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- 
lenger Ridge 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 circulation 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 in 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 Færöe Islands, with branches towards Ice- 
land and the coast of Portugal. 
An examination of an isothermal ehart of the Atlantie (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 
THE GULF STREAM. 
1 In the Pacific, the amount of cold 
water flowing into it through the narrow 
and shallow Behring’s Strait is infinitesi- 
mal eompared with the mass of cold 
water ereeping northward into the Paci- 
fie gulf from the depths of the Southern 
Ocean. 
2 The direction from which the cur- 
rents come is plainly shown by the nature 
of the bottom specimens, made up in 
part of globigerine brought by the warmer 
southerly surface currents, and in part 
of northern foraminifera and of voleanie 
sand derived from Jan Mayen and Spitz- 
bergen. “The dividing lines between these 
deposits may be considered as the boun- 
daries of the aretie current where it passes 
under the Gulf Stream, 
