= 
28 COSMICAL ASPECTS OF GEOLOGY. [Boox I. 
against this corner; but as the greater portion of the current les a — 
little to the north of the corner, it flows westward into the Gulf of 
Mexico and forms the Gulf-stream. A considerable portion of the 
water, however, strikes the land to the south of the cape, and is _ 
deflected along the shore of Brazil into the Southern Ocean, formin 
what is known as the Brazilian current. Now, it is obvious that the 
shifting of the equatorial current of the Atlantic only a few degrees 
to the south of its present position—a thing which would certainly 
take place under the conditions which we have been detailing— 
would turn the entire current into the Brazilian branch, and instead 
of flowing chiefly into the Gulf of Mexico, as at present, it would all 

flow into the Southern Ocean, and the Gulf-stream would con- — 
sequently be stopped. The stoppage of the Gulf-stream, combined 
with all those causes which we have just been considering, would 
place Europe under a glacial condition, while at the same time the 
temperature of the Southern Ocean would, in consequence of the 
enormous quantity of warm water received, have its temperature 
(already high from other causes) raised enormously. And what 
holds true in regard to the currents of the Atlantic holds also true, 
though perhaps not to the same extent, of the currents of the Pacific. 
“Tf the breadth of the Gulf-stream be taken at 50 miles, its 
depth at 1000 feet, its mean velocity at 2 statute miles an hour, the 
temperature of the water when it leaves the Gulf at 65°, and the 
return current at 40° F.,1 then, as has been shown in Climate and 
Time, chapter ii., the quantity of heat conveyed into the Atlantic 
by this stream is equal to one-fourth of all the heat received from 
the sun by that ocean from the Tropic of Cancer to the Arctic 
Circle. From principles discussed at considerable length in Climate 
and Time, it is shown that, but for the Gulf-stream and other 
currents, London would have a mean annual temperature 40° lower 
than at present. : 
“But there is still another cause which must be noticed :—a 
strong undercurrent of air from the north implies an equally strong 
upper current ¢o the north. Now if the effect of the undercurrent 
would be to impel the warm water at the equator to the south, the 
effect of the upper current would be to carry the aqueous vapour 
formed at the equator to the north; the upper current, on reaching 
the snow and ice of temperate regions, would deposit its moisture in 
the form of snow; so that it is probable that, notwithstanding the 
great cold of the glacial epoch, the quantity of snow falling in the 
northern region would be enormous. ‘This would be particularly the 
case during summer, when the earth would be in the perihelion and 
1 Sir Wyville Thomson states that in May, 1873, the Challenger expedition found 
the Gulf-stream, at the point where it was crossed, to be about sixty miles in width, 
100 fathoms deep, and flowing at the rate of three knots per hour. This makes the 
volume of the stream one-fifth greater than the above estimate. 
* The quantity of heat conveyed by the Gulf-stream for distribution is equal to 
77, 479,650,000,000,000,000 foot-pounds per day. The quantity received from the sun 
by the North Atlantic is 310,923,000,000,000,000,000 foot-pounds. 
