CHAPTER V. 



THEORY OF THE FORMATION OF THE DIFFERENT 

 CLASSES OF CORAL-REEFS. 



The atolls of the larger archipelagoes are not formed on submerged 

 craters, or on banks of sediment. — Immense areas interspersed with 

 atolls. — Their subsidence. — The effects of storms and earthquakes 

 on atolls. — Recent changes in their state. — The origin of barrier- 

 reefs and of atolls. — Their relative for ?ns. — The step-formed ledges 

 and walls 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 annular reefs. — The disseverment of large 

 atolls. — The union of atolls by linear reefs. — The Great Chagos 

 Bank. — Objections from the area and amount of subsidence required 

 by the theory, considered. — The probable composition of the loxver 

 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 wonderful 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 III., Fig. 5) ; or like 

 that of Menchicoff Island (Plate I., Fig. 2), with its three 

 loops, together sixty miles in length; or like Rimsky 

 Korsacoff, narrow, crooked, and fifty-four miles long ; or 



