where the snow which falls in the winter does not entirely disappear in the course of the following year; while that which falls on the lower glacier is almost always melted in the course of the summer, and never combines with the ice. Hugi maintains that the point at which firm changes to glacier is unvariable among the Alps; and his investigations fix it at an elevation of about 7800 feet above the sea-level.*

Ebel has computed the number of glaciers among the Swiss Alps at 400, and the extent of surface occupied by them at 130 square leagues; this, however, must be but a vague estimate. They vary from a few square yards to acres and miles in extent, covering, in some instances, whole districts, filling up entirely the elevated hollows, and basins between the peaks and ridges of the Alps, and sending forth arms and branches into the inhabited valleys, below the region of forests, and as far down as the level at which corn will grow.

It is such offsets of the glacier as these that are presented to the view of the traveller from the villages of Chamouni and Grindelwald. These, however, are, as it were, but the skirts and fringes of that vast, everlasting drapery of ice which clothes all the upper region of the Alps. These fields or tracts of uninterrupted glacier have been called "Seas of Ice" (Mers de Glace, Eismeeren), and there are three such among the Swiss and Savoyard Alps which merit especial mention; that around Mont Blanc, that around the Monte Rosa and the Cervin, and that of the Bernese Oberland, around the Finster-Aar-horn. The last sends out no less than thirteen branches, and its extent has been estimated at 125 square miles.

The greatest thickness of the glaciers has been commonly estimated at between 600 and 800 feet. This is probably an exaggeration. Hugi rarely met with any thicker than 150 feet; he estimates the average depth at between 60 and 100 feet, and the greatest thickness of the Mer de Glace near Chamouni at 180 feet. Saussure had calculated it at 600 feet.

Notwithstanding their great extent and solidity, the glaciers are by no means stationary, except in the winter, although the movement is slight. They are undergoing a perpetual process of renovation and destruction. The arms or skirts descending into the lower valleys are gradually dissolved by the increased temperature which prevails at so low a level. The summer sun, aided by particular winds, acts upon the surface, so that, in the middle of the day, it abounds in pools, and is traversed by rills of water. The

* A serious error is conveyed by the common expression," the line of perpetual snow," or, "where snow never melts." There is no spot on the Alps, nor on any other snow-clad mountains, where snow does not melt under the influence of a summer sun at mid-day. It melts even on the top of Mont Blanc; but there, and on the summits of the other high Alps, the accumulation of snow is so great, and the duration of the sun's heat so short, that, in the end, there is far more snow than the sun can dissolve. What is called "the snowline," does not depend on elevation alone, and can be taken only as a very general test of it. Independent of its variation, according to the degree of latitude in which the mountain is situated, it varies on the two sides of the same mountain, being higher on the S. side than the N. The snow will likewise rest longer, and extend lower down, upon a mountain of granite than upon one of limestone, in proportion as the two rocks are good or bad con. ductors of heat, and this is the case even in contiguous mountains, members of the same

chain,

constant evaporation from every part exposed to the air produces great diminution in the upper beds; but, above all, the temperature of the earth, which is at all seasons greater than that of ice, is constantly melting away its lower surface. The vacancy thus caused from below is entirely filled up from above by the winter's snow falling upon the mountain-tops, and on the whole upper region of the High Alps, which is drifted into the higher valleys, and pressed down by its own weight. After 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, scantily transmitted through the mass of ice above, prevailed in these caverns of ice, not sufficient to allow one to read, except close to the fissures which directly admitted the day-light. 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 surface of the mountain, however hard, is subjected to an extraordinary process of grinding and polishing from the vast masses of ice constantly passing over it. The harder fragments, such as crystals of quartz interposed between the ice and the rock, act like diamonds on glass, and scratch deep and long grooves on the surface. The seat of ancient glaciers, which have now entirely disappeared, may still be discovered by the furrows left behind them on the rocks.

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, upheaved, 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.

In those cases in which the glacier passes over two or more steep declivities, these aiguilles and obelisks of ice being pressed together at the bottom of the descent, close up again, and, as soon as the surface of the mountain below them is level, assume a nearly level and compact character on their own surface.

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 Crevasses, 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 icefield, but narrowing out at the extremities, so that when they gape too wide to leap across they may always 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, 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 Vevay: 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 crevasses, though chiefly formed mechanically by the movement of the glacier to fill up vacancies, and the unequal pressure of its 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 crevasses 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

stone, dirt, and rubbish are common to most glaciers, and are called Moraines, in German Guffer, running along the glacier in parallel lines at the sides (called Moraines laterales, or Gandecker), or in the middle (Gufferlinéen, or Moraines médéanes). They are formed in the following manner. The edges of the glacier, at its upper extremity, receive the fragments of rock detached from the mountains around by the destructive agency of moisture and frost; but as the glacier itself is constantly descending, this fallen rubbish goes along with it, increased from behind by the debris of each succeeding winter, so that it forms a nearly uninterrupted line from the top of the ice-field to the bottom. Wherever the glacier from one valley meets that of another, the moraines from the two unite and form one, running down the centre of the united glacier instead of along its margin, as before. Such a confluence of moraines is well seen on the glacier of the Aar (Route 28.), and upon the great glaciers descending from Monte Rosa six or eight may be seen running side by side, each traceable to its origin by the nature of the rocks composing it.

The waters collected by the melting of the ice from all parts of the surface of a glacier often accumulate into torrents, which, traversing the glacier, at length precipitate themselves into a hole or fissure in its surface in the form of a cascade.

A singular circumstance occurs when a single 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 lowered, it remains supported on a pedestal or table, like a mushroom on a stalk, often attaining a height of several feet. The glaciers of the Aar furnish fine examples of these tables des glaciers as they are called. The surface of the glacier has been ascertained to lose 3 feet of surface by melting in as many weeks. An exactly opposite phenomenon occurs when a small stone, not more than an inch thick, rests upon the ice. As it absorbs the sun's rays with greater rapidity than the ice, not merely their surface but its entire substance is warmed through, and instead of protecting melts the ice below it, and gradually sinks, forming a hole which not unfrequently pierces the glacier through and through. 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 glacier is the occurrence of Red Snow. This phenomenon, which at one time was treated with incredulity, is of common occurrence among the High Alps, and is produced either by minute insects and their eggs, or 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.

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 versâ 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. The glaciers throughout the Alps appear to have made a general movement in advance between the years 1817 and 1822, in consequence of the coldness of the six preceding summers. The glaciers of Boissons and Bois, in the valley of Chamouni, and that of Grindelwald, in the Bernese Alps, extended so far in width as well as length as to overthrow large trees of the growth of many centuries. Afterwards they began to retreat, and soon regained their original limits. Instances have occurred of the sudden advance of a glacier, as in 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 newlyformed 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 perpetually grinding down the surface of the rock beneath it may have, in many instances, considerably enlarged the bed of the glacier.

Professors Agassiz and Hugi have recently made some interesting experiments and observations upon the movement and rate of progress of the glaciers. In 1829 Hugi noted the position of numerous loose blocks lying on the surface of the lower glacier of the Aar, relatively 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, 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 eighteen 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