of the Fishery Board for Scotland. 



351 



Methil. This region deserves to be more fully studied. The curves for 

 bottom salinity show that tidal change extends only from the river to 

 Station IV. (off Blackness), and the rate of change is everywhere similar 

 to that for surface salinity, but more uniform. As far as Station VII. 

 (Inchkeith), surface salinity is always, but decreasingly, less than that at 

 the bottom, and seaward of Inchkeith the surface water is scarcely 

 at all fresher than that beneath, until some little distance beyond the 

 mouth of the Firth, where the freshening action of the Tay appears super- 

 ficially. Between Inchkeith and Alloa the difference in salinity between 

 bottom and surface water is about equal to that at the same level between 

 stations from 4 to 6 miles apart. For instance, bottom water at Grange- 

 mouth is about as salt as surface water at Blackness, and bottom water 

 at Blackness as salt as surface water midway between Queensferry and 

 the Oxcar Rock. 



The variations to which the salinity at any one point are subject appear 

 from Table I. ; but we may take as a concrete example the state of 

 matters in November 1884, when, after long-continued heavy rains, the 

 Firth was fresher than at any other time during the range of these observa- 

 tions. The figures for the 10th and 11th of that month are given in Table 

 II., along with the average at each station for the particular phase of tide. 

 Figure 4 (Plate XXII.) shows these results graphically. The bottom 

 salinity was entirely unaffected by the flood. 



Table II. — Salinity of Surface Water. 

 Station, I. IT. III. IV. V. VI. VII. VIII. IX. X. 



Nov. 1884, 0-000 0-475 1-968 2-337 2-652 2-751 3-246 3-318 3-373 3-409 



Mean, 0-833 1-532 2-577 2 972 3'142 3-220 3-342 3'373 3-388 3*405 



Difference, 0*833 1*057 0-609 0*635 0-490 0-469 0-096 0*055 0-015 0-004 



Stations VII. to X. were visited on the 10 th, Stations I. to VI. on the 

 11th, and, although the degree of dilution was probably greater on the 

 second day, its effect certainly extended on the first to ten miles seaward 

 of Inchkeith. 



With regard to variation of salinity at different distances from the 

 shore comparatively few observations have been made. The influence of 

 rivers above Queensferry is probably as much felt in the centre as near 

 the margin, because the estuary is narrow there. From Queensferry to 

 the Leven no streams of importance enter on the north shore of the Firth, 

 and the conditions are the same as in the centre. The influeuce of the 

 Leven is inconsiderable, but east of Anstruther a quite perceptible 

 freshening is met with, due to the Tay brackish water coining round Fife 

 Ness. A number of rivers enter on the south side. The Almond at low 

 water runs out to the west of Cramond Island, and freshens the centre 

 of the Firth on the surface, and may even have some effect on the north 

 shore ; at high tide and during the first half of ebb the river passes 

 between Cramond Island and the mainland, carrying fresh water on the 

 surface all along the coast. In fact, at Granton the surface water is 

 fresher at high tide than at low tide for this reason. The Water of Leith 

 appears to have little influence on the salinity, but the Esk, flowing over 

 the extensive sands that lie between Leith and Gullane Ness, produces a 

 very marked effect near shore. There are no data for determining the in- 

 fluence of the rivers entering further to the east. Several trips were made 

 across the widest part of the Firth, from Methil to Morrison's Haven, a 

 distance of 16 miles, in 1885. The mean surface salinities for each 4 miles 

 are given in Table III., and graphically in figure 5 (Plate XXII.). 



Table III. — Salinity of Cross- Section. 

 Position, Off Methil. 4 miles south. 8 miles south. 12 miles south. Off Morrison's Haven- 

 Salinity, 3-383 3*355 3*352 3*348 3*255 



2 Y 



