776 BULLETIN OF THE BUREAU OF FISHEEIES 



but little influenced by the slope water in the bottom of the basin near by, but con- 

 tinues through the summer at about the same salinity that characterizes the over- 

 lying stratum in early spring. 



Stellwagen Ledge, at the mouth of Massachusetts Bay, also isolates the deeper 

 water behind it to some extent, as shown by the correspondence between the contour 

 of the bank and the isohaline for 32 per mille on the profile for August, 1922, and by 

 the homogeneity of the deeper water contrasted with the wide vertical range in the 

 shoaler strata (fig. 140). 



Although the deep sink to the west of Jeffreys Ledge is open to the north, 

 where its rim has a depth of about 134 meters, the narrowness of the opening on this 

 side combines with the north-south direction of the axis of the ledge and with the 

 shoalness (48 to 64 meters) and comparative steepness of the latter to hinder the 

 drift of bottom water westward from the open basin of the gulf. Two stations in 

 the trough for August 15, 1913, are especially interesting in this connection because 

 the southern (inner) one of the pair was nearly homogeneous in salinity at depths 

 greater than 50 to 60 meters, though the outer one showed a rapid increase in 

 salinity from the surface downward to a depth of about 90 meters. Evidently com- 

 paratively little interchange was then taking place along the trough in the deep 

 strata. 



Sometimes, however, bottom water of high salinity does drift inward, around 

 the northern end of Jeffreys Ledge, into this trough in much greater volume; as in 

 August, 1914, for instance, when a difference of 0.4 per mille in salinity was recorded 

 between the 40 to 50 meter level and the bottom (station 10252) . 



The relationship between the deep strata of the Bay of Fundy and the basin 

 outside, from which it is separated by a low submarine ridge, is of this same order 

 in summer, with the vertical rise in salinity much more rapid above than below the 

 50 to 70-meter level in the bay (Mavor, 1923), whereas the increase in salinity with 

 depth in the basin oft" its mouth is most rapid near the bottom (fig. 114).'^ A 

 difference in vertical distribution of this sort shows as clearly as does the much 

 higher salinity (34 per mille) of the bottom of the basin that only a small amount 

 of water from the deeps of the latter was then entering the bay. 



The distribution of sahnity has been more uniform, regionally, at most of our 

 summer stations in the inner parts of the basin of the gulf down to a depth of about 

 200 meters. In the western branch, where the superficial stratum is influenced by 

 the dispersal of land water, slight geographic diffei-ences in the locations of the sta- 

 tions and secular changes in the surface currents produce corresponding differences 

 ia the curves for salinity, dependiug on the precise state of the surface water. At 

 greater depths the vertical salting may either continue at an undiminished rate right 

 down to the bottom, as was the case on August 31, 1915 (station 10307, fig. 138), or 

 the deepest stratum (more saline than 34 per mille) may form a homogeneous blan- 

 ket on the bottom, 50 to 60 meters thick, as we found it on August 22, 1914 (sta- 

 tion 10254, fig. 112). 



A much thicker and considerably more saline (35 per mille) layer had blanketed 

 the bottom of the southeastern part of the basin a month earlier that summer (sta- 

 tion 10225, fig. 131), but with the salinity increasing rapidly with depth in the 



"Stations 10097 (August, 1913), 10246 (August, 1914), and 10304 (August 6 and 7, 1915). 



