160 DISTRIBUTION OF CORAL-REEFS. Ch. VI. 



exist. Secondly, of coasts where the sea is extremely 

 shallow; and the reefs in this case generally lie far 

 from the land, and are very irregular, so that they 

 cannot always be classed. Thirdly, reefs which appear 

 merely to coat submerged banks of rock or of sedi- 

 ment ; for such reefs differ in some essential respects 

 from those which owe their whole thickness to the 

 growth of corals. Fourthly, in the Red Sea> and 

 within some parts of the East Indian Archipelago 

 (if the imperfect charts of the latter can be trusted), 

 there are many scattered reefs of small size, repre- 

 sented by mere dots, which rise out of deep water; 

 and these have likewise been left uncoloured. In the 

 Eed Sea, however, some such reefs seem once to have 

 formed parts of a continuous barrier. There exist, 

 also, scattered in the open ocean, some linear and 

 irregularly-formed reefs which are probably, as shown 

 in the last chapter, remnants of atolls; but as they 

 cannot safely be placed in this class, they have not 

 been coloured ; they are, however, few in number, and 

 of insignificant dimensions. Lastly, some reefs have 

 been left uncoloured from the want of sufficient in- 

 formation ; and some because they are intermediate 

 in character between barrier and fringing-reefs. The 

 value of the map is lessened, in proportion to the 

 number of reefs which I have thus been obliged to 



apparently volcanic, issuing from the Chief Comoro Island, and that the 

 Arabs assured him that they were volcanic, adding that the volcano 

 burnt more during the wet season : I have marked this as a volcano, 

 though with some hesitation, as the flames may have arisen from 

 gaseous sources. 



