SALINITY, GASES 57 



In tropical regions the prevailing winds 

 drive the surface waters westwards to the 

 eastern shores of the continents, where ac- 

 cordingly there is a greater depth of warm 

 and saline water than elsewhere (except where 

 the rainfall is abnormally heavy). On the 

 other hand, on the eastern sides of the oceans 

 whence the trade winds start on their course, 

 as off the west coasts of Africa and South 

 America, the warm saline surface water is 

 driven seaward, and the colder and fresher 

 water from below wells up to take its place. 



In the "North Atlantic the prevailing winds 

 do not blow home to the eastern coasts of the 

 United States, where the prevailing winds are 

 south-westerly, and consequently the higher 

 salinities occur some distance seaward. To 

 the south of lat. 40° N. the prevailing winds 

 become more westerly as they advance in their 

 easterly course, and gradually become north- 

 westerly and then northerly on approaching 

 the north-west coast of Africa, where they 

 blow home, and where the higher salinities 

 are found close to the coast. In the South 

 Atlantic the south-east trade winds blow home 

 to the South American coast between Cape 

 St. Roque and the La Plata estuary, and it 

 is off this coast that the higher salinities are 

 found. 



The effect of the prevailing winds is also 



