In a small ⅂-shaped hill in lat. 28° 46½′ N., long. 28° 48′ E. of G. a mass of basalt occurs which appears to be mainly the remains of a large pipe or “neck.” The igneous rock here shows flow-structure at the sides, being hard and crystalline in the centre. It has altered the sandstones at the contact very considerably, converting them into a greenish rock full of chalcedony. Here, as in the other deposits, the basalt shows distinct columnar jointing and the resulting blocks weather into spheroidal masses where exposed. The igneous rocks of Baharia are therefore Post-Cretaceous in age and it seems reasonable to assume, as suggested by Mayer-Eymar,[57] that they are of Lower Oligocene age, contemporaneous with the basalt-sheets of the Fayum, of Abu Roash and the desert to the west, and of Abu Zabel. The andesite neck passed on the road between Maghagha and the oasis (p. 22) and the larger masses of Bahnessa and other places in the Western Desert were likewise probably erupted at the same time. RECENT. 1.—SAND-DUNES, SALINES AND SUPERFICIAL DEPOSITS. _Blown Sand_, carried along by the prevailing north and north-west winds, is heaped up against all obstacles in its path, such as hills and vegetation; sometimes it is carried over these obstacles, only to fall and accumulate in the wind-shadow on the other side. The cultivated lands of the villages are for the most part surrounded by sand-accumulations, and some low dunes occur in various parts of the oasis; the positions of the latter will be better gathered from the maps than from any mere description. Baharia itself is more free from sand than any of the oases to the south of it, but even here the deposits of this material are very considerable, and as already mentioned extensive sand-dunes occur on the desert to the east, at a short distance from the depression. _Salt-swamps_ occur in the north of the oasis, having probably been produced by the overflowing of springs forming lagoons, which have taken the salt from the surrounding clays, the water from the springs only containing a small percentage of salt. The salt-swamps round Mandisha are now covered with a thin rough dry white crust of salt mixed with clay and sand; when this is broken through a salty sludge is seen to exist below, sometimes in a quite liquid state; the depth of sludge is probably not very great, but there is enough to immerse a camel up to its neck, as was found by experience during the survey. _Clays._—Sandy clays of recent origin occur at isolated spots on the floor of the oasis, notably near Ain el Haiss, where they are now being rapidly removed by the action of the wind. Many of the springs are also depositing a certain amount of clay on the low ground. THE TECTONICS OF THE OASIS. The rocks of the district have undergone a considerable amount of disturbance along certain lines.