Vol. 67.] DURING THE CRETACEOUS AND EOCENE TERIODS. 133 



first Eocene beds in the synclines would be re-assorted and current- 

 affected rocks of the same litbological constitution ; while the 

 worn-down summits of the domes would be the surfaces upon 

 which the new Eocene fauna of nummulites and Operculines* or 

 in the shallower portions, of large sea-urchins and bivalves, would 

 flourish. Should the views here stated be in accordance with the 

 true course of history at this period, it might be possible eventually 

 to map out the original domes and basins of the transition, and 

 trace (just as has been done in the previous pages for the Cretaceous 

 advance) the gradual gain of land from sea in the Eocene Period, 

 by fold effects, in which the flexures occurring in the deepest-water 

 area, namely, Northern Egypt, are the most pronounced, and conse- 

 quently would be unconformably overlain by the youngest Eocene 

 beds. In the shallow basins between the folds the easily denuded 

 members would first be redeposited, and then the Eocene life would 

 be developed in normal zonal succession according to principles which 

 are as yet very obscure. 



VIII. The Eaunal History of Egypt during Eocene Times. 



Offering this theoretical suggestion for consideration to explain 

 the differing character of the strata immediately overlying the 

 well-determined Cretaceous series, and leaving the unfossiliferous 

 ' remade ' white limestones as a problem for special study, 1 may 

 next direct attention to some of the marked zonal variations ob- 

 served in the stratigraphical succession during the Eocene Period. 

 The change is at once marked by the incoming of the Tertiary 

 foraminifera (Operculum hjhica Schwag., Nummulites variolarius 

 Lam., and N. curvlspira Men.) : the Operculines being present in 

 vast numbers in the lowest zone, from the Nile Valley to the 

 Southern Oases. Closely associated with these are strata rich in 

 well-developed sea-urchins (Conoclypeus delanouei de Lor., Rhabdo- 

 cidaris libi/ensis Greg., Linthia cavernosa de Lor., etc.) and large 

 bivalves (Lucina thebaica Zitt.), there being among the larger 

 invertebrates as marked a dominance of sea-urchins and oysters as 

 in the Egyptian Cretaceous. Brachiopoda, on the other hand, are 

 almost absent in both. 



The beds forming the lowest Eocene strata in Egypt, termed 

 ' Lower and Upper Libyan ' by Zittel, are enormously developed, 

 extending in the Nile Valley from north of Minia to the faulted 

 belt near Kom Ombo. 



In the Western Desert they extend to Dungul in lat. 23° 30' N., 

 and from the eastern or northern boundaries of the principal oases, 

 namely : Kharga, Dakhla, Farafra, and Baharia. In the Eastern 

 Desert of Egypt the Lower Libyan Series is equally developed, being 

 an important constituent in the broad limestone-plateau which 

 extends from the Nile and Wadi Qena and from the Galala Hills, 

 and being also present in the faulted outliers near Qosseir. 



Well-defined subdivisions of these strata are not easily deter- 

 minable, owing partly to the inaccessible nature of the regions in 



