xv VUI-NA-SAVU RIVER 225 



up the river, a bare bluff, overlooking the valley on the east, is 

 formed of a decomposed trachytic rock remarkable for the fact that it 

 displays, as described on page 370, faint magnetic polarity. Above 

 Vitina, a mile or two farther up, I found a similar rock but amyg- 

 daloidal in character. On the head-waters of the river is situated 

 the hamlet of Nawi, where, as mentioned on page 211, a plutonic 

 rock of the gabbro type occurs. Tuffs and agglomerates appear to 

 prevail in the low coast tract between the Vui-na-Savu river and 

 Thawaro Bay. 



In drawing some general inferences respecting the acid for- 

 mations, mostly fragmental in character, that are displayed in the 

 sea-border between Lambasa and Thawaro Bay, it is necessary to 

 distinguish between the deposits west and east of the Langa-langa 

 River. Between Lambasa and the river just named the tuffs may 

 usually be regarded as the products of sub-aerial eruptions. Some 

 of the specimens might have been obtained, as far as their characters 

 go, from the pumice-districts in the island of Lipari. Their lime- 

 less condition and the apparent absence of organic remains are 

 noteworthy features, though of course the products of sub-aerial 

 eruptions may be deposited under the sea. It is, however, remark- 

 able that no compact obsidian came under my notice. The frag- 

 ments of rhyolitic glass, intermediate in structure between compact 

 obsidian and pumice, that were imbedded in the pumice-tuffs in one 

 locality, were probably ejected from some sub-aerial vent. 



In the region between the Langa-langa River and Thawaro 

 Bay acid tuffs and agglomerates prevail ; but they have all been 

 subjected to alteration by the deposition of secondary silica, and 

 the pumice-structure when present is largely disguised. They have 

 evidently, in part at least, been derived from compact rhyolitic and 

 trachytic rocks, and are probably in some measure the products of 

 marine erosion. Although neither lime nor organic remains were 

 detected, the presence of the altered " Globigerina " clay near 

 Visongo is very suggestive and indicates a considerable submer- 

 gence of this region at some distant period. 



Much, however, remains to be done in the examination of the 

 peaks of the coast ranges of this part of Vanua Levu ; and it is 

 likely that some interesting results will be obtained from such an 

 exploration. 



