442 Mr Gardiner, The Coral Reefs of [Mar. 7, 



(ii) Outside the boat channel is the boulder zone (Fig. 4 cc) 

 formed of fragments, torn off the reef outside and piled up for 

 1 — 2 feet above low tide level with isolated boulders 2 feet 

 higher. It is not generally well-defined except on the windward 

 face, its greatest breadth here being about 70 yards. It is in 

 reality a layer of boulders, lying on the edge of the reef-flat, 

 which here commences and up to which the boat channel gradually 

 for some distance shoals ; it is separated merely for convenience 

 as it should properly be described with the next zone. 



Undoubtedly these boulders have been broken off and piled up 

 by the sea, but after a severe easterly gale the examination of a 

 part, well hunted over on several occasions, showed but few 

 additions 1 . 



(iii) The reef-flat (Fig. 4 dd) consists of a smooth platform 

 of reef- rock with a depth varying from 1 — 3 feet below low tide level. 

 As it is cut off by the boulder zone from the boat channel and by 

 the rim from the sea, it always retains at low tide approximately 

 the same depth of water. Its bottom varies enormously, in some 

 places being smooth and almost bare of corals, but in the position 

 of the section, where it is about 60 yards broad, growing corals 

 cover about 25 per cent, of its surface. Madrepora are extremely 

 abundant, adapting themselves to the depth of the water by 

 spreading out horizontally ; of this genus I obtained 9 species 

 from this area, of which Madrepora rotumana is by far the most 

 abundant. Other genera represented include Pocillopora, Stylo- 

 phora, Pavonia, Coeloria, Montipora, Prionastrea, Plesiastrea, 

 Heliastrea and Favia. Incrusting nullipores are absent except for 

 a few yards on the outer side. 



(iv) The last zone slopes up to the rim (Fig. 4, e and Fig. 5) 

 but is separated from it by an abrupt rise of 6 inches, for a few 

 yards above and below which the reef is covered by white nulli- 

 pores. A platform, gradually sloping upwards, succeeds, here 

 about 6 yards broad with upwards of 5 per cent, of its surface 

 covered with Prionastrea, Pocillopora and Stylophora of low 

 growing species, between which the surface is almost hidden by 

 white, pink and red nullipores. Fissures commence at the outer 

 side and run through the crest of the rim, which is about 4 yards 

 broad and presents the same appearance as the extreme edge of 

 the reef at Funafuti. The fissures, however, are narrower and in 

 no way drain the reef-flat ; their sides, too, do not overhang. 



Outside the rim the reef has a slope of 10° — 15° for about 

 15 yards, but is much broken up into buttresses, masses and 

 ridges, which extend as deep as the bottom can be seen. Sound- 



1 I was informed by the natives that about 1881 most of the boulders were swept 

 away in an hurricane, and that the zone has only been gradually reforming since. 



