The principal point attended to in the topographical mapping by the survey was the accurate delineation of the bounding scarps of the oasis and of the large number of hills within it. These features, of which an accurate map was essential for any proper consideration of the geology, had been only rapidly sketched by previous travellers, and the precise shape of the oasis was still unknown. In the cultivated spots, on the other hand, much had been done by Cailliaud, Jordan and Ascherson towards mapping the detail. Hence, beyond re-determining the precise positions of the main points and the general limits of the cultivated areas, no attempt at detailed mapping in these areas was undertaken by the Survey parties, it being felt that it would be preferable in the limited time available to concentrate attention on the almost totally unknown features, so essential to any geological consideration, rather than to devote considerable time to the details of the inhabited spots. Thus, while the field maps resulting from the survey represented the oasis for the first time in its true shape, and the hills within it in their true relative magnitudes and positions, they fell somewhat short of the maps of Ascherson and Cailliaud in the number of springs, ruins, etc., shown. The more important ruins overlooked by the survey have, however, been inserted approximately from existing maps, and the whole result (Plates I, III and VII), is an advance on the existing representations. The _geology_ of the oasis was very carefully investigated, this being a field in which comparatively little had been done, and a number of very interesting results were obtained. The principal points in this connection worthy of note resulting from the detailed examination of the scarps and hills are— (i) The existence of a marked unconformity between the Upper Cretaceous and Eocene strata, thus confirming the unconformity between these two great systems which had been noted[15] earlier at Abu Roash; this unconformity has now been remarked in many parts of Egypt.[16] The palæontological proofs of this unconformity were obtained from the western scarp, the beds of the eastern side, though they show the same thickening, being much poorer in fossils; (ii) The occurrence of an extensive series of Upper Cretaceous beds of Cenomanian to Danian age within the depression and forming a large part of the desert to the west; (iii) The precise extent and relations of the dolerite capping some of the sandstone hills in the north of the depression; (iv) The existence of well-marked folding having an important bearing on the origin of the oasis; (v) The presence of ferruginous sandstone deposits of later origin than the primary formation of the oasis-hollow, though long anterior to the date when the work of excavation, which gave the oasis its present form, took place. These points will be found discussed at some length in the chapter on the geology of the oasis.