Coral reefs fringe almost the entire coast-line of South-Eastern Egypt, rendering the coast one of the foulest in the world for shipping. Coral forms the islands of Wadi Gemal, Gulhan, Mukawar, Mirear, Seyal, and Halaib, these rising to a few metres above the sea; but in general it is not met with on the main land except close to the shore. The reefs may extend, slightly raised, some distance inland, but cannot be seen owing to the sand and downwash from the mountains which covers the sloping coast-plain. At low water great expanses of nearly level coral reef, stretching out for a kilometre or more from the shore, are exposed in places, especially near Ras Benas. Frequently a line of reefs can be seen running for many miles parallel to the coast at a distance of a kilometre or more from it; these outer reefs can be traced in windy weather by the breaking of waves on them, and in calm weather by the lighter colour of the water over them. There is frequently deep water between the outer reefs and the shore. Openings in the outer reefs, through which boats can pass into the sheltered water within, are called _mersas_ by the Arab boatmen; they frequently occur opposite the mouths of the larger wadis. Coral reef forms a tough, hard, and very porous limestone, with an extremely rough surface on which the structure of the astraean and other corals composing it can be clearly seen. It has been used for building the jetty at Halaib, and rough blocks of it were anciently employed for building at Berenice, as well as in the tombs at Suakin el Qadim; but its porosity and intractability would never recommend it as a building stone if any other could be found locally. In close association with coral reefs are beach deposits of Pleistocene age. These occur round the hills near the tip and on the north side of the peninsula of Ras Benas, where they cover the slopes of the gypseous limestone hills. Low hills and banks of very white aspect occur near the sea further north; these are probably also raised beaches, though they have not been visited and may possibly be gypsum. Near the tip of Ras Benas these beach deposits are gritty limestones with abundant casts of lamellibranchs and gasteropods, mostly in bad preservation, as well as various echinoids, among which M. Fourtau has identified the species _Brissus carinatus_ as one of the most abundant. =Blown Sand.= The dune-forming sand in South-Eastern Egypt is exactly similar to that which covers such large areas in the Libyan Desert. It consists of well-rounded quartz grains, averaging about a millimetre in diameter; the grains are usually of a golden-yellow colour, owing to their being coated with a thin superficial film of iron oxide.