LIFE OF JAMES DWIGHT DANA 



below 1 20 feet ? We should say it were utterly impos- 

 sible, if we might without being justly charged with con- 

 tempt of evidence. I visited one island which is now 

 elevated 225 feet above the waves, or about twice the 

 depth to which corals may extend ; and yet it was made 

 of the reef rock to low-tide level ; and how many hun- 

 dreds of feet below this I cannot say. 



" We must admit, then, that the corals of each coral 

 island were planted upon land within 120 feet of the sur- 

 face ; and as the foundation or basement is now, in the 

 case of many atolls, at a depth of 1000 or 2000 feet or 

 more, it could have reached such a depth only by sink- 

 ing. There is hence indubitable evidence of a subsidence 

 greater or less than this for every coral atoll. 



" Land beneath the sea, within a hundred feet of the 

 surface, is of very rare occurrence, except along the shores 

 of islands or continents. In the formation of the atoll, 

 therefore, the coral reef may have once been a reef en- 

 circling an ordinary hilly island. Indeed, there are many 

 such reefs in the Pacific ; and they are in all stages, from 

 the first step to the last, in the transition to atolls. 

 There are islands with reefs bordering the shore or fring- 

 ing it all around, the reef in such cases usually lying at 

 low-tide level, and sometimes more or less wooded. 

 There are other cases where the island has partly sub- 

 sided, and the reef stands far off from its shores. There 

 are others in which only one or two mountain peaks are 

 left above the sea. There are others, again, in which the 

 last rock of the old island has sunk out of sight, and the 

 reef, which was ever increasing upward by the growth of 

 the corals and the help of the waves, remains alone at the 

 surface. Thus by a gradual sinking of the land the old 

 island has disappeared. The subsidence may have been 

 only a yard or two in a century ; it was certainly so slow 

 that the coral animals by their growth could keep pace 

 with it. Whatever the rate, the coral atoll is finally 

 alone. Whenever this slow subsidence ceased, the waves 

 would then begin to prepare it for verdure, the verdure 

 for birds, and all for man's use and enjoyment. I might 

 touch upon the depth of the submergence in the case of 

 various atolls and reefs, and prove that, in some cases, it 

 amounted to thousands of feet ; but I promised you brief 

 remarks, and I forbear. 



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