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.
By the Nonni and Mongolia.
The only towns of any importance are Tsitsihar and Mergen, both situated on the Nonni and Khailar in the west.
Lower terrace is fringed by a massive border-range - the Khinganwhich runs in a north-easterly direction from the Great Wall of China to the sources of the Nonni-ula, A narrow alpine region (40 to 50 m.), consisting of a series of short secondary chains parallel to the border-range, fringes this latter on 'its eastern face.
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.
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.
South-eastern Mongolia is the part of Mongolia which lies on the eastern slope of the Great Khingan Mountains, entering like a wedge between the lower course of the Nonni river and the middle Sungari.