TRANSMUTABLE. 199 



was so mild, that the elephant, lion, buffalo, 

 and mastodon, inhabited what is now the Arctic 

 regions, and of course the limits of the tropical 

 and temperate flora must have been extended in 

 a corresponding degree in the northern direction. 

 Again, during the previous glacial epoch the 

 climate of the Arctic regions was extended 

 southward over what is now the temperate zone, 

 and the temperate climate existed in regions now 

 tropical. Isothermal lines were the same then 

 as now, and California had a climate like that 

 of New England at the present day. The 

 Allegliany and Cattskill Mountains contain evi- 

 dence of the presence, during the glacial period, 

 of plants now confined to the Arctic regions. 

 Twice, then, have the floras of the eastern portion 

 of North America, and the eastern portion of 

 Asia, been gradually brought together, and twice 

 gradually separated by great climatal revolutions; 

 and in this way a certain amount of intermingling 

 <>t' species has occurred." (Op. Cit., page 300.) 

 Such is the simple and most probable expla- 

 nation, by a distinguished botanist, of facts which 

 Mr. Darwin attributes to inter-migration. Mr. 

 Darwin believes that during the older pliocene 

 period, and before the glacial, the climate of 

 the world was warmer than it is now; that the 

 progenitors, or a great part of them, of present 

 species, lived in the circuinpolar land; that, as 

 the climate became less warm, they migrated 

 southwards, both in the Old and New World, 

 and that we now see their descendants in a 



