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1st, Substances which correct the defects of the soil, and adaptit for its various functions in the production of vegetables.
2d, Such as facilitate the decomposition of vegetable foodlodged in the soil.
3d, Such as directly furnish food to growing plants, f
But the author above mentioned justly observes, that substan-ces used as manures may be adapted to more than one of the a-bove purposes, and, of coarse, cannot, with strict propriety, bearranged under any of the above classes. To avoid this dilem-ma, we are obliged to resort to the other mode of classification,and arrange all manures according to the origin from whencethey are derived. And having placed all the substances, knownto have any efFect as manures under the particular classes towhich they naturally seem to belong, by examining each in theirorder, inquiring into their respective properties,, and the differenteffects they ought to produce, so far as science or experience hasinstructed, the husbandman may be enabled to judge how to ap-ply any of them, in all circumstances, with the greatest proprie-ty, and with the surest prospect of success. The classificationwill thus be the following.
1st, Fossil manures; that is, substances taken from the earth,or having the character of Earths, as defined in Sect . I.
2d, Animal; the exuvise and remains of animal bodies.
3d, Vegetable ; all vegetable substances, after vegetable, lifehas ceased.
4th, Composite ; by which is meant the mixtures of the threeformer, which husbandmen commonly use as manures.
Under the three first will be specified, all substances whichhave been used as manures, either separately or mixed, makingsome inquiries concerning the qualities of each; but as these sub-stances, particularly those of the second and third class, are sel-dom applied in a separate state, these mixtures, in their differentproportions, and the manner in which they are managed, mustbe considered at some length under the last class.
Fossil Manures.
Fossil manures are of three kinds ; 1st, Calcareous ; 2d, Non-calcareous ; 3d, Mixed.
1st. -Calcareous .—The calcareous manures are limestone andmarble, burnt and reduced to powder ; marble earth, sea-shells :Shell marl, soaper’s waste, and Mitchell’s manure, till better
f Tlie heads under which Dr Hope of Edinburgh distributes manures in hishectares on Chemistry, are, 1. Those which furnish nourishment to plants; 2.Those which act by stimulating the vegetable fibre; 3. Those which operate bybringing the remains of organized bodies into a state fit for nourishing plants;4. Those which ameliorate the texture of the soil; and, 5 . Those which correctany noxious impregnation in the soil, inimicalto vegetation. It is obvious thatsome substances may act in more ways than one; they are then arranged underUnit head which embraces their principal mode of operation.