This mould is generally of a blackish colour and a few
inches in thickness. In different districts it differs but little
in appearance, although it may rest on various subsoils. The
uniform fineness of the particles of which it is composed is one of
its chief characteristic features; and this may be well observed in
any gravelly country, where a recently-ploughed field immediately
adjoins one which has long remained undisturbed for pasture, and
where the vegetable mould is exposed on the sides of a ditch or
hole. The subject may appear an insignificant one, but we shall
see that it possesses some interest; and the maxim "de minimis non
curat lex," does not apply to science. Even Elie de Beaumont, who
generally undervalues small agencies and their accumulated effects,
remarks: {1} "La couche tres-mince de la terre vegetale est un
monument d'une haute antiquite, et, par le fait de sa permanence,
un objet digne d'occuper le geologue, et capable de lui fournir des
remarques interessantes." Although the superficial layer of
vegetable mould as a whole no doubt is of the highest antiquity,
yet in regard to its permanence, we shall hereafter see reason to
believe that its component particles are in most cases removed at
not a very slow rate, and are replaced by others due to the
disintegration of the underlying materials.
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