262 RATE OF OYSTER-GROWTH. 



of materials of any of the great classes of rocks, are- 

 naceous, argillaceous, or calcareous, provided they con- 

 tain 



" 3. More or less of a fine, flocculent, highly hydrated 

 silt, rich in organic matter, which indicates that diato- 

 macese, rhizopoda, infusoria, and other minute creatures 

 abound. ' 



" 4. That the character and abundance of such small 

 organisms in a locality seems to be the true test of a suc- 

 cessful oyster-ground. 



" 5. And, lastly, that although oysters do undoubtedly 

 assimilate copper from water where mine-water contain- 

 ing traces of that metal flows into the sea in the neigh- 

 bourhood of the oyster-beds, the copper is .chiefly, if not 

 exclusively, confined to the body of the oyster, and does 

 not appear to reach the mantle or beard ; that the so-called 

 green oysters of Essex, Maremies, and other places, on the 

 other hand, are green-bearded, and contain 110 copper, nor 

 can the most minute trace of copper be detected in the 

 soil of the oyster - grounds where such green -bearded 

 oysters are produced." 



The ratio of oyster-growth, an important consideration 

 in connection with oyster-farms, is thus estimated by a 

 very accurate and judicious writer : * 



While in the spat state, a bushel measure will contain 

 25,000 oysters. The spawn, when two years old, is called 

 brood, and while in this condition a bushel-measure will 

 hold 5500. In the next stage of growth, oysters are 

 called ware ; and it takes about 2000 of them to fill the 

 bushel. In the final stage a bushel contains about 1500 



* Bertram, "Harvest of the Sea," pp. 367, 368. 



