view is furnished by the decided unconformity of the limestone upon the greensand in the Gharabi escarpment — although too much stress must not be laid on this point, owing to the number of faults running parallel with the escarpment, some of which may have something to do with the apparent unconformity. The ordinary rule of geological reasoning would perhaps be best satisfied by putting the whole of the chalky beds with flints into the Nummulitic series, as, in addition to the Nummulitic form near Gharandel, the few small fossils found in Wady Taibe, Wady Husseid, and the Marcha are, for the most part, when recognizable, Tertiary forms. As far as I can gather from books, a somewhat similar difficulty is experienced in Egypt, where the upper line of the chalk is rather arbitrarily drawn at certain soft limestones which are not very different in character, except as regards their fossils, from the lower Nummulitic beds immediately next in succession. This makes it probable that the transition from the Cretaceous to the Tertiary period in these regions was not marked by any great break physically, the beds immediately before and after the change having been accumulated under similar conditions ; and probably in the Red Sea at the present day the beds accumulating are of an essentially chalky nature. In more recent times, however, a great break must have occurred between the Nummulitic and the flint- conglomerate formations, as the latter is entirely made up of the waste of the rocks immediately preceding it ; and how considerable this waste must have been is evidenced in the ridge of Abooalagha, where a mass of strata, about 600 feet thick, is about half composed of conglomerates, none of which contain a single pebble that can be referred to the New Red Sandstone, all being of flints.
After leaving the New Red Sandstone in Wady Ferran, the whole of the country up to the convent of St. Katherine, in Sinai, with the exception of the fossiliferous alluvium in Wady el Scheick, is made up of crystalline and metamorphic rocks, which will not be further alluded to here, as I hope to make them the subject of a future communication to the Society.
Conclusion. — The order of succession of the rocks mentioned in the foregoing account may be summarized as follows, in ascending order: —
1. Gneiss and granites. 2. Triassic rocks, including 1. Lower Red Sandstones.
2. Limestone with encrinites.
3. Upper Brown Sandstone.
3. Cretaceous rocks. Green sands with Echinoderms, sandy limestones, and shales.
4. White limestone with flints.
Lower part possibly Cretaceous. Upper part bituminous, with Nummulites. Eocene.
5. Flint-conglomerate with corals. Miocene.
6. Great gypseous series of Wady Taragi.
7. Reconstructed gypseous series and conglomerates.
8. Raised beaches and Miliolitic Limestones.
9. Alluvium and Desert Drift.
Volcanic rocks appear at two periods ; the older are post-Triassic
