Dif, Hodein and Abraq limiting the view to the south-west. The rock of Gebel Abu Dahr is highly magnetic, and several pieces which I examined showed strong polarity. The compass needle points in all sorts of directions as one moves about the mountain. Gebel Abu Dahr and the high hills round it, especially to the south, form an important rain-collecting area, the drainage from which feeds, wholly or in part, the wells of Betan, Rahaba, Abu Reye, Abu Beid, and Gahlia, all of which are within a radius of about fifteen kilometres of the summit of the mountain. The relative abundance of water in this area is caused by two main factors. In the first place, the situation of the mountain on the eastward side of the watershed, only about forty kilometres from the coast, and its considerable height, condition the frequent accumulation of clouds about its summit, with relatively high rainfall as a consequence. And in the second place, the steepness of the slopes, and the fact that the serpentine rocks are not only of an impermeable nature, but are so crushed that the downwash into the gullies around is chiefly composed of smooth faced blocks rather than of absorbent sand, condition a higher ratio of run off to rainfall than exists in the case of most other localities in the Eastern Desert. A similar state of things is found in the case of Gebel Gerf, which, as will be mentioned further on, likewise consists of serpentine and is the centre of a district relatively rich in good wells; while in the case of the mountains of Faraid, which are much higher and closer to the sea, but consist of granite weathering into sand, though the rainfall is probably greater, the absorption by the sand is so rapid that there are no wells known to exist in their neighbourhood. Between Gebel Abu Dahr and Gebel Um Bisilla there are three remarkable little groups of granite hills. =Gebel Abu Arta= is a small range of red peaks six kilometres south of Um Bisilla; =Gebel Hendusi=, five kilometres further south, is a very conspicuous sharp granite peak rising to 678 metres above the sea and forming a good landmark; while =Gebel Abu Husenat=, four kilometres east of Hendusi, has another well-marked peak rising to 725 metres above sea-level. =Gebel Abu Sieiyil= is a many-peaked hill range running north and south for about four kilometres, situated eight kilometres west of the beacon on Gebel Abu Dahr. It has the appearance of being composed of a pink gneiss, but has not been visited. Its central peak, fixed by triangulation, is 833 metres above sea. The Wadi Abu Beid el Azrak runs south-westward past the south end of the range, through a gap between it and a smaller hill range to the east.