DURATION OP EARTHY MANURES. 205 



Most farmers are so accustomed to consider manures as being 

 fleeting in their operation and existence in soil, as are the ordinary 

 putrescent manures, that it is difficult for them to have any con- 

 ception of any kind lasting and acting for ever. And this difficulty 

 of conception, stands much in the way of my argument. But, how- 

 ever little used by farmers, or even thought of, in this light, it ig 

 obvious and undeniable, that certain mineral manures will continue 

 in operation, and without abatement of effects, as long as the soil, 

 or the habitable globe itself, shall exist. Thus, clay is a manure 

 for sandy soil, serving to stiffen and compact its before too light, 

 loose, and open texture. Sand also is a manure for stiff clay soils, 

 serving to correct their tenacity when wet, and their obduracy when 

 dry, and make them more open, light, and permeable j more easy 

 to cultivate, and more safe for production. And in either of these 

 manuring operations, it is self-evident, and not admitting of ques- 

 tion, that the continuance of these manures, and their good effects, 

 will be eternal. 



Carbonate of lime in soil, whether supplied by nature or art, 

 like sand and clay, is a ponderous earth, and but to small extent 

 liable to waste or loss by any natural agency. It is insoluble by 

 water, except so far as water may contain carbonic acid, which 

 renders water a solvent of carbonate of lime. But this impregna- 

 tion of water in soil is very limited. It can scarcely occur at all 

 except in the usual mode, by rain-water, when descending through 

 the atmosphere, absorbing and bringing to the earth the very small 

 and strictly limited quantity of carbonic acid in the lower atmos- 

 phere. Except in this respect, and for the still more minute and 

 scarcely appreciable quantity of lime taken up by growing plants, (as 

 stated above), carbonate of lime in soil would seem to be as inde- 

 structible, and as surely abiding through all future time, as the clay 

 or the sand which might also have been given as manure, or other- 

 wise held as natural ingredients of the same soil. As rain-water 

 always brings to the earth some carbonic acid, though in extremely 

 small quantity, still, to that small extent, the carbonate of lime in 

 the soil is liable to be dissolved; and when so dissolved, if there 

 were no counteracting agencies, some of the dissolved earth might 

 be lost (possibly) by nitration through the soil, or, less improbably, 

 by being floated off from the surface, in the flowing away of any 

 excess of rain-water. But there are counteracting agencies ope- 

 rating to prevent the loss of lime in this, and also in other soluble 

 forms. According to my own early (and then unsupported) views 

 of the formation of acid in soil, as well as according to the now 

 received general opinions on that subject, the carbonate of lime 

 would soon begin to be changed to other salts of lime, by combina- 

 tion with other acids in the soil. Some one or more of these newly 

 formed salts might be much more soluble in water than the carbo- 

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