=Wadi Shab=, with a basin of about 1,250 square kilometres, drains the eastern and southern portions of the great group of mountains of which Gebel Gerf is the centre, and reaches the sea in latitude 22° 52′, a little to the north of Mersa Shab. It has a great number of heads, most of which bear special names, the name Shab being applied collectively to them from the locality near the hill of Qrein Salama, about forty kilometres from the sea, where they begin to unite together into one great trunk channel. From the circumstance that its heads are situated in a high mountain mass where the rainfall is relatively great, and moreover have steeply falling stony beds which absorb but little of the precipitation, the upper portions of Shab and its feeders are well stocked with trees. Only in the last stages of its course to the sea, where the absorption of its drainage by the sandy coast plain becomes great, does the abundance of vegetation fall off and the channel become barren. Its principal heads and feeders are Wadi Radad (fed by Wadi Shellal el Sharqi), Wadi Tikosha, Wadi Muqur (fed by Wadi Ti Ilak), Wadi Qadiloi (fed by Tilat Tihu Shana), Wadi Baaneit, Wadi Kilanai, Wadi Um Saha, Wadi Diqdib, Wadi Sherefa el Sharqi, and Kwat Hewah. At least three of these contain good water sources, Bir Muqur, Bir Baaneit, and Bir Diqdib being situated in the upper parts of the wadis bearing the same names. The various heads and feeders of Shab will be described in detail below, commencing from the northernmost one. =Wadi Radad= may be more properly described as a tributary than as one of the heads of Wadi Shab, as it joins the trunk wadi some fifteen kilometres below the other feeders. It originates in a rugged tract of high hills near Bir Meneiga, and courses eastward for about thirty-six kilometres, joining Wadi Shab on the coast-plain near the low hills of Ti Qireira, about twenty-four kilometres up from the point where Wadi Shab enters the sea. It has not been surveyed in detail, but its course was mapped from the triangulation station of Gebel Gerf and from other occupied stations whence portions of it were visible. =Wadi Shellal el Sharqi=, a large feeder of Wadi Radad, originates in the mountains between Bir Diqdib and Bir Muqur. It has many heads, the best known of which is one coming from the west, leading to a pass into Wadi Shellal el Gharbi, a tributary of Wadi Madi; while another, a little further south, leads to another pass into Wadi Um Reddam and forms a possible road to Bir Sararat Seyet. Wadi Shellal el Sharqi follows generally a northward course, with a rapid fall, and joins Wadi Radad about eighteen kilometres below the head of the latter.