3 1 8 THE DEPTHS OF THE SEA. . [CHAP, vn 



1,000 fathoms ...;.;. 3- 5 C. 



1,250 . 3-3 



1,476 . ^ . 2-7 



We have here on a large scale, as Dr. Carpenter 

 has pointed out, conditions very analogous to those 

 which exist in comparatively shallow water, and on a 

 small scale in the cold area in the Faeroe Channel. 

 There is a surface layer of about 50 fathoms, super- 

 heated in August by direct solar radiation, and, as we 

 see by the variations of surface isotherm als, varying 

 greatly with the seasons of the year. Next, we have a 

 band extending here to a depth of nearly 800 fathoms, 

 in which the thermometer sinks slowly through a 

 range of about 5C. Then a zone of intermixture 

 of about 200 fathoms, where the temperature falls 

 rapidly, and finally a mass of cold water from a depth 

 of 1,000 fathoms to the bottom, through which, what- 

 ever be its depth, the thermometer falls almost im- 

 perceptibly, the water never reaching the dead cold 

 of the Arctic undercurrent in the Fasroe Channel, 

 and the lowest temperature being universally at the 

 bottom (Fig. 58). 



The area investigated during the second cruise of 

 the ( Porcupine ' at the mouth of the Bay of Biscay, 

 about a couple of hundred miles west of Ushant, 

 may be regarded as simply a continuation southwards 

 of the tract between Scotland and Ireland and the 

 Rockall ridge. As, however, the depths were greater 

 than any attained on any former occasion were so 

 great, indeed, as probably to represent the average 

 depth of the great ocean basins at may be well to 

 describe the methods of observation and the condi- 

 tions of temperature somewhat in detail. 



