Cii. VI. DISTRIBUTION OF CORAL-REEFS. 
163 
value of the map is lessened, in proportion to the 
number of reefs which I have thus been obliged to 
leave uncoloured ; hut their number is not very great, 
as will be seen by comparing the map with the state- 
ments in the Appendix. I have experienced more 
difficulty in colouring fringing-reefs than in colouring 
barrier-reefs, as the former, from their small size, 
have not much attracted the attention of navigators. 
As I have had to seek my information from all kinds 
of sources, I do not venture to hope that the map is 
free from errors. Nevertheless, I trust it will give 
an approximately correct view of the general distri- 
bution of the coral-reefs throughout the 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 ill-defined from the nature of the 
objects classified, have been adopted by most voyagers. 
I may further remark, that the dark-blue colour repre- 
sents land entirely composed of coral-rock ; the pale 
blue, land with a wide and thick border of coral-rock ; 
and the red, land with a mere narrow fringe of coral-rock. 
Looking now at the map under a theoretical point 
of view, the two blue tints signify that the foundations 
of the reefs thus coloured have largely subsided, and 
that the rate of subsidence has been less than the up- 
ward growth of the corals. It is also probable that in 
many cases the foundations are still subsiding. The red 
signifies that the shores thus coloured support fringing- 
reefs ; and they have not, as a general rule, recently 
