THE AFTER-HISTORY OF THE ATOLL 26S 



of activity, and so with increasing tidal excursion a greater 

 elevation of island-building is possible. 



The influence of great storms upon the height of island- 

 building is easily seen, for it is simply a question of how far 

 up the debris slope may the largest waves of the greatest 

 storms hurl any additional fragments. Pumice represents 

 the tell-tale of maximum wave action, for a fairly large frag- 

 ment of light pumice is the float that the spindrift of a broken 

 roller will carry farthest in front of it ; and pumice, in most of 

 the islands, has been flung over the crest of the sea beaches 

 and on to the island land. Storms of exceptional violence, 

 such as that which visited this atoll in 1876, have overridden 

 their rampart so completely that waves have swept into the 

 islands for a distance of 150 yards from their seaward margins. 

 It is only the possession of positive data of this kind that 

 makes it possible to realise how any sea could toss some of 

 the enormous rocks of massive corals to a height of fifteen 

 feet or so, after a journey of more than a hundred yards across 

 the reef flats. 



Upon the lee side of the atoll the waves may only toss 

 fragments to the top of a bank some three or four feet high, and 

 in Pulu Tikus the most exposed portion only has been sea 

 built to a height of thirteen feet. Upon the windward side 

 the building rises higher, the wall of the sea beach is steeper, 

 and is composed of far larger boulders than the sea beaches of 

 the lee side. The rampart here may be piled to a height of 

 twenty feet, and the blocks that enter into its composition are 

 often far too large for any man to move. 



When the pile of debris has risen as high as the waves 

 can cast their burdens, it must cease from further growth from 

 sea influence unless some storm of quite exceptional violence 

 visits the group, or unless the seaward edge of the barrier reef 

 grows farther seaward. Since we have seen that the distance 

 of the island from the barrier edge is regulated by the force 

 of the waves — the windward islands being farther from the 

 edge than the leeward islands — it is evident that the seaward 

 margins of the island will advance as the seaward margin of 



