THE OYSTER. I 35 



out, and the bottom once more pounded while it is 

 is drying. If the bottom is sandy it is necessary to 

 render it impermeable, so that the water may not leak 

 out, and also to consolidate it. To accomplish this 

 the ground is worked over and covered with a layer 

 of coarse gravel or fragments of shells, upon which is 

 laid a layer of clay lo to 12 inches in thickness, which 

 is then treated as already mentioned for the marly 

 bottoms. Surrounding the ground thus prepared are 

 built the dikes which are to retain the water in the 

 basins. These should be at least six feet in height 

 above the bottom, so that a depth of water of from 

 four to five feet can be maintained over the oysters, 

 not all the time, as generally a depth of from a foot to 

 eighteen inches is best, but when it is very cold, to 

 prevent the injurious effects of frosts, and when it is 

 very warm, to prevent the water becoming too salt 

 from evaporation. These dikes should be constructed 

 very solid, so as to resist the great pressure which is 

 brought to bear upon them at every spring tide, and 

 should also be covered upon the inside the same as 

 the bottom, with a layer of clay or hydraulic cement, 

 so as to prevent all leakage, which is very disastrous 

 in these basins, since the water is renewed only at 

 long intervals. The upper portion of the larger of 

 these dikes should be sufficiently broad and firm to 

 permit the workmen to traverse it easily and with- 

 out danger, for all the necessary manipulations of 

 working and inspection. If the height of the ground 

 permits, these claires can be formed by excavating in 

 the solid earth, in which case it will only be necessary 

 to cover the slopes of the banks with a layer of stones 



