OYSTERS AND METHODS OP OYSTER-CULTUEE. 331 



transverse crossbars b h, of figs. 1, 2, 3, and 4, npon which the permeable diaphragm 

 rests. Fig. 1 represents the trunk A secured within a pair of quadrangular frames, 

 F F, and partially in sectional elevation in place in the trench or canal leading from 

 the pond to the open water; fig. 2 represents the construction of the end of the trunk 

 next tlie open water, and fig. 3 that of the end next the pond, while fig. 4 shows the 

 trunk as viewed from above. 



On the crossbars b b a, single screen of galvanized wire cloth, W, fig. 1 (galvan- 

 ized after it is woven), is superimposed, having meshes, say, one-half iuch in diameter; 

 upon tlie wire screen a layer of guuny-cloth, C, figs. 1 and 4, is laid, upon which a 

 layer of fine, clean sand, S, is spread evenly from one end of the trunk to the other. 

 The end board e, extending halfway up at the outer end of the box, runs up jiast 

 the level of the wire and cloth to confine the sand at that extremity, as shown in 

 fig. 2, while the sand is confined by the board i at the other end of the trunk next 

 the pond, as shown in fig. 3. The wire clotli and bars b b constitute the support 

 for the sand as it lies upon the gunny-cloth, which is supported in turn by the wire 

 cloth or screen JV. This is essentially the construction of the filtering apparatus in 

 which the layer of sand, <S', is at all times accessible, so that it can be removed if it 

 becomes clogged with ooze carried in by successive tides under the gate G, figs. 1, 

 2, and 4. This layer of sand can also be increased or diminished in thickness so as 

 to strain the inflowing and outflowing water more or less elfectually, as may be 

 desired, or in order to more or less efiectually prevent the escape of any eggs or 

 embryos of oyster which may be developing within the pond and wafted to and fro 

 by the ebbing and flowing currents which are carried in and out of the pond through 

 the diaphragm by tidal action. The gunny-cloth, C, fig. 4, may possibly be replaced 

 by, first, a layer of coarse gravel, then a layer of finer gravel superimposed upon 

 that, which would prevent the fine sand from sifting through the supporting wire 

 screen W. Gravel would be more durable tlian gunny-cloth or sacking, which, like 

 all other textile fabrics, will rot if immersed in salt water for a few weeks. In 

 practice, however, a mode of getting overall such difficulties would soon be devised. 

 A coarse sacking to be used for the purpose might be saturated with a drying oil or 

 with tar diluted with oil of turpentine, which when dry Avould act as a preservative 



of the material, but not cause it to become impervious. 



j> # * * * * # 



When the trunk A is put in place (which should be done before the water is let 

 into a freshly excavated pond, and also before the water is let into the trench from 

 the; sea end), it should be securely placed in position and the earth tightly rammed 

 in along the sides so as to prevent auy sea water from finding its way into the pond, 

 except such as passes through the filtering diaphragm. It is also unnecessary to 

 insist that the trunk be constructed in such a way that it will be practically water- 

 tight, and not liable to leak between the planks or at the corners. The wire cloth, 

 sacking, or gravel, and sand having been got into place, and when complete forming 

 a stratum having a total thickness of 5 or 6 inches, the operator is ready to cut 

 away the barrier at the sea end of the trench and let in the water. 



If then the trunk A has been let down into the trench deep enough the sea level 

 at low tide ought to be somewhat above the upper edge of the board e. The water 

 will tlien, as the tide rises, flow back over the sand as far as the board i, and will per- 

 colate through the diaphragm into the space /, under the latter, and so find its way 

 into the ponil. After a day or so the pond will be filled with sea water which has 

 practically been filtered, and filtered more or less effectually in proportion to the 

 thickness of the stratum of sand constituting the diaphragm. After the pond has 

 once been iilled with the rise and fall of the tide in the open water the level of the 

 latter and that in the pond will be constantly changing ; in other words, when the tide 

 is ebbing the water level in the pond will be higher than that of the water outside, 

 as in fact represented at wl and tl in tig. 1. Under these circumstances there will 

 be a supjdy of water flowing out through the under division / of the trunk A, up 

 through the sand and out over its surface through the outlet O under the gate G. 

 After the ebb tide is over and flood tide begins these levels will be reversed and wl 



