TERMINATION OF THE WHOLE SERIES OF SUBMARINE DEPOSITS. 333 
distinctly learn from him, that whilst these modern shells extend along the valley 
of the Petchora or its slopes, the higher grounds are occupied by sand, gravel and 
clay, containing here and there the bones of Mammoths. His inference, therefore, 
is that bays of the sea (such as that of the Petchora) , in which the Arctic shells 
lived, entered far into low lands, the interior of which were then inhabited by 
great extinct Mammalia ; and thus it would appear, that these last raised shelly 
oceanic deposits of the north are probably in the parallel (as to time) of the desic- 
cated steppe of Astrakhan, into which the remains of similar mammals were 
washed from the adjacent lands of those regions. For, as no regular beds with 
subfossil shells, covered with gravel and sand, like those upon the Dwina and the 
Vaga, have been observed upon the Petchora, it may, after all, be maintained, that 
the broken and superficial shells in the latter tract are marine residue of a still 
more recent elevation. 
Upon this point, however, some uncertainty must prevail, until a greater number 
of species of shells be collected and the tract be more examined. 
Conclusion of Part I. — If we at once proceeded to complete our geological sketch 
of Russia in Europe, we ought now to enter upon the discussion of the relative 
antiquity of other superficial deposits in which no sea-shells occur, such as the 
coarse detritus with foreign blocks, the “ black earth,” the Mammoth alluvia, &c. 
Before we do so, however, the structure and outlines of the great regions inha- 
bited by lost species of mammals, as well as the relation of the Ural Mountains to 
the adjacent parts of Siberia and Russia, must be explained, both anterior to and 
during those comparatively recent periods. Although, therefore, wide tracts in 
Northern Russia are covered with varied detritus of sand, clay, erratic northern 
blocks and black earth, nearly all of which were, we believe, deposited under water, 
we think it expedient, for the better comprehension of the whole subject, to defer 
that discussion. 
Some naturalists have, indeed, regarded the phenomenon of erratic blocks as 
one of a purely terrestrial nature, and have connected their transport with the 
movement of enormous glaciers over the surface of the earth. Differing as we do 
entirely from such a hypothesis, in reference to the detritus ot R-ussia, we beg to 
argue that case separately and entirely upon its own merits. Before, however, we 
venture upon this difficult question, the whole of the data must be got together ; 
for unless the reader shall have previously obtained a clear conception of the ante- 
cedent changes by which the relations of land and water were established, he will 
2 x 
