RIDGES ON THE BANKS OF LAKES FORMED BY ICE. 
5G9 
we had ever seen on lake or river-banks in the British Isles and Western Europe, 
the three ridges must be connected with ancient lacustrine conditions, and that 
however produced, they would be found to indicate, that in former periods of our 
own sera (long subsequent to the deposit of the northern blocks, none of which, 
as we have said, are found in this local detritus) the Lake Onega occupied a much 
wider space, and stood at much higher levels (c cc), from which it had been suc- 
cessively let off to its present state. The modern glacial action of the Dwina sub- 
sequently seen, explained to us, indeed, very perfectly, how during more extended 
glacial action on its banks, the vast Lake Onega might have produced the more 
striking ledges of Petrozavodsk ; and thus we were led to believe, that the fresh- 
water lakes of the interior of Russia had been drained off at intervals by successive 
elevations of the land, and that the present lakes are but the remnants of former 
and much more extensive waters, which stood at higher levels. A traveller from 
the Alps, well-versed in the phenomena of glaciers, but unacquainted with the 
peculiar glacial action of Russia, especially of that which we detected on the 
Dwina, might perhaps, on seeing these ledges near Petrozavodsk, have identified 
them with Swiss “ moraines,” and, honestly imbued with his own theory, might 
have so written as to lead others to adopt his views. Now, we refer these ledges 
to a natural operation common to the extreme climate of Northern Russia, which 
in the expansion of water and the rupture of ice, frequently dislodges whole layers 
of stone, and piles them up in a broken talus above the ordinary edge of the lake 
or river, and even, as proved by M. Bbhtlingk, in the case we have cited, leaves 
large blocks suspended in the lower forks of the trees. In furtherance of this view 
it may be stated, that, for a long time, all European Russia must have been much 
more extensively covered with water than at present. A mere inspection of the 
great detailed map of the Noi’th of Russia, in which so many lakes, some of them 
already half-dried up, are laid down, would lead the geographer to the same con- 
clusion. In short, geological phenomena, ancient tradition and modern history all 
combine to establish the fact, that as a great portion of the flat and central regions 
of Russia in Europe were beneath the sea at a very recent period, so the depressions 
in the higher and rocky lands which lie to the north, must afterwards have been 
occupied by lakes, the waters of which were successively let off ; the shallower of 
such depressions having been in many instances first converted into marshes, then 
into forests, tenanted by bears, elks and other wild animals, and, lastly, into plains 
or valleys occupied by man. 
