From the top of Gebel Um Reit, which itself is granite, the sandstone limit could be seen to the north and east; the beds dip 30° in places; in those on the east the direction of dip is about south. The region round Um Reit is evidently one of considerable disturbance, but the sandstone is too far off for one to get any precise idea of its nature from the summit.
Fig. 62.—Sketch of faulting near Wadi Saalek.
Going northwards from Um Reit across the Wadi Saalek and up one of its branches into the head of Wadi Muegil, there is a good exposure of faulted sandstone overlying schists just before reaching the pass. Here (see [Fig. 62]) one of the faults is a distinct overthrust, with a north-easterly strike, and there are other faults in a parallel direction.
From the Wadi Muegil northwards past the Galt el Aguz to Gebel Um Harba there are gentle dips and curvings of the sandstone beds, with a predominant dip about north-east. At the Galt el Aguz the sandstone rocks are much tumbled about, but this appears to be due to fall of over-hanging beds.
At the pass from Wadi Um Arta into the head of Wadi Silsila, the dip of the sandstone is north-north-east. In its lower part, Wadi Silsila passes between sandstone ridges the dip of which is constantly east-north-east.
Round Bir Abraq and the triangulation station on Gebel Abraq (see large scale map on [Plate XV]) the main direction of dip is east-south-east; the pool of Bir Abraq itself is under projecting slabs of sandstone dipping in this direction. Bir el Sunta, a little further north, appears to lie in a syncline, the beds of the hills to the north dipping south-east, while those to the south dip north-west.
Approaching the sandstone from the east by Wadi Hodein, one traverses granite country with felsite dykes and enters suddenly into high sandstone plateaux. The beds at the Abu Saafa Springs dip about 5° northwards.
The beds of Gebel Dif and Gebel Anfeib have a prevalent dip on the west side to the east and north-east, while on the east face the dip appears to be in the reverse direction. This great mass of sandstone plateau may thus be a syncline with a north-westerly strike (i.e., a strike roughly parallel to the main direction of the watershed mountain ranges), but the eastern face was not examined in detail, and it may be that the whole mass dips to the north-east; some outlying small sandstone masses near the head of Wadi Edunqul show no reversal, the dip being still east-north-east. At Bir Dif the sandstones are variously tilted, and probably faulted.
The sandstones on the east side of the watershed ranges, near Gebel Ranga, were observed by Dr. Hume to dip towards the sea. In the south part of the region there are some low hills forming two series of ridges between the sea and Gebel Kolaiqo, separated by hills of red aplitic granite; these hills were not actually visited, but were mapped from some little distance, and the dip of the beds was not measured, but the nature of the rocks was confirmed by specimens of sandstone brought back by guides sent to the place.