A scarcely less remarkable feature is the series of depressions comprising the oases of Kharga, Dakhla, Abu Mungar, and Farafra; while Baharia occupies a more isolated position about midway between Farafra and the Faiyum. In contrast with those of the northern series, these southern depressions do not penetrate to sea-level. The lowest points in Kharga Oasis are probably at or just below the level of the sea, but the general level of the Kharga floor is about 70 metres above that datum. The lowest point of Farafra is somewhat higher than the general level of Kharga; those of Dakhla and Abu Mungar are higher still, while in Baharia, though it lies farther to the north, the floor-level averages some 130 metres above sea. A noteworthy thing about the larger depressions is that their northern boundaries are formed by steep escarpments, while to the south the slope is more gradual. This is the case, for instance, with the Faiyum, Qattara, Siwa, Kharga, Dakhla, Abu Mungar, and Farafra. Baharia is unique in being entirely surrounded by escarpments, as also in containing a large number of hills approximating in height to that of the bounding scarps. In the majority of cases the greater steepness of the northern boundaries can be correlated with geological structure; the northern walls of the Qattara and Siwa depressions, for instance, mark the southern limit of certain Miocene strata, while those of Kharga and Dakhla coincide with the southern limit of the Eocene limestones. To the south-west of Dakhla Oasis there stretches a broad tract of rising ground, with the Gilf Kebir and the peaks of Arkenu, Owenat, and Kissu as conspicuous features. On either side of this tract the general level falls, on the one hand towards Kufra and Cyrenaica, and on the other hand towards the Nile. The Gilf Kebir is a great broken plateau of sandstone, rising very nearly to the 1000-metre contour and stretching in a direction a little west of south for over 100 kilometres. I saw the south end of this plateau from several points on the way from Terfawi to Owenat when travelling with Prince Kemal el Din in 1925, and fixed its position by compass-bearings. As seen from the south, the plateau appeared to be merely a flat-topped hill; its true form and extent were discovered by the Prince in the following year, when he passed along its eastern foot on his way from Pottery Hill to Owenat. The highest peak of Arkenu, in about lat. 22° 17′, long. 24° 46′, I estimated to rise to approximately 1410 metres above sea. The altitude of Gebel Owenat far transcends Hassanein Bey’s previous estimate of 1100 metres; a trigonometric measurement which I made in 1925 gave its summit as 1907 metres above sea. The general level of the ground at the foot of Owenat I found to average about 600 metres, thus agreeing with Hassanein Bey’s figures. Gebel Kissu, though lower than Gebel Owenat, is considerably higher than Gebel Arkenu, and being an isolated mountain with a single