TEMPERATURES. 231 
100 fathoms, of 14° to 17° at 200 fathoms, of 9° to 13° at 300 
fathoms, of 7° to 8° at 400 fathoms, and of 2° to 4° at the five- 
hundred-fathom line. The temperatures of the long lines from 
Mexico to Florida bring out the same differences, with the ex- 
ception that there is a marked rise of the cold-water belt along 
the edge of the Florida Bank, which may be due to the general 
rising of the cold water, as in other sections along the planes of 
steep slopes. A comparison of the lines running north and 
south shows that the line from Vera Cruz to Galveston (Fig. 
155) is colder than that from the Yucatan Bank to Louisiana. 
(Fig. 156.) The latter, in its turn, is colder than the line from 
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Dry Tortugas cet) Stet (Cuba) 
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Fig. 157. 
Yucatan to Santa Rosa, and that again colder than the line from 
the Yucatan Bank to the Tortugas. The presence of this 
thick layer of cold water between 150 fathoms and 600 fathoms 
— water colder than we find at the same depths in the adjoin- 
ing Caribbean, or at the same depths in the Atlantic — can per- 
haps be explained by the increased evaporation of the super- 
heated upper stratum cooling the water below it. 
The sections from the Tortugas to Cuba (Fig. 157), and from 
Cape Florida across to Gun Key (Fig. 158), agree remarkably 
in their general character with the Yucatan section. The de- 
crease of temperature is nearly the same. The layer of warm 
water is thicker close to the Cuban and Bahama side of the sec- 
