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 lime-kiln formerly stood in a grass-field near Leith Hill Place in
Surrey, and was pulled down 35 years before my visit; all the loose
rubbish had been carted away, excepting three large stones of quartzose
sandstone, which it was thought might hereafter be of some use. An old
workman remembered that they had been left on a bare surface of broken
bricks and mortar, close to the foundations of the kiln; but the whole
surrounding surface is now covered with turf and mould. The two largest
of these stones had never since been moved; nor could this easily have
been done, as, when I had them removed, it was the work of two men with
levers. One of these stones, and not the largest, was 64 inches long, 17
inches broad, and from 9 to 10 inches in thickness. Its lower surface
was somewhat protuberant in the middle; and this part still rested on
broken bricks and mortar, showing the truth of the old workman’s account.
Beneath the brick rubbish the natural sandy soil, full of fragments of
sandstone was found; and this could have yielded very little, if at all,
to the weight of the stone, as might have been expected if the sub-soil
had been clay. The surface of the field, for a distance of about 9
inches round the stone, gradually sloped up to it, and close to the stone
stood in most places about 4 inches above the surrounding ground. The
base of the stone was buried from 1 to 2 inches beneath the general
level, and the upper surface projected about 8 inches above this level,
or about 4 inches above the sloping border of turf. After the removal of
the stone it became evident that one of its pointed ends must at first
have stood clear above the ground by some inches, but its upper surface
was now on a level with the surrounding turf. When the stone was
removed, an exact cast of its lower side, forming a shallow crateriform
hollow, was left, the inner surface of which consisted of fine black
mould, excepting where the more protuberant parts rested on the
brick-rubbish. A transverse section of this stone, together with its
bed, drawn from measurements made after it had been displaced, is here
given on a scale of ½ inch to a foot (Fig. 6). The turf-covered border
which sloped up to the stone, consisted of fine vegetable mould, in one
part 7 inches in thickness. This evidently consisted of worm-castings,
several of which had been recently ejected. The whole stone had sunk in
the thirty-five years, as far as I could judge, about 1½ inch; and this
must have been due to the brick-rubbish beneath the more protuberant
parts having been undermined by worms. At this rate the upper surface of
the stone, if it had been left undisturbed, would have sunk to the
general level of the field in 247 years; but before this could have
occurred, some earth would have been washed down by heavy rain from the
castings on the raised border of turf over the upper surface of the
stone.
Public-domain text, read in full here on John Shaqi.
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