Three separate mountain-systems exist in South America:--that of the Andes on the west, Guiana and Venezuela on the north, and the serras of Brazil in the centre. The surface of the remainder of the continent is occupied by vast level, or undulating tracts of different elevations. The chief portion of the region through which the Amazon flows, but slightly raised above its surface, is covered with the richest and most varied vegetation to be found on any part of the globe, extending on either side of its course, as also along the shores of the Atlantic, north and south, for many hundreds of miles. Here enormous trees of many descriptions, of varied shapes and heights, grow in wonderful profusion. The candelabra, sumaumera, the manicaria, and raphia, with their enormous leaves, and other palms innumerable, tower towards the sky. To the south of the Orinoco is another thickly-wooded region, known as the Silvas; which, united to the woods of Guiana and those of Brazil, Eastern Peru and Bolivia, form one enormous forest. From the north bank of the last-named river, the ground gently rises towards the interior at the rate of five feet in a mile. At a distance of one hundred miles from its hanks, at a slightly increased elevation, appears a sandy terrace--the greater portion barren, though in some places bearing grasses, and supplying water to the wide-extending plains below. This barren region, which occupies the most northern part of South America, is called the Llanos Altos. A far wider and more level country extends between the base of the Andes and the banks of the Orinoco, at a height of between two hundred and five hundred feet. Not a stone or rock, not even a pebble, is to be seen on these vast plains. So level are they, that the currents of the rivers crossing them are almost imperceptible, and are frequently sent back towards their sources when met by strong winds. They are covered with grass, which affords pasturage to large herds of wild cattle--the only other species of vegetation being a few bushes growing on the banks of the streams; while here and there, scattered at considerable distances apart, a few tall palm-trees are seen, reminding the traveller of the deserts of Arabia.