The universal geography : earth and its inhabitants

THE REGION OF LAKES. :;2.-730 west of the Valaam group ; but the mean depth is estimated at no more than300 feet, which would give the whole basin a volume about nineteen times greaterthan that of Lake Geneva. The amount, however, varies considerably with theseasons and years, observations continued for fourteen years showing a differenceof no less than 7 feet between low water and the floods. The monks of Valaamassert, on the strength of an otherwise unauthenticated tradition, that the generallevel rises and falls alternately from century to century.Notwithstanding the muddy contributions of such rivers as the Volkhov, thewater of Ladoga is generally so pure that the smallest objects lying at thebottom are perfectly visible in depths of 14 or 16 feet. It is always very cold,Fig. 174. Stkije and Asar. about Lake Sog.Scale 1 : 1,200,000.E of 33D'Height in Feet.130 to 330. 83° to 190. 490 to 660.Strite.« 60 to S20. b-u to St=0.A£ar.except perhaps in August, when the temperature about the surface may occasionallyrise to 50° or 55° Fahr. But even in Jul}- it is scarcely safe to drinkit, and at the thaw towards the end of May the surface water is about 2° abovefreezing point. The temperature between the surface and lower depths usuallyvaries less than 1°, the latter being somewhat higher in winter, when the lake isice-bound. Lying somewhat south and to the west of Onega, it remains frozen fora shorter period, usually about one hundred and twenty days, from the middle ofDecember. Some of the central parts occasionally remain open throughout the year,whereas Onega is nearly always completely ice-bound for one hundred and fifty-sixdays. But sufficient air is still retained in the lower depths of these basins to keeptheir fauna alive during the winter season. Both of them are inhabited by a sealvol. v. v