8 '2 



PROFESSOR T. W. EDGEWORTH DAVID AND MR. G. SWEET. 



On the east side of the lao-oon tlie edo-e of the cUft' face is somewhat cavernous and 

 friable, owing chiefly to the destructive work of burrowing organisms, such as 

 gephyrean worms ; the constructive growth of Lithothamnion and coral and Ualimcda, 

 checked on this side of the lagoon by heavy silting, scarcely availing to keep pace 

 with the agents of destruction. On the western shore of the lagoon platform, 

 however, the edge of the low cliif faced with O.L.IO is firmer, a fact due, no doubt, 

 to the comparatively rapid growth there of both Lithothamnion and coral. Apparently 

 then the small lagoon cliff owes its origin to a cause somewhat similar to that of 

 the great submarine cliff bounding the atoll on the ocean side, viz., to the fact 

 that the chief reef- building organisms grow most rapidly in comparatively shallow 

 water, the tendency thus being for the upper portion of the atoll rim to grow 

 outwards faster than the bottom. On the ocean side of the reef, however, the force 

 of the waves and ocean current is sufficient to bevel the edge of the submarine cliff 

 down to a level of about 30 fathoms, whereas, in the calmer water of the lagoon, no 

 such bevelling has taken place ; hence, in the latter case, the cliff falls straight down 

 for 2 to 3 flithoms from the level of low tide, except in places where it has been 

 obliterated by detritus swept lagoon wards over the reef platform.* Deposition of 

 silt at its base has undoubtedly in places much lessened its height. This low 

 submarine cliff at Funafuti is shown to a limited extent on Section 10 of Plate 9, 

 where there are two drops close together of |- fathom each. Near Pava and Fualifeke, 

 however, as well as off Funamanu and Funangongo, the drop amounts to 3 to 4 fathoms. 

 The following table of areas occupied by the various types of rock at Funafuti, 

 noted in the geological index, has been kindly prepared for us by Mr. G. H. 

 Halligan : — 



Table of Total Areas, in British Acres. 



Rock. 



Area in 



j 



Rock. 



Area in 



Rock. 



Area in 





acres. 





acres. 





acres. 



O.L.IO 



545-430 



O.2.D. 



87-747 



L.7.B. 



174-871 



0.4 



215-678 



O.2.E. 



256-081 



L.7.A. 



90-319 



0.3 



1042-434 



O.L.I 



1002-104 



L.6 



33 • 865 



0.2. A. 



44-076 



L.9.A. 

 i and 

 L.9.B. 



101-705 



L.5 



11-496 



O.2.B. 



176-010 



L.8.B. 



18-805 



L.3 



12-855 



O.2.C. 



32 - 689 



L.8.A. 



35-077 



L.2.B. 

 L.2.A. 



7-383 

 3-973 



* This cliff has also been referred to by Mr. Stanley Gardinkh, ' Camb. Proc. Phil. Soc.,' 1895-8, 

 vol. 9, p. 424. Reference has also been made to the existence of a similar cliff on what was, doubtless, at 

 one time the edge of the lagoon platform of Christmas Island, in the Eastern Indian Ocean, by Dr. C. W. 

 Andrews ("A Monograph of Christmas Island (Indian Ocean), Physical Features and Geology," 1900, 

 p. 13). He states : " The flat surface is similar to the reef flat of an atoll, fhe inner cliff to the sudden drop 

 of two m- iliree failwms which often occurs on the layoon side of the reef flat." (The italics are ours.) 



