AMUR, the chief river of Eastern Asia north of the Hwang-ho and about 3,00o miles in length. It traverses from west to east a series of tilted earth-blocks which present a steep face to the south-east and a gentle back-slope to the north-west. The course of the river is, therefore, alternately towards the north-east, when it flows parallel to the north-east to south-west trending ridges and towards the south-east, when it cuts across them. It is formed by the confluence of the Shilka, rising in Transbaikalia, and the Argun, rising on the back-slope of the Great Khingan, one of these earth-blocks. It receives its most important tributaries, the Sungari and the Ussuri, from the similar back-slope of the earth-block overlooking the Sea of Japan. Both tributaries enter from the south. Since the late 17th century, when the Chinese came into contact with the extending power of Russia, the Amur has had considerable political signifi cance. The Argun head-stream was taken as part of the boundary between the two empires at the Treaty of Ner chinsk (1689), and the present boundary between Manchuria and Siberia follows the line of the Argun, Amur and Ussuri, thus forming one of the longest river frontiers in the world. The river is high est in summer, the season of rains, and then the Sungari, draining North Man churia, has a greater volume of water than the Amur itself. In win ter the river is frozen over and navigation is confined to the six months from May to October. For boats drawing four feet of water, the Amur is then navigable for over 2,000 miles up to Stret ensk and the Sungari up to Kirin. But the fact that its outlet lies so far to the north deprives the Amur of much of its value and, moreover, it has as a competitor the Chinese Eastern rail way which is linked with more southerly ports at Vladivostok and in Manchoukuo.