Geology. 297 



continued to the present time. The period of rest between the 

 upward and downward movement of the sea-level must have been 

 a prolonged one, for it was during this time that the atoll condition 

 existed, and the great bulk of the detrital limestone derived from 

 the destruction of the living reefs, and now forming the mass 

 of the first inland cliff, was deposited : the great accumulation of 

 guano that must have taken place would also have required a vast 

 period of time for its formation. 



In Java the later Eocene deposits include limestones, in which is 

 found the Discocycline Oriitoides dispansa as in Christmas Island, 

 but accompanied by numerous INummulites, which, curiously 

 enough, according to Messrs. Jones & Chapman, are entirely 

 wanting in the limestones described by them, while on the other 

 hand large Heterostegines occur abundantly. Above these Eocene 

 deposits comes a great mass of volcanic rocks, including andesites, 

 diabases, and other lavas, some derived from submarine eruptions. 

 This volcanic series seems to correspond in time to the basalts and 

 tuffs which overlie the older limestone at Flying Eish Cove. 

 The Miocene rocks consist of three divisions, the lower made up 

 chiefly of volcanic breccias, the middle of soft marls, the upper 

 oi calcareous rocks with some dolomites and marls. In f^hristmas 

 Island these are probably all represented by the massive Orbitoidal 

 limestone, the absence of terrigenous material being only what 

 might be expected. In both areas the calcareous rock is crowded 

 with Lepidocycline Orbitoides, but although some of the Christmas 

 Island forms occur in Sumatra and Borneo none are recorded from 

 Java, and most are described as new ; the fact that the Orbitoides 

 of the two areas have been described by different authors may 

 in part account for the discrepancy. 



It will be seen that the rocks of South Java, if we make allowance 

 for the proximity to land at the time of their deposition, resemble 

 in their general characters and succession those of Christmas Island, 

 and like them they often terminate on the south coast in abrupt 

 faces, or show other indications that they formerly extended farther 

 south, but have been cut back by faulting and slipping. As to the 

 possibility that these rocks in the two localities were deposited 

 in a continuous area, it can only be said that the difficulties in the 

 way of supposing this to have been the case are very great. If it 

 w^ere so it must be imagined that the enormous depth between the 

 two islands has been attained since the Miocene by a general 

 depression of the sea bottom south of the fault line forming the 

 southern margin of the Malayan platform ; and further, that 

 during this depression the small area which forms the elevation 

 on which Christmas Island now stands escaped thQ movement, and 

 in fact forms a 'horst,' on all sides of which the sea bottom has 

 been faulted down about 2,400 fathoms. These suppositions, 

 however, appear untenable, and most of the difficulties are avoided 

 by regarding the base of Christmas Island as a volcanic peak which 

 has accumulated in consequence of repeated eruptions. In this case, 



