There are some reefs in the Red Sea quite of the Atoll form, of which the largest is Sanganeb, the plan of which, on the map on page 137, is sufficiently explanatory. Another is Tella Tella Seghir, which is elevated to 40 feet above sea-level, and consists of a ring of high ground enclosing a depression, once a lagoon though its floor is now a little above sea-level. The elevation of this ring-shaped reef has been at least two stages, the lagoon having contained water to about one-third of its depth comparatively recently, since a line of undermined cliffs occurs at this level. The _Admiralty Pilot_ remarks that the edge of the ridge bears numerous cairns. Some of these are artificial I am told, but those I examined were large coral colonies, in the position in which they grew, left exposed by the removal of the softer stuff in which they were embedded. One example of the coral genus _Mussa_ was especially conspicuous, as much so as the corals illustrated on Plate XXXVII on the top of Jebel Têtâwib. SUMMARY OF GEOLOGICAL HISTORY OF THE RED SEA. (1) There was originally a _shallow_ sea covering the space between the high mountains of both sides of the present Red Sea. In this sea were laid down sandy and gravelly sediments, and limestones were formed which are now found in the sandstone hills of the maritime plain, &c. The gypsum beds found here are the result of the drying up of the water of this shallow sea. (2) The beds of rock thus formed were broken up by the sinking in of a long strip of the earth’s crust forming the Rift Valley, which extends from Jordan to Tanganyika. Part of this valley was filled by sea water and became the Red Sea. (3) There have been three successive systems of barrier reefs along the Red Sea coast, which by continual uplift have become, (_a_) A range of sandstone hills rising from the alluvial maritime plain. (_b_) A fringe of limestone along the present coast-line. (_c_) The present barrier system. (4) These three ridges were formed by the faulting of sedimentary rocks which overlay the bases of the Archean hills at the time of the great movement which opened the Red Sea section of the Great Rift Valley. (5) The northern ends of several sections of the present barrier reefs are elevated above sea-level, and examination of these, and of the hills of the maritime plain, enable us to reach the above conclusions. (6) At the same time Rawaya gives evidence of a seaward movement as well as uplift, Khor Dongonab and some at least of the channel within the barrier reefs being recent fault depressions, not merely an anticlinal fold formed at the opening of the Rift Valley. The harbours and other fissures in the coral limestones, &c. of both coast-land and of the barrier reefs are due to the same secondary faulting.