CHAEACTERISTICS AND DISTRIBUTION OF LAKES 585 
Only two lakes of any importance are associated with the River River Danabe. 
Danube, viz. Lakes Balaton and Ferto in Hungary, on the right 
bank of the river. 
Lake Balaton (or Flatten See) is about 50 miles in length, by 
5 miles in average breadth, and has an area of about 250 square miles, 
oscillating with the rainfall. According to Halbfass, the maximum 
depth is 36 feet, but its average depth is only 10 feet, and therefore 
the volume of water contained in it is relatively very small, viz. 
69,700 million cubic feet. It lies 344 feet above sea-level, and in 
some places on the south its shores are low and swampy, so that 
it has frequently been proposed to drain it, and an attempt has 
been made to reclaim its banks to some extent for cultivation. 
In consequence of its slight depth, the annual range of temperature 
in the lake is very great, the extreme being from 32° to about 
82° Fahr. (0° to 27° '8 C). The water temperature follows the air 
temperature fairly closely, and sudden great changes in the latter, 
whether due to wind or the fall of rain, snow, etc., are immediately 
reflected in the former. The very marked narrowing of the lake at 
the peninsula of Tihany divides it into two separate basins, and 
uninodal seiches of each have been observed. The principal seiche 
of the whole loch is the uninodal, and the depth being very slight 
relatively to the length, the period of this is very great — from ten 
to twelve hours — but the amplitude is relatively small compared 
with other great lakes. According to Cholnoky,^ mirages are pro- 
duced when the lowest strata of air are warmer than the upper, a 
condition fulfilled on the Balaton Lake chiefly in late autumn, when 
mirages are of almost daily occurrence and are observed in the 
morning. In these mirages, objects appear to be lifted up and to 
float in the air above the surface of the lake; the imag-es are 
duplicated by the reflection below. Its waters are slightly brackish, 
in consequence of the efflorescences of salt formed on the Tertiary 
strata in the neighbourhood of the lake, and also on account of 
evaporation being at times greater than precipitation : twice in the 
last fifty years, for a period of many months the lake has had no 
outflow. The outlet of the lake to the Danube is by the Sio and 
Sarviz Rivers. The longer axis of the lake is parallel to a line of 
local volcanic action, and Judd^ concludes that it is a depression 
due to the settling down of surface rocks into a cavity emptied 
by the ejection of lava. On account of the shallowness of the 
lake, there is no pure plankton, the organisms which constitute 
the plankton in deeper lakes, though present, being mingled with 
1 Resultate der wissefischaftlichen Erforschung des Plattensees. heraurgegeben von 
der Plattensee Commission der Ung. Geogr. Gesellsch., Wien, 1897-1906, 
Geol. Mag., vol. iii. \). 6, 1876. 
