The W Siberian Plain is principally drained by the Yenesei and Ob-Yrtish. Between them they discharge 1024 km³/yr, 30% of the surface drainage of the USSR. The early history of these rivers is not clear as they did not drain in the most probable direction, but during and after glacial times there is better understanding of their alignment and evolution. The first terrace is 15 000 BP is 10-15m above low water level, so the history of the Pleistocene and Holocene is well known with good stratigraphical evidence. Thick peats developed during the Holocene. -K.Clayton