1922] MADRAS PEARL FISHERIES I 5 I 



ground. Equally significant is the fact that on rougher ground and 

 on areas where bulky cultch occurs, no depredation whatever took 

 place. From this I infer that the presence of fragmentary material 

 is a safeguard against rays; they are unable to differentiate 

 between oysters and rubble when feeding, and when the latter 

 is present, mastication being prevented, the rays find the ground 

 unsuitable and move away. 



Hence the cultching of the Tolayiram Par would serve two 

 purposes of vital importance ; it would give additional and much 

 needed holding ground to oysters and would tend largely to 

 diminish the damage liable to result from the inroads of rays. 



Much more sediment is held in suspension in the water on the 

 Indian banks than in the case of the Ceylon banks. I do not how- 

 ever consider that this exercises any greatly deleterious effects 

 upon oysters on the outer banks of the central and southern 

 divisions ; on the Kilakarai banks the profusion of muddy sedi- 

 ment is excessive, as it also is on some of the inner of the more 

 southern banks, and in such places we cannot expect any spat-fall 

 ever to reach maturity. From the mouths of all the rivers along 

 this coast great amounts of mud are poured forth annually and 

 this in conjunction with the growth of new fringing coral reefs 

 along the shore, each successive one further seaward than its 

 predecessor, causes encroachment upon the sea. The old pars are 

 thus brought more within the harmful influence of river sediment. 

 The process is an exceedingly slow one and the danger to the beds 

 appears greater on paper than it is in reality, even though we 

 know that Korkai, the Kolkhoi of the Grasco-Romans of 1,800 years 

 ago, and the great pearling centre of that day, is now several miles 

 inland, and its successor, Kayal, converted as well from a flourish- 

 ing seaport into an inland village. 



Again while the presence cf so much sediment is harmful, at 

 least to the inshore banks, it has beneficial effects upon the pros- 

 perity of the chank-beds, which flourish most vigorously wherever 

 there is a plentiful admixture of mud with the sand, especially if 

 there be much organic matter present, as happens off the mouths of 

 rivers. 



To this great abundance of mud is due the superior richness of 

 the Tuticorin chank-beds over those in the neighbourhood of the 

 Ceylon Pearl Banks, where the sand is composed largely of a 

 coarse clean quartz-grit. 



