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



movement of the shore line in this part of the atoll to the extent of at least 16 feet. 

 The conclusion, therefore, seems to follow that at Funafuti there has been such a 

 movement of the shore line to the extent of at least G feet and almost certainly 

 16 feet. 



The interspaces between the large radiating branches of Ileliopora ccBrulea, at 

 the Mangrove Swamp, are filled with "sand" composed of foraminifera and broken 

 fragments of Lithothamniou and of molluscan shells. The tidal water finds an easy 

 passage through the sand between these branches, from the ocean side of the reef to 

 the lagoon j)latform. As the tide outside the atoll rises, the water wells up from 

 a great number of holes in the lagoon platform. These are from a small fraction of 

 an inch ujj to about 6 inches in diameter. In fact, the rock of the atoll rim, in its 

 upper portion at all events, seemed as porous as a huge sponge, being honeycombed 

 in all directions with tortuous irregular hollows, generally filled with foraminiferal 

 sand. It was these countless hollows in the reef rock, filled with running sand, which 

 rendered the task of boring the rock so difficult, as the sand was continually being 

 washed in from them so as to choke our bore-hole, wherever its sides were not lined 

 with the steel pijjes. One of the largest of these openings is that known as " the 

 blow-hole," near the north extremity of the Mangrove Swamp. (See I'late 9.) This 

 might be more correctly described as a swallow-hole. It is about 4 feet in diameter, 

 and is distant 130 yards from the inner edge of the reef platform at low tide. 

 Nevertheless, the surface of the water in it pulsates in unison with the movements of 

 the waves outside the reef Plate C, fig. (1) shows the general appearance of this 

 swallow-hole. 



As regards colour the Ileliopora carulea of the rock type O.L.I retains its original 

 indigo-blue colour only in cases where it has been protected, as on the reef platform, 

 by some such covering as that afforded by Lithoth amnion or Carpenieria. In long 

 exposed positions it is mostly bleached superficially to a joale grey, passing inwards 

 into a greenish tint.* 



On the lagoon platform the dead Heliopora cwrulea reef terminates lagoonwards 

 in a low cliff, veneered with Lithothamnion as described in Section VI. 



At the Taro Plantation, west of the Mangrove Swamp, where the old Ileliopora 

 aerulca reef attains its highest level, the presence of 6 per cent, of phosphoric acid 

 in the soil shows that this part of the atoll has perhaps a certain amount of guano 

 deposited upon it.t The fact, however, sliould be mentioned that the soil there has 

 been enriched in places by material carried there by the natives from other islets in 

 this atoll, and we were informed that a little of the soil had been brought over as ballast 

 from Samoa. 



* For the chemical composition of this colouring matter, see MOSELEY, ' Report, Challengei,' vol. 2, 

 pp. 109-110; and Livbrsidge, 'Roy. Soc. Proc, N. S. Wales,' vol. 32, 1898, p. 256. 



t The following analysis is quoted from ' Memoir III.,' Part I., of the Australian Museum, Sydney, 

 " The Atoll of Funafuti," p. 76 :— 



