SEA-BOTTOMS AND CALCEETES. 157 



direction and overlapping. Lying on the sea floor with their concave surfaces facing 

 upwards, they have heen filled with sand. This has afterwards been cemented, and 

 the shells subsequently dissolved. Thus viewing the specimen from one side we see 

 the smooth cast of the interior of the shells, and on turning over only sand is visible. 

 Other shells attached to the mass and still retaining their tests are Cardiwm, Pecten, 

 Mitrex, and Cerithium. Colonies of Polyzoa and worm tubes have attached them- 

 selves to the smooth surfaces of the casts since the shells were removed. 



Dutch Modragam Paar, to the southwards, lies 10 miles due west of Kodramallai 

 Point. It is 1^- miles in diameter and has a depth of 8 to 14 fathoms. 



From this paar two specimens were obtained, one a piece of Madrepore coral about 

 2 inches thick, with numerous borings of Molluscs proceeding downwards and obliquely 

 from the upper surface. White Nullipore covered parts of the upper surface, and the 

 byssus of pearl oysters occurred attached to both the top and bottom. 



The other sample was a coarse calcrete, consisting of sand grains very uniform in 

 size, each measuring 3 to 4 millims. in diameter. The grains were clear, well rounded 

 quartz and felspar, loosely cemented by carbonate of lime and thickly encrusted by 

 Nullipore and Polyzoa. 



Muttuvaratu Paar lies 5 miles west of Karativo, and has a depth of 5 to 10 fathoms. 

 Here dead coral, bored in all directions by Molluscs, was brought up. It was covered 

 by green Nullipore, a few colonies of Polyzoa and worm tubes, and much byssus of 

 pearl oysters was adherent to both upper and lower surfaces. 



Dredging in the neighbourhood, at a depth of 7 fathoms, showed the bottom to 

 consist of calcareous sand containing 7 8 '36 per cent, of carbonate of lime. Hetero- 

 stegina depressa was the chief constituent, and some of the larger forms were covered 

 with green Nullipore. Other organisms present were Alveolina, small univalves, 

 Diatoms, and spicules of Leptocliiium, Holothurian plates and shell fragments. 



Chilaw Paar, the largest paar on this southern part of the west coast, lies 7 miles 

 west of Chilaw. It is 8 miles in length and averages 2 miles in width. The depth 

 varies from 9^ to 10 fathoms. 



North of the Paar, at 10 fathoms, a calcareous sand was obtained, the finer 

 material of which on analysis gave 95 '5 per cent, of carbonate of lime. The small 

 amount of inorganic matter present consisted of quartz grains, '5 milliin. in diameter, 

 plagioclase felspar, zircon, garnet, tourmaline, kyanite and rutile. 



Among the larger organisms present were shells and Nullipores in about equal 

 proportions, containing such forms as Pecten, Area, Pectuncuhis, Astarte, Turbinella, 

 Capulus, Nassa, Turritella and Echinoci/amus. Most of these were rotten and 

 covered with Nullipores, Polyzoa and Serpulse. 



The finer material comprised many Foraminifera, including Heterostegina, Polytrema, 

 Alveolina and Globigarina, Echinoid spines, young Molluscs, Crista, Pteropods, and 

 spicules of sponges, Holothuria, Alcyonium and Leptoclinum. 



South of Chilaw, at 8A fathoms, the bottom was mostly composed of Nnlli- 



