Explanation of the Plate, 



descend into the aperture, and as it is important that the marsh 

 should be drained as nearly down to low water mark as possible, 

 it will be proper to observe, that this trunk, whatever may be 

 its width or depth from 1 to 2, fig. 1. should not be placed with 

 the interior surface of the top, more than six inches above tiie 

 ordinary low water mark ; because there should be room left for 

 the water, pouring into the aperture from the marsh, to clear 

 itself over the valve, which floats on the low tide, or descend?, 

 on the tides receding so much, to the bottom of the trunk. The 

 height from low water mark to the top of the trunk, being so 

 much deducted from the depth to which the marsh can be drain- 

 ed by the trunk ; it should, therefore, to pass the greatest quan- 

 tity of water, be made broad in proportion to its depth, so as to 

 allow of a large aperture, and be placed as low as is compatible 

 with its object and utility. 



If one trunk should not be adequate to the necessary draining, 

 two or more may be inserted, and as the tides are irregular, 

 and often fall lower than common, it might be well to place one 

 trunk lower down on a level, with such uncommon low tides, so 

 as to take advantage of the greatest degree of draining which 

 such tides would aftbrd." 



i 



