The north portion of the Gerf mass, sometimes called Gebel Meneiga, is drained by the Wadi Kreiga, which is a tributary of Wadi Hodein. One of the principal feeders of Wadi Kreiga is the stony Wadi Meneiga, important as containing perennial springs of good water, easily accessible to camels. The eastern and southern parts of the mass are drained by various feeders of Wadi Shab, the principal of these feeders being Wadi Shellal el Sharqi, Wadi Muqur, Wadi Baaneit, Wadi Diqdib, and Wadi Sherefa el Sharqi. The Wadis Muqur, Baaneit, and Diqdib, all contain wells or springs, that in Wadi Diqdib being right in the heart of the mountain mass, while the others are nearer to its periphery. The western flanks of the Gerf mass are drained by the feeders of Wadis Feqoh and Madi, the principal being the Wadis Sherefa el Gharbi, Eirahimib, Shellal el Gharbi, and Korbiai. The Wadi Sherefa el Gharbi is important as leading to the Sherefa Pass (907 metres) which forms a direct road from Bir Sararat Seyet to the well of Um Rasein, while Wadi Korbiai contains an excellent well at its head, easily reached by camels. =Gebel Dreb= is a many-peaked mass of mountains covering some sixty square kilometres, situated south-west of the Gerf mass, from which it is separated by the Sherefa Pass. Its highest peak is 1,293 metres above sea, but there are numerous other peaks of but little inferior altitude. Its south-western portion looks on to the plain at the head of Wadi Feqoh, while to the south-east it is separated from Gebel Medarai by an easy pass leading from the head of Kwat Hewah westwards into the head of Wadi Kreim, a tributary of Wadi Feqoh. Another pass is said to exist leading from Wadi Sherefa el Sharqi into the head of Wadi Dreb, where there is a well called Bir Bint el Dreb. =Gebel Medarai=, the next mountain mass to the south-east, is separated from Gebel Dreb by the pass into Wadi Kreim above referred to, while at its south faces it is separated from Gebel Abu Hireiq by another pass leading from one of the heads of Wadi Medarai westwards into the Wadi Kirwau, a tributary of Wadi Feqoh. The highest point of Gebel Medarai, marked by a large cairn, is in latitude 22° 30′ 58″, longitude 35° 12′ 5″, and rises to 1,299 metres above sea-level. The north faces of the mass are drained by Kwat Hewah, a tributary of Wadi Shab; the eastern flanks by Wadi Medarai, a tributary of Wadi Ibib, while the western faces drain by various feeders into Wadi Feqoh. =Gebel Abu Hireiq=, the mountain-mass next south of Medarai, extends eastwards, as a broad tract of many high ridges, almost to the gneiss-boss of Um Rasein, while to the south it is united with Gebel Abu Hodeid. The highest point of Abu Hireiq is 1,319 metres above sea. Its eastern flanks are drained by tributaries of Wadi Ibib, while the western parts drain into Wadi Feqoh.