THE GEOLOGY OF FUNAFUTI. 7!) 



gained on the ocean by the width of the living rim, O.L. 10, which, as shown by 

 Mr. HallictAn's section, is represented by the difference between 170 feet and 

 266 feet, that is a distance of 96 feet. This does not, of course mean that the edge 

 of the reef platform of the atoll has advanced seawards, as the result of peripheral 

 outgrowth, by a similar amount in the interval of time during which the belt O.L. 10 

 was being reclaimed, but simply that as a result of the retreat of the sea-line as well as 

 of the upgrowth, and perhaps to a limited extent outgrowth of O.L. 10, an extra width 

 of reef platform amounting to about 96 feet is noAv uncovered at low tide. It is not 

 necessary to assume a combined upgrowth and outgrowth of more than a few inches 

 in order to account for this widening of the atoll by 96 feet, as reference to Plate 17 

 will show that there are numerous piers of reef-rock, only a few inches below low 

 water, lying just beyond the low water line, and consequently a downward movement 

 of the shore-line only a few inches in amount, assisted by upgrowth and outgrowth 

 of Lithothamnion, would considerably widen the reef platform. 



(2) The death of the Lithothamnion, &c., in 0.3 is due to a slight downward 

 movement of the shore line amounting approximately to the difference between the 

 general levels of the surfaces of 0.3, and of O.L. 10 respectively, which amounts to 

 between 7 and 8 inches. Thus the downward movement, of which evidence has 

 already been supplied by the raised Heliopora ccerulea reef, the breccia outliers, the 

 older terraced deposits of the lagoon side of the islets, &c., has probably been 

 prolonged into quite recent time and may even yet be in progress. 



It might be argued that the death of the Litliothamnion in 0.3 might result from 

 its removal from the reach of the sea-spray at low tide through the ujDward growth 

 of the Lithothamnion of^ O.lj.lO interposing a strip of reef at low tide between 0.3 and 

 the line of breakers. This explanation w^ould be reasonable if 0.3 were on the same 

 level as O.L. 10, but, as stated, it is not, 0.3 being from 6 to 7 inches above the level 

 of O.L. 10. In view of the observations by Mr. Finckh, that if the Lithothamnion be 

 exposed for only one hour to sunlight above low tide, in a position where it is not 

 bathed by the sea or sea-spray, it dies, and inasmuch as the dead Lithothamnion of 

 0. 3 is now exposed under the above conditions for fully 2 hours at low spring tides, it 

 follows that Lithothamnion could not live now where we now find it at 0.3 unless there 

 were an upward movement of the shore line of perhaps about 6 inches, or some change 

 of conditions which would admit of sea-spray being w^ashed over 0.3 at low tide. 

 Hence we consider that we are justified in assuming that a downward movement of 

 about 6 to 7 inches has probably taken place since the time when the Lithothamnion 

 of 0.3 was alive. 



It will be noticed that on our geological map of the atoll a very large po]:'tion of the 

 reef platform of the western rim of the atoll has been mapped in as 0.3. It is quite 

 possible that old LLeliopora ccerulea reef may underlie the 0.3, there as it does on the 

 eastern rim. It w^ill be noticed that in Plate 17 Mr. Finkijkh shows that some of the 

 long channels which penetrate the living Lithothamnion zone O.L. 10, terminate in 



