470 THE CONTINENTAL ORIGIN OP FIJI, 



of the latter certainly represent volcanic "plugs." A very 

 remarkable rock mass is met with in the mountain Namulowai 

 (Plate xxvii., fig. 9). It consists of a mass of solid augite andesite 

 shaped exactly like a thimble. The estimated height from base 

 to summit is about 250 feet. It is split up by vertical joints so 

 as to possess an obscurely prismatic structure. Its position with 

 regard to the surrounding high agglomerate mountains is not 

 suggestive of a volcanic neck, and I am rather at a loss to explain 

 it. Its shape is very like that of the " mamelons " figured in 

 geological text-books, but from its composition (a basic augite 

 andesite) I think the lava would probably be too tluid to assume 

 such a form. 



The water-parting between the Waidina and Navua Rivers 

 follows a curved line a little to the west of that joining the 

 mountains Nairibiribi on the north and Naitabuaitui on the 

 south. Its altitude where the track crosses it is 530 feet above 

 sea-level (aneroid).* 



The western vertical face of Nairibiribi is certainly composed 

 of agglomerate and shows a distinct dip to the southward at 26°. 

 The true dip appears to be greater than this and towards the 

 east of south. 



The slope from the water-parting to the bed of the Navua 

 River is very steep. The river is struck at the point where a 

 small tributary (Waimala) from the east enters it. This tribu- 

 tary rises in the neighbourhood of Nairibiribi, and its bed is 

 choked with huge fragments of andesite agglomerate ujd to 40 feet 

 in diameter. The actual bank is formed by a solid outcrop of 

 light-coloured andesite. This is highly jointed; the main set of 

 joints dip W.S.W. at 55°, the others being rather irregular. 



The differences between the districts on opposite sides of the 

 stream are very marked. On the eastern side are immense hills 

 of andesite agglomerate rising for hundreds of feet in sheer 

 precipices. To the west the country consists mainly of rather 



* Heights expressed thus were taken by means of a good aneroid barometer 

 and corrected for sea-level by comparison with the official readings of the 

 standard barometer at Suva. 



