Vol. 67.] DURING THE CRETACEOUS AND EOCENE PERIODS. 139 



As regards this lower division of the Middle Eocene, the evidence 

 points to a general similarity of marine conditions at its commence- 

 ment, the Nwmmulites-gizehensis Beds being developed within my 

 own experience at such widely-separated localities as the desert 

 west of Moela Oasis, Gebel Shaira (60 miles east of Beni Suef), 

 and the well-known exposures at the Pyramids and in the Moqattam 

 Hills. Its upper members, however, commence to show those local 

 variations which make a study of the higher Eocene formations 

 much more complicated than that of the Lower Eocene or Cre- 

 taceous conditions. 



A striking example of this variation is present in the immediate 

 neighbourhood of Cairo. When tracing the Upper Moqattam Beds 

 along the western border of the Nile Valley from the Pyramids to 

 Wasta, the most persistent member was a stratum rich in Carolia 

 placunoides Cantr. and Plicatula polymorplia Bell, which served as 

 a useful guide. Below it follows the remarkable series of un- 

 fossiliferous impure limestones and marls, in which the famous 

 tombs at Sakkara have been excavated, and to which I have con- 

 sequently given the name of the Sakkara Limestones. These only 

 contain numerous worm-tubes and rare casts of a Lucina. Com- 

 parison with the highly fossiliferous strata of the Moqattam Hills 

 (in which sea-urchins are especially abundant) and with the corre- 

 sponding beds in the Fayum Series bears evidence as to the local 

 variability in character. Earthier south-west, at the extreme 

 western edge of the Fayum, the changes become still more con- 

 spicuous, detrital materials almost entirely replacing the fossiliferous 

 members between the Nummidites-gizehensis Zone and the Upper 

 Beds containing Carolia placunoides and Ostrea fraasi. The cliff 

 at this point, probably 100 metres high, is (except for an over- 

 hanging ledge near the summit containing the above mentioned 

 Carolia and Ostrea) entirely composed of green clays, spotted sands, 

 and striped clays. 



South-east of the Fayum, in the hill of Der el Gahannem, the 

 detrital materials play a most important part, a saliferous clay rich 

 in Ostrea fraasi, Carolia placunoides, and various species of 

 Turritella, being 20 metres thick. Below it is a series of sands 

 forming a striking vertical cliff, estimated as 40 metres high. In 

 the upper part are isolated blocks composed of nummulites, sug- 

 gesting unconformity between the true Upper Moqattam Beds and 

 the underlying fossiliferous strata rich in nummulites, from which 

 they are separated by a thick series of sands, showing remarkable 

 current -bedding. 



This question of unconformity between the strata referred to the 

 Upper and to the Lower Moqattam respectively was urged by Barron 

 in his Memoir on the Cairo-Suez region, and the facts so far observed 

 tend to enhance its significance. 



Farther south the Upper Moqattam Beds give rise to a steep scarp 

 overlooking the broad plain formed by the Nummulites-gizeliensis 

 Series. Here a highly fossiliferous layer forms a hard cap at the 

 summit of the cliff 1 , the succession being (in descending order) as 

 follows : — 



