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.
(7) The maritime plain had its maximum seaward extension after the growth of coral on the second and third barriers. Owing to elevation nothing has been added to its seaward slopes since the formation of the features of the present coast-line by secondary faulting.
(8) The filling in of valleys and the completion of the connection of the second barrier with the maritime plain has been largely due to blown sand. The process is continuing, e.g. an extensive plain near Dongonab shews perfect uniformity in its formation.