REPORT ON DREDGING AT FUNAFUTI. 153 



saud. ^vas fairly abiuidaut at 40 fathoms. As regards the distribution of this sand 

 and fine rubble generally on the submarine slope of the atoll, it would appear that it 

 is absent for the most part from a little below low tide down to about 20 fathoms, 

 wave action being probably sufficiently effective above this level to wash the fine 

 detritus down from the upper part of the reef slope into the deeper water. A glance at 

 the submarine contour of the atoll shows that at about 45 fathoms its submarine 

 slope steepens suddenly from an angle of 25° or 30° up to 50°, 60°, or 70°, in 

 places even becoming vertical. Hence the Halimeda zone is limited downwards 

 to the depth of about 45 fathoms."* On this steep slope below 45 fathoms it might 

 be thought impossible for any sand or fine rubble to lodge, but as a matter 

 of fact we found that off Fuafatu the former occurred in small pockets even 

 at depths of 70 fathoms, where the angle of slope was 70°. As living horny alcyo- 

 narian corals, belonging to the Gorgonidse, were so abundant on this steep slope, 

 between 40 and 100 fathoms, as to form a low scrub, it seems probable that they play 

 an important part in arresting the sand and fine rubble in its downward progress. 

 Numerous small projections likely to entrap rolling sand are also formed by lumps of 

 living Lithothamnioii, bristling with Polytrema and encrusted by tubes of Serpulce, 

 skeletons of Polyzoa, valves of small lamellibranchs, especially Spondylus, &c., as 

 well as small solitary sea corals. 



Here and there too, on this steep slope, loose flatfish pieces of reef rock were found 

 varying in size from a few inches up to 12 inches in diameter. Such fragments, 

 entangled temporarily amongst the horny stems of the alcyonarians, would form 

 traps for the foraminiferal and Halimeda sand descending from above. They would 

 then, in common with the sand at their back, become overgrown by deep-sea 

 organisms, particularly by the encrusting variety of LitJiotJuwiJiion, until the whole 

 of the fragmental material had been firmly cemented to the face of the submarine 

 slope of the reef. Each fragment brought to the surface from these levels was a 

 perfect curiosity shop of encrusting organisms. It was from such a one that 

 Mr. Hedley obtained his specimen of the rare brachiopod T/iecidea maxilla. 

 He states in regard to iff : " This species was attached in considerable numbers, 

 horizontally, perpendicularly, or obliquely to loose sheets of dead coral, which I 

 pulled up by tangles in 40 to 80 fathoms on the western slope of Funafuti." Living 

 specimens of the brachiopod Crania were also occasionally found off Falefatu and 

 Tutanga at depths of 38 to 200 fathoms. 



The fact that most of the loose fragments secured by us from the steep slope were 

 flat in shape is, we think, significant. Such fragments would slip down slowly 

 with an oscillatory or "butterfly" movement, like that of a coin sinking in water, 



* This growth limit is no doubt chiefly clue to the fact that being a green plant it caiuiot live below 

 45 fathoms, as the red and yellow solar rays which it needs for decomptising COo and manufacturing 

 chlorophyll are probably absorbed at depths greater than 45 fathoms, as FoL and Sarazin have shown. 



t Australian Museum, Sydney. Memoir III. Part 8, 1899, p. 509. 



X 



