ession of seasons we often note the occurrence of
winters during which the precipitation of snow is much above the
average, though it can not be explained by a considerable climatal
change. We have to account for these departures from the normal
weather by supposing that the atmospheric currents bring in more than
the usual amount of moisture from the sea during the period when great
falls of snow occur. In fact, in explaining variations in the humidity
of the land, whether those of a constant nature or those that are to
be termed accidental, we have always to look to those features which
determine the importation of vapour from the great field of the ocean
where it enters the air. We should furthermore note that these
peculiarities of climate are dependent upon rather slight geographic
accidents. Thus the snowfall of northern Europe, which serves to
maintain the glaciation of that region, and, curiously enough, in some
measure its general warmth, depends upon the movement of the Gulf
Stream from the tropics to high latitudes. If by any geographical
change, such as would occur if Central America were lowered so as to
make a free passage for its waters to the westward, the glaciers of
Greenland and of Scandinavia would disappear, and at the same time the
temperature of those would be greatly lowered. Thus the most evident
cause of glaciation must be sought in those alterations of the land
which affect the movement of the oceanic currents.

Applying this principle to the northern hemisphere, we can in a way
imagine a change which would probably bring about a return of such an
ice period as that from which the boreal realm is now escaping. Let us
suppose that the region of not very high land about Bering Strait
should sink down so as to afford the Kuro Siwo, or North Pacific
equivalent of our Gulf Stream, an opportunity to enter the Arctic Sea
with something like the freedom with which the North Atlantic current
is allowed to penetrate to high latitudes. It seems likely that this
Pacific current, which in volume and warmth is comparable to that of
the Atlantic, would so far elevate the temperature of the arctic
waters that their wide field would be the seat of a great evaporation.
Noting once again the fact that the Greenland glaciers, as well as
those of Norway, are supplied from seas warmed by the Gulf Stream, we
should expect the result of this change would be to develop similar
ice fields on all the lands near that oce