290 Christmas Island. 



had been exposed by a change in the relative levels of the land 

 and sea. Another condition favourable for the accumulation of 

 guano is absence, or at least scantiness, of rainfall, and the low 

 and, as they must at first have been, treeless islets would certainly 

 have a much smaller rainfall than at present occurs. Moreover, 

 at the time when the first upward movement took place, the 

 conditions prevailing in the Malay Archipelago were very different 

 from at present. In Java, for instance, late Miocene or early 

 Pliocene deposits are found at an elevation of 900 metres, so 

 that a smaller land-area was then exposed, and, furthermore, the 

 volcanic mountains were much less elevated than now. These 

 circumstances may have considerably modified the meteorological 

 conditions of Christmas Island, which lies near the southern edge 

 of the region affected by the monsoon (see p. 17). 



The phosphates, as they now exist, are probably the remains 

 of beds of limestone, which have been altered by the overlying 

 guano, the carbonate of lime being replaced by phosphate. The 

 phosphatization occurred somewhat irregularly, and the removal 

 of the more soluble portions of the beds by the action of perco- 

 lating water has left behind a thick bed of blocks and nodules of 

 phosphate, which covers a large area and extends to a considerable 

 depth (upwards of 10 feet in places). The most important of 

 these deposits is at Phosphate Hill, where a large area is covered 

 by them, but other beds are to be found on some of the hills on 

 the east coast. Moreover, at the present day small nodules of 

 phosphate of lime are scattered widely over the plateau, and 

 particularly on the outer slopes of the island. These nodules also 

 occur embedded in the later limestones, and sometimes may have 

 been formed in situ by segregation, but in most cases are simply 

 derived from the higher beds. In any case the terraces, particularly 

 the shore terrace, are in places thickly strewn with a sort of shingle 

 of nodules of phosphate of lime, which have either weathered out 

 of the limestones or fallen from the beds above. 



In many places on the plateau the level surface of the soil is 

 thickly strewn with small round black bodies varying in size from 

 that of No. 10 shot to that of small peas. Mr. E. Irvine informs 

 me that these pellets consist of a central nucleus of phosphate 

 of lime, surrounded by a fairly thick coat of manganese dioxide, 

 the whole being again covered with a thin layer of phosphate ; 

 they contain about 18 per cent, of manganese dioxide. This is 

 probably derived from the volcanic tuffs which were extensively 

 exposed on the higher parts of the island, and, as already 

 mentioned, must be to a large extent the parent rock from 

 which the thick soil of the island is derived. Their decomposition 

 may have given rise to mud deposits on the lagoon bottom. 



The phosphate itself is a very peculiar substance. It is intensely 

 hard (between 6 and 7), and this, combined with the waxy lustre 

 of a newly fractured surface, gives the impression that it is siliceous, 

 though as a matter of fact it contains little or no silica (less than 



