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



blow-holes in the surface of 0.3. These aj^pear to represent what were formerly open 

 channels which have subsequently become roofed in, except at the blow-holes O.L.IO. 

 The rock thus indicated forms an almost continuous fringe around both the outer and 

 inner edges of the leef platform, which Mr. Hedley likens to a carpet of dull crimson.* 

 It is thus defined in our Index : — " Uj)per portion of the living Lithothamnion 

 zone which is a\vash at low water of spring tides. This is chiefly developed at the 

 edge of the reef platform facing the ocean, but is also present in places along the edge 

 of the lagoon platform. On the ocean j)latform it forms conspicuous fringes at the 

 edges of tlie channels and blow-holes and around the latter, where it is bathed by the 

 spray, it forms numerous strong lip-like elevations or low mounds. Its surfece is 

 pitted, partly by burrowing echinoderms, and is tubercular, and usually slightly 

 raised above that of zone 0.3." This last statement is correct only for areas 

 where O.L.IO is developed around blow-holes or channels, for as shown by Mr. G. H. 

 Halltgan's levels, the general level of O.L.IO is below that of 0.3, and as already 

 stated, in his section on Plate 17, the rim of O.L.IO is raised about 6 inches above 

 the inner portion of the same zone. Since this was written Mr. F. Chapman has 

 sliown that mucli of the material around the blow-holes and edges of the channels is 

 Polytrema and Carpenteria, more or less interstratified with Lithothamnion. 



Mr. A. E. Fixckh's careful and detailed plan on Plate 17 gives an excellent idea of 

 the shape of the bound-iry-line seawards of the living Lithothamnion zone. Its 

 general appearance is shown on the lower figure of Plate E.f In the latter the 

 O.L.IO zone extends from the lower edge of the photograph almost as far as 

 to where the suction pipe from the diamond drill enters the water at a pool com- 

 municating with one of the channels. As is shown by Plate 17, the rock of O.L.IO 

 luiis out seawards in a ninnber of irregular piers separated from one auotiier by 

 niunerous chainiels. At low tide the sea rolls up these channels and Ijlow-holes Avith 

 considerable violence, and Allien this is accompanied by a general rush of water from 

 a large breaking wave over the edge of the reef, the expression "running a traverse" 

 acquires for those engaged on such a work a new and literal significance. 



Further seawards below the level of low tide the Lithothamnion zone is continued 

 in the form of irregular mounds, as shown in the " Detail Plan of Channel ' by 

 Mr. Halligan on Plate 1*J. At first sight one is apt to form an exaggerated 

 idea of the depths of these channels. Actual measurements by Mr. Finc;kh shows 

 that their deptli does not exceed from 10 to 12 feet. A cross-section of five of them 

 is shown on Plate 17, and a description of them is given by Mr. Finckh in Section VI. 

 He states that Millepora alcicornis grows sparingly on tlie sides of the channels 



* " The Atoll of Funafuti," 'Memoir III.,' Part I., p. 13, Australian Museum, Sydney, 1896. 



T This is taken opposite to the main drill bore-hole. In the foreground is the living LitJiothrvnniion 

 zone (O.L.IO), with the head of one of the channels. Next inshore is 0.3 (near the end of the suction 

 pipe for the drill). Then comes the breccia, O.2.B., O.2.C., and 0.2.0., surmounted by the Hurricane 

 Bank. 



