=Gebel Gerf= (_see_ map on Plate XVII) is a mass of rugged mountains, roughly circular in plan, some twenty kilometres in diameter, extending between latitudes 22° 35′ and 22° 50′, and between longitudes 35° 8′ and 35° 20′. Its highest point, marked by a beacon 1,419 metres above sea-level, is somewhat north of the centre of the mass, being situated in latitude 22° 42′ 6″ N., longitude 35° 12′ 16″ E. Approached from any side, Gerf blocks out the entire view ahead. The central parts of the mass are entirely impassable for camels. There is no possible track across it from north to south, nor is there any east to west pass across it north of the Sherefa Pass (which skirts its south end) except by the heads of Wadi Shellal. The northern part of the mass, which is semi-detached by the passes in the heads of Wadi Shellal above-mentioned, is sometimes called =Gebel Meneiga= or =Gebel Korbiai= after the important water sources of the same name in the wadis draining from it; and the north-eastern peaks are sometimes called =Gebel Muqur= from the spring Bir Muqur. But these names are, I am told, quite local, and the entire mass is usually known to the Arabs as Gebel Gerf. This application of a single name to an entire group of mountains, with scores of separate peaks, extending over about 500 square kilometres, is very unusual, especially when, as in this case, it is drained by wadis containing good wells and plenty of vegetation. The explanation given to me by the guides was quite comprehensible; they stated that Gerf was the only mountain mass in that part of the desert which was so extensive in every direction as to prevent them getting a clear idea of its true shape in their wanderings over it. They can get all round it only by a rough journey of several days, and any endeavour to cross its main portion met with failure, so that they had perforce to regard it as a single great mass, of the true structure of which they could form no satisfactory notion. The immense interest which the guides took in the mapping of this particular mountain tract fully confirmed the explanation given. The mapping was accomplished by making an entire circuit of the mass, and ascending a few of the principal summits. PLATE XVII. [Illustration: MAP OF THE DISTRICT OF GEBEL GERF. Ball. Geography & Geology of South-Eastern Egypt. Photo-Metal-Process. Survey Dept. Cairo 1910. (60-190)]