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
Coal-cinders had been strewed over another field, at a date which could
not be positively ascertained, so thickly that they formed (October,
1837) a layer, 1 inch in thickness at a depth of about 3 inches from the
surface. The layer was so continuous that the over-lying dark vegetable
mould was connected with the sub-soil of red clay only by the roots of
the grasses; and when these were broken, the mould and the red clay fell
apart. In a third field, on which coal-cinders and burnt marl had been
strewed several times at unknown dates, holes were dug in 1842; and a
layer of cinders could be traced at a depth of 3½ inches, beneath which
at a depth of 9½ inches from the surface there was a line of cinders
together with burnt marl. On the sides of one hole there were two layers
of cinders, at 2 and 3½ inches beneath the surface; and below them at a
depth in parts of 9½, and in other parts of 10½ inches there were
fragments of burnt marl. In a fourth field two layers of lime, one above
the other, could be distinctly traced, and beneath them a layer of
cinders and burnt marl at a depth of from 10 to 12 inches below the
surface.
[Picture: Fig. 5: Section of the vegetable mould in a field. Fig. 6:
Traverse section across a large stone]
A piece of waste, swampy land was enclosed, drained, ploughed, harrowed
and thickly covered in the year 1822 with burnt marl and cinders. It was
sowed with grass seeds, and now supports a tolerably good but coarse
pasture. Holes were dug in this field in 1837, or 15 years after its
reclamation, and we see in the accompanying diagram (Fig. 5), reduced to
half of the natural scale, that the turf was ½ inch thick, beneath which
there was a layer of vegetable mould 2½ inches thick. This layer did not
contain fragments of any kind; but beneath it there was a layer of mould,
1½ inch in thickness, full of fragments of burnt marl, conspicuous from
their red colour, one of which near the bottom was an inch in length; and
other fragments of coal-cinders together with a few white quartz pebbles.
Beneath this layer and at a depth of 4½ inches from the surface, the
original black, peaty, sandy soil with a few quartz pebbles was
encountered. Here therefore the fragments of burnt marl and cinders had
been covered in the course of 15 years by a layer of fine vegetable
mould, only 2½ inches in thickness, excluding the turf. Six and a half
years subsequently this field was re-examined, and the fragments were now
found at from 4 to 5 inches beneath the surface. So that in this
interval of 6½ years, about 1½ inch of mould had been added to the
superficial layer. I am surprised that a greater quantity had not been
brought up during the whole 21½ years, for in the closely underlying
black, peaty soil there were many worms. It is, however, probable that
formerly, whilst the land remained poor, worms were scanty; and the mould
would then have accumulated slowly. The average annual increase of
Public-domain text, read in full here on John Shaqi.
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