THE GEOLOGY OF FUNAFUTI. 87 



level of low tide down to a depth of about 8 or 10 fathoms) on the northern and 

 western sides of the atoll. While the islets were slowly retreating lagoonwards 

 before the intermittent attacks of the trade-winds and monsoons, the zone marked 

 0.3 (dead Lithothamnion) was at that time living Lithothammon O.L.IO, and formed 

 the boundary oceanwards of such portion of the reef platform as was then above low 

 water. Later a further downward movement of perhaps about 6 to 7 inches occurred, 

 and the Lithothamnion in 0.3 now died, and gradually an outer zone, the present 

 O.L.IO, was raised above low water, partly through the above movement, and partly 

 by up-growth and to a limited extent by out-growth of Lithothanmioii, &c. 



Since 1878, when immense rafts of pumice arrived at Funafuti, the outer Hurricane 

 Banks have been pushed further back, so that there is now at least 2 feet, in places 3 feet, 

 in thickness of fragmental breccia and coral piled above the pumice horizon. With 

 regard to human testimony as to any changes which have taken place in the shape 

 of the atoll, the late trader at Funafuti, Mr. O'Brien, informed us that within his 

 memory a good deal of land had been washed away between the north end of Tengako 

 and the south end of Amatuku. One of us (Mr. Sweet) comments on the fact that 

 the native name Motuloa, meaning " Long Island," is now applied to a comparatively 

 short island, and unless this term has been applied on the lucus a non lucendo 

 principle, it is singularly inappropriate. On the other hand, it is probable that when 

 this term was applied, Motuloa was joined to Motusanapa and Telele, as seems obvious 

 from the geological evidence. 



It is difficult to predict what will be the immediate future of Funafuti Atoll. 

 Much depends on whether stable conditions or a change in the shore line will 

 predominate in the near future. On the one hand, it is clear that the islets are 

 being denuded away, and the materials of which they are formed are being washed 

 over the reef platform into the lagoon. This helps to silt up the lagoon, but only to 

 a very limited extent. The same is being done by the growth of Halimeda in 

 particular, and, to a much less extent the development of foraminiferal shells. The 

 accumulation of the Halimeda sand appears, however, to be considerably checked 

 through its removal from the lagoon by tidal scour. On both the ocean and lagoon 

 edges of the reef platform, growth, due to calcareous organisms, chiefly Lithothamnion, 

 is taking place oceanwards and lagoonwards respectively, so that the atoll rim is being 

 probably widened outwards and inwards, but at a very slow rate, as compared with 

 that of marine erosion. Then, too, there is the slow downward movement of the 

 shore-line which appears to be yet in progress, and against it must be set the 

 corrosive and erosive action of the heavy tropical rains. 



We are of opinion that the southern part of the lagoon, the " Pocket," will in time, 

 provided there is no upward movement of the shore-line, be completely silted up and 

 become a sand island. We think it, however, probable, that several of the smaller 

 islets on the atoll rim of Funafuti, unless they are saved and added to by further 

 downward movement, will be driven into the lagoon, where there is ample accommoda- 



