102 UNIFORMITY OF CLIMATE IN PAST AGES. 



great. The same species of plants lived all over the 

 world in the earlier geological ages. In view of this fact, 

 any great difference in the mode of the application of 

 that force seems impossible ; and, still more, because 

 in more recent times, i. e., in the miocene and pliocene, 

 the very species originated in circumpolar regions, which 

 nave since furnished the forests of our southern states. 



It seems to me that the fossil plants and animals of 

 polar countries afford the strongest evidence possible in 

 the nature of the case, that down to the pliocene the 

 earth's axis was nearly perpendicular. 



To this two serious objections may be made : (1) The 

 stability of the position of the earth's axis, which astron- 

 omers assure us cannot be XDermanently disturbed by 

 any force known to science; (2) the fact, .as shown by 

 Meech and repeated by Croll, that, other things remain- 

 ing as they are, a perpendicular axis would make the 

 circumpolar climate colder even than it now is. 



As to the stability of the axis, astronomers prove too 

 much. If the nebular hypothesis be true, the moon and 

 earth should revolve around axes perpendicular to the 

 ecliptic, for no force of avulsion could change their posi- 

 tion. They could not revolve around two axes when 

 one body ; hence it must have been after they were sepa- 

 rate bodies that one or both became tilted. 



The moon now is nearly in the normal position ; there- 

 fore, the great change has been in the earth. Hence, it 

 follows that if our earth was developed mechanically, it 

 somehow, by some "force unknown to science," got 

 into its present position, and the only question that con- 

 cerns us is that of the date. Astronomers may declare 

 their own ignorance, nevertheless, the event occurred, 

 for we see that the axis is inclined. 



The only theory for the formation of our system other 

 than the nebular hypothesis is that which relegates the 



