316 THE DEPTHS OF THE SEA. (CHAP. VII. 
of the ocean for the parallel of latitude. At a 
depth of 200 fathoms, however, the divergence be- 
tween the curves of the warm and cold areas is most 
remarkable. The curve of the warm area, No. 87, 
shows a fall of scarcely half a degree at 500 fathoms, 
and less than one degree more at 767 fathoms at 
the bottom. Between 200 and 300 fathoms the cold 
area curves run down from 8° C. to 0° C., leaving 
only one degree more of gradual descent for the 
next 300 fathoms. The temperature of the ‘hump’ 
on the curves of the ‘cold area’ between 50 and 
200 fathoms corresponds so nearly with that of the 
long gradual sinking of the curve of the warm area 
from the surface nearly to the bottom, that it seems 
natural to trace it to the same source. We there- 
fore conclude that a shallow layer of Gulf-stream 
water drifting slowly northwards overlies in the cold 
area an indraught of cold water represented by the 
sudden and great depression of the curves, while in 
the warm area this cold indraught is absent, the 
Gulf-stream water reaching to the bottom. 
Tracing the ‘warm area’ southwards from the 
mouth of the Féroe Channel along the coast of Scot- 
land, we find that the area between Féroe, the Lews, 
and Rockall, is a kind of plateau with a depth of 
from 700 to 800 fathoms; and we may be certain from 
analogy, although this region has not yet been actu- 
ally examined, with a bottom temperature not lower 
than 4°5 C. Commencing opposite Rockall, and ex- 
tending between the great shoal which culminates 
in the Rockall fishing banks and the singular isolated 
rock, and the west coast of Ireland, there is a wide 
trough deepening gradually southwards, and at length 
