232 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
near the eastern edge of the Bank. And although the observations are 
insufficient for any definite mapping of currents in a region where the 
tides are so strong, it is certainly suggestive that this northerly trend 
near the eastern end of the Bank corresponds with the salt tongues 
which were found in the eastern side of the Gulf in both 1912 and 1913. 
But an easterly and northeasterly movement of water on the Shoals 
and over George’s Bank, does not mean that there is a general easterly 
long-shore current, both because there is no dominant drift at Nan- 
tucket light-ship (U. S. Coast Pilot, 1912, p. 10), and because the 
various records agree in crediting the coast waters south of Marthas 
Vineyard as a whole with a westerly, southwesterly, or northwesterly 
drift. In short, present indications point to the conclusion that the 
movements of surface water are tidal there, in the form of an irregular, — 
perhaps intermittent eddy, which receives greater or less accessions 
of Gulf water on its northern side, and of ocean water along its south- 
ern and southeastern edge. The latter is an important factor in 
summer when it must influence hydrographic conditions on the banks 
profoundly, just as it does over the continental shelf further west — 
(p. 198). And it exerts an unmistakable influence on the oceanog- — 
raphy and plankton of the Gulf of Maine as well. 
The outrush of comparatively fresh water from Long Island Sound, 
shown by the salinity curves, is substantiated by current records; 
and the northwesterly current over the forty fathom curve south of 
Block Island, represented on the current’ chart in the Coast Pilot, 
corresponds with our current records over the same part of the shelf 
a few miles further west. But the changes which take place in the | 
surface salinity of this region at different seasons show that it is by 
no means a permanent phenomenon, probably being reversed in __ 
spring by the outrush of shore water. 
The combined evidence of the various records of ocean currents, | 
our own included, points to the conclusion that the dominant drift 
over the continental shelf, south of New York, is to the southwest; | 
and this is certainly the prevalent opinion of practical navigators and | 
hydrographers. But it does not necessarily follow that this drift is 
a simple, long-shore current, as has so often been suggested. On the | 
contrary, surface salinity shows that it is interrupted by outpourings | 
of comparatively fresh water off the rivers and bays, at least in spring — 
and summer, and, conversely, by shoreward movements of salt ocean — 
water. Furthermore little evidence was. found of any appreciable | 
southerly flow on the bottom, even in water as shallow as twenty-four | 
fathoms, though there was an unmistakable southwesterly current On — 
