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§ 17.-Glaciers; Crevices.

it has concreted into ice, the slope of the mountain-sides, and the descent of the valleys in which the glaciers lie, serve as inclined planes, down which the ice slides by the force of gravity, assisted by the melting on its under surface, which prevents any adhesion to the rock below it. Indeed the German word Gletscher comes from glitschen, to glide. Hugi, in one of his journeys, found his way under a glacier, by following the bed of a dried-up torrent which passed below it. He wandered about beneath the ice for the distance of a mile. The ice was everywhere eaten away into dome-shaped hollows, varying from 2 to 12 feet in height, so that the whole mass of the glacier rested at intervals on pillars or feet of ice, irregular in size and shape, which had been left standing. As soon as any of these props gave way a portion of the glacier would of course fall in and move on. A dim twilight prevailed in these caverns of ice, not sufficient to allow one to read, except close to the fissures which admitted the day-light from above. The intense blue of the mass of the ice contrasted remarkably with the pure white of the icy stalactytes, or pendents descending from the roof. The water streamed down upon him from all sides, so that after wandering about for 2 hours, at times bending and creeping to get along under the low vaults, he returned to the open air, quite drenched and half frozen.

The nature of the upper surface of the ice depends upon that of the ground on which it rests; where it is even or nearly so, the ice is smooth and level; but whenever the supporting surface becomes slanting or uneven, the glacier begins to split and gape in all directions. As it approaches a steeper declivity or precipice the layers of ice are displaced, up-heaved, and squeezed one above another; they rise in toppling crags, obelisks, and towers of the most fantastic shapes, varying in height from 20 to 80 feet Being unequally melted by the wind and sun, they are continually tottering to their fall, either by their own weight or the pressure of other masses, and tumbling headlong, are shivered to atoms with a roar like thunder.

The glaciers assume this fractured character only when the foundation on which they rest is very uneven, generally near their lower extremity, when they begin to bend down towards the valley.

The crevices, or fissures, which traverse the upper portion of the glacier, before it becomes entirely fractured and disruptured, run in a transverse direction, never extending quite across the ice-field, but narrowing out at the extremities, so that when they gape too wide to leap across they may generally be turned by following them to their termination. These rents and fissures are the chief source of danger to those who cross the glaciers, being often concealed by a treacherous coating of snow, and many a bold chamois-hunter has found a grave in their recesses. Ebel mentions an instance of a shepherd who, in driving his flock over the ice to a high pasturage, had the misfortune to tumble into one of these clefts. He fell in the vicinity of a torrent which flowed under the glacier, and,

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§ 17.-Glaciers; Crevices.

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by following its bed under the vault of ice, succeeded in reaching the foot of the glacier with a broken arm. More melancholy was the fate of M. Mouron, a clergyman of Grindelwald: he was engaged in making some scientific researches upon the glacier, and was in the act of leaning over to examine a singular well-shaped aperture in the ice, when the staff, on which he rested, gave way; he was precipitated to the bottom, and his lifeless and mangled body was recovered from the depths of the glacier a few days after.

These crevices, though chiefly formed mechanically by the movement of the glacier to fill up vacancies, and the unequal pressure of different parts, are greatly assisted by the action of the sun and wind. The S.E. wind, in Uri and among the Bernese Alps, is very instrumental in causing the glacier to split, and the loud reports thus occasioned, called by the herdsmen the growlings (brullen) of the glacier, are regarded as a sign of bad weather. The traveller who ventures to cross the Mer de Glace of Chamouni or Bern may, at times, both hear and see the fissures widening around him. The crevices exhibit in perfection the beautiful azure blue colour of the glacier; the cause of which has not been satisfactorily accounted for. It is the same tint of ultramarine which the Rhone exhibits at Geneva, after leaving all its impurities behind it in the lake; and the writer has even observed the same beautiful tint in footmarks and holes made in fresh-fallen snow, not more than a foot deep, among the high Alps on the borders of Tyrol.

The traveller who has only read of glaciers is often disappointed at the first sight of them, by the appearance of their surface, which, except when covered with fresh-fallen snow, or at very great heights, has none of the purity which might be expected from fields of ice. On the contrary it exhibits a surface of dirty white, soiled with mud and often covered with stones and gravel. Such beds of dirt and rubbish are common to most glaciers, and are called, in German, Guffer. They are supposed to be formed in the following manner:- -the edge of the glacier receives the masses of stone and sand falling from the mountains above, produced by the disintegra tions of moisture and frost. During the summer heat the glacier shrinks away from the rocks that bound it, and carries away the rubbish lying upon it. The intervening space between the foot of the mountains and the ice is filled up by the snow of winter, which is gradually changed into ice, and receives a fresh heap of gravel from above. This again is carried forward by the shrinking of the glacier. Thus these lines of loose stones are constantly advancing, one behind another, like waves; and where the glacier from one valley joins that out of another, the heaps are often confounded and intermixed.

A singular circumstance occurs when a boulder, or large mass of rock, has fallen upon the glacier; the shade and protection from the sun's rays afforded by the stone prevents the ice on which it rests from melting, and, while the surface around is gradually diminished, it remains supported on a pedestal or table, often attaining a height

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§ 17.-Glaciers; their Advance and Retreat.

of several feet. When a leaf, insect, or such light body falls upon the ice, it gradually sinks, and at length disappears.

Another circumstance peculiar to the surface of the snow-field or upper glacier (firn) is the occurrence of Red Snow. This pheno menon, which at one time was treated with incredulity, is of common occurrence among the high Alps, and is produced by a species of fungus, called Palmella Nivalis, or Protococcus, a true vegetable, which plants itself on the surface of the snow, takes root, germinates, produces seed, and dies. In the state of germination it imparts a pale carmine tint to the snow; this increases, as the plant comes to maturity, to a deep crimson blush, which gradually fades, and, as the plant decays, becomes a black dust or mould. By collecting some of the coloured snow in a bottle, and pouring it on a sheet of paper, the form of the plant may be discovered with a microscope, as soon as the water has evaporated.

Increase and Diminution, Advance and Retreat of the Glaciers.

It has been already observed that the vacancy caused by the melting of the lower portion of the glacier is filled up by the winter snow from above. But, as may be supposed, it often happens, after mild winters and warm summers, that the supply is not equal to the void, and, vice versa, after severe winters and rainy summers, the glacier is overloaded, as it were; indeed, it is scarcely possible that an exact equilibrium of supply and consumption should be preserved. Yet it seems probable, after all that has been said on the subject, that there is no material variation either in the extent or position of the glaciers among the Alps. Instances have occurred of the sudden advance of a glacier, as în the Gadmenthal (Route 32), where a road has been destroyed by this cause, and even of the formation of new glaciers within the memory of man, as in the Upper Engadine (?), and at the base of the Titlis; but these have been followed by a similar retrocession, and the newly-formed ice-fields are rarely permanent. It is certain that, at present, both the Mer de Glace, under Mont Blanc, and the Grindelwald Glacier, appear to have shrunk, and sunk considerably below the level they once attained; but this may be merely temporary, or even only their dimensions in summer, when most reduced. Another circumstance has been lost sight of in the consideration of this subject, viz., that the erosive powers of the ice may have, in many instances, considerably enlarged the bed of the glacier.

Professor Hugi has recently made some interesting experiments and observations upon the movement and rate of progress of the glaciers. In 1829 he noted the position of numerous loose blocks lying on the surface of the lower glacier of the Aar, relative to the fixed rocks at its sides. He also measured the glacier and erected signal-posts on it. In 1836 he found everything altered; many of the loose blocks had moved off and entirely disappeared, along with the ice that supported them. A hut, which he had hastily erected,

§ 17.-Glaciers; Moraines.

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to shelter himself and his companions, had advanced 2184 feet; two blocks of granite, between which it stood, then eight feet apart, had been separated to a distance of 18 feet, the beams and timbers had fallen in between them, and the nails and pieces of iron used in fastening them exhibited not the slightest trace of rust. A mass of granite, containing 26,000 cubic feet, originally buried under the snow of the firn, which was now converted into glacier, had not only been raised to the surface, but was elevated above it, in the air, upon two pedestals, or pillars, of ice; so that a large body of men might have found shelter under it. A signal-post, stuck into a mass of granite, had not only made as great an advance as the hut, but the distance between the two had been increased 760 feet by the expansion of the glacier. The mass of the glacier had grown or increased near the point where it begins to deseend 206 feet; lower down there was less augmentation perceptible. The advance of the ice-field of the Mer de Glace is calculated at between 400 and 500 feet yearly, and for 8 or 10 years past, the mass of the glacier has been shrinking and retiring gradually.

At the extremity of almost all glaciers a high transverse ridge of rubbish, called The Moraine, exists; it consists of fragments of rock. which have fallen from the surrounding mountains, the transported debris of the Guffer, and of masses detached by the glacier itself. These are heaped up sometimes to a height of 80 or 100 feet. Not unfrequently there are 3 or 4 such ridges, one behind another, like so many lines of intrenchment. The broken stones, mud, and sand, mixed with shattered fragments of ice, of which they are composed, have an unsightly and shabby appearance, being perfectly barren of vegetation; but each heap is, as it were, a geological cabinet, containing specimens of all the neighbouring mountains. The glacier, indeed, seems to have a natural tendency to purge itself from impurities, and whatever happens to fall upon it is gradually discharged in this manner. It likewise exerts great mechanical force, and, like a vast millstone, grinds down, not only the rock which composes its channel, but all the fragments interposed between it and the rock; forming, in the end, a sort of stone-meal. The extent of the moraine depends on the character of the strata of the mountains around the glacier: where they are of granite, or other hard rock, not easily decomposed by the weather, the moraine is of small extent; and it is largest where the boundary rocks are of brittle limestone and fissile slate. Recent researches of Swiss naturalists (Agassiz and Charpentier) have discovered extensive moraines, not only in the lower part of the Vallais, but even on the shores of the Lake Leman, at a height of not more than 200 or 300 feet above it; clearly proving that, during some anterior condition of our planet, the valley of the Rhone was occupied by glaciers, in situations at present 40 or 50 miles distant from the nearest existing ice-field, and 3000 or 4000 feet below it.

It is highly interesting to consider how important a service the glaciers perform in the economy of nature. These dead and chilly

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§ 18. Avalanches and Snow-Storms.

fields of ice, which prolong the reign of winter throughout the year, are, in reality, the source of life and the springs of vegetation. They are the locked-up reservoirs, the sealed fountains, from which the vast rivers traversing the great continents of our globe are sustained. The summer heat, which dries up other sources of water, first opens out their bountiful supplies. When the rivers of the plain begin to shrink and dwindle within their parched beds, the torrents of the Alps, fed by melting snow and glaciers, rush down from the mountains and supply the deficiency; and, at this season (July and August), the rivers and lakes of Switzerland are fullest.

During the whole summer, the traveller who crosses the glaciers hears the torrents rustling and running below him at the bottom of the azure clefts. These plenteous rills gushing forth in their subglacial beds, are generally all collected in one stream, at the foot of the glacier, which, in consequence, is eaten away into a vast domeshaped arch, sometimes 100 feet high, which gradually increases, until the constant thawing weakens its support, and it gives way and falls in with a crash. Such caverns of ice are seen in great perfection in some years, at the source of the Arveyron, in the valley of Chamouni, and in the glaciers of Grindelwald. The streams issuing from glaciers are distinguished by their turbid, dirty-white, or milky colour.

18. AVALANCHES AND SNOW-STORMS.

"The avalanche,-the thunderbolt of snow."-Byron. Avalanches (Germ. Lawinen) are those accumulations of snow which precipitate themselves from the mountains, either by their own weight or by the loosening effects of the sun's heat, into the valleys below, sweeping everything before them, and causing, at times, great destruction of life and property. The fearful crash which accompanies their descent is often heard at a distance of several leagues.

The natives of the Alps distinguish between several different kinds of avalanches. The staub-lawinen (dust avalanches) are formed of loose fresh-fallen snow, heaped up by the wind early in the winter, before it has begun to melt or combine together. Such a mass, when it reaches the edge of a cliff or declivity, tumbles from point to point, increasing in quantity as well as in impetus every instant, and spreading itself over a wide extent of surface. It descends with the rapidity of lightning, and has been known to rush down a distance of 10 miles from the point whence it was first detached; not only descending one side of a valley, but also ascending the opposite hill, by the velocity acquired in its fall, overwhelming and laying prostrate a whole forest of firs in its descent, and breaking down another forest, up the opposite side, so as to lay the heads of the trees up the hill in its ascent.

Another kind of avalanche, the grund lawinen, occurs in spring,

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