154 CEYLON PEARL OYSTER REPORT. 



subsequent growth may enclose them. IAihodomus crypts and worm tubes, when 

 deserted by their occupants, may also be rilled with sand and become incorporated in 

 the substances of the Nullipore. We shall return to this subject when discussing a 

 Nullipore deposit from Chilaw. It is sufficient for the present to point out the 

 importance of Polyzoa as cementing organisms, and indicate the criteria by which we 

 can recognise their action. 



South end of Periya Pa ar. Here four pieces were obtained. Three <>f 

 these were calcretes cemented mainly by Polyzoa, exactly similar to the one 

 described, and containing grains of quartz, rutile, tourmaline, felspar, corundum and 

 ilmenite, with shell fragments, Foraminifera, and sponge spicules ; while the fourth 

 was a piece of dead Coral, very rotten, covered with encrusting organisms, and bored 

 bv Saxicava. 



Cheval Paar. This paar lies to the south-east of Periya Paar. It is U-shaped, 

 consisting of east and west arms with a connecting bar at the south. 



The east arm is G miles long by L mile broad, and the depth averages GV fathoms. 

 Outliers to the north are seen at Periya Paar Iverrai, and Vankali Paar, and to the 

 south lie Kondatchi and Jaggerboom paars. 



The west arm measures 4 miles long by \\ to 2 miles broad, the depth is 7 to 

 8 fathoms. The connecting piece at the south end is 5 miles broad, runs north-east to 

 south-west with a prolongation at the middle towards the south-east. Two small 

 isolated paars, North Modragam and South Modragam, extend south-east from the 

 prolongation. 



Seven samples of the dredged material were kept from the parts surrounding the 

 Paar, and 10 specimens of rock were obtained from the Paar itself and Periya Paar 

 Kerrai. 



Pearl Banks off Ghilavaturai, Q>\ fathoms. The coarser part of this haul 

 consisted mainly of drifted shells, including Pearl Oysteij Mactra, Pectunculus, Venus, 

 Nassa, and Trochus. They were nearly all broken, rotten, and some were bored 

 by Clione and encrusted with Nullipore, Polyzoa. and Serpuke. Echinids and Starfish 

 also contributed to the contents of the sample as dredged. The only living organisms 

 were Polyzoa. 



The portion of medium size consisted of clear and milky quartz grains, well rounded 

 and polished, averaging 5 millims. in diameter, echinoid spines and a few shell 

 fragments. 



The part which passed through a sieve of 1 millim. mesh was mostly quartz sand 

 with 7 '04 per cent, of carbonate of lime. On concentrating the heavy minerals by a 

 high-density fluid magnetite, ilmenite and leucoxene, garnets, kyanite, tourmaline, 

 rutile, corundum, and zircon were found : while in the lighter fractions were 

 comminuted shells, Nullipores, Foraminifera, Echinoid spines, and spicules of 

 IlulotJtiiria, Alcyonium, and sponges. 



The material has all the appearances of a drifted shell bank swept by strong 

 currents. 



