APPENDIX. 249 



slightly sinuous, and extending parallel to the mainland at 

 the distance of five miles from it, with very deep water 

 within; in one spot soundings were not obtained with 205 

 fathoms, Some leagues further south, there is another 

 linear reef, very narrow, ten miles long, with other small 

 portions of reef, north and south, almost connected with it ; 

 and within this line of reefs (as well as outside) the water 

 is profoundly deep. There are also some small linear and 

 sickle-formed reefs, lying a little way out at sea. All these 

 reefs are covered, as I am informed by Capt. Moresby, by 

 living corals. Here, then, we have all the characters of 

 reefs of the barrier class; and in some outlying reefs we 

 have an approach to the structure of atolls. The source of 

 my doubts about the classification of these reefs, arises 

 from having observed in the Dhalac and Farsan groups 

 the narrowness and straightness of several spits of sand and 

 rock : one of these spits in the Dhalac group is nearly 

 fifteen miles long, only two broad, and it 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. 

 There is, also, in this space (lat. 21 ) a peninsula, bordered 

 by cliffs, with its extremity worn down to the level of the 

 sea. and its basis fringed with reefs : in the line of prolonga- 

 tion of this peninsula, there lies the island of Macowa 

 (formed, according to Capt. Moresby, of the usual tertiary 

 deposit), and some smaller islands, large parts of which 

 likewise appear to have been worn down, and are now 

 coated with living corals. If the removal of the strata 

 in these several cases had been more complete, the reefs 

 thus formed would have nearly resembled those barrier- 

 like ones now under discussion. Notwithstanding these 

 facts. I cannot persuade myself that the many very small, 



