These accumulations of stones are called morains. - The destruction of granitic and schistose mountains, it has been before observed, is generally effected by water penetrating between the fissures, and becoming suddenly expanded by frost. The overthrow of calcareous rocks is effected in a different manner; and the vast éboulements which they occasion, are more terrific and destructive, than the éboulements from the primary mountains, as they generally take place in more thickly inhabited districts.

The destruction of the calcareous mountains in the Alps, depends on the peculiar composition and structure of these mountains. In the year 1821, I passed a great part of the summer in examining the calca reous mountains in Savoy, the structure of which was then not generally understood, or at least had not been described, in any geological work that I had met with. It was generally believed that the calcareous mountains were entirely composed of beds of limestone, with lofty mural precipices on the upper part; and that the lower parts, sloping from these precipices, were formed of the débris of the limestone. So far from this being the case, the calcareous mountains of the Alps, which comprise all the English formations, from the magnesian limestone or chalk, alternate, like the English formations, with enormous beds of soft shale and sandstone; and it is to this alternation, they owe the frequent destruction of the upper parts of the mountains.

If all our English secondary formations, were by some powerful cause elevated six or seven thousand feet above their present level, and the beds bent into curves, constituting several ranges of mountains, we should have precisely what is found in the calcareous ranges of the Alps. This arched form of the calcareous mountains is represented, Plate II. fig. 1., and fig. 2. x, y. Now, if one thick bed of limestone, or a portion of it, be broken off as at 2, fig. 2, the action of continued rains on the soft bed on which it rests, will undermine it, until other portions of the limestone will fall

down; and if this process take place on both sides of the mountain, the whole of the bed of limestone will fall, except the part which rests flat upon the summit: in this manner have been left the enormous caps of limestone, like immense castles, that compose the summits of the calcareous mountains, near the lake of Annecy, and in the Bauges. -Sometimes the mountain caps, which form an extended range in front, present the appearance of a narrow ridge when seen in profile.

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The mountain called the Dent d'Alençon, near the Lake of Annecy, offers a remarkable instance of this. See Plate II. fig. 6. The mass of limestone on its summit, which I found by trigonometrical measurement to rise 3840 feet above the lake, and to be nearly five hundred feet in thickness, was undoubtedly once a continuous bed, covering the mountain like a mantle, as represented by the dotted lines: in the course of ages, the side a a has fallen down, and the action of rain on the soft bed, c, on the other side, is undermining the steep escarpment b, and preparing for its further destruction. The soft bed cc, which forms the talus or slope, being covered with vegetation on the side bc, is in some parts protected from rapid disintegration. On the opposite side of the valley, I found that the thick bed which formed the talus or slope under the limestone, was lias clay. I was not able to ascend the Dent d'Alençon, and therefore did not ascertain whether the bed c was soft sandstone or lias. In numerous instances, the upper beds of limestone in the mountains of Savoy, may be observed overlapping and overhanging, as at a a, Plate II. fig. 1., and are thus prepared to fall, whenever the rain and frost has widened the longitudinal natural fissures in the limestone. In Plate II. fig. 2., the mountain at y, which had the arched stratification, has been so broken as to present a steep escarpment: such instances are very common in Savoy. The present state of Mont Grenier, south of Chamberry, and the vast ruins in the plain below,

offer a striking illustration of the causes which are in operation, to disintegrate the vast calcareous mountains of Savoy. The following description, with the cut, is taken from the first volume of my Travels: — "A part of Mont Grenier fell down in the year 1248, and entirely buried five parishes, and the town and church of St. André. The ruins spread over an extent of about nine square miles, and are called les Abymes de Myans. After a lapse of so many centuries, they still present a singular scene of desolation. The catastrophe must have been most awful when seen from the vicinity; for Mont Grenier is almost isolated, advancing into a broad plain, which extends to the valley of the Isère. It is several miles in length, and is connected with the mountains of the Grand Chartreux, but it is very narrow. Its longitudinal direction is from east to west: near the middle it makes a bend towards the north, forming a kind of bay or concavity on the southern side.

"Mont Grenier rises very abruptly upwards of 4000 feet above the plain. It is capped with an immense mass of limestone strata, not less than 600 feet in thickness, which presents on every side the appear. ance of a wall. The strata dip gently to the side which fell into the plain. This mass of limestone, rests on a foundation of softer strata, probably molasse, under which are distinctly seen thin strata, alternating with soft strata. The annexed cut represents the east wing of the mountain, and a small part of the Abymes de Myans. There can be little doubt that the catastrophe was caused by the gradual erosion of the soft strata, which undermined the mass of limestone above, and projected it into the plain. It is also probable, that the part which fell, had for some time been nearly detached from the mountain by a shrinking of the southern side, as there is at present a rent at this end, upwards of 2000 feet deep, which seems to have cut off a large section from the eastern end, that now

Hangs in doubtful ruins round its base,'

as if prepared to renew the catastrophe of 1248. The Abymes de Myans are hills, or rather monticules, of a conical shape, varying in height from twenty to thirty feet; they cover about nine square miles: the monticules are composed of fragments of calcareous strata, some of which are of immense size. They consist of yellowish oolitic limestone, strongly resembling the lower oolites in Gloucestershire; a gray limestone, harder and more crystalline than lias, which, however, it may probably be; and a thin slaty arenaceous limestone, much resembling Stonesfield slate. Fragments of schistose chert were interstratified with some of the limestone.

"The largest masses have evidently fallen from the upper bed of limestone by which Mont Grenier is capped. The velocity they would acquire by falling from so great a height, making due allowance for the resistance of the atmosphere, could not be less than 300 feet per second; and the projectile force they gained by striking against the base of the mountain, or against each other, has spread them far into the plain. In the course of years, the rains or currents of water from dissolving snows, have furrowed channels between the larger masses of stone, and, washing away part of the loose earth, have left the immense number of detached conical hills which are seen at present. So deep and vast was the mass of ruins that covered the town of St. André and the other parishes, that nothing belonging to them has been discovered, except a small bronze statue."- Vol. i. p. 201.

A part of a mountain near Servos, on the road to Chamouny, fell down in the year 1751. The fall continued for many days, and the air was darkened with immense volumes of black dust, which extended for twenty miles, and is still remembered by some of the oldest inhabitants of Chamouny. A continued succession of reports, like those of cannon, announced the successive falling of rocks, day and night. The mountain did not, like that of Mont Grenier, fall at