surface of the plain is still composed in part of gypseous deposits, with occasional outcrops of the underlying limestone, the surface being covered with a certain amount of loose sand with rounded flints and their broken fragments. In the neighbourhood of Jebel el Ghudda the plain consists of limestone with numerous individuals of the large _Nummulites gizehensis_, and are thus of Lower Mokattam age. Much of the limestone is crystalline. The hills of Jebel el Ghudda are formed by younger overlying beds consisting of hard silicified sandstones and grits (quartzites), which lithologically are very similar to the beds of Jebel Ahmar near Cairo, of Oligocene age. They may, however, belong to the Upper Eocene series, so well developed above the Upper Mokattam in the escarpments to the north of the Fayum, as this series contains similar beds with similar silicified wood. They enclose bands of coarse conglomerate and have a peculiar blackish burnt colour. Occasional patches of these grits are here and there met with right up to the depression of El Bahr, and the silicified wood passed at 92 kilometres belongs to the same series of beds. From the scrub area at 93½ kilometres till the road approached El Bahr there was hardly a sign either of the grits or of section anywhere met with on this road. The depression is cut down through the upper series of sandstones and grits into the fossiliferous white limestones and sandstones below. The eastern scarp showed the following beds:— _Top._ Soft white Sandstone. { Limestone with _Nummulites gizehensis_. } MIDDLE { } Lower EOCENE. { Limestone with _Ostrea_, _Exogyra_ and } Mokattam. { _Lucina_, etc. } The floor is covered in places with numerous weathered out individuals of _N. gizehensis_ and large oysters. Some of the hills occurring within the depression showed brown siliceous limestone overlying white limestones with beds containing _Nummulites gizehensis_, _Ostrea_, etc., below. In some of these hills the beds show evidences of folding, which like that within the Baharia Oasis may have partly caused the formation of the depression by bringing the softer beds to the surface within the reach of the agents of denudation. On ascending the western scarp, beds with _Ostrea_, _Turritella_, etc., were crossed, and near the top thick yellowish sandstones crowded with _Ostrea_ occur. Two of the species of _Ostrea_ were afterwards examined by Dr. Blanckenhorn, one of which he regarded as nearly related to _O. Fraasi_, and the other as a new species with affinities to _O. Hess_, May-Eym.