The Formation of Vegetable Mould Through the Action of Worms / With Observations on Their Habits

by Charles Darwin

THE FORMATION OF
VEGETABLE MOULD
THROUGH THE ACTION OF WORMS
WITH OBSERVATIONS ON THEIR HABITS.

BY CHARLES DARWIN, LL.D., F.R.S.

THIRTEENTH THOUSAND
WITH ILLUSTRATIONS

LONDON
JOHN MURRAY, ALBEMARLE STREET
1904

PRINTED BY
WILLIAM CLOWES AND SONS, LIMITED,
LONDON AND BECCLES.

CONTENTS.

Introduction	Page [1]–6
CHAPTER I. HABITS OF WORMS.
Nature of the sites inhabited—Can live long underwater—Nocturnal—Wander about at night—Often lieclose to the mouths of their burrows, and are thus destroyed inlarge numbers by birds—Structure—Do not possess eyes,but can distinguish between light and darkness—Retreatrapidly when brightly illuminated, not by a reflexaction—Power of attention—Sensitive to heat andcold—Completely deaf—Sensitive to vibrations and totouch—Feeble power of smell—Taste—Mentalqualities—Nature offood—Omnivorous—Digestion—Leaves before beingswallowed, moistened with a fluid of the nature of the pancreaticsecretion—Extra-stomachal digestion—Calciferousglands, structure of—Calcareous concretions formed in theanterior pair of glands—The calcareous matter primarily anexcretion, but secondarily serves to neutralise the acidsgenerated during the digestive process.	[7]–15
CHAPTER II. HABITS OF WORMS—continued.
Manner in which worms seize objects—Their power ofsuction—The instinct of plugging up the mouths of theirburrows—Stones piled over the burrows—The advantagesthus gained—Intelligence shown by worms in their manner ofplugging up their burrows—Various kinds of leaves and otherobjects thus used—Triangles of paper—Summary ofreasons for believing that worms exhibit someintelligence—Means by which they excavate their burrows, bypushing away the earth and swallowing it—Earth alsoswallowed for the nutritious matter which it contains—Depthto which worms burrow, and the construction of theirburrows—Burrows lined with castings, and in the upper partwith leaves—The lowest part paved with little stones orseeds—Manner in which the castings are ejected—Thecollapse of old burrows—Distribution ofworms—Tower-like castings in Bengal—Gigantic castingson the Nilgiri Mountains—Castings ejected in allcountries.	[52]–120
CHAPTER III. THE AMOUNT OF FINE EARTH BROUGHT UP BYWORMS TO THE SURFACE.
Rate at which various objects strewed on the surface ofgrass-fields are covered up by the castings of worms—Theburial of a paved path—The slow subsidence of great stonesleft on the surface—The number of worms which live within agiven space—The weight of earth ejected from a burrow, andfrom all the burrows within a given space—The thickness ofthe layer of mould which the castings on a given space would formwithin a given time if uniformly spread out—The slow rateat which mould can increase to a greatthickness—Conclusion.	[121]–163
CHAPTER IV. THE PART WHICH WORMS HAVE PLAYED IN THEBURIAL OF ANCIENT BUILDINGS.
The accumulation of rubbish on the sites of great citiesindependent of the action of worms—The burial of a Romanvilla at Abinger—The floors and walls penetrated byworms—Subsidence of a modern pavement—The buriedpavement at Beaulieu Abbey—Roman villas at Chedworth andBrading—The remains of the Roman town atSilchester—The nature of the débris by which theremains are covered—The penetration of the tesselatedfloors and walls by worms—Subsidence of thefloors—Thickness of the mould—The old Roman city ofWroxeter—Thickness of the mould—Depth of thefoundations of some of the Buildings—Conclusion.	[164]–208
CHAPTER V. THE ACTION OF WORMS IN THE DENUDATION OFTHE LAND.
Evidence of the amount of denudation which the land hasundergone—Sub-aerial denudation—The deposition ofdust—Vegetable mould, its dark colour and fine texturelargely due to the action of worms—The disintegration ofrocks by the humus-acids—Similar acids apparently generatedwithin the bodies of worms—The action of these acidsfacilitated by the continued movement of the particles ofearth—A thick bed of mould checks the disintegration of theunderlying soil and rocks. Particles of stone worn ortriturated in the gizzards of worms—Swallowed stones serveas mill-stones—The levigated state of thecastings—Fragments of brick in the castings over ancientbuildings well rounded. The triturating power of worms notquite insignificant under a geological point of view.	[209]–236
CHAPTER VI. THE DENUDATION OF THELAND—continued.
Denudation aided by recently ejected castings flowing downinclined grass-covered surfaces—The amount of earth whichannually flows downwards—The effect of tropical rain onworm castings—The finest particles of earth washedcompletely away from castings—The disintegration of driedcastings into pellets, and their rolling down inclinedsurfaces—The formation of little ledges on hill-sides, inpart due to the accumulation of disintegratedcastings—Castings blown to leeward over level land—Anattempt to estimate the amount thus blown—The degradationof ancient encampments and tumuli—The preservation of thecrowns and furrows on land anciently ploughed—The formationand amount of mould over the Chalk formation.	[237]–279
CHAPTER VII. CONCLUSION.
Summary of the part which worms have played in the historyof the world—Their aid in the disintegration ofrocks—In the denudation of the land—In thepreservation of ancient remains—In the preparation of thesoil for the growth of plants—Mental powers ofworms—Conclusion.	[280]–288

INTRODUCTION.

The share which worms have taken in the formation of the layer of vegetable mould, which covers the whole surface of the land in every moderately humid country, is the subject of the present volume. This mould is generally of a blackish colour and a few inches in thickness. In different districts it differs but little in appearance, although it may rest on various subsoils. The uniform fineness of the particles of which it is composed is one of its chief characteristic features; and this may be well observed in any gravelly country, where a recently-ploughed field immediately adjoins one which has long remained undisturbed for pasture, and where the vegetable mould is exposed on the sides of a ditch or hole. The subject may appear an insignificant one, but we shall see that it possesses some interest; and the maxim “de minimis non curat lex,” does not apply to science. Even Élie de Beaumont, who generally undervalues small agencies and their accumulated effects, remarks: [2] “La couche très-mince de la terre végétale est un monument d’une haute antiquité, et, par le fait de sa permanence, un objet digne d’occuper le géologue, et capable de lui fournir des remarques intéressantes.” Although the superficial layer of vegetable mould as a whole no doubt is of the highest antiquity, yet in regard to its permanence, we shall hereafter see reason to believe that its component particles are in most cases removed at not a very slow rate, and are replaced by others due to the disintegration of the underlying materials.

As I was led to keep in my study during many months worms in pots filled with earth, I became interested in them, and wished to learn how far they acted consciously, and how much mental power they displayed. I was the more desirous to learn something on this head, as few observations of this kind have been made, as far as I know, on animals so low in the scale of organization and so poorly provided with sense-organs, as are earth-worms.