

xiii THE VALANGA RANGE 183 



bastite, whilst the surface often sparkles with pyrites (see page 



297). 



(2) NGONE HILL. This is a curious conical hill, about 700 feet 

 in height, that rises up on the right side of the Vunimbua River 

 about i miles above the village of that name and near the foot of 

 the range. It evidently represents a " volcanic neck," and doubt- 

 less this vent was the source of the large blocks forming the basic 

 agglomerate that occurs in huge masses in the river-course in the 

 vicinity of this hill. On its lower flanks is exposed a hard com- 

 pacted tuff, showing pyroxene crystals, which is composed prin- 

 cipally of fragments of a palagonitised vacuolar basic glass, the 

 minute cavities being often rilled with opal. In the upper part of 

 the hill is displayed a massive altered augite-andesite penetrated 

 by fine veins of chalcedony. Numerous irregular cavities filled 

 with the same material occur in its dark opaque glassy groundmass. 



The blocks of the agglomerates found in the vicinity of the hill 

 vary in size from 4 to 1 8 inches. They are composed of a compact 

 blackish semi-vitreous basic andesite (sp. gr. 273) of the type 

 characteristic of the basic agglomerates over most of the island. 

 The matrix of the agglomerate is hard and somewhat altered, and 

 is chiefly made up of fragments, ranging up to 5 mm. in size, of 

 a vacuolar basic glass, sometimes but slightly changed, though 

 usually converted into palagonite, the vacuoles being filled with 

 chalcedonic opal. The large masses of coarse tuffs displayed in 

 the bed of a stream-course close to Ngone Hill are non-calcareous 

 and composed of palagonitic materials. Palagonite-tuff clays are 

 also exposed in the river-course a little above Vunimbua. About 

 half-way between the village and the hill there occurs in posi- 

 tion at the river-side an amygdaloidal basic rock, the amygdules 

 being formed of chalcedonic opal. 



It is apparent that this hill represents a lesser vent which 

 probably dates back to the period before the emergence. All the 

 products of its eruption are, however, more or less altered. From 

 the absence of sorting in the blocks of the agglomerates, and from 

 the character of the matrix, it may be inferred that these deposits 

 have been accumulated directly from the ejected materials without 

 the intervention of the agency of marine erosion. 



(3) THE WESTERN FLANK OF THE VALANGA RANGE. 

 One of the boldest pieces of coast in the island lies on the eastern 

 side of Savu-savu Bay, between the mouth of the Ndreke-ni-wai 

 River and Valanga Harbour. Here a number of lofty headlands 

 separated by broad valleys descend with precipitous fronts to the 



