Continental and Island Life [pp. 1-29]

8THE PRINCE TON RE VIEW.
countries would themselves become colder. The northern ice,
drifting down into the Atlantic, would not as now be melted
rapidly by the warm water which it meets in the Gulf Stream.
Much larger quantities of it would remain undissolved in summer, and thus an accumulation of permanent ice would take
place, along the American coast at first, but probably at length
even on the European side. This would still further chill the
atmosphere, glaciers would be established on all the mountains
of temperate Europe and America, the summer would be kept
cold by melting ice and snow, and at length all eastern America
and Europe might become uninhabitable, except by arctic animals and plants, as far south as perhaps 40~ of north latitude.
This would be simply a return of the glacial age. I have
assumed only one geographical change; but other and more
complex changes of subsidence and elevation might take place,
with effects on climate still more decisive.
We may suppose an opposite case. The high plateau of Greenland might subside or be reduced in height, and the opening of
Baffin's Bay might be closed. At the same time the interior
plain of America might be depressed, so that, as we know to
have been the case in the Cretaceous period, the warm waters of
the Mexican gulf might circulate as far north as the basins of
the present great American lakes. In these circumstances there
would be an immense diminution of the sources of floating ice,
and a correspondingly vast increase in the surface of warm water.
The effects would be to enable a temperate flora to subsist in
Greenland, and to bring all the present temperate regions of
Europe and America into a condition of subtropical verdure.
It is only necessary to add that we actually know that changes
not dissimilar from those above sketched have actually occurred
in comparatively recent geological times, to enable us to perceive
that we can dispense with all other causes of change of climate,
tho admitting that some of them may have occupied a secondary place. This will give us in dealing with the distribution of
life the great advantage of not being tied up to definite astronomical cycles of glaciation which do not well agree with the
geological facts, and of correlating elevation and subsidence of
the land with changes of climate affecting living beings. It will,
however, be necessary, as Wallace well insists, that we shall hold
8