114 x-OYE. 



Excepting the region of basalts, just referred to, and another (Hs- 

 trict underhiin by rhyoHtic types, the volcanic rocks of the rest of the 

 island are prevailingly andesites and are characterized by the mineral 

 hypersthene. Hypersthene-augite andesites are widely distributed 

 from the Mbua district at the extreme western to Kimbalau point at 

 the extreme eastern side of the island. 



In a class called acid andesites, Guppy includes hypersthene ande- 

 sites, hornblende-hypersthene andesites, and quartz-hornblende- 

 hypersthene andesites or dacites. The hornblende of many of these 

 andesites has reaction rims of magnetite and augite siich as are com- 

 mon in the hornblende andesites of Kandavu and ^Slbcnglia. These 

 rocks are said to " compose in mass, numerous isolated hills that rise 

 up in the interior of the central portion of the island. Such hills, 

 or mountains, as they might be often termed, usually attain a height 

 of from 700 to 1200 feet above the sin-rounding coimtry, and possess 

 precipitous slopes and frequently perpendicular cliff-faces." From 

 this description it would appear that andesites have been more deeply 

 eroded than the basalts. 



Hypersthene andesites are especially common at the northwestern 

 side of the Wainunu tableland in west-central Vanua Levu, also in 

 the district between Savu Savu and Natewa Bays. 



Hornblende-hypersthene andesites occur north and northwest of 

 the Wainunu tableland and, in general, are closely associated with 

 the hypersthene andesites. In fact, all the hypersthene rocks grade 

 into each other, from augit* andesites with little hypersthene to hypers- 

 thene andesites and hornblende andesites with little augite. Hypers- 

 thene-bearing dacites are reported from the northwestern slope of 

 the Wainunu tableland. 



The district, east of Lambasa, along the northern coast of ^'anua 

 Levu, is characterized by rhyolitic rocks. In general the northern 

 half of the peninsula, north of Natewa Bay, and, as well, the whole 

 end of the peninsula near Undu Point, are composed of these rocks. 

 The boundary, between the hypersthene andesites to the southwest 

 and the rhyolites to the northeast, is an irregular line. Guppy does 

 not state the relative ages of these rocks. The writer formed the 

 opinion, from a study of the district east of Lambasa, about Mount 

 Avuka, that the rhyolites were the first to be extrudetl. Oligoclasc 

 trachytes occur at the extreme northeastern end of Undu Promon- 

 tory in association with ((uartz porphyries. Along the northern coast 

 pumice-tuffs are most fre([uently found. 



