INTRODUCTION.
The share which worms have taken in the formation of the layer of
vegetable mould, which covers the whole surface of the land in every
moderately humid country, is the subject of the present volume. 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.