It is noteworthy that all the basaltic rocks of the oasis occur on the north-west side, and at no great distance from this syncline. To the north-east of Jebel Hefhuf the line of fold passes apparently between the range of elongated hills west of Harra and the larger somewhat triangular hill to the north of it, and although the limestones and clays of these hills show a considerable amount of folding they do not exhibit it in so striking a manner as Jebel Hefhuf. Continuing the line till it cuts the last scarp, we arrive at a prominent sandstone headland, in the gullies on either side of which the folding can be very well seen. To the west of the headland the beds are thrown sharply up in the valley so as to be nearly vertical; this up-throw has resulted in an actual fault, the denuded edges of the vertical sandstone and clay-beds being overlain by a horizontal bed of limonite. The nose of the promontory is of sandstone, this being thrown up somewhat on the south-east side of the fault; the upper sandstone and clay beds dip south-east again somewhat sharply on the face of the headland and come down to the level of the oasis floor. It would seem therefore that at this point we have the syncline between two sharp anticlines, the north western of which has culminated in the fault. The southern end of the oasis is cut out in a well-marked gentle anticline. On the west side from Ain el Haiss southwards the whole succession of Cretaceous rocks dip steadily to the north-west at from four to five degrees, while those on the east scarp show an equally constant dip to the south-east, which increases further north, till in the neighbourhood of lat. 28° 5′ its magnitude reaches 45°; it becomes gradually less further northwards. Owing to this strong tilting of the beds, the large hill near the scarp consists entirely of sandstones and clays with a cap of quartzite and limonite, although nearly or quite as high as the scarp; the beds here recover their nearly horizontal position at a very short distance north-west of the line of folding, as do also those of the plateau on the other side the line. Besides the above-described disturbances of the beds, there are some smaller local disturbances which are extremely well-marked. Thus for instance the large flat-topped hill in N. lat 28° 7′ and E. long. 28° 48′, like several smaller hills E.S.E. of it, bears a cap of limestones, although its height is less than that of the sandstone hills around it. The section of this hill at its western side is as follows:— _Top._ Metres. Silicified limestone 0·6 Hard impure chalk 2·4 Silicified limestone 1·2 Pale green soft sandy and clayey limestone 6·1 Sandy ferruginous conglomerate 0·3