116 THE ANTIQUITY OF MAN. 



» 



which in the present case seems to have been of oak.* This would 

 be of longer continuance, and would, independently of human 

 agency, only be replaced by beech, if, iu the course of ages, the 

 latter tree proved itself more suitable to the soil, climate, and other 

 conditions. Both oak and beech are of slow extension, their 

 seeds not being carried by the winds, and only to a limited degree 

 by birds. On the other hand the rechanges of forests caunot have 

 been absolute or universal. There must have been oak and beech 

 groves even in the pine woods ; and the growing and increasing 

 beech woods would be contemporary with the older and de- 

 caying oak forest, as this last would probably perish not by fire, 

 but by decay, and by the competition of the beeches. In like 

 manner the growth of peat is very variable even in the same loca- 

 lity. It goes on very rapidly when moisture and other conditions 

 are favourable, and especially when it is aided by wind-falls, drift- 

 wood, or beaver-dams, impeding drainage and contributing to the 

 accumulation of vegetable matter. It is retarded and finally ter- 

 minated by the rise of the surface above the drainage level, 

 by the clearing of the country, or by the establishment of natural 

 or artificial drainage. On the one hand all the changes observ- 

 ed in Denmark may have taken place within a minimum time of 

 two thousand years. On the other hand no one can affirm that 

 either of the three successive forests may not have flourished 

 for that length of time. A chronology measured by years, and 

 based on such data, is evidently worthless. 



Possibly a more accurate measurement of time might be de- 

 duced from the introduction of bronze and iron. If the former 

 was, as many antiquarians suppose, a local discovery, and not in- 

 troduced from abroad, it can give no measurement of time 

 whatever ; since, as the facts so clearly detailed by Dr. Wilson 

 show, while a bronze age existed in Peru, it was the copper age 

 in the Mississippi valley, and the stone age elsewhere ; these 

 conditions might have co-existed for any length of time, and could 

 give no indication of relative dates. On the other hand the 

 iron introduced by European commerce spread at once over the 

 continent, and came into use in the most remote tribes, and its in- 

 troduction into America clearly marks an historical epoch- 



* The details of this process, as it occurs in America, will be found 

 njticed in a paper by the writer iu the Edin. Phil. Journal for 1847- 

 Such changes are constantly in progress in the American forests. 



