Report of the Board of Shell Fish Commissioners 191 



soft mud, soft mud, sticky sandy mud, hard muddy sand, hard 

 clay, very hard sand, shifting sand, and gravel. 



A probe with which to ascertain the depth of the bottom and 

 the composition of its deeper strata has not been used because 

 of the necessity for speed in making the examinations, but accu- 

 rate tests of the hardness of the bottom of a few characteristic 

 natural oyster grounds are being made, with an apparatus de- 

 signed for the purpose by Dr. H. F. Moore, in order to establish 

 a standard by which to gauge the fitness of barren bottoms for 

 oyster culture. 



Depth of Water. 



The depth of water is taken at each sounding and at the 

 examination stations. As the depth varies with the tide at any 

 point, each observed depth is reduced to mean low-water level 

 before it is plotted on the charts. The Coast and Geodetic 

 Survey, having established "bench marks," marking the level of 

 mean low water, at several points on the Chesapeake, the reduc- 

 tion of the soundings is easily made. A daily record is kept at 

 some point, such as a light house, within the region being sur- 

 veyed, showing the variation of the tide at every hour, from 

 the level of low mean water. A record of the exact time when 

 all soundings are made is also kept on the survey and examina- 

 tion boats. By adding (or subtracting) the variation of the 

 height of the tide from the level of mean low water, observed at 

 the time the soundings were made, to the depth of each sound- 

 ing, the actual depth of each sounding at mean low water is 

 obtained. 



These soundings are not all published at this time, but the 

 charts, published by the Coast and Geodetic Survey, showing 

 the results of the survey, have the 6-foot, 18-foot and 30-foot 

 curves plainly delineated. The average depths of water over 

 each of the natural bars are given in the part of this report in 

 which the oyster grounds are discussed. 



