254 APPENDIX. 



Linear strips of coral-reefs and small knolls project from 

 many of the isolated, as well as coast-banks ; sometimes 

 they occur quite irregularly placed, as on the Mosquito 

 Bank, but more generally they form crescents on the 

 windward side, situated some little distance within the outer 

 edge of the banks : — thus on the Serranilla Bank they form 

 an interrupted chain which ranges between two and three 

 miles within the windward margin : generally they occur, as 

 on Roncador, Courtown, and Anegada Banks, nearer the 

 line of deep water. Their occurrence on the windward 

 side is conformable to the general rule, of the efficient 

 kinds of corals flourishing best where most exposed ; but 

 their position some way within the line of deep water I 

 cannot explain, without it be, that a depth somewhat less 

 than that close to the outer margin of the banks, is most 

 favourable to their growth. Where the corals have formed 

 a nearly continuous rim, close to the windward edge of a 

 bank some fathoms submerged, the reef closely resembles 

 an atoll ; but if the bank surrounds an island (as in the 

 case of Old Providence), the reef resembles an encircling 

 barrier-reef. I should undoubtedly have classed some of 

 these fringed banks as imperfect atolls, or barrier-reefs, 

 if the sedimentary nature of their foundations had not 

 been evident from the presence of other neighbouring 

 banks, of similar forms and of similar composition, but 

 without the crescent-like marginal reef: in the third 

 chapter, I observed that probably some atoll-like reefs 

 did exist, which had originated in the manner here 

 supposed. 



Proofs of elevation within recent tertiary periods abound, 

 as referred to in the sixth chapter, over nearly the whole 

 area of the West Indies. Hence it is easy to understand 

 the origin of the low land on the coasts, where sediment 



