132 DE. W.E. HUME OF SECELAE OSCILLATION IN EGYPT [Feb. I9H, 



Cretaceous insular area. Still more remarkable is the unconformity 

 which has come under my notice in the Southern Galala Hills, 

 where the lower slopes consist of a well-stratified series of white 

 chalk beds weathering to a biscuit colour. Immediately overlying 

 these was a highly fossiliferous stratum, the fauna of which has 

 been identified by M. Eourtau as Lower Moqattam or Middle Eocene 

 in age, so that the whole of the Libyan strata (commonly classed 

 as Lower Eocene) are entirely absent. These beds are in their 

 turn apparently succeeded by conformable subcrystalline lime- 

 stones, which in many cases are true marbles. Only 

 many miles away to the west, near Gebel Shaira, do these contain 

 the slightest trace of fossils, those obtained being Nummulites gizeh- 

 ensis de la Harpe, and large specimens of Velates schmiedeli Chemn., 

 present in a crystalline matrix. 



Any theory of the relations between the Cretaceous and the 

 Eocene Periods must take account of three essential factors : — 



(1) The slight change in lithology, but marked difference in fossil contents 



exhibited in the South of Egypt. 



(2) The striking resemblance in petrographical character, but difference 



in physical structure, suggesting current-bedding, exhibited in Central 

 Egypt. 



(3) The existence of marked unconformities between the two formations 



in Northern Egypt. 



Incidentally, two other factors have to be considered : these are : — 



(4) The prevalence of subcrystalline limestones at the summit of the Cre- 



taceous or the base of the Eocene, where these meet ; and 



(5) Volcanic activity, which is particularly well marked at the close of 



the Eocene Period. 



"We have seen that, during the Upper Cretaceous Period, there is 

 strong evidence for the gradual advance of a wide-spreading sea 

 over the whole of this portion of Africa, organic deposits gradually 

 becoming preponderant over those of detrital origin. Examination 

 of the Eocene and Cretaceous areas in the outer deserts has already 

 revealed that the tectouic relations are not so simple as had been 

 generally supposed, but that closer mapping will probably indicate 

 a marked if gentle folding — the long axes of which have an east- 

 ward and westward tendency. The exact extent and magnitude of 

 such foldings can only be determined by accurate levelling, but the 

 Abu Roash-Moqattam anticlinal system and the Wadi-Araba anti- 

 cline in the north find a counterpart farther south in the well- 

 marked anticlines near the head of Wadi Qena, and in the hills 

 south-east of the Qena bend of the Nile. It is a fair inference that 

 such folds were the first cause of the great change so universally 

 noted, the first basis of the new Tertiary world. 



The anticlines or domes would give rise to islands or submarine 

 ridges where erosion would be active, while the basins would form 

 centres within the areas of which the denuded materials could be 

 deposited. As the Danian limestones were widely distributed, the 



