752 
cene and pliocene shells, and all these groups are copiously developed 
and clearly recognisable by their respective mollusca. 
The geological survey of the flat regions of Russia, add the 
authors, in affording the best proof which has yet been obtained in 
any part of the world of the same eatent, that distinct forms of animal 
life were successively created and entombed in each succeeding de- 
posit, has also demonstrated that the successive obliteration of these 
classes was not caused by the outburst of contiguous plutonic rocks 
or great physical disturbances of the strata; for in this region, as 
large as the whole of those districts of the continent of Europe where 
geology has been most studied, no intrusive rocks are visible, and 
the wide-spread formations from the Silurian to the youngest ter- 
tiary, which must have occupied so vast a lapse of time in their ac- 
cumulation, as well as the beds of retired modern seas, all repose 
conformably upon each other. And yet with this regular sequence 
throughout so vast a series and the absence of any great ruptures, 
the contents of each succeeding system of older strata are as clearly 
separable from each other as in those parts of the world where 
younger rocks are incumbent on the uplifted edges of those which 
had been previously dislocated. 
But whilst they offer no traces of great and violent upheavals, 
the horizontal rocks of Russia bespeak most clearly that their sur- 
face has been so far acted upon by elevatory or subsiding movements, 
that in some tracts great thicknesses of strata are omitted. Bounded 
as this large geographical basin has been in remote epochs by the plu- 
tonic eruptions of Lapland and Sweden on the north, of the Ural on 
the east, of the granitic steppe on the south, and of the trappean 
rocks of Poland and Silesia on the west, it is possible, however, 
that the changes which were evolved in these regions may have 
affected and influenced the distribution of animal life in the great 
Muscovite depression which they surrounded. As every geological 
phenomenon in the strata of the plains of Russia indicates a sub- 
marine succession, so does the surface announce the same conditions. 
In the far northern districts the bottom of the Arctic Sea has been 
shown, by the presence of many existing species of shells, to have 
once extended over a wide tract of land, now 150 or 200 feet above 
the sea-level ; and in the south-west it is known by like proofs that 
the Caspian once covered still wider districts of the steppes. Again, 
the authors have endeavoured to show that the mammoth alluvia, 
the boulders of the North and the black earth of Central and South- 
ern Russia, have all been accumulated under water. 
In reference to the question of the transport of the northern 
‘blocks, the authors conceive that their last survey has tended very 
materially to strengthen the opinions which they previously ex- 
pressed, that such materials were carried to their present positions 
by floating icebergs liberated from ancient glaciers in Scandinavia 
and Lapland, at a period when Russia in Europe was submerged. 
The examination of the Ural has in the meantime convinced them 
of the utter inapplicability of a terrestrial glacial theory even to all 
mountainous tracts of the earth; for these mountains, the peaks of 
