That a river flowed during late Eocene or early Oligocene times in a north-easterly direction through what is now the Libyan Desert, and entered a sea near what is now the Faiyum, can scarcely be questioned; for it is only by the existence of such a river that we can account for the assemblage of fossil trees and curious remains of Eocene animals (including the ancestors of the elephant) discovered by Mr. Beadnell north of the Birket el Qarun and described by the late Dr. Andrews.[10] As to the size, length, and exact position of this river of the geological past there is very great doubt; but neither its situation nor even its existence can be considered material to our present inquiry. No one conversant with the known facts bearing on the general geological history of Egypt during late Tertiary and Quaternary times could make the mistake of thinking that the path of an Eocene river might be traceable in the present desert relief. The evidences of such path must be purely of a geological nature. In his endeavours to suggest what might possibly have been the course of the river on whose banks the Eocene animals lived, Mr. Beadnell found in two localities deposits which might have been formed along the ancient drainage-line; and in both these localities the deposits now occupy the summits of hills. There is insufficient evidence of any kind to justify so exact a location of the Eocene river as Blanckenhorn’s maps would suggest, and none whatever of any relationship, either between the present surface- configuration of the desert and Eocene or Oligocene drainage-lines, or between those drainage-lines and the River Nile. The appellation “Ur- Nile” of Blanckenhorn is thus a misleading one. If we are to look for traces of a dried-up river in the surface-forms of the Libyan Desert of to-day, it must be a river which, like the streams which eroded the great wadis of the Eastern Desert, existed in geologically recent times, and which became dry either through the continual deepening of the present Nile-channel, with consequent capturing of the former drainage, or through climatic changes causing a diminution of rainfall in the collecting area.