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 ofdifferent finely-divided earthy mat- 

 " ters, with animal or vegetable substances, in a 

 *' state of decomposition, and certain saline ingre- 

 ** clients. The earthy matters are the true basis 

 " of the soil ; the other parts, whether natural, 

 *' or artificially introduced, operate as manures. 

 " Four earths generally abound in the soils : the 

 " 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 siUceous, 

 " calcareous, and argillaceous particles j often 



