The Formation of Vegetable Mould Through the Action of Worms: With Observations on Their HabitsDarwin, Charles
Science
The Formation of Vegetable Mould Through the Action of Worms: With Observations on Their Habits
Darwin, Charles
Earthworms; Humification; Soils
A narrow path running across part of my lawn was paved in 1843 with small
flagstones, set edgeways; but worms threw up many castings and weeds grew
thickly between them. During several years the path was weeded and
swept; but ultimately the weeds and worms prevailed, and the gardener
ceased to sweep, merely mowing off the weeds, as often as the lawn was
mowed. The path soon became almost covered up, and after several years
no trace of it was left. On removing, in 1877, the thin overlying layer
of turf, the small flag-stones, all in their proper places, were found
covered by an inch of fine mould.
Two recently published accounts of substances strewed on the surface of
pasture-land, having become buried through the action of worms, may be
here noticed. The Rev. H. C. Key had a ditch cut in a field, over which
coal-ashes had been spread, as it was believed, eighteen years before;
and on the clean-cut perpendicular sides of the ditch, at a depth of at
least seven inches, there could be seen, for a length of 60 yards, “a
distinct, very even, narrow line of coal-ashes, mixed with small coal,
perfectly parallel with the top-sward.” {136a} This parallelism and the
length of the section give interest to the case. Secondly, Mr. Dancer
states {136b} that crushed bones had been thickly strewed over a field;
and “some years afterwards” these were found “several inches below the
surface, at a uniform depth.”
The Rev. Mr. Zincke informs me that he has lately had an orchard dug to
the unusual depth of 4 feet. The upper 18 inches consisted of
dark-coloured vegetable mould, and the next 18 inches of sandy loam,
containing in the lower part many rolled pieces of sandstone, with some
bits of brick and tile, probably of Roman origin, as remains of this
period have been found close by. The sandy loam rested on an indurated
ferruginous pan of yellow clay, on the surface of which two perfect celts
were found. If, as seems probable, the celts were originally left on the
surface of the land, they have since been covered up with earth 3 feet in
thickness, all of which has probably passed through the bodies of worms,
excepting the stones which may have been scattered on the surface at
different times, together with manure or by other means. It is difficult
otherwise to understand the source of the 18 inches of sandy loam, which
differed from the overlying dark vegetable mould, after both had been
burnt, only in being of a brighter red colour, and in not being quite so
fine-grained. But on this view we must suppose that the carbon in
vegetable mould, when it lies at some little depth beneath the surface
and does not continually receive decaying vegetable matter from above,
loses its dark colour in the course of centuries; but whether this is
probable I do not know.
Public-domain text, read in full here on John Shaqi.
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