careous 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 debris 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 to chalk, alternate like the English formations, with enormous beds of shale and soft 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 2. fig. 1. and fig. 2. x, y. Now if one thick bed of limestone, or a portion of it, be broken off as at %, 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 and 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 the Bauges.Sometimes when the mountains are seen in profile, the caps which form an extended range in front,

present the appearance of a narrow ridge when seen in profile.

The mountain called the Dent d'Alençon, near the Lake of Annecy, offers a remarkable instance of this. See Plate 2. 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 steep escarpment on the other side at b, is at present undermining, by the action of rain on the soft bed c c, and preparing for a further disintegration. The soft bed cc, which forms the talus or slope, being partly covered with vegetation on the side b c, 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 3. fig. 1, and are thus prepared to fall, whenever the rain and frost has widened the longitudinal natural fissures in the limestone. The present state of Mont Grenier, south of Chambery, 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 is copied from the 1st 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 Alymes 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 appearance 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 Alymes 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 de