GENERAL SUMMARY AND RECOMMENDATIONS. Ill 



When the bottom on the pearl hanks is not calcrete, it is formed of a coarse sand, 

 in some places almost wholly inorganic, containing large quartz grains, and derived 

 from the waste of the granulitic rocks of Central Ceylon brought down by the rivers; 



Fig. 1. Lump of calcrete showing large quartz grains and felspars with fragments of coral, shells 

 and worm tubes, along with many Polyzoa colonies. From Jokkenpiddi Paar. 



Elsewhere the sand is of organic origin, and is formed chiefly of the shells of large 

 bottom-living Foraminifera, such as Amphistegina lessonii, Alvcolina raelo, Hetero- 

 stegina depressa and Orbitolites marginalis, mixed with the calcareous remains of 

 many other kinds of animals (see Report upon the Foraminifera in this volume). 

 The divers distinguish between a hard bottom (the "paar ") suitable for pearl oysters, 

 and a sandy one which is more or less useless. The sand, however, in the neighbour- 



Fig. 2. Diagram showing the arrangement of pearl oysters (large and small) in clumps on the sand 



and singly attached to flat ledges of rock. 



hood of paars often bears considerable numbers of oysters in clumps (fig. 2) adhering 

 to fragments of dead coral, to old molluscan shells, or more frequently to nullipore 

 nodules (Lithothamnion fruticulosum), see fig. 3. 



Such pieces of natural cultch are of enormous importance to the prosperity of the 



