EXCURSIONS OF AN EVOLUTIONIST 



the warm waters of the southern tropical ocean 

 being carried into the northern seas, the case 

 would be just the reverse. The great ocean- 

 currents, instead of all tending northward, as 

 they do to-day, would all tend southward. A 

 very little deflection of this sort would, at the 

 easternmost point of Brazil, turn the whole of 

 the Gulf Stream southward down the coast of 

 South America, and prevent any part of it from 

 flowing up into the North Atlantic, and in this 

 way the progressing refrigeration of Europe and 

 North America would be most powerfully en- 

 hanced. 



Thus, when the eccentricity of the earth's 

 orbit was three or four times as great as at 

 present, and during the period when aphelion 

 in the northern hemisphere occurred in the 

 winter season between September and March, 

 the tendency must have been toward perpetual 

 snow and ice over a large part of the north- 

 ern hemisphere, and toward perpetual spring 

 throughout the southern hemisphere. But 

 when winter aphelion occurred in the southern 

 hemisphere, then everything was reversed ; then 

 the tendency south of the equator was toward 

 glaciation, and north of the equator it was to- 

 ward perpetual spring. In Europe you would 

 have, for 10,500 years, a period during which 

 the climate would gradually become more and 

 more arctic for 5250 years, thenceforward 

 56 



