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
When the castings near Nice had been ejected on an inclined surface, the
disintegrated fragments rolled downwards, without losing their
distinctive shape; and in some places could “be collected in basketfuls.”
Dr. King observed a striking instance of this fact on the Corniche road,
where a drain, about 2½ feet wide and 9 inches deep, had been made to
catch the surface drainage from the adjoining hill-side. The bottom of
this drain was covered for a distance of several hundred yards, to a
depth of from 1½ to 3 inches, by a layer of broken castings, still
retaining their characteristic shape. Nearly all these innumerable
fragments had rolled down from above, for extremely few castings had been
ejected in the drain itself. The hill-side was steep, but varied much in
inclination, which Dr. King estimated at from 30° to 60° with the
horizon. He climbed up the slope, and “found every here and there little
embankments, formed by fragments of the castings that had been arrested
in their downward progress by irregularities of the surface, by stones,
twigs, &c. One little group of plants of _Anemone hortensis_ had acted
in this manner, and quite a small bank of soil had collected round it.
Much of this soil had crumbled down, but a great deal of it still
retained the form of castings.” Dr. King dug up this plant, and was
struck with the thickness of the soil which must have recently
accumulated over the crown of the rhizoma, as shown by the length of the
bleached petioles, in comparison with those of other plants of the same
kind, where there had been no such accumulation. The earth thus
accumulated had no doubt been secured (as I have everywhere seen) by the
smaller roots of the plants. After describing this and other analogous
cases, Dr. King concludes: “I can have no doubt that worms help greatly
in the process of denudation.”
_Ledges of earth on steep hill-sides_.—Little horizontal ledges, one
above another, have been observed on steep grassy slopes in many parts of
the world. The formation has been attributed to animals travelling
repeatedly along the slope in the same horizontal lines while grazing,
and that they do thus move and use the ledges is certain; but Professor
Henslow (a most careful observer) told Sir J. Hooker that he was
convinced that this was not the sole cause of their formation. Sir J.
Hooker saw such ledges on the Himalayan and Atlas ranges, where there
were no domesticated animals and not many wild ones; but these latter
would, it is probable, use the ledges at night while grazing like our
domesticated animals. A friend observed for me the ledges on the Alps of
Switzerland, and states that they ran at 3 or 4 ft. one above the other,
and were about a foot in breadth. They had been deeply pitted by the
feet of grazing cows. Similar ledges were observed by the same friend on
our Chalk downs, and on an old talus of chalk-fragments (thrown out of a
quarry) which had become clothed with turf.
Public-domain text, read in full here on John Shaqi.
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