CORAL REEFS By Charles Darwin CONTENTS DETAILED TABLE OF CONTENTS DESCRIPTION OF THE PLATES THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS INTRODUCTION CHAPTER I.—ATOLLS OR LAGOON-ISLANDS CHAPTER II.—BARRIER REEFS CHAPTER III.—FRINGING OR SHORE-REEFS CHAPTER IV.—ON THE DISTRIBUTION AND GROWTH OF CORAL-REEFS CHAPTER V.—THEORY OF THE FORMATION OF THE DIFFERENT CLASSES OF CORAL-REEFS CHAPTER VI.—ON THE DISTRIBUTION OF CORAL-REEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION APPENDIX INDEX DETAILED TABLE OF CONTENTS DESCRIPTION OF THE PLATES INTRODUCTION CHAPTER I.—ATOLLS OR LAGOON-ISLANDS SECTION I.—DESCRIPTION OF KEELING ATOLL. Corals on the outer margin.—Zone of Nulliporæ.—Exterior reef.—Islets.—Coral-conglomerate.—Lagoon.—Calcareous sediment.—Scari and Holuthuriæ subsisting on corals.—Changes in the condition of the reefs and islets.—Probable subsidence of the atoll.—Future state of the lagoon. SECTION II.—GENERAL DESCRIPTION OF ATOLLS. General form and size of atolls, their reefs and islets.—External slope.— Zone of Nulliporæ.—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. SECTION III.—ATOLLS OF THE MALDIVA ARCHIPELAGO—GREAT CHAGOS BANK. Maldiva Archipelago.—Ring-formed reefs, marginal and central.—Great depths in the lagoons of the southern atolls.—Reefs in the lagoons all rising to the surface.—Position of islets and breaches in the reefs, with respect to the prevalent winds and action of the waves.—Destruction of islets.—Connection in the position and submarine foundation of distinct atolls.—The apparent disseverment of large atolls.—The Great Chagos Bank.—Its submerged condition and extraordinary structure. CHAPTER II.—BARRIER REEFS Closely resemble in general form and structure atoll-reefs.—Width and depth of the lagoon-channels.—Breaches through the reef in front of valleys, and generally on the leeward side.—Checks to the filling up of the lagoon-channels.—Size and constitution of the encircled islands.— Number of islands within the same reef.—Barrier-reefs of New Caledonia and Australia.—Position of the reef relative to the slope of the adjoining land.—Probable great thickness of barrier-reefs. CHAPTER III.—FRINGING OR SHORE-REEFS Reefs of Mauritius.—Shallow channel within the reef.—Its slow filling up.—Currents of water formed within it.—Upraised reefs.—Narrow fringing-reefs in deep seas.—Reefs on the coast of E. Africa and of Brazil.—Fringing-reefs in very shallow seas, round banks of sediment and on worn-down islands.—Fringing-reefs affected by currents of the sea. —Coral coating the bottom of the sea, but not forming reefs. CHAPTER IV.—ON THE DISTRIBUTION AND GROWTH OF CORAL-REEFS SECTION I.—ON THE DISTRIBUTION OF CORAL-REEFS, AND ON THE CONDITIONS FAVOURABLE TO THEIR INCREASE. SECTION II.—ON THE RATE OF GROWTH OF CORAL-REEFS.