John Milne — Geological Notes on Cairo. 353 



centre of gravity, and of course, as a consequence, the greater is the 

 displacement of the ocean. It may be observed also that, other 

 things being equal, the thinner the solid crust or shell is, and the 

 greater the difference in the density of the fluid materials in the 

 interior, the greater will be the extent of the displacement of the 

 ocean, because the greater will be the displacement of the centre of 

 gravity. 



It follows that if we knew (1) the extent of the general sub- 

 mergence of the Glacial epoch, and (2) the present amount of ice on 

 the southern hemisphere, we could determine whether or not the 

 earth is fluid in the interior. 



IV. — Geological Notes from the Neighbouehood of Cairo. 

 By John Milne, F.G.S. 



THIS neighbourhood has already been described by several authors, 

 — the most complete account of the Tertiary beds being by Dr. 

 Fraas, Aus dem Orient, 1867. Dr. Figari Bey, in vol. i. of Studi 

 Scientifici sull' Egitto; H. Bauerman, Esq., and Dr. C. Le Neve 

 Foster, in the Quart. Journ. Geol. Soc. 1869, vol. xxv. p. 40, have 

 also written on the district, the latter observers referring especially 

 to the occurrence of Celestine in the Moccattam quarries. 



The surroundings, of Cairo, being by no means a geological terra 

 incognita, there will perhaps be but little to be gleaned in the way 

 of additional particulars respecting this district from the following 

 brief communication ; it is therefore hoped it will be accepted rather 

 as a note to accompany the few specimens collected^ than as an 

 independent paper. 



Middens or Bubbish Heaps. — Outside Cairo, and noticeably so be- 

 tween its N.E. and S.W. sides, there are a number of dark-coloured 

 low hills, forming a range about four or five miles in length, with 

 an undulating surface, — in contour not unlike the Downs of our 

 southern counties. In places these approach so closely to the city as 

 partially to bury the walls with which it is surrounded, above which 

 they rise rather steeply, at an angle of 25^^ to 28°, to a height of 

 from 100 to 125 feet. On the opposite side, that is, towards the S.E., 

 they slope more gradually, descending by a series of undulations and 

 small valleys of the same depth as the hills are in height. The 

 summit uf these hills, which may be averaged at a quarter of a 

 mile in width, and which, with the lateral ridges, is sufficient for the 

 accommodation of numerous windmills, affords an extensive view 

 towards the S.W. across Cairo to the Pyramids of Gizeh, and towards 

 the E. over the plain in which are situated the Tombs of the Caliphs 

 to the range of Moccattam. This view is represented as a diagram, 

 in order to show the relation of the Eed Hills to the Limestones of 

 Moccattam, and also the dip of the strata. (See Woodcut, Fig. 1.) 



It is not until these hills are approached and closely examined that 

 their nature can be determined, after which one contemplates them 



^ The specimens referred to, have been presented by the author to the British 

 Museum. 



DECADE II. — VOL. I. — NO. Till. 23 



