4 
INTRODUCTION. 
labola, 1 one of the Society Islands. Here, as in Whit- 
sunday Island, the whole of that part of the reef which 
is visible is converted into land. This is a circum- 
stance of rare occurrence ; more usually a snow-white 
line of great breakers, with here and there an islet 
crowned by cocoa-nut trees, separates the smooth 
waters of the lagoon-like channel from the waves of 
the open sea. The barrier reefs of Australia and of 
New Caledonia, owing to their enormous dimensions, 
have excited much attention : in structure and form 
they resemble those encircling many of the smaller 
islands in the Pacific Ocean. 
With respect to fringing, or shore reefs, there is 
little in their structure which needs explanation ; and 
their name expresses their comparatively small ex- 
tension. They differ from barrier reefs in not lying 
far from the shore, and in not having within them a 
broad channel of deep water. Eeefs also occur around 
submerged banks of sediment and of worn-down rock ; 
and others are scattered quite irregularly where the 
sea is very shallow ; these are allied in most respects 
to fringing reefs, but are of comparatively little 
interest. 
I have given a separate chapter to each of the 
above classes, and have described some one reef or 
island, on which I possessed most information, as 
typical ; and have afterwards compared it with others 
of a like kind. Although this classification is useful 
1 I have taken the liberty of simplifying the foreground, and 
leaving out a mountainous island in the far distance. 
