FUNAFUTI: THE STORY OF A CORAL ATOLL. 



393 



SliCllMl STACK. 



will cease, and the reef will begin to pass into decay, from the shore 

 edge outward. So long as the island remains stationary, neither rising 

 nor falling with respect to the sea level, this is practically all that 

 will happen, and the final result is a reef not much exceeding 25 

 fathoms in thickness (fig. 2, first stage). But let us next suppose that 

 the island begins slowly to sink into the sea, carrying the reef with it; 

 the upward limit to the growth 



of the corals will be displaced; enc.rcun& reef 



they will commence to flourish 

 afresh, and the reef will continue 

 to extend upward till the level 

 of the low tides is once more 

 encountered, and growth again 

 arrested. This process of sub- 

 mergence and upward growth 

 may of course be repeated in- 

 definitely, and by the time the 

 island has descended 50 fathoms 

 below its original position, the 

 reef will have acquired a corre- 

 sponding thickness. In such a case the unfavorable conditions to the 

 coral growth which prevail on the inner side of the reef, together with 

 the retreating slope of the flanks of the island, will have led to the 

 formation of a channel of sea water between the reef and the shore (fig. 

 2, second stage). Finally, let the submergence of the island continue 

 till it is completely swallowed up by the sea, not a vestige of its summit 

 remaining to mark its place; the upward growth of the corals, con- 

 stantly proceeding, will bring 

 ATOLL them once more to the level of 



low tides, and the result will be 

 the formation of a ring-shaped 

 reef surrounding a central la- 

 goon, or, in other words, of an 

 atoll (fig. 2, third stage). 



If this hypothetical scheme 

 of the progress of events corre- 

 spond to the facts, we may ex- 

 pect to find its various stages 

 still represented among the 

 numerous islands of the Pacific, 

 and this, as Darwin endeavored to show, is clearly the case. The first 

 stage, in which the reef is no more than 25 fathoms thick, and forms a 

 selvage accurately following the margin of the land, is represented by 

 that numerous class known as "fringing" reefs. The second, in which 

 a comparatively thick reef surrounds an island with an intervening salt- 

 water channel, is illustrated by another class, known as "encircling" or 



Fig. 2. 



THIRD STAGE. 



