46 FOYE. 



The Exploring Group consists of six large islands lying about the 

 border of a lagoon nearly 30 miles in diameter. All but one of the 

 islands are composed of both volcanic rocks and limestone. The one 

 exception, IMunia, consists only of volcanic rocks and will be considered 

 later. 



Vanua Mhalavu. The largest island of the group, Vanua Mbalavu, 

 is long, narrow, and shaped somewhat like a question mark. Its 

 greatest length lies approximately in a north-south line. Its extreme 

 northern and southern ends are composed of limestone, while its 

 center is composed of volcanic rocks. As indicated in the accompany- 

 ing map (Figure 20), the volcanic rocks form the greater part of the 

 island. 



The volcanic rocks were erupted in two different periods which will 

 be called the andesitic and basaltic periods of extrusion. The ande- 

 sites were eroded to late maturity. They were then submerged and 

 coralliferous limestones were laid on them unconformably. Later 

 they were uplifted with the overlying limestones and both were 

 deeply eroded. During the later volcanic period, this eroded topog- 

 raphy was buried beneath basaltic flows and ash-beds and the 

 basaltic slopes, in their turn, have been eroded to maturity. 



The late-mature hills somewhat south of the center of the island, 

 near the village of Loma Loma, represent the older or andesitic period. 

 They slope gradually to the south from an elevation of 300 to 400 feet, 

 and disappear beneath the elevated coralliferous limestone which 

 unconformably overlies the andesite. A few, very vesicular basalt 

 flows of the later eruptive period occur in the extreme southwestern 

 part of the island, but their source was not found. 



Toward the north, at a point near the center of the large curve of 

 the question mark, the slopes of the late-mature hills of andesite 

 continue beneath the limestone. Just south of this point (near Tota) 

 isolated patches of a shell and coral-rubble limestone rest uncon- 

 formably on the andesite, and further south near the bottom of the 

 curve (Mualevu) other isolated patches lie within a broad valley 

 extending 2 or 3 miles inland.^ Near the northern edge of this valley, 

 these patches arc seen to be overlain by more recent basaltic flows and 

 are colored red, probably due to baking. 



Along the sea-coast on the western side of the island (Dalithoni), 

 and near the northern contact of the volcanic rocks with the elevated 

 limestones, there is a series of instructive exposures. A small bay is 

 bounded to north and south by limestone headlands. The southern 

 headland is composed of a foraminiferal limestone containing bits of 



