THE GULF STREAM, 243 



amount of cold water can find its way south. In the Eastern 

 Atlantic/ the principal cooling agent must be the cold water 

 slowly flowing northward from the Antarctic between the Chal- 

 lenoer Rido-e and Africa. 



The shape of the northern extremity of South America, 

 together with the action of the southerly trades, is such as to 

 split the southern equatorial current, and to drive a consider- 

 able part of this southern current northward to join the west- 

 erly drift which flows to the northward of the Greater Antilles 

 and Bahamas. The phenomena of oceanic circidation in their 

 simplest form are here seen to consist of westerly currents 

 impinging upon continental masses, deflected by them to the 

 northward and eastward, and gradually lost m their polar ex- 

 tension. 



There is on the west side of the North Atlantic an immense 

 body of warm water, of which the Gulf Stream forms the west- 

 ern edge, flowing north over a large body of cold water that 

 comes from the poles and flows south. The limits of the line 

 of conflict between these masses are constantly changing, accord- 

 ing to the seasons : at one time the colder water from Davis's 

 Straits spreads like a fan near the surface, driving the Gulf 

 Stream to the east ; ^ and at another, large masses of warm water 

 extend towards the Fseroe Islands, with branches towards Ice- 

 land and the coast of Portugal. 



An examination of an isothermal chart of the Atlantic (Figs. 

 168, 169) clearly shows the effect of the isolation of the North- 

 ern Atlantic ; the area of maximum temperature (82^) extends 

 over a far greater space in the North than in the South Atlantic. 

 The Gulf of Mexico and the Caribbean become greatly super- 

 heated in September (to above 86°), the effect of this super- 

 heating in conjunction with the westerly equatorial drift being 



^ In the Pacific, the amount of cold of the bottom specimens, made up in 



water flowing into it through the narrow partofglobigerinfe brought by the warmer 



and shallow Beliring's Strait is infinitesi- southerly surface currents, and in part 



mal compared with the mass of cold of northern foraminifera and of volcanic 



water creeping northward into the Paci- sand derived from Jan Mayeu and Spitz- 



fic gulf from the depths of the Southern bergen. The di\-iding lines between these 



Ocean. deposits may be considered as the bouu- 



^ The direction from wliieh the cur- daries of the arctic current where it passes 



rents come is plainly shown by the nature under the Gulf Stream. 



