ward sides of the reefs lining the lagoon are built up 

 into a series of sand banks and small islets which to- 

 gether form a ring shaped island interrupted by gaps 

 which give access from the lagoon to the ocean. These 

 islands may possess a certain amount of soil and be 

 covered with vegetation, particularly coconut palms, 

 the large seeds or nuts of which are able to drift thous- 

 ands of miles across the ocean before being cast ashore. 



Figure 5. Section of an atoll. Not to scale. 



One of the most typical of these formations is the 

 Cocos-Keeling Atoll which lies in the open ocean sur- 

 rounded by water more than 6,000 feet deep at a dist- 

 ance of less than six miles from the shore. Moreover 

 it is situated in a part of the ocean which is more than 

 500 miles from the nearest land. It was first studied 

 by Charles Darwin when he visited it on board H.M.S. 



25 



