Beds of this group are chiefly found in the south of the depression. The wadis Rayan and Muêla, as already shown by Schweinfurth and Mayer-Eymar[37], are cut out in clays and limestones of Lower Mokattam age; the upper beds of limestone, containing among other fossil[38] numerous examples of the large Nummulites gizehensis, form the greater part of the floor of the depression west of the Fayûm cultivation, stretching from Jebel Rayan to the foot of Gar el Gehannem,[39] 28 kilometres west of the western end of the Birket el Qurûn ([Section XX]). Near the latter hill examples of N. gizehensis of inordinately large size occur.[40]
At the conical hill at the southern entrance to Wadi Muêla the following beds were noticed:—
| Top of hill. | |
|---|---|
| 1. | Hard white limestone with smallnummulites, Lucina, Callianassa, and echinids. Saltoccurs in thin deposits along joint-planes. The lower part of thisbed is largely composed of small nummulites and bryozoa. Thisgenerally white limestone passes down into |
| 2. | Brown, usually sandy, limestone withoysters and small nummulites. In it are intercalated thin beds ofgreenish brown sandstone and clayey sand with impressions ofbryozoa. Some of the brown sandy limestones are full of smallnummulites. Ostrea and Carolia numerous. The beds arenot constant, the clayey sandstones passing insensibly into sandylimestones. |
| 3. | Softer beds with large nummulites,corals, Ostrea, Nautilus. |
| 4. | Soft green and brown clays, withoccasional oyster-beds. |
At the corner of the cliff 7½ kilometres N.N.W. of the monastery of Der el Galamûn, in Wadi Muêla, occur about 80 metres of hard white nummulitic limestones, with beds of argillaceous sandstone and sandy clays. Fossils are numerous and include nummulites of several species (N. gizehensis, etc.), Carolia placunoides, different species of Ostrea, with gastropods (among others Terebellum sopitum), bryozoa, etc. It is very noticeable that the nummulites, especially the small species, occur in remarkable profusion not only in the limestones but often in the clays.
The following section will give a good idea of the general alternations found in this area; it was measured at Jebel Rayan,[41] 24 kilometres west of the western end of the cultivation of Gharaq basin.
| Top of plateau. | Metres. | |
|---|---|---|
| 1. | Hard snow-white limestone with occasionalnummulites passing down into hard highly nummulitic limestone;N. gizehensis, Ostrea sp., Lucina sp.,Mitra sp., and Carolia placunoides occur amongothers | 31 |
| 2. | Vertical-faced bed of greenish clayeysands and sandy clays (glauconitic) with Carolia,Ostrea and Nummulites. Near top of bed there is muchgypsum. The nummulites in this bed are often collected together soas to form hard concretionary masses; these masses, by becomingmore numerous, finally form a hard bed of nummulitic limestoneintercalated in the clays near the top. The junction of the clayswith the limestone of Bed No. 1 is very irregular | 16 |
| 3. | Greenish shelly sands and sandy clayeybands, interbedded with impure chalky nummulitic limestones withN. gizehensis, N. curvispira, and a third smallerspecies; Ostrea sp. This bed is much obscured by debris | 11 |
| 4. | Hard slate-blue shales, weathering topaper-shales | 2 |
| 5. | Brownish marls passing up into clays | 2 |
| Limestone band largely made up of smalland large nummulites and echinids | 1 | |
| Glauconitic (?) and clayey sands andsandy clays, with Ostrea, Carolia, and nummulites,weathering with a vertical face. In some bands large numbers ofsmall and large nummulites lie embedded in every position, as iftossed about by currents during the process of becoming buried bysediment. Gypsum occurs in thin veins and often encloses thenummulites | 36 | |
| 6. | Hard markedly-white nummulitic limestonefull of N. gizehensis and other species (N.curvispira, etc.); the rock usually has a dark brown colourwhen freshly fractured. A shelly band rich in corals occurs ninemetres from the top. The upper part is more marly and lessnummulitic than the rest of the bed. Base invisible | 30 |
| Total thickness of beds in the above section | 129 | |
Plate V.
ALLUVIAL DEPOSITS OVERLYING MARLY LIMESTONES (RAVINE BEDS) IN EL WADI, RAVINE NEAR QASR GEBALI.
The following is a section of the beds exposed in Wadi Muêla compiled from a paper by Mayer-Eymar on this oasis:—