392 



FUNAFUTI: THE STORY OF A CORAL ATOLL. 



DARWIN 

 INCINC REE. 



mountain, is formed of the same material. Not perhaps a strictly logi- 

 cal conclusion, yet, as events have proved, in the main correct. 



Chamisso's opinion was not destined to remain long unchallenged, 

 for two famous French naturalists — Quoy and Gaiinard — asserted, as 

 the result of their observations, that the coral rock of an atoll is only 

 skin-deep — i. e., it forms, according to them, a mere superficial crust, 

 not more than about 25 feet in thickness; the rest (Chamisso's "table 

 mountain" ) being, on this view, of volcanic, or at all events of inorganic, 

 origin. 



Few of the arguments by which it was attempted to sustain this 

 erroneous conclusion strike one as being very satisfactory, but they 

 include one highly important observation, viz, that reef-building corals 

 do not live at greater depths than 25 feet below the level of low tides. 

 Subsequent inquiry, while fully confirming the existence of a limit, 

 has at the same time extended it down to a depth of as many as 25 or 

 perhaps even 40 fathoms. Yet, even with this modification, the unex- 

 pected discovery of Quoy and 

 Gaimard seems to stand in 

 flagrant contradiction to the 

 views of Chamisso. If corals 

 can not grow below a depth 

 of 25 fathoms, how could they 

 possibly have built up islands 

 of over 100 fathoms in thick- 

 ness? 



The answer to this question, 

 as is well known, was given 

 by Charles Darwin. If. we 

 admit the truth of both the 

 apparently conflicting state- 

 ments, it is obvious that the corals at the base of a reef 100 fathoms 

 in thickness must have been situated within the limit of 25 fathoms 

 at the time they were alive. But in order to bring them within this 

 limit it is only necessary to suppose that the foundation on which they 

 grew originally stood 75 fathoms nearer the sea level than it does 

 now 5 or, in other words, that since the lower layers of the reef were 

 alive and flourishing, the ground which supported them has sunk 75 

 fathoms deeper in the sea. No fact is better established than the rise 

 and fall of islands situated in mid-ocean, and thus there is nothing 

 antecedently improbable in this supposition. But once grant it, and 

 Darwin's explanation of atolls naturally follows. Thus, let a be an 

 island with its summit rising 100 fathoms above the sea; let its shores* 

 become peopled with corals, which extend seaward down to the limit 

 of 25 fathoms, beyond which, as we admit, they can not proceed; a reef 

 is thus started, which will continue to grow, rising upward till it 

 reaches the level of low tides; when this is attained upward growth 



Fig. 2. 

 FIRST STAGE. 



