a and land, we know
that there is annually some small variation in their respective
geographical positions, and that in every century the land is in some
parts raised, and in others depressed in level, and so likewise is the
bed of the sea. By these and other ceaseless changes, the configuration
of the earth's surface has been remodelled again and again, since it was
the habitation of organic beings, and the bed of the ocean has been
lifted up to the height of some of the loftiest mountains. The
imagination is apt to take alarm when called upon to admit the formation
of such irregularities in the crust of the earth, after it had once
become the habitation of living creatures; but, if time be allowed, the
operation need not subvert the ordinary repose of nature; and the result
is in a general view insignificant, if we consider how slightly the
highest mountain-chains cause our globe to differ from a perfect sphere.
Chimborazo, though it rises to more than 21,000 feet above the sea,
would be represented, on a globe of about six feet in diameter, by a
grain of sand less than one-twentieth of an inch in thickness.

The superficial inequalities of the earth, then, may be deemed minute in
quantity, and their distribution at any particular epoch must be
regarded in geology as temporary peculiarities, like the height and
outline of the cone of Vesuvius in the interval between two eruptions.
But although, in reference to the magnitude of the globe, the unevenness
of the surface is so unimportant, it is on the position and direction of
these small inequalities that the state of the atmosphere, and both the
local and general climate, are mainly dependent.

Before considering the effect which a material change in the
distribution of land and sea must occasion, it may be well to remark,
how greatly organic life may be affected by those minor variations,
which need not in the least degree alter the general temperature. Thus,
for example, if we suppose, by a series of convulsions, a certain part
of Greenland to become sea, and, in compensation, a tract of land to
rise and connect Spitzbergen with Lapland,--an accession not greater in
amount than one which the geologist can prove to have occurred in
certain districts bordering the Mediterranean, within a comparatively
modern period,--this altered form of the land might cause an interchange
between the climate of certain parts of North America and of Europe,
which lie in corresponding