284 CORAL AISSD ATOLLS 



of elevation may be present, still it must be remembered that 

 the result seen may be brought about by changed conditions of 

 sea-level or violent storms. 



When a raised breccia platform is found upon the seaward 

 barrier, the breccia platforms of the island and of the lagoon 

 shore of course share in the movement. The land undergoes 

 the same slight alteration of level, and the slabs of breccia on 

 the lagoon shore become tilted. At the eastern end of Pulu 

 Tikus these effects are well seen, for the old breccia platform 

 has become undermined by the lagoon wavelets, and has 

 become cracked and broken, and in many places moved from 

 its original site. 



I have not included among the possible signs of an upward 

 movement those large blocks of coral rock that are found 

 isolated upon the barrier, and in some atolls have been given 

 the name of " negro heads." There are many enormous 

 " negro heads " upon the windward barrier flats of the southern 

 islands of the Cocos-Keeling atoll, but I never regarded them 

 as being anything else than the tell-tales of the efforts of 

 unusual storms. The experience of living on the atoll during 

 a spell of cyclone weather confirmed this view, and I conceive 

 the storm-driven waves to be capable of tossing up the largest 

 " negro head *' that I have ever seen. The power of the waves 

 to move these blocks has been denied by Semper (English 

 Trans., 1883, p. 239) and by Wilks, but the recent work of 

 Hedley on the Great Barrier Reef leaves no doubt that " negro 

 heads " are in reality wave-cast boulders. That the matter 

 should become a subject of theoretical speculation seems 

 almost absurd, for the people who have been born in the 

 atoll, and have lived all their lives upon it, know of these 

 things, and remember the advent of outstanding "negro heads" 

 during the many cyclones which have passed over the islands. 



An interesting point is to be noted in connection with some 

 of the elevated rocks of the barrier, and that is the fact that 

 some of them are capable of producing musical sounds. By 

 the action of the sea they become hollowed and tunnelled 

 so that the water rushing into them causes the air to be 



