From Teneriffe to Sombrero. 6i 



the Antilles (Plate 2). It affords an instructive example of the 

 contrast which has been observed between the two portions of 

 the North Atlantic divided from each other by the central plateau, 

 as regards distribution of temperature. In the eastern basin the 

 temperatures are lower at the surface, higher in the deeper strata 

 than in the western basin ; while in the latter they are higher at the 

 surface, and lower in the deeper strata when compared with the 

 former. The isotherm of io° C, which throughout the section 

 remains at about the same level, marks the turning-point of the 

 change. Station 13, placed upon the central plateau, may be con- 

 sidered as dividing the two areas of circulation, which, however, as 

 might be expected, encroach upon each other. In the western 

 basin, the warm surface-stratum due to the North Atlantic 

 Bqtiatorial Cttrrent, and extending down to lOO fathoms, stretches 

 eastwards beyond Station 13 as far as Station 10, and, gradually 

 thinning off, disappears near Station 8, where it makes room for the 

 North Atlantic Polar Current, which forms the surface-stratum 

 of the eastern basin. The cold stratum below 400 fathoms, 

 which in the west has a temperature of 5° C. at about 600 

 fathoms, shows in the east a fall of this isotherm down to 840 

 fathoms — in other words, a rise in the temperature of the lower 

 strata, which, as the difference in bottom-temperature (Table I.) 

 indicates, extends to the bottom. As we pass from the cold 

 water accumulated to westward of the central ridge by the North 

 Atlantic Polar JJjider-current, we enter already, at Station 15, 

 into a warmer stratum caused by the mixture of the North Atlantic 

 Polar Current with the North Atlantic Equatorial Return Ctu^- 

 rent, flowing down together in the eastern basin. In the western 

 basin, the surface and the deeper strata flow in opposite direc- 

 tions — one north, the other south, and the curves show a more or 

 less abrupt transition from the warm upper strata to the cold lower 

 strata ; whilst in the eastern basin, the currents flowing in the 

 same direction, i.e., south, the heavier equatorial return current 



