Page:Popular Science Monthly Volume 29.djvu/380

366 not be necessary to go far to the north to meet perpetual snow. For snow once fallen, or ice once formed, would never melt, but, accumulating through the ages, would force its way by its own weight equatorward until it reached a region where the heat of the sun was sufficient to melt it away. The uplifts in high latitudes intensified the results. Vice versa, when the axis became oblique, more solar heat fell within the polar circle, those regions became warmer, and the Glacial epoch departed. If these conditions—a perpendicular axis and high uplifts—could be to-day restored, the atmosphere remaining as it is, the Glacial epoch would return.

The removal of the ice was hastened by the depression of high latitude lands. This depression was very extensive. Vast tracts were submerged. In this is found, I think, the cause of the mild climate of the Champlain, while the cold (the minor Glacial epoch) that followed was due to another upward movement, or movements, comparatively limited in extent—in fact, confined mostly to Europe and Asia.

Subsequent changes left us the climate of to-day.

In the briefest possible space, I sum up as follows:

The uniformity of plant-life, regardless of latitude, to near the close of the Tertiary, indicates uniformity of biological conditions i. e., of light, or actinic force, and heat.

The former indicates that the earth's axis was approximately perpendicular—a conclusion in harmony with the belief that the moon and earth were once one body, and consequently that their axes were originally parallel.

The uniformity of temperature in high latitudes through the year is also accounted for by a perpendicular axis, and, so far as I can see, only by that.

Astronomy tells only of present conditions. As to how or when the axis took its present obliquity, it is unable to say.

Geology fixes the date by the record which solar influences have left on organic forms, and places it near or just after the close of the Tertiary.

The warmth of arctic regions—for there might have been uniformity without warmth—was due to the "double blanket" of carbonic acid and aqueous vapor.

The cold of the Glacial epoch was due to the loss of CO2 and aqueous vapor, aided by high-latitude uplifts.

The disappearance of the ice and cold was due to the earth's axis being made to incline as now, and to the reduction of the uplifts.

The warmth of the Champlain was due to depression of the land.

The second or minor ice period was due to another uplift confined to (or at least much greater in) Europe and Asia.

The depression of the land to somewhat near the present level, with present amount of CO2 and H2O in the atmosphere, resulted in present climatic conditions.