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 GramMpuUS 
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 that 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, 7. ¢., 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, 
. 
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