270 THE ATLANTIC. [chap. v. 



coast of North America and the shoal -water extending across 

 to Greenland, to the east by the median ridge, and to the south 

 by the spur of the ridge joining the coast of South America at 

 Cape Orange ; and the south- western basin bounded to the north 

 by this spur, to the west by the coast of South America, to the 

 east by the median ridge, and to the south entirely open to the 

 Antarctic Sea. In all our serial soundings in the eastern and 

 the north-western basins, the temperature slowly fell to a depth 

 of about 2000 fathoms, and from that depth it remained nearly 

 uniform to the bottom, the difference in the readings beyond 

 2000 fathoms being so slight as to be well within the limits of 

 error of observation with Six's thermometers, but, on the whole, 

 showing a tendency to sink, or, at all events, showing no tend- 

 ency to rise on the correction for pressure being applied, which 

 they ought to have done had the temperature been absolutely 

 tlie same. The bottom temperatures and the recorded temper- 

 atures below 2000 fathoms were slightly, but constantly, lower 

 in the north - western than they were in the eastern basin, in 

 the former averaging about 1°"6 C, and in the latter a little 

 under l°-9 C. 



In the south-western basin the vertical distribution of tem- 

 perature is different, and this difference appears to give the key 

 to the whole question of the distribution of temperature at 

 great depths in the Atlantic. On our return voyage, in Febru- 

 ary, 1876, four observing stations, numbered on Plates XXXIY. 

 and XXXY. from CCCXYII. to CCCXX., were established. 

 Two of these M^ere in comparatively shallow water near the 

 edge of, but still upon, the plateau which extends from the 

 coast of South America to a distance of nearly 400 miles, and 

 includes the Falkland Islands ; the two remaining soundings, 

 CCCXVIII. and CCCXIX., were well beyond the cliff of the 

 plateau at depths greater than 2000 fathoms. All these sound- 

 ings, the two deep ones particularly, indicate the presence of a 

 great underlying mass of cold water, the isothermobath of 2° C. 



