68 ON THE CULTIVATION OF THE EARTH. 



" which are the constituent parts of vegetables, 

 " in carbon, hydrogene, and oxygene. 



" The circumstances necessary for the putre- 

 " faction of animal substances are similar to those 

 " required for the fermentation of vegetable sub- 

 " stances ; a temperature above the freezing 

 " point, the presence of water, and the presence 

 " of oxygene, at least in the first stage of the 

 " process." 



He likewise says, " Soils in all cases consist of 

 " a mixture of different finely-divided earthy mat- 

 " ters, .with animal or vegetable substances, in a 

 " state of decomposition, and certain saline ingre- 

 " dients. The earthy matters are the true basis 

 " p^jthejtjQil ^ the other parts, whether natural, 

 " or artificially introduced, operate as manures. 

 " Four earths generally abound in the soils : the 

 41 aluminous, the siliceous, the calcareous, and the 

 " magnesian. These earths, I have discovered, 

 " consist of highly inflammable metals united to 

 " pure air or oxygene ; and they are not, as far 

 " as we know, decomposed or altered in vege- 

 tation." 



Mr. Kirwan says, " All plants (except the 

 " sub-aqueous,) grow in a mixed earth, moist- 

 " ened with rain and dew, and exposed to the 

 " atmosphere. If this earth be chemically exa- 

 " mined, it will be found to consist of siliceous, 

 " calcareous, and argillaceous particles ; often 



