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 crystalline floor is exposed in the valleys of the Madeira, Xingu, &c. Some of the rocks thus exposed are, however, eruptive (e.g.
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 Xingu, the next large river west of the Tocantins, is a true tributary of the Amazon.
These three streams form the Xingu, or Parana-xingu, which, from 73 m.
Near its mouth, the Xingu expands into an immense lake, and its waters then mingle with those of the Amazon through a labyrinth of canos (natural canals), winding in countless directions through a wooded archipelago.
The first high land met in ascending the river is on the north bank, opposite the mouth of the Xingu, and extends for about 1 s o m.
On the south side, above the Xingu, a line of low bluffs extends, in a series of gentle curves with hardly any breaks nearly to Santarem, but a considerable distance inland, bordering the flood-plain, which is many miles wide.