84 Our Food Mollusks 



firm by a covering of shells or of sand and gravel, and 

 that this' covering need be only a few inches in thickness. 

 Shifting sand on which oyster parks are built is also 

 held in place by a layer of clay. 



In the simple basins illustrated in Figure 20, oysters 

 of sufficient size are spread over the bottom and left to 

 grow. At low tide they remain covered, and may thus 

 continue to feed until a new supply of water comes with 

 the flood tide. They are also protected from the sun of 

 summer and the frost of winter seasons. Not all sedi- 

 ment will drain away, even though the gates are opened 

 frequently, and though the bottoms have been arched 

 from center to margins. When a quantity of mud has 

 collected, oysters are removed from one basin to an- 

 other until the bottom has been cleaned. 



But the entire process of removing young oysters 

 cannot be carried on in basins as simple as those shown 

 in the illustration. So much mud is deposited that small 

 oysters would be smothered. These seed oysters are 

 from half an inch to an inch in diameter, and must be 

 protected from sediment until they are much larger. 



This necessity for the protection of the very young 

 has led to the construction of racks or boxes designed to 

 suspend them above the bottom. It is very important 

 also to insure a free flow of water within the boxes, so 

 these are made with narrow wooden sides, the tops and 

 bottoms being constructed of galvanized wire netting. 

 The top netting is fastened to a wooden frame provided 

 with hinges, or so fitted that it may be lifted off. The 

 box is then suspended a few inches above the bottom on 

 stakes. 



Such boxes are represented in Figure 21. Evidently 

 they are roughly and cheaply made, but a large number 



