70 bulletin: museum of comparative zoology. 



fathom curve from JNIt. Desert Island to the southwestern end of the 

 Grand Manan Channel. 



Over the central part of the Gulf, including Piatt's Bank as well as 

 most of the 100-fathom basin, the salinity at twenty-five fathoms was 

 above 33%. But the curve for that value runs off shore far enough to 

 exclude the whole of Jeffrey's Bank, thus suggesting the southerly 

 swing of the curve of 32.4 on the surface, though not exactly duplicat- 

 ing it. It then turns northward toward the coast, including in its 

 sweep the whole of the eastern branch of the deep basin, as well as 

 part of the coastal bank off Nova Scotia. The saltest water found at 

 this depth was not at Station 31, as was the case on the surface, but 

 at Station 28 (33.4). In spite of this discrepancy, however, the 

 twenty-five fathom level corresponds to the surface in the presence of 

 intrusions of comparatively fresh water off Cape Ann and off the mouth 

 of the Penobscot, and in the fact that the saltest water was over the 

 eastern edge of the 100-fathom basin. 



Saliniti/ at fifty fat Jioms. — The curves at fifty fathoms (Plate 3) show 

 the same influx of fresh water off Massachusetts Bay as do the charts 

 for twenty-five fathoms and for the surface, though to a less degree. 

 But I must point out that the charts for the different levels are not 

 strictly comparable with one another in this region, because almost 

 the whole of Massachusetts Bay, as well as the long ridge formed by 

 Jeffrey's Ledge, running some forty-five miles northeasterly from Cape 

 Ann, is shallower than fifty fathoms. The salinity over most of the 

 Gulf at this level was above 33. But along the shore from Cape Ann 

 northward, in the trough west of Jeffrey's Ledge and as far as Monhe- 

 gan, the salinity was lower, between 32.8 and 33. ; and in the isolated 

 basin in the mouth of Massachusetts Bay (Station 2), the salinity 

 at fiftv fathoms was 32.8. The curves at this level hardlv show the 

 southerly swing off the mouth of Penobscot Bay so pronounced at 

 higher levels, the curve for 33 running parallel to the coast, along the 

 fifty fathom line, from Matinicus Rock eastward. This fact, of course, 

 shows that the fresh water from the Penobscot had little or no influence 

 at this depth, although its presence was evident nearer the surface. 

 Over the eastern branch of the 100 fathom basin the fifty fathom salin- 

 ity was above 33.6, the highest being 33.8 at Station 28, while at 

 Station 31, so salt at the surface, the fifty fathom reading was only 

 33.5. The lowest salinity at this depth was in the Grand Manan 

 Channel, 32.65, practically the same as at the surface. 



Bottom salinity. — ^ The bottom salinities of the Gulf of ]Maine 

 (Plate 3) are largely dependent on depth, for, as we have seen, there 



