THE OCEAN FEEDING-GROUNDS 77 



impart their own movement to the surface waters of 

 the sea. 



The physiology of the North Atlantic is dominated by 

 the Gulf Stream. At its emergence from the Gulf of 

 Mexico it measures 36 miles in width, 200 fathoms in 

 depth, and runs at the rate of 6 or 7 knots ; its tem- 

 perature is 86 to 89-6. Off the coast of France and 

 of Iceland it has become an enormous river, 360 miles in 

 width and over 500 fathoms in depth. It has become 

 colder and less swift ; its pace has fallen to a bare 

 4 knots, while the temperature does not exceed 60*8 or 

 64*4. It is probable that the Gulf Stream sends a 

 branch up the Channel ; it certainly gives rise to a back- 

 wash as far as Cape Finistere. The Rennell current 

 for such is its name runs along the northern coast of 

 Spain into the heart of the Bay of Biscay, then, suddenly 

 turning towards the north-north-west, it sweeps the 

 French portion of the continental plateau and flows 

 northward towards Ireland, and perhaps as far as 

 Iceland. In the latitude of the Gironde it sends off 

 circular eddies to the right, which tend toward the 

 south. 



For a long time it was believed that Iceland was 

 surrounded by the Gulf Stream as by a ring. The 

 reality is more complex. The Atlantic waters of the 

 stream divide, to the west of the Wyville Thomson ridge 

 at the island of Rockall, to be precise into two 

 unequal branches, flowing towards the north-east ; one 

 passes between the Shetlands and the Faroes, and is 

 by far the more voluminous of the two ; the other, 

 which is very much smaller, smaller even than the 

 Irminger current, crosses the ridge between Iceland and 

 the Faroes. So much for the warm currents ; let us 

 now consider the cold currents. The Polar current 



