64 FOYE. 



The Ono Group presents many similarities to Totoya, lying to the 

 northwest, except for the lack of uplifted limestones in Totoya. The 

 crater wall of Totoya is breached in only one place and is not broken 

 into separate islands, as at Ono. The old crater of Totoya has an 

 average depth of water of 28 to 29 fathoms, while the lagoon depths 

 between the reef and the volcanic islands average IS to 20 fathoms. 

 This contrast is reversed at Ono, where the maximum depths within 

 the crater are 6 to 8 fathoms and those in the outer lagoon are 8 to 

 10 fathoms. 



The topography of Ono is of a type showing this island to be older 

 than Totoya. The longer erosion has tended more completely to 

 fill the crater depression with silts from the volcanic hills, as well as 

 with debris from the eastern reef. 



The 100-foot bench on Ndoi, already noted, may be correlated with 

 the uplifted barrier reef and possibly the surface of the reef has been 

 reduced by erosion from 100 feet to 10 or 15 feet in the period since 

 the uplift. If so, the reduction of the lagoon depths by 100 feet, 

 would be an important factor to consider in accounting for the present 

 shallow water about the islands. 



The Ono Group presents a good opportunity to compare known 

 facts with theory. The remnants of elevated coral limestone stand 

 approximately at the edge of the present reef. If the limestone origi- 

 nated in pre-Pleistocene times, they were elevated either before, or 

 after, an inferred period of Pleistocene wave-cutting. If they were 

 elevated before, it would seem that wave-cutting should have destroyed 

 these evanescent forms near the edge of the reef. If they were ele- 

 vated after the Pleistocene, barrier reefs, accepting the postulate 

 that the corals are of pre-Pleistocene age, must have existed in pre- 

 Pleistocene times; for the ordinary agents of erosion would hardly 

 destroy the inner parts of a fringing reef and leave the outer in the 

 form of a barrier reef. But the Glacial-control theory conceives that 

 the existing barrier reefs and atolls are special forms of coral growth, 

 developed on platforms cut in the Glacial epoch, and that they were 

 much rarer before that epoch than at presenl. 



However, the elevated limestones may have developed not in pre- 

 Pleistocene but in Pleistocene or Recent times. It is possible tliat a 

 bench was formed about the Ono Group by Pleistocene wave-cutting; 

 that a barrier reef grew up about the islands, with the return of the 

 waters after the Glacial epoch; and that, later, the barrier reef was 

 uplifted. 



If this hypothesis be true, a mnnber of events must have occurred 



