Ch. III. 
FRINGING REEFS. 
79 
to the land like barrier-reefs, although not belonging 
to that class ; — but there are, as I believe, in the Red 
Sea some true barrier-reefs. The reefs of this sea and 
of the West Indies will be described in the Appendix. 
In some cases, fringing-reefs appear to be considerably 
modified in outline by the course of the prevailing 
currents ; Dr. J. Allan informs me that on the east 
coast of Madagascar, almost every headland and low 
point of sand has a coral-reef extending from it in 
a S.W. and N.E. line, parallel to the currents on that 
shore. I should think the influence of the currents 
chiefly consisted in causing an extension, in a certain 
direction, of a proper foundation for the attachment 
of the coral. Round many intertropical islands, for 
instance the Abrolhos on the coast of Brazil sur- 
veyed by Captain FitzRoy, and, as I am informed by 
Mr. Cuming, round the Philippines, the bottom of the 
sea is entirely coated by irregular masses of coral, 
which although often of large size, do not reach the 
surface and form proper reefs. This must be owing 
either to insufficient growth, or to the absence of those 
kinds of corals which can withstand the breaking of 
the waves. 
The three classes, atoll-formed, harrier, and fringing 
reefs, together with the modifications just described of 
the latter, include all the most remarkable coral-forma- 
tions anywhere existing. At the commencement of 
the last chapter in the volume, where I detail the 
principles on which the map (Plate III.) is coloured, 
the exceptional cases will be enumerated. 
