250 APPENDIX, 



isolated, and sickle-formed reefs and others, long, nearly 

 straight, and very narrow, with the water unfathomably 

 deep close round them, could possibly have been formed 

 by corals merely coating banks of sediment, or the abraded 

 surfaces of irregularly-shaped islands. I feel compelled to 

 believe that the foundations of these reefs have subsided, 

 and that the corals, during their upward growth, have given 

 to these reefs their present forms : I may remark that the 

 subsidence of narrow and irregularly-shaped peninsulas and 

 islands, such as those existing on the coasts of the Red 

 Sea, would afford the requisite foundations for the reefs in 

 question. 



The West Coast from lat. 2 2° to 24 . — This part of the 

 coast (north of the space coloured blue on the map) is 

 fronted by an irregularly shelving bank, from about 10 to 

 30 fathoms deep; numerous little reefs, some of which 

 have the most singular shapes, rise from this bank. It 

 may be observed, respecting one of them, in lat. 23 10', 

 that if the promontory in lat. 24° were worn down to the 

 level of the sea, and coated with corals, a very similar and 

 grotesquely formed reef would be produced. Many of the 

 reefs on this part of the coast vn^y thus have originated ; 

 but there are some sickle, and almost atoll-formed reefs 

 lying in deep water off the promontory in lat. 24 , which 

 lead me to suppose that all these reefs are more probably 

 allied to the barrier or atoll classes. I have not, however, 

 ventured to colour this portion of coast. — On the west 

 coast from lat. 19° to 17 (south of space coloured blue on 

 the map), there are many low islets of very small dimen- 

 sions, not much elongated, and rising out of great depths 

 at a distance from the coast ; these cannot be classed either 

 with atolls, or barrier or fringing-reefs. I may here remark 

 that the outlying reefs on the west coast, between lat. 19 



