THE ATOLL AS A WHOLE 141 



but is stamped on every constituent piece of land in the atoll 

 structure. This is a very important point,, and any explanation 

 of atoll formation must also furnish some satisfactory reason 

 for this shape belonging to the individual islands of the atoll 

 ring. The incurving of the ends of the islands leads to the 

 formation of the secondary lagoons that are present in Pulu 

 Atas and in Pulu Panjang, and are foreshadowed in Pulu 

 Pandan and Pulu Ampang. 



One of the constituent islands is in reality an atollon, and 

 encloses a lagoon which has altogether ceased to communicate 

 with the sea. This island is the leeward one, named Pulu 

 Luar, and the lagoonlet is situated to its leeward side ; a few 

 feet of water rise and fall in it, reaching it by tidal percolation ; 

 but a debris beach cuts it off from any direct communication 

 with the leeward shore, where its entrance used to be. The 

 changes that have taken place in this very interesting atollon 

 will be further discussed when the method of formation of the 

 islands is under consideration. 



THE NOETHERN ATOLLON 



KEELING ISLAND 



Keeling Island lies some fifteen miles to the north of the 

 Cocos atoll proper ; it is an island that has been very rarely 

 visited, and it is one of great interest. It is somewhat over a 

 mile long from north to south, and is about half as broad as 

 it is long. In its present condition it is an almost complete 

 circle of land that encloses a shallow lagoon still communi- 

 cating with the open sea. The lagoon contains something 

 rather less than a fathom of water, and it is not the site of 

 coral growth, but is occupied mostly by sediment banks and 

 seaweed. The sea is admitted through a narrow gap on the 

 eastern side — and much has been made of the fact that this 

 opening is on the windward shore ; but a glance at the chart 

 will show that this is not in reality a lagoon entrance, and 

 that no gap in the barrier is to be found opposite the channel. 



