Vol. 5 O.J PHYSIOGRAPHY OF THE LIBYAN DESERT. 535 



These Cretaceous rocks, making their appearance first in the Nile 

 Valley near Esna, skirt the Eocene escarpment, of which they form 

 the base, as far as the oases of Kharga, Dakhla, and Earafra, where 

 they are exposed over a large area forming the floors of those oases. 



In the Baharia Oasis, 5 miles N.N.E. of the village of Zubbo, I 

 found a bed of Exogyra, examples of which Dr. Zittel has identified 

 as undersized specimens of Eccogyra Ovemvegi. Thus the sands, 

 marls, and loam occurring in this oasis are of Upper Cretaceous 

 age, and members of the Overwegi-series, although they occur here 

 at most 100 feet below beds of the Upper Mokattam series. 



Ah outlying mass of the Exogyra Overivegi-series occurs at Bir 

 Murr, 80 miles south of the Kharga Oasis, and perhaps the limestone * 

 recorded as occurring at the Selima Oasis is another outlier of these 

 beds. 



In the neighbourhood of Cairo the Cretaceous beds are brought 

 up by faults at Abu Roash, 6 miles north of the Giza pyramids 

 (described by Prof. Walther), and at Jebel Atakka, near Suez. North 

 of these Upper Cretaceous beds, the Eocene stretch away, forming 

 the desert plateau, and are divided by Zittel 2 into 



(a) the Upper Eocene beds. 

 (6) the Mokattam series, 

 (c) the Libyan series. 



The lowest of these consists generally of limestone-beds, with 

 some of a more sandy and marly character, and are characterized 

 by Operculina libyca and Alveolina. The Mokattam beds consist 

 of a lower portion of white limestone mainly characterized 

 by banks of Nummulites gizensis, and an upper portion of brown- 

 coloured clay, loam, and sand, with beds of limestone, and banks 

 of oysters (Ostrea Cloti, 0. cairensis, etc.). 



At the north-east and east of the Baharia Oasis the Upper 

 Mokattam Beds, characterized by Ostrea Fraasi and 0. Cloti (as 

 kindly determined by Dr. Zittel), occur 30 miles north-east and 20 

 miles east of Upper Cretaceous beds containing Exogyra Ovenvegi 

 in the oasis, and with a difference in altitude of less than 200 feet. 

 As there is no marked dip of the beds, we have evidently an overlap 

 of the remainder of the Cretaceous beds and the Libyan and Lower 

 Mokattam Beds of the Eocene, and this inference is borne out by 

 the short distance between the Cretaceous and Miocene outcrops to 

 the west on Dr. Zittel's route to Siwa. 



The Upper Eocene rocks have at present only been recognized in 

 two localities, namely, near the Siwa Oasis and on an island in the 

 Birket-el-Kurun in the Fayum. 



IV. The Miocene and Pliocene Strata. 



To the west and north-west this Eocene series passes under 

 Miocene 3 strata in the neighbourhood of the Siwa Oasis, which 



1 W. Willcocks, ' Report on Perennial Irrigation and Flood Protection for 

 Egypt,' Cairo, 1894, App. iii. p. 5. 



2 Zittel, op. jam cit. pp. 96 et seqq. 3 Ibid. pp. 128 et seqq. 



