The east coast of South America has few islands and these, except Trinidad, off the coast of Venezuela, and the islands at the mouth of the Amazon, are mostly small. Trinidad (area 1,755 sq.m.) is separated from the continent by the Gulf of Paria but along its northern edge is a range of mountains averaging about 3,00o ft. high which is geologically a continuation of the Cumana range of Venezuela. On the south side of this island is the famous asphalt lake—the largest known deposit of its kind. West and north of Trinidad and lying farther off the coast are several small islands of historical interest and considerable commercial importance : Tobago, Margarita, Blanquilla, and the Curacao group. The main island of the Fernando de Noronha group of volcanic islands 230 m. off Cape Sao Roque has an area of only 12 sq.m. Although separated from the mainland by a channel 13,00o ft. deep, it really stands upon the submerged corner of the continent. The Falkland islands in lat. 51° S. also stand upon the submerged edge of the continent. Their fauna and flora indicate that they were once a part of the mainland from which they are now separated by shallow water. On the west coast north of the Patagonian archipelagos are the Juan Fernandez islands west of Valparaiso, the famous guano islands close to the mainland of Peru, the Galapagos islands on the equator, and the islands of the delta of the Guayas river near Guayaquil.
The Andes, north of their Patagonian section, have been, until recently, described as a series of more or less parallel but dis tinct ranges. It is now known that, except in the two widest sec tions (the Central Andes of Bolivia, where they consist of two ranges bordering the high altiplano, and the Andes of Colombia, where they finger out into three distinct ranges), they form a broad plateau, carved far over toward its western border by tribu taries of the great river systems of the Atlantic slope and sur mounted by narrow ridges and isolated mountains (many of them volcanoes of various ages) which include some of the highest peaks in the world. (For further details see article on the ANDES.) The South America lowlands, so-called, include the llanos of the Orinoco, the Amazon plains, the Chaco, and the Pampa, and form a more or less continuous belt reaching from the mouth of the Orinoco to the northern border of Patagonia north of the Rio Negro. Patagonia, however, may also be properly included in the lowland belt. There is no sharp line of division between it and the Pampa; much of its surface has a steppe-like character, and its soil-cover is alluvial like that of the rest of the lowland belt. This alluvial cover, throughout the lowland belt, is mainly of Andean origin supplemented locally by elements derived from isolated mountain masses that here and there break the general level. In the regions of heavy rainfall the alluvial soils are almost entirely distributed by water. In the Chaco, where the rainfall is distinctly seasonal in character and the network of streams from the Andes does not reach far into the lowlands, the transpor tation of alluvial deposits is assisted by the winds during the dry season. On the Pampa it is almost entirely transported by the
winds. The cover of rounded pebbles characteristic of large sec tions of Patagonia is believed to be of glacial origin distributed from the fronts of the old glaciers by water before the streams had been confined to definite beds and since that time by action of the winds. Throughout the lowland belt are evidences of im perfect stability, of movements of uplift and subsidence that have given rise to new local cycles of erosion and alluviation.
Geologists now recognize a close relationship between the high lands of Guiana and those of eastern Brazil. Both are composed of a shield of ancient crystalline granites and gneisses and of old folded schists and quartzites on platforms of sandstone, and belong to an old continental mass recently raised by vertical movements to its present elevation. At the edge of the Brazilian plateau falls still occur even on the largest rivers, some of which, like the Sao Francisco, flow on the surface of the plateau, while others, as in the southern part of Goyaz and Minas Geraes, have eroded deep gorges there. The interior is occupied by high monot onous surfaces at various levels and in a more or less perfect state of peneplanation. In the Guianas, however, and in the Serra do Mar of Brazil the mountains have the convex-dome shape char acteristic of crystalline mountains under the action of intense tropical rainfall. The mountains of the Serra do Mar are ex tremely picturesque. At many points they rise directly from the seashore to an elevation of 2,000 ft., forming in places bare granite walls. In other places they are covered with luxuriant tropical vegetation. Their highest point (7,323 ft.) is in the Serra dos Orgaos near Rio de Janeiro.
Rivers and Lakes.—The most important river systems of South America—the Amazon, Orinoco, and the Parana-La Plata system—have the greater part of their drainage basins in the lowland belt.. The chief headwater tributaries of the Amazon and the Orinoco have their sources on the Andean plateau where they have cut deep valleys. The principal sources of the Parana-La Plata system are in the Brazilian plateau, although the Pilcomayo and Bermejo (right bank tributaries of the Paraguay) rise in the Andes of southern Bolivia and northern Argentina. These three river systems together drain an area of about 3,700,000 sq.m. During the rainy season all of them overflow their banks and flood large sections of the central lowland belt. The Amazon is the largest river in the world. The main stream is navigable for ocean steamers as far as Iquitos, while many of its tributaries are navigable for steam launches almost to the foot of the Andes. In the time of high water the main stream of the Orinoco is navigable for i ,000 m. or more. Other important rivers are the Magdalena in Colombia, the Essequibo in British Guiana, and the Sao Francisco in Brazil. The Magdalena is navigable, in two sections separated by the rapids at Honda, for river steamers as far as Girardot, the river port of Bogota. The Sao Francisco which rises in the highlands of Minas Geraes is navigable nearly to the falls of Paulo Affonso, 140 m. from its mouth, and also above the falls.