114 



If the land continues to subside, and the Coral reef continues 

 to grow upwards on its old foundations, whilst the water gains 

 on the land until the highest peak is submerged, there will 

 remain only a perfect Atoll, of which Mg. 5 represents a vertical 



a.j:f 



Fig. 5. 



section. In this figure (r" r") is the living and growing outer 

 margin of the reef, and the lagoon channel is now converted 

 into the calm central lagoon (1) of the Atoll, as seen in 

 Whitsunday Island (Fig. 1.) 



This internal lagoon is itself often encumbered by inner reefs 

 of Coral, growing on banks formed of Coral sand and other 

 debris, or perhaps springing, like an old stunted branch or crag 

 of rock, from one of the peaks of the Coral strand. In Fig. 6 an 



A r- 



Fig. 6. 



