236 ORIGIN OF METALLIFEROUS DEPOSITS. [XII. 



animal and vegetable growth as themselves purely chemical 

 and physical. That this is to a great extent true must be 

 admitted, though I am not prepared to concede that we have 

 in chemical and physical processes the whole secret of organic 

 life. Still we are, in many respects, approximating the phe- 

 nomena of the organic world to those of the mineral kingdom ; 

 and we at the same time learn that these so fur interact and 

 depend upon each other that we begin to see a certain truth 

 underlying the notion of those old philosophers who extended 

 to the mineral world the notion of a vital force, which led them 

 to speak of the earth as a great living organism, and to look 

 upon the various changes in its air, its waters, and its rocky 

 depths, as processes belonging to the life of our planet. 



