402 bulletin: museum of comparative zoology. 



near Cape Porpoise is important as showing that there is a south- 

 westerly long-shore movement of the river water at this season, its 

 chief som'ces on this part of the coast being the Merrimac, the Kenne- 

 bec, and possibly the Penobscot. x\nd this agrees with our sum- 

 mer data {Loc. cit., p. 91), as well as with the common report of a 

 "spring current" flowing across the mouth of Casco Bay from north- 

 east to southwest. The Merrimac water evidently flows around Cape 

 Ann; but that it hardly enters Massachusetts Bay, is shown by the 

 comparatively high salinities encountered by Mr. Douthart (p. 419), 

 while summer salinities suggest that it must swing eastward off Cape 

 Ann. 



It is not known of course, how closely the changes outlined above 

 are reproduced in other years; but to judge from the climate of the 

 neighboring land mass, there is every reason to assume that they 

 represent the normal cycle, though no doubt there are slight differ- 

 ences in salinity and temperature from year to year. 



The Georges Bank records show that the water was considerably 

 warmer there in April than it was close to the western coast of the Gulf 

 at the same season; and salter than the latter is at any season. 

 Furthermore the Bank water showed no sign of the spring freshening 

 so evident near shore. 



Our winter records do not afford any evidence that the low tempera- 

 tures of winter are caused by an influx of northern water into our Gulf. 

 On the contrary, the cooling is no more rapid, nor extreme, than can be 

 accounted for by the winter climate of the neighboring land mass. 

 And the data show clearly that the surface chilling depends closely 

 on air temperature, a conclusion which is equally pertinent to the 

 waters of Georges Bank in spring. But this does not prove that St. 

 Lawrence water never affects the Gulf, for this source of supply may be 

 expected to exert its greatest influence in autumn, as shown by Dick- 

 son's charts of salinities off Nova Scotia. 



The salinities on Georges Bank in April are so low as to forbid the 

 idea that the water there is chiefly Atlantic bottom water, though of 

 course there may be some upward movement over the continental 

 slope: and this is even more true of the Gulf itself, for nowhere does 

 the water of the latter, at any depth, or at any season, approach the 

 high sahnity (34.9) of the abyssal water of the North Atlantic, so far 

 as we know. The Gulf Stream certainly exerts little influence on 

 the Gulf of Maine in winter; but plankton records show that there 

 are irregular penetrations of its surface layers in summer. 



