PLANETARY INCLINATIONS. 27 



earth's axis, in modifying the mean temperature 

 of different latitudes. It is generally supposed 

 to have been demonstrated theoretically by La- 

 place, that the total variation of the planetary 

 inclinations must be comprised within the nar- 

 row limits of 3. That in so vast and complicated 

 a problem as that of perturbation, geometers may 

 have overlooked some important elements in their 

 calculations, would seem highly probable from 

 the limited period since which accurate observa- 

 tions have been made ; for they admit that the 

 disturbing influence of all the planets and their 

 satellites upon each other is such, that millions 

 of years are required to bring about one cycle. 



But if it w r ere wholly impossible to determine 

 the exact amount of variation in the plane- 

 tary inclinations, during the countless ages that 

 have past, geology affords the most conclusive 

 evidence, that at some remote period of the 

 earth's existence, the inclination of its axis must 

 have been far less than at present ; or the 

 equator and poles must have been reversed. For 

 it has been discovered that the secondary for- 

 mations at Melville Island, and other parts of 

 the polar regions, are filled with the fossil re- 

 mains of plants and animals, which could have 

 been produced only in a warm climate ; and that 

 the newest tertiary deposits in Siberia, abound 

 with bones of the Mastodon or mammoth, which 

 seems to have been as common in the higher 



