CONTENTS. 



PAGE 



Introduction . . . . . ,15 



CHAPTER I. 



ATOLLS OR LAGOON-ISLANDS. 



Section I. — Description of keeling atoll. 



Corals on the outer margin. — Zone of Nulliporae. — Exterior 

 reef. — Islets. — Coral - conglomerate. — Lagoon. — Cal- 

 careous sediment. — Scari and Holuthuriae subsisting 

 on corals. — Changes in the condition of the reefs and 

 islets. — Probable subsidence of the atoll.— -Future state 

 of the lagoon . . . . 19 to 36 



Section II.— General description of atolls. 



General form and size of atolls, their reefs and islets. — 

 External slope. — Zone of Nulliporae. — Conglomerate. 

 — Depth of lagoons. — Sediment. — Reefs submerged 

 wholly or in part. — Breaches in the reef. — Ledge- 

 formed shores round certain lagoons. — Conversion of 

 lagoons into land . . . . . 36 to 50 



Section III. — Atolls of the maldiva archi- 

 pelago—great chagos bank. 



Maldiva Archipelago. — Ring-formed reefs marginal and 

 central. — Great depth in the lagoons of the southern 



