THREE ORUISES OF THE “ BLAKE.” 
224 
miles in a depth of 56 fathoms. This cold water may come 
from the colder water of the deeper channel on the east of the 
island. The water is also colder near San Domingo, where we 
find at 339 fathoms 49°, while seven miles to the eastward, 
toward Porto Rico, it is 51° in 337 fathoms. This section is 
very similar to that of the Anegada Channel. 
The temperature sections of the passages between the Wind- 
ward Islands on the eastern side of the Caribbean — Dominica, 
Martinique, St. Lucia, and St. Vincent—are in striking con- 
trast to those of the northern side, the Anegada, Mona, and 
Windward Passages. Ata depth of 75 fathoms there is a dif- 
ference of no less than 9°; at 200 fathoms, one of 10°; and one 
of 5° at 300 fathoms. The equilibrium is only restored at a 
depth of 600 fathoms, where we have again the temperature of 
40°. We find repeated here on a smaller scale the variations of 
temperature at given depths near the equator and in the more 
temperate zones. A temperature of 41° has been observed in 
the Atlantic near the equator at a depth of only about 250 
fathoms, while in the temperate latitudes both north and south 
of the equator we must goto a depth of at least 600 fathoms 
in one case, and of over 400 fathoms in the other, to obtain the 
same temperature. In other words, there must be an active 
lateral and upward flow of the cold water, and this establishes 
one of the primary causes of the equatorial oceanic circulation. 
It also shows that the temperature of the deepest point of the 
ridge which separates an inland sea, and thereby forms a med- 
iterranean, is not necessarily that of the bottom of the enclosed 
sea. It is very evident that, supposing the ridge to have been 
only 300 fathoms deep, we could have a bottom temperature of 
50°, which would indicate an oceanic ridge of 350 fathoms, on 
the same principles that have led Dr. Carpenter and others to 
speak of the bottom temperature of enclosed seas as assuming 
that minimum temperature. 
The section across the Windward Passage (Fig. 149) bears a 
close resemblance to the oceanic temperature section of that 
region. The belt of water between 400 and 800 fathoms 18, 
however, considerably warmer. It also resembles the section 
between Jamaica and San Domingo (Fig. 150), though the belt 
