GLACIERS, a name given to extensive fields of ice amongst the Alps. Mr Coxe observes of these mountains in general, that they are composed of many parallel chains, the highest of which occupy the centre, and the others gradually diminish in proportion as they recede from thence. The central chain appears covered with pointed rocks, all parts of which, that are not absolutely perpendicular, he hid under perpetual snow and ice even in summer. On each side of this ridge are fertile and cultivated valleys, interspersed with numerous villages, and watered by numerous streams. The elevated peaks of the central chain are covered with snow; but their declivities, excepting those which are extremely steep, have all a covering of ice as well as snow; the intermediate parts being filled with vast fields of ice, terminating in the cultivated valleys above mentioned. The same phenomena, though on a smaller scale, occur in those chains which are at a distance from the principal one. In those which are most remote, no ice, and scarcely any snow, is observed, unless upon some of the most elevated summits; and the mountains diminishing in height and ruggedness, appear covered with verdure, until at last they terminate in small hills and plains.

Thus the glaciers may be divided into two sorts; one occupying the deep valleys situated in the bosom of the Alps, and distinguished by the name of ice valleys; the other being those which clothe the declivities and sides of the mountains. These two kinds of glaciers are distinguished by Mr Coxe into the upper and lower glaciers.

The lower glaciers are by far the most considerable, some of them extending several leagues in length. They do not communicate with each other, as has been generally supposed, few of them being parallel to the central chain; but, stretching mostly in a transverse direction, they are bordered at the higher extremity by inaccessible rocks, and at the lower extend into the cultivated valleys. The thickness of the ice varies in different parts. In the Glacier des Bois, which extends more than fifteen miles in length, and upwards of three in breadth, Saussure found it generally from eighty to a hundred feet; but he was credibly informed, that in some places it was not less than six hundred feet, and even more. These vast masses of ice usually rest on an inclined plane; where, being pushed forward by their own weight, and but weakly supported by the rugged rocks beneath them, they arc intersect-ed[7:10:530] by large crevices, and have an appearance of walls, pyramids, and the like, according to the position of the eye in viewing them. In those parts, however, where they lie upon even ground, or have only a gentle inclination, the surface of the ice is nearly uniform, the crevices being few and narrow, and the glacier being crossed by travellers on foot without any difficulty. The surface of the ice is rough and granulated, so that people may walk upon it, excepting at such places as have a steep descent. It is opaque, full of small bubbles about the size of a pea, very porous, and greatly resembles a mixture of snow and water congealed. A vast quantity of stones and earth falls down from the mountains upon the glaciers, and is by them thrown off on each side according to the descent of the ice. The place upon which∙these rest is harder and more elevated than the rest of the ice, and is very difficult to walk upon; the earth is likewise laid upon them in such regular heaps, that it appears to have been done by art. This collection of earths and stones is termed by the natives the moraine.

The upper glaciers may be subdivided into those which cover the summits, and those which extend along the sides of the Alps. Those upon the very summits, however, though they have the appearance of ice, are not so in reality, but consist entirely of snow hardened by the extreme cold. Saussure found that which covered the top of Mont Blanc to be penetrable, though with difficulty, by a stick; but below this hard crust was a soft snow without coherence. The sides are covered with a mixture of ice and snow, produced by the power of the summer sun in dissolving the snow, which afterwards congeals into hard ice.

Several conjectures have been hazarded concerning the formation of these extraordinary bodies of ice. Coxe agrees with Gruner in opinion, that they are produced by the continual dissolution of the snow in summer, and its congelation by the succeeding frosts. Hence, on the summits of the mountains, where the sun has very little power, the glacier is soft, and contains no ice; but as we descend the mountains the consistence becomes firmer, because there is a considerable mixture of snow water, the congelation of which augments the hardness; and in the valleys, the glacier is hardest of all, because the portion of water is there much superior to that of the snow. Hence it seems plain that the glaciers derive their origin from the melting of the snow on the upper parts of the mountains, and the congelation of the water as it advances; and to this cause Saussure adds the quantity of snow which often rolls down into the valleys, and congeals along with the water just mentioned.