Possible Former Extent of the Eocene Rocks.
Eocene rocks are entirely absent from the district, and the same is the case with Cretaceous rocks younger than the Nubian sandstone. But if we go westward along the parallel of Berenice, across the Nile into longitude 23° 30′, we come to the plateau face of Gebel Garra, where there are exposed thicknesses of about ninety metres of Eocene limestone and 240 metres of Cretaceous marls. These beds cover great expanses further west and north; they evidently once extended beyond their present limits, and we may ask whether they ever reached over the Red Sea mountains here, as is the case in North-Eastern Egypt. To this question no answer can be given; from Berenice to Gebel Garra is a distance of over 300 kilometres, and even a very gradual thinning of the beds eastward would account for their absence from the main mountains; at the same time the denudation which has removed every trace of the hard Eocene limestone from the plain between Gebel Garra and the Nile may well have done the same further east.