BY D. MAWSON. 455 



The limestone from the lower portions of a reef is always 

 fragmentary, and though invariably coralliferous, may often be 

 most largely composed of remains of mollusca, calcareous algae, 

 and foraminifera, with a cement-like base of calcareous mud; in 

 addition a small percentage of inorganic matter is often present, 

 resulting in a greater or less degree of staining. 



In the upper part of the reefs is a zone, never relatively very 

 thick, where prior to elevation the polyps thrived — here the 

 limestone is quite white and is composed of large upright heads 

 of coral. 



Dr. Hinde examined two specimens of coralliferous limestone 

 from the raised reefs of Efate and found Lithothamnion con- 

 tributing largely to its formation. 



Professor Liversidge has also recorded analyses of two samples 

 of raised reef limestone from this locality.! 



iii. Lepidocyclina-Lithothamnion Lim e- 

 STONES . — Lepidocyclina-Lithothamnion limestones of Miocene 

 age are found widely distributed both in Santo and Malekula. 

 On account of their greater compactness and even fracture, they 

 are readily distinguishable from the more recent coralliferous 

 limestones just described. Among the most conspicuous of the 

 organisms^' represented is Lepidocydina, specimens of which are 

 common, 6 mm. in diameter; branching and encrusting forms of 

 Lithothamnion are also present in considerable quantity. 



Inorganic matter of the nature of mineral fragments and 

 pellets of volcanic rocks are always present, though in variable 

 amount, resulting in varieties differing considerably in colour and 

 composition. The purer types are almost white, but far more 

 common is a light grey to plum-coloured limestone, containing 

 upwards of 20% of inorganic matter. 



t Loc. cit. p. 160. 

 * For microphotographs, a complete list of the forms present in these beds, 

 and for detailed descriptions of several of the specimens, see Mr. Chapman's 

 paper {antea, p. 261). 



