=Gebel Elba=,[111] the most northerly mountain of the main group, is cut off from the mountains to the south by the Wadis O Sir Hadal and Serimtai; there is a pass between the heads of these wadis, so that a complete circuit of the mountain can be made, although from almost any aspect Elba appears to be joined on to the other mountains of the group. In plan, Gebel Elba is nearly a square of about fifteen kilometres sides, with its diagonal in the meridian. It is a bristling mass of light-coloured granite peaks, flanked on the south and west by rugged hills of darker rocks. The highest point, the “high peak” of the Admiralty Chart, is in latitude 22° 10′ 3″, longitude 36° 21′ 52″, and 1,435 metres above sea; another peak, slightly lower, but more conspicuous and nearer the centre of the mass, was chosen for the site of the triangulation station. The beacon on this latter peak is 1,428 metres above sea, and has the position latitude 22° 11′ 27″, longitude 36° 20′ 52″. The peak which bears the triangulation station forms a centre from which drainage lines radiate in all directions. The principal of these drainage lines, which are all well wooded, are the Wadi Yahameib, which with its feeders Wadis Akau and Kansisrob drains the north faces of the mountain, and unites with Wadi Aideib, which drains the north-east flanks; Wadi Serimtai, which by its feeder the Wadi O Sir Eirab drains the south part of the mass and then curves round north-eastwards to the sea; and the Wadi Yoider, which drains the western parts of the mountain by its three main heads called respectively Wadi Akwamtra, Wadi Qeirat, and Wadi O Sir Hadal, and then courses northward to reach the sea. The approach to Gebel Elba by the coast-plain from the north-west is said to be difficult, on account of having to cross an extensive tract of sand dunes, called I Hubal, which lies to the north and north-east of Gebel Sul Hamid. The survey expedition reached the mountain by marching eastward from Bir Meheriqa in the Wadi Di-ib. On this road the sand was not found a serious hindrance, though progress was rather slow through O Harbub, a sand-choked wadi which was entered on turning eastwards just after leaving Bir Meheriqa. Skirting the south side of Gebel Sul Hamid over a sandy plain, we continued eastward with a slight northerly bend till the jagged mass of Qash Amir came into view; then striking due east again we entered some low hills and dropped by an easy pass into Wadi Siamtit, a little feeder of Wadi Yoider; crossing the main channel of Yoider, we continued our course eastward across very sandy minor wadis, and turning a little southward we reached Bir Akwamtra, where we found a fairly large Bisharin camp, in a stony wadi full of trees.