DEATH OF A FOREST-TREE. 97 



a considerable layer was formed, several inches in 

 depth, mainly consisting of the material formed 

 by the decay of successive generations of plants. 

 Such is briefly the history of the vegetable soil of 

 this valley. 



In examining the chemical history of this 

 substance, it may be profitable to select an 

 anecdote of forest life, in regions where sun, and 

 air, and rain, together with other co-operating 

 causes, act more powerfully than in our temperate 

 climate. 



The inhabitants of the vast primeval forests 

 of the New World are frequently startled by 

 the crash of falling timber, shaking even the 

 solid ground under foot. Proceeding in the 

 direction of the noise, it is found to have arisen 

 from the downfall of some vast vegetable mo- 

 narch, which, after centuries of increasing 

 strength and grandeur, has at length fallen a 

 victim to the exhaustive influences of time 

 and old age, and lies on a heap of humbler 

 forest-trees, which it has dashed to the ground 

 in its descent. No sooner has it fallen than 

 a number of agents set to work to effect 

 its complete destruction. The rain-drops 

 from heaven saturate it, the burning solar 

 ray darts down upon and heats it, and fa- 

 voured by the temperature, the air begins 

 to act chemically upon the prostrate trunk. 



H 



