chap, viii.] THE GULF-STREAM. 401 



expected if the Gulf-stream came close to the western 

 shore. 



While the communication between the North 

 Atlantic, and the Arctic Sea — itself a second cul 

 de sac — is thus restricted, limiting the interchange of 

 warm and cold water in the normal direction of the 

 now of the Gulf-stream, and causing the diversion of 

 a large part of the stream to the southwards, the 

 communication with the Antarctic basin is as open as 

 the day ; — a continuous and wide valley upwards of 

 2,000 fathoms in depth stretching northwards along 

 the western coasts of Africa and Europe. 



That the southern water wells up into this valley 

 there could be little doubt from the form of the 

 ground; but here again we have curious corroborative 

 evidence on the map in the remarkable reversal of the 

 curves of the isotherms. The temperature of the bot- 

 tom water at 1,230 fathoms off Rockall is 3°22 C, 

 exactly the same as that of water at the same depth in 

 the serial sounding, lat. 47° 38' N., long. 12° 08' W. in 

 the Bay of Biscay, which affords a strong presumption 

 that the water in both cases is derived from the same 

 source ; and the bottom water off Bockall is warmer 

 than the bottom water in the Bay of Biscay (2°'5 C), 

 while a cordon of temperature soundings drawn from 

 the north-west of Scotland to a point on the Iceland 

 shallow gives no temperature lower than 6 0, 5 C. This 

 makes it very improbable that the low temperature 

 of the Bay of Biscay is due to any considerable por- 

 tion of the Spitzbergen current passing down the west 

 coast of Scotland; and as the cold current to the 

 east of Iceland passes southwards considerably to the 

 westward, as indicated on the map by the successive 



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