=Gebel Nugrus=, the central and highest mountain of this northerly group, is a great boss of red granite rising to a height of 1,505 metres among schists and gneisses. It is an almost isolated mass, for though the Hangalia and Hafafit ranges close in on it from either side, there are passes both east and west of it by which a circuit of the mountain can be made. In plan, it is a pear-shaped mass, about fourteen kilometres in length by six kilometres in width, having its long axis north-west and south-east. Gebel Nugrus is on the main watershed; its north parts are drained Nilewards by the Wadi Hangalia and other feeders of Wadi Gerf, while the drainage from its south portion passes by the Wadi Nugrus and Wadai el Nom to the Wadi Gemal and thence to the sea. The ascent of the mountain was made from a camp about four kilometres west of the summit, at the top of the pass leading into the stony head of Wadi Nugrus. The divide here is flat and sandy, at an altitude of 691 metres above sea-level, so that the ascent from camp to summit was 814 metres. Striking eastwards over the lower ridges which flank the main back-bone of the mountain, the summit was reached after a climb of nearly four hours. When ascended from this side, there appear to be two main peaks, of which the further one, marked by a beacon, is the triangulation point; the best way up is between the two peaks, as the passage from one to the other is very rough and steep. Though tiring, the climb is not very difficult. The top of the mountain (_see_ Plate VII) is a mass of great rounded knobs of granite, on which a suitable place for setting up instruments was only found after some searching. The beacon, in latitude 24° 48′ 34″, longitude 34° 35′ 47″, is on a rounded eminence not large enough to receive an instrument, so that eccentric observations were necessary; the distance between the eccentric point of observation and the beacon had to be found by a subtense method, as the roughness of the mountain top rendered any process of chaining or taping impossible. The view from the summit is very fine. To the west, one sees the pinnacles of Migif and the nearer long range of Hafafit; to the north-east is the black cone of Atut; northward, seen over a sea of hills, is Igli; to the east is the high ridge of Hangalia, culminating to the south in Gebel Zabara.