5 20 THE POPULAR SCIENCE MONTHLY. 



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 aerial chill caused by the melting snow. 



The leading agent in the southward creep of the snow, how- 

 ever, 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 south- 

 erly 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 snow- 

 fall, 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 



