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 



