BOTTOM AND WATER SPECIMENS. 



The specimens of bottom were obtained from large amounts of sand, mud, and gravel, brought 

 up by the dredge or tongs. When the bottom was hard, an ordinary bottom specimen cup screwed 

 into a 25-pound lead was used, but over the solid beds, or where the bottom was of hard sand, it 

 was very difficult to obtaiu anything, either with dredge, tongs, or lead. 



The specimens of bottom water were secured by using the drop-water cylinders, which are 

 fully described by Lieut. Frederick Collins, U. S. N., Assistant Coast and Geodetic Survey, iu his 

 report on the "Densities of the Waters of Chesapeake Bay and Tributaries," published by the 

 Survey in the Eeport for 1877, Appendix No. 14. The cylinders worked as successfully as during 

 the previous summer, and there can be no doubt that the water brought up by them was a speci- 

 men of that at the bottom. All the specimens were tested with a hydrometer, and the readiugs 

 reduced to those at the standard temperature of 60° F. 



SUBSTRATUM OF BOTTOM. 



The character of the bottom beneath the surface was roughly ascertained by means of an iron 

 probe, 5 feet in length, attached to a long wooden staff. The probe was thrust as far as possible 

 into the bottom, and the composition and character of the substratum estimated, the different 

 constituents, whether sand, shell, mud, clay, or gravel, being easily recognized. Owing to the 

 velocity of the currents, the speed of the vessel, and the difficulty of handling a long staff, but few 

 determinations of the character of the substratum were made when the depth of water was greater 

 than 3 fathoms. 



CURRENTS. 



The currents were measured by a current meter, or by an ordinary chip log, though the latter 

 was not used frequently. The position of the stations for measuring the current was left to the 

 discretion oi the officer of the boat, but a sufficient number have been occupied to show the set and 

 strength of the main current, and the effect on them of the prevailing winds. 



NUMBER OF OYSTERS TO THE SQUARE YARD. 



The number of oysters to the square yard was found by using a ground log in connection with 

 the dredge. From the information derived from experienced oystermen, and from our own exam- 

 ination of those beds that had been dredged, I was of the opinion that a dredge, when of consid- 

 erable size, and dragged slowly, usually collected everything met by it in its course. Considering 

 that, at the suggestion of Mr. Eice, I used a small ground log to measure the distance traveled by 

 the dredge. As that instrument was exactly one yard in width, it was concluded that it swept 

 approximately clean one square yard for every linear yard it passed over. The ground log consisted 

 of a small lead, a few ounces in weight, attached to a light line 1,000 feet long; between the lead 

 and line was a length of copper wire of 20 feet; the line was marked every 5 fathoms and kept in 

 a tub or on a reel ready for use; the lead was conical in shape to prevent its catching on shell 

 clusters. When the dredge was thrown over. the lead was dropped to the bottom and allowed to 

 remain there, the line running out freely until the dredge was lifted off the bottom, when the line 

 was stopped and the number of fathoms run off with the number of oysters in the dredge recorded. 

 The dredge was not allowed to remain on the bottom long euough to be filled, consequently none 

 of the oysters were lost from its inability to receive them. 



Though the foregoing method was imperfect it was the best that could be devised under the 

 circumstances, and a similar method was used by Moelius in ascertaining the number of oysters on 

 the Schleswig-Holstein bed. From the very small number of oysters to the square yard, as shown 

 by the method, from the small number of oysters it assigns to the beds, and from comparison of 

 the latter number with the number known to have been taken off the beds during our stay in the 

 sounds, it is evident that the "number to the square yard" given in the records of the work are 

 useful for comparison only; for in almost all cases the number of oysters given to the square yard 

 must be considered as far below the real number. For instance, the number of oysters on the 

 beds in Tangier Sound, south of Jane's Island Light-House, was estimated from the data of the 



