GEOLOGICAL OBSERVATIOXS IN FIJI. 



53 



floor of the depression is formed of andesite; on either side rise corul- 

 Hferous Hniestones. 



The southwestern side of the island is a mass of andesitic agglom- 

 erate, in cliffs SO to 100 feet high. The contacts of the limestone 

 with the andesitic rocks are dilHciilt to find. At observed contacts 

 no shell conglomerate with inclusions of the andesite was discovered. 

 But, since the limestone overlies large areas of agglomerate and ash 

 and rests on a very uneven surface, it must be inferred that the vol- 

 canics were first deposited, later carved into mature hills, and then 

 depressed and overlain by coralliferous limestones. The adjoining 

 sketches (Figure 24) serve to show the areal distribution of the lime- 

 stone and volcanic rocks and their relation to one another. 



Figure 24. Sketch Map of Thikombia-i-lau, Exploring Group. 

 Black — elevated coral reef. White — volcanic rocks. Lined — sandy- 

 flats. 



Crossing the island from the small village at its southwestern corner, 

 one first climbs to a bench, 75 feet above sea level. Then follows a 

 steep rise to a second bench at 210 feet, and then a gradual rise to the 

 central valley at 360 feet. The valley is a relatively level floor, a 

 quarter of a mile wide, and extending for a mile or more through the 

 center of the island. Precipitous cliffs of limestone, 200 feet high, 

 rise on either side of the valley. 



