CALCAREOUS MANURES— THEORY. 59 



the surface to the enriching matters furnished by the growth and decay of 

 plants. And therefore, before being brought into cultivation, a poor clay 

 soil would derive scarcely any benefit from its small power of combining 

 chemically with putrescent matters. If then it is considered how small is 

 the power of both silicious and aluminous earths to receive and retain pu- 

 trescent manures, it will cease to cause surprise that such soils cannot be 

 thus enriched, with profit, if at all. It would indeed be strange and un- 

 accountable, if earths and soils thus constituted could be enriched by pu- 

 trescent manures alone. 



Davy states that both aluminous and calcareous earth will combine with 

 any vegetable extract, so as to render it less soluble, (and consequently not 

 subject to the waste that would otherwise take place,) and hence " that the 

 soils which contain most alumina and carbonate of lime, are those which 

 act with the greatest chemical energy in preserving manures." Here is 

 high authority for calcareous earth possessing the power which my argu- 

 ment demands, but not in so great a degree as I think it deserves. Davy 

 apparently places both earths in this respect on the same footing, and allows 

 to aluminous soils retentive powers equal to the calcareous. But though 

 he gives evidence (from chemical experiments) of this power in both earths, 

 he does not seem to have investigated the difference of their forces. Nor 

 could he deem it very important, holding the opinion which he elsewhere 

 expresses, that calcareous earth acts " merely by forming a useful earthy 

 ingredient in the soil," and consequently attributing to it no remarkable 

 chemical effects as a manure. I shall offer some reasons for believing that 

 the powers of attracting and retaining manure, possessed by these two 

 earths, differ greatly in their degrees of force. 



Our aluminous and calcareous soils, through the whole of their virgin 

 state, have had equal means of receiving vegetable matter ; and if their 

 powers for retaining it were nearly equal, so would be their acquired fer- 

 tility. Instead of this, while the calcareous soils have been raised to the 

 highest condition, many of the tracts of clay soil remain the poorest and 

 most worthless. It is true that the one labored under acidity, from which 

 the other was free. But if we suppose nine-tenths of the vegetable matter 

 to have been rendered useless by that poisonous quality, the remaining 

 tenth, applied for so long a time, would have made fertile any soil that had 

 the power to retain the enriching matter. 



Many kinds of shells are partly composed of gelatinous animal matter, 

 which, I suppose, must be chemically combined with the calcareous earth, 

 and by that means only is preserved from the putrefaction and waste that 

 would otherwise certainly and speedily take place. Indeed, the large pro- 

 portion of animal matter which thus helps to constitute shells, instead of 

 making them more perishable, serves to increase their firmness and solidity. 

 When long exposure, as in fossil shells, has destroyed all animal matter, 

 the texture of the calcareous substance is greatly weakened. A simple 

 experiment will serve to separate, and make manifest to the eye, the animal 

 matter which is thus combined with and preserved by the calcareous earth. 

 If a fresh-water muscle-shell is kept for some days immersed in a weak 

 mixture of muriatic acid and water, all the calcareous part will be gra- 

 dually dissolved, leaving the animal matter so entire, as to appear still to 

 be a whole shell — but which, when lifted from the fluid which supports it, 

 will prove to be entirely a flaccid, gelatinous, and putrescent substance, 

 without a particle of calcareous matter being left. Yet this substance, 

 which is so highly putrescent when alone, would have been preserved in 

 combination with calcareous matter, in the shell, for many years, if exposed 

 to the usual changes of air and moisture; and if secured from such 

 changes, would be almost imperishable. 



