ATOLL AND REEF FORMATION 215 



all ordered investigations of scientific subjects, still, in the 

 history of the theories of atoll formation, it lasted long ; and 

 many careful researches must be made and accepted before 

 an explanation so easy and so comfortable is quite forgotten. 



It was in a great measure the increasing knowledge of the 

 conditions of the ocean bottom that tended most to modify 

 the prevalent ideas of the nature of atolls, and as we have 

 learned more and more of ocean soundings so have our ideas 

 of coral islands been slowly corrected. Many of the theories 

 that were put forward in the early days are not without 

 interest to-day, for in many cases the modern theories are but 

 compromises, in which the remnants of an older explanation 

 are easily detected. 



One of the older theories that must claim some share of 

 attention — for, in a modified condition, it survives still — is that 

 which seeks to explain the usual form of atolls by assuming 

 the island ring to be a coral growth built around the crater of 

 a volcano. The well-known cone shape of the typical volcano 

 gives rise to the characteristic form of the atoll ; the lagoon is 

 the water-filled crater, round which the islands stand in a 

 more or less perfect ring, being built wherever the rim of the 

 crater comes sufficiently near to the surface of the sea. This 

 theory received authority by appearing in Lyell's " Principles of 

 Geology" (vol. ii.) in 1832 ; but, even if no rival theory had 

 so soon been destined to overthrow it, the many and obvious 

 objections to it would have rendered its general acceptance 

 impossible. No terrestrial volcanoes are known Avith craters 

 so vast as are many atoll lagoons, and no mountain chain 

 so strangely level as are the low island groups scattered in 

 the Pacific Ocean. Despite the improbability of this view, 

 the majority of the stray visitors who have come to this atoll 

 have fancied that somewhere in the lagoon was the deep hole 

 of the crater, and have believed themselves to be living on the 

 rim of a vast volcano. The Rev. E. C. Spicer, who as naturalist 

 accompanied H.M.S, Espoir in 1885 on behalf of the Straits 

 Government, was struck by the appearance of the narrow strip 

 of land and the enclosed lagoon, and said " the resemblance 



