26 ATOLLS. Ch. I* 



stead of being deposited within it. The deposition, 

 moreover, of sediment, checks the growth of coral reefs, 

 so that these two agencies cannot act together with full 

 effect in filling up the lagoon. We know so little of 

 the habits of the many different species of corals, which 

 form the lagoon-reefs, that we have no more reason for 

 supposing that their whole surface would grow up as 

 quickly as the coral did in the schooner-channel, than 

 for supposing that the whole surface of a peat-moss 

 would increase as quickly as parts are known to do in 

 holes, where the peat has been cut away. These 

 agencies, nevertheless, tend to fill up the lagoon ; but 

 in proportion as it becomes shallower, so must the 

 polypifers be subject to many injurious agencies, such 

 as impure water and loss of food. For instance, Mr. 

 Liesk informed me, that some years before our visit 

 unusually heavy rain killed nearly all the fish in the 

 lagoon, and probably the same cause would likewise 

 injure the corals. The reefs also, it must be remem- 

 bered, cannot possibly rise above the level of the 

 lowest spring-tide, so that the final conversion of the 

 lagoon into land must be due to the accumulation of 

 sediment : and in the midst of the clear water of the 

 ocean, and with no surrounding high land, this process 

 must be exceedingly slow. 



