PINAKI. 123 



materials necessary for such a change. The existence of such high dunes 

 (35 feet) at Nukutavake and at Pinaki introduces an element which had not 

 been taken into account as a factor in the building up of coral islands. 

 Elsewhere also, as in the Marsliall Islands, the changes produced by the 

 movement of great masses of sand are perhaps more marked and more im- 

 portant in shaping the outline and extent of the land rim as well as the 

 extent and area of the lagoon flats. The encroachment of the sand dunes 

 on the land rim and the killing of bushes and Pandanus and trees by sand 

 dunes take place at Pinaki as at Nukutavake, but not on such an extensive 



scale. 



We can suppose the old ledge mass of Pinaki, after being elevated to a 

 moderate height, to have little by little been cut down to the level of the 

 sea, this cutting down to have been partly mechanical and partly chemical. 

 The former action produced a mass of material, moving backwards and 

 forwards, which must have formed the earliest shingle beaches on the 

 periphery of the atoll or on one side or face of it, additions being made 

 to this mass from the death and decay and decomposition of the corals 

 which had found a favorable place for growth on the slopes of the old 

 ledge mass. 



Thus we can readily imagine Pinaki to have grown ; the beaches thrown 

 up on the circumference finally enclosed a comparatively shallow lagoon, con- 

 stantly becoming shallower by accretions both from the outside and inside ; 

 accretions from the inside by the decay of the corals and shells, and from 

 the outside by the mass of coral shingle and boulders thrown into the lagoon 

 at the beginning of the building of the atoll, and also of the sand blown 

 in by the gradual advance and rising of the dunes. 



At first there may have been more than one opening into the lagoon ; 

 the land rim may, as in other atolls, have consisted of small islets separated 

 by gaps, which with the diminution in size and depth of the lagoon were 

 no longer kept open by the in and out flow of water over the half-submerged 

 gaps. Indications of two such gaps can be seen in the stretch of low vege- 

 tation indicated in PI. 72, fig. 1, and in the low gap covered with coarse 

 shingle shown in PI. 73, fig. 2. The outer beach of the land rim in the 

 former has become as high as the adjacent coral sand beaches, while the 



