and a lake began to form, which soon attained a considerable magnitude. It was obviously in the highest degree probable that the icy barrier would not be able to hold out long against the increasing pressure of the waters, and the sudden efflux of such a mighty volume as was collected, would as certainly desolate the Val de Bagnes. To avoid this calamity, which every day became more impending, an engineer started the bold scheme of tunnelling the rampart of ice, and was employed by the government of the canton for that purpose. This scheme, says the memoir of M. Escher upon it, “was begun on the 10th of May, and finished on the 13th of June, under the direction of M. Venetz. The gallery was sixty-eight feet long, and during its formation the workmen were exposed to the constant risk of being crushed to pieces by the falling blocks of ice, or buried under the glacier itself." The lake at this time contained at least 800 millions of cubic feet of water, which in three days was reduced to 530 millions, by the discharge from the gallery. The sequel may best be related in the words of the memoir :

"As soon as the water flowed from the lower end of the gallery the velocity of the cascade melted the ice, and thus wore away the gallery at its mouth. The water which had penetrated the crevices of the glacier caused enormous fragments of ice to fall from the lower sides of it; so that owing to these causes the body of the glacier, which formed the retaining wall of the lake, was so much diminished in thickness that the floor of the gallery was reduced from its original length of 600 to 8 feet. As soon as the cascade had cut through the cone of ice, it attacked the debris of the base of Mauvoisin, upon which the cone rested; that is to say, the torrent undermined the glacier by washing away the loose materials forming the bed of the stream, on which the mass of ice had been piled up; and having carried it off by degrees, it became able to push the soft soil from the foot of Mont Mauvoisin, and excavate for itself a passage between the glacier and the rocky beds which compose the mountain. As soon as this happened, the water rushed out, the ice gave way with a tremendous crash, the lake was emptied in half-an-hour, and the sea of water which it contained precipitated itself into the valley, with a rapidity and violence which it is impossible to describe. The fury of this raging flood was first stayed by the narrow gorge below the glacier formed between Mont Pleureur and a projecting breast of Mont Mauvoisin; here it was engulfed with such force that it carried away the bridge of Mauvoisin, ninety feet above the Dranse, and even rose several fathoms above the advanced mass of the mountains. From this narrow gorge, the flood spread itself over a wider part of the valley, which again contracted into another gorge; and in this way, passing from one basin to another, it acquired new violence, and carried along with it forests, rocks, houses, barns, and cultivated land. When it reached Le Chable, one of the principal villages of the valley, the flood, which seemed to contain more debris than water, was pent up between the piers of a solid bridge, nearly fifty feet above the Dranse, and began to attack the inclined plaue upon which the church and the chief part of the village is built. An additional rise of a few feet would have instantly undermined the village; but at this critical moment the bridge gave way, and carried off with it the houses at its two extremities. The flood now spread itself over the wide part of the valley between Le Chable and St. Branchier, undermining, destroying, and hurrying away the houses, the roads, the richest crops, and the finest trees, loaded with fruit. Instead of being encumbered with these spoils, the moving chaos received from them new force; and when it entered the narrow valley extending from St. Branchier to Martigny, it continued its work of destruction till its fury became weakened by expanding itself over the great plain formed by the valley of the Rhone. After ravaging Le Burg and the village of Martigny, it fell with comparative tranquillity into the Rhone, leaving behind it the wreck of houses and of furniture, thousands of trees torn up by the roots, and the bodies of men and of animals whom it had swept away."

It was calculated by the writer of the memoir, that the flood for the first four miles swept along at the rate of twenty miles an hour, nearly the speed of a locomotive, and furnished about 300,000 cubic feet of water every second an efflux five times greater than that of the Rhine at Basle. In six hours and a half, it arrived at the Lake of Geneva, having passed into the Rhone, a distance of forty-five miles. Among the physical alterations effected by this debacle, there was the deposition of a stratum of alluvial matter over the whole of the lower part of the Val de Bagnes. This was several feet in thickness, and was so distributed that roads were obliged to be cut through it in some places, as when the snows have blocked up our thoroughfares. There was the transportation of an immense number of isolated masses of rock to a considerable distance, some of which must have been many tons in weight. One of these, fairly projected out of the gorge of the valley into the plain, measured twenty-seven paces round, twelve feet in height, and twelve feet across in one direction, and even larger masses bore indubitable marks of having been in motion. For some time the course of the Dranse fluctuated, and when at last it settled down into a channel, it was one widely different from that which had before been followed. Captain Hall visited Martigny a few weeks after this visitation, and found every land-mark obliterated under one uniform mass of detritus, which had levelled all distinctions in a "sweeping and democratic confusion."

The removal of loose materials, the tearing up of fragments of rock, and their transportation to a distant site, transpire under the action of those temporary torrents which are produced by heavy rains in mountainous districts. The pen of Captain Hall has sketched in a lively manner a specimen of their vigour as exhibited in the high lands behind the town of Funchal in the island of Madeira. The whole of the upper part of the mountain is split into crevices, in some instances deep enough to be called ravines, or in the larger cases even valleys, which have been cut by the rapid rush of the descending currents. Many of these crevices run into one another, so that when the rain falls in any quantity, the whole series are set in operation at once, like so many gigantic sluices, to conduct the water into the main channels which convey it into the sea. In less precipitous countries, the minor streams take some time to collect their waters; but at Madeira, where the hills are steep, the whole is done almost at a blow, and with an impetuosity that seems formidable to eyes unaccustomed to it. A few hours after a heavy rain has commenced, the torrents are all at work. Behind Funchal, the side of the mountain is indented by a valley of considerable dimensions, into which a number of ravines run, and bring down the discharges of rain from the highest ridges of the island. This is frequently the bed of a torrent, filled to the depth of twenty feet, partly with water and partly with stones, many of them of great dimensions, and moving together with a noise like continuous loud thunder. The angle which the bed makes with the horizon is sufficient to cover. the surface of the stream with waves more tumultuous than those of the Canadian rapids, bearing along rocks with the utmost velocity, which the St. Lawrence would not cause to budge an inch. Sometimes huge blocks are jerked half out of the stream by the violence with which they are dashed against one another, or against some opposing angle of the channel, the bottom and sides of which, every time the torrent is in action, undergo an amount of wear and tear which effects great changes in the course of years. The writer before referred to describes this torrent, when in full play, as the grandest thing possible, requiring an effort of considerable resolution to advance to its brink, and far surpassing the surfs, breakers, and rapids, in any part of the world, in the impression of irresistible power it makes upon the senses. The roar is such that hardly any elevation of the voice can make two persons audible to one another, though standing side by side, while the ground trembles in a manner indicating the enormous weight passing over the surface. Soon after the rain ceases, this immense

water-course becomes dry, and exhibits a pavement covered with blocks of stone, variously distributed, which the current has conveyed from the upland regions, to be transported farther when its flow is renewed.

Many remarkable cases of change produced by streams in flood might be quoted from the records of ancient and modern times. One of the rivers of the Roman plain, the Anio, now called the Teverone, has repeatedly committed extensive ravages in that land of classic recollections. Silius Italicus speaks of its gentle flow into the Tiber, but Horace gives it the epithet of præceps, impetuous or headlong, with an eye probably to its appearance in inundation. The patrician families of Rome retired to villas upon its banks in summer, attracted by the coolness of its waters, a quality mentioned by Virgil, and by the striking scenery, as at Tivoli, where the beautiful remains of the temple of Vesta, and the fall of the river, constitute a picture which has few equals. In the time of the younger Pliny, there was a flood on the Anio, which is the subject of one of his letters to Macrinus :-"Is the season with you as rude and boisterous as it is with us? All here is tempest and inundation; the Tiber has swelled its channel, and overflowed its banks far and wide; though the wise precaution of the Emperor had guarded against this evil, by cutting several outlets to the river; it has nevertheless flooded all the fields and valleys, and entirely overspread the whole face of the flat country. It seems to have gone out to meet those rivers which it used to receive and carry off in one intermingled stream; and has driven them back to deluge those countries it could not reach itself. That most delightful of rivers, the Anio, which seems invited and detained in its course by the charming villas that are situated upon its banks, has almost entirely rooted up and carried away the woods which shaded its borders. It has overthrown whole mountains, and in endeavouring to find a passage through the ruins that obstructed its way, has forced down houses, and rises over the desolation it has occasioned. The inhabitants of the hill countries, who are situated above the reach of this inundation, have been the melancholy spectators of its dreadful effects, having seen costly furniture, instruments of husbandry, ploughs, and oxen with their drivers, whole herds of cattle, together with the trunks of trees, and beams of the neighbouring villas, floating about in different parts. Nor indeed have these higher places themselves, to which the waters could not rise, escaped the calamity. A continued heavy rain, as destructive as the river itself, poured down in torrents upon them, and has destroyed all the enclosures which divided that fertile country. It has damaged likewise, and even overturned, some of the public buildings, where numbers had been miserably buried in the ruins." Such is Pliny's account of a rise of the Anio, probably in the first century of the Christian era. It is an interesting illustration of the constancy of natural phenomena, that after the lapse of some seventeen centuries, in the year 1826, the scene upon its banks might be described in nearly the words of the preceding relation. After heavy rains in November the river broke its bounds, at the same time permanently widening its own channel in many places, by the power of the current undermining and destroying the cliffs along its course. A considerable eminence, on which stood the church of St. Lucia, and near forty houses of the town of Tivoli, were carried away, and the precipice crowned with the relics of Vesta's temple might have shared the same fate, had the flood risen a few feet higher.

During the storm of 1829, which ravaged Morayshire and some of the neighbouring countries, a storm, which bore a more remarkable resemblance to a tropical hurricane than any which has visited our climate, at least in recent times, some striking examples occurred of the power of a strong current, in detaching fragments of rock, apparently firmly fixed in their native beds, bearing them away in a mass, and the whole district subject to the influence of the swollen waters of the Spey, Findhorn, Divie, Dee, and Dow, was, at various points, largely modified in its physical aspect. The heavy con