CHAPTER XII 



THE SUBMARINE BANK ON WHICH THE ATOLL 

 RESTS 



The submarine slopes, by wbich the edges of the atoll reef 

 descend to ocean depths, are perhaps the most important 

 features in the whole of the structure of the atoll. 



Every theory that attempts an explanation of the formation 

 of atolls and reefs must be concerned with this decline from 

 wave-beaten barrier to deep-sea bottom. Some misconcep- 

 tion in the estimation of the gradient of this slope has 

 probably caused certain inaccuracies in the ideas as to atoll 

 formation. Since there is but very little reliance to be placed 

 on some of the older soundings of very deep water, the nature 

 of the ridge on which this atoll is situated has been always a 

 good deal obscured ; and such concrete expressions of its slope 

 as have appeared in publications are shown by more recent 

 soundings to have been mostly fallacious. The statement that 

 the older soundings are often inaccurate is, I think, easy 

 enough to substantiate, for with old-fashioned paying-out 

 gear, errors were extremely difficult to avoid in very deep 

 water. 



Ten miles of sounding-line have been paid out, and no 

 bottom found, in a place where the bottom was no more than 

 three miles distant (see Maury, &c.) ; and, in the neighbour- 

 hood of this atoll, the older soundings are often contradicted 

 by the more modern ones. The accuracy of the soundings of 

 Fitzroy around the atoll, in which he found no bottom at 1200 

 fathoms 6600 feet from the shore, has been questioned by 

 Admiral Sir W. L. Wharton (see Nature, June 19, 1890). I 

 had not the apparatus, nor the opportunity, for making 

 soundings ; and I do not regret the fact, for deep-sea soundings 



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