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



varies in depth up to 20 fathoms, having a bottom of dark grey 

 muddy sand with which the shore platform is also covered; in 

 many places too the reef has its breadth considerably increased 

 by the same deposit on its landward face, and shoals are covered 

 by it. 



The delta of the Rewa forms the whole south-east corner of 

 Viti Levu ; here the reef fringes and is as much as 3 miles broad. 

 This great breadth is apparently due to the sand with the earth 

 carried down by the river having filled up the lagoon. By the 

 island of Nukulau is the largest passage ; it has a bottom free of 

 mud and . the bottom of the river too is for some distance clean 

 and hard, appearing to be formed of reef-rock. It seems to me 

 that the reef here formerly extended up under the delta of the 

 Rewa, and by the deposition of mud was gradually killed, growing 

 up afresh outside. The bottom is distinctly visible in the 

 Nukulau passage ; it is by no means bare of corals and nullipores, 

 and has further a small reef awash in the middle. Yet the 

 fresh water and detritus of the river must have a considerable 

 effect or there should be patches and shoals of coral-rock in the 

 lagoon. 



Muddy sand is found on all the inner reefs and patches to the. 

 east of Viti Levu and the inner reefs of Ovalau are all coated by 

 it ; that it forms often merely a thin layer over the reef- rock can 

 be plainly seen, but in many places it is undoubtedly filling up 

 the lagoon by its deposition. It varies largely in its composition 

 with its proximity to rivers and streams, but shells of Foraminifera, 

 fragments of Mollusca and Echinodermata, segments of such 

 algae as Halimeda and sponge spicules can usually be found. 

 It occurs further on all the inner reefs and some of the outer reefs 

 to the north of Viti Levu and Vanua Levu. Under water it sets 

 firm and hard, but does not apparently consolidate ; sponges and 

 green . algae grow on it luxuriantly, but corals and incrusting 

 nullipores are never found. 



Round the north of Viti Levu from Ovalau for some distance 

 there is a much broken barrier reef with one or two sandbanks, 

 like supplementary barriers between it and the shore, which 

 always has some sort of a platform. These inner barriers are 

 covered by the same muddy sand, which is of a lighter colour 

 owing to a less admixture of river washings. Thakau Moi, a shoal 

 to the north of Viti Levu, is a part of this barrier reef; its land- 

 ward side has a steep face, succeeded by a broad flat with a 

 central depression, which is covered by the same sand. The true 

 reef is a narrow strip on the outside, and it is only on the outer 

 face of this that corals, or reef-building nullipores, grow in any 

 luxuriance. I shall have occasion to refer again to this sand, 

 when noticing the raised reefs of Viti Levu ; it enters largely into 



