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
The second stone was larger that the one just described, viz., 67 inches
in length, 39 in breadth, and 15 in thickness. The lower surface was
nearly flat, so that the worms must soon have been compelled to eject
their castings beyond its circumference. The stone as a whole had sunk
about 2 inches into the ground. At this rate it would have required 262
years for its upper surface to have sunk to the general level of the
field. The upwardly sloping, turf-covered border round the stone was
broader than in the last case, viz., from 14 to 16 inches; and why this
should be so, I could see no reason. In most parts this border was not
so high as in the last case, viz., from 2 to 2½ inches, but in one place
it was as much as 5½. Its average height close to the stone was probably
about 3 inches, and it thinned out to nothing. If so, a layer of fine
earth, 15 inches in breadth and 1½ inch in average thickness, of
sufficient length to surround the whole of the much elongated slab, must
have been brought up by the worms in chief part from beneath the stone in
the course of 35 years. This amount would be amply sufficient to account
for its having sunk about 2 inches into the ground; more especially if we
bear in mind that a good deal of the finest earth would have been washed
by heavy rain from the castings ejected on the sloping border down to the
level of the field. Some fresh castings were seen close to the stone.
Nevertheless, on digging a large hole to a depth of 18 inches where the
stone had lain, only two worms and a few burrows were seen, although the
soil was damp and seemed favourable for worms. There were some large
colonies of ants beneath the stone, and possibly since their
establishment the worms had decreased in number.
The third stone was only about half as large as the others; and two
strong boys could together have rolled it over. I have no doubt that it
had been rolled over at a moderately recent time, for it now lay at some
distance from the two other stones at the bottom of a little adjoining
slope. It rested also on fine earth, instead of partly on brick-rubbish.
In agreement with this conclusion, the raised surrounding border of turf
was only 1 inch high in some parts, and 2 inches in other parts. There
were no colonies of ants beneath this stone, and on digging a hole where
it had lain, several burrows and worms were found.
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