234 bulletin: museum of comparative zoology. 



as it were, down the density gradient, from near the surface over the 

 100 fathom contour to about twelve fathoms over the thirty-five 

 fathom contour, with the heavier, though fresher, bottom water of 

 the shelf moving seaward below it. Density points to a similar type 

 of circulation off Chesapeake Bay. But this phenomenon must be 

 transitory, because as the coast water grows warmer with the advance 

 of the season its density on the bottom must fall as low as that of the 

 Salter water off shore. 



The band of uniform salinity which we traced from Station 10063 to 

 Station 10069 (p. 194) was not the result of vertical mixing; had it been 

 temperature like salinity would have been equalized. Its origin is 

 obscure. 



Neither density, salinity, nor temperature indicates any general 

 longshore movement of the bottom waters on the shelf. 



Previous records of temperature and salinity Cape Cod to 

 Chesapeake Bay. 



The existence of a band of cold water between the Gulf Stream and 

 the coast has been recognized since the days of the early voyages to 

 these shores. By 1850 its general geographic limits were well under- 

 stood (Maury, 1855), since which time a vast body of surface tempera- 

 ture readings has been taken over the continental shelf by vessels 

 entering the ports of New York, Philadelphia, and Chesapeake Bay, 

 as well as by various expeditions and government services. But 

 most of these have never been published; and since, in any e\'ent, the 

 general range of summer temperature is now well known, I need refer 

 here to only a few of the more important sets of observations. The 

 data obtained by the U. S. Fish Commission south of Marthas 

 Vineyard between 1880 and 1882, (Tanner, 1884a, 1884b; Verrill, 

 1880-1884b), show the general rise of temperature passing off shore 

 from the southern coast of New England. And records have con- 

 stantly been kept at .Woods Hole since that time, so that there are 

 very satisfactory data of the temperature close to shore in that region. 

 The more recent of these are summarized by Sumner, Osburn, and 

 Cole (1913), who find that the monthly surface mean for a five year 

 period, at the Woods Hole Station, is 31° in February, 43.9° in April, 

 68.8° in July, 69.7° in August, 48.2° in November. In Vineyard 

 Sound the mean surface temperature, August, 1907, was 64.7°, Novem- 

 ber, 1907, 50.9°; March, 1908, 36.6°; June, 1908, 56.5°. The surface 



