liflflVEKSAEY ADJ)KESS OF THE PEESIDENT. I09 



level. But on the theory of elevation or of gradual building up by 

 volcanic outbursts, it is Scarcely credible that all should have been 

 brought v^ithin 20, 100, or even 500 fathoms of the surface, but 

 that not one should have been raised above the sea. If the atolls 

 occupied the site of rocky islands worn dov^n to a little below 

 the sea-level by marine denudation, the atoll-form remains to be 

 explained ; for marine denudation could not make lagoons 30 or 40 

 fathoms deep. Moreover the formation of the coral-reefs would 

 surely here and there have protected and preserved some little knoll 

 formed of the original foundation rock. Further, if, as has been 

 urged, atolls are founded on the summits of submarine elevations 

 formed by volcanic eruptions or on the remains of volcanic islands 

 worn down to a little below the surface of the water by marine 

 denudation, they should be most abundant amongst groups of vol- 

 canic islands, where both the forms of shoal just specified would be 

 most likely to occur. But this is not the case : the atolls are found 

 by themselves over large areas of ocean, where no other island 

 emerges from the surface and where no trace of volcanic action is 

 observed, and there are either no atolls, or, so far as I can learn, 

 very few and small atolls, amongst the Archipelagoes that mani- 

 festly owe their origin to volcanic action. 



Other and most important facts in favour of subsidence in the 

 case of the Pacific atolls and barrier-reefs have been brought to 

 notice so recently and so ably by Prof. Dana *, that it is unnecessary 

 to do more than advert to them. The proofs afforded of subsidence 

 in the eastern islands of the Fiji group, and in several other cases 

 where islands indented by deep inlets are surrounded by barrier- 

 reefs, must be convincing to all who have paid attention to the 

 evidence of elevation and subsidence along coast-lines. The curious 

 examples of vertical walls descending to depths of 300 and, in one 

 case, 600 fathoms are also easily explicable as the results of sub- 

 sidence, but not, so far as I can see, in any other way, unless the 

 very improbable hypothesis be adopted that they are due to faulting. 



It is necessary to recall attention to the leading points of evi- 

 dence, because in the discussion of details the broad facts on which 

 Darwin's theory was originally founded are liable to be over- 

 looked. 



In concluding what has, I fear, been a somewhat dreary recapitu- 

 ation of details, one pleasant task remains. When I returned from 



'^ Am. Journ. Sc. ser. 3, xxx. pp. 89, 169 (1885). 



