part 1] PHOSPHATE DEPOSIT OF OCEAN ISLAND. 15 



smaller limestone islands of the Pacific. There might be signi- 

 ficance in the occurrence of thick deposits of phosphate-rock in 

 the Pacific on ' high islands ' only, whereas ' low islands ' supplied 

 inferior surface-material, presumably owing to shorter occupation by 

 birds. Perhaps a short time ago, geologically speaking, the low- 

 lying islands were under water, which would also account for the 

 late arrival of Man. 



The Author replied that most of the terraced limestone-islands 

 •of the Pacific have been noted as approximating 100 metres 

 (328 feet), and Ocean Island conforms to the general rule. 

 Apparently, however, no evidence of slight tilting has been noted 

 before. The reason that all the deposits of any great value occur 

 on such islands may be due to the very uneven surface which a 

 platform of eroded coral offers, the guano being thus trapped in a 

 way that would be impossible on the smooth surface of the low- 

 lying islands. The reasons for the disappearance of the birds are 

 obscure ; but it may be noted that the really extensive and older 

 phosphate deposits of the Pacific tend to occur in the west, while 

 the smaller and more recent deposits are found most frequently in 

 the east. 



