By what agents were these beds raised to their present elevation? Satisfactory solutions to all these enquiries will probably long remain desiderata in geology, though, in some instances, we can now arrive at a high degree of probability, by referring to causes in present operation. These scattered fragments or masses of rock, with beds of loose stones and gravel, or of superficial sand or clay, are comprised by French geologists under the appropriate name of terrains de transport; a name, however, which cannot well be introduced into our language. We shall, therefore, divide them into three groups, adopting the names generally received. Scattered blocks of rock; diluvial beds or diluvium; and alluvial beds or alluvium; using the two latter without any reference to theory. Alluvial beds, consist of the sand, soil, or stones, brought down by rivers, and deposited in their beds, or scattered upon their banks, or carried into the sea or into lakes, forming deltas at the mouths of rivers. Diluvium, or diluvial beds, comprise both the scattered blocks of rock, and the beds of stone or gravel, that are carried into distant districts. They are called diluvial, on the supposition that they were transported during some great convulsion, by deluges or inundations; or, in other words that they were removed by causes more powerful than any which are seen in constant operation.

In order to form a more distinct idea of the causes which have transported the beds and fragments of stone into their present situation, we shall first consider the causes that are daily wearing down the loftiest mountains and cliffs, or undermining the solid ground on the sea shore. The disintegration of rocks and mountains is constantly taking place, by the incessant operation of atmospheric causes. The infiltration of water into the fissures of rocks, and its expansion by frost, often produces sudden falls of immense masses of rock. The slow operation of descending currents, excavates the soft beds in the lower parts of mountains; and the upper rocks, being undermined, fall, with a tremendous crash, into the vales below. Instances of this kind have occurred in our own times. By both these causes, the process of disintegration is rapidly going on in the Alps; but such is the immensity of these enormous mountain ranges, that ages pass away, before any diminution of their bulk is perceived.

In Alpine districts of great elevation, there is also another cause, more exposed to observation, which is ever in action during the summer months. The snow upon the mountains below the line of eternal congelation, when it begins to dissolve, forms numerous rivulets, that unite into large streams, and descend in cataracts with impetuous force, excavating deep ravines in the lower rocks. To use the words of Professor Playfair, they are "Nature's saws, incessantly at work, cutting down the mountains."

The vignette in the titlepage of this volume represents the upper part of the valley of Sext, in Savoy, in which the water, descending from the Alpine snow on the Buet and other mountains, is seen rush

ing in numerous cascades to the lower valley. But the most powerful effects of these cataracts may be observed during thunder storms, or after an unusually rapid thaw, when the upper rivulets overflow their accustomed boundaries, and carry with them the loose stones or masses of rock they meet in their descent, and dash them with inconceivable violence into the lower waterfalls, breaking down the solid rocks on each side, and deepening and enlarging the ravines into which they fall. The operation of this cause will be again referred to in the following chapter.

We need not indeed travel to the Alps to prove, that the mountains have been, and are still wearing down. The rocky fragments in Borrowdale; the deep ravines made by torrents in the sides of Skiddaw; the immense blocks of granite torn from Wastdale Crag, in Westmoreland, and scattered, many miles, over the adjacent counties offer striking proofs of this. The central parts of England had once, a greater elevation than at present; pebbles, formed of the Charnwood Forest rocks, are spread all over the midland counties. Masses of the rocks of Cumberland and Wales, more or less water-worn, occur almost every where under the alluvial plains of Cheshire and Lancashire. Beds of flint gravel, formed by disintegration of chalk rocks in which flints were imbedded, occur in many parts of England at a considerable distance from the sea, or from the chalk districts.

The transportation of these masses of rock, or beds of stones and gravel, cannot have been effected by any thing like the present action of rivers in England, and is generally referred to the more extensive operation of deluges, during great convulsions of the globe; but if we return to the Alps, and view the effects now taking place, we must admit, that it is not always easy to make the distinction between alluvial and diluvial depositions.

Innumerable blocks of granite and other primary rocks, torn from the central range of the Alps, are scattered over the calcareous mountains, at a great distance from this range, or are spread in heaps in many of the distant valleys. All of the great rivers that issue from the Alps, where the valleys open into the plains, have made deep sections in beds composed of the ruins of the mountains, and exhibit proofs of the vast destruction that has taken place. The river Doire, where it enters the plains of Piedmont, has cut through a mass of fragments more than 1500 feet in depth; these fragments consist of irregular blocks of granite, mica slate, and serpentine, frequently more than thirty cubic yards in extent, covered by smaller fragments, and by earthy matter from the decomposition of the softer rocks; the fragments decrease in size as their distance increases from the parent mountain..

Whoever has ascended the lofty eminences immediately below the highest pinnacles of the Alps, can scarcely fail to have received sensible proofs, of the daily and hourly disintegration of the mountains.

Here, placed nearly above the region of vegetable or animal existence, and surrounded by the sublimest objects in nature, the deep silence which prevails around is truly solemn and impressive; but it is broken from time to time, by sounds like the rolling of distant thunder, or by a nearer and louder crash, which is repeated by the echoes from rock to rock. These sounds proceed from the falling of avalanches, or from glaciers splitting and discharging the loose rocks upon their surface, or from éboulements of rock, detached from the bare and exposed sides of the pinnacles and aiguilles. The fragments generally fall into the elevated mountain valleys, and are scattered over the surface of the higher glaciers, which extend from thence into the lower Alpine valleys. As the glaciers in these valleys are gradually melting during summer, the ice above progressively moves downward, bearing with it the cargoes of stones on its surface, which it discharges in heaps at its feet and sides. 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, 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 calcareous 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 composed entirely 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, that 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 z, 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.

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 c'c, which forms the talus or slope, being 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 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.