EDITORIAL NOTE
Although in some respects more technical in their subjects and style thanDarwin’s “Journal,” the books here reprinted will never lose their value andinterest for the originality of the observations they contain. Many parts ofthem are admirably adapted for giving an insight into problems regarding thestructure and changes of the earth’s surface, and in fact they form a charmingintroduction to physical geology and physiography in their application tospecial domains. The books themselves cannot be obtained for many times theprice of the present volume, and both the general reader, who desires to knowmore of Darwin’s work, and the student of geology, who naturally wishes to knowhow a master mind reasoned on most important geological subjects, will be gladof 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 specialvalue.
G.T.B.
THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS.
Chapter I—ATOLLS OR LAGOON-ISLANDS.
Section I—DESCRIPTION OF KEELING ATOLL.
Corals on the outer margin.—Zone of Nulliporæ.—Exteriorreef.—Islets.—Coral-conglomerate.—Lagoon.—Calcareoussediment.—Scari and Holuthuriæ subsisting on corals.—Changes in thecondition of the reefs and islets.—Probable subsidence of theatoll.—Future state of the lagoon.
Section II—GENERAL DESCRIPTION OFATOLLS.
General form and size of atolls, their reefs andislets.—External slope.—Zone ofNulliporæ.—Conglomerate.—Depth of lagoons.—Sediment.—Reefssubmerged wholly or in part.—Breaches in the reef.—Ledge-formed shoresround certain lagoons.—Conversion oflagoons into land.
Section III—ATOLLS OF THE MALDIVAARCHIPELAGO—GREAT CHAGOS BANK.
MaldivaArchipelago.—Ring-formed reefs, marginal and central.—Great depthsin the lagoons of the southern atolls.—Reefs in the lagoons all rising tothe surface.—Position of islets and breaches in the reefs, with respectto the prevalent winds and action of the waves.—Destruction ofislets.—Connection in the position and submarine foundation of distinctatolls.—The apparent disseverment of large atolls.—The Great ChagosBank.—Its submerged condition and extraordinary structure.
Closely resemble in general form and structure atoll-reefs.—Width anddepth of the lagoon-channels.—Breaches through the reef in front ofvalleys, and generally on the leeward side.—Checks to the filling up ofthe lagoon-channels.—Size and constitution of the encircledislands.—Number of islands within the same reef.—Barrier-reefs ofNew Caledonia and Australia.—Position of the reef relative to the slopeof the adjoining land.—Probable great thickness of barrier-reefs.
Chapter III—FRINGING OR SHORE-REEFS.
Reefs of Mauritius.—Shallow channel within the reef.—Its slowfilling up.—Currents of water formed within it.—Upraisedreefs.—Narrow fringing-reefs in deep seas.—Reefs on the coast of E.Africa and of Brazil.—Fringing-reefs in very shallow seas, round banks ofsediment and on worn-down islands.—Fringing-reefs a