Among the inequalities of the glacier-worn surfaces which deserve especial notice, are the so-called "_roches moutonnees_." They are knolls of a peculiar appearance, frequent in the Alps, and first noticed by the illustrious De Saussure, who designated them by that name, because, where they are numerous and seen from a distance, they resemble the rounded backs of a flock of sheep resting on the ground. These knolls are the result of the prolonged abrasion of masses of rocks separated by deep indentations wide enough to be filled up by large glaciers, overtopping the summits of the intervening prominences, and passing over them like a river, or like tide-currents flowing over a submerged ledge of rock. It is evident that water rushing over such sunken hills or ledges, adapting itself readily to all the inequalities over which it flows, and forming eddies against the obstacles in its course, will scoop out tortuous furrows upon the bottom, and hollow out rounded cavities against the walls, acting especially along preexisting fissures and upon the softer parts of the rock,--while the glacier, moving as a solid mass, and carrying on its under side its gigantic file set in a fine paste, will in course of time abrade uniformly the angles against which it strikes, equalize the depressions between the prominent masses, and round them off until they present those smooth bulging knolls known as the "_roches moutonnees_" in the Alps, and so characteristic everywhere of glacier-action. A comparison of any tide-worn hummock with such a glacier-worn mound will convince the observer that its smooth and evenly rounded surface was never produced by water.