GEOLOGICAL OBSEUVATIONS IN FIJI. 47 



andcsitic ash. The Hinrstone is 30 or 40 feet thick and (hps eastward. 

 It may be followeil around the bay to the north, but its contact with 

 the overlying rocks is not exposed. It is seen, however, to dip con- 

 formably beneath a layer of coralliferous limestone which forms the 

 basal layer of the northern headland. The coral limestone is com- 

 posed of coral heads in place, with reef rubble between, and is 5 feet 

 in thickness. The coral heads form about two-thirds of the deposit. 

 An agglomerate, 10 feet in thickness, overlies this deposit conformably. 

 The agglomerate consists of large, angular coral-heads which occupy 

 irregular positions, with angular boulders of vesicular andesite, 5 to 

 6 feet in diameter, fixed in a paste of andesitic ash and lapilli. This 

 peculiar bed is overlain by 15 to 20 feet of a cream-colored corallif- 

 erous limestone which in turn is overlain by 20 feet of a pink coral- 

 liferous limestone. All the beds are conformable and dip 20° east. 



The basal layers of the outcrops just described indicate volcanic 

 activity at the time they were deposited. Yet the upper coralliferous 

 limestone proved to be continuous with the elevated limestones of 

 the entire northern part of the island, and those limestones uncon- 

 formably overlie the maturely-eroded andesites to the east. Since coral 

 heads in place occur in the northern limestone at an elevation of 350 

 feet, and also within the mass of the limestone at the bottom of the 

 deposit just described, it is probable that subsidence to the extent of 

 200 feet, more or less, occurred during the deposition of these rocks. 



These relations point to the conclusion that, at the close of the long 

 period occupied by the erosion of the andesites and the development 

 of coral reefs off-shore, new andesitic eruptions broke out, and that 

 soon afterward the island subsided. 



The discovery of a limestone layer, underlying later lavas on the 

 eastern side of the island, has already been noted; further evidence of 

 a later extrusive period is found along the northwestern side, within 

 the large curve of the question mark. Flows of vesicular basalt 

 follow the valleys cut in the limestone along this shore. 



The small outlying island, Andivathi, is composed of andesitic 

 agglomerates and ash, dipping 30° E. The western beds, representing 

 the low^er members of the series, are coarse agglomerate with vesicular 

 blocks of lava, a foot or more in diameter. The upper beds become 

 finer and finer and show many small fragments of pumice. The total 

 thickness of the beds is about 200 feet. The eastern side of Andivathi 

 is composed of elevated coralliferous limestone. Both ash and lime- 

 stone are cut by a net-work of basic dikes. All the dikes are deeply 

 eroded and their upward extensions are gone. The largest observed 



