OBSERVATIONS ON MIGRATION. 15 



Spitzbergen were identical with those of our own coal- 

 measures of Durham and Northumberland. 



The whole theory obviously depends on the presumption 

 that the earth's axis has remained comparatively stationary. 

 But has this been so ? This, again, is a problem the 

 answer to which depends on a consideration of an intricate 

 congeries of facts and forces all of which must be studied 

 and their effects calculated. Nor can they be examined 

 separately ; they must be regarded as a great moving whole, 

 a vast aggregation of forces acting and re-acting on each other 

 with ever-varying results. The whole system on which the 

 earth moves through space, the effects upon it of attraction, 

 counter-attraction, and even such complexities as the pre- 

 cession of the equinoxes, all have their bearing on the 

 question. It is, however, sufficient here merely to name 

 such awe-inspiring topics, and to add that a consideration of 

 them appears to justify a conclusion that the earth's axis has 

 not materially altered in relation to the sun. 



There is abundant evidence of tropical periods at the Pole ; 

 but no trace of glacial conditions in the tropics, nor indeed 

 further south than the Continent of Europe. The Arctic 

 regions have from time to time occupied somewhat different 

 zones of land they have extended as far southward as the 

 Pyrenees, but not much, if at all, beyond. A Polar varia- 

 tion to that extent is explained by the phenomenon known 

 as the " nutation of the earth " that is, the oscillation of its 

 axis accordingly as the attraction of the sun, and the counter- 

 attractions of various other planets alternately predominate. 

 Beyond these limits, the position of the axis appears to have 

 been stationary that is, it has not altered to a degree which 

 would be destructive to the theory of the Polar origin of 

 life. 



Granting, then, the substantial accuracy of what I have 

 feebly attempted to describe, it follows that the Polar regions 

 (I refer to the Northern Hemisphere) would be the first spot 

 on the globe adapted to sustain life : that they were, at 

 first, the cradle of all life; and afterwards, as the cold 

 gradually intensified, the centre of dispersal whence the 

 various forms were distributed throughout the world, as its 



