GEOLOGICAL OHSERVATIONS L\ FIJL 65 



since Pleistocene times. There must have been a period of still- 

 stand during which the barrier reef was formed and a bench cut in 

 the volcanic rocks of the central islands. This period was followed 

 by one of uplift. Since then, the inner bench has been largely de- 

 stroyed, the elevated limestones reduced from 100 to 10 or 15 feet, and 

 a bench, 100 to 300 feet wide, cut in the volcanic rocks at the present 

 level. The rapidity of subaerial erosion in the South Sea islands 

 allows the writer to believe that such a series of events is not impossible 

 in the time postulated. 



If the barrier reef were formed by subsidence according to Darwin's 

 theory, it would be important to know the amount of the subsidence. 

 The prevailing slopes of the volcanic flows interbedded with the 

 agglomerates today, average between 12° and 15°. The barrier reef, 

 in developing from a fringing reef, would probal)ly not build itself 

 up vertically, but as this method of formation would give the maxi- 

 mum value for the subsidence, the calculation will be made on this 

 basis. 



The barrier reef is now on an average 1§ miles from the volcanic 

 hills. A fair average of the slope of the original hills would be 15°. 

 From these data the maximum amount of subsidence is calculated to 

 be approximately 2000 feet. The outward growth of the reef and the 

 erosion of the central volcanic hills would tend to reduce the figure for 

 the subsidence; so that the actual subsidence necessary to produce 

 the present barrier reef by Darwin's theory would be well under 

 1500 feet. 



That Ono should subside 1500 feet is not at all incredible in view 

 of the great subsidence of the larger islands; yet this hypothesis 

 involves the nearly complete filling of the lagoon. 



The persistence of frail islet masses of uplifted limestone, near the 

 edge of the Ono reef, forces one to the conviction that the waves are 

 very impotent just behind a barrier reef, and that their cutting can- 

 not have significantly enlarged the present lagoons. 



Kambara (Figures 31 and 32). 



Kambara offers one of the most puzzling problems found .among 

 the smaller islands. It is an oval mass of limestone, 6 or 7 miles long, 

 3 to 4 miles wide, and surrounded by precipitous cliffs on nearly all 

 sides. An irregular ridge, about 200 feet high, follows the nearly 

 circular shore-line. The inner slopes of the ridge converge toward 



