Jebel Hefhuf is, perhaps, the most striking part of the fold. The southern portion owes its existence entirely to this syncline, consisting as it does of a long, and remarkably narrow, ridge-shaped hill of folded rocks. Dips of 50° and 60° are common in places, and the limestones implicated in the fold are usually rendered hard and highly crystalline. The highest crystalline limestones in Jebel Hefhuf probably represent the White Chalk, but the beds are too crystalline to show any traces of fossils.
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 andclayey limestone | 6·1 | ||
| Sandy ferruginousconglomerate | 0·3 | ||
| Clays with sandy and ferruginous layers,extending to oasis floor. | approximately | 22·0 | |
| 32·6 | |||
The beds are horizontal, and the neighbouring smaller hills which possess a similar limestone covering are precisely of the same height. It would seem impossible to account for these limestone caps in the midst of higher sandstone hills except by assuming that they mark the positions of islands, subsequently denuded, in the post-Eocene lake which deposited the limonite caps on the other hills; at the same time they evidently represent part of a synclinal fold, though the horizontal position and non-crystalline character of the beds show that this syncline must have been wide and shallow. It is scarcely possible to think there can have been a locally calcareous deposit from the lake which generally deposited the sandstone and limonite; the sudden transition from the black sandstone and limonite of the surrounding hills to the snow-white limestones of those under consideration is so strongly marked in the field as to forbid such a supposition. At the same time, no fossils were found in the beds, so they cannot be satisfactorily correlated with the limestones of the oasis-scarps, and they are of somewhat variable character at different points of the hill.
It is evident then that in the south part of the depression the Cretaceous beds as a whole form a large flat anticline, which is continuous with that of Farafra to the south.[58] This bears out the statement of Capt. H. G. Lyons,[59] some years ago, that he believed Baharia and Farafra Oases to lie on an anticlinal at right angles to that of Dakhla and Kharga. The anticlinal and synclinal folds of Baharia are parallel and were evidently produced by the same earth-movements.
Age of the folding.Within the oasis-area too, some other traces of folding are visible; in lat. 28° 11′ N., long. 29° 1′ E. are two small hills of clays and sandstones (the latter locally green in colour), the beds of which dip about 30° E. and W. respectively, showing a local anticline whose axis runs nearly north-and-south. In this neighbourhood, as in the oasis generally, it is not possible to trace the folding in the beds of the low ground, owing to its thick sandy covering.