The orography of the Aldan region is little known; but travellers who journey from the Aldan (tributary of the Lena) to the Amur or to the Sea of Okhotsk have to cross the same plateau and its border-range.
It is this Wale ' circumstance that facilitated the rapid invasion of Siberia Wal er l by the Russian Cossacks and hunters; they followed the omm courses of the twin rivers in their advance towards the east, and discovered short portages which permitted them to transfer their boats from the system of the Ob to that of the Yenisei, and from the latter to that of the Lena, a tributary of which - the Aldan - brought them close to the Sea of Okhotsk.
In 1628 the Russians reached the Lena, founded the fort of Yakutsk in 1637, and two years later reached the Sea of Okhotsk at the mouth of the Ulya river.
In 1643 Poyarkov's boats descended the Amur, returning to Yakutsk by the Sea of Okhotsk and the Aldan, and in1649-1650Khabarov occupied the banks of the Amur.
In winter, for example, when the northern monsoon begins to blow, numbers of denizens of the Sea of Okhotsk swim southward to the more genial waters of north Japan; and in summer the Indian Ocean and the Malayan archipelago send to her southern coasts a crowd of emigrants which turn homeward again at the approach of winter.
