THE FALL OF THE YEAR. 223 



certain that our existing continents have 

 been steadily growing up for a vast period 

 of time, and that our existing oceans have 

 been oceans and nothing else ever since the 

 aqueous vapour of our planet first condensed 

 and cooled into water. Hence it follows 

 that the South Pole has always been isolated 

 in the midst of an enormous stretch of ocean, 

 while the North Pole has always been the 

 point from which the great land masses of 

 Europe, Asia, Africa, and America have 

 radiated southward. In both hemispheres 

 we find the land widening out towards the 

 North Pole, but tapering away towards the 

 South ; and we know that South America 

 and South Africa were till recently isolated 

 outliers of their respective continents, while 

 Australia remains an isolated outlier of Asia 

 to the present day. Thus, every .great wave 

 of animal or plant population must have set 

 out always from the North Pole, must have 

 spread southward in concentric circles, and 

 must have but slowly reached the outlying 



