192 ON THE COMPOSITION OF SOILS, &C. 



lengths he has gone, and given the ingredients 

 and proportions of several fertile soils ; he has 

 also described the method of analyzing soils; 

 but the quantity of earth required by plants, for 

 their various compounds, is so small, as beyond 

 all doubt to sustain Mr. Kirwan's opinion, that 

 it is supplied by water. 



That the clearest spring water contains a 

 quantity of earth, every person may obtain oc- 

 ular demonstration of, by examining the inside 

 of a tea kettle, in which water has been boiled for 

 some time; the earth that will be found adhering 

 to it, must have been deposited from water. 



Thus then, as far as the earths are concerned 

 as an article of consumption, or a necessary 

 component in the food of plants, we may rest 

 satisfied with the natural composition of most 

 soils, and direct our attention only to its consti- 

 tution, as it influences the absorption, retention, 

 and distribution of water ; and to its chemical 

 powers, in regulating and determining the ex- 

 tent and effect of the different fermentations, 

 combinations, and decompositions, which are 

 requisite for the reduction and preparation of 

 the various substances which constitute the food 

 of plants. 



If the earth was left solely to the action of 

 the natural and chemical principles of affinity. 



