When one has continually seen and heard these falls, it is easily understood why the glaciers are laden with moraines. The wonder is, not that they are sometimes so great, but that they are not always greater. Irrespective of lithological considerations, one knows that this débris cannot have been excavated _by_ the glaciers. The moraines are _borne_ by glaciers, but they are _born_ from the ridges. They are generated by the sun, and delivered by the frost. “Fire,” it is well said in Plutarch’s life of Camillus, “is the most active thing in nature, and all generation is motion, or at least, with motion; all other parts of matter without warmth lie sluggish and dead, and crave the influence of heat as their life, and when that comes upon them, they immediately acquire some active or passive qualities.”(162) 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.(163) 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; 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 those of glaciers upon rocks, are as follow. The former take advantage of cracks, fissures, joints, and soft places; the latter do 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 produce constantly _diminish_, because the area of the surfaces operated upon becomes less and less, as they become smoother and flatter.