In 1894, Capt. H. G. Lyons, R.E.,[38] visited Baharia, and 5 miles N.N.E. of Zubbo discovered a bed containing small examples of _Exogyra_. These were examined by Prof. Zittel and referred to as undersized specimens of _Exogyra Overwegi_ Beyr.[39] This discovery of Capt. Lyons’ thus showed the series to be undoubtedly of Upper Cretaceous age. In the latest edition of Prof. Zittel’s map, the depression was shown as consisting of Cretaceous beds surrounded by an Eocene plateau, which was also supposed to separate it from the oasis of Farafra to the south. [Sidenote: Geological Survey, Oct.-Dec. 1897.] A glance at Plate I will be sufficient to show that the work of the Geological Survey has resulted in large and important additions to our knowledge of this oasis. The Eocene is seen to form the surrounding plateau only on the north; while the Cretaceous, consisting of several well-marked divisions, occupies not only the depression itself, but forms part of the surrounding plateaux on the east and west sides, and is continuous with that of Farafra to the south. Moreover, the relations of the two great formations of Cretaceous and Eocene are now shown to be those of unconformability and overlap. The actual extent of volcanic rocks and post-Eocene lacustrine deposits, the latter a newly-discovered and important series, is now shown for the first time.[40] Important folding has been detected and numerous organic remains have been discovered. The deposits met with in the district admit of classification as follows:— RECENT. 1. Sand-dunes, salines, and superficial deposits. POST EOCENE (OLIGOCENE?). 2. Basalt and Dolerite intrusions. 3. Ferruginous sandstones and quartzites, with limonite and pisolitic iron-ore, probably lacustrine in origin. EOCENE (MIDDLE-LOWER.) LOWER MOKATTAM- { 4. Limestones with _Nummulites_, _Operculina_, UPPER LIBYAN. { Echinids, _Lucina_, etc. UPPER CRETACEOUS. DANIAN | 5. Thick-bedded White Chalk and grey crystalline limestone. CENOMANIAN } (Some TURONIAN } 6. Limestones and variegated sandstones. or SENONIAN). } CENOMANIAN | 7. Sandstones, clays and marls. These groups will now be dealt with in succession, commencing with the oldest. UPPER CRETACEOUS. CENOMANIAN.