248 



PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



material is not incorporated in the sediments. As the mouth of Haddon 

 Brook is west of the Hne along which the samples were taken, the detritus 

 brought to the sea by it would be moved westward. Furthermore, as the 

 rainfall on Murray Island is rather low, only 32.66 inches per year, accord- 

 ing to information furnished me by Dr. Mayer, the quantity of terrigenous 

 material washed into the sea may be small. 



The specimen from line III, north end of the island, cast up on the reef, 

 1,700 feet from shore, differs from the samples taken from below water-level 

 in having a large percentage of fine gravel (49.4 per cent) and in having more 

 MgCOa (7.57 per cent). There may have been some secondary concentra- 

 tion of magnesia. 



Analyses of Corallinacea from Murray Island and Cocos-Keeling Islands. 



(By A. A. Chambers.) 



The specimen of limestone from 500 to 700 feet above sea-level is 

 indurated, light yellowish-gray in color, somewhat horny in texture, with a 

 conchoidal fracture. It is largely coral, with numbers of embedded fora- 

 minifera, of which Miliolidae are the most noticeable in a thin section. The 

 chemical analysis shows it to be 98.97 per cent CaCOs, a remarkably pure 

 limestone. As the percentage of MgCOa is only 0.60 per cent, there has 

 been no dolomitization of this specimen, at least. This is coral-reef rock. 

 Analyses of other specimens would probably show more MgCOs, as a few 

 fragments of Lithothamnion or a few foraminifera would increase its per- 

 centage. Haddon, SoUas, and Cole report that "analysis shows a fragment 

 from the summit of Gilam to be largely dolomitic."^ 



'Trans. Roy. Irish Acad., vol. 30, p. 433, 1894. 



