=Wadi el Abiad=, likewise a tributary of Wadi Gemal, derives its name from the coarse white granitic sand which forms its floor. Its heads are situated near latitude 24° 20′, among the granite mountains called Gebel el Abiad and on the northerly slopes of Gebel Um Heshenib. There is a very steep pass from its head, east of Gebel Um Heshenib, into Wadi Huluz. Pursuing an almost northerly course and falling rather rapidly, Wadi el Abiad is at first very wide, with high granite hills on each side. It narrows further down, at a point opposite Gebel Shoab, where a small eastern feeder leads by an easy sandy pass into the Wadi Shoab. A little lower down, passing into diorite country, it turns more to the east, and after receiving the =Wadis Um Seyal el Foqani= and =el Tahtani= from the south-east, enters the Wadi Gemal near Madaret Um Gamil. The wadis called Um Seyal receive their name from the abundance of acacia trees in them; at the head of Wadi Um Seyal el Foqani there is a pass leading by the Wadai el Anz into Wadi Um el Abbas. =Wadi Nugrus=, an important tributary of Wadi Gemal, commences its course on the main watershed west of Gebel Nugrus, in latitude 24° 48′, at the pass into Wadi Gerf, 690 metres above sea-level, and courses south-east in almost a straight line for nearly forty kilometres to join the Wadi Gemal in latitude 24° 34′ and longitude 34° 50′. The fall to this point is some 450 metres, or an average of over ten metres per kilometre, but the fall is most rapid near the head, where the floor of the wadi is rocky and steep; the slope for the first few kilometres is over double the average. The approach to the head of Wadi Nugrus from the north, by one of the heads of Wadi Gerf, is almost a plain. But as soon as Wadi Nugrus is entered one becomes very sensible of the greater steepness of the eastern drainage by the stony nature of the track and the rapid fall. The wadi here is in fact only a narrow gorge with the huge mountains of Hafafit and Nugrus on the west and east sides respectively. Some three kilometres below the pass, close to the west side of the wadi, in a narrow gorge, is the spring called =Megal el Harami=, situated in gneiss rocks, and giving supplies of good water; the water infiltrates slowly, however, so that the yield is not sufficiently rapid to supply large quantities at once. Lower down, the wadi broadens out considerably, with a sandy floor in the middle of which low dark hills rise like islands. About thirteen kilometres below the head, an important feeder, the =Wadai el Nom=, comes in from the north-east. This wadi drains the south-east flanks of Gebel Nugrus and the west flanks of Gebel Hangalia; it contains rock basins holding water for some time after rain, and leads to a steep winding pass which enables one to make a circuit round the great granite mountain of Gebel Nugrus. The pass is, however, impracticable for baggage camels, and one has to dismount from a riding camel in order to get over.