GENERAL ACCOUNT HEDLEY. 11 



four feet across rise a few inches above the general level. Just 

 such masses occur as living coral in the reefs in the lagoon, and 

 on flaking off a chip these prove to be a small-pored Porites. 

 From these bosses of Porites extend in rays for several yards in 

 every direction, thin flat stones on edge like tiles along a garden 

 walk. A glance at a fragment serves to identify the latter as 

 slabs of blue coral, Heliopora ccerulea. On drawing Prof. Solias' 

 attention to this formation, he suggested that the Porites and its 

 surrounding star of Heliopora evidently both lived in situ, and 

 that they could not have existed at their present level where high 

 tide alone bathes them. I am of opinion that the action of the 

 tides is impeded in the Mangrove Swamp, but that the high tide, 

 not the low one, must be the affected level ; the height of coral 

 growth is determined by the low tide not the high. 



We are therefore here facing unequivocal evidence of elevation 

 in Funafuti to the extent at least of the range of the tide, since 

 low water springs is the highest level to which the Porites and 

 Heliopora could have reached. They probably also grew in 

 smooth and sheltered water. The cone in which the island rises 

 from the abyss suggests the proximity of volcanic force to give 

 an upward thrust. In Honden Island and Osnaburgh Island 

 Dana* has given striking instances of slightly upheaved atolls. 



Around the western edge of the Mangrove Swamp, and most 

 noticeable in the north arm, is an old beach where a breccia of 

 coral fragments in a platform two or three feet above the swamp 

 has been eaten back by wave action. That this breccia formerly 

 extended as a sheet over what is now the surface of the swamp, 

 is indicated by a few isolated and worn cakes of it, outliers in 

 other words, near the centre of the flat ; but whether or not it 

 overlaid the Heliopora I possess no evidence to show, although I 

 incline to the opinion that it did.f 



The beach outside the Mangrove Swamp is furthest to wind- 

 ward of any land in the atoll ; reverting to my comparison of the 

 islet to a Liangle, this spot corresponds to the blade of the weapon. 

 In other words it is the most exposed corner of Funafuti. 



The history of the Mangrove Swamp as indicated by these 

 features seems to me to be, that a hurricane breaking on the 

 eastern face of Funafuti, tore down the shingle rampart and 



*Loc. cil., pp. 333 and 335. Darwin declined (Structure and Distri- 

 bution of Coral Keefs, 1874, p. 169) to accept these evidences of slight 

 elevation, and endeavoured to otherwise explain an apparent instance of 

 it which he observed (op. cit., p. 21) at Keeling Island. 



fA too brief note (Qt. Journ. Geol. Soc., 1872, xxviii., p. 381) by 

 S. J. Whitnell (? Rev. S. J. Whitmee) upon raised coral rock in situ at 

 Funafuti, may refer to the place I have here described, but I rather 

 suppose that the subfossil coral exposed by the beach section of breccia 

 was mistaken for coral in the position of growth. 



