GEOLOGICAL OHSKKVATIONS IN FIJI. 11'! 



occurs as euhedral crystaLs plcocliroic, yellow to dark olive ^'reen. 

 The mineral has no reaction rim of magnetite such as is common to 

 the hornhlende andesite of Kandavu and Vanua Levu. 



\\. Rocks from Vanua Levu. 

 a. summary of the petrography of vanua levu as given by 



GUPPY. 



Plutonic Rocks. Three varieties of plutonic rocks are listed by 

 Guppy from seven different localities. All these localities lie along a 

 mountainous ridge, running parallel to Natewa bay, i. e. in a N. E.- 

 S. W. direction. 



Hypersthene gabbros or norites are common throughout the dis- 

 trict. A hornblende gabbro is described from the extreme southern 

 end of the range and diorites were found in relations which indicate 

 a close association between the two rock types. 



Throughout the larger part of Vanua Levu, plutonic rocks are, there- 

 fore, very uncommon. They are not found west of a line connecting 

 Savu Savu Bay and Ivambasa, nor east of Natewa bay. 



Volcanic Rocks. The volcanic rocks of Vanua Levu are grouped by 

 Guppy into an elaborate classification of which the following members 

 are most important : — 



olivine basalts, 



basaltic augite andesites, 



hypersthene-augite andesites, 



hypersthene andesites, 



hornblende-hypersthene andesites, 



dacites, 



oligoclase trachytes, 



quartz porphyries. 



Olivine basalts compose the wide cone at the extreme southwestern 

 end of Vanua Levu, known as Mount Seatura. The flow rocks form- 

 ing the low lands west of this area are basaltic augite andesites. It is 

 important to note that Guppy (1903, pp. 02-63) speaks of Mount 

 Seatura as a well preserved volcanic cone, having slopes of 3 to 4 

 degrees which are, in certain cases, unscarred by subsequent erosion. 

 It would appear that this mountain represents a comparatively late 

 period of volcanic activity. 



