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 1 have taken the liberty of simplifying the foreground, and leaving 

 put a mountainous island in the far distance. 



