THE REGION OF LAKES. 



82^ 



730 west of the Valaam group ; but the mean depth is estimated at no more than 

 300 feet, which would give the whole basin a volume about nineteen times greater 

 than that of Lake Geneva. The amount, however, varies considerably with the 

 seasons and years, observations continued for fourteen years showing a difference 

 of no less than 7 feet between low water and the floods. The monks of Valaam 

 assert, on the strength of an otherwise unauthenticated tradition, that the general 

 level rises and falls alternately from century to century. 



Notwithstanding the muddy contributions of such rivers as the Volkhov, the 

 water of Ladoga is generally so pure that the smallest objects lying at the 

 bottom are perfectly visible in depths of 14 or 16 feet. It is always very cold, 



Fig. 174. — Stei.i-; and Asar about Lake Sog. 

 Scale 1 : 1,200,000. 



Heic-ht in Feet 



es^ i: 



1(ju to aao. &« to 4U0. 41)0 to efivO. eeo to 820. 820 to 1 



\ StriSR. \ Asar. 

 =_ 10 Miles. 



except perhaps in August, when the temperature about the surface may occa- 

 sionally rise to 50° or 05° Fahr. But even in July it is scarcely safe to drink 

 it, and at the thaw towards the end of May the surface water is about 2° above 

 freezing point. The temperature between the surface and lower depths usually 

 varies less than 1°, the latter being somewhat higher in winter, when the lake is 

 ice-bound. Lying somewhat south and to the west of Onega, it remains frozen for 

 a shorter period, usually about one hundred and twenty days, from the middle of 

 December. Some of the central parts occasionally remain open throughout the year, 

 whereas Onega is nearly always completely ice-bound for one hundred and fifty-six 

 days. But sufficient air is still retained in the lower depths of these basins to keep 

 their fauna alive during the winter season. Both of them are inhabited by a seal 



