138 FOYE. 



ern Yanua Levu has not progressed any further than that of the hyper- 

 sthene andesites. It was, therefore, conchided that some of the 

 rhyoHtes were extruded in the second andesitic period. 



The extrusion of the hypersthene andesites took place, in large part, 

 beneath the sea. Their ash and agglomerates form palagonitic tuffs 

 which were not uplifted until about the same date as the uplift of the 

 marls of the coastal series in Viti Levu. 



The second andesitic period of Vanua Levu is considered to have 

 closed with the uplift just mentioned. 



From Guppy's description, the oli^•ine basalts forming the prom- 

 ontory at the extreme southwestern end of Vanua Levu, were not 

 erupted beneath the sea; and their sculpturing is so recent that it 

 is believed they were extruded after the uplift of the hypersthene 

 andesites. 



In general outline, the succession of lavas in Vanua Levu is not 

 unlike that in Viti Levu. The succession is as follows: — 



First epoch — andesite, rhyolite, 



Second epoch — rhyolite, hypersthene andesite, 



Third epoch — basalt. 



It should be stated that the folded sediments of Viti Levu are not 

 found in Vanua Levu and that the deposits of the second andesitic 

 period have no known period of erosion separating them from the 

 first andesitic period. Therefore, it would, perhaps, be preferable 

 to consider the first and second periods, indicated above, as one. For 

 the sake of comparison with Viti Levu, the two periods are retained. 

 In other words, after the erosion of the gabbro of Vanua Levu, the 

 island subsided and was not again uplifted till the period of uplift 

 of the coastal sediments of Viti Levu. During this time of depression, 

 no marls or sandstones are known to have been deposited above the 

 gabbro; instead there are a series of palagonitic tuffs. 



Volcanic Succcssioti in the Lau Group. 



Three periods of vulcanism have been recognized in the Lau islands. 

 Little is known of the first period which is now represented by pyritized, 

 pumice-tuffs. The lavas of the second or andesitic period are pre- 

 vailingly andesites, though they are allied to augite basalts and, 

 occasionally, as in the island of Lakemba, carry a little olivine. The 

 analysis of the andesitic basalt fromThikombia-i-lau (p. 12()) is typical 

 of this series. 



