CLIMATE GRADUALLY CHANGING. 291 



autumn, with its heats aud tempests, despoils the 

 trees of their beautiful verdure ; then, with the same 

 regularity of succession, winter hangs her snowy- 

 garlands on the branches, and strikes with sudden 

 paralysis the mountain torrent. The same succes- 

 sion of phenomena appears to be continually repro- 

 duced, with such modifications as would suggest a 

 capricious and ill-regulated will. Notwithstanding 

 that apparent regularity, within certain limits, the 

 climate of the earth is undergoing a slow but con- 

 stant variation. The debris of every kind found in 

 the earth's crust affords demonstrative proof that 

 the distribution of temperature on the surface of the 

 globe has been very different at remote periods from 

 what it is at present. The surface, beyond doubt, 

 has been subject to numerous vicissitudes; but at 

 least, you will say, the centre of the earth has re- 

 mained unchangeably the same. 



This, however, cannot * be the case ; for, as the 

 earth has grown gradually cooler, its ciust has in- 

 creased in thickness and solidity. The contraction 

 towards the centre has been the cause of breakages 

 and cramplings in the earth's crust, and, consequently, 

 of the upheaval of mountains and continents, the 

 sinking of the surface to form valleys, and, generally 

 speaking, of such variations of the terrestrial land- 

 scape as could only be produced through a long 



