162 CEYLON PEARL OYSTER REPORT. 



casts themselves, in many instances, have been reduced to shapeless spongy masses of 

 cemented sand. It is not improbable that these shells were filled with sand previous 

 to the building of the Bridge, when the currents were sufficiently powerful to carry 

 coarser material. 



Some of the deposits, as at Galle Bay and Palk Bay, are evidently very old. They 

 represent the remains of a fauna where solution and chemical changes have been at 

 work. The shells left are mostly composed of calcite, not aragonite, and many of 

 them have become partially converted into phosphate of lime. 



Stable minerals such as quartz, garnet, kyanite, tourmaline, and zircon are found 

 everywhere, whereas the less resistent felspars only occur near the coasts in the Gulf 

 of Manaar in places where material has been recently deposited, or in calcretes, or in 

 the interior of shells where they have been preserved from kaolinisation. 



My thanks are due to Professor Herdman for much kindly help, and to Mr. C. C. 

 Moore, F.I.C., of Liverpool, for the care he has taken in analysing some of the 

 deposits for the purpose of this report. 



EXPLANATION OE TLATE I. 



Fig. 1. Concretions, shells and casts from Palk Bay. 



Fig. 2. Casts of Pearl Oyster and other shells cemented together from Periya Paar Kerrai. 

 Fig. 3. Coarse calcrete from Jokenpiddi Paar. 



Fig. 4. Nullipore balls, some broken to show red spongy interior. A fragment of Sabellaria is shown 

 at the extreme right of the middle line from South of Chilaw Paar. 



