318 THE DEPTHS OF THE SEA. {CHAP. VIL. 
12000 tathontsws: JAS GE) Oa Ee Roane 
1a ae hh oni aL ee 
LANG. 25 Aparna Geran sree a OL 
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 Féroe 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 isothermals, varying 
ereatly 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 5° C. 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 Féroe 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 
creat, indeed, as probably to represent the average 
depth of the great ocean basins—it may be well to 
describe the methods of observation and the condi- 
tions of temperature somewhat in detail. 
