The northern slope of this great plateau is drained by the AraguayaTocantins, Xingu, Tapajos and Guapore-Mamore-Madeira, which flow northward, and, except the first, empty into the Amazon; the southern slope drains southward through a multitude of streams flowing into the Parana and Paraguay.
Add to these the eroded river basins of the Xingu, Tapajos and Guapore 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.
It includes the river basins of the Tocantins-Araguaya, Xingu, Tapajos, and the eastern tributaries of the Guapore-Madeira.
The lower river valleys of the Tocantins-Araguaya, Xingu, Tapajos and Paraguay are essentially tropical, their climate being hot and humid like that of the Amazon.
The Tapajos, running through a humid, hot and unhealthy valley, pours into the Amazon 500 m.