A glacier is a moving stream of ice formed in the transverse valleys and furrowed gorges of alpine chains. They are of great depth and indefinite length; and as they proceed slowly but progressively in their courses they carry along with them all the loose and prehensible mountain debris with which they come in contact. On their surface they bear every falling splinter, small and great, from the overhanging rocks. The sides and bottom of the ravines through which they pass are stripped, polished, and striated. The avalanche breaks upon them with its accumulated load; and every mountain rill, upon the melting of the snows in summer, deposits over their flanks the materials with which they are charged. Immense masses of matter are, in these various ways, collected and transported from the higher into the lower valleys: these at the outgoing of the glacier generally assume a ridge shaped form, and are termed _moraines_. The underlying blocks are all rounded and grooved: those borne on the surface are sharp and angular, until they are swept away by the torrents into the rivers, where they are in turn subjected to their smoothing operations. There can be no doubt, therefore, either as to the disintegrating or transporting power of this mighty agent. When I stood upon the Mer de Glace I saw before me, in one gorge of the mountain, a continuous stretch of icy machinery fourteen miles in length by two to three in breadth, and several hundred feet in depth. The whole was in motion; and, whether we adopt as the principle of translation the mechanical pressure of Agassiz, or the hydraulic law of Forbes, the instrument of an incalculable carriage-power was there. And yet, upon the first glance, it shrank into a span, or appeared but as a small lake, as we viewed the glacier pouring down that deep gorge of Mont Blanc; a sheer depth of dark perpendicular rocks rising on its edges many thousand feet in height; several of the sharp-pointed Aiguilles, the Grandes Mullets, and above all, the Peak de Dru, unrivaled in symmetrical grandeur, penetrating still higher into the clear sky above. How many such glaciers are dispersed through that vast alpine chain; and how immense, upon any rule of calculation, have been the earthy and rocky materials which they have borne downward in the lapse of time!