INTRODUCTION. XV 



named above, stretches of disconnected fringing reefs occur along the 

 southern shores. Rose Island is the only atoll of the Samoan Islands ; 

 it is described as such by Wilkes ; he states that outliers of volcanic 

 rock are found upon the encircling reef. An excellent sketch of the 

 atoll is given in Graeffe's Samoa, " Journ. d. Museum Godeffroy," Heft I., 

 1873, p. 32, PI. 1. 



The Paumotu Archipelago consists of more than seventy atolls, many of 

 great size and of elevated islands composed of coralliferous limestone. The 

 low atolls have been cut down from the denudation and submarine erosion 

 of higher islands, forming sounds or sinks surrounded at first by high rims 

 subsequently cut into islands or islets with passes leading into the sounds, 

 until the land rims were reduced to the level they now occupy. The 

 successive stages of denudation and submarine erosion are represented 

 by such islands as Makatea, Niau, Rangiroa, Hao, and others. Some of the 

 easternmost of the Paumotu atolls are diminutive, and such atolls as 

 Pinaki, Nukutipipi, Anu-Anurunga, Anu-Anuraro are admirable epitomes 

 of the structure of the larger ones. 



Some of the smaller of the Paumotu Islands have a central sink or 

 apparent depression formed by the closing in of a part of the summit of a 

 reef flat by beaches thrown up on the sea faces of the islands. If the island 

 flat is somewhat below low-water mark a shallow lagoon is formed, and 

 according to the height of the reef flat a dry sink may be enclosed, to 

 be filled only during the rainy season. 



The Paumotus are flanked on the east by Manga Reva, a cluster of 

 volcanic islands encircled by a barrier reef, and on tlie west by the Society 

 Islands. This group is, with the exception of Tetiaroa, composed of 

 volcanic islands surrounded by barrier reefs, edging often a very wide 

 barrier reef flat, enclosing a lagoon of moderate depth. The fringing reefs 

 of the Society Islands are also noted for their great breadth ; on Tahiti the 

 reefs of the northwest and western coast show admirably how a wide fring- 

 ing reef may gradually become gouged out into a barrier reef edging a 

 shallow lagoon, and ultimately a wide and deep barrier reef lagoon. On 

 some of the Society Islands the islands on the barrier reef form a nearly 

 continuous belt, covered with a luxuriant growth of cocoanut trees and 



