84 SEA FISHERIES 



mentions another cause. Currents flowing in opposite 

 directions, he says, can transmit their movement to the 

 masses of water situated between them, whence a com- 

 pensating current ascending from the bottom. Vertical 

 compensating currents are frequent in the polar and the 

 equatorial regions. In the Mediterranean there are 

 possibly cyclonic movements. The lighter water would 

 be at the periphery of the cyclone ; the more con- 

 centrated water is in the centre, in a vertical column. 

 It is in the centre of such cyclones that Pettersen sees 

 the formation of the "abysmal" water of the Irminger 

 Sea and Nansen that of the Norwegian Sea. 



IV 



I have now spoken of the currents of the North 

 Atlantic, the Channel, the North Sea, and the Mediter- 

 ranean. I must now proceed to deal with those of the 

 Moorish coast. The transition is natural enough, for 

 there also the Gulf Stream plays an important part. 



In the southern hemisphere the average temperature 

 of the sea is lower along the western coasts of America, 

 Africa, and Australia than on the eastern coasts of the 

 same continents ; in the northern hemisphere the converse 

 is true. "All navigators," writes M. Gruvel, "who have 

 sailed the Moorish waters and the Bay of Senegal know 

 that there is a current running from north to south all 

 along this coast, and apparently almost exactly parallel 

 to it. This current is often a powerful one. It is origin- 

 ally formed by a branch of the Gulf Stream, which, 

 having skirted the coast of Portugal, forming what is 

 known as the Great Canary current, splits up at an 

 indefinite and probably variable point off the Moorish 

 coast into two secondary currents ; the western branch, 

 much the more important of the two, going to form the 



