1898.] Funafuti, Rotuma and Fiji. 473 



I have already pointed out that several of the islands have 

 a greater thickness of limestone than 600 feet ; Tuvutha further 

 is 800 feet high, and Vatu Vara 1030, with a cliff over 900 feet. 

 It is important to note that the latter is the greatest vertical 

 thickness of coral-limestone yet recorded. Prof. Crosby estimates 

 the thickness of the reef on El Yunque, Cuba, at 1000 feet but, as 

 he allows 200 feet for denudation, and the base of the mountain 

 consists of " eruptive rocks with some slates " and its summit is 

 " three-quarters of a mile long and a third as broad," it is probable 

 that his estimate is far too high, much of the thickness perhaps 

 being due to the talus on the slope of the original reef. 



I see nothing inconsistent, with any of the theories of the 

 formation of atolls and barrier reefs, in the shallow reef, together 

 with the talus slope, advancing outwards in a long period of rest 

 and so getting a spurious thickness. Darwin and Dana, however, 

 do not seem to have considered the possibility of such a period in 

 the slow subsidence they require. The real depth of the limestone 

 of Vatu Vara to the rock on which the island is founded might have 

 to be somewhat reduced owing to such a cause, but in contradistinc- 

 tion to El Yunque the elevated reef of Vatu Vara is small at the 

 base and precipitous above, with a flat top not more than 100 yards 

 across in any direction. The same remarks may apply also to a 

 limited extend to Funafuti, where a thickness of 693 feet has 

 lately been obtained, and to Vavau, Tonga, where the cliffs are 

 .500 feet high. Of other Pacific Islands Dana gives a thickness of 

 250 feet at Metia, Society Group, and of 300 at Mangaia, Hervey 

 Group ; the sailing directions, however, for the Eastern Pacific 

 give the height of the latter island as 650 feet 1 . 



In contradistinction to these Guppy asserts that the raised 

 reefs of the Solomon Islands are nowhere more than 150 feet 

 thick. 



The mud, coating the bottom of the lagoon at Fulanga, has 

 apparently been formed by the wearing action of the sea on the 

 raised limestone cliffs. It has no trace, except in a few small 

 pieces of shell, of any organic origin, and is quite different from 

 what is known as coral mud. As Dana's description 2 of the 

 chalk of Oahu, Sandwich Islands, applies equally well to this 

 mud, I would suggest that it was formed in a similar way, and on 

 upheaval solidified. Oahu has the same kind of hard limestone, 

 and the recurrent eruptions, which have taken place on that 

 island, might well account for all traces of its origin being lost. 



1 Pacific Islands, Vol. in. 1885, p. 14. 



2 Loc. cit. p. 395. 



