232 THE SEAS 



(page 229) with a result that a current flows out through 

 the Straits of Florida, the Gulf " Stream." On reaching 

 more northern latitudes, however, the driving force on the 

 Gulf Stream ceases to be a difference in water level, but it 

 is now sucked in towards the ice in polar regions and 

 considerably aided by persistent South-West winds which 

 drift the surface water along in a North-Easterly direction, 

 so that the waters that bathe our coasts are more correctly 

 termed those of the North Atlantic " Drift " than the Gulf 

 Stream. 



These types of water movement, drifts and currents, 

 are to be found always around our coasts. There is for 

 instance a prevalent drift of surface water up the English 

 Channel and through the Straits of Dover into the North 

 Sea. In fact " drift bottles" (i.e. special bottles used for 

 measuring water movements [see page 257]) liberated in 

 the western end of the English Channel have been known 

 to travel in the surface drift on to the Swedish and Nor- 

 wegian coasts in just over a hundred days, a distance of 

 about 700 miles. One indeed was picked up on the north 

 shore of Norway after having travelled a distance of 1,440 

 miles at a speed of about 7-6 miles a day. In these 

 instances, however, there was no actual movement of water 

 mass at anything approaching this speed. 



When a strong wind has been blowing for some days on 

 to the shore, the surface water then becomes piled up on 

 the shore on which the wind is blowing with the result 

 that a head of water is produced and water flows outwards 

 in the deeper layers to replace the water that has been 

 driven in by the wind (Fig. 48). 



There remains one other type of water movement, and 

 this is movement of bodies of water in a vertical direction, 

 either upwelling or sinking. Sinking water masses are 

 produced in various ways, such as in the case of water of a 



