If volume of water is to be considered, then probably the main stream of the Bahr-al-Ghazal is the Jur or Dyur, which, in its upper waters, is known as the Sue or Swe. The Sue-Jur rises in about 4° north latitude, not many days’ journey to the east of Mbomu. (The Mbomu is an important tributary of the Welle-Ubangi, which again is one of the principal tributaries of the Congo.) There is nearly continuous steam navigation up the Welle-Ubangi and the Mbomu to within a few days’ journey of the Nile basin. It was up this stream (from the Congo) that Marchand and his intrepid companions travelled in 1897. From the waters of the Mbomu they carried their little steam-launch overland to the Upper Sue. They were then able to descend this river for hundreds of miles to the Bahr-al-Ghazal and the main Nile. Near Mashra-ar-Rak, at the commencement of what the Sudanese style the Bahr-al-Ghazal, the Jur is joined by another important stream called, in its lower course, the Tonj, which has many tributaries coming from the vicinity of the Welle. Nearly parallel with this river to the east are the Roa and the Rōl (or Yalo), both of which enter the Bahr-al-Ghazal not far from its confluence with the main Nile. There is also a river Yei or Ayi, the direction of which is not fully determined. This river, which flows nearly parallel with the main Nile, some sixty miles to the west of Lado, either enters the Rōl and thus the Bahr-al-Ghazal, or turns into the main Nile not far from the bifurcation of the Bahr-az-Ziraf. The Bahr-az-Ziraf is an eastern branch of the main Nile, which leaves the parental river near Bor (about latitude 6° 40′ north) and flows very tortuously northwards, rejoining the White Nile about sixty miles east of Lake No (Bahr-al-Ghazal). The Ziraf or Giraffe River has other communicating channels with the main Nile, and also throws off sluggish contributions to the Khor Felus,--a western tributary of the Lower Sobat. The Giraffe River (so named by the Arabs for the many giraffes once sighted from its banks) receives from the south an important stream known (perhaps incorrectly) as the Oguelokur, which, through its component rivers the Tu and Kos, drains the northern slopes of the Lotuka Mountains.