CHAP, v.] GENERAL CONCLUSIONS. 269 



Atlantic is the steady increase in tlie volume of warm water 

 from the south northward. For example, between Montevideo 

 and Tristan d'Acunha we find the isothermobath of 7° C. at an 

 average depth of about 250 fathoms. Along the equator at 

 nnder 300 fathoms, between Teneriffe and Sombrero it occnrs 

 at a depth of 500 fathoms, and between Bermudas and Madeira 

 at about 600 fathoms. The principal accumulation of warm 

 water at depths below 400 fathoms, in the North Atlantic, is 

 to the eastward. 



We now pass to the more difiicult problem of the distribution 

 of temperature in the mass of water filling up the trough of the 

 Atlantic beneath the uniform belt. The isothermobath of 3° 

 C. may, perhaps, be regarded as the first line decidedly within 

 the upper boundary of the cold water, and we learn something 

 by observing its position. In the most northern cross-section, 

 between Bermudas and Madeira, it occurs at a depth of from 

 1000 to 1200 fathoms below the surface. In the next cross-sec- 

 tion, from Teneriffe to Sombrero, it has nearly the same position, 

 becoming a little deeper toward the eastward. In the next sec- 

 tion, along the equator, it is at a depth of from 1000 to 1100 

 fathoms, nearly as before. Between San Salvador and the 

 Cape of Good Hope it rises to a mean depth of 600 fathoms, 

 and between the Falkland Islands and Tristan d'Acunha it is at 

 a depth of fi"om 500 to 600 fathoms. The broad fact thus be- 

 comes patent, that as the volume of warm water at a tempera- 

 ture above 7° C. increases to the northward, so the mass of cold 

 water at a temperature below 3° C. increases toward the open- 

 ing of the Atlantic into the Southern Sea. 



I must now refer again to the frontispiece, and recall the 

 general distribution of depth in the Atlantic. In discussing 

 this question, I will speak of the eastern basin of the Atlantic, 

 stretching from the west coast of Britain nearly to the Cape of 

 Good Hope, and bounded to the westward by the median ridge ; 

 the north-western basin, bounded to the west and north by the 



