. The earth and its inhabitants ... Geography. 252 AMAZONIA AND LA PLATA. The divide between tlie sources of the Guaporé and the headwaters of the Paraguay scarcely exceeds 1,G5(J feet in altitude, and the Brazilian uplands appear to be connected with those of the Chiquitos territory only by a very narrow isthmus of ancient rocks. Here is the true geographical centre of South America. On the maps a continuous chain of mountains is traced between the Madeira and Tapajoz basins, then between the Tapajoz and Paraguay, and lastly between the Tapajoz and the Araguaya. Yet it is certain that this se
. The earth and its inhabitants ... Geography. 252 AMAZONIA AND LA PLATA. The divide between tlie sources of the Guaporé and the headwaters of the Paraguay scarcely exceeds 1,G5(J feet in altitude, and the Brazilian uplands appear to be connected with those of the Chiquitos territory only by a very narrow isthmus of ancient rocks. Here is the true geographical centre of South America. On the maps a continuous chain of mountains is traced between the Madeira and Tapajoz basins, then between the Tapajoz and Paraguay, and lastly between the Tapajoz and the Araguaya. Yet it is certain that this semi-circular ridge has but a fragmentary existence. The heights dominating the j^lains of the upper Paraguay and its affluents are in reality merely the escarpments of a plateau disposed in horizontal or very slightly inclined strata, and eroded by the streams now descending towards the Amazons. The rampart itself has a mean Fig. 110.—Tapajoz and Paraguay Watershed. Scale 1 : .^.50'::, 125 Miles. elevation of no more than 1,650 feet, and above the edge of the plateau rise a few isolated crests, attaining here and there a height of some 3,000 feet. Thus the orographic system of the Matto Grosso watershed, indifferently called " cordilheira " or " campos " dos Parexi, from the local Indian tribe, presents a mountainous aspect, only as seen from the south. On this steep side the face of the escarpments is carved into rocky walls, sharp peaks, or needles. Bat on the opposite side, facing the Tapajoz and Xingu basins, nothing is seen except a long gently-inclined slope gradually merging in the Amazonian plains. The southern parts of the Araxa, as the edge of the plateau is generally called, date probably from paleozoic times, and here are represented carboniferous, devonian, and silurian formations. Farther north, in the zone of cataracts traversed by the Madeira, Tapajoz, Xingu, Tocantins, and their affluents, the rocks exposed by the erosions of these st
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