822 OYSTERS, AND ALL ABOUT THEM. 



unassisted causes, their great increase in area during the 

 last thirty years must be assigned to other agents. 



The diminution of the number of oysters may be 

 effected by several causes. An increased deposit of earthy 

 or vegetable matter upon the beds would, if in sufficient 

 quantities to bury the oyster, effect the destruction of both 

 old and young ; but no such deposit has been noticed, nor 

 could it well occur without showing its presence in other 

 ways, principally by changing the channels and causing 



shoals, and no such changes have occurred 



A change in the character of the water and bottom, which 

 would probably follow a change of channel, and might 

 occur without such change, might, by depriving the animals 

 of their proper food, cause their deterioration and destruc- 

 tion ; but such a change, though it would certainly diminish 

 the number on the beds, would do so suddenly, and the 

 evil effects would be noticed in the oysters remaining, their 

 quality and flavour, indeed their vitality, being very much 

 impaired. No such impairment has been observed, how- 

 ever, the oysters being larger and finer than when the beds 

 were first discovered. That fact alone will eliminate many 

 quantities from the equation, for any natural cause injurious 

 to all the oysters on the beds would be evident at once by 

 an examination of those found at present. If, however, 

 the destruction or non-production of the necessary number 

 of young is accomplished by means that are not harmful to 

 the mature oyster, a cause is discovered for the diminution 



of all, in harmony with the existing facts The 



destruction of the young . . by the falling of the 

 " spat" on unfavourable grounds, the prevalence of heavy 

 freshets, . . . the ravages of various enemies 

 all these causes have been in operation continually since 

 the first formation of the beds, and the animals have sur- 



