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CORAL REEFS

by CHARLES DARWIN

EDITORIAL NOTE.

Although in some respects more technical in their subjects and style than Darwin's "Journal," the books here reprinted will never lose their value and interest for the originality of the observations they contain. Many parts of them are admirably adapted for giving an insight into problems regarding the structure and changes of the earth's surface, and in fact they form a charming introduction to physical geology and physiography in their application to special domains. The books themselves cannot be obtained for many times the price of the present volume, and both the general reader, who desires to know more of Darwin's work, and the student of geology, who naturally wishes to know how a master mind reasoned on most important geological subjects, will be glad of the opportunity of possessing them in a convenient and cheap form.

The three introductions, which my friend Professor Judd has kindly furnished, give critical and historical information which makes this edition of special value.

G.T.B.

CORAL REEFS.

TABLE OF CONTENTS.

CRITICAL INTRODUCTION.

INTRODUCTION.

CHAPTER I.—ATOLLS OR LAGOON-ISLANDS.

SECTION 1.I.—DESCRIPTION OF KEELING ATOLL. Corals on the outer margin.—Zone of Nulliporae.—Exterior reef.—Islets.— Coral-conglomerate.—Lagoon.—Calcareous 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.

SECTION 1.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.

SECTION 1.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