The Selima Sand Sheet, the hyperarid core of the eastern Sahara first described by Bagnold (1931), is a relatively flat, sand-covered surface of ca. 40,000 sq. km. extending 1.5° of latitude either side of the Egyptian-Sudanese border (22°N) between 26° and 29°W longitude. The topography, ranging from absolutely flat to undulations (giant ripples) up to 10 m high and 1 km apart, is broken only by a few widely spaced low outcrops of quartzite bedrock that appear to the traveler as islands in a calm sea. Northward it is bounded by the rise of a sandstone cuesta, to the west by the forelands of the Gilf Kebir plateau and Gebel Oweinat, to the east by low sandstone outcrops and the El Tawil granite, and southward the sand sheet thins out on low sand-blasted outcrops of quartzitic sandstone.