Below Kuhsan it receives fresh tributaries from the west.
The Amur, the upper tributaries of which rise on the eastern border-range of the high plateau, is similar.
The other great rivers are tributaries of the Ucayali.
As Lake Baikal is approached the stream of Russian immigration becomes narrower, being confined mostly to the valley of the Angara, with a string of villages up the Irkut; but it widens out again in Transbaikalia, and sends branches up the Selenga and its tributaries.
The rubber forests are on the Orinoco and its tributaries of the Guiana highlands.