Of the two highland regions of Brazil, that of the northern slope of the Amazon basin belongs physically to the isolated mountain system extending eastward from the Negro and Orinoco to the Atlantic, the water-parting of which forms the boundary line between the Guianas and Brazil. The culminating point is near the western extremity of this chain and its altitude is estimated at 8500 ft. The ranges gradually diminish in elevation towards the east, the highest point of the Tumuc-Humac range, on the frontier of French Guiana, being about 2600 ft. The Brazilian plateau slopes southward and eastward, traversed by broken ranges of low mountains and deeply eroded by river courses. The table-topped hills of Almeyrin (or Almeirim) and Ereré, which lie near the lower Amazon and rise to heights of 800 and 900 ft., are generally considered the southernmost margin of this plateau, though Agassiz and others describe them as remains of a great sandstone sheet which once covered the entire Amazon valley. Its general elevation has been estimated to be about 2000 ft. It is a stony, semi-arid region, thinly wooded, having good grazing campos in its extreme western section. Its semi-arid character is due to the mountain ranges on its northern frontier, which extract the moisture from the north-east trades and leave the Brazilian plateau behind them with a very limited rainfall, except near the Atlantic coast. The more arid districts offer no inducement for settlement and are inhabited only by a few roving bands of Indians, but there were settlements of whites in the grazing districts of the Rio Branco at an early date, and a few hundreds of adventurers have occupied the mining districts of the east. In general, Brazilian Guiana, as this plateau region is sometimes called, is one of the least attractive parts of the republic.
The great Brazilian plateau, which is the most important physical division of Brazil, consists of an elevated tableland 1000 to 3000 ft. above the sea-level, traversed by two great mountain systems, and deeply eroded and indented by numerous rivers. A thick sandstone sheet once covered the greater part if not all of it, remains of which are found on the elevated chapadas of the interior and on isolated elevations extending across the republic toward its western frontier. These chapadas and elevations, which are usually described as mountain ranges, are capped by horizontal strata of sandstone and show the original surface, which has been worn away by the rivers, leaving here and there broad flat-topped ridges between river basins and narrower ranges of hills between river courses. From the valleys their rugged, deeply indented escarpments, stretching away to the horizon, have the appearance of a continuous chain of mountains. The only true mountain systems, however, so far as known, are the two parallel ranges which follow the contour of the coast, and the central, or Goyana, system. The first consists of an almost continuous range crossing the northern end of Rio Grande do Sul and following the coast northward to the vicinity of Cape Frio, and thence northward in broken ranges to the vicinity of Cape St Roque, and a second parallel range running from eastern São Paulo northeast and north to the eastern margin of the São Francisco basin in northern Bahia, where that river turns eastward to the Atlantic. The first of these is generally known as the Serra do Mar, or Coast Range, though it is locally known under many names. Its culminating point is in the Organ Mountains (Serra dos Orgãos), near Rio de Janeiro, which reaches an elevation of 7323 ft. The inland range, which is separated from the Coast Range in the vicinity of Rio de Janeiro by the valley of the Parahyba do Sul river, is known as the Serra da Mantiqueira, and from the point where it turns northward to form the eastern rim of the São Francisco basin, as the Serra do Espinhaço. This range is also known under various local names. Its culminating point is toward the western extremity of the Mantiqueira range where the Itatiaya, or Itatiaia-assu, peak rises to an elevation of 8898 ft. (other measurements give 9823 ft.), probably the highest summit in Brazil. This range forms the true backbone of the maritime mountainous belt and rises from the plateau itself, while the Coast Range rises on its eastern margin and forms a rim to the plateau. North of Cape Frio the Coast Range is much broken and less elevated, while the Serra do Espinhaço takes a more inland course and is separated from the coast by great gently-sloping, semi-barren terraces. The second system—the Central or Goyana—consists of two distinct chains of mountains converging toward the north in the elevated chapadão between the Tocantins and São Francisco basins. The eastern range of this central system, which crosses western Minas Geraes from the so-called Serra das Vertentes to the valley of the Paracatú, a western tributary of the São Francisco, is called the Serra da Canastra and Serra da Matta da Corde. Its culminating point is toward its southern extremity in the Serra da Canastra, 4206 ft. above sea-level. The western range, or what is definitely known of it, runs across southern Goyaz, south-west to north-east, and forms the water-parting between the Paraná and Tocantins-Araguaya basins. Its culminating point is in the Montes Pyreneos, near the city of Goyaz, and is about 4500 ft. above sea-level.
The great part of this immense region consists of chapadões, as the larger table-land areas are called, chapadas or smaller sections of the same, and broadly excavated river valleys. How extensive this work of erosion has been may be seen in the Tocantins-Araguaya basin, where a great pear-shaped depression, approximately 100 to 500 m. wide, 700 m. long, and from 1000 to 1500 ft. deep, has been excavated northward from the centre of the plateau. Southward the Paraná has excavated another great basin and eastward the São Francisco another. Add to these the eroded river basins of the Xingú, Tapajós and Guaporé on the north and west, the Paraguay on the south-west, and the scores of smaller rivers along the Atlantic coast, and we may have some conception of the agencies that have been at work in breaking down and shaping this great table-land, perhaps the oldest part of the continent. The most southern of these chapadões, that of the Paraná basin, in which may be included the northern part of the Uruguay and eastern part of the Paraguay basins, includes the greater part of the states of Rio Grande do Sul, Santa Catharina, Paraná and São Paulo, the south-western corner of Minas Geraes, a part of southern Goyaz, and the south-eastern corner of Matto Grosso. The greatest elevation is on its eastern or Atlantic margin where the average is about 3280 ft. above sea-level. The plateau breaks down abruptly toward the sea, and slopes gradually some hundreds of feet toward the south and west. There has been considerable denudation toward the west, the eastern tributaries of the Paraná rising very near the coast. The northern and western parts of this plateau have an average elevation a little less than that of the Atlantic margin, and their slopes are toward the south and east, those of Goyaz and Matto Grosso being abrupt and deeply eroded. This great chapadão is in many respects the best part of Brazil, having a temperate climate, extensive areas of fertile soil, rich forests and a regular rainfall. Its Atlantic slopes are heavily wooded, but the western slopes exhibit grass-covered campos between the river courses. The São Francisco chapadão, which has a general elevation of about 2600 ft., covers the greater part of the states of Minas Geraes and Bahia, and a small part of western Pernambuco, and might also be considered continuous with those of the Parnahyba and Tocantins-Araguaya basins. This region is more tropical in character, partially barren, and has an uncertain rainfall, a large part of the São Francisco basin and the upper Atlantic slope of its eastern rim being subject to long-continued droughts. This region is well wooded along the river courses of Minas Geraes, the lower Atlantic slopes of Bahia, which are perhaps outside the plateau proper, and on the weather side of some of the elevated ridges where the rainfall is heavy and regular. It has extensive campos and large areas of exposed rock and stony steppes, but is richly provided with mineral deposits. It breaks down less abruptly toward the Atlantic, the slopes in Bahia being long and gradual. The Parnahyba chapadão covers the state of Piauhy, the southern part of Maranhão, and the western part of Ceará. Its general elevation is less than that of the São Francisco region, owing to the slope of the plateau surface toward the Amazon depression and to denudation. It resembles the São Francisco region in its uncertain rainfall and exposure to droughts, and in having large areas of campos suitable for grazing purposes. It is thinly wooded, except in the north, where the climatic conditions approach those of the Amazon valley. Its climate is more tropical and its development has gone forward less rapidly than in the more temperate regions of the south. The Amazonian chapadão, which includes the remainder of the great Brazilian plateau west of the São Francisco and Parnahyba regions and which appears to be the continuation of these tablelands westward, is much the largest of these plateau divisions. It covers the greater part of the states of Matto Grosso and Goyaz, a large part of southern Pará, the southern margin of Amazonas, and a considerable part of western Maranhão. It includes the river basins of the Tocantins-Araguaya, Xingú, Tapajós, and the eastern tributaries of the Guaporé-Madeira. A considerable part of it has been excavated by these rivers to a level which gives their valleys the elevation and character of lowlands, though isolated hills and ranges with the characteristic overlying horizontal sandstone strata of the ancient plateau show that it was once a highland region. The southern margin of this plateau breaks down abruptly toward the south and overlooks the Paraná and Paraguay basins from elevations of 2600 to 3000 ft. There is great diversity in the character and appearance of this extensive region. It lies wholly within the tropics, though its more elevated districts enjoy a temperate climate. Its chapadas are covered with extensive campos, its shallow valleys with open woodlands, and its deeper valleys with heavy forests. The rainfall is good, but not heavy. The general slope is toward the Amazon, and its rivers debouch upon the Amazonian plain through a succession of falls and rapids.
There remains only the elevated valley of the Parahyba do Sul, lying between the so-called Serra das Vertentes of southern Minas Geraes and the Serra do Mar, and extending from the Serra da Bocaina, near the city of São Paulo, eastward to Cape Frio and the coastal plain north of that point. It includes a small part of eastern São Paulo, the greater part of the state of Rio de Janeiro, a small corner of Espirito Santo, and a narrow strip along the southern border of Minas Geraes. It is traversed by two mountain chains, the Serra da Mantiqueira and Serra do Mar, and the broad, fertile valley of the Parahyba do Sul which lies between them, and which slopes gently toward the east from a general elevation exceeding 2000 ft. in São Paulo. This region is the smallest of the chapadão divisions of the great plateau, and might be considered either a southward extension of the São Francisco or an eastward extension of the Paraná chapadão. It is one of the most favoured regions of Brazil, having an abundant rainfall, extensive forests of valuable timber, and large areas of fertile soil. The mountain slopes are still masses of dense forest, though their lower elevations and neighbouring valleys have been cleared for cultivation and by dealers in rosewood and other valuable woods. This elevated valley is noted for its fertility and was once the principal coffee-producing district of Brazil.
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Outside the two great river systems of the Amazon and river Plate (Rio de la Plata), which are treated under their respective titles, the rivers of Brazil are limited to the numerous small streams and three or four large rivers which flow Rivers. eastward from the plateau regions directly into the Atlantic. The Amazon system covers the entire north-western part of the republic, the state of Amazonas, nearly the whole of Pará and the greater part of Matto Grosso being drained by this great river and its tributaries. If the Tocantins-Araguaya basin is included in the hydrographic system, the greater part of Goyaz and a small part of Maranhão should be added to this drainage area. The Tocantins is sometimes treated as a tributary of the Amazon because its outlet, called the Rio Pará, is connected with that great river by a number of inland channels. It is an entirely separate river, however, and the inland communication between them is due to the slight elevation of the intervening country above their ordinary levels and to the enormous volume of water brought down by the Amazon, especially in the flood season. As the outlet of the Tocantins is so near to that of the Amazon, and their lower valleys are conterminous, it is convenient to treat them as parts of the same hydrographic basin.
In the extreme north-east corner of the republic where the Brazilian Guiana plateau slopes toward the Atlantic there is a small area lying outside the drainage basin of the Amazon. Its rivers flow easterly into the Atlantic and drain a triangular-shaped area of the plateau lying between the northern frontier and the southern and western watersheds of the Araguary, whose extreme limits are about 0° 30′ N. lat. and 53° 50′ W. long. The more important of these rivers are the Araguary, Amapá, Calçoene, Cassiporé and Oyapok. The Araguary rises in the Tumuc-Humac mountains, in about 2° 30′ N. lat., 52° 10′ W. long., and follows a tortuous course south and north-east to the Atlantic. Its largest tributary, the Amapary, rises still farther west. Little is known of the country through which it flows, and its channel is broken by rapids and waterfalls where it descends to the coastal plain. The Amapá is a short river rising on the eastern slopes of the same range and flowing across a low, wooded plain, filled with lagoons. The Calçoene and Cassiporé enter the Atlantic farther north and have a north-east course across the same plain. All these small rivers are described as auriferous and have attracted attention for this reason. The Oyapok, or Vicente Pinzon, is the best-known of the group and forms the boundary line between Brazil and French Guiana under the arbitration award of 1900. It rises in about 2° 05′ N., 53° 48′ W., and flows easterly and north-easterly to the Atlantic. Its course is less tortuous than that of the Araguary.
The rivers of the great Brazilian plateau which flow directly to the Atlantic coast may be divided into two classes: those of its northward slope which flow in a northerly and north-easterly direction to the north-east coast of the republic, and those which drain its eastern slope and flow to the sea in an easterly direction. The former reach the coastal plain over long and gradual descents, and are navigable for considerable distances. The latter descend from the plateau much nearer the coast, and are in most cases navigable for short distances only. In both classes navigation is greatly impeded by sandbars at the mouths of these rivers, while in the districts of periodical rainfall it is greatly restricted in the dry season. The more important rivers of the first division, which are described in more detail under the titles of the Brazilian states through which they flow, are the following: the Gurupy, Tury-assú, Mearim, Itapicurú and Balsas, in the state of Maranhão; the Parnahyba and its tributaries in Piauhy; Jaguaribe in Ceará; and the Apody and Piranhas in Rio Grande do Norte. Of these the Parnahyba is the most important, having a total length of about 900 m., broken at intervals by rapids and navigable in sections. It receives only one important tributary from Maranhão—the Rio das Balsas, 447 m. long—and five from Piauhy, the Urussuhy-assú, Gurgueia, Canindé, Poty and Longa. Piauhy is wholly within its drainage basin, although the river forms the boundary line between that state and Maranhão throughout its entire length. All the rivers in this division are influenced by the periodical character of the rainfall, their navigable channels being greatly shortened in the dry season (August-January). In Ceará the smaller rivers become dry channels in the dry season, and in protracted droughts the larger ones disappear also.
The rivers of the second division are included in a very great extension of coast and are influenced by wide differences in climate. Their character is also determined by the distance of the Serra do Mar from the coast, the more southern rivers having short precipitous courses. The more northern rivers are subject to periodical variations in volume caused by wet and dry seasons, but the greater distance of the coast range and the more gradual breaking down of the plateau toward the sea, give them longer courses and a greater extent of navigable water. North of the São Francisco the watershed projecting from the plateau eastward toward Cape St Roque, known as the Serra da Borborema in Parahyba and Rio Grande do Norte where its direction becomes north-east, leaves a triangular section of the easterly slope in which the river courses are short and much broken by rapids. The rainfall, also, is limited and uncertain. The largest of this group of small rivers is the Parahyba do Norte, belonging to the state of Parahyba, whose length is said to be less than 200 m., only 5 or 6 m. of which are navigable for small steamers. The São Francisco, which belongs to the inland plateau region, is the largest river of the eastern coast of Brazil and exists by virtue of climatic conditions wholly different from those of the coast where it enters the Atlantic. The tributaries of the lower half of this great river, which belong to the Atlantic coast region, are small and often dry, but the upper river where the rainfall is heavier and more regular receives several large affluents. The river is navigable up to the Paulo Affonso falls, 192 m. from the coast, and above the falls there is a much longer stretch of navigable water.