idable as they seem to us, are
to the frozen masses of that secular winter but as the patches of snow
and ice lingering on the north side of our hills after the spring has
opened; let us expand them in imagination till they extend over half the
continent, and we shall have a sufficiently vivid picture of this frozen
world. And a temperature which would bring the climate of Greenland down
to the fortieth degree of latitude would not only render the field of
ice far more extensive, but thousands of feet thicker than it is at
present. The physical configuration of Greenland also confirms the
possibility of a glacial period in America, for there we have at this
moment a wide expanse of land unbroken by mountains, over which a
uniform sheet of ice moves southward, with occasional variations of its
trend according to the undulations of the surface. The interesting
accounts of Dr. Rink show that in reality Greenland is a miniature
picture of the ice-period. The immense number of icebergs breaking off
and floating southward every summer gives us some idea of the annual
waste and renewal of the ice. How can we doubt, that, when, under the
same latitude, Norway, Sweden, Scotland, England, and Ireland were
covered by sheets of ice many thousand feet in height, the ice-fields of
Greenland must have shared in the same climatic influences, and have
been much thicker and far more extensive than they are at present?

Notwithstanding the absence of lofty mountain-chains in America, we are
not wholly without the means of measuring the thickness of the
ice-sheet, by comparing it, as in Europe, with some of our highest
elevations. The slopes of the Alleghany range, wherever they have been
examined, are glacier-worn to the very top, with the exception of a few
points; but these points are sufficient to give us data for the
comparison. Mount Washington, for instance, is over six thousand feet
high, and the rough, unpolished surface of its summit, covered with
loose fragments, just below the level of which glacier-marks come to an
end, tells us that it lifted its head alone above the desolate waste of
ice and snow. In this region, then, the thickness of the sheet cannot
have been much less than six thousand feet, and this is in keeping with
the same kind of evidence in other parts of the country; for, wherever
the mountains are much below six thousand feet, the ice seems to have
passed directly over them, while the few peaks rising to that hei