too far, so that the lake forms an efficient barrier to the 
migration of fish from one river to another. At present the organisms 
inhabiting the lake are a species of Artemia (a crustacean known 
from other brine lakes in Europe and North America), the larva of 
a species of dipterous insect, most probably allied to EpJiydra^ and 
green vegetable masses, which are described by George Murray^ 
as composed of bacterial zoogloeae of micrococci invested by a 
number of small diatoms. Several fresh-water sponges appear at 
the foot of a conical hill that rises abruptly from the margin of 
the lake. 
^ Lord Ciirzon of Kedleston, Persia, p. 532, London, 1892. 
- See Proc. Roy. Soc, vol. Ixv. p. 312, 1899. 
3 Journ. Lin?i. Soc. Load., Zool., vol. xxvii. p. 356, 1899. 
