GEOLOGICAL OBSERVATION'S IN FIJI. 



59 



Along the boundary of the volcanic area are isolated remnants of 

 elevated limestone which once encircled the island. Such remnants 

 unconformably overlie the andesite and rise to a maximum elevation 

 of 320 feet. A castle-shaped mass, with the height mentioned, occurs 

 on the northwestern coast. A mile east of this locality, spur-ridges and 

 their intervening valleys are covered with a mantle of shell and coral 

 rubble mixed with volcanic pebbles up to an elevation of 100 feet. 

 The diagram (Figure 27) illustrates the position of the limestone with 

 respect to the andesite. The average dip of the contact between the 

 andesite and the limestone is 18° N.; the dip of the conglomerate is 

 12° N. 



Following along the coast to the southwest, the conglomerate sweeps 



Figure 27. Sketch of Spur-hills, Northern Lakemba. 



inland and, toward the sea, is overlain by coralliferous limestone. 

 The contact between the two deposits is transitional, as may be seen 

 by tracing the conglomerate from its inland contact with the andesite 

 to the coralliferous limestone cliffs near the sea. The same fact is 

 revealed in the sea-cliffs ; their lower portions are often formed of shell 

 and coral waste bearing volcanic pebbles and passing upward into 

 reef-limestone. 



Peculiar drainage conditions obtain here. Descending the mature 

 valleys carved in the andesite of the interior, one would naturally 

 expect to reach the coast easily. In some instances this is true, but 

 usually a wall of limestone, 75 to 100 feet high, cuts across the valley. 

 Beneath the wall the surface waters run down amidst a collection of 

 boulders swept from the andesite hills, and flow to the sea by under- 

 ground channels, truly remarkable caverns. Many of the cavern roofs 

 have collapsed, affording open passage-ways to the sea. To the 



