At Yakutsk navigation is generally practicable from the middle of May to the end of October, and at Kirensk, at the confluence of the Lena and the Kirenga, from the beginning of May to about the same time.
The gold-bearing gravels of East Siberia, especially those of the Lena and the Amur, are relatively more prolific than those of West Siberia.
The three principal rivers - the Ob, the Yenisei, and the Lena - take their rise on the high plateau or in the alpine regions fringing it, and, after descending from the plateau and piercing the alpine regions, flow for many hundreds of miles across the high plains and lowlands before they reach the Arctic, Ocean.
A typical feature of the north-eastern border of the high plateau is a succession of broad longitudinal 5 valleys along its outer base, ' The wide area between the middle Lena and the Amur, as well as the hilly tracts west of Lake Baikal, and the Yeniseisk mining region are in this condition.
On the Lena and the Vitim there are steamers, and a small railway connects the Bodoibo river port with the Olekma gold-washings.
Rock-salt occurs at several places on the Lena and in Transbaikalia, and salt-springs are numerous - those of Ust-kutsk on the Lena and of Usolie near Irkutsk being the most noteworthy.
They are described under different names in Siberia - the Altai Mountains in West Siberia, the Kuznetskiy Ala-tau and the Us and Oya Mountains in West Sayan, the Nizhne-Udinsk taiga or gold-mine district, several chains pierced by the Oka river, the Kitoi Alps in East Sayan, the mountains of the upper Lena and Kirenga, the Olekminsk gold-mine district, and the unnamed mountains which project north-east between the Lena and the Aldan.
Bering Strait, at 1 The Lena at Verkholensk is navigable for 170 days, at Yakutsk for 153 days: the Yenisei at Krasnoyarsk for 196 days.
Owing to the fact that the great plateau separates the Lena from the Amur, no easy water communication can be established between the latter and the other Siberian rivers.
Between the Volga and the Lena in Manchuria and northern China, rather more considerable increase in Korea, Siam and Japan.