THE GEOLOGY OF FUNAFUTI. ' 67 



concentric and radiating cracks, nearly vertical, were plainly visible. As shown on 

 Section 9 of Plate 9, a raised reef of HeUopoi'a ccerulea attains in the Mangrove 

 Swamp a level of about 4|- feet above low water, and rises a little above the level 

 of high water in the plantation to the west. The occurrence of this raised reef has 

 already been noticed and described by Professor Sollas."^ This occurrence indicates 

 a downward movement (see note at end of this section) of the shore line (possibly due 

 to an actual elevation of the land) of from 4|- to over 6^ feet. It has, however, been 

 suggested that the occurrence in situ of coral heads of Heliopora ccerulea up to the 

 level of high water at Funafuti can be explained otherwise than by such a movement. 

 Messrs. Halltgan and Finckh have pointed out that on the north side of the islet of 

 Amatuku (see Plate 12 for plan and also Section 4 of same Plate), in this atoll, small 

 heads of Heliopora ccerulea are found living in a tidal pool on the reef platform at a 

 level of between 1 and 2 feet above low water. 



At Funamanu Islet also we observed one or two small stocks of Heliopora ccBrulea 

 living a few inches above the level of low water. We also noted the fact that at 

 the atoll of Nukulailai, 52 nautical miles S.E. from Funafuti, the level of the lagoon, 

 even when the tide had fallen, remained several feet above the level of low* water. 

 This was due to the channels and tunnels in the reef rim at that atoll being 

 insufficient to lower the level of the lagoon at a rate rapid enough to keep pace with 

 the fall of the tide outside the reef It has been suggested that formerly similar 

 conditions may have obtained at the Mangrove Swamp at Funafuti, and that the 

 raised Heliopora ccerulea reef there developed may have grown in a part of the 

 lagoon, the level of which was permanently that of high water, through being 

 completely land-locked. This view, however, does not explain the fact that at its 

 highest point, as at the plantation south of Fongafale, the dead Heliopora ccerulea 

 appears to extend above the level of high water, while the dead Lithothamnion, 

 of the encrusting type, which so largely forms the cementing material of the breccia 

 sheet, certainly extends in numerous places up to quite 2 feet above high water. 



It may also be mentioned that numerous Porites heads in situ, like those at 

 Tutanga, Te Falaoingo and Tefala, and those at Pava in the Funafuti Atoll are in 

 many cases over a foot, some at Te Falaoingo 4 feet above high water. These 

 immense heads could not have grown in land-locked reef pools, but must have 

 flourished under the most favourable conditions, such as free access to food-bringing 

 currents, &c., would provide. Outliers too of the reef breccia, to be described 

 presently, show that coral and Lithothamiiion occur in situ upon them up to levels 

 of over 5 feet, in one case 10 feet above high water. At the islet of Motusanapa 

 one of us (Mr. Sweet) has observed the largest and highest breccia outlier as yet 

 noticed at this atoll. Its summit is 1 feet above the level of high water, and as he 

 considers from its surroundings that it was all originally cemented and consolidated 

 at a level not exceeding; that of low tide, this occurrence would indicate a downward 



* 'Nature,' vol. 55, 1897, p. 376. See also supra p. 20. 



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