198 bulletin: museum of comparative zoology. 



is even more pronounced at 100 meters than at the shallower levels, 

 besides approaching much nearer the land, to swing, eddy like, west- 

 ward along the coast. 



The sudden east-west rise in salinity in the Northern Channel 

 between Brown's Bank and Cape Sable, the only direct connection be- 

 tween the coast water off southern Nova Scotia, and the Gulf of Maine 

 at this level, is discussed below (p. 238). 



At 200 meters (Fig. 35) the salinity was about 33%o-34%o in the 

 basin as a whole, rising to 35%o in its southeastern corner and in the 

 Eastern Channel; and to 35.3%o off the southern face of Georges 

 Bank. And the salinity was slightly higher (34.4-34. 9%o) in the 

 basins off southern Nova Scotia than in the inner parts of the Gulf. 



Temperature and Salinity on the Bottom. — The Cruise of 1914 allows 

 the salinity and temperature of the bottom water to be charted for 

 the entire breadth of the continental shelf east of Cape Cod, for the 

 first time. But even these charts (Fig. 36, 37) are, of course, for mid- 

 summer only: in the cold months hydrography would be different. 

 However, they are of interest as showing the physical environment 

 of the bottom fauna in that year and season. 



The most interesting feature of the temperature chart (Fig. 36) is 

 that the bottom waters, independent of depth, are coldest in the 

 western part of the Gulf of Maine (3.6° in the trough west of Jeffrey's 

 Ledge), and off southern Nova Scotia, these two cold areas being 

 separated by considerably warmer water (7°-8°) in the eastern part 

 of the Gulf of Maine, just as is the case in the mid-depths (p. 179). 

 In the western part of the Gulf the coldest bottom water formed a 

 band between the 75 and 100 meter contours; off Nova Scotia, the 

 minimum, l°-2°, lay between 20 and 50 meters, with much higher 

 bottom temperatures (8°-9°) in the deeps off Halifax. 



The bottom temperature was much higher (10°-12°) on Georges 

 Bank as a whole, and on the outer part of the continental shelf oft' 

 Marthas Vineyard than anywhere in the Gulf, at an equal depth, 

 or on either German Bank (9°-10°), Brown's Bank (8°-9°) or Le 

 Have Bank (2°-3°). And, judging from past years (1914a, 1915) 

 Nantucket Shoals were probably likewise colder than Georges Bank 

 on the bottom, while the curves show an indentation of 7°-8° water 

 from the northeast on the eastern end of the latter (p. 179). 



In the Gulf, bottom salinity (Fig. 37) corresponds much more closely 

 with depth than does bottom temperature, the shoal coastal zone 

 being, as a whole, the freshest, as exemplified by the zone of 32-33%o, 

 which follows the coast all the way from Marthas Vineyard to Halifax, 



