The cliffs of Jebel Muailla to the north are capped by a hard dark bed of limestone, which weathers with a vertical face, while the more gentle slopes, generally more or less hidden with sand, are doubtless formed of softer limestones, marls, and clays. During the survey of the Fayum (see foot-note, p. 17) the hills surrounding Wadi Muailla were found to be formed of Lower Mokattam beds (Middle Eocene) and the hills seen from this road are doubtless composed of the same beds. The ridges crossed at 20 kilometres are formed of hard, compact, close-grained crystalline limestone, covered with more or less gypsum and flint gravel; the limestone beds forming these ridges show dips which suggest the existence of a fault running N.E.-S.W., parallel to the trend of the cliff behind, and this may be part of the extensive faults and folds of the Nile Valley. In one small hill (22 kilometres) shales with _Ostrea_ were noticed at the base, with occasional hard oyster-limestone bands; the upper part was formed of 10 metres of gravel consisting of well-rounded limestone pebbles. This superficial deposit must be classed as Pleistocene and may be a sea-beach, though no conclusive evidence was obtainable on this point. The escarpment passed at 23 kilometres is capped by a bed of white limestone, shales forming the slope, but was not examined at close quarters. The floor of the bay formed by the receding cliff shows outcropping brown limestone with _Ostrea_, and the escarpment on the far side is capped by a hard white crystalline limestone with much flint, the latter forming bands. On the surface is a thin calcareous gypseous gravel deposit, doubtless of the same age as the gypseous beds already mentioned as occurring on the plain below. The flanks of the scarp are hidden by downwash. The cliff bounding this strip of plateau, 1½ kilometres further on, is composed of the same beds, the limestone being here silicified, with large silicified _Conidæ_. With regard to the age of these limestones and clays they are probably equivalent to part of the Lower Mokattam series already mentioned as forming the hill-masses round Wadi Rayan, although no _Nummulites gizehensis_ beds were observed in the sections examined. A conspicuous black knob among the low gravelly hills left two kilometres on the right at 32 kilometres, was found to be a neck of hard dark andesitic basalt, one of the few occurrences of igneous rocks in the Western Desert. Several other similar looking dark hills were in sight, but time did not admit of their examination. The dark well-marked range 6-7 kilometres to the left of the road is probably identical with a range of hills occurring 10 kilometres west of Bahnessa, which was mapped[23] during the survey of the Nile Valley in 1899, and found to consist of a mass of andesitic basalt similar to that forming the small neck on this road. Doubtless they are both parts of the same intrusion. The