222 CONSERVATIVE ORGANS. [LECT. V. 



a chalk soil was heated to 69' only under simi- 

 lar circumstances. But when removed into the 

 shade at 62', the mould lost, in half an hour, 

 15 : and the chalk only 4 U *. In many respects, 

 therefore, the considering caloric as a general 

 component of soils, is not too great a refinement 

 to be adopted. 



The last component of soils which we have to 

 mention, has always been regarded as the most 

 important of the whole. We allude to animal and 

 vegetable matter in a state of decomposition, from 

 which the black mould which constitutes the rich- 

 ness of soils is almost altogether formed. But the 

 analysis of some of the most fertile soils has 

 proved, that their fertility does not depend on the 

 presence of a large proportion of these substances. 

 Thus Sir H. Davy found that the soil of a very 

 fertile field in East Lothian, contained nine parts 

 only in the hundred of decomposed animal and 

 vegetable matter ; and a soil from the low parts 

 of Somersetshire, long celebrated for yielding large 

 crops of Wheat and Beans without manure, con- 

 tained five parts of these principles only in the 

 hundred-}-. It is indeed true, that the carbonaceous 

 matter contained in plants can be derived most 

 easily from decomposing animal and vegetable sub- 



* Elements of agricultural Chemistry, 2d edit. p. 179. 

 t Ibid. 



