268 CORAL AND ATOLLS 



it will start its growth wherever the waves toss it. This may 

 be seen at any point of the atoll, for the nuts that are dropped 

 into the sea will be washed up again upon some other beach, 

 and, if they come to rest upon a patch of sand, they will start 

 their growth straight away. 



Other hard seeds arrive and are blown by the wind into 

 places that are suitable for their growth, and an abundant 

 vegetation grows up. Another source of land-building is now 

 added, for as the vegetation increases, leaves and branches 

 become added to the sand accumulations, and the covering of 

 the coral debris proceeds with added rapidity. It might be 

 thought that, with the luxuriance of tropical vegetation, a 

 vegetable mould would very rapidly accumulate, but as a 

 matter of fact it is not so, and, on the islands that have no 

 depth of sand, the perpetual addition of dead leaves and nut 

 husks seems to make but very little difference. The reason 

 for this is the presence of the heavy annual rainfall, for as 

 fast as the leaves fall and rot, the rain washes their remains 

 into the interstices of the porous coral heap. 



With the addition of the vegetation the atoll island is 

 completed, and the condition of a sand-built vegetated strip 

 of land is one that lasts for a long time in its history. 



The sand that is made by the barrier waves and by the 

 fish is not all flung upon the land and built up by the winds, 

 for some of it is always rushing through the inlets to the 

 lagoon, and being deposited from the water in various places. 

 We have already noted the method of incurving the island's 

 ends by the tailing out of sand-banks into the lagoon, and 

 this process is one that continues all through the life of the 

 island. With the elongation of the horns, the area of 

 smoother water that stretches between them increases and 

 becomes the site of more sand deposit : in this way the 

 lagoon shores become widened. This process again takes place 

 with greater rapidity at the windward side of the atoll, for 

 there the supply of sand is the greatest, and the lagoon beaches 

 are under the shelter of the islands. Wide stretches of sandy 

 beaches are therefore laid down upon the windward side of 



