Page:The fairy tales of science.djvu/286

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that clothes the slopes undergoes a corresponding change, and at the margin of the snow we find plants resembling those of the arctic circle.

In the upper regions of the ice-world water descends from the clouds in the form of snow but never in the form of rain. The average fall of snow, in the region of the Swiss Alps, from 8000 to 10,000 feet above the level of the sea, has been estimated at sixty feet, that is to say, sufficient snow descends in one year to form a bed of this thickness. What becomes of all this frozen water? How is it that the mountains do not become topheavy? Be patient, gentle reader, we shall be in a position to answer these momentous questions soon, but at present we must confine our attention to the structure of the snow-beds that are formed on the vast tablelands of these elevated regions.

The snow-bed is generally called the névé, and is formed of layers of more or less crystalline snow, which diminish in thickness as their depth increases; in other words, each layer is thinner than that immediately above it. At a certain depth these layers can scarcely be distinguished one from another, and still lower the substance of the névé passes into clear ice. The separate layers represent each considerable fall of snow that has taken place, and their gradual consolidation arises from the percolation of water coming from above, and the pressure of fresh strata of snow which continually accumulate overhead.