254 APPENDIX. 



Here, then, we have all the characters of reefs of the barrier 

 class, and some of the outlying reefs partially resemble atolls. 

 My only source of doubt arises from the narrowness and 

 straightness of the spits of sand and rock in the Dhalac and 

 Farsan groups ; one of these spits in the former group is nearly 

 fifteen miles long, only two broad, and is bordered on each 

 side with deep water ; so that, if worn down by the surf, and 

 coated with living corals, it would form a reef nearly similar 

 to those within the space under consideration. Nevertheless 

 I cannot believe that the many small, isolated, and sickle- 

 formed reefs, as well as others long, nearly straight, and very 

 narrow, with the water unfathomably deep close round them, 

 could have been formed by corals merely coating banks of sedi- 

 ment or the abraded surfaces of irregularly shaped islands. 

 It seems more probable that the foundations of these reefs have 

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

 given to them their present forms. I have, therefore, with 

 much hesitation coloured this part blue. 



The West Coast, from Zat. 22° to 24°.— This part of the 

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

 by an irregularly shelving bank, from 10 to 30 fathoms deep ; 

 numerous little reefs, some of which have the most singular 

 shapes, rise from this bank. Many of them may have been 

 formed by the growth of coral on small abraded islets ; but 

 some almost atoll-formed reefs rising from deep water near a 

 promontory in lat. 24°, are probably allied to the barrier class. 

 I have not, however, ventured to colour this portion of coast 

 blue. — On the ivest coast, from lat. 19° to 17° (south of the 

 space coloured blue on the map), there are many low islets of 

 small dimensions, 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. 



Eastern Coast. — There are many small outlying coral- 

 reefs along this whole line of coast ; but as the greater number 

 rise from banks not very deeply submerged, their origin, as 



