22 ATOLLS. . Ch. I. 



grown outwards. On the western side of the atoll, the 

 c flat ' lying between the margin of the reef and the 

 beach, is very wide : and in front of the regular beach 

 with its conglomerate basis, there is, in most parts, a 

 bed of sand and loose fragments with trees growing 

 out of it, which apparently is not reached even by the 

 spray at high water. It is evident some change has 

 taken place since the waves formed the inner beach : 

 that they formerly beat against it with violence was 

 evident, from a remarkably thick and water- worn point 

 of conglomerate at one spot, now protected by vegeta- 

 tion and a bank of sand ; that they beat against it in 

 the same peculiar manner in which the swell from 

 windward now obliOjUely curls round the margin of the 

 reef, was evident from the conglomerate having been 

 worn into a point projecting from the beach in a simi- 

 larly oblique manner. This retreat in the line of 

 action of the breakers may have resulted, either from 

 the surface of the reef in front of the islets having 

 formerly been submerged, and afterwards having been 

 raised by accumulated fragments, or from the mounds 

 of coral on the margin having grown outwards. That 

 an outward growth of this part is in process, can 

 hardly be doubted from the existence of the mounds 

 of Porites with their summits apparently lately killed, 

 and their sides only three or four inches lower down 

 thickened by a fresh layer of living coral. But there 

 is a difficulty in this supposition which I must not 

 pass over. If the whole, or a large part of the ' flat,' 

 had been formed by the outward growth of the margin, 



