208 Christmas Island. 



groups, in accordance with Mr. Andrews' account ^ of the structure 

 of the island. The groups are the limestones of — 



1. The sea cliffs. 3. The central plateau. 



2. The inland cliffs. 4. The central nucleus. 



The intei-pretation of the evidence of the fossil corals as to the 

 ages and relations of the Christinas Island limestones is difficult, 

 as so little is yet known of the coral fauna of Malaysia between 

 early Miocene and recent times. Many Miocene corals fi'om Java 

 have been described by Duncan, von Reuss, and Martin ; and the 

 existing Malaysian coral fauna is fairly well known. But from 

 the intervening period no corals have previously been described. 

 ^Nevertheless, the evidence of Mr. Andrews' collection is tolerably 

 clear. 



The limestones of the sea cliff contain corals many of which 

 are of the same species as those now growing on the fringing reef 

 of Christmas Island; so that the date of those limestones is no 

 doubt Pleistocene. At the other end of the series are the 

 limestones of the central nucleus : they have yielded three 

 determinable species, of which two are new, and the third 

 ( Orhicella herldotsi) is found in the older Miocene of Java ; of 

 the other two species one belongs to a genus elsewhere known 

 only in the Miocene, and the other is a coral of an ancient aspect, 

 though its genus was founded on a living species from the Eed 

 JSea. The limestones of the central nucleus are therefore probably 

 Miocene in age. But the evidence of the corals is insufficient 

 for positive opinion, or for the suggestion of a more precise date. 

 As opportunities for further geological collecting in Christmas 

 Island will probably arise, it may be worth while directing' 

 attention to the desirability of obtaining more specimens of corals 

 from the central limestones. 



On the central plateau reefs of recent limestone are said to 

 occur ; this age is assigned to the rocks on the evidence of the 

 foraminifera. But there are no corals of recent species in the 

 collection from the central plateau. The evidence of the corals 

 renders it probable that outcrops of the central limestones occur 

 on the floor of the plateau. 



The majority of the specimens were obtained from the limestones 

 of the inland cliffs. Most of the species from this zone are still 

 living, and four of them also occur in the rocks of the sea cliffs. 

 But others are of older aspect, and the occun^ence of a weathered 

 specimen of Orhioella herklotsi and Anisocmnia favoidea shows that 

 the Miocene limestones are exposed in some parts of the inland 

 cliffs. Whether the rest of the cliffs, containing the species 



1 C. TV. Andrews, '*A Description of ChiistmaB Island (Indian Ocean)": 

 Geogr. Journ., 1899, vol. siii, pp. 20-2i. 



