XVIII. BOOK ginous garnets. Thus the mountains may be destroyed even by the influence of that imperceptible humidity which is inherent in all terrestrial substances. General sinking of the globe. cavations. There can be no doubt that these two kinds of subsiding, must have contributed to the formation of the existing surface of the globe. We perceive everywhere around us nothing but wrecks and ruins; those beds of rocks, displaced, overturned, shattered; those lakes so deeply excavated; those caverns which reach down towards the centre of the earth; those peaks which tower to the sky; those precipitous coasts which surround as with an immense rampart all the seas of the globe; those Alps which overhang Italy; those Andes which plunge their gigantic sides into the ocean; those forests, those races of quadrupeds, those aquatic animals buried into the earth in mingled confusion; all these circumstances impress us with the awful and overwhelming thought, how vast must have been the heavings and agitations which have contributed to give to the globe its present appearance. M. Deluc has very happily applied this physical truth to illustrate the account of a universal deluge contained in the sacred writings. According to him, this catastrophe, which some have endeavoured to represent as impossible, may be naturally explained, merely on the supposition of a general sinking down of the inhabited regions of the earth; then the waters of the sea, instead of being elevated, as has been generally imagined, would have needed only to follow the laws of gravitation, in order to cover the antediluvian world, and leave dry our present continent. But we wish to speak here of facts of which history has preserved the details. Subsidings The subsidings which take place from excavations made through ex-by water, happen yearly in mountainous countries along rivers. It is thus that the Rhone has formed the vault under which it appears to lose itself; it is thus that the Adige swallowed up the town of Neumark and others in 1767. In the south of Norway, the rapid Glommen descends from the summit of the Dofrine mountains towards the North Sea, and forms, a little above its mouth, the fine cascade of BOOK Sarpen. The eddy of the waters of the cascade have form- XVIII. ed under the bank a subterranean lake 600 feet in depth. On the 5th February 1702, the Castle of Borge, with all its dependencies, was engulphed in this excavation, and entirely disappeared, so that there appeared nothing in its place but a lake 800 feet long, and from 300 to 400 broad.* The disaster which befel the town of Pleurs, in the country of Chiavenna, arose from a similar cause. Rivulets and springs without number wore away the frail foundations of Mount Conto; on the 25th August, 1618, the masses of rock of which that mountain was composed, separated from each other and rolled upon the town, which they completely overwhelmed, as well as the small town of Schilano; 2430 individuals perished; a lake occupied the place where 200 elegant houses once stood. All the wealth, which for a century commerce had amassed, was at once restored to the maternal bosom of the earth.t ous forests. The plains experience depressions of another kind. The platforms of turf suspended upon water, sink under the weight of forests, houses, and inhabitants. Ireland every Origin of year sees the number of its lakes increase by the sinking in subterraneof its bogs. It is to these that subterraneous forests, in some measure, owe their origin. There are some which, like those on the shores of Lincolnshire,‡ are formed conjointly by the sinking down of marshy coasts, and by ancient invasions of the sea. Others, like those which have been discovered near Morlaix, appear to owe their subterraneous situation to changes anterior to the existing state of the globe, but for the most part, they are met with in turf or peat grounds. In the Isle of Man, accordingly, in the midst of a marsh, at the depth of 20 feet, fir trees are found still on their roots. At Halfield-chace, we find trees Pontoppidan, Hist. Nat. de la Norwège, i. ch. 3. § 14. + Camerari, Dissertat. vi. Corréa de Serra, dans les Annales des Voyages, i. 169. s94. BOOK which have their nuts and acorns lying at their sides. HolXVIII. land, Switzerland, and France, present similar facts; but it Lakes is Sweden which furnishes us with the most curious example. Near Asarp, in West Gothland, there are two peat bogs composed of a thick mud, and of a slight turf. We discover there a great quantity of trunks, and roots, which are carried off every year to serve as fuel; the following year they are equally abundant, which arises unquestionably from an immense collection of trees buried in this great ground, and raised to the surface by the annual thaw.* In the Electoral Marche of Brandenburg, there is the subsidings, lake of Arendt, formed by two subsidings, the one, it is believed, happened in 815, and the other in 1685. How many lakes are thus formed in Prussia and in Poland! How many other events are there of this nature, the knowledge of which is lost to us, or has been disfigured by tradition! Strabo tells us, that around the Lake Copaïs, in Bæotia, the sinkings of the ground were very numerous, and often changed the course of the river Cephissus, which at last flowed in subterraneous canals constructed by the hand of man. As these canals are no longer kept in repair, and as the lake Copaïs is changed into a marsh, we may ask, what is become of the waters of the Cephissus? It appears only too probable that they have hollowed out a subterraneous reservoir, an invisible lake, but which may one day swallow up Bæotia, and thus renew the deluge of Ogyges. We have spoken of subterraneous lakes, and amongst others of that in the West Friezland, which was discovered in the 12th century; by degrees there was formed on its surface a crust of peaty and slimy substances, which in their turn were covered with vegetable mould. This crust is now strong enough for a carriage to pass over it, and to be laboured, sown, and reaped. At the same time the inhabitants have only to make two or three holes, four * Bergmann, Géographie-Physique, ii. 244. Rothof, Mém. de l'Academie des Sciences de Stockholm, 1767. feet deep, to find water to serve them for steeping their flax. BOOK There probably exists a subterraneous lake near Narbonne, XVIII. in the territory of Liviere. We there see five abysses, named the Oeliols, of an extraordinary depth, and filled with fish; the earth which surrounds them tumbles under the steps of the adventurous peasants who are attracted thither for the sake of fishing. We may easily conceive the disasters which, from time Ground to time, indicate the existence of these subterraneous lakes, over lakes. suspended in places where no one suspects them. In 1792 a lake was formed in the town of Lons-le-Saulnier; several houses disappeared, as well as a part of the high road from Lyons to Strasbourg.* It is supposed that this was an old pond of brackish water; on which at first there was formed a pellicle, then a slight vegetable crust, and then ground, to all appearance, solid; but a great drought having made the subterraneous waters fall, this crust was deprived of support, and consequently sunk down. Mount Jura presents a number of vestiges of similar sinkings. The Pyrenees, another calcareous chain, exhibit them in as great abundance. Buffon relates, that a mountain in 1678, having sunk down into subterraneous cavities filled with water, caused a great inundation in a part of Gascony. The Julian Alps, where the famous lake of Cirknitz is, contain in their numerous caverns many similar reservoirs. Justly, then, might Seneca ask, "In what part of the globe has not nature waters at her command, to assail us with, whenever she pleases? Our excavations, our pits, almost every where terminate in water. Let us add, also, those immense invisible lakes, those subterraneous seas, those rivers which are enveloped in continual night. How many causes are there of inundation in those waters which flow beneath us and around us? For a long time prisoners, they will one day set themselves at liberty; the rocks, open on all sides, will furnish numerous currents of water, Bertrand, Nouv. Principes de Géologie, p. 198. BOOK XVIII. without cohesion. which will rush towards the ocean. These deluges of water or fire happen whenever it pleases the Almighty to recommence a more perfect order of things." We are now to speak of subsidings, in which the agency of water has not been immediate and predominant; for rarely does a disaster happen, in the production of which this element is entirely inactive. Mountains Many mountains, as we have seen, are originally composed of large stones, perfectly detached from each other. There are many such mountains between Norway and Sweden. A transverse section of Mount Quedlie shews a mass or stratum of 240 feet, composed of small flat stones-some calcareous, some sandy, and always without any cement to bind them together. The slightest force is sufficient to roll down these masses, which have been formed by changes anterior to the records of history. Effects of cold. Skeletons tains. There are other causes which concur in decomposing the most solid mountains; extreme cold often makes large blocks of rock burst asunder and tumble down. In West Gothland, near Hunneberg, there are two regular pillars detached from a rock, solely by the action of frost.* Norway suffers great devastations from the avalanche of stones, which are in like manner occasioned by the effects of cold. In the milder climates, the successive action of cold and heat is not less destructive, though more silent. In these same mountains of West Gotbland, of which we have just now spoken, Bergmann has observed that the rocks of trapp had a paler and more porous crust on the side lying towards the sun. In a great many places the skeletons of mountains attest of moun- these changes. Near Adersbach, in Bohemia, you pass through a sort of labyrinth of blocks of free-stone, placed perpendicularly from 100 to 200 feet high, and of a circumference equal to the half of their height. These columns, or rather these square towers, occupy a space of ground a league and one-third in length, and half a league Bergmann, Geographie Physique, ii, 242. |