Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/114

 2. On the Occurrence of Celestine in the Nummulitic Limestone of Egypt. By H. Bauerman, Esq., F.G.S. and C. Le Neve Foster, D.Sc, B.A., F.G.S.

The fact of the occurrence of sulphate of strontia in the Eocene rocks forming the great escarpment of Mokattam to the east of Cairo has already been noticed by geologists, the latest and most complete account being that contained in Dr. Fraas's description of the Tertiary strata of Egypt*. The object of the present communication is to furnish some additional particulars in connexion with the position and mode of occurrence of the mineral.

The Mokattam escarpment forms a long connected line of cliff, for the most part nearly inaccessible in front, but which can be easily ascended from some of the numerous lateral ravines. The highest point even commands the old citadel, and has therefore been fortified. The height is probably about 800 feet above the Nile ; that of the citadel being 567 feet, by a single barometrical observation. The beds are almost flat, having but a slight dip towards the desert. In a northerly direction the hill diminishes rapidly in height until it is covered by the red quartzose millstone -rock of Jebel Achmar.

Apart from palaeontological considerations, the Nummulitic escarpment, owing to a well-marked physical division, may be divided into two parts, the white and the brown beds, the latter being the higher member of the group. The lower, or white beds, are said by Dr. Figari Bey†, to rest upon tufaceous and slightly argillaceous limestone, representing the upper part of the Cretaceous formation.

The following is the observed section in ascending order, commencing in a quarry at the back of the Tombs of the Caliphs, where the ridge is not quite so high as it is behind the citadel‡: —

1. Soft white limestone, compact and without joints over ft. in. ft. in. the entire quarry-bank. It is worked for flooring-slates 10 4 2. Buff and brown limestone, more fossiliferous than No. 1 14 10 3. Sandy marl parting 0 5 4. Bluish-grey limestone with Nautili and large Nummulites 48 0 116 7 5. Bubbly oyster-bed, thickness variable 4 0 6. Soft shelly beds, covered by quarry-rubbish 9 0 7. White limestone, seamed with brown streaks 30 0 8. Compact brown sandy limestone, the upper part cindery, containing celestine 4 0 9. Marls, with fibrous gypsum (have been worked) 4 5 10. Hard, brown, sandy limestone, with casts of fossils 3 9 11. Variegated yellowish-brown and white sand 4 0 12. Hard, brown limestone, much honeycombed 5 3 13. Sand and shale 2 0 14. Hard brown stone, like No. 12 3 10 15. Brown honeycombed limestone, irregularly bedded, with sand and brown iron-ore interspersed 22 5 16. Brown beds like No. 15, but more calcareous 5 0 171 3


 * Aus dem Orient, Stuttgart, 1867.

† Studi scientifici sull' Egitto, vol. i. p. 136.

‡ The character of these rocks varies rapidly in a short distance. The height of the section in the escarpment behind Old Cairo is about 400 ft. ; and the white and brown beds are separated by nearly 100 ft. of gypseous shales with nodules of pyrites, which have been changed into brown iron-ore and gypsum. The dip is generally N. 70° E. at an angle of from 3° to 5°.