(5) Be this as it may, as indicated by Mr. Moon, the Nubian Sandstone proper was met with in typical form a little north of El Harrash (Zieghen). The specimens obtained from this point onward to the junction with the igneous rocks about 30 km. north of Arkenu are all varied members of the same sandstone formation which in Egypt proper and the Sudan spreads over enormous areas.
(6) Great interest attaches to the discovery of typical granite in the oases of Ouenat and Arkenu. The main rock is of pegmatitic type, being composed of well-shaped felspars, glassy quartz, and hornblende. A point brought out by the photograph is the intense action of temperature variation on these igneous rocks. The whole of the hillside is strewn with gigantic boulders, some of which have been split into large pieces which obviously once formed part of the same block.
As regards the nature of the relations between the granite and the Nubian Sandstone, it is to be noted that the granite difference of level might be explained (a) by the existence of a fold, (b) by the presence of a fracture line or fault, (c) by intrusion of the granite when in a molten condition into the overlying sandstone.
After conversation with Hassanein Bey, and a closer examination of his photographs from this point of view, one is led to the following conclusion:
(1) A fold seems possible, because the sandstone (which dips or slopes off the granite in certain folds in the south of Kharga Oasis) is seen to be obviously dipping toward the spectator in the cinema photograph of camels coming through the valley of Ouenat. Taking (c) first, we have no proof anywhere in Egypt that granite has been intruded into the Nubian Sandstone, in all cases where the relations are clearly displayed the granite having obviously been worn down before the sandstone was deposited on it.
(2) We are consequently disposed to adopt the view, pending further study, that the differences of level may be due to the existence of a fold. The alternative would be the presence of a fracture line, along which the granite has been pushed up in a solid form to a higher level than the sandstone which normally overlies it, or the sandstone has been led down along the line of weakness against the granite.
A very interesting feature is the presence of well-made drawings of giraffes and ostriches on the granite boulders. As Hassanein Bey points out, the camel is absent, and it is to be regretted that there are no pictures of human beings. These graffiti may be of ancient date, being drawn at a period when rainfall was greater in this portion of North Africa than it is at present.
Hassanein Bey’s expedition has thus indicated that both the Miocene strata in the north and the great Nubian Sandstone formation further south continue well to the west of the western Egyptian boundary with unchanged characteristics, while the discovery of the granitic oasis, as I understand within the boundaries of Egyptian territory, opens up the possibility of developing alternative routes to Darfur from Dakhla Oasis, and also indicates a water-base of great importance in connection with the exploration of the unknown territory lying west of the route followed by Hassanein Bey. Its further study from the geological standpoint would be of great interest.