Further south, near Gebel Zergat Naam, much more decided evidences of folding, and even of dislocation, were met with. The head of the Wadi el Kreim, south-west of Zergat Naam (see the geological map on [Plate XX]) is probably a line of fault, for here on the south-west of the wadi we have sandstones coming right down to the wadi floor, with a dip of 30° to the south-west near the edge, becoming flatter the further we go from the wadi, while on the other side are crushed and brecciated schists. Going further west, in the sandstone hill-mass which lies twelve kilometres west of Zergat Naam, the dip of the beds is in the opposite direction, being 10° to 15° north-east, and granite appears at the foot of the steep west-south-west slope; this, with the preceding observation, seems to indicate a synclinal fold terminated near Zergat Naam by a fault up-thrusting the schists and syenite.
Where the Wadi Garara cuts through the sandstone hills to receive the Wadi el Kreim, the beds dip markedly to the south, the observed inclinations being 60° or more at the north edges, rapidly falling to 20° or less further south; the north faces show granite and schists at their base.
Further west, on the way to Gebel Um Harba, the sandstone of the hills showed dips to the east of 15°. At Gebel Um Harba itself there are thick beds of sandstone dipping 13° east-north-east, while all around the mountain one looks out over beds having approximately the same inclination.
At Gebel Um Khafur, the dip is 13° to 14° to the north-north-east, and is very constant over a large area. From the north side, where the plain is 380 metres above sea-level, the hills rise with a succession of dip slopes and basset-edges over a horizontal distance of 2·9 kilometres (measured perpendicular to the strike) to the triangulation beacon at 560 metres above sea, the beds all along dipping at 13° or 14°. Unless there is step-faulting here along the strike-wadis (see [Fig. 60]) the total thickness of Nubian sandstone here is over 450 metres. This is a much greater thickness than has been noted anywhere else in Egypt, and I am inclined to think that there is step-faulting along at least two of the strike wadis which separate the hill-mass into ridges.
Fig. 60.—Section of Sandstone at Gebel Um Khafur.
In approaching Gebel Awamtib from the north-west, I crossed over a small patch of diorite in the sandstone at the pass from Wadi Um Terbi into Wadi Awamtib, and a basic dyke was found cutting the sandstone of a spur of Gebel Awamtib. The beds of Awamtib itself dip pretty uniformly a little north of west.
Fig. 61.—Sketch section of junction of sandstone with granite, west of Gebel Um Keit.
About nine kilometres to the south of Gebel Awamtib, a station was taken on a sandstone headland with schists and quartz veins at its floor, and afterwards I skirted the limit between sandstone and granitic rocks on the way to Gebel Um Reit. All along this route there was no suggestion of sharp folding or faulting; the beds were nearly horizontal right up to the limit, where the granite hills rise suddenly (see [Fig. 61]).