189 



ON THE COMPOSITION OF SOILS, AND THE 

 AGENCY OF THE EARTHS IN VEGETATION, 



The surface of the earth is a variable com- 

 pound, but as it respects vegetation, it is not 

 necessary to pursue its analysis beyond the fol- 

 lowing simple divisions, viz. calx, or the cal- 

 careous ; silex, or the siliceous ; clay, or the 

 argillaceous ; magnesia, or the magnesian j and 

 carbon, or the carbonaceous, or, as this is com- 

 monly called, mould. 



The first four substances, are what Miller 

 properly calls the containing part, or body, bed, 

 or couch J and the fifth substance or mould, 

 (which is the result of decayed animal and ve- 

 getable matter,) the part contained. 



It is clearly proved that neither of the four 

 substances, calx, clay, magnesia, or silex, in a 

 simple state, whether separate or combined, will 

 support a plant ; and that the vegetative power of 

 ever}'^ part of the earth, is determined by the 

 quantity of mould, or animal and vegetable mat- 

 ter it contains. 



On the earths, as forming a component part 

 of plants, Mr. Kirwan says, *' The next most 



