CffAr. XIX.] THE SURFACE OF THE EARTH. 213 



that the zones, instead of being continuous, are inter- 

 sected by undulations running north and south. 



In the north there is the depression which contains 

 the Arctic Ocean, surrounded by the continents of 

 Europe, Asia, and America ; then there is the de- 

 pression of which the Mediterranean and Caribbean 

 Seas, separating Europe and North America from 

 Africa and South America, form a part ; and thirdly, 

 there is the greatest hollow, which contains the 

 Southern Ocean, separating the continents just men- 

 tioned from the lands of the Antarctic regions. 



Though the centrifugal force resulting from axial 

 rotation might be expected in some measure to neu- 

 tralise the undulating action of lateral pressure acting 

 north and south, so that the greatest apparent effects 

 of undulating force should result from the pressure 

 acting east and west ; this would not account for any 

 one of the meridional undulations being greater than 

 any other. But, as far as the forces thus far con- 

 sidered are concerned, all the meridional undula- 

 tions on our hypothetical globe would be equal and 

 similar. There are, however, on the surface of the 

 earth two meridional undulations immensely greater 

 than all others, the crests of which form respectively 

 the Old and New Worlds ; the depressions between 

 them containing respectively the Atlantic and Pacific 

 Oceans. 



Such a meridional division of land and water 

 would naturally result from a change of the earth's 



