152 CEYLON PEARL OYSTER REPORT. 



F v o m the s u r f a c e of the actual Bank, at 9 fathoms, a quartz sand was 

 obtained. It contained, in addition, numerous shells, not overgrown with encrusting 

 organisms, Litlwthammon , brown Algae and horny worm tubes. The tine material 

 24 '20 per cent, of carbonate of lime was principally clear quartz sand well 

 rounded, and as rarer constituents, tourmaline, garnets, zircon, kyanite, rutile, and 

 ilmenite. 



Comminuted shell fragments, Echinoid spines, and Foraminifera Heterostegina 

 principally made up the bulk of the calcareous portion. 



Outside the Paar, to the West, at 20 fathoms, a Foraminiferal sand 

 containing very little inorganic matter was obtained. The tine stuff yielded 85'8G 

 per cent, of carbonate of lime. Heterostegina depressa and Alveolina were the 

 principal constituents, and there were also included Polyzoa Crista and Scrupo- 

 cellaria Alcyoniurn spicules, Holothurian plates, and the spat of young bivalves. 



Another haul. Outside, on the West, from 80 fathoms, brought up Foramini- 

 feral sand with no large forms except a few broken shells. It contained 7G'50 per 

 cent, of carbonate of lime. Unlike the Foraminiferal sand from shallower depths. 

 Heterostegina was not abundant, giving place in this group to small Nummulites, 

 Globigemna, and Textularia ; while Pteropods, the fry of Molluscs, Echinoid spines, 

 nodes of Crisia, Nullipores, Halimeda, Alcyoniurn and Leptoclinum spicules, and a 

 simple Coral were the other notable contents. 



Turning now to the rocks occurring on this paar, we find : 



The North Part is composed of a fine-grained calcareous sandstone or calcrete. 

 grey in colour, and containing a considerable number of black grains in patches.'"" 

 The block brought up is thickly encrusted with Polyzoa, both adnate and erect, and 

 Nullipores, green and white. Shells, such as Chama, are attached to the stone, and 

 these in turn are covered with encrusting organisms. On the fractured surface, the 

 centre is seen to be compact, but a thin band of less compact texture separates the 

 interior from the organisms on the surface. Sometimes the Polyzoa lie directly on 

 the sandstone, at other times a thin layer of Nullipore intervenes. 



The quartz is clear and of fairly even grain, and between the particles the calcite 

 is seen filling up spaces or lying as thin rods across the grains. A few shell fragments 

 and Foraminifera occur along with the quartz. 



A thin slice examined under the microscope shows quartz, mostly angular, and 

 averaging about t millim. in diameter, with inclusions of apatite, zircon and 

 tourmaline, felspars, both orthoclase and plagioclase, showing no signs of kaolinisation, 

 green tourmaline, shell fragments, and sections of Nummulites. 



Calcite occurs as a granular mass filling up spaces between the grains, and often as 

 curved rods. The rods, as a rule, enclose sand grains ; they are sometimes pitted 

 transversely, and a dark line in some cases runs down the length of the rod. Brown 



* Fooi'E, op. tit., mentions a sandstone containing magnetic iron sand as occurring in Valimukkam 

 L'litis, un the coast of India. 



