3o8 John Milne — Geological Notes on Cairo. 



which in places is clayey, this latter appearance being probably due 

 to the decomposition of certain bands rather than to a breaking up 

 of the whole. The White Beds are the well-known Nummulitic 

 Limestone. This is soft, easily worked, and, when freshly 

 broken, is perfectly white; but on exposure, it becomes slightly 

 yellowish. Standing a short distance away from the face of this 

 rock, a division in the beds is to be seen, marked by yellowish hori- 

 zontal lines, which are in certain cases somewhat siliceous. In 

 addition to these markings, there are others, more strongly defined, 

 indicating fissures and cracks, which are often filled with a yellow 

 oxide of iron, in certain cases of a sufficiently good quality to be 

 used for a pigment. 



Commencing at the summit of the hills behind the Citadel, the 

 general succession of beds in their descending order is represented 

 as follows. The letters refer to the fossils. 



I. — Bed Beds, 



A. 1. — The capping beds here consist of a coarse limestone, almost 



wholly made up of shells. It is much weathered, and its sur- 

 face is strewn with dark-coloured stones, the angles of which are 

 much rounded. Externally these are very vesicular, like a hard 

 burnt cindery slag ; but on being broken, they are seen to be 

 more compact, showing transverse sections of shells. These 

 probably formed portions of still higher beds, which have been 

 by a subaerial degradation carried away ; their vesicular character 

 being due to the dissolving out of a portion of the shelly matter 

 of which they are almost wholly made up. 



These top beds are traversed in various directions by a few 

 small veins of gypsum, which are generally not more than a 

 quarter of an inch in thickness. 



B. 2. — About 30 feet below these beds of limestone we get a reddish 



yellow band of soft calcareous sandstone. In places this is 

 siliceous, and from its friability almost becomes a sand, whilst in 

 its lower portions it resembles a loam. It contains but few 

 fossils, but in one portion it is full of numerous small nests of 

 crystallized carbonate of lime. These crystals are small, but all 

 more or less assume the same geometrical form, — that of a 

 scalenohedron, terminated by the planes of an obtuse rhom- 

 bohedron. 

 3. — At the base of this there is a band apparently wholly made up 

 of Oyster-shells. 



C. 4. — Below this there are six feet of a yellowish earthy band, which 



is followed by a three-foot band of Oysters. 



D. 5. — Still lower we come on more yellow sandstone and a thin 



band of shells, the base of which is about 60 feet from the 

 summit of the hill. 



E. 6. — Below this 60-foot level the sides of the hill are covered with 



a soft earthy mass of sand, produced by the disintegration of 

 the rocks above, which to a great extent conceals the underlying 

 strata. A slight efflorescence of salt, giving a whitish appearance 



