32 CORAL-REEFS. 



cannot happen, and the inhabitants observe that the tide 

 rises to a less height, during a high S.E. wind, at the head 

 than at the mouth of the lagoon. The corals, which, under 

 the former condition of things, had attained the utmost 

 possible limit of upward growth, would thus occasionally be 

 exposed for a short time to the sun, and be killed. 



Besides the increase of dry land, indicated by the fore- 

 going facts, the exterior solid reef appears to have grown 

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

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

 the same peculiar manner in which the swell from windward 

 now obliquely curls round the margin of the reef, was 

 evident from the conglomerate having been worn into a 

 point projecting from the beach in a similarly oblique 

 manner. This retreat in the line of action of the breakers 

 might result, either from the surface of the reef in front of 

 the islets having been submerged at one time, and after- 

 ward having grown upwards, or from the mounds of coral 

 on the margin having continued to grow outwards. That 

 an outward growth of this part is in process, can hardly be 

 doubted from the fact already mentioned of the mounds of 

 Pontes 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 on this 



