OYSTER BEDS OF MOBILE BAY. 
327 
execution of the survey there were erected seventeen of these tripod signals, which 
with dag pole were about 20 feet high. These signals, together with known triangu- 
lation points, such as Mobile Bay Light, Fort Morgan Light, Sand Island Light, 
and others, enabled us to locate ourselves in any part of the bay at all times. 
Most of the signals were erected by Mr. James A. Smith, whose general executive 
ability and long experience in hydrographic surveying were of much value in the 
successful execution of our work. 
The method of procedure was generally as follows : After having obtained from the 
local oystermen the approximate position of the oyster beds, or reefs” as they are 
locally designated, the locality in the immediate vicinity was subjected to a careful 
examination by running a series of sounding lines covering the entire area. The 
soundings were taken with a pole whenever the depth permitted it. In addition, a 
chain let off from the bow of the tug and dragging along the bottom was found to be 
of great assistance, the lack or the intensity of the rambling of the chain invariably 
indicating whether it was passing over mud, sand, broken shells, or live oyster beds. 
As often as necessary the position of the boat was fixed by measuring with sex- 
tant the angles between three or more of the triangulation signals. In this manner 
a sufficient number of points marking the outline and extent of the oyster beds 
were determined. Frequent stops were made and samples of the bottom dredged up 
and examined. 
During most of the time that the survey was in progress, tidal observations were 
made in the bay at Sliellbank Bayou. From these observations a mean low-water 
plane was established, to which the soundings shown on the chart have been reduced. 
In determining the density of the water, United States Fish Commission hydro- 
meters Nos. 7114, 7164, 7145, and 7152 were used. They are of the type described in 
Appendix 10, Coast and Geodetic Survey Report for 1874, except that in those now 
used the centigrade thermometer has been substituted in place of the Fahrenheit and 
the hydrometer graduated to give densities referred to pure water at 4° C. 
In obtaining the water from places other than the surface the Haskell hydrophore, 
or water- speci men cup, was used and found to give satisfaction. This instrument, 
devised by Mr. E. E. Haskell, formerly of the Coast Survey, enables one to obtain the 
specimens of water with the certainty that the water brought up comes from the level 
to which the instrument had been lowered. 
The examinations were made from February 10 to March 24, 1894, and December 
1 to 7, 1894. The following is a summary of the field work : 
Number of days on which field work was done 23 
Number of days during which field work was prevented by stormy weather and 
other causes 26 
Number of soundings and determinations of bottom 3, 220 
Number of angles taken 1, 400 
Number of density observations 394 
Number of temperature observations 591 
Number of signals erected 17 
Number of days of tidal observations 23 
Area examined roughly, square miles 200 
Area examined more minutely, square miles 50 
Area of natural oyster reefs located, acres 3, 105 
Number of miles of sounding lines and determinations of bottom 177 
Number of specimens collected 35 
