ary
period, and to exhibit not only the actual existence of land where there
was once sea, but also the extent of surface now submerged which may
once have been land, the map would still fail to express all the
important revolutions in physical geography which have taken place
within the epoch under consideration. For the oscillations of level, as
was before stated, have not merely been such as to lift up the land from
below the water, but in some cases to occasion a rise of many thousand
feet above the sea. Thus the Alps have acquired an additional altitude
of 4000, and even in some places 10,000 feet; and the Apennines owe a
considerable part of their present height to subterranean convulsions
which have happened within the tertiary epoch.

On the other hand, some mountain chains may have been lowered during the
same series of ages, in an equal degree, and shoals may have been
converted into deep abysses.[200] Since this map was recast in 1847,
geologists have very generally come to the conclusion that the
nummulitic limestone, together with the overlying fucoidal grit and
shale, called "Flysch," in the Alps, belongs to the older tertiary or
Eocene group. As these nummulitic rocks enter into the structure of some
of the most lofty and disturbed parts of the Alps, Apennines,
Carpathians, Pyrenees, and other mountain chains, and form many of the
elevated lands of Africa and Asia, their position almost implies the
ubiquity of the post-Eocene ocean, not, indeed, by the simultaneous, but
by the successive, occupancy of the whole ground by its waters.[201]

_Concluding remarks on changes in physical geography._--The foregoing
observations, it may be said, are confined chiefly to Europe, and
therefore merely establish the increase of dry land in a space which
constitutes but a small portion of the northern hemisphere; but it was
stated in the preceding chapter, that the great Lowland of Siberia,
lying chiefly between the latitudes 55 degrees and 75 degrees N. (an
area nearly equal to all Europe), is covered for the most part by marine
strata, which, from the account given by Pallas, and more recently by
Sir R. Murchison, belongs to a period when all or nearly all the shells
were of a species still living in the north. The emergence, therefore,
of this area from the deep is, comparatively speaking, a very modern
event, and must, as before remarked, have caused a great increase of
cold throughout the globe.

Upon a review,