If the Alps were granted a perfectly invariable temperature, if they were no longer subjected, alternately, to freezing blasts and to scorching heat, they might more correctly be termed 'eternal.' They might still continue to decay, but their abasement would be much less rapid.
When rocks are covered up by a sheet of glacier they do enjoy an almost invariable temperature. The extremes of summer and winter are unknown to rocks which are so covered up,—a range of a very few degrees is the most that is possible underneath the ice.[1] There is, then, little or no disintegration from unequal expansion and contraction. Frost, then, does not penetrate into the heart of the rock, and cleave off vast masses. The rocks, then, sustain grinding instead of cleaving. Atoms, then, come away instead of masses. Fissures and overhanging surfaces are bridged, for the ice cannot get at them;[2] and after many centuries of grinding have been sustained, we still find numberless angular surfaces (in the lee-sides) which were fashioned before the ice began to work.
The points of difference which are so evident between the operations of heat, cold, and water, and the action of glaciers upon rocks, are as follow. The former take advantage of cracks, fissures, joints, and soft places; the latter does not. The former can work underneath overhanging masses; the latter cannot. The effects produced by the former continually increase, because they continually expose fresh surfaces by forming new cracks, fissures, and holes. The effects which the latter produces constantly diminish, because the area of the surfaces operated upon becomes less and less, as they become smoother and natter.
What can one conclude, then, but that sun, frost, and water, have
- ↑ Doubtless, at the sides of glacier-beds, the range of temperature is greater. But there is evidence that the winter cold does not penetrate to the innermost recesses of glacier-beds in the fact that streams continue to flow underneath the ice all the year round, winter as well as summer, in the Alps and (I was informed in Greenland) in Greenland. Experimental proof can be readily obtained that even in midsummer the bottom temperature is close to 32° Faht.
- ↑ See pp. 143-4.
