STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 35 



finds this shown in the Sudd of the Upper Nile. Willey-^ speaks of 

 that as the serious obstacle to navigation between Khartoum and 

 Gondokoo. The principal interruption is 25 miles long and within 

 150 miles there are three others aggregating 60 mjles. The growth 

 is very rapid after an unusually high fiood in the upper rivers, which 

 brings down much vegetation and sediment; but if the rainy season 

 be short, the growth is checked and the current carries out the 

 young plants, not yet strong enough to resist. The top in the older 

 denser areas is so dry that it can be burned, but the mass is so 

 matted that it must be cut wnih saws and the pieces dragged away. 

 This Sudd consists mostly of w^ater-papyrus and a bamboo, known 

 as elephant grass, with a convolvulus creeping over all. Besides 

 this ;'// situ material is more or less of transported stuff. One would 

 imagine that this last would be in comparatively small proportion on 

 the low^er sections as most of it would be stopped by the first raft. 



Wright-- cites Willcox to the effect that the Sudd interferes seri- 

 ously with the river's flow. It causes division into numerous 

 streams, wdiich lose themselves, north from Lado, N.L. 6°, in the 

 extensive swamps ; Willcox suggested that the channel could be 

 opened by dredging and could be kept open by planting willows 

 on the banks, which would enable the strong current to prevent 

 closing. The absence of willows along the banks makes control 

 of the swamps impossible. Wright cites also Lord Cromer, who 

 notes Major Peake's discovery that the Sudd is not simply a tangle 

 of vegetation floating on the water, but is a mass of decayed vege- 

 tation, papyrus roots and earth, much like peat in consistence and 

 so compressed by the current that at places elephants can cross it 

 safely. According to Willey, the thickness is only a few feet in 

 the overflowed swampy area but increases abruptly to 15 and 20 

 feet in the channel. The close resemblance to the floating mat of 

 more familiar types of sedges is evident. Were it not for the rapid 

 current underneath, the whole channel would soon be filled by the 

 more or less decayed material from the under side of the mat. But 



21 D. A. Willey, " The Barrage of the Nile," Nat. Geog. Mag., Vol. XXL, 

 1910, pp. 174, 184. 



-- G. F. Wright, " Scientific Confirmations of Old Testament History," 

 Oberlin, 1906, pp. 74-77. 



