52 



OYSTER BOTTOMS OF MISSISSIPPI SOUND, ALA. 



The top of the bench mark accorded with reading 3.65 on the 

 scale of the staff gauge. 



The tides in this region, as in general on the Gulf coast, are small, 

 averaging from 1 to 1^ feet in height, but reaching 2^ feet under cer- 

 tain conditions of wind, etc. 



No special observations were made of the velocity of the currents, 

 but in general they are sufficient for the transport of food and water 

 to the oysters in all places covered by the survey. 



SALINITY OF THE WATER. 



As is well known, the quantity of salt in the water is an important 

 factor m determming the growth and character of oysters. Neither 

 fresh water nor that of full oceanic saltness is suitable for the oyster 

 itself, and, moreover, the degree of saltness often determines the pres- 

 ence, absence, or relative abundance of such oyster enemies as the 

 drill or borer. During the survey upward of 300 specific-gravity 

 observations were made to determme the condition of the water in 

 respect to its content of salt. Three tests were made daily on the 

 Fish Hawk, and m addition observations were taken on the oyster 

 beds and in their immediate vicinity. The following table is a sum- 

 mary of all of the ship's observations, supplemented by some of those 

 taken on and near the unportant natural beds : 



Specific Gravity of Water at Various Places and Dates. 



