BIGELOW: COAST WATER EXPLORATION OF 1913. 233 



the surface. The correct explanation is that the movement of the 

 surface waters over the shelf is chiefly a series of great eddies, receiving 

 water, on the one hand from the Gulf Stream off shore, on the 

 other, from the land. The accompanying chart (Plate 2) shows an 

 attempt to reconstruct the surface currents, for the summer months; 

 but so intricate is the problem, and so scanty the reliable information 

 yet at hand, that it is only tentative. 



It is even more difficult to reconstruct the movements of the sub- 

 surface water, because we must rely almost wholly on the Grampus 

 observations. These current measurements do not prove any domi- 

 nant flow on the bottom north or south of Delaware Bay (p. 230), and 

 it is questionable whether any general flow can be deduced from them 

 south of Long Island. But salinity, density, and temperature show 

 that the bottom and intermediate waters over the shelf are far from 

 being stagnant, though their movements, other than tidal currents, 

 are probably slow as compared with the surface currents. 



The density profile across Nantucket Shoals does not suggest any 

 flow into, or out of the Gulf of Maine in this region at any depth; 

 nor does the density of the bottom water of the Gulf suggest any 

 influx of ocean water from the zone between fifty and 130 fathoms, 

 via the Eastern Channel. 



The seaward dip of the density curves south of Nantucket together 

 with the cold tongue (p. 165) shows that the bottom water was flowing 

 seaward down the shelf from the fifty fathom curve, indenting into 

 and mixing with the ocean water over the slope (Fig. 10) ; and this 

 agrees with the salinity curves. But south of Long Island, the fact 

 that the density curves are just the reverse, together with the sudden 

 rise of salinity immediately below the cold tongue, suggests tha,t here 

 the ocean water was sinking, obliquely, toward the land below the 

 cold, fresh coast water. And to judge from the densities, a similar 

 movement of water must have been taking place over the outer part 

 of the shelf off Barnegat also. 



The salt tongue which indents the fresher coast water in the mid- 

 depths over the continental shelf between Delaware Bay and Chesa- 

 peake Bay (p. 198) is as interesting as the cold tongue off Long Island. 

 Just south of Delaware Bay, there seems to have been an actual move- 

 ment of surface water toward the coast (Fig. 60), gradually mixing with 

 and sinking below the much fresher, hence lighter coast water. At 

 twelve fathoms, i. e., the axis of the salt tongue, the density was uni- 

 form, east and west; below twelve fathoms, the density gradient 

 dipped from land to sea. Thus ocean water must have been coasting, 



