26 



THE POLAR WORLD. 



forest are continiuilly wasted by extensive fires, kindlecl accidentally or inten- 

 tionally, which spread with raj>idity over a wide extent of country, and cou- 



timu' to 1)11111 until they are extiiiujuislied hy a lieavy rain. Sooner or later a 

 new growth of tinil.cr springs nj), but the soil, being generally enriched and 

 saturate! witli iilknii, now uo longer brings forth its aboriginal firs, but gives 

 birtli to a thii-ket ol lu'cches {Bctuki alba) in Asia, or of aspens in America. 



I 



