Vol. 67.] DURING THE CRETACEOUS AND EOCENE PERIODS. 123- 



Sandstone, these being underlain by an alternating series of sand- 

 stones (jointed in large blocks), limestones, and thin greensand bands, 

 the limestones containing diademoid sea-urchins (like Bachiosoma) 

 and intermediate bivalves. Farther north, at the head of Wadi 

 Abu Had and Wadi Tarfa, these strata contain enormous numbers of 

 JS'ueleolitcs, in Abu Had associated with the diademoid form. Near 

 the watershed of Tarfa and Hawashia, they immediately overlie a 

 thick series of sandstone (flaggy, fine-grained, white varieties and red 

 ferruginous layers alternating), which in its turn rests upon green 

 shales. This typical Nubian succession is probably at least 50 metres 

 thick, and Holcctypus turonensis is found in the uppermost portion 

 of these sandstones ; in the green shales below them sharks' teeth 

 (Scaphorhynclms) are present. 



7. This great mass of Mi dd le Nubian Sandstone (for there is no 



difference in its character from that of the typical Nubian Sandstone 

 farther south) forms conspicuous secondary ridges to the west of 

 Wadi Qena, and in part determines the watershed between the 

 Hawashia and Tarfa drainages. Its age is left in no doubt, as it 

 immediately overlies 



8. The limestones rich in ammonites, which are present in vast numbers 



in many localities south of the Galala Hills : these ammonites, 

 which often attain a large size, are mainly species of Hemitissoiia and 

 PseudoHssotia. Though not of great thickness, indeed rarely exceeding 

 2 metres, these limestones are of importance, as they have such marked 

 Lower Turonian characteristics. 



9. They immediately overlie the Cenomanian Series, already well known 



from the researches of Schweinfurth and Zittel ; the strata appear 

 in a series of zones, which, due to the comparatively steep dip, form a 

 succession of broad bands, and give rise to characteristic scarps or 

 plains. The most conspicuous of these are thick limestones, almost 

 entirely composed of Ostrea olisiponensis Sharpe, and forming a 

 well-marked low scarp wherever present. Underlying them are the 

 following in regular succession : 



10. An Ostrea-flabellata Zone, with Hemiaster pseudofotirneli P. & G., Venus 



rcyne&i Coq., etc. 



11. Ostrea-africana Zone, with Neolobites fourtaui Perv. and N. schwein- 



furthi Eck. 



12. Ostrea-suborbiculata Zone, in which this oyster is present in vast 



quantities. 



These Cenomanian strata form the summit of the high cliff (150 

 metres) which hounds Wadi Qena on the west, and immediately 

 overlie the white friable sandstone (13), the Lower Nubian 

 Sandstone, which is highly calcareous in its upper portion, and 

 contains well-rounded quartz-pebbles sparsely distributed through 

 it. The beds at the base of the cliff are lithologically very similar 

 to those at the summit, there being no evidence that any portion of 

 the sandstone is of earlier date than the period of the Cenomanian 

 advance of the sea. It may, therefore, be stated with some degree 

 of certainty that, apart from the Carboniferous sandstones of 

 Northern Egypt and Sinai, the great mass of the Nubian Sand- 

 stone hitherto studied was formed during the Cretaceous depression, 

 and in the Wadi Qena area was a distinct marine deposit, repre- 

 senting temporary increase of activity in the accumulation of 

 detrital materials, due either to climatic or to tectonic changes. 



