190 THE GULF STREAM. 
Antaretic Ocean. The South Atlantic is shut off from its northern area 
by the ridge extending from St. Paul’s Rocks to Ascension, at a depth 
of about 2,000 fathoms. The Challenger Ridge runs nearly north and 
south, leaving a free communication between the Antarctic Ocean and 
the eastern and western basins of the South Atlantic. The North At- 
lantic is subdivided into an eastern and western basin at a depth of 
about 1,500 fathoms by the Dolphin Rise, which follows in a general 
way the course of the S-shaped Atlantic basin. Ridges separating the 
Atlantic from the Arctic Ocean extend across Denmark Straits, proba- 
bly at a shallow depth. From Greenland to Iceland the depth has an 
average of 500 fathoms; from Iceland to the Fverées, an average of about 
300 fathoms, and from there to the Orkneys, of not more than 220 fath- 
oms. From the configuration of the bottom it is evident that a larger 
amountof cold water must reach the tropics from the Antaretie than from 
the Arctic regions,* which are shut off from the Atlantic by submarine 
ridges. Over these and through the channels of Baffin’s Bay but a 
limited amount of cold water can find its way south. In the eastern 
Atlantict the principal cooling agent must be the cold water slowly 
flowing northward from the Antarctic between the Challenger 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 equa- 
torial current, and to drive a considerable part of this southern eurrent 
northward to join the westerly drift which flows to the northward of 
the Greater Antilles and Bahamas. The phenomena of oceanic circula- 
tion 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 extension. 
There is on the west side of the North Atlantic an immense body of 
warm water, of which the Gulf Stream forms the western 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 con- 
* The temperature line run diagonally across the Atlantic from Madeira to Tristan 
da Cunha by the Challenger brings out the remarkably shallow stratum of warm 
water of that part of the equatorial regions which corresponds to the regions of the 
tradewinds both north and south of the equator. The temperatures of the belts of 
water between 200 and 500 fathoms north and south of the line plainly show that the 
colder water found south of the equator can not come from the warmer northern belt 
of the same depth, but must come from the colder belt adjoining the equatorial re- 
gion. In other words, the cold water may be said to rise towards the surface near 
the equator; and from the temperature of the two sides of the North Atlantic it is 
also evident that the supply of cold water flowing from the Antarctic into the At- 
lantic is greater than that coming from the Arctic regions. This vertical cireula- 
tion, characteristic of the equatorial belt, is insignificant, however, when compared 
with the great horizontal oceanic currents. 
tIn the Pacific the amount of cold water flowing into it through the narrow and 
shallow Bering Strait is infinitesimal compared with the mass of cold water creep- 
ing northward into the Pacific gulf from the depths of the Southern Ocean, 
ee 
