The double river-systems of the Volga and Kama, the Ob and Irtysh, the Angara and Yenisei, the Lena and Vitim on the Arctic slope, and the Amur and Sungari on the Pacific slope, are instances.
Asia, the same fauna extending in Siberia as far as the Yenisei and the Lena.
The Ob,Yenisei and Lena,which traverse Siberia, are among the largest rivers in the world.
The northern land-mass begins in the north with the area which lies between the Yenisei and the Lena.
Attempts are being made to render the Angara navigable below Irkutsk down to the Yenisei.