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 foraminiferal white chalk (Danian) 60 to 100 metres thick, especially developed in the region of the oases to the west of the Nile. The Nubian Sandstone, the oldest sedimentary deposit in Egypt, occupies a very large area, especially in the south; wherever its base is exposed and has been critically examined, the sandstone is found to be laid on to the denuded surface of the underlying crystalline rocks. Thinner argillaceous bands are almost everywhere associated with the sandstones and the latter vary much in colour, texture, and hardness. In its widest sense the term “Nubian Sandstone” includes deposits of much greater age than Upper Cretaceous, undoubted Carboniferous fossils having been detected in some localities. The formation must be regarded as representing the slow accumulation of sediment in immense inland lakes during a great lapse of time. Although temporary marine invasions left their mark at intervals, it was not until the Cenomanian that continued depression caused a steady recession of the shore line from north to south, so that in Senonian times practically the whole of the country was occupied by the Cretaceous sea.