82 CORAL-REEFS. 



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, barrier, and fringing- 

 reefs, together with the modifications just described of 

 the latter, include all the most remarkable coral formations 

 anywhere existing. At the commencement of the last 

 chapter in the volume, where I detail the principles on 

 which the map (Plate V.) is coloured, the exceptional 

 cases will be enumerated. 



