706 MESSES. F. CHAPMAN AND D. MAWSON ON [Nov. I906, 



the rock being rich in organisms, including besides Halimeda, Litho- 

 thamnion, gastropoda, echinoid-fragments, and tunicate-spicules. 



At 120 feet Halimeda was abundant, associated with echinoderms, 

 polyzoa, tunicate-spicules, and Lithothamnion. At 190 feet (near 

 the top of the second terrace), Halimeda was again abundant,, 

 also Lithothamnion, gastropoda, polyzoa, echinoid-spines, and many 

 foraminifera. 



At 200 feet the limestone contained Halimeda, as well as corals, 

 echinoderms, Lithothamnion, and an abundance of tunicate- 

 spicules. 



Tonga Islands (Friendly Islands). 



In the island of Eua, Sherlock found Halimeda associated with 

 Lithothamnion, gastropoda, and foraminifera, in the third terrace at 

 a height of 250 feet. In his remarks on Halimeda in these elevated 

 reefs, Mr. Sherlock (Bull. Mus. Comp. Zool. vol. xxxviii, 1903* 

 p. 362) says that it 



' is much less widely distributed (than Lithothamnion). It occurs in nine 

 sections, coming from Mango, Niue, and Eua. It is much less stable than 

 Lithothamnion, and this may account, to some extent, for its more limited 

 distribution.' 



It may be remarked, a propos of this feature of instability, that 

 the disintegration of Halimeda under certain conditions may give 

 rise to the fine, impalpable, and microscopically-granular mud so often 

 observed accompanying lagoon-deposits. Evidence for this was 

 afforded by the elevated plateau-limestones of Christmas Island* 

 already mentioned. The same type of mud was also observed by 

 one of us at various levels in the Eunafuti main boring. 



III. Description of the Halimeda-Liwestohtls 

 of the New Hebrides. 



Amongst the raised reef-limestones of the New Hebrides* 

 scattered joints of Halimeda obtain a wide distribution ; on several 

 occasions, the remains (well preserved) were found in association 

 with foraminiferal tests and gastropod-shells, among the basement- 

 grits * underlying the actual reef-limestones. Such material might, 

 it is thought, have been transported considerable distances. 



Calcareous rocks, formed almost entirely of the remains of 

 Halimeda-jomts, are represented in three of the islands cf the New 

 Hebrides, namely, Malekula, Espiritu Santo, and Elate. 2 



The several examples from these three localities difTer considerably 

 from one another in the condition of preservation of the chief 

 organic constitutent Halimeda, in the associated smaller organisms, 



1 Composed largely of volcanic glass and mineral particles ; described by 

 Mr. O. Hedley as containing mollusca similar to those dredged by him in 

 15 fathoms of water oft' the Palm Islands. 



2 See D. Mawson, 'Geology of the New Hebrides,' Proc. Linn. Soc. N. S. W. 

 vol. xxx (1905) pp. 400-84.. 



