THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. I. 



No. VII.— JULY, 1884. 



(D:RXG-XlSr.^lL, ^^liTIOTjSS. 



I. — Notes on the Geology of the Nile Valley. 



By Professor J. W. Dawson, C.M.G., LL.D., F.E.S., F.G.S., etc. 

 Principal of McGill College, Montreal. 



1. Raised Sea Margins. 



SHOETLY after my arrival in Cairo, Dr. Scliweinfurth, of that city, 

 was so kind as to conduct me to a remarkable sea-terrace at 

 the foot of the Mokattam hill, behind the tombs of the Caliphs, and 

 stated, on the authority of Col. Ardagh, R.E., to be at an elevation 

 of about 200 feet above the level of the sea, and which, I believe, 

 was first described by Oscar Fraas. At this place a cliff of hard 

 Eocene limestone, about 30 feet in height, has been perforated by 

 Lithodomi, whose burrows are now filled with a grey calcareous 

 deposit, and valves of a small species of oyster are also attached to 

 the surface of the rock. The burrows resemble those of an ordinary 

 Mediterranean species of Lithodomus, but I did not see the shells. 

 The oyster has been described by Fuchs as a new species, under 

 the name 0. pseiido-cucidlata ; but, according to Dr. Schweinfurth, it 

 does not seem distinguishable, except as a variety, from 0. cucullata, 

 Born. (=0. Forskali, Chemn.), of the Eed Sea. Since the locality 

 was observed by Fraas, Dr. Schweinfurth has discovered other 

 shells in the crevices of the rock, more especially a Pecten, a Tere- 

 hratida, and a Balanus, all modern species. The recent character of 

 these shells and their mode of occurrence and state of preservation, 

 oblige us, I think, to assign them to the Pleistocene, or at farthest 

 the later Pliocene period, though I am aware that they have been 

 regarded as Miocene. 



Shortly after visiting this place, I was so fortunate as to discover 

 on the opposite side of the Nile a similar exposure, associated with 

 an old sea beach, which I subsequently examined more carefully 

 in company with Dr. Schweinfurth. It occurs at the summit of 

 a rocky knoll, called by the Arabs Het-el-Orab, or the Crow's Nest, 

 a short distance to the south-west of the Pyramids of Gizeh, and 

 separated from the plateaux of the Pyramids by the depression 

 which contains the Sphinx, and which is partly natural, but in great 

 part produced by excavation, of which evidences exist not only in 

 the remaining chips of stone, but also in the Sphinx itself, and in 

 the tomb crowning an isolated mass of rock farther to the west. 



DECADE III. VOL. I. NO. VII. 19 



