136 On the Change of Climate during Geological Epochs. 



the atmosphere is to pass from the polar to the equatorial regions. 

 We have already seen that, as the excentricity of the earth's orbit 

 increases, the severity of the winter in the one hemisphere is 

 augmented, while that in the other hemisphere is diminished. 

 The glacial epoch, as we have already found, probably occurred 

 in Europe at the time when the winters in the northern hemi- 

 sphere were at their severest, and those in the southern hemi- 

 sphere at their mildest condition. The great accumulation of ice 

 and snow in the northern regions, arising from the severity of 

 the seasons, and its comparative absence in the southern hemi- 

 sphere, would tend to keep the air in the northern regions of the 

 globe much colder than the air in the southern hemisphere, and 

 the consequence would be that the aerial currents from the north 

 would be stronger than those from the south. The general 

 effect of this state of things would be to diminish the Gulf- 

 stream, as we shall presently see. 



According to Captain Duperrey, the constant ocean currents, 

 of which the Gulf-stream is one, seem all to take their rise from 

 three great currents of cold water from the south pole. We 

 have first the great equatorial current of the Pacific, taking its 

 rise in a cold current from the south pole. A portion of this 

 equatorial current passes through the Asiatic archipelago and 

 joins a second cold stream flowing into the Indian Ocean from 

 the south. The current then flows westward, passes round the 

 Cape of Good Hope, where it joins the third southern current, 

 which passes along the western coast of Africa, and then takes a 

 westerly direction, forming what is called the equatorial current 

 of the Atlantic. On approaching Cape St. lloque, this current 

 divides itself into two portions; the principal portion flowing 

 into the Gulf of Mexico, and forming what is known as the 

 Gulf-stream, the other portion directing its course to the south 

 along the coast of Brazil. 



The diminution of the aerial currents in the southern hemi- 

 sphere would tend in the first place to reduce the great currents 

 of cold water from the south pole which feed the equatorial cur- 

 rents ; and this in turn would diminish the equatorial current 

 of the Atlantic, the feeder of the Gulf- stream. The equatorial 

 current being reduced, the Gulf-stream would also be reduced. 

 But there is another way in which the Gulf-stream is affected 

 by this state of things. At present the S.E. trades of the At- 

 lantic blow with greater force than the N.E. trades, and the 

 consequence is that the S.E. trades sometimes extend to 10° or 

 15° N. lat., whereas the N.E. trades seldom blow south of the 

 equator. But during the glacial epoch the very reverse must 

 have occurred. Hence the great equatorial current of the Atlantic 

 must during that period have been driven considerably to the 



