Of these three chains, the most northern, or that of Venezuela is the highest, and also the narrowest. Its greatest height is found at that place where it takes the name of Sierra de Nevada de St Martha, it latitude 10° 2', and of Sierra Nevada de Merida, in latitude 8° 30'.
The farmer is about 5000, the latter 5400 Spanish ells, or 2350 toises in height. The Paramo de la Rosa, and the mountain of Merida, are continually covered with snow; and boiling water, with hydrogenated sulphur, issues from their sides. It deserves to be remarked, that these high mountains of St Martha and St Merida, stand almost insulated, being surrounded by few high ridges. To the west of Santa Fe, no snow-clad peaks are to be seen, and the Sierra de Merida stands at the edge of the plain of Carraccas, which is scarcely 40 toises above the level of the sea. That part of the chain which extends from Merida to Trinidad encloses three valleys, lying east and west, which give certain signs of their having been formerly lakes, the water of which has eva porated, or run off by opening for itself a passage. These three valleys are enclosed by two parallel ranges of mountains, into which the chain of the coast divides it self from Cape Veto. to Cape Cordera ; the northern range is a continuation of St Martha, the southern a prolongation of St Merida. It is remarkable, that the level of these three valleys of Carraccas, Aragua, and Monai, are above the surface of the ocean. By repeated barometric measurements, the first was found to be 416 toises, the second 212, and the third not more than 80 or 100, above the level of the sea. The general height of the chain of the coast is from 600 to 800 toises, the Nevada of Merida is 2350, and the Silla de Carraccas 1316, lowering towards the cast, so that Cape Codera is only 176 toises. This depression, however, is only of the primitive rock, for there are secondary calcareous mountains from Cape Unara, which are higher than the gneiss and mica slate. These calcareous mountains follow this chain on its southern side, and increase in height towards the eastern point of the continent. The chain of the coast is more steep towards the north than the south ; and there is a dreadful perpendicular preci pice of 1300 toises, in the Silla de Carraccas, above savalledo. This appearance, which seems to contradict the generally received opinion, that all mountains de cline more abruptly to west and south, Humboldt en deavours to explain by supposing, that the northern part of this chain was torn away by the force of 'the water, during the great catastrophe which produced the gulf of Mexico.
The chain of Parima no where seems to rise to an equal height with the northern range ; the mountain of Duida, whose volcano is in latitude 3° 13', not far from Esmeralda, is reckoned the highest, and, according to Humboldt, rises 1323 toises above the level of the sea. This is a picturesque and majestic mountain, ejecting flames towards the close of the rainy season, and situat ed near a beautiful plain, covered with ananas and palms. This chain seems to contain not a single alluvial rock ; nothing is to be seen but granite, gneiss, mica-slate, and hornblende slate.
Little is known respecting the third chain. The high est summits appear to be between 15° and 20° south latitude, from the circumstance of the rivers here tak ing opposite courses, some passing to the river of the Amazons, and some to that of La Plata.
Between these three ridges, are three immense val leys ; that of Orinoco, that of the river of Amazons, and that of the Pampas of Buenos Ayres, all opening to the east, but shut on the west by the Andes. The middle valley, or that of the Amazons, is covered with forests so thick, that the rivers alone form roads ; while those of Orinoco and Pampas, are savannahs or grassy plains, with a few scattered palms; and so level, that sometimes for 800 square leagues, there is no elevation exceeding eight or ten inches. In the northern plain. the primitive rock is covered with lime-stone, gypsum, and free-stone, while in that of the Amazons, the gra nite every where appears. The general inclination is to the north-west, which, according to Humboldt, is the usual arrangement of primitive rocks. In the Andes, pctrifactions are uncommon, but there are sometimes patches of gypsum, and secondary limestone; while the range of Parima consists entirely of granite, and other primitive rocks. But in the calcareous freestone of the northern ridges of the coast, Humboldt found many shells, seemingly of recent petrifaction, as they arc those of the sea, now at the distance of nine leagues. In the plain of Orinoco, arc found petrified trees, in a coarse breccia. Granite forms the chain of Parima ; but in that of the coast, it is covered with gneiss and mica slate. It is sometimes stratified in beds from two to three feet thick, and sometimes contains large crystals of feldspar. The mica slate sometimes presents red garnets and saphore, and in the gneiss of the mountain of Avila green garnets appear. In the range of Parima, there occur large masses of most brilliant talc, formerly imparting such reputation to the Dorado, situated be tween the rivers Essequibo and Mao, and other moun tains, which, like burnished gold, reflect the light of the sun, and have hence been denominated the shining mountains. Smectite, or soft jad, is formed into idols; and Condamine discovered that hard jad, called Amazons stone. Chlorite slate also occurs; and beautiful horn blende slate rises through the streets of Guaiana, or St Thome. Humboldt, at the end of his Paper in the Journal de Physique, has furnished us with the follow ing sketch of the order in which the rocks occur, in the chain of the coast, and that of Parima. He divides them into primary and secondary. Both these classes of rocks rest upon massive granite, often mixed with jad and plumbago. This is followed in the primary by foliated granite, mica slate, with garnets ; primitive slate, with beds of native alum; slate mixed with hornblende, green-stone, amydalow ; and above all, porphyry slate. In the secondary, the granite is covered by gneiss, with beds of primitive lime-stone, the mica slate with horn blende and lime-stone ; and this with beds of Lydian stone, petrisolen, gypsum, and calcareous free-stone.
For further information respecting the Andes, our readers may consult Voyage Historique de l'?Inzeri971C Illeridiunalc, par Don Antonio de Ulloa ; La Figure de la Terre, par Bouguer; Journal de Condamine ; Helms' Tagebuch, Z..7'c. or Journal of a Journey through Peru, from Buenos .Ayres to Lima ; Journal de Physique, ilIes sidor, ?n. ix. July 1801, or Philosophical Magazine, vol. xvii. xviii.; Pinkerton's Modern G eography, vol. ii., and Molina's Nat. Hist, of Chili, vol. i. (e)