31 G THE DEPTHS OF THE SEA. [chap. vn. 



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 707 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 ' hum]) ' 

 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. AVe 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, Avhile 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 lYeroe Channel along the coast of Scot- 

 land, we find that the area between Fseroe, the Lews, 

 and llockall, 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 1 '5 C. Commencing opposite ROckall, and ex- 

 lending between the great shoal which culminates 

 in the llockall fishing banks and the singular isolated 

 rock, and tin 1 west coast of Ireland, there is a wide 

 trough deepening gradually southwards, and at length 



