Page:Popular Science Monthly Volume 38.djvu/536

520 at hand. The wind thus seems to play a double role in conveying cold southward—one through the direct carriage of the snow, the other through the aërial chill caused by the melting snow.

The leading agent in the southward creep of the snow, however, is the glacier, and its offspring, the iceberg. The glacier is due to an important relation of the snows to the solar rays; namely, to that in which the stored cold is too great in quantity for the whole year's supply of heat to overcome, so that a part of each year's snow-fall is carried over to the next. There can be no glacier where the whole of the snow-fall is melted, even if the heat of the whole season is occupied in melting it; but, wherever a portion of the snow-supply is carried over from winter to win-, ter, glacial action is inevitable. In every such case the snows must steadily accumulate, their thickness increasing year by year. The growing pressure converts the under portions of this snow mass into ice, and this, through its normal plasticity, is forced by the weight upon it toward lower levels or more southerly regions, until it reaches its limit at that point in which the melting power of the sun balances the growth of the glacier.

The localities of glacial action are, therefore, the peaks and valleys of lofty mountains and the elevated regions of the frigid zones, or the lower regions of the latter in localities of abundant snow-fall. In all such places the heat derived from the sun is insufficient to melt the snow, which, therefore, necessarily creeps to warmer regions in the form of glacial ice. The principal seats of glacier formation in the north frigid zone are Greenland and Alaska. The remaining surface of northern America and that of Siberia are too low in elevation, and perhaps too light in snowfall, to permit any important glacial effect. Of the northern glacier-forming localities, Greenland is much the most important, and its refrigerating influence upon the coast lands of Europe and America is considerable. The mountains of snow which are heaped upon its elevated regions send down huge glaciers to the coast, which not only aid to chill the waters of the southward flowing currents, but send south an annual fleet of icebergs, borne upon these cold currents, and making their way far into the Gulf Stream domain of the Atlantic. No small quantity of the heat supply of this warm current is exhausted in melting the floating mountains of ice. This heat is lost to the northern continents, and their temperature reduced in consequence, possibly much more than we imagine. There is thus an annual battle between the earth's stores of heat and cold. The former, in the condition of warm ocean currents, makes its way far north. The latter, brought down from mid-air by the snows, and locked up in the glaciers, and their offspring—the—icebergs makes its way far south. They meet in mid-ocean, where an active conflict takes