BULLETIN OF THE UNITED STATES FISH COMMISSION. 23 



is intended that the apparatus is to be operated. The figures also give 

 a very good idea of how the diaphragm and trunk are to be constructed ; 

 the first four figures being drawn to a common scale of one inch to three 

 feet. 



THE POND. 



In Fig. 5 I have represented a pond in vertical section to which a 

 diaphragm D, of the form above described, has been adapted and fitted 

 into the connecting trench T leading to the open water B. This pond 

 P, it is supposed, has been dug out of a salt-marsh of the type so com- 

 mon adjacent to waters well adapted to the cultivation of oysters along 

 the shores of the shallow bays and sounds of the Eastern United States. 

 The French are in the habit in some places of walling up or facing the 

 sides of the rearing ponds with cement or tough clay, or even building 

 the sides of stone. That breeding ponds should in some way have their 

 sides made firmer when dug out of a mere salt-marsh, would hardl}' be 

 doubted by any one, because such an arrangement is an important safe- 

 guard against the bad effects of rains and frost in causing the sides of 

 the pond to crumble and wash down into the bottom as mud and sedi- 

 ment, thus tending to cover and smother the oysters at the bottom. It 

 cannot be questioned either that in case the pond is excavated on salt- 

 marsh lands, which are often merely large accumulations of sediment- 

 ary deposits consisting of ooze or mud which has been piled up along 

 the shore by the waves during ages, the bottom should be covered with 

 at least a coating of loam or clay, to, in a measure, interceijt the poison- 

 ous marsh gases coming up from below. To render such an artificial bot- 

 ^tom firmer, old oyster shells scattered thickly over the bottom would ren- 

 der the loam or clayey sand firmer atid less liable to give way under the 

 soft and yielding bottom, which is really in a viscous, yielding condi- 

 tion at a depth of a few feet, so much so that when a horse or other 

 heavy animal walks over the surface the thick turf usually vibrates up 

 and down perceptibly on the soft stratum below. In such situations 

 it is therefore plain that a preparation of the bottom of the pond excii- 

 vated would be necessary. In other situations, such as, for example, in 

 the vicinity of Point Lookout at the mouth of the Potomac River, where 

 there is a firm clay bottom near the surface, oyster ponds might be ex- 

 cavated and a bottom found which would need no preparation, and at 

 a level which would require no more digging to get below tide-level 

 than in the salt-marshes adjacent to Chincoteague Bay. 



The deposition of sediment which is held in suspension by the ebbing 

 and flowing tides on the bottom of ponds has been ver^' troublesome to 

 the French in the conduct of i)Oud-culture, and it will be one of the dif- 

 ficulties to be overcome in this country', as a very cursory glance at a 

 few facts will readily show. Here, as well as there, ooze is very rapidly 

 deposited on the bottom of oyster coves or confined natural areas, which 

 in this country represent rudely, in some cases, the "claires" in which 



