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SECTION VII. 



REPORT ON DREDGING AT FUNAFUTI. 

 By Professor T. W. Edgewoeth David, F.R.S., G. H. Halligan, and 



A. E. FiNCEH. 



Dredging was carried on by us during the 1897 and 1898 Expeditions partly in 

 the lagoon and partly on the seaward slope outside the atoll. 



As regards the lagoon dredging, the a]3paratus used was chiefly the sand pump 

 with the brass ball- valve. Sand j)ui^^ps fitted with brass flap- valves were also 

 employed, but were found far less satisfactory than the former type, as they were 

 liable, wherever sand was met with, to become jammed at the hinges. Subsequent 

 experiments by one of us (G. H. H.) has shown that a sand pump fitted with a good 

 leather flap-valve is superior to both the preceding types, since, for tubes of the same 

 diameter, the latter valve affords a larger opening and freer passage than the ball- 

 valve, and is not liable, as is the brass flajD-valve, to become jammed at the hinge 

 by the entrance of grit or sand. As regards the method of using, the sand pump 

 was lowered until it reached the floor of the lagoon, when it was alternately raised 

 and dropped quickly through a vertical range of from 1 to 3 feet, until it was filled, 

 when, of course, it was drawn to the surface and the material sorted and preserved. 



The result of these dredgings proved that the floor of the lagoon at all depths from 

 12 fathoms down to its greatest depth (30 fathoms) is comjjosed chiefly of Halimeda 

 debris with foraminiferal shells and fragments of moUuscan shells and pieces of sea- 

 weed. The question here suggests itself as to whether or not the Halimeda is alive on 

 the floor of the lagoon at these deeper levels. We observed very numerous patches 

 of live Halimeda forming a nearly continuous belt from, at all events as far south as 

 Funamanu, to at least as far round the lagoon shore in a north-Avesterly direction as 

 Pava, a distance of 8 miles. Numerous round patches of Halimeda flourished on this 

 part of the lagoon platform near the level of low tide, and from about low tide to a 

 depth of at least 20 fathoms. In the deeper portions of the lagoon we occasionally 

 recovered living Halimeda at depths of upwards of 20 fathoms, but it ajDpeared to be 

 growing there less vigorously than at shallow levels. Near the sheltered north-eastern 

 shore of the lagoon living Hcdimeda was more abundant than on its western shores. 



A series of dredgings was made by two of us (G. H. H. and A. E. F.) at 

 ^ mile intervals as determined by hydrophic methods, on a line running westerly 

 from the Mission Church to the islet of Fuafatu. The positions of these dredgings 

 are shown on Plate 1. No less than 17 out of the 18 samples obtained were 



