ANDKEWS: LIMESTONES OF THE FIJI ISLANDS. 25 



Munia. — It is described most accurately by calling it " a miniature 

 Ovalau." The same rugged cliffs of andesite agglomerate occur on a 

 smaller scale, the total height here being 1000 feet. 



Lakemba. — The mass of the island is composed of andesite hills, 

 crowding thickly one upon the other and rising at the highest point to 

 720 feet above high-water mark. The former state of the island is 

 represented by a mere fringe of coralline limestone on the southwestern 

 extension of the volcanic mass. The whole configuration of the older 

 limestone has been altered, unless, indeed, Lakemba was at one time an 

 extensive limestone island. A little bigger volcanic display, and not a 

 vestige of the older limestone would have remained, except perhaps as 

 blocks in andesite ash beds, as is the case with some of the Mango 

 limestones. 



The great attraction of Lakemba is its cave, piercing the fragment of 

 limestone that skirt the volcanic slopes. The white residents describe 

 it as an immense tunnel, easy of examination, and running for about two 

 miles through the hill. Measurements by myself reduce this great 

 length to 500 yards. Even thus the statement is misleading, for the 

 cave disappears in the hill, describes an arc of a circle, and by so doing 

 reappears round the corner of the same bluff that it started at. From 

 entrance to exit is about 200 yards measured round the outside of the 

 cliff, and the exit is 100 feet above the entrance. The cave is more 

 easily explored than any I have visited, the floor being fairly smooth, 

 wide, and of even slope. Generally the roof is about 50 feet above the 

 floor. The walls, where clean, reveal the structure of a raised reef, 

 composed of corals and fragments of mollusca. 



Lines of Beach Erosion. — These may be divided into two groups, the 

 ancient and the modern lines of tidal wear. 



In the islands of the Lau Group, and confined almost exclusively to 

 the limestone formations, the effects of recent beach erosion are very 

 pronounced. r "When a group of islands, of which the hundred isles of 

 Ngillaugillah (Plates 22, 35) and Mba Vatu may be cited as illustra- 

 tions, have their windward face overlooking a fairly deep lagoon or are 

 placed directly opposite an opening like the Ngillangillah Passage, 

 we find small islands quite undermined by wave agency, while others 

 project in mushroom form above the surface of the lagoon (Plate 35). 

 On the windward side of the Ngillangillah Group the erosive action 

 has extended as much as 8 to 10 feet vertically and into the cliff face 

 from 14 to 15 feet. 1 To the leeward this cutting into the cliff rarely 



1 See A. Agassiz, /. c, Plates 73, 74, 92, 93. 



