112 THE OYSTER. 



case the shells should not be uniformly distributed, 

 but placed in piles or ridges. If these ridges are 

 properl}' arranged with reference to the direction of 

 the current, they will produce secondary currents, and 

 will thus cause the soft mud to flow off between them. 

 In this way any bottom which is bare or nearly bare 

 at low tide, and which is exposed to the winds and 

 waves, may in time be swept nearly clear of mud. 

 Each time the tide comes in the mud is stirred up and 

 suspended in the water, and as the tide ebbs this sus- 

 pended matter is swept into the channels between the 

 obstructions and is carried away. Shells are very 

 effective as spat-collectors. Shell wharves built out 

 into deep water, so as to catch and turn the passing 

 current, are often found to be covered with young oys- 

 ters at all stages of growth and in good condition for 

 planting. 



The month of June is usually the best time for 

 shelling the bottom. The early part of the month for 

 warm seasons and shallow water, and the end of the 

 month for cold springs, or for deep water. The 

 quantity of shells varies according to circumstances, 

 but in most cases looo bushels to the acre are not 

 too many. 



In shallow waters, where the shells are uncovered at 

 low tide, they may be examined to pick out, for distri- 

 bution upon the planting grounds, those which have 

 young oysters upon them, but in deeper waters the 

 shells must be picked up with tongs or dredges, or 

 they may be strung upon wires and sunk in deep 

 water on suitable frames. 



The chief objection to the use of shells is that the 



