[Line 130: Carry back these tidings.]
[Line 133: The sacred trio of St. Peter, St. James, and St. John.]
EXTERNAL APPEARANCE OF GLACIERS.
Thus far we have examined chiefly the internal structure of the glacier; let us look now at its external appearance, and at the variety of curious phenomena connected with the deposit of foreign materials upon its surface, some of which seem quite inexplicable at first sight. Among the most striking of these are the large boulders elevated on columns of ice, standing sometimes ten feet or more above the level of the glacier, and the sand-pyramids, those conical hills of sand which occur not infrequently on all the large Alpine glaciers. One is at first quite at a loss to explain the presence of these pyramids in the midst of a frozen ice-field, and yet it has a very simple cause.
I have spoken of the many little rills arising on the surface of the ice in consequence of its melting. Indeed, the voice of the waters is rarely still on the glacier during the warm season, except at night. On a summer's day, a thousand streams are born before noontide, and die again at sunset; it is no uncommon thing to see a full cascade come rushing out from the lower end of a glacier during the heat of the day, and vanish again at its decline. Suppose one of these rivulets should fall into a deep, circular hole, such as often occur on the glacier, and the nature of which I shall presently explain, and that this cylindrical opening narrows to a mere crack at a greater or less depth within the ice, the water will find its way through the crack and filter down into the deeper mass; but the dust and sand carried along with it will be caught there, and form a deposit at the bottom of the hole. As day after day, throughout the summer, the rivulet is renewed, it carries with it an additional supply of these light materials, until the opening is gradually filled and the sand is brought to a level with the surface of the ice. We have already seen, that, in consequence of evaporation, melting, and other disintegrating causes, the level of the glacier sinks annually at the rate of from five to ten feet, according to stations. The natural consequence, of course, must be, that the sand is left standing above the surface of the ice, forming a mound which would constantly increase in height in proportion to the sinking of the surrounding ice, had it sufficient solidity to retain its original position. But a heap of sand, if unsupported, must very soon subside and be dispersed; and, indeed, these pyramids, which are often quite lofty, and yet look as if they would crumble at a touch, prove, on nearer examination, to be perfectly solid, and are, in fact, pyramids of ice with a thin sheet of sand spread over them. A word will explain how this transformation is brought about. As soon as the level of the glacier falls below the sand, thus depriving it of support, it sinks down and spreads slightly over the surrounding surface. In this condition it protects the ice immediately beneath it from the action of the sun. In proportion as the glacier wastes, this protected area rises above the general mass and becomes detached from it. The sand, of course, slides down over it, spreading toward its base, so as to cover a wider space below, and an ever-narrowing one above, until it gradually assumes the pyramidal form in which we find it, covered with a thin coating of sand. Every stage of this process may occasionally be seen upon the same glacier, in a number of sand-piles raised to various heights above the surface of the ice, approaching the perfect pyramidal form, or falling to pieces after standing for a short time erect.
The phenomenon of the large boulders, supported on tall pillars of ice, is of a similar character. A mass of rock, having fallen on the surface of the glacier, protects the ice immediately beneath it from the action of the sun; and as the level of the glacier sinks all around it, in consequence of the unceasing waste of the surface, the rock is gradually left standing on an ice-pillar of considerable height. In proportion as the column rises, however, the rays of the sun reach its sides, striking obliquely upon them under the boulder, and wearing them away, until the column becomes at last too slight to sustain its burden, and the rock falls again upon the glacier; or, owing to the unequal action of the sun, striking of course with most power on the southern side, the top of the pillar becomes slanting, and the boulder slides off. These ice-pillars, crowned with masses of rock, form a very picturesque feature in the scenery of the glacier, and are represented in many of the landscapes in which Swiss artists have endeavored to reproduce the grandeur and variety of Alpine views, especially in the masterly Aquarelles of Lory. The English reader will find them admirably well described and illustrated in Dr. Tyndall's work upon the glaciers. They are known throughout the Alps as "glacier-tables"; and many a time my fellow-travellers and I have spread our frugal meal on such a table, erected, as it seemed, especially for our convenience.
Another curious effect is that produced by small stones or pebbles, small enough to become heated through by the sun in summer. Such a heated pebble will of course melt the ice below it, and so wear a hole for itself into which it sinks. This process will continue as long as the sun reaches the pebble with force enough to heat it. Numbers of such deep, round holes, like organ-pipes, varying in size from the diameter of a minute pebble or a grain of coarse sand to that of an ordinary stone, are found on the glacier, and at the bottom of each is the pebble by which it was bored. The ice formed by the freezing of water collecting in such holes and in the fissures of the surface is a pure crystallized ice, very different in color from the ice of the great mass of the glacier produced by snow; and sometimes, after a rain and frost, the surface of a glacier looks like a mosaic-work, in consequence of such veins and cylinders or spots of clear ice with which it is inlaid.
Indeed, the aspect of the glacier changes constantly with the different conditions of the temperature. We may see it, when, during a long dry season, it has collected upon its surface all sorts of light floating materials, as dust, sand, and the like, so that it looks dull and soiled,—or when a heavy rain has washed the surface clean from all impurities and left it bright and fresh. We may see it when the heat and other disintegrating influences have acted upon the ice to a certain superficial depth, so that its surface is covered with a decomposed crust of broken, snowy ice, so permeated with air that it has a dead-white color, like pounded ice or glass. Those who see the glacier in this state miss the blue tint so often described as characteristic of its appearance in its lower portion, and as giving such a peculiar beauty to its caverns and vaults. But let them come again after a summer storm has swept away this loose sheet of broken, snowy ice above, and before the same process has had time to renew it, and they will find the compact, solid surface of the glacier of as pure a blue as if it reflected the sky above. We may see it in the early dawn, before the new ice of the preceding night begins to yield to the action of the sun, and the surface of the glacier is veined and inlaid with the water poured into its holes and fissures during the day and transformed into pure, fresh ice during the night,—or when the noonday heat has wakened all its streams, and rivulets sometimes as large as rivers rush along its surface, find their way to the lower extremity of the glacier, or, dashing down some gaping crevasse or open well, are lost beneath the ice.