DEVELOPJMENT OF THE ATOLL 259 



dignity, it will mark the limit of the march of the waves across 

 the barrier flats, for they will break upon its edge, and any- 

 thing that they may sweep over the flats will be added to its 

 growing pile. There is, however, a limit to the extent of the 

 building seaward, for the force of the waves will not permit 

 the resting of fragments till they have become spent by some 

 lengthy journey over the flats. There is also a limit to the 

 land building lagoonwards, for the force of the spent waves is 

 not sufficient to carry material any farther ; and so the rim of 

 land must of necessity be a narrow one. There is, however, one 

 way in which the land pile may spread — and that is by the 

 extension of its extremities in crescent form. The currents that 

 make thetailing-off of the sand-bank in the diverging lines from 

 a single obstruction come into play at the extremities of the 

 linear island, with the result that the land becomes bent 

 inwards, and runs towards the lagoon as incurved banks. 

 Meanwhile, on other spots of the barrier flats, others of these 

 island nuclei will be developed, and the history of them all 

 will be similar; save that those to the lee side may be ex- 

 pected to develop more slowly and to rise to lesser heights. 

 These nuclei will therefore grow around the ring, ever reaching 

 out towards each other, and tending to form a dry land circle. 

 But, as they approach each other, the channel that separates 

 them becomes filled by a more rapidly moving stream of 

 water ; its rush becoming steadily increased as its channel 

 becomes narrowed. There is therefore a limit to the growth 

 of adjacent islands under normal conditions, for the streams 

 that pour through the gaps between them are too rapid to 

 allow of the resting of sediment. We may therefore expect 

 to find the adjacent extremities of two islands to be carried 

 lagoonwards as incurved banks, and to be separated by 

 a channel of rapidly flowing water. In the description of 

 the lagoon this condition was pictured, and the depositing 

 of the sediment carried by the current, as banks farther out in 

 the lagoon, was described. 



The whole of this method of island building has been 

 pictured as though it proceeded regularly, and gradually, over 



