except limestone, trap, and serpentine. Cobalt and nickel also occur in transition mountains, and in sandstone.

Arsenic, in primary and transition mountains, and in porphyry.

Manganese, in primary and transition mountains, and occasionally in the lower stratified rocks.

Molybdena and tungsten, uranium and titanium, in granite, gneiss, mica-slate, and slate. The latter metals, with chromium, columbium, cerium, and tellurium, are very rare in nature, and can only be reduced to the metallic state with great difficulty.

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CHAPTER XVIII.

ON THE DESTRUCTION OF MOUNTAINS.—ALLUVIAL AND DILUVIAL DEPOSITIONS. THE FORMATION OF SOILS.-AND ON THE BONES OF QUADRUPEDS IN BEDS OF GRAVEL AND CLAY, AND IN CAVERNS.

Proofs of the Disintegration of Rocks.-The rapid destruction of Mountains dependent on their Structure.-The Fall of Mont Grenier and other Mountains in the Alps.-The breaking down of the Barriers of Mountain Lakes.-Masses of Rock scattered over Valleys and Hills.-On the Increase and Decrease of Continents and Islands, and the Formation of productive Soils.-Recent Strata formed in Lakes.-Peat and Peat Moors.-Human Bodies preserved in Peat.-Inundations of Sand.--Coral Islands.-The Remains of Land Quadrupeds found in Bogs, in Beds of Clay or Gravel, and in Caverns.

THE disintegration of rocks and mountains is constantly taking place by the incessant operation of the elements; all bare and lofty cliffs and eminences are gradually wearing down; and the process will go on, until they are covered with soil and vegetation, which protect them from further decay. Beside the causes which at present operate to reduce the most exposed and prominent parts of the earth's surface, and transport their materials into plains, or to the sea shore, there are evident indications of the destructive effects of ancient inundations, which have swept over the surface of the present continents, have excavated new valleys, torn off the summits of the loftiest mountains, and

spread their ruins in immense fragments over distant regions. The sand, soil, or fragments, brought down by rivers, and spread along their banks or at their mouths, are called alluvial depositions. The blocks of rock, and the beds of gravel spread or scattered on the surface of the ground, composed of stone or fragments foreign to the district in which they are spread, and which frequently cover the bones of unknown species of quadrupeds, are called diluvial depositions, viz. depositions which have been formed by a deluge. We shall first consider the causes which are at present wearing down the surface of islands and continents: these are sometimes adequate to produce the most tremendous effects, and to overthrow mountain masses of immense magnitude. By considering these effects, we shall be better prepared to admit the mighty action of diluvial agency in remote epochs. Indeed it is not always easy, to distinguish with certainty the effects of alluvial from diluvial agency. We have, however, incontestible evidence, that the disintegration of mountains has been effected by both

causes.

Instances have occurred in our own times of mountains suddenly falling down, and burying the inhabitants of the vales below, under their ruins. In the Alps, the process of disintegration is rapidly going on; but such is the immensity of these enormous mountains, that ages pass away, before any diminution of their bulk is perceived.

According to the account of Patrin, who had travelled in Northern Asia, the whole of that country is covered to the depth of many hundred feet

by innumerable beds of micaceous and argillaceous sand, washed down by inundations from the high range of mountains in the interior of Asia, and carried as far as Siberia. The deserts of Arabia are also covered with alluvial or diluvial depositions. C. Leckie, Esq. informed me, that between Hit and Tahiba, the soil is composed of sand and gravel, on which may be seen small volute and bivalve shells; but the sand is not loose like that in the deserts of Libya.

That the mountains of our island have once been much higher than at present, is evident to every one who has attentively examined them. The rocky fragments in Borrowdale, the deep ravines made by torrents in the sides of Skiddaw, the immense blocks of granite from Westdale Crag in Westmoreland, scattered over the neighbouring counties, offer striking proofs of this. The central parts of England have also once had a greater elevation. The white quartz pebbles and fragments of quartz rock, sienite and flinty slate, spread over the midland counties, are the remains of the decomposed hills in Charnwood Forest, and of others once connected with them, which are now worn down. Beds of flint-gravel, are formed by the disintegration of chalk rocks, in which flints are imbedded, as may be seen on the sea shore under chalk cliffs; but beds of flint-gravel, are also spread over many parts of England distant from chalk rocks, and at a considerable elevation above the level of the sea. Hence we have evidence that chalk rocks once covered a larger portion of England than at present. It is however in the vicinity of the Alps

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that the disintegrating effects of the elements, and those of diluvial agency, are most strikingly displayed. Innumerable blocks of primary rocks torn from the central range of mountains, are spread over the calcareous mountains, and in the valleys, to the distance of one hundred miles or more from their native beds. Blocks of great size are also found immediately under the mountains from whence they have fallen, or scattered over the surface of glaciers; and as the lower parts of the glaciers are gradually melting, the upper parts progressively move down into the valleys, and deposit the fragments in heaps at their feet:-these depositions of stone are called morains. The destruction of granitic and schistose mountains, that are divided by nearly vertical seams or partings, is often rapidly effected; water, insinuating itself into the interstices or seams, becomes expanded by frost, and tears down great masses of rock, with a sudden explosion like that of gunpowder. The overthrow of calcareous rocks is effected in a different manner, and the vast eboulements which they occasion, are more terrific and destructive than the eboulements 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 understood, or at least had not been described in any geological work that I had met with. It was generally believed that the cal