156 CORAL-REEFS. 



more difficulty in colouring fringing-reefs than in colouring 

 barrier-reefs, as the former, from their much less dimensions, 

 have less attracted the attention of navigators. As I have 

 had to seek my information from all kinds of sources, and 

 often from indirect ones, I do not venture to hope that 

 the map is free from many errors. Nevertheless, I trust 

 it will give an approximately correct view of the general 

 distribution of the coral-reefs over the whole world (with 

 the exception of some fringing-reefs on the coast of Brazil, 

 not included within the limits of the map), and of their 

 arrangement into the three great classes, which, though 

 necessarily very imperfect from the nature of the objects 

 classified, have been adopted by most voyagers. I may 

 further remark, that the dark blue colour represents land 

 entirely composed of coral-rock ; the pale blue, land with a 

 wide and thick border of coral-rock ; and the red, a mere 

 narrow fringe of coral-rock. 



Looking now at the map under the theoretical point of 

 view indicated in the last chapter, the two blue tints signify 

 that the foundations of the reefs thus coloured have subsided 

 to a considerable amount, at a slower rate than that of the 

 upward growth of the corals, and that probably in many cases 

 they are still subsiding. The red signifies that the shores 

 which support fringing-reefs have not subsided (at least to 

 any considerable amount, for the effects of a subsidence on 

 a small scale would in no case be distinguishable) ; but that 

 they have remained nearly stationary since the period when 

 they first became fringed by reefs; or that they are now 

 rising or have been upraised, with new lines of reefs suc- 

 cessively formed on them : these latter alternatives are 

 obviously implied, as newly formed lines of shore, after 

 elevations of the land, would be in the same state with 

 respect to the growth of fringing-reefs, as stationary coasts. 



