MODERN CHANGES IN THE SURFACE OF RUSSIA. 
565 
But whether the tchornozem was originally the residue of a sea, or of great 
internal lakes, we specially dwell upon the probability, that during the elevation 
of the tracts occupied by it, the mire from which it has been derived, being then 
in a putrescent state, acquired its nitrogen and possibly in part its colour, from the 
decomposition of aqueous plants and microscopic animals, the remains of which 
may yet be looked for. Although, therefore, we would not be held to maintain, 
that the sea necessarily covered all the tracts now occupied by black earth, or that 
this substance was necessarily derived from the black Jurassic shale, we distinctly 
assert, that, from its composition and distribution, it must have been formed under 
water. 
Modern Changes in the surface of Russia in Europe. — The former sea-bottoms of 
European Russia having been, as we believe, desiccated, and converted by elevation 
into a continent, we proceed to consider the changes which have since taken place, 
and are still occurring on the surface of this great mass of land. We have already 
stated, that the scratches on the rocks, the great fissures now occupied by the 
northern lakes, and the course of the remotely-drifted materials (as far as the flat 
regions of Russia in Europe are concerned), have nearly all common and undeviating 
directions. During the modern epoch, however, a new order of operations has 
arisen. The detritus is now carried down in every direction by the existing water- 
courses, wherever the inclination of the country favours such transport. In truth, 
some materials which were formerly transported from north to south, are annually 
carried back a part of their journey to the north, and others which had equally 
travelled from the north, are borne both to the east and west. The banks of most 
of the rivers in northern and central Russia consist, in fact, of the foreign drift 
which has been described ; and hence it is evident, that on mouldering away, these 
accumulations must fall into the water, the northern erratics thus often becoming 
imbedded in the winter’s ice. In the spring, when the ice is broken up, many of 
these blocks are occasionally borne in small floes, which, when they get into the 
central current, will follow the stream for a certain distance, until stranding on its 
bottoms or sides, they melt and deposit their stony loads. The protrusion of an 
irregularity or rock in the bed of a stream, having once given rise to the accumu- 
lation of such materials, the impediments to navigation are periodically increased 
by the accession of fresh loads of boulders. In this manner, blocks which had 
been transported by the old erratic drift to the edge of the Valdai Hills, are 
brought back northwards by the currents of the Volkof and the Msta. The great 
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