ATOLL AND REEF FORMATION 227 



says, however : " Turning now to the lagoons and lagoon channels 

 of coral islands, it is hdieved * that large quantities of carbonate 

 of lime are in the same way being dissolved from these shallow 

 basins as well as from the deposits of the deep sea, but under 

 somewhat different circumstances. In the case of a shell 

 falling to the bottom of the sea, it is continually brought into 

 contact with new layers of water, which has the same effect as 

 if a continuous stream of water were passing over the shell. 

 In the case of the lagoons this last is what takes place. The 

 water which flows in and out of the lagoons twice in twenty- 

 four hours passes over great beds of growing corals, and from 

 all the observations we have is largely charged with carbonic 

 acid, owing probably to the larger number of animals on the 

 outer reef over which the water passes on its way to the lagoon." 



Throughout the writings of Sir John Murray much stress 

 is laid on " the water which flows in and out of the lagoons 

 twice in twenty-four hours," and this for the reason that it 

 gives the operations of solution a better chance to act. It is 

 true that the level of the lagoon rises and falls with the cycles 

 of the tide, and that the alterations in level give rise to local 

 currents in the inlets of the lagoon ; but this does not affect 

 the whole lagoon, and to imagine the process as anything 

 akin to that which happens as a shell falls through the depths 

 of the sea is a mere fallacy. 



When a shell falls from the surface of the sea to greater 

 depths it passes through new layers of water, each, with the 

 increasing depth, being more potent for solution. In the 

 case of the lagoons this last is what does not take place. The 

 rising tide raises the lagoon waters, the falling tide lowers 

 them, but the waters of the lagoon are not changed twice in 

 twenty-four hours. The action of " solution " in the lagoons of 

 atolls may therefore be accepted as being only a theoretical 

 action, and the actual proofs of its working do not seem to 

 have been established. 



Although there seem to be no published observations to 

 prove that material is " carried away in solution " from a 

 '■' Italics by present author. 



