here be understood to mean aged; for the dimensions assigned by him to the fossil cranium from Picardy, are analogous to those of the skulls of full grown, though not old, beavers from Hudson's Bay in the College Museum. That this is his meaning, is further proved by his description of the skulls of the adult Canadian beavers; in which he observes, "the temporal crests approach each other," so as, at the mesial line, to form a single elevated crest; a tendency which is visible in the cranium of the aged beaver already mentioned as being in Dr Barclay's collec

tion.

CANONMILLS, 20th April 1819.

ART. XXXIV.-Account of the Formation of the Lake of Mauvoisin, by the Descent of a Glucier, and of the Inundations of the Val de Bagnes in 1595 and 1818. Drawn up from the Memoir of M. Escher de la Linth, &c. and illustrated with a map and drawings, communicated by Professor Pictet of Geneva,

THE Val de Bagnes is a valley in Switzerland about ten leagues in length, which stretches from east to west, and, after having joined the valley of Entremont at St Branchier, opens into the extensive valley of the Rhone. It intersects several chains of the great Alpine range which separates Switzerland from Piedmont, and is watered by the river Dranse, which flows in a rocky bed, contracting its channel between precipitous banks, where it cuts the mountainous ridges, and again spreading out upon level and fertile plains covered with smiling cottages, and presenting the most picturesque and beautiful situations.

The river Dranse has its origin in the glaciers of Tzermotane and Mont Durant, (shewn at E and F in the map, Plate IV.) It traverses the valley of Tozembic (shewn at L); and after flowing through a very narrow and deep channel, it passes the bridge of Mauvoisin (C), which connects the two sides of the valley. This bridge is built upon perpendicular rocks, about eighty feet above the bed of the river; and the narrow gorge which it crosses, is formed by the approximating flanks of Mont Pleureur (G) on one side, and Mont Mauvoisin (1) on

the other. Between Mont Pleureur and Mont Getroz (H), is a narrow and deep channel, at the top of which lies the glacier of Getroz (D). Enormous masses of ice are constantly precipitating themselves from this glacier into the ravine below, and, descending to the bottom of the valley, fill up the contracted channel of the Dranse.

So early as the year 1595*, the valley above the bridge of Mauvoisin was completely shut up by the descent of immense avalanches of ice. The water rose to an enormous height, and, on the evening of Sunday the 4th of June, the icy barrier which confined it, was weakened by the influence of the heat, and suddenly gave way. The accumulated waters took a whole hour to escape from their confinement. They descended the valley with irresistible fury, carrying along with them masses of rock of enormous magnitude; tearing up every thing that obstructed their progress; desolating the plains of Bagnes, St Branchier, and Bovernier; and destroying the whole town of Martigny. The unfortunate inhabitants were reduced to the most abject poverty, and no fewer than from sixty to eighty perished in the torrent +.

For several years previous to 1818, the progress of the Dranse had begun to be obstructed by the blocks of ice and avalanches of snow that descended from the glacier of Getroz; and as soon this accumulation was able to resist the heats of summer, it acquired new magnitude during every preceding winter, till it became a homogenous mass of ice of a conical form. This cone, which is shewn in the perspective view of the Lake, Plate IV. had its summit in the ravine, about 100 feet above the Dranse, and, descending at an angle of 45 degrees, its base rested upon the precipitous flanks of Mont Mauvoisin.

The waters of the Dranse, however, still found their way beneath the icy cone till the month of April, when they were observed to have been dammed up, and to have formed a lake about half a league in length. The danger of a sudden efflux of the water was now apparent, and it was deemed necessary to

M. Ebel informs us, that the village of Bagnes, from which the valley receives its name, was destroyed in 1545 by an inundation, in which 140 persons perished. Manuel d'un Voyageur en Suisse, tom. ii. p. 188.

Biblioth. Universelle, Septembre 1818, p. 89.

cut a subterraneous gallery for the purpose of effecting a gradual discharge. With this view, the lower end of the gallery was sixty feet below the line of contact of the cone of ice with the flank of Mont Mauvoisin, and its upper extremity was fixed at the height to which the lake might be calculated to have risen when the gallery was finished. In this way, the water entering the upper extremity of the gallery, might be expected to deepen it by degrees, and thus permit the surface of the lake to descend gradually, till it was nearly emptied. This ingenious and bold scheme was begun on the 10th of May, and finished on the 13th of June, under the direction of M.Venetz, an able engineer of the Valais. 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.

During the thirty-four days which were spent in the formation of the gallery, the lake had risen sixty-two feet, but from particular causes, the upper entrance to the gallery was still many feet above the surface of the lake. Without waiting for the farther rise of the waters, M. Venetz sunk the floor of the gallery several feet, and the water began to enter it on the 13th of June. At this period, the length of the lake was from 10,000 to 12,000 feet; its average breadth, at the surface, about 700 feet, and, at the bottom, about 100 feet. Its absolute average breadth was 400 feet; its average depth 200 feet; and its contents at least 800 millions of cubic feet.

After the 14th of June, at 11 o'clock, the floor of the gallery began to wear down, and at 5 o'clock the lake was lowered one foot. On the 15th of June, at 6 o'clock A. M. the height of the lake was diminished ten feet; twenty-four hours afterwards, it was diminished thirty-six feet; and on the 16th of June, at 6 o'clock P. M. the total diminution was forty-five feet. The effect of the gallery, therefore, had been to reduce the lake from 800 to 530 millions of cubic feet.

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