Ch. II. BARRIER REEFS. 63 



itself; while Taha and Eaiatea (fig. 3, Plate I.), both 

 moderately large islands, of nearly equal size, are in- 

 cluded in one reef. Within the reef of the Grambier 

 group there are four large and some smaller islands 

 (fig. 8, Plate I.); within that of Hogoleu (fig. 2, 

 Plate I.) nearly a dozen small islands are scattered over 

 the expanse of one vast lagoon. 



After the details now given, it may be asserted that 

 there is not one point of essential difference between 

 encircling barrier-reefs and atolls ; — the latter enclose a 

 simple sheet of water, the former encircle an expanse 

 with one or more islands rising from it. I was much 

 struck with this fact, when viewing, from the heights 

 of Tahiti, the distant island of Eimeo standing within 

 smooth water, and encircled by a ring of snow-white 

 breakers. Remove the central land, and an annular 

 reef like that of an atoll in an early stage of its forma- 

 tion is left ; remove Bolabola, and there remains a 

 circle of linear coral-islets crowned with tall cocoa- 

 nut trees, like one of the many atolls scattered over the 

 Pacific and Indian oceans. 



The barrier-reefs of Australia and of New Caledonia 

 deserve a separate notice from their great dimensions. 

 The reef on the west coast of New Caledonia (fig. 5, 

 Plate II.) is 400 miles in length ; and for a length of 

 many leagues seldom approaches within eight miles of 

 the shore. Near the southern end of the island, the 

 space between the reef and the land is sixteen miles in 

 width. The Australian barrier extends, with a few 

 interruptions, for about eleven hundred miles ; its 



