APPENDIX. 251 



and 24 , are the only ones in the Red Sea, which approach 

 in structure to the true atolls of the Indian and Pacific 

 Oceans, but they present only imperfect miniature likenesses 

 of them. 



Eastern Coast — I have felt the greatest doubt about 

 colouring any portion of this coast, north of the fringing- 

 reefs round the Farsan Islands in 16 10'. There are many 

 small outlying coral-reefs along the whole line of coast ; but 

 as the greater number rise from banks not very deeply sub- 

 merged (the formation of which has been shown to be only 

 secondarily connected with the growth of coral), their origin 

 may be due simply to the growth of knolls of corals, from an 

 irregular foundation situated within a limited depth. But 

 between lat. 18 and 20 , there are so many linear, elliptic, 

 and extremely small reefs, rising abruptly out of profound 

 depths, that the same reasons, which led me to colour blue 

 a portion of the west coast, have induced me to do the same 

 in this part. There exist some small outlying reefs rising 

 from deep water, north of lat. 20 (the northern limit 

 coloured blue), on the east coast ; but as they are not very 

 numerous and scarcely any of them linear, I have thought 

 it right to leave them uncoloured. 



In the souther ?i parts of the Red Sea, considerable spaces 

 of the mainland, and of some of the Dhalac islands, are 

 skirted by reefs, which, as I am informed by Capt 

 Moresby, are of living coral, and have all the characters of 

 the fringing class. As in these latitudes, there are no out- 

 lying linear or sickle-formed reefs, rising out of unfathom- 

 able depths, I have coloured these parts of the coast 

 red. On similar grounds, I have coloured red the 

 northern parts of the western coast (north of lat. 24 30'), 

 and likewise the shores of the chief part of the Gulf of 

 Suez. In the Gulf of Acaba^ as I am informed by Capt. 



