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CHAPTER V. 



THEORY OF THE FORMATION OF THE DIFFERENT CLASSES 

 OF CORAL-REEFS. 



The atolls of the larger archipelagoes not formed on submerged craters, 

 or on banks of sediment— Immense areas interspersed withatolh— 

 Their subsidence — The effects of storms and earthquakes on atolls^— 

 Becent changes in their state — The origin of barrier-reefs and of 

 atolls — Their relative forms — The step-formed ledges and walli round 

 the shores of some lagoons — The ring -formed reefs of the Maldiva 

 atolls — The submerged condition of parts or of the whole of some annu- 

 lar reefs — The dissevcrment of large atolls — The union of atolls by linear 

 reefs — The great Chagos Bank — Objections considered arising from the 

 area and amount of subsidence required by the theory — The probable 

 composition of the lower parts of atolls. 



The naturalists who have visited the Pacific, seem to 

 have had their attention riveted by the lagoon-islands 

 or atolls, — those singular rings of coral-land which rise 

 abruptly out of the unfathomable ocean, — and have 

 passed over, almost unnoticed, the scarcely less won- 

 derful encircling barrier- reefs. The theory most 

 generally received on the formation of atolls, is that 

 they are based on submarine craters: but where can we 

 find a crater of the shape of Bow atoll, which is five 

 times as long as it is broad (Plate I. fig. 4); or like 

 that of Menchicoff Island (Plate II. fig. 3), with its 



