The greater part of the marls and clays met with from 18·5 to 112·5 metres below the surface in the boring at Medinet el Fayûm in all probability belong to the Ravine beds.
The maximum thickness of this series is 70 metres, measured at Gar el Gehannem.
C.—Birket el Qurun Series (Operculina-Nummulite Beds).
The above designation is convenient and applicable to these beds, which form the escarpment immediately overlooking the lake on the north side throughout its length.
The group includes all the beds between those last described and the well-marked Qasr el Sagha series, homotaxial with the Upper Mokattam (the brown beds) of Jebel Mokattam, near Cairo. It thus appears to be the equivalent of the upper part of the white beds (quarried limestones) of the Mokattam section, although the lithological characters are entirely different, the massive limestones of Jebel Mokattam being represented in the Fayûm by an arenaceous and argillaceous series, deposited probably in water of far less depth. Where the different members of this series are well exposed certain beds are found to be characterized by the abundance of two foraminifera, the one a small thin-shelled Operculina (O. discoidea)., and the other a small thick nummulite.[43] The tests of these foraminifera sometimes make up entire bands of rock. In addition, the series includes certain beds which at times become very fossiliferous, and contain a well-preserved molluscan fauna.
The series is well seen in the desert separating the Fayûm from the Nile Valley; on the south-east and east sides of the former; along the northern boundary of the cultivation and the Birket el Qurûn; and westwards in the cliffs to beyond the outlying hill-mass of Gar el Gehannem.
The following section was measured on the south-west of the Fayûm, from Ezba Qalamsha (on the confine of the cultivation) to the ridge summit 5 kilometres to the south-east.
| Top. | Metres. | |||
|---|---|---|---|---|
| Summit of ridge 5 kilometressouth-east of Ezba Qalamsha. | ||||
| Pliocene Raised Beach withoccasional Ostrea cucullata, Born., made up of gravels withblocks of limestone. | ||||
| Birket el Qurun Series. | 1. | Ochre-coloured calcareous sandstone andsandy limestone crowded with foraminifera (NummulitesFraasi, etc.), Ostrea, etc. | 38 | |
| 2. | Sandy limestone, largely made up offoraminifera (Operculina discoidea ?) | 2 | ||
| 3. | Sandy shale | 2 | ||
| 4. | Sandstone, partly calcareous, with muchgypsum | 3 | ||
| 5. | Calcareous sandstone with concretionaryweathering | 17 | ||
| 6. | Shale with gypsum | 2 | ||
| 7. | Calcareous sandstone | 4 | ||
| 8. | Shale with gypsum | 2 | ||
| 9. | Calcareous sandstone, hard andyellowish | 2 | ||
| 10. | Gypseous shale with numerous small shells(Tellina sp.) passing down into sandy limestone. (This bedis the uppermost member of the Ravine beds) | 6 | ||
| Total thickness | 78 | |||
| Base, cultivation level. | ||||
To the north of the Lahûn pyramid the beds agree generally with the above. The following are the chief divisions here:—
| Top of Hills. | Metres. | |
|---|---|---|
| Gravel Terrace (Pliocene) 22 metresthick. | ||
| 1. | Calcareous sandstone and sandy limestonesfull of nummulites; also Ostrea, etc. | 31 |
| 2. | Ochre-coloured calcareous sandstone orsandy limestone, often crowded with Operculina discoidea andsome Nummulites Fraasi, etc. | 12 |
| 3. | Sandy limestone with small foraminiferaat top and some shells. The upper part of this bed has beenquarried | 20 |
| 4. | Shales and shaly limestone; gypsum | — |
| Total thickness | 63 | |