APPENDIX. 
2fi8 
of the isolated, as well as from the coast hanks ; sometimes 
they are irregularly placed, as on the Mosquito hank, but 
more generally they form crescents on the windward side, 
situated some little distance within the outer edge : — 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 Eoncador, 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 I cannot explain their position 
some way within the line of deep water unless it be that a 
depth somewhat less than that close to the outer margin 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 ; and if the bank surrounds an island (as 
in the case of Old Providence), the reef resembles an encir- 
cling 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 re- 
marked that some atoll-like reefs probably 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 near those coasts where sedi- 
ment is now accumulating ; for instance, on the northern 
part of Yucutan, and on the N.E. part of Mosquito. Hence, 
also, the origin of the great Bahama banks, which are 
bordered on their western and southern edges by narrow, 
long, singularly-shaped islands, formed of sand, shells and 
