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 small nummulites, _Lucina_, _Callianassa_, and echinids. Salt occurs in thin deposits along joint-planes. The lower part of this bed is largely composed of small nummulites and bryozoa. This generally white limestone passes down into 2. Brown, usually sandy, limestone with oysters and small nummulites. In it are intercalated thin beds of greenish brown sandstone and clayey sand with impressions of bryozoa. Some of the brown sandy limestones are full of small nummulites. _Ostrea_ and _Carolia_ numerous. The beds are not constant, the clayey sandstones passing insensibly into sandy limestones. 3. Softer beds with large nummulites, corals, _Ostrea_, _Nautilus_. 4. Soft green and brown clays, with occasional 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 occasional nummulites passing down into hard highly nummulitic limestone; _N. gizehensis_, _Ostrea_ sp., _Lucina_ sp., _Mitra_ sp., and _Carolia placunoides_ occur among others 31