GEOLOGICAL OUSEKVATIONS L\ FIJL 



49 



honeycombing of tUo limestone hy immense eaves. The roofs of the 

 caves coUapse and eontinued sohition, followed by later water-action, 

 create rifts in the nearly vertical walls surrounding a limestone island. 

 The rifts then develop into fringing bays with almost vertical sides, 

 extending far inland. It is believed that the deep bays in northern 

 Vanua jNIbalavu ha\e been largely so formed. 



Avea. Avea is an oblong island with its longest axis lying nearly 

 northeast by southwest. It is 3 miles long and 1^ miles wide and 

 has an elongated spit of sand to the southwest, as indicated in the 

 accompanying map, (Figure 21). 



Figure 21. Sketch Map of Avea, Exploring Group. 

 Black — elevated coral reef. White — pyritized tuff, 

 beach. 



Dotted — sandy 



The oldest rock formation of Avea, seen on its northwestern side, is 

 a brecciated, highly pyritized tuff, which was eroded into mature hills. 

 After dissection, these hills were submerged and on them were laid 

 down, unconformably, 310 feet or more of coralliferous limestone. The 

 whole mass was later uplifted and eroded to an irregular island with a 

 sharp, central ridge, with precipitous cliffs of limestone about its shore, 

 except on the northern side, where the tuff is exposed. No exact 



