OYSTER CULTURE IN AMERICA. 791 



7. The determination of the density of the water, with 

 special reference to the question of displacement of the 

 salt water by the fresh water from adjacent streams and 



rivers.' 



The Superintendent also desired that the examination 

 should at first be confined to a limited area, and made 

 exhaustive. Subsequently the investigation was to be 

 extended, as far as the means at the disposal of the Survey 

 would permit. 



The instructions were received on the 3rd August, 

 1878. On the 7th of that month the vessel sailed from 

 Baltimore, Md., to execute them, and the party remained 

 actively in the field until the i5th October, when the 

 season closed. As the investigation was novel in design 

 and execution, and as the difficulties encountered by the 

 party were mainly due to the absence of all experience and 

 previous exertions in the same field, I have thought it best 

 to preface the account of the results of our labours by a 

 short description of the methods employed in making the 

 several determinations required by my instructions. 



METHOD OF CONDUCTING THE INVESTIGATION. 



The examination of the beds was carried on in the 

 following manner : 



DELINEATION OF THE BEDS. 



The services of an oysterman of experience, and who 

 was well acquainted with the localities of the different 

 beds, was first obtained ; the vessel w r as then anchored in 

 such a position as to enable her use as one of the points 

 for angling upon, and her position carefully fixed by sex- 

 tant angles, upon all points recognizable upon the chart. 

 At the same time angles were taken upon any object that 

 might be useful subsequently in fixing positions, either of 



