442 SCIENCE i PROGRESS 



lay upon those who assume that reef foundations have not 

 subsided. 



The Origin of Atolls. — The problem of sea-level atolls is, as 

 above noted, different from that of fringing, barrier, and ele- 

 vated reefs, inasmuch as the geological history of atolls cannot 

 be made out by surface observation. True, the foundations 

 of the atolls in the northern part of the Seychelles group must 

 in all probability have suffered movements very similar to those 

 suffered by Malie" and the other granitic islands. Similarly, the 

 atolls of the Fiji group can hardly have had stationary founda- 

 tions while the neighbouring volcanic islands suffered the varied 

 and diverse changes of level that are testified to by their many 

 kinds of reefs ; for the reefs of this most interesting group 

 include, besides a number of typical atolls, many narrow and 

 unconformable sea-level fringes, unconformable sea-level bar- 

 riers at various distances from their embayed islands, and little 

 dissected and much dissected elevated reefs at different alti- 

 tudes, most of which are strongly unconformable on their 

 foundations. 



Again, the atoll foundations in the Society group must have 

 shared in the movements of subsidence by which the neigh- 

 bouring volcanic islands have been deeply embayed. But the 

 central Pacific archipelagoes, consisting of atolls only, must 

 long remain objects of surmise, except in so far as the evidence 

 for subsidence given by the Funafuti boring * is held to apply 

 to other atolls ; for, as far as the visible features of those 

 atolls are concerned, they can be explained by any one of 

 several theories, provided the postulates and the processes 

 of the theories are accepted. 



The Glacial-control Theory. — For example, if it be assumed 

 that the ocean bottom in the region of atoll archipelagoes has 

 long remained fixed, then the changes of ocean level and tem- 

 perature, assumed to have been caused by the climatic changes 

 of the Glacial period, together with the alternation of reef 

 growth and extinction that has been assumed to accompany 

 these oceanic changes, will suffice to account for the superficial 

 features of atolls as they are now observed ; but the absence 

 of clift shores on the central islands of fringing and barrier 

 reefs in other parts of the Pacific compels me, as I have else- 



1 The best summary of this evidence is given by E. W. Skeats, Amer. Journ. 

 Set. xlv. 1 91 8, 81-90. 



