— Ill — 
populated strip o£ alluvial land, formed and watered by the Nile. In the 
southern sandstone country the river occupies only a shallow valley, but to the 
north flows over the floor of a deep gorge cut down from the surrounding lime- 
stone plateaux. On either side of the river are alluvial plains of varying extent, 
composed of the finest loam, a fertile soil for the most part formed by the 
disintegration of the volcanic rocks of the Abyssinian highlands, annually denuded 
by rains and brought down by the Afcbara and Blue Nile floods and deposited in 
the lower courses of the river. Unlike most countries therefore, the soil of Egypt 
has no connection with the underlying rocks, being entirely of extraneous origin 
and owing its existence absolutely to the peculiar conditions of rainfall in 
Abyssinia and the direction of drainage from the watersheds of that country. 
46. Igneous rocks. The most ancient rocks in Egypt are found in the central 
igneous ranges of the Red Sea Hills and in the crystalline floor underlying the 
sandstones in the southern part of the country. 
In Nubia the crystalline rocks consist largely of granite and gneiss, with 
associated diorites and schists, traversed by basaltic and f elsitic dykes. Cataracts 
have been formed at those points where the river crosses the hard igneous belts, 
which may be regarded as the summits of the higher ridges of an old eroded 
continental land surface. 
In the Red Sea Hills the most ancient rocks are the gneisses, schists, and slates, 
constituting the metamorphic series of Jebel Meeteq. Next in succession is a 
volcanic group, consisting of dolerite and sheared diabases in the south and of 
dolerites, andesites, tuffs and agglomerates in the north. These volcanic rocks 
are underlaid and intruded by still younger quartz-diorites and grey granites, 
and like them are pierced by masses of red granite and dykes of quartz felsite 
and dolerite. The red granite is itself traversed by dykes of diabase, which are 
thus the youngest of all, except for the still more recent andesitic intrusions into 
the Eocene limestones (occasional occurrences of which are met with on the 
plateaux on both sides of the Nile valley), and the basaltic sheets which commonly 
mark the base of the Oligocene sandstones in the north of the country. 
The whole of the Red Sea Hills igneous complex has been planed down by 
marine erosion, the oldest sedimentary deposits being laid on to the smoothed 
denuded surfaces. 
47. Sedimentary rocks. Geologically the sedimentary deposits of Egypt are 
not of great age. Broadly they consist of a great development of Upper Cretaceous 
and Eocene strata, followed by more restricted deposits of Oligocene and Miocene 
age, the still younger formations being represented only by comparatively local 
though important, accumulations. As a general rule the different members of the 
Cretaceous and Tertiary succeed each other in regular order from south to north, 
the strata being undisturbed and dipping northwards at a very low angle. 
48. Upper Cretaceous. The Cretaceous system in Egypt is divisible into 
three main groups, (1) a great thickness of freshwater arenaceous sediments 
known as the Nubian Sandstone, of Senonian age in the south (Dakhla, Nile 
valley, and southern part of Eastern Desert), and Cenomanian age in the north 
(Baharia, Abu Roash(?), and Wadi Araba); (2) 300 metres of argillaceous 
deposits with bone-beds near the base, of Senonian age ; (3) a deep water forami- 
