BOOK VII. Valleys are formed by the separation of chains of mountains or of hills. Those which are found between high mountains are commonly narrow and long, as if they had originally been only fissures dividing their respective chains, or for the passage of extensive torrents. The angles of their direction sometimes exhibit a singular symmetry. "We see in the Pyrennees," says M. Raymond, "some valleys, whose salient and re-entrant angles so per-. fectly correspond, that if the force which separated them. were to act in a contrary direction, and bring their sides together again, they would unite so exactly, that even the fissure would not be perceived." This fact has been observed in the Alps for the first time by Bourguet, who has generalised it too much; for there are some valleys, situated on a high level, totally different. We see some which have a great extent in length without being cut into any angles whatever, forming a sort of elevated plains; such are generally those which lie on the side of the principal chains, the Valais, for example. There are others which are large or swelling; Bohemia or Cachemire are instances of this sort. It is asserted, that they have been the basins of some ancient lake, which had become dry from the breaking down of the bank or dam formed by the surrounding mountains. This hypothesis, developed by Lamanon and Valleys in the form of Sulzer, appears to be one of the best founded of any which geologists have proposed. There are also some highly situated valleys, containing rivers and lakes which have not outlets or streams. There is a remarkable example of this in Peru, in the large valley which contains the lake of Titicaca. Central Asia abounds in such valleys. Several nearly of the same sort are to be met with in other countries; and many more will one day be discovered in the interior of Africa. basins. Observations sur les Pyrénées. Memoire sur la Theorie de la Terre, à la suite des Lettres Philosophique sur les Sels et Cristaux, p. 181. Comp. Buffon, Hist. Nat. edit. 12mo. i. p. 105. Sulzer, Encyclop. Method. Phys. Geogr. i. art. Delamétherie, 1514, &c. VII. valleys. High valleys present also some remarkable circumstances BOOK as to their form. Some have declivities equal on all sides; others slope only on one side, and to a great extent, while the opposite side is steep and abrupt. Most of these high Inclination valleys have their surface upon a level with the summits of and level of the secondary mountains in the neighbourhood. The level of the lake of Joux, in a valley of Mount Jura, is considerably higher than that of the lake of Geneva.* In a few instances these high valleys have been observed to enlarge themselves at different and successive periods, and gradually to become identified with the plains. They have been for ages almost completely barred and confined by some projecting angle of the chain of mountains, which girds them in. The sort of narrow passage, by which we enter into Passes, dethese valleys, is called a pass or defile, and as formerly each files, &c. valley contained a small independent nation or tribe, these passes are called by the French "les portes des nations." Such were the passes of Caucasus, the Caspian passes, the pass of Issus, rendered celebrated by the victory of Alexander; that of Thermopyle, immortalized by the devoted patriotism of Leonidas and his band of Spartans. The Caudinæ Ferculæ, where Rome saw the glory of her unjust arms deservedly tarnished. There is between Norway and Sweden one of these passes, formed by several masses of rock, cut by nature into the shape of long parallelograms, and which have between them a passage, shut in by perpendicular walls. This pass is near Skiærdal. Another of the same kind is at "Portfeld," or the mountain of the gate. These openings exactly resemble those by which the Hudson River in North America passes through successive chains of mountains, which seem desirous of checking its course. The Cordilleras of the Andes present the most stupendous passes of this kind, that are known; they are Saussure, Voyages, p. 376, sq. + Bergmann, Geog. Physique, i. 185. Cronstedt. Description de la Temptie. dans les Mem. de l'Acad. de Stockholm, 1763, p. 275. f Kalm's Travels in America, iii. 161. (in Swedish.) VOL. I. VII. BOOK from four to five thousand feet deep. The lower valleys appear to us under a very different aspect; they widen as they recede from the secondary mountains from which they originate, and gradually lose themselves in the plains. Their opposite angles generally correspond very regularly, but these angles are very obtuse. Low valleys. High and Plains, like valleys, are of two classes: the high plains, low plains. which are found between two chains of mountains, are frequently of great extent, and are placed as it were upon the shoulders of the secondary mountains: such are the elevated plains of Tartary, of Persia, and probably of the interior of Africa. The plains of Quito are 12,000 feet above the level of the sea: those of Karakorum, in Chinese Mongolia, are probably as elevated. The low plains, whose soil is composed of sand, gravel, and shells, seem formerly to have been the basins of interior seas. Such are the plains on the north side of the Caspian, the large plain to the south of the Baltic, and that through which the river of the Amazons flows; the Tehama of Arabia, the Delta of Egypt and others of a similar nature; which seem to have been once covered by the waters of the ocean and its gulphs. Coasts steep and indented, &c. The coasts or shores of the sea, and of lakes, deserve also great attention. These are the extreme limits of our system of mountains. Some shores are broken and steep; this happens, when a mass of rock extends, either beneath or above the surface of the soil quite to the water; as in Gallicia, in Bretagne, in Norway, and in Scotland. This description of coasts admits of two subdivisions. 1st, We have those which are abrupt and broken, and as it were notched, formed by various masses of rocks united at their bases, either above or beneath the surface of the water: these rocks often form clusters of islands, which surround the coasts; such are the "garden of the king," and of the "queen," at Cuba, the archipelago of Mergui in India, the * Humboldt, Vues des Cordilleras, p. 9. VII. coasts of New South Wales, the Skiergôrd of Norway and BOOK Sweden. This class may again be subdivided according as the steepness of the shore, arises from true granitic and other rocks, or from those masses of coral formed by the polypi which fill the seas between the two tropics. 2dly, We have coasts where the shore or boundary is equally steep above and below the surface of the water, leaving the sea itself quite free; these are, strictly speaking, the "steep coasts." Such, in general, are those of the Mediterranean and of the Black Sea: those of Dalmatia and some parts of the Archipelago more properly belong to the first division. America possesses scarcely any other variety of coasts on the side of the Pacific Ocean, beginning at Cape Horn and proceeding to Behring's Straits. This is the largest continuation of steep shores known upon the globe. Mariners call a coast bold bluff, when it meets the ocean with a rapid declivity, and clear, when it is not bristled with rocks. These Such formed by hills. Low coasts are formed by land of a softer quality, ap- Coasts proaching the water by a gentle and gradual slope. may be thus classed; 1. Coasts formed by hills. are those of all the Danish islands, of Scania and Pomerania, consisting chiefly of calcareous matter. Shores of this kind seem more particularly to belong to lakes and small inland seas, although indeed the basins containing these are often surrounded by steep shores, as grand and bold as those which border the ocean. 2. Flat coasts, formed by Coasts sands and substances which the sea has deposited. These formed by appear under the form of sandy or marshy plains, and ex- flats. tend a long way into the sea, leaving the water more or less shallow. They are, however, of various kinds. They are sometimes like those in Gascogne and Jutland, the ancient sides of low hills, round which the sea has collected masses of sand, which are either fixed or shifting: sometimes they are a sort of downs,* formed by the sea, The low and flat ground at Yarmouth, in Norfolk, between the sea and the river, is called the Danes or Daines, evidently from the French word Dunes." T. downs or VII. BOOK together with soil deposited by large rivers, as in Holland, in Egypt, and at the mouth of the Mississippi. A collection of slimy matter is also sometimes formed by the ocean, as in the flat and flooded lands on the shores of French Guiana. The low coasts are sometimes exposed without any natural rampart, to all the fury of the waves, and then we may, with Tacitus, be uncertain whether to regard them as constituting a part of the land or a part of the sea; others are secured by a chain of downs that are fixed and mingled with rocks like North Jutland. It was only by a skilful and persevering imitation of these natural barriers, that the Dutch recovered the soil of their country from the empire of the ocean. Islands. Flat. Islands of great extent exhibit on a small scale the same appearances as the continents do on a large one. The smaller islands, however, deserve a distinct consideration. These may be classed in various ways. They are single, or in groups or chains. Among the low or flat islands, there are some which are only banks of sand, scarcely raised above the surface of the water; sometimes they consist of masses of shells or petrifactions, as the isles of Lachof to the north of Siberia, which are nothing but masses of ice, sand, and the bones of the mammoth. The greater number of the islands of the South Sea, formed, or at least enlarged by polypi, are composed solely of coral or Volcanic. madrepores. Among the more elevated islands, we find very many, which owe their foundation, in a great measure at least, to the action of volcanoes, which, after bursting forth from the original summit of the island, have continued to discharge lava from their crater in all directions, until by slow and gradual accumulation they have formed those vast and lofty peaks, which serve as land marks to the distant Chains and mariner. When groups of islands are placed near each other, we may fairly conjecture that they are only the different summits of one extensive submarine mass. So also, when they appear to follow one constant direction, they probably form only the eminences of a chain of submarine mountains. Such, when situated in the same line with the groups of islands. |