GEOLOGICAL ORSKUVATIOXS IX FIJI. 



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The unconfonnably overlying limestone is shelly, and of a red color, 

 because much impregnated by iron. The rain descentling on the 

 central volcanic hills is led away by underground channels along the 

 contact of limestone and andesite. No rivers occur on the island. 

 Only one fresh-water spring was found. This appears near sea-le\el 

 at the contact of the limestone with the antlesite, on the northwestern 



side. This method of drain- 

 age causes the replacement 

 of the limestone by many of 

 the elements carried in solu- 

 tion from the volcanic hills. 

 No pebbles of the under- 

 lying andesite are found in 

 the shell limestone. How- 

 ever, the contact is consid- 

 ered to be unconformable 

 for three reasons; (1) there 

 is no evidence of thermal 

 action of the andesite on the 

 limestone; (2) the contour 

 of the andesites beneath the 



Figure 25. Sketch Map and Profile of Tuvuthd. 

 Black — elevated coral reef. White — volcanic rocks. 



limestones is that of maturely eroded hills ; and (3) the texture of the 

 andesite does not become finer near the contact. 



The contact of limestone and volcanic rock on the northern side of 

 the island is less conclusive. It is true that a volcanic breccia, ce- 

 mented by calcite, underlies the limestone and indicates erosion 

 previous to subsidence, but elsewhere the contacts are so dike-like 

 that it is difficult to imagine how an eroded surface could assume such 

 forms. Reviewing all the evidence, however, it is concluded that the 

 limestone, throughout the greater part of the island unconfonnably 

 overlies the andesite. 



