THE AFTER-HISTORY OF THE ATOLL 271 



stantly lagoonwards. These currents always carry large 

 quantities of coral sand, and as the stream becomes first 

 retarded at its margins, the first sediment to be deposited is 

 in lines along its sides, forming the continuation of the island 

 extremities which we have seen. The central part of the 

 stream sweeps on, and only becomes slowed down as it loses 

 itself in the waters of the lagoon ; — the sediment that it con- 

 tains will therefore be deposited op2JOsite the gap in the island 

 ring. 



It is easy to see that if the lagoon were only a small one, 

 and the islands that composed the ring were very few, then it 

 might chance that the windward inlet into the lagoon came to 

 lie opposite to the leeward entrance to the lagoon. It might 

 also happen that the sediment brought in by the windward 

 inlet would not be carried right through the lagoon and out 

 into the ocean beyond, but would be dropped as a bank actually 

 in the entrance itself. It is maintained that this is what in 

 reality happens in some atolls. The condition that would be 

 met with, when the process was completed, would be a wind- 

 loard entrance to the lagoon; — hut this windioard entrance is guarded 

 hy a harrier reef. This is exactly the condition that is found 

 to-day in North Keeling atollon. The gap is to the windward, 

 but the windward barrier is complete — there is no entrance to 

 the leeward, but the lee barrier is absent. The current that 

 has swept into the lagoon, through the windward gap, has 

 made the sand-spits incurving the land which were noted by 

 Dr. Guppy ; and it has also raised a sand-bank, so large that 

 it has blocked up the real leeward entrance to the lagoon. 

 The sand-bank that is deposited by the current becomes raised 

 high enough for the waves to cast some of it above their 

 reach ; the wind then comes into play, and a wide sand-barrier 

 is made across the old lagoon entrance. The sand-bar con- 

 tinues to grow, and the whole of the leeward side of the atoll 

 becomes a wide sandy stretch, probably far broader than the 

 original dry land of the windward island. 



It is almost impossible to judge of the method of formation 

 of any atoll not actually visited and examined ; but from the 



