274 CORAL AND ATOLLS 



the entrance to the lagoon. In this way the windward part 

 of the lagoon will commence to shoal. The shoaling of 



Fig. 66. 



Diagram to illustrate the Development or 

 Keeling Atoll. 



Stage III. — The further development of the formation 

 of sand-banks in the leeward lagoon entrance. 



the lagoon of the Cocos -Keeling atoll is proceeding steadily, 

 and year by year more and more sediment is laid down upon 

 its bed. Such shallowing is the probable fate of all lagoons. 

 Two agencies are at work ; coral growth tends to fill up the 

 lagoon slowly, and sedimentation tends to fill it up more 

 rapidly; but, as we have seen, these two factors cannot act in 

 the same area. As a matter of fact the two processes work 



