710 MESSRS. F. CUAPMAN AND D. MAWSON ON [Nov. I906, 



structure on decalcification for a depth of 35| feet below the floor 

 of the lagoon, and the central tubes were still visible at 50 feet 

 down. If we presume that the conditions for rapid mineralization 

 are favourable, the structure is thereby permanently preserved, 

 and we have examples such as those just described from the 

 JNew Hebrides. In the lagoon at Funafuti, Halimeda was found 

 growing so densely as to be comparable with a turf of green seaweed, 

 while the underlying mass was aptly compared by Prof. Judd with a 

 peat-bog. In the case of both Balimeda-SLCCu.mula,tion and peat-bog, 

 although disintegration takes place to a certain extent, it may still 

 form a deposit more or less recognizable as due to the agency of 

 the original plants. 



Much of the fine powdery limestone associated with coral-reefs, 

 and more especially with upraised coral-islands such as Christmas 

 Island (Indian Ocean), may be primarily due to lagoon or other 

 deposits formed by the agency of Balimeda, which under adverse 

 conditions have broken up into a finely -granular or amorphous 

 material, very suitably conditioned for ready alteration by in- 

 tiltering solutions. 



In speaking of the alga-formed limestones of the Trias, 

 Prof. A. C. Seward l refers to the obliteration of structure in many 

 limestone-rocks that may have owed their origin to the agency 

 of calcareous seaweeds. 



From their stratigraphical association, we conclude that the 

 oldest of the Balimeda-Ijimestones of the New Hebrides, described 

 above, is that from Malekula (109, p. 707), which probably dates 

 back as far as early Pliocene. 



EXPLANATION OF PLATES XLIX-LI. 



Plate XLIX. 



Fig. 1. Thin section of Halimeda-Ij\mestorie. 100 feet above Bartaleppe, 

 Malekula. x 14. (See p. 707.) 

 2. Halimeda-'Limestone, Malekula. Surface of fractured specimen. 

 Natural size. (See p. 707.) 



Plate L. 



Fig. 1. Thin section of Hcdimeda-~L\mestone, from boulders out of the bed of 

 the Atsone River, S. Santo. X 14. (See p. 708.) 

 2. Hcdimeda-Limestone, Atsone River, S. Santo. Fractured surface of 

 rock. Natural size. (See p. 708.) 



Plate LI. 



Fig. 1. Thin section of Halimeda-Limestoue, Shepherd's Hill, Vila, Efate, New 

 Hebrides. X 14. (See p. 709.) 

 2. Halimeda-Jjimestone, Shepherd's Hill, Efate. Fractured surface of the 

 limestone, showing its rough;, somewhat incoherent texture. Natural 

 size. (Seep. 708.) 



Fossil Plants ' vol. i (1898) p. 175. 



