atisfactory. It is well known that the chief factors in the
production of glaciers are moisture and cold. Cold alone is not
sufficient; neither is moisture, unless we can precipitate it in the
form of snow. Cold is opposed to the production of moisture, and this is
a flaw in the argument presented by the last theory, unless we can
couple with it another set of conditions which we will discuss later.

The solution, if it is ever reached, is perhaps more likely to be found
in the realm of meteorology than geology.

It is unnecessary to change the conditions of temperature or the amount
of moisture now existing in order to produce the great glacier again,
provided this moisture could be precipitated, enough of it, in the right
place as snow. For instance, if in Switzerland, where the conditions are
nearly balanced, the annual precipitation could be slightly increased we
should have a condition that would precipitate more snow in winter than
would melt in summer. And the glaciers would gradually accumulate in
size until they would fill the valleys and gorges to the same extent as
formerly prevailed. There only needs to be such a change in the
meteorological conditions as will cause a greater precipitation in that
part of the globe favorable to glaciers, as, for instance, in the
northern part of North America toward Alaska. This might be produced by
a change in the conditions of the equatorial current, so that
evaporation would be more rapid in the northern Pacific than it now is.
When we consider that evaporation increases in proportion as the heat
increases, we can see that heat is just as important a factor in the
production of glaciers as cold. If evaporation could be increased in the
Pacific Ocean west of Alaska, which would be carried by the wind over
the mountains upon the land, and precipitated as snow, the great
glaciers in that region would begin to grow instead of gradually
receding, as is the case at present, and this without any change in the
temperature of the world as a whole or in the amount of heat received
from the sun. One can readily see how changes in the elevation of the
bottom of the ocean would have such an effect upon the tropical stream
as would either increase or decrease the temperature of the thermal
river that flows up the western coast of Alaska.

Whatever may have been the cause that created the great ice age in North
America, so that a sheet of ice covered considerably more than half of
the