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Fig. 85. Peninsula of Rawaya and reef systems connected with it
The narrow fringing reef along shore of mainland shaded as are coral beds in Khor Dongonab. Small Islands are black. Dotted areas are reefs free from coral.
-·-·-·-·- 10 (and in south basin 20) fathom line.
--------- 100 fathom line.
The conversion of such low-lying land as Rawaya into a reef maze follows at once from the action of the sea, restrained by coral growth, described in Chapter VIII, but the diagrams make the case clearer.
A is the first stage, the thin line representing the outline of a partly submarine hill range, the undulations of which are much exaggerated in the diagram. The horizontal dotted line is the sea-level, so the diagram represents one summit above the sea, an island, another submerged, and a third emerging to the right.
Diagram 10. Conversion of a line of low hills, partly submarine, into a maze of surface reefs
- A First stage. B after elevation and second period of abrasion.
- ----- sea level.
- additions made by coral growth.
- Coarse shading = remains of original hill after abrasion.
- Fine shading = coral mud or sand.
In A the first summit to the left appears above water as a rounded island, which is cut down considerably and much of its area converted into reef flat, and the deep lagoon to the right is narrowed by coral growth on both this reef flat and over the next summit, as indicated by zigzag shading in the diagram.
As this second summit is at about the right depth below the surface, coral grows vigorously upon it forming a surface reef, slightly hollowed out in the middle. The third summit is like the first.