=Gebel Um Heshenib= is a great ridge situated twenty-two kilometres north-west of Gebel Hamata. The beacon on its highest point, in latitude 24° 20′ 49″, longitude 34° 50′ 53″, has an altitude of 1,135 metres above the sea. Its lower parts are granite, but the upper third is of dark schists, while the actual ridge on which the beacon stands is a grey porphyrite. Gebel Um Heshenib is drained to the north by the Wadi el Abiad, a tributary of Wadi Gemal, and to the south by tributaries of Wadi Huluz. I ascended it on two occasions from opposite sides. The north approach is the easier road for camels, as they can pass easily up the broad and sandy Wadi el Abiad, while to reach it from Wadi Huluz one has to journey over a rather stony pass and along narrow stony wadis. But the climb is longer from the north side, being one of 635 metres against 380 metres from the south, and the southern climb is easier as well as shorter. It is interesting to note that as the ground south of the mountain lies at an average level of 250 metres higher than that to the north, the plumb-line ought from theoretical considerations to be attracted to the south by several seconds, and this was found to be the case when the mountain was used as a latitude station (_see_ p. 47) There is a very difficult pass east of the mountain from the head of Wadi el Abiad into a tributary of Wadi Huluz; I was told that loaded camels could not possibly get over the pass, and have reason to believe the statement true, as although I did not consent my men were desirous of going over it and volunteered to carry the baggage over themselves to relieve the camels.