200 bulletin: museum of comparative zoology. 



depths over the shelf is also to be seen in the profile abreast of Chesa- 

 peake Bay (Fig. 42) ; and it has about the same extent and conforma- 

 tion there as further north, the curve of 35%o rising from the sea floor 

 at about the fifty fathom curve, with fresher water underneath it. 

 But here the water near shore was much fresher dowm to five fathoms 

 than in the preceding profile ; the immediate surface layer fresher than 

 any water we encountered further north, as might be expected from the 

 volume of river water which debouches from the Bay in spring. 

 And though this layer was very thin, the salinity rising from 29.25%o 

 on the surface to 33.5%o on the bottom in ten fathoms at the shore 

 end of the profile, its influence is unmistakable out to the edge of the 

 continental shelf. At the outer end of the profile (Station 10076) the 

 water was saltest at 50-100 fathoms (about 35.4%o), just as at the 

 other deep water stations; below that level salinity decreased very 

 slowly, as it does over the north Atlantic as a whole. 



The change in salinity from north to south over the shelf north of 

 Delaware Bay is illustrated by a profile following the forty fathom 

 contour from Nantucket Shoals (Station 10060) to Station 10070 

 (Fig. 43). Below about ten fathoms there is a general increase in 

 salinity, depth for depth, from northeast to southwest. But the 

 surface water is freshest at the southern end of the profile (32.2%o), 

 saltest at Station 10062 (32.86%o), and fresher once more (32.63%o) 

 over the slope of Nantucket Shoals. 



Salinity in the Gulf of Maine. 



Surface Salinity. Early in July the surface salinity (Plate 2) of 

 Massachusetts Bay, immediately off Gloucester, was about 31.56%o, 

 arise of about .5 since the middle of May (1914b, p. 393), and it was 

 31.9%o off Cape Cod (Station 10057, p. 205) with 32.4%o over the 

 southern part of the basin (Station 10058), and 33%o on the southwest 

 side of George's Bank (Station 10059). When we returned to the 

 Gulf of Maine a month later, the water was slightly salter along the 

 eastern shore of Cape Cod (32.05%o, Station 10085; 32.09%o, Station 

 10086), while a greater increase of salinity had taken place off Glouces- 

 ter (to 32.03%o). And by the 25th of August it had risen to 32.16%o 

 in the mouth of Massachusetts Bay (Station 10106). The water 

 immediately abreast of the Bay and along Cape Cod (Plate 2) was 

 32-32. 2%o, the curve for the latter value swinging eastward from the 

 mouth of Vineyard Sound, and then northerly, toward Penobscot Bay. 



