Where did Life Begin? 29 



(and all the northern hemisphere) is cor- 

 rugated north and south with alternate con- 

 tinents and deep sea-channels almost from 

 pole to pole. Both the eastern and western 

 continents extend with unbroken land con- 

 nections from the arctic zone through the 

 northern temperate, the torrid, and through 

 the southern temperate, almost to the antarctic 

 zone. Between these great continents lie the 

 deep oceans, whose channels run north and 

 south through as many degrees of latitude. 

 The great air and ocean currents run north 

 or south ; all the mountain ranges of the west- 

 ern continent and many of the eastern contin- 

 ents run mainly north and south. Nearly all 

 the great rivers of the northern hemisphere 

 run north or south. To a southern migra- 

 tion — in other words, a mig^ration from the 

 arctic region toward the equator — these pe- 

 culiarities of topography, these great corruga- 

 tions and mountain ranges, these channels and 

 currents, are roads and vehicles, guides and 

 helps ; while to an east and west migration the 

 same features are not only obstacles and hin- 

 drances, but in the main barriers insuperable. 



G> 1 



