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.
Its principal tributaries from the south are the Sungari, which the Chinese consider to be the true head-river of the Amur, and the Usuri; from the north it receives the Oldoi, Zeya, Bureya, Kur, Gorin and Amgun.
From the Khingan ranges to the Pacific, south of the Amur, stretch the rich districts of Manchuria, a province which connects Russia with the Korea by a series of valleys formed by the Sungari and its affluents - a land of hill and plain, forest and swamp, possessing a delightful climate, and vast undeveloped agricultural resources.
In its course through Eastern Manchuria it forms the watershed of the Sungari, Usuri and other rivers, and in the south that of the Ya-lu and many smaller streams. it also forms the eastern boundary of the great plain of Liao-tung.
The three principal rivers of Manchuria are the Sungari,Mutankiang and Usuri already mentioned.
Of these the Sungari, which is the largest, rises on the northern slopes of the Chang pai Shan range, and runs in a north-westerly direction to its junction with the Nonni, from which point it turns north-east until it empties itself into the Amur.
The Mutan-kiang takes its rise, like the Sungari, on the northern slopes of the Chang pai Shan range, and not far from the sources of that river.
It takes a north-easterly course as far as the city of Ninguta, at which point it turns northward, and so continues until it joins the Sungari at San-sing.
By the Sungari, on the S.
Kirin, the capital of the province, occupies a magnificent position, being surrounded on the north, west and south by a semicircular range of mountains with the broad stream of the Sungari flowing across the front.
A-She-ho, on the Ashe, with a population of 60,000; Petuna (Chinese, Singchung), on the Sungari, population 30,000; San-sing, near the junction of the Sungari and Mutan-kiang; La-lin, 120 m.
By the Sungari, and on the W.
Between the Nonni 'and the Sungari, and the rich plains of the Bureya and Silinji in the Amur province belong to this belt, 400 m.
Opportunities for administrative work, however, were scanty, and in 1864 Kropotkin accepted charge of a geographical survey expedition, crossing North Manchuria from Transbaikalia to the Amur, and shortly afterwards was attached to another expedition which proceeded up the Sungari River into the heart of Manchuria.
The boundary line which separates Mongolia from Manchuria runs past Dalai-nor and Lake Buir, crossing the Great Khingan in 47° 30' N., towards Tsit g ihar in Manchuria; then, crossing the Nonni river, it strikes the Sungari at Khulanchen, where it turns westwards up this river, reaching the Shara-muren river in 123° 30' E.
Below Chita, with Vladivostok, and sends off a branch from Kharbin, on the Sungari, to Dalny and Port Arthur.
East Siberia suffers less from this plague than the marshy Baraba steppe; but on the Amur and the Sungari large gnats are an intolerable plague.