ANALYSIS OF SOILS. 19 



a considerable portion of sand, and vegetable earth : 

 but though I know the probable cause of this field 

 bearing such good wheat, I cannot bring the sur- 

 rounding and inferior ones into a like constitution, 

 the expense far exceeding any hope of remuneration. 

 Rudolph Glauber obtained gold from common sand, 

 but it was an expensive article ! Temporary food 

 for a crop may be found in animal, vegetable, or 

 earthy manures, but these are exhaustible ; and when 

 aliment ceases, the crop proportionably diminishes. 

 In one respect, chemical investigation may import- 

 antly aid the agriculturist, by pointing out the 

 proportion of magnesian earth in certain limes used 

 for manure, and thus indicate its beneficial or 

 injurious effects on vegetation. I should not like 

 lime containing twenty per cent, of this earth ; but 

 when it contains a much smaller proportion, I should 

 not think it very deleterious. This earth acts as a 

 caustic to vegetation, and, neither being soluble 

 in water, nor possessing the other virtues of lime, 

 diminishes the number of bushels used according 

 to its existence, and thus deprives the crop of that 

 portion of benefit: but after all, as Kirwan says, 

 the secret processes of vegetation take place in the 

 dark, exposed to the various and indeterminable 

 influences of the atmosphere ; and hence the dif- 

 ficulty of determining on what peculiar circumstance 

 success or failure depends, for the diversified ex- 

 perience of years alone can afford a rational 

 foundation for solid and specific conclusions. 



The real goodness of a soil consists principally, 



c 2 



