Yol. 67.] DURING THE CEETACEOUS AND EOCENE PERIODS. 145 



Lower Eocene deposits represent the first evidence of the reversion 

 in the secular oscillation, the land gaining on the sea, and being 

 accompanied by folding. The new Eocene fauna flourished on the 

 worn surfaces of the shallow arches, while the denuded Cretaceous 

 material was deposited in the deeper basins. 



6. As the Cretaceous beds in the North of Egypt were deeper 

 beneath the sea at the close of the Cretaceous Period, they only 

 became exposed late in Eocene times, thus accounting for the strong 

 unconformities between the Cretaceous and the Eocene (mainly 

 Middle Eocene) strata noted in Northern Egypt. 



7. The above explanation would account for {a) the slight change 

 in lithology, accompanied by the marked difference in fossil contents; 

 (b) the striking resemblance in petrographical character, but dif- 

 ference of physical structure, in the biscuit-coloured limestones of 

 Eastern Egypt ; aud (c) the presence of strong unconformities 

 between the two formations in Northern Egypt. The origin of the 

 crystalline limestones is still too much wrapped in obscurity for a 

 definite opinion on this subject to be given. 



8. Palgeontologically, there are the usual well-marked differences 

 between the faunas of the uppermost Cretaceous and the lowest 

 Eocene deposits — great groups, especially the Ammonites, entirely 

 disappearing at the close of the Cretaceous ; while the Nummulites 

 and Operculina appear in vast numbers in the earliest strata of 

 Eocene age. 



9. Though this great change be of prime importance, yet both 

 periods bear a strong mutual resemblance in the dominance of 

 oysters and sea-urchins over the other classes of animals. 



10. A notable feature is the extreme rarity of the Brachiopoda 

 in Egypt throughout Eocene and Cretaceous time ; as a point of 

 interest, apart from the general question under consideration, it may 

 also be noted that no Belemnites, so far as I am aware, have ever 

 been recorded from the Egyptian Cretaceous. 



C. — With regard to the distribution and variation of the Eocene 

 beds, we may note : — 



11. The apparent uniformity of the fossiliferous Lower Eocene 

 beds wherever developed in Southern Egypt ; the triple zonation 

 into Upper Libyan, or Callianassa-nilotica Zone, and Lower Libyan, 

 including the Ostrea-multv-ostata and Operculina -libyca Zones; 

 Conocl'ipeus delanouei, Lucina thebaica, and various species of 

 Alveolina are, in addition, among the more characteristic forms. 



12. In the Middle Eocene this uniformity is replaced by dif- 

 ferentiation, only the lowest, or Nummulites- yizehert sis Zone, being 

 traceable throughout the whole area where these beds are exposed. 

 Comparison of the sections in the well-known regions of the Fayum 

 and the Moqattam Hill with the Western Desert area specially 

 described in this paper reveal how great are the variations, both 

 lithological and palseontological. 



In the desert between Baharia, Moela, and the Fayum Oases, 

 three major zones have been recognized in the Lower Moqattam 

 Q. J. G. S. No. 265. l 



