180 CORAL AND ATOLLS 



and as rapidly dies; during droughts the islands will be 

 parched and brown, every plant save the coco palms will 

 look leafless and dead : but the next day if rain comes, the 

 whole appearance of one of the more barren islands like Pulu 

 Tikus will wholly change, and all the white coral surface 

 of the land will be green with sprouting seeds. The rapidity 

 of the cycles of vegetation is a thing to be reckoned with in 

 considering the alteration of the primitive structure of the 

 islands. 



In connection with the formation of vegetable mould, the 

 influence of the heavy rainfall must be considered, for the 

 rate of the washing of surface accumulations through the 

 loosely strewn coral chips is very wonderful. In Pulu Tikus 

 coco palms have lived and died for generations, their trunks 

 have decayed, their leaves rotted : and yet on the surface of 

 the greater part of the island no soil accumulation is to be 

 seen. As a matter of fact the extreme barrenness of the 

 islands is more apparent than real, for if a few inches of the 

 coral debris be scraped from the surface, the vegetable earth 

 is found below, intermixed with the lower layers of coral, 

 where it has been washed by the rain. On Pulu Tikus forty 

 tons of earth were imported from the Botanical Gardens of 

 Singapore ; in 1902 it was landed, in 1905 any trace of it 

 was hard to find. It is such facts as these that make the 

 presence of phosphates deep in the soil of high coral islands 

 easy to explain : for every shower that falls dissolves any 

 surface substance readily soluble, and carries it in solution as it 

 percolates through successive layers of loosely packed coral, 

 thus giving it the very best opportunity to enter into chemical 

 combination. 



Another factor in the after-history of the island is the 

 drift sand, which, under the influence of the winds, builds up 

 the surface of the island beyond the limit of the sea action. 

 Many of the islands are thickly covered with sand ; some are 

 even entirely composed of sand, and an interesting charac- 

 teristic of those islands, into whose formation no large frag- 

 ments of coral have entered, is their uniformity of contour. 



