186 On plaster of Paris. 



what means, its own decomposition is effected; so as to 

 let loose its operative parts, that they may act on the sub- 

 stances promotive of vegetation : are subjects of diifer- 

 ence and speculation. Many of the causes of effects, we 

 see in this and other substances, are hidden among the 

 arcana of nature. We shall therefore find it more satis- 

 factory to make accurate observations on effects; and 

 thus trace, as decisively as necessary f r practical men to 

 know, the immediate causes producing such effects. 

 Now we always perceive, that, on the first application of 

 plaster to o/c? fields, the effect is wonderful. We know 

 that, in such fields, decayed and decaying vegetable, and 

 often animal, matter, is abundant. Is it then not reason- 

 able to suppose, that the inert vegetable matter, which 

 is chiefly the connponent part of the surface or super 

 stratum of such fields; is the pabulum for the plaster? 

 And that when this is exhausted it must be renewed ?-— 

 It is in vain to say, that, in newly cleared land, where ve- 

 getable matter profusely abounds ; plaster shews little or 

 no effect. Nature in its prime needs no artificial auxili- 

 ary. Like the poet's description of female beauty, which 

 " needs not the foreign aid of ornament ;'' it has fertility 

 enough in itself ; and indeed often requires checks, more 

 than stimulants. Nor is it an argument against this view 

 of the subject, that, on lands in high culture by dung, &c. 

 strips plastered, and those to which gypsum has not been 

 applied, shew litde, if any difference. The fertility of 

 such lands is equalised and ample ; and no additional sti- 

 mulant is necessary. Over-dunged soils, (seldom occur- 

 ring) are over luxuriant ; and not desirable. 



The question, then, is ; ho\t to restore the lost pabu- 

 lum consumed by applications of plaster? Experience 

 suggests to me, the practical answer. — Plough in a small 

 proportion of dung ; or, what is more attainable, green 

 manures. I am aware that my much respected revolu- 



