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 event, 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 
