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The Formation of Vegetable Mould through the action of worms with observations of their habits by Charles Darwin

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20. Trench 31 inches deep (31)

Field on the western side of the space enclosed within the old

21. Trench 28 inches deep, when undisturbed sand was reached (16)

22. Trench 29 inches deep, when undisturbed sand was reached (15)

23. Trench 14 inches deep, and then came upon a building (14)

Dr. Johnson distinguished as mould the earth which differed, more
or less abruptly, in its dark colour and in its texture from the
underlying sand or rubble. In the specimens sent to me, the mould
resembled that which lies immediately beneath the turf in old
pasture-land, excepting that it often contained small stones, too
large to have passed through the bodies of worms. But the trenches
above described were dug in fields, none of which were in pasture,
and all had been long cultivated. Bearing in mind the remarks made
in reference to Silchester on the effects of long-continued
culture, combined with the action of worms in bringing up the finer
particles to the surface, the mould, as so designated by Dr.
Johnson, seems fairly well to deserve its name. Its thickness,
where there was no causeway, floor or walls beneath, was greater
than has been elsewhere observed, namely, in many places above 2
ft., and in one spot above 3 ft. The mould was thickest on and
close to the nearly level summit of the field called "Shop
Leasows," and in a small adjoining field, which, as I believe, is
of nearly the same height. One side of the former field slopes at
an angle of rather above 2 degrees, and I should have expected that
the mould, from being washed down during heavy rain, would have
been thicker in the lower than in the upper part; but this was not
the case in two out of the three trenches here dug.

In many places, where streets ran beneath the surface, or where old
buildings stood, the mould was only 8 inches in thickness; and Dr.
Johnson was surprised that in ploughing the land, the ruins had
never been struck by the plough as far as he had heard. He thinks
that when the land was first cultivated the old walls were perhaps
intentionally pulled down, and that hollow places were filled up.
This may have been the case; but if after the desertion of the city
the land was left for many centuries uncultivated, worms would have
brought up enough fine earth to have covered the ruins completely;
that is if they had subsided from having been undermined. The
foundations of some of the walls, for instance those of the portion
still standing about 20 feet above the ground, and those of the
marketplace, lie at the extraordinary depth of 14 feet; but it is
highly improbable that the foundations were generally so deep. The
mortar employed in the buildings must have been excellent, for it
is still in parts extremely hard. Wherever walls of any height
have been exposed to view, they are, as Dr. Johnson believes,
still perpendicular. The walls with such deep foundations cannot
have been undermined by worms, and therefore cannot have subsided,
as appears to have occurred at Abinger and Silchester. Hence it is
very difficult to account for their being now completely covered
with earth; but how much of this covering consists of vegetable
mould and how much of rubble I do not know. The market-place, with
the foundations at a depth of 14 feet, was covered up, as Dr.
Johnson believes, by between 6 and 24 inches of earth. The tops of
the broken-down walls of a caldarium or bath, 9 feet in depth, were
likewise covered up with nearly 2 feet of earth. The summit of an
arch, leading into an ash-pit 7 feet in depth, was covered up with
not more than 8 inches of earth. Whenever a building which has not
subsided is covered with earth, we must suppose, either that the
upper layers of stone have been at some time carried away by man,
or that earth has since been washed down during heavy rain, or
blown down during storms, from the adjoining land; and this would
be especially apt to occur where the land has long been cultivated.
In the above cases the adjoining land is somewhat higher than the
three specified sites, as far as I can judge by maps and from
information given me by Dr. Johnson. If; however, a great pile of
broken stones, mortar, plaster, timber and ashes fell over the
remains of any building, their disintegration in the course of
time, and the sifting action of worms, would ultimately conceal the
whole beneath fine earth.

Conclusion. --The cases given in this chapter show that worms have
played a considerable part in the burial and concealment of several
Roman and other old buildings in England; but no doubt the washing
down of soil from the neighbouring higher lands, and the deposition
of dust, have together aided largely in the work of concealment.
Dust would be apt to accumulate wherever old broken-down walls
projected a little above the then existing surface and thus
afforded some shelter. The floors of the old rooms, halls and
passages have generally sunk, partly from the settling of the
ground, but chiefly from having been undermined by worms; and the
sinking has commonly been greater in the middle than near the
walls. The walls themselves, whenever their foundations do not lie
at a great depth, have been penetrated and undermined by worms, and
have consequently subsided. The unequal subsidence thus caused,
probably explains the great cracks which may be seen in many
ancient walls, as well as their inclination from the perpendicular.


Evidence of the amount of denudation which the land has undergone--
Sub-aerial denudation--The deposition of dust--Vegetable mould, its
dark colour and fine texture largely due to the action of worms--
The disintegration of rocks by the humus-acids --Similar acids
apparently generated within the bodies of worms--The action of
these acids facilitated by the continued movement of the particles
of earth--A thick bed of mould checks the disintegration of the
underlying soil and rocks. Particles of stone worn or triturated
in the gizzards of worms--Swallowed stones serve as mill-stones--
The levigated state of the castings--Fragments of brick in the
castings over ancient buildings well rounded. The triturating
power of worms not quite insignificant under a geological point of

No one doubts that our world at one time consisted of crystalline
rocks, and that it is to their disintegration through the action of
air, water, changes of temperature, rivers, waves of the sea,
earthquakes and volcanic outbursts, that we owe our sedimentary
formations. These after being consolidated and sometimes
recrystallized, have often been again disintegrated. Denudation
means the removal of such disintegrated matter to a lower level.
Of the many striking results due to the modern progress of geology
there are hardly any more striking than those which relate to
denudation. It was long ago seen that there must have been an
immense amount of denudation; but until the successive formations
were carefully mapped and measured, no one fully realised how great
was the amount. One of the first and most remarkable memoirs ever
published on this subject was that by Ramsay, {57} who in 1846
showed that in Wales from 9000 to 11,000 feet in thickness of solid
rock had been stripped off large tracks of country. Perhaps the
plainest evidence of great denudation is afforded by faults or
cracks, which extend for many miles across certain districts, with
the strata on one side raised even ten thousand feet above the
corresponding strata on the opposite side; and yet there is not a
vestige of this gigantic displacement visible on the surface of the
land. A huge pile of rock has been planed away on one side and not
a remnant left.

Until the last twenty or thirty years, most geologists thought that
the waves of the sea were the chief agents in the work of
denudation; but we may now feel sure that air and rain, aided by
streams and rivers, are much more powerful agents,--that is if we
consider the whole area of the land. The long lines of escarpment
which stretch across several parts of England were formerly
considered to be undoubtedly ancient coast-lines; but we now know
that they stand up above the general surface merely from resisting
air, rain and frost better than the adjoining formations. It has
rarely been the good fortune of a geologist to bring conviction to
the minds of his fellow-workers on a disputed point by a single
memoir; but Mr. Whitaker, of the Geological Survey of England, was
so fortunate when, in 1867, he published his paper "On sub-aerial
Denudation, and on Cliffs and Escarpments of the Chalk." {58}
Before this paper appeared, Mr. A. Tylor had adduced important
evidence on sub-aerial denudation, by showing that the amount of
matter brought down by rivers must infallibly lower the level of
their drainage basins by many feet in no immense lapse of time.
This line of argument has since been followed up in the most
interesting manner by Archibald Geikie, Croll and others, in a
series of valuable memoirs. {59} For the sake of those who have
never attended to this subject, a single instance may be here
given, namely, that of the Mississippi, which is chosen because the
amount of sediment brought down by this great river has been
investigated with especial care by order of the United States
Government. The result is, as Mr. Croll shows, that the mean level
of its enormous area of drainage must be lowered 1/4566 of a foot
annually, or 1 foot in 4566 years. Consequently, taking the best
estimate of the mean height of the North American continent, viz.
748 feet, and looking to the future, the whole of the great
Mississippi basin will be washed away, and "brought down to the
sea-level in less than 4,500,000 years, if no elevation of the land
takes place." Some rivers carry down much more sediment relatively
to their size, and some much less than the Mississippi.

Disintegrated matter is carried away by the wind as well as by
running water. During volcanic outbursts much rock is triturated
and is thus widely dispersed; and in all arid countries the wind
plays an important part in the removal of such matter. Wind-driven
sand also wears down the hardest rocks. I have shown {60} that
during four months of the year a large quantity of dust is blown
from the north-western shores of Africa, and falls on the Atlantic
over a space of 1600 miles in latitude, and for a distance of from
300 to 600 miles from the coast. But dust has been seen to fall at
a distance of 1030 miles from the shores of Africa. During a stay
of three weeks at St. Jago in the Cape Verde Archipelago, the
atmosphere was almost always hazy, and extremely fine dust coming
from Africa was continually falling. In some of this dust which
fell in the open ocean at a distance of between 330 and 380 miles
from the African coast, there were many particles of stone, about
1/1000 of an inch square. Nearer to the coast the water has been
seen to be so much discoloured by the falling dust, that a sailing
vessel left a track behind her. In countries, like the Cape Verde
Archipelago, where it seldom rains and there are no frosts, the
solid rock nevertheless disintegrates; and in conformity with the
views lately advanced by a distinguished Belgian geologist, De
Koninck, such disintegration may be attributed in chief part to the
action of the carbonic and nitric acids, together with the nitrates
and nitrites of ammonia, dissolved in the dew.

In all humid, even moderately humid, countries, worms aid in the
work of denudation in several ways. The vegetable mould which
covers, as with a mantle, the surface of the land, has all passed
many times through their bodies. Mould differs in appearance from
the subsoil only in its dark colour, and in the absence of
fragments or particles of stone (when such are present in the
subsoil), larger than those which can pass through the alimentary
canal of a worm. This sifting of the soil is aided, as has already
been remarked, by burrowing animals of many kinds, especially by
ants. In countries where the summer is long and dry, the mould in
protected places must be largely increased by dust blown from other
and more exposed places. For instance, the quantity of dust
sometimes blown over the plains of La Plata, where there are no
solid rocks, is so great, that during the "gran seco," 1827 to
1830, the appearance of the land, which is here unenclosed, was so
completely changed that the inhabitants could not recognise the
limits of their own estates, and endless lawsuits arose. Immense
quantities of dust are likewise blown about in Egypt and in the
south of France. In China, as Richthofen maintains, beds appearing
like fine sediment, several hundred feet in thickness and extending
over an enormous area, owe their origin to dust blown from the high
lands of central Asia. {61} In humid countries like Great Britain,
as long as the land remains in its natural state clothed with
vegetation, the mould in any one place can hardly be much increased
by dust; but in its present condition, the fields near high roads,
where there is much traffic, must receive a considerable amount of
dust, and when fields are harrowed during dry and windy weather,
clouds of dust may be seen to be blown away. But in all these
cases the surface-soil is merely transported from one place to
another. The dust which falls so thickly within our houses
consists largely of organic matter, and if spread over the land
would in time decay and disappear almost entirely. It appears,
however, from recent observations on the snow-fields of the Arctic
regions, that some little meteoric dust of extra mundane origin is
continually falling.

The dark colour of ordinary mould is obviously due to the presence
of decaying organic matter, which, however, is present in but small
quantities. The loss of weight which mould suffers when heated to
redness seems to be in large part due to water in combination being
dispelled. In one sample of fertile mould the amount of organic
matter was ascertained to be only 1.76 per cent.; in some
artificially prepared soil it was as much as 5.5 per cent., and in
the famous black soil of Russia from 5 to even 12 per cent. {62}
In leaf-mould formed exclusively by the decay of leaves the amount
is much greater, and in peat the carbon alone sometimes amounts to
64 per cent.; but with these latter cases we are not here
concerned. The carbon in the soil tends gradually to oxidise and
to disappear, except where water accumulates and the climate is
cool; {63} so that in the oldest pasture-land there is no great
excess of organic matter, notwithstanding the continued decay of
the roots and the underground stems of plants, and the occasional
addition of manure. The disappearance of the organic matter from
mould is probably much aided by its being brought again and again
to the surface in the castings of worms.

Worms, on the other hand, add largely to the organic matter in the
soil by the astonishing number of half-decayed leaves which they
draw into their burrows to a depth of 2 or 3 inches. They do this
chiefly for obtaining food, but partly for closing the mouths of
their burrows and for lining the upper part. The leaves which they
consume are moistened, torn into small shreds, partially digested,
and intimately commingled with earth; and it is this process which
gives to vegetable mould its uniform dark tint. It is known that
various kinds of acids are generated by the decay of vegetable
matter; and from the contents of the intestines of worms and from
their castings being acid, it seems probable that the process of
digestion induces an analogous chemical change in the swallowed,
triturated, and half-decayed leaves. The large quantity of
carbonate of lime secreted by the calciferous glands apparently
serves to neutralise the acids thus generated; for the digestive
fluid of worms will not act unless it be alkaline. As the contents
of the upper part of their intestines are acid, the acidity can
hardly be due to the presence of uric acid. We may therefore
conclude that the acids in the alimentary canal of worms are formed
during the digestive process; and that probably they are nearly of
the same nature as those in ordinary mould or humus. The latter
are well known to have the power of de-oxidising or dissolving per-
oxide of iron, as may be seen wherever peat overlies red sand, or
where a rotten root penetrates such sand. Now I kept some worms in
a pot filled with very fine reddish sand, consisting of minute
particles of silex coated with the red oxide of iron; and the
burrows, which the worms made through this sand, were lined or
coated in the usual manner with their castings, formed of the sand
mingled with their intestinal secretions and the refuse of the
digested leaves; and this sand had almost wholly lost its red
colour. When small portions of it were placed under the
microscope, most of the grains were seen to be transparent and
colourless, owing to the dissolution of the oxide; whilst almost
all the grains taken from other parts of the pot were coated with
the oxide. Acetic acid produced hardly any effect on his sand; and
even hydrochloric, nitric and sulphuric acids, diluted as in the
Pharmacopoeia, produced less effect than did the acids in the
intestines of the worms.

Mr. A. A. Julien has lately collected all the extant information
about the acids generated in humus, which, according to some
chemists, amount to more than a dozen different kinds. These
acids, as well as their acid salts (i.e., in combination with
potash, soda, and ammonia), act energetically on carbonate of lime
and on the oxides of iron. It is also known that some of these
acids, which were called long ago by Thenard azohumic, are enabled
to dissolve colloid silica in proportion to the nitrogen which they
contain. {64} In the formation of these latter acids worms
probably afford some aid, for Dr. H. Johnson informs me that by
Nessler's test he found 0.018 per cent. of ammonia in their

It may be here added that I have recently been informed by Dr.
Gilbert "that several square yards on his lawn were swept clean,
and after two or three weeks all the worm-castings on the space
were collected and dried. These were found to contain 0.35 of
nitrogen. This is from two to three times as much as we find in
our ordinary arable surface-soil; more than in our ordinary pasture
surface-soil; but less than in rich kitchen-garden mould.
Supposing a quantity of castings equal to 10 tons in the dry state
were annually deposited on an acre, this would represent a manuring
of 78 lbs. of nitrogen per acre per annum; and this is very much
more than the amount of nitrogen in the annual yield of hay per
acre, if raised without any nitrogenous manure. Obviously, so far
as the nitrogen in the castings is derived from surface-growth or
from surface-soil, it is not a gain to the latter; but so far as it
is derived from below, it is a gain."

The several humus-acids, which appear, as we have just seen, to be
generated within the bodies of worms during the digestive process,
and their acid salts, play a highly important part, according to
the recent observations of Mr. Julien, in the disintegration of
various kinds of rocks. It has long been known that the carbonic
acid, and no doubt nitric and nitrous acids, which are present in
rain-water, act in like manner. There is, also, a great excess of
carbonic acid in all soils, especially in rich soils, and this is
dissolved by the water in the ground. The living roots of plants,
moreover, as Sachs and others have shown, quickly corrode and leave
their impressions on polished slabs of marble, dolomite and
phosphate of lime. They will attack even basalt and sandstone.
{65} But we are not here concerned with agencies which are wholly
independent of the action of worms.

The combination of any acid with a base is much facilitated by
agitation, as fresh surfaces are thus continually brought into
contact. This will be thoroughly effected with the particles of
stone and earth in the intestines of worms, during the digestive
process; and it should be remembered that the entire mass of the
mould over every field, passes, in the course of a few years,
through their alimentary canals. Moreover as the old burrows
slowly collapse, and as fresh castings are continually brought to
the surface, the whole superficial layer of mould slowly revolves
or circulates; and the friction of the particles one with another
will rub off the finest films of disintegrated matter as soon as
they are formed. Through these several means, minute fragments of
rocks of many kinds and mere particles in the soil will be
continually exposed to chemical decomposition; and thus the amount
of soil will tend to increase.

As worms line their burrows with their castings, and as the burrows
penetrate to a depth of 5 or 6, or even more feet, some small
amount of the humus-acids will be carried far down, and will there
act on the underlying rocks and fragments of rock. Thus the
thickness of the soil, if none be removed from the surface, will
steadily though slowly tend to increase; but the accumulation will
after a time delay the disintegration of the underlying rocks and
of the more deeply seated particles. For the humus-acids which are
generated chiefly in the upper layer of vegetable mould, are
extremely unstable compounds, and are liable to decomposition
before they reach any considerable depth. {66} A thick bed of
overlying soil will also check the downward extension of great
fluctuations of temperature, and in cold countries will check the
powerful action of frost. The free access of air will likewise be
excluded. From these several causes disintegration would be almost
arrested, if the overlying mould were to increase much in
thickness, owing to none or little being removed from the surface.
{67} In my own immediate neighbourhood we have a curious proof how
effectually a few feet of clay checks some change which goes on in
flints, lying freely exposed; for the large ones which have lain
for some time on the surface of ploughed fields cannot be used for
building; they will not cleave properly, and are said by the
workmen to be rotten. {68} It is therefore necessary to obtain
flints for building purposes from the bed of red clay overlying the
chalk (the residue of its dissolution by rain-water) or from the
chalk itself.

Not only do worms aid directly in the chemical disintegration of
rocks, but there is good reason to believe that they likewise act
in a direct and mechanical manner on the smaller particles. All
the species which swallow earth are furnished with gizzards; and
these are lined with so thick a chitinous membrane, that Perrier
speaks of it, {69} as "une veritable armature." The gizzard is
surrounded by powerful transverse muscles, which, according to
Claparede, are about ten times as thick as the longitudinal ones;
and Perrier saw them contracting energetically. Worms belonging to
one genus, Digaster, have two distinct but quite similar gizzards;
and in another genus, Moniligaster, the second gizzard consists of
four pouches, one succeeding the other, so that it may almost be
said to have five gizzards. {70} In the same manner as
gallinaceous and struthious birds swallow stones to aid in the
trituration of their food, so it appears to be with terricolous
worms. The gizzards of thirty-eight of our common worms were
opened, and in twenty-five of them small stones or grains of sand,
sometimes together with the hard calcareous concretions formed
within the anterior calciferous glands, were found, and in two
others concretions alone. In the gizzards of the remaining worms
there were no stones; but some of these were not real exceptions,
as the gizzards were opened late in the autumn, when the worms had
ceased to feed and their gizzards were quite empty. {71}

When worms make their burrows through earth abounding with little
stones, no doubt many will be unavoidably swallowed; but it must
not be supposed that this fact accounts for the frequency with
which stones and sand are found in their gizzards. For beads of
glass and fragments of brick and of hard tiles were scattered over
the surface of the earth, in pots in which worms were kept and had
already made their burrows; and very many of these beads and
fragments were picked up and swallowed by the worms, for they were
found in their castings, intestines, and gizzards. They even
swallowed the coarse red dust, formed by the pounding of the tiles.
Nor can it be supposed that they mistook the beads and fragments
for food; for we have seen that their taste is delicate enough to
distinguish between different kinds of leaves. It is therefore
manifest that they swallow hard objects, such as bits of stone,
beads of glass and angular fragments of bricks or tiles for some
special purpose; and it can hardly be doubted that this is to aid
their gizzards in crushing and grinding the earth, which they so
largely consume. That such hard objects are not necessary for
crushing leaves, may be inferred from the fact that certain
species, which live in mud or water and feed on dead or living
vegetable matter, but which do not swallow earth, are not provided
with gizzards, {72} and therefore cannot have the power of
utilising stones.

During the grinding process, the particles of earth must be rubbed
against one another, and between the stones and the tough lining
membrane of the gizzard. The softer particles will thus suffer
some attrition, and will perhaps even be crushed. This conclusion
is supported by the appearance of freshly ejected castings, for
these often reminded me of the appearance of paint which has just
been ground by a workman between two flat stones. Morren remarks
that the intestinal canal is "impleta tenuissima terra, veluti in
pulverem redacta." {73} Perrier also speaks of "l'etat de pate
excessivement fine a laquelle est reduite la terre qu'ils
rejettent," &c. {74}

As the amount of trituration which the particles of earth undergo
in the gizzards of worms possesses some interest (as we shall
hereafter see), I endeavoured to obtain evidence on this head by
carefully examining many of the fragments which had passed through
their alimentary canals. With worms living in a state of nature,
it is of course impossible to know how much the fragments may have
been worn before they were swallowed. It is, however, clear that
worms do not habitually select already rounded particles, for
sharply angular bits of flint and of other hard rocks were often
found in their gizzards or intestines. On three occasions sharp
spines from the stems of rose-bushes were thus found. Worms kept
in confinement repeatedly swallowed angular fragments of hard tile,
coal, cinders, and even the sharpest fragments of glass.
Gallinaceous and struthious birds retain the same stones in their
gizzards for a long time, which thus become well rounded; but this
does not appear to be the case with worms, judging from the large
number of the fragments of tiles, glass beads, stones, &c.,
commonly found in their castings and intestines. So that unless
the same fragments were to pass repeatedly through their gizzards,
visible signs of attrition in the fragments could hardly be
expected, except perhaps in the case of very soft stones.

I will now give such evidence of attrition as I have been able to
collect. In the gizzards of some worms dug out of a thin bed of
mould over the chalk, there were many well-rounded small fragments
of chalk, and two fragments of the shells of a land-mollusc (as
ascertained by their microscopical structure), which latter were
not only rounded but somewhat polished. The calcareous concretions
formed in the calciferous glands, which are often found in their
gizzards, intestines, and occasionally in their castings, when of
large size, sometimes appeared to have been rounded; but with all
calcareous bodies the rounded appearance may be partly or wholly
due to their corrosion by carbonic acid and the humus-acids. In
the gizzards of several worms collected in my kitchen garden near a
hothouse, eight little fragments of cinders were found, and of
these, six appeared more or less rounded, as were two bits of
brick; but some other bits were not at all rounded. A farm-road
near Abinger Hall had been covered seven years before with brick-
rubbish to the depth of about 6 inches; turf had grown over this
rubbish on both sides of the road for a width of 18 inches, and on
this turf there were innumerable castings. Some of them were
coloured of a uniform red owing to the presence of much brick-dust,
and they contained many particles of brick and of hard mortar from
1 to 3 mm. in diameter, most of which were plainly rounded; but all
these particles may have been rounded before they were protected by
the turf and were swallowed, like those on the bare parts of the
road which were much worn. A hole in a pasture-field had been
filled up with brick-rubbish at the same time, viz., seven years
ago, and was now covered with turf; and here the castings contained
very many particles of brick, all more or less rounded; and this
brick-rubbish, after being shot into the hole, could not have
undergone any attrition. Again, old bricks very little broken,
together with fragments of mortar, were laid down to form walks,
and were then covered with from 4 to 6 inches of gravel; six little
fragments of brick were extracted from castings collected on these
walks, three of which were plainly worn. There were also very many
particles of hard mortar, about half of which were well rounded;
and it is not credible that these could have suffered so much
corrosion from the action of carbonic acid in the course of only
seven years.

Much better evidence of the attrition of hard objects in the
gizzards of worms, is afforded by the state of the small fragments
of tiles or bricks, and of concrete in the castings thrown up where
ancient buildings once stood. As all the mould covering a field
passes every few years through the bodies of worms, the same small
fragments will probably be swallowed and brought to the surface
many times in the course of centuries. It should be premised that
in the several following cases, the finer matter was first washed
away from the castings, and then all the particles of bricks, tiles
and concrete were collected without any selection, and were
afterwards examined. Now in the castings ejected between the
tesserae on one of the buried floors of the Roman villa at Abinger,
there were many particles (from to 2 mm. in diameter) of tiles and
concrete, which it was impossible to look at with the naked eye or
through a strong lens, and doubt for a moment that they had almost
all undergone much attrition. I speak thus after having examined
small water-worn pebbles, formed from Roman bricks, which M. Henri
de Saussure had the kindness to send me, and which he had extracted
from sand and gravel beds, deposited on the shores of the Lake of
Geneva, at a former period when the water stood at about two metres
above its present level. The smallest of these water-worn pebbles
of brick from Geneva resembled closely many of those extracted from
the gizzards of worms, but the larger ones were somewhat smoother.

Four castings found on the recently uncovered, tesselated floor of
the great room in the Roman villa at Brading, contained many
particles of tile or brick, of mortar, and of hard white cement;
and the majority of these appeared plainly worn. The particles of
mortar, however, seemed to have suffered more corrosion than
attrition, for grains of silex often projected from their surfaces.
Castings from within the nave of Beaulieu Abbey, which was
destroyed by Henry VIII., were collected from a level expanse of
turf, overlying the buried tesselated pavement, through which worm-
burrows passed; and these castings contained innumerable particles
of tiles and bricks, of concrete and cement, the majority of which
had manifestly undergone some or much attrition. There were also
many minute flakes of a micaceous slate, the points of which were
rounded. If the above supposition, that in all these cases the
same minute fragments have passed several times through the
gizzards of worms, be rejected, notwithstanding its inherent
probability, we must then assume that in all the above cases the
many rounded fragments found in the castings had all accidentally
undergone much attrition before they were swallowed; and this is
highly improbable.

On the other hand it must be stated that fragments of ornamental
tiles, somewhat harder than common tiles or bricks, which had been
swallowed only once by worms kept in confinement, were with the
doubtful exception of one or two of the smallest grains, not at all
rounded. Nevertheless some of them appeared a little worn, though
not rounded. Notwithstanding these cases, if we consider the
evidence above given, there can be little doubt that the fragments,
which serve as millstones in the gizzards of worms, suffer, when of
a not very hard texture, some amount of attrition; and that the
smaller particles in the earth, which is habitually swallowed in
such astonishingly large quantities by worms, are ground together
and are thus levigated. If this be the case, the "terra
tenuissima,"--the "pate excessivement fine,"--of which the castings
largely consist, is in part due to the mechanical action of the
gizzard; {75} and this fine matter, as we shall see in the next
chapter, is that which is chiefly washed away from the innumerable
castings on every field during each heavy shower of rain. If the
softer stones yield at all, the harder ones will suffer some slight
amount of wear and tear.

The trituration of small particles of stone in the gizzards of
worms is of more importance under a geological point of view than
may at first appear to be the case; for Mr. Sorby has clearly shown
that the ordinary means of disintegration, namely, running water
and the waves of the sea, act with less and less power on fragments
of rock the smaller they are. "Hence," as he remarks, "even making
no allowance for the extra buoying up of very minute particles by a
current of water, depending on surface cohesion, the effects of
wearing on the form of the grains must vary directly as their
diameter or thereabouts. If so, a grain of 1/10 an inch in
diameter would be worn ten times as much as one of an inch in
diameter, and at least a hundred times as much as one of 1/100 an
inch in diameter. Perhaps, then, we may conclude that a grain 1/10
of an inch in diameter would be worn as much or more in drifting a
mile as a grain 1/1000 of an inch in being drifted 100 miles. On
the same principle a pebble one inch in diameter would be worn
relatively more by being drifted only a few hundred yards." {76}
Nor should we forget, in considering the power which worms exert in
triturating particles of rock, that there is good evidence that on
each acre of land, which is sufficiently damp and not too sandy,
gravelly or rocky for worms to inhabit, a weight of more than ten
tons of earth annually passes through their bodies and is brought
to the surface. The result for a country of the size of Great
Britain, within a period not very long in a geological sense, such
as a million years, cannot be insignificant; for the ten tons of
earth has to be multiplied first by the above number of years, and
then by the number of acres fully stocked with worms; and in
England, together with Scotland, the land which is cultivated and
is well fitted for these animals, has been estimated at above 32
million acres. The product is 320 million million tons of earth.


Denudation aided by recently ejected castings flowing down inclined
grass-covered surfaces--The amount of earth which annually flows
downwards--The effect of tropical rain on worm castings--The finest
particles of earth washed completely away from castings--The
disintegration of dried castings into pellets, and their rolling
down inclined surfaces--The formation of little ledges on hill-
sides, in part due to the accumulation of disintegrated castings--
Castings blown to leeward over level land--An attempt to estimate
the amount thus blown--The degradation of ancient encampments and
tumuli--The preservation of the crowns and furrows on land
anciently ploughed--The formation and amount of mould over the
Chalk formation.

We are now prepared to consider the more direct part which worms
take in the denudation of the land. When reflecting on sub-aerial
denudation, it formerly appeared to me, as it has to others, that a
nearly level or very gently inclined surface, covered with turf,
could suffer no loss during even a long lapse of time. It may,
however, be urged that at long intervals, debacles of rain or
water-spouts would remove all the mould from a very gentle slope;
but when examining the steep, turf-covered slopes in Glen Roy, I
was struck with the fact how rarely any such event could have
happened since the Glacial period, as was plain from the well-
preserved state of the three successive "roads" or lake-margins.
But the difficulty in believing that earth in any appreciable
quantity can be removed from a gently inclined surface, covered
with vegetation and matted with roots, is removed through the
agency of worms. For the many castings which are thrown up during
rain, and those thrown up some little time before heavy rain, flow
for a short distance down an inclined surface. Moreover much of
the finest levigated earth is washed completely away from the
castings. During dry weather castings often disintegrate into
small rounded pellets, and these from their weight often roll down
any slope. This is more especially apt to occur when they are
started by the wind, and probably when started by the touch of an
animal, however small. We shall also see that a strong wind blows
all the castings, even on a level field, to leeward, whilst they
are soft; and in like manner the pellets when they are dry. If the
wind blows in nearly the direction of an inclined surface, the
flowing down of the castings is much aided.

The observations on which these several statements are founded must
now be given in some detail. Castings when first ejected are
viscid and soft; during rain, at which time worms apparently prefer
to eject them, they are still softer; so that I have sometimes
thought that worms must swallow much water at such times. However
this may be, rain, even when not very heavy, if long continued,
renders recently-ejected castings semi-fluid; and on level ground
they then spread out into thin, circular, flat discs, exactly as
would so much honey or very soft mortar, with all traces of their
vermiform structure lost. This latter fact was sometimes made
evident, when a worm had subsequently bored through a flat circular
disc of this kind, and heaped up a fresh vermiform mass in the
centre. These flat subsided discs have been repeatedly seen by me
after heavy rain, in many places on land of all kinds.

On the flowing of wet castings, and the rolling of dry
disintegrated castings down inclined surfaces.--When castings are
ejected on an inclined surface during or shortly before heavy rain,
they cannot fail to flow a little down the slope. Thus, on some
steep slopes in Knole Park, which were covered with coarse grass
and had apparently existed in this state from time immemorial, I
found (Oct. 22, 1872) after several wet days that almost all the
many castings were considerably elongated in the line of the slope;
and that they now consisted of smooth, only slightly conical
masses. Whenever the mouths of the burrows could be found from
which the earth had been ejected, there was more earth below than
above them. After some heavy storms of rain (Jan. 25, 1872) two
rather steeply inclined fields near Down, which had formerly been
ploughed and were now rather sparsely clothed with poor grass, were
visited, and many castings extended down the slopes for a length of
5 inches, which was twice or thrice the usual diameter of the
castings thrown up on the level parts of these same fields. On
some fine grassy slopes in Holwood Park, inclined at angles between
8 degrees and 11 degrees 30 seconds with the horizon, where the
surface apparently had never been disturbed by the hand of man,
castings abounded in extraordinary numbers: and a space 16 inches
in length transversely to the slope and 6 inches in the line of the
slope, was completely coated, between the blades of grass, with a
uniform sheet of confluent and subsided castings. Here also in
many places the castings had flowed down the slope, and now formed
smooth narrow patches of earth, 6, 7, and 7.5 inches in length.
Some of these consisted of two castings, one above the other, which
had become so completely confluent that they could hardly be
distinguished. On my lawn, clothed with very fine grass, most of
the castings are black, but some are yellowish from earth having
been brought up from a greater depth than usual, and the flowing-
down of these yellow castings after heavy rain, could be clearly
seen where the slope was 5 degrees; and where it was less than 1
degree some evidence of their flowing down could still be detected.
On another occasion, after rain which was never heavy, but which
lasted for 18 hours, all the castings on this same gently inclined
lawn had lost their vermiform structure; and they had flowed, so
that fully two-thirds of the ejected earth lay below the mouths of
the burrows.

These observations led me to make others with more care. Eight
castings were found on my lawn, where the grass-blades are fine and
close together, and three others on a field with coarse grass. The
inclination of the surface at the eleven places where these
castings were collected varied between 4 degrees 30 seconds and 17
degrees 30 seconds; the mean of the eleven inclinations being 9
degrees 26 seconds. The length of the castings in the direction of
the slope was first measured with as much accuracy as their
irregularities would permit. It was found possible to make these
measurements within about of an inch, but one of the castings was
too irregular to admit of measurement. The average length in the
direction of the slope of the remaining ten castings was 2.03
inches. The castings were then divided with a knife into two parts
along a horizontal line passing through the mouth of the burrow,
which was discovered by slicing off the turf; and all the ejected
earth was separately collected, namely, the part above the hole and
the part below. Afterwards these two parts were weighed. In every
case there was much more earth below than above; the mean weight of
that above being 103 grains, and of that below 205 grains; so that
the latter was very nearly double the former. As on level ground
castings are commonly thrown up almost equally round the mouths of
the burrows, this difference in weight indicates the amount of
ejected earth which had flowed down the slope. But very many more
observations would be requisite to arrive at any general result;
for the nature of the vegetation and other accidental
circumstances, such as the heaviness of the rain, the direction and
force of the wind, &c., appear to be more important in determining
the quantity of the earth which flows down a slope than its angle.
Thus with four castings on my lawn (included in the above eleven)
where the mean slope was 7 degrees 19 seconds, the difference in
the amount of earth above and below the burrows was greater than
with three other castings on the same lawn where the mean slope was
12 degrees 5 seconds.

We may, however, take the above eleven cases, which are accurate as
far as they go, and calculate the weight of the ejected earth which
annually flows down a slope having a mean inclination of 9 degrees
26 seconds. This was done by my son George. It has been shown
that almost exactly two-thirds of the ejected earth is found below
the mouth of the burrow and one-third above it. Now if the two-
thirds which is below the hole be divided into two equal parts, the
upper half of this two-thirds exactly counterbalances the one-third
which is above the hole, so that as far as regards the one-third
above and the upper half of the two-thirds below, there is no flow
of earth down the hill-side. The earth constituting the lower half
of the two-thirds is, however, displaced through distances which
are different for every part of it, but which may be represented by
the distance between the middle point of the lower half of the two-
thirds and the hole. So that the average distance of displacement
is a half of the whole length of the worm-casting. Now the average
length of ten out of the above eleven castings was 2.03 inches, and
half of this we may take as being 1 inch. It may therefore be
concluded that one-third of the whole earth brought to the surface
was in these cases carried down the slope through 1 inch. {77}

It was shown in the third chapter that on Leith Hill Common, dry
earth weighing at least 7.453 lbs. was brought up by worms to the
surface on a square yard in the course of a year. If a square yard
be drawn on a hillside with two of its sides horizontal, then it is
clear that only 1/36 part of the earth brought up on that square
yard would be near enough to its lower side to cross it, supposing
the displacement of the earth to be through one inch. But it
appears that only of the earth brought up can be considered to flow
downwards; hence 1/3 of 1/36 or 1/108 of 7.453 lbs. will cross the
lower side of our square yard in a year. Now 1/108 of 7.453 lbs.
is 1.1 oz. Therefore 1.1 oz. of dry earth will annually cross each
linear yard running horizontally along a slope having the above
inclination; or very nearly 7 lbs. will annually cross a horizontal
line, 100 yards in length, on a hill-side having this inclination.

A more accurate, though still very rough, calculation can be made
of the bulk of earth, which in its natural damp state annually
flows down the same slope over a yard-line drawn horizontally
across it. From the several cases given in the third chapter, it
is known that the castings annually brought to the surface on a
square yard, if uniformly spread out would form a layer 0.2 of an
inch in thickness: it therefore follows by a calculation similar
to the one already given, that 1/3 of 0.2x36, or 2.4 cubic inches
of damp earth will annually cross a horizontal line one yard in
length on a hillside with the above inclination. This bulk of damp
castings was found to weigh 1.85 oz. Therefore 11.56 lbs. of damp
earth, instead of 7 lbs. of dry earth as by the former calculation,
would annually cross a line 100 yards in length on our inclined

In these calculations it has been assumed that the castings flow a
short distance downwards during the whole year, but this occurs
only with those ejected during or shortly before rain; so that the
above results are thus far exaggerated. On the other hand, during
rain much of the finest earth is washed to a considerable distance
from the castings, even where the slope is an extremely gentle one,
and is thus wholly lost as far as the above calculations are
concerned. Castings ejected during dry weather and which have set
hard, lose in the same manner a considerable quantity of fine
earth. Dried castings, moreover, are apt to disintegrate into
little pellets, which often roll or are blown down any inclined
surface. Therefore the above result, namely, that 24 cubic inches
of earth (weighing 1.85 oz. whilst damp) annually crosses a yard-
line of the specified kind, is probably not much if at all

This amount is small; but we should bear in mind how many branching
valleys intersect most countries, the whole length of which must be
very great; and that earth is steadily travelling down both turf-
covered sides of each valley. For every 100 yards in length in a
valley with sides sloping as in the foregoing cases, 480 cubic
inches of damp earth, weighing above 23 pounds, will annually reach
the bottom. Here a thick bed of alluvium will accumulate, ready to
be washed away in the course of centuries, as the stream in the
middle meanders from side to side.

If it could be shown that worms generally excavate their burrows at
right angles to an inclined surface, and this would be their
shortest course for bringing up earth from beneath, then as the old
burrows collapsed from the weight of the superincumbent soil, the
collapsing would inevitably cause the whole bed of vegetable mould
to sink or slide slowly down the inclined surface. But to
ascertain the direction of many burrows was found too difficult and
troublesome. A straight piece of wire was, however, pushed into
twenty-five burrows on several sloping fields, and in eight cases
the burrows were nearly at right angles to the slope; whilst in the
remaining cases they were indifferently directed at various angles,
either upwards or downwards with respect to the slope.

In countries where the rain is very heavy, as in the tropics, the
castings appear, as might have been expected, to be washed down in
a greater degree than in England. Mr. Scott informs me that near
Calcutta the tall columnar castings (previously described), the
diameter of which is usually between 1 and 1.5 inch, subside on a
level surface, after heavy rain, into almost circular, thin, flat
discs, between 3 and 4 and sometimes 5 inches in diameter. Three
fresh castings, which had been ejected in the Botanic Gardens "on a
slightly inclined, grass-covered, artificial bank of loamy clay,"
were carefully measured, and had a mean height of 2.17, and a mean
diameter of 1.43 inches; these after heavy rain, formed elongated
patches of earth, with a mean length in the direction of the slope
of 5.83 inches. As the earth had spread very little up the slope,
a large part, judging from the original diameter of these castings,
must have flowed bodily downwards about 4 inches. Moreover some of
the finest earth of which they were composed must have been washed
completely away to a still greater distance. In drier sites near
Calcutta, a species of worm ejects its castings, not in vermiform
masses, but in little pellets of varying sizes: these are very
numerous in some places, and Mr. Scott says that they "are washed
away by every shower."

I was led to believe that a considerable quantity of fine earth is
washed quite away from castings during rain, from the surfaces of
old ones being often studded with coarse particles. Accordingly a
little fine precipitated chalk, moistened with saliva or gum-water,
so as to be slightly viscid and of the same consistence as a fresh
casting, was placed on the summits of several castings and gently
mixed with them. These castings were then watered through a very
fine rose, the drops from which were closer together than those of
rain, but not nearly so large as those in a thunderstorm; nor did
they strike the ground with nearly so much force as drops during
heavy rain. A casting thus treated subsided with surprising
slowness, owing as I suppose to its viscidity. It did not flow
bodily down the grass-covered surface of the lawn, which was here
inclined at an angle of 16 degrees 20 seconds; nevertheless many
particles of the chalk were found three inches below the casting.
The experiment was repeated on three other castings on different
parts of the lawn, which sloped at 2 degrees 30 seconds, 3 degrees
and 6 degrees; and particles of chalk could be seen between 4 and 5
inches below the casting; and after the surface had become dry,
particles were found in two cases at a distance of 5 and 6 inches.
Several other castings with precipitated chalk placed on their
summits were left to the natural action of the rain. In one case,
after rain which was not heavy, the casting was longitudinally
streaked with white. In two other cases the surface of the ground
was rendered somewhat white for a distance of one inch from the
casting; and some soil collected at a distance of 2.5 inches, where
the slope was 7 degrees, effervesced slightly when placed in acid.
After one or two weeks, the chalk was wholly or almost wholly
washed away from all the castings on which it had been placed, and
these had recovered their natural colour.

It may be here remarked that after very heavy rain shallow pools
may be seen on level or nearly level fields, where the soil is not
very porous, and the water in them is often slightly muddy; when
such little pools have dried, the leaves and blades of grass at
their bottoms are generally coated with a thin layer of mud. This
mud I believe is derived in large part from recently ejected

Dr. King informs me that the majority of the before described
gigantic castings, which he found on a fully exposed, bare,
gravelly knoll on the Nilgiri Mountains in India, had been more or
less weathered by the previous north-east monsoon; and most of them
presented a subsided appearance. The worms here eject their
castings only during the rainy season; and at the time of Dr.
King's visit no rain had fallen for 110 days. He carefully
examined the ground between the place where these huge castings
lay, and a little watercourse at the base of the knoll, and nowhere
was there any accumulation of fine earth, such as would necessarily
have been left by the disintegration of the castings if they had
not been wholly removed. He therefore has no hesitation in
asserting that the whole of these huge castings are annually washed
during the two monsoons (when about 100 inches of rain fall) into
the little water-course, and thence into the plains lying below at
a depth of 3000 or 4000 feet.

Castings ejected before or during dry weather become hard,
sometimes surprisingly hard, from the particles of earth having
been cemented together by the intestinal secretions. Frost seems
to be less effective in their disintegration than might have been
expected. Nevertheless they readily disintegrate into small
pellets, after being alternately moistened with rain and again
dried. Those which have flowed during rain down a slope,
disintegrate in the same manner. Such pellets often roll a little
down any sloping surface; their descent being sometimes much aided
by the wind. The whole bottom of a broad dry ditch in my grounds,
where there were very few fresh castings, was completely covered
with these pellets or disintegrated castings, which had rolled down
the steep sides, inclined at an angle of 27 degrees.

Near Nice, in places where the great cylindrical castings,
previously described, abound, the soil consists of very fine
arenaceo-calcareous loam; and Dr. King informs me that these
castings are extremely liable to crumble during dry weather into
small fragments, which are soon acted on by rain, and then sink
down so as to be no longer distinguishable from the surrounding
soil. He sent me a mass of such disintegrated castings, collected
on the top of a bank, where none could have rolled down from above.
They must have been ejected within the previous five or six months,
but they now consisted of more or less rounded fragments of all
sizes, from 0.75 of an inch in diameter to minute grains and mere
dust. Dr. King witnessed the crumbling process whilst drying some
perfect castings, which he afterwards sent me. Mr. Scott also
remarks on the crumbling of the castings near Calcutta and on the
mountains of Sikkim during the hot and dry season.

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 2.5 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 1.5 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 degrees to 60
degrees 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.

My son Francis examined a Chalk escarpment near Lewes; and here on
a part which was very steep, sloping at 40 degrees with the
horizon, about 30 flat ledges extended horizontally for more than
100 yards, at an average distance of about 20 inches, one beneath
the other. They were from 9 to 10 inches in breadth. When viewed
from a distance they presented a striking appearance, owing to
their parallelism; but when examined closely, they were seen to be
somewhat sinuous, and one often ran into another, giving the
appearance of the ledge having forked into two. They are formed of
light-coloured earth, which on the outside, where thickest, was in
one case 9 inches, and in another case between 6 and 7 inches in
thickness. Above the ledges, the thickness of the earth over the
chalk was in the former case 4 and in the latter only 3 inches.
The grass grew more vigorously on the outer edges of the ledges
than on any other part of the slope, and here formed a tufted
fringe. Their middle part was bare, but whether this had been
caused by the trampling of sheep, which sometimes frequent the
ledges, my son could not ascertain. Nor could he feel sure how
much of the earth on the middle and bare parts, consisted of
disintegrated worm-castings which had rolled down from above; but
he felt convinced that some had thus originated; and it was
manifest that the ledges with their grass-fringed edges would
arrest any small object rolling down from above.

At one end or side of the bank bearing these ledges, the surface
consisted in parts of bare chalk, and here the ledges were very
irregular. At the other end of the bank, the slope suddenly became
less steep, and here the ledges ceased rather abruptly; but little
embankments only a foot or two in length were still present. The
slope became steeper lower down the hill, and the regular ledges
then reappeared. Another of my sons observed, on the inland side
of Beachy Head, where the surface sloped at about 25 degrees, many
short little embankments like those just mentioned. They extended
horizontally and were from a few inches to two or three feet in
length. They supported tufts of grass growing vigorously. The
average thickness of the mould of which they were formed, taken
from nine measurements, was 4.5 inches; while that of the mould
above and beneath them was on an average only 3.2 inches, and on
each side, on the same level, 3.1 inches. On the upper parts of
the slope, these embankments showed no signs of having been
trampled on by sheep, but in the lower parts such signs were fairly
plain. No long continuous ledges had here been formed.

If the little embankments above the Corniche road, which Dr. King
saw in the act of formation by the accumulation of disintegrated
and rolled worm-castings, were to become confluent along horizontal
lines, ledges would be formed. Each embankment would tend to
extend laterally by the lateral extension of the arrested castings;
and animals grazing on a steep slope would almost certainly make
use of every prominence at nearly the same level, and would indent
the turf between them; and such intermediate indentations would
again arrest the castings. An irregular ledge when once formed
would also tend to become more regular and horizontal by some of
the castings rolling laterally from the higher to the lower parts,
which would thus be raised. Any projection beneath a ledge would
not afterwards receive disintegrated matter from above, and would
tend to be obliterated by rain and other atmospheric agencies.
There is some analogy between the formation, as here supposed, of
these ledges, and that of the ripples of wind-drifted sand as
described by Lyell. {78}

The steep, grass-covered sides of a mountainous valley in
Westmoreland, called Grisedale, was marked in many places with
innumerable lines of miniature cliffs, with almost horizontal,
little ledges at their bases. Their formation was in no way
connected with the action of worms, for castings could not anywhere
be seen (and their absence is an inexplicable fact), although the
turf lay in many places over a considerable thickness of boulder-
clay and moraine rubbish. Nor, as far as I could judge, was the
formation of these little cliffs at all closely connected with the
trampling of cows or sheep. It appeared as if the whole
superficial, somewhat argillaceous earth, while partially held
together by the roots of the grasses, had slided a little way down
the mountain sides; and in thus sliding, had yielded and cracked in
horizontal lines, transversely to the slope.

Castings blown to leeward by the wind.--We have seen that moist
castings flow, and that disintegrated castings roll down any
inclined surface; and we shall now see that castings, recently
ejected on level grass-covered surfaces, are blown during gales of
wind accompanied by rain to leeward. This has been observed by me
many times on many fields during several successive years. After
such gales, the castings present a gently inclined and smooth, or
sometimes furrowed, surface to windward, while they are steeply
inclined or precipitous to leeward, so that they resemble on a
miniature scale glacier-ground hillocks of rock. They are often
cavernous on the leeward side, from the upper part having curled
over the lower part. During one unusually heavy south-west gale
with torrents of rain, many castings were wholly blown to leeward,
so that the mouths of the burrows were left naked and exposed on
the windward side. Recent castings naturally flow down an inclined
surface, but on a grassy field, which sloped between 10 degrees and
15 degrees, several were found after a heavy gale blown up the
slope. This likewise occurred on another occasion on a part of my
lawn where the slope was somewhat less. On a third occasion, the
castings on the steep, grass-covered sides of a valley, down which
a gale had blown, were directed obliquely instead of straight down
the slope; and this was obviously due to the combined action of the
wind and gravity. Four castings on my lawn, where the downward
inclination was 0 degrees 45 seconds, 1 degree, 3 degrees and 3
degrees 30 seconds (mean 2 degrees 45 seconds) towards the north-
east, after a heavy south-west gale with rain, were divided across
the mouths of the burrows and weighed in the manner formerly
described. The mean weight of the earth below the mouths of
burrows and to leeward, was to that above the mouths and on the
windward side as 2.75 to 1; whereas we have seen that with several
castings which had flowed down slopes having a mean inclination of
9 degrees 26 seconds, and with three castings where the inclination
was above 12 degrees; the proportional weight of the earth below to
that above the burrows was as only 2 to 1. These several cases
show how efficiently gales of wind accompanied by rain act in
displacing recently ejected castings. We may therefore conclude
that even a moderately strong wind will produce some slight effect
on them.

Dry and indurated castings, after their disintegration into small
fragments or pellets, are sometimes, probably often, blown by a
strong wind to leeward. This was observed on four occasions, but I
did not sufficiently attend to this point. One old casting on a
gently sloping bank was blown quite away by a strong south-west
wind. Dr. King believes that the wind removes the greater part of
the old crumbling castings near Nice. Several old castings on my
lawn were marked with pins and protected from any disturbance.
They were examined after an interval of 10 weeks, during which time
the weather had been alternately dry and rainy. Some, which were
of a yellowish colour had been washed almost completely away, as
could be seen by the colour of the surrounding ground. Others had
completely disappeared, and these no doubt had been blown away.
Lastly, others still remained and would long remain, as blades of
grass had grown through them. On poor pasture-land, which has
never been rolled and has not been much trampled on by animals, the
whole surface is sometimes dotted with little pimples, through and
on which grass grows; and these pimples consist of old worm-

In all the many observed cases of soft castings blown to leeward,
this had been effected by strong winds accompanied by rain. As
such winds in England generally blow from the south and south-west,
earth must on the whole tend to travel over our fields in a north
and north-east direction. This fact is interesting, because it
might be thought that none could be removed from a level, grass-
covered surface by any means. In thick and level woods, protected
from the wind, castings will never be removed as long as the wood
lasts; and mould will here tend to accumulate to the depth at which
worms can work. I tried to procure evidence as to how much mould
is blown, whilst in the state of castings, by our wet southern
gales to the north-east, over open and flat land, by looking to the
level of the surface on opposite sides of old trees and hedge-rows;
but I failed owing to the unequal growth of the roots of trees and
to most pasture-land having been formerly ploughed.

On an open plain near Stonehenge, there exist shallow circular
trenches, with a low embankment outside, surrounding level spaces
50 yards in diameter. These rings appear very ancient, and are
believed to be contemporaneous with the Druidical stones. Castings
ejected within these circular spaces, if blown to the north-east by
south-west winds would form a layer of mould within the trench,
thicker on the north-eastern than on any other side. But the site
was not favourable for the action of worms, for the mould over the
surrounding Chalk formation with flints, was only 3.37 inches in
thickness, from a mean of six observations made at a distance of 10
yards outside the embankment. The thickness of the mould within
two of the circular trenches was measured every 5 yards all round,
on the inner sides near the bottom. My son Horace protracted these
measurements on paper; and though the curved line representing the
thickness of the mould was extremely irregular, yet in both
diagrams it could be seen to be thicker on the north-eastern side
than elsewhere. When a mean of all the measurements in both the
trenches was laid down and the line smoothed, it was obvious that
the mould was thickest in the quarter of the circle between north-
west and north-east; and thinnest in the quarter between south-east
and south-west, especially at this latter point. Besides the
foregoing measurements, six others were taken near together in one
of the circular trenches, on the north-east side; and the mould
here had a mean thickness of 2.29 inches; while the mean of six
other measurements on the south-west side was only 1.46 inches.
These observations indicate that the castings had been blown by the
south-west winds from the circular enclosed space into the trench
on the north-east side; but many more measurements in other
analogous cases would be requisite for a trustworthy result.

The amount of fine earth brought to the surface under the form of
castings, and afterwards transported by the winds accompanied by
rain, or that which flows and rolls down an inclined surface, no
doubt is small in the course of a few scores of years; for
otherwise all the inequalities in our pasture fields would be
smoothed within a much shorter period than appears to be the case.
But the amount which is thus transported in the course of thousands
of years cannot fail to be considerable and deserves attention. E.
de Beaumont looks at the vegetable mould which everywhere covers
the land as a fixed line, from which the amount of denudation may
be measured. {79} He ignores the continued formation of fresh
mould by the disintegration of the underlying rocks and fragments
of rock; and it is curious to find how much more philosophical were
the views maintained long ago, by Playfair, who, in 1802, wrote,
"In the permanence of a coat of vegetable mould on the surface of
the earth, we have a demonstrative proof of the continued
destruction of the rocks." {80}

Ancient encampments and tumuli.--E. de Beaumont adduces the present
state of many ancient encampments and tumuli and of old ploughed
fields, as evidence that the surface of the land undergoes hardly
any degradation. But it does not appear that he ever examined the
thickness of the mould over different parts of such old remains.
He relies chiefly on indirect, but apparently trustworthy, evidence
that the slopes of the old embankments are the same as they
originally were; and it is obvious that he could know nothing about
their original heights. In Knole Park a mound had been thrown up
behind the rifle-targets, which appeared to have been formed of
earth originally supported by square blocks of turf. The sides
sloped, as nearly as I could estimate them, at an angle of 45
degrees or 50 degrees with the horizon, and they were covered,
especially on the northern side, with long coarse grass, beneath
which many worm-castings were found. These had flowed bodily
downwards, and others had rolled down as pellets. Hence it is
certain that as long as a mound of this kind is tenanted by worms,
its height will be continually lowered. The fine earth which flows
or rolls down the sides of such a mound accumulates at its base in
the form of a talus. A bed, even a very thin bed, of fine earth is
eminently favourable for worms; so that a greater number of
castings would tend to be ejected on a talus thus formed than
elsewhere; and these would be partially washed away by every heavy
shower and be spread over the adjoining level ground. The final
result would be the lowering of the whole mound, whilst the
inclination of the sides would not be greatly lessened. The same
result would assuredly follow with ancient embankments and tumuli;
except where they had been formed of gravel or of nearly pure sand,
as such matter is unfavourable for worms. Many old fortifications
and tumuli are believed to be at least 2000 years old; and we
should bear in mind that in many places about one inch of mould is
brought to the surface in 5 years or two inches in 10 years.
Therefore in so long a period as 2000 years, a large amount of
earth will have been repeatedly brought to the surface on most old
embankments and tumuli, especially on the talus round their bases,
and much of this earth will have been washed completely away. We
may therefore conclude that all ancient mounds, when not formed of
materials unfavourable to worms, will have been somewhat lowered in
the course of centuries, although their inclinations may not have
been greatly changed.

Fields formerly ploughed.--From a very remote period and in many
countries, land has been ploughed, so that convex beds, called
crowns or ridges, usually about 8 feet across and separated by
furrows, have been thrown up. The furrows are directed so as to
carry off the surface water. In my attempts to ascertain how long
a time these crowns and furrows last, when ploughed land has been
converted into pasture, obstacles of many kinds were encountered.
It is rarely known when a field was last ploughed; and some fields
which were thought to have been in pasture from time immemorial
were afterwards discovered to have been ploughed only 50 or 60
years before. During the early part of the present century, when
the price of corn was very high, land of all kinds seems to have
been ploughed in Britain. There is, however, no reason to doubt
that in many cases the old crowns and furrows have been preserved
from a very ancient period. {81} That they should have been
preserved for very unequal lengths of time would naturally follow
from the crowns, when first thrown up, having differed much in
height in different districts, as is now the case with recently
ploughed land.

In old pasture fields, the mould, wherever measurements were made,
was found to be from 0.5 to 2 inches thicker in the furrows than on
the crowns; but this would naturally follow from the finer earth
having been washed from the crowns into the furrows before the land
was well clothed with turf; and it is impossible to tell what part
worms may have played in the work. Nevertheless from what we have
seen, castings would certainly tend to flow and to be washed during
heavy rain from the crowns into the furrows. But as soon as a bed
of fine earth had by any means been accumulated in the furrows, it
would be more favourable for worms than the other parts, and a
greater number of castings would be thrown up here than elsewhere;
and as the furrows on sloping land are usually directed so as to
carry off the surface water, some of the finest earth would be
washed from the castings which had been here ejected and be carried
completely away. The result would be that the furrows would be
filled up very slowly, while the crowns would be lowered perhaps
still more slowly by the flowing and rolling of the castings down
their gentle inclinations into the furrows.

Nevertheless it might be expected that old furrows, especially
those on a sloping surface, would in the course of time be filled
up and disappear. Some careful observers, however, who examined
fields for me in Gloucestershire and Staffordshire could not detect
any difference in the state of the furrows in the upper and lower
parts of sloping fields, supposed to have been long in pasture; and
they came to the conclusion that the crowns and furrows would last
for an almost endless number of centuries. On the other hand the
process of obliteration seems to have commenced in some places.
Thus in a grass field in North Wales, known to have been ploughed
about 65 years ago, which sloped at an angle of 15 degrees to the
north-east, the depth of the furrows (only 7 feet apart) was
carefully measured, and was found to be about 4.5 inches in the
upper part of the slope, and only 1 inch near the base, where they
could be traced with difficulty. On another field sloping at about
the same angle to the south-west, the furrows were scarcely
perceptible in the lower part; although these same furrows when
followed on to some adjoining level ground were from 2.5 to 3.5
inches in depth. A third and closely similar case was observed.
In a fourth case, the mould in a furrow in the upper part of a
sloping field was 2.5 inches, and in the lower part 4.5 inches in

On the Chalk Downs at about a mile distance from Stonehenge, my son
William examined a grass-covered, furrowed surface, sloping at from
8 degrees to 10 degrees, which an old shepherd said had not been
ploughed within the memory of man. The depth of one furrow was
measured at 16 points in a length of 68 paces, and was found to be
deeper where the slope was greatest and where less earth would
naturally tend to accumulate, and at the base it almost
disappeared. The thickness of the mould in this furrow in the
upper part was 2.5 inches, which increased to 5 inches, a little
above the steepest part of the slope; and at the base, in the
middle of the narrow valley, at a point which the furrow if
continued would have struck, it amounted to 7 inches. On the
opposite side of the valley, there were very faint, almost
obliterated, traces of furrows. Another analogous but not so
decided a case was observed at a few miles' distance from
Stonehenge. On the whole it appears that the crowns and furrows on
land formerly ploughed, but now covered with grass, tend slowly to
disappear when the surface is inclined; and this is probably in
large part due to the action of worms; but that the crowns and
furrows last for a very long time when the surface is nearly level.

Formation and amount of mould over the Chalk Formation.--Worm-
castings are often ejected in extraordinary numbers on steep,
grass-covered slopes, where the Chalk comes close to the surface,
as my son William observed near Winchester and elsewhere. If such
castings are largely washed away during heavy rains, it is
difficult to understand at first how any mould can still remain on
our Downs, as there does not appear any evident means for supplying
the loss. There is, moreover, another cause of loss, namely, in
the percolation of the finer particles of earth into the fissures
in the chalk and into the chalk itself. These considerations led
me to doubt for a time whether I had not exaggerated the amount of
fine earth which flows or rolls down grass-covered slopes under the
form of castings; and I sought for additional information. In some
places, the castings on Chalk Downs consist largely of calcareous
matter, and here the supply is of course unlimited. But in other
places, for instance on a part of Teg Down near Winchester, the
castings were all black and did not effervesce with acids. The
mould over the chalk was here only from 3 to 4 inches in thickness.
So again on the plain near Stonehenge, the mould, apparently free
from calcareous matter, averaged rather less than 3.5 inches in
thickness. Why worms should penetrate and bring up chalk in some
places and not in others I do not know.

In many districts where the land is nearly level, a bed several
feet in thickness of red clay full of unworn flints overlies the
Upper Chalk. This overlying matter, the surface of which has been
converted into mould, consists of the undissolved residue from the
chalk. It may be well here to recall the case of the fragments of
chalk buried beneath worm-castings on one of my fields, the angles
of which were so completely rounded in the course of 29 years that
the fragments now resembled water-worn pebbles. This must have
been effected by the carbonic acid in the rain and in the ground,
by the humus-acids, and by the corroding power of living roots.
Why a thick mass of residue has not been left on the Chalk,
wherever the land is nearly level, may perhaps be accounted for by
the percolation of the fine particles into the fissures, which are
often present in the chalk and are either open or are filled up
with impure chalk, or into the solid chalk itself. That such
percolation occurs can hardly be doubted. My son collected some
powdered and fragmentary chalk beneath the turf near Winchester;
the former was found by Colonel Parsons, R. E., to contain 10 per
cent., and the fragments 8 per cent. of earthy matter. On the
flanks of the escarpment near Abinger in Surrey, some chalk close
beneath a layer of flints, 2 inches in thickness and covered by 8
inches of mould, yielded a residue of 3.7 per cent. of earthy
matter. On the other hand the Upper Chalk properly contains, as I
was informed by the late David Forbes who had made many analyses,
only from 1 to 2 per cent. of earthy matter; and two samples from
pits near my house contained 1.3 and 0.6 per cent. I mention these
latter cases because, from the thickness of the overlying bed of
red clay with flints, I had imagined that the underlying chalk
might here be less pure than elsewhere. The cause of the residue
accumulating more in some places than in others, may be attributed
to a layer of argillaceous matter having been left at an early
period on the chalk, and this would check the subsequent
percolation of earthy matter into it.

From the facts now given we may conclude that castings ejected on
our Chalk Downs suffer some loss by the percolation of their finer
matter into the chalk. But such impure superficial chalk, when
dissolved, would leave a larger supply of earthy matter to be added
to the mould than in the case of pure chalk. Besides the loss
caused by percolation, some fine earth is certainly washed down the
sloping grass-covered surfaces of our Downs. The washing-down
process, however, will be checked in the course of time; for
although I do not know how thin a layer of mould suffices to
support worms, yet a limit must at last be reached; and then their
castings would cease to be ejected or would become scanty.

The following cases show that a considerable quantity of fine earth
is washed down. The thickness of the mould was measured at points
12 yards apart across a small valley in the Chalk near Winchester.
The sides sloped gently at first; then became inclined at about 20
degrees; then more gently to near the bottom, which transversely
was almost level and about 50 yards across. In the bottom, the
mean thickness of the mould from five measurements was 8.3 inches;
whilst on the sides of the valley, where the inclination varied
between 14 degrees and 20 degrees, its mean thickness was rather
less than 3.5 inches. As the turf-covered bottom of the valley
sloped at an angle of only between 2 degrees and 3 degrees, it is
probable that most of the 8.3-inch layer of mould had been washed
down from the flanks of the valley, and not from the upper part.
But as a shepherd said that he had seen water flowing in this
valley after the sudden thawing of snow, it is possible that some
earth may have been brought down from the upper part; or, on the
other hand, that some may have been carried further down the
valley. Closely similar results, with respect to the thickness of
the mould, were obtained in a neighbouring valley.

St. Catherine's Hill, near Winchester, is 327 feet in height, and
consists of a steep cone of chalk about 0.25 of a mile in diameter.
The upper part was converted by the Romans, or, as some think, by
the ancient Britons, into an encampment, by the excavation of a
deep and broad ditch all round it. Most of the chalk removed
during the work was thrown upwards, by which a projecting bank was
formed; and this effectually prevents worm-castings (which are
numerous in parts), stones, and other objects from being washed or
rolled into the ditch. The mould on the upper and fortified part
of the hill was found to be in most places only from 2.5 to 3.5
inches in thickness; whereas it had accumulated at the foot of the
embankment above the ditch to a thickness in most places of from 8
to 9.5 inches. On the embankment itself the mould was only 1 to
1.5 inch in thickness; and within the ditch at the bottom it varied
from 2.5 to 3.5, but was in one spot 6 inches in thickness. On the
north-west side of the hill, either no embankment had ever been
thrown up above the ditch, or it had subsequently been removed; so
that here there was nothing to prevent worm-castings, earth and
stones being washed into the ditch, at the bottom of which the
mould formed a layer from 11 to 22 inches in thickness. It should
however be stated that here and on other parts of the slope, the
bed of mould often contained fragments of chalk and flint which had
obviously rolled down at different times from above. The
interstices in the underlying fragmentary chalk were also filled up
with mould.

My son examined the surface of this hill to its base in a south-
west direction. Beneath the great ditch, where the slope was about
24 degrees, the mould was very thin, namely, from 1.5 to 2.5
inches; whilst near the base, where the slope was only 3 degrees to
4 degrees, it increased to between 8 and 9 inches in thickness. We
may therefore conclude that on this artificially modified hill, as
well as in the natural valleys of the neighbouring Chalk Downs,
some fine earth, probably derived in large part from worm-castings,
is washed down, and accumulates in the lower parts, notwithstanding
the percolation of an unknown quantity into the underlying chalk; a
supply of fresh earthy matter being afforded by the dissolution of
the chalk through atmospheric and other agencies.


Summary of the part which worms have played in the history of the
world--Their aid in the disintegration of rocks--In the denudation
of the land--In the preservation of ancient remains--In the
preparation of the soil for the growth of plants--Mental powers of

Worms have played a more important part in the history of the world
than most persons would at first suppose. In almost all humid
countries they are extraordinarily numerous, and for their size
possess great muscular power. In many parts of England a weight of
more than ten tons (10,516 kilogrammes) of dry earth annually
passes through their bodies and is brought to the surface on each
acre of land; so that the whole superficial bed of vegetable mould
passes through their bodies in the course of every few years. From
the collapsing of the old burrows the mould is in constant though
slow movement, and the particles composing it are thus rubbed
together. By these means fresh surfaces are continually exposed to
the action of the carbonic acid in the soil, and of the humus-acids
which appear to be still more efficient in the decomposition of
rocks. The generation of the humus-acids is probably hastened
during the digestion of the many half-decayed leaves which worms
consume. Thus the particles of earth, forming the superficial
mould, are subjected to conditions eminently favourable for their
decomposition and disintegration. Moreover, the particles of the
softer rocks suffer some amount of mechanical trituration in the
muscular gizzards of worms, in which small stones serve as mill-

The finely levigated castings, when brought to the surface in a
moist condition, flow during rainy weather down any moderate slope;
and the smaller particles are washed far down even a gently
inclined surface. Castings when dry often crumble into small
pellets and these are apt to roll down any sloping surface. Where
the land is quite level and is covered with herbage, and where the
climate is humid so that much dust cannot be blown away, it appears
at first sight impossible that there should be any appreciable
amount of sub-aerial denudation; but worm-castings are blown,
especially whilst moist and viscid, in one uniform direction by the
prevalent winds which are accompanied by rain. By these several
means the superficial mould is prevented from accumulating to a
great thickness; and a thick bed of mould checks in many ways the
disintegration of the underlying rocks and fragments of rock.

The removal of worm-castings by the above means leads to results
which are far from insignificant. It has been shown that a layer
of earth, 0.2 of an inch in thickness, is in many places annually
brought to the surface; and if a small part of this amount flows,
or rolls, or is washed, even for a short distance, down every
inclined surface, or is repeatedly blown in one direction, a great
effect will be produced in the course of ages. It was found by
measurements and calculations that on a surface with a mean
inclination of 9 degrees 26 seconds, 2.4 cubic inches of earth
which had been ejected by worms crossed, in the course of a year, a
horizontal line one yard in length; so that 240 cubic inches would
cross a line 100 yards in length. This latter amount in a damp
state would weigh 11.5 pounds. Thus a considerable weight of earth
is continually moving down each side of every valley, and will in
time reach its bed. Finally this earth will be transported by the
streams flowing in the valleys into the ocean, the great receptacle
for all matter denuded from the land. It is known from the amount
of sediment annually delivered into the sea by the Mississippi,
that its enormous drainage-area must on an average be lowered
.00263 of an inch each year; and this would suffice in four and
half million years to lower the whole drainage-area to the level of
the sea-shore. So that, if a small fraction of the layer of fine
earth, 0.2 of an inch in thickness, which is annually brought to
the surface by worms, is carried away, a great result cannot fail
to be produced within a period which no geologist considers
extremely long.

Archaeologists ought to be grateful to worms, as they protect and
preserve for an indefinitely long period every object, not liable
to decay, which is dropped on the surface of the land, by burying
it beneath their castings. Thus, also, many elegant and curious
tesselated pavements and other ancient remains have been preserved;
though no doubt the worms have in these cases been largely aided by
earth washed and blown from the adjoining land, especially when
cultivated. The old tesselated pavements have, however, often
suffered by having subsided unequally from being unequally
undermined by the worms. Even old massive walls may be undermined
and subside; and no building is in this respect safe, unless the
foundations lie 6 or 7 feet beneath the surface, at a depth at
which worms cannot work. It is probable that many monoliths and
some old walls have fallen down from having been undermined by

Worms prepare the ground {82} in an excellent manner for the growth
of fibrous-rooted plants and for seedlings of all kinds. They
periodically expose the mould to the air, and sift it so that no
stones larger than the particles which they can swallow are left in
it. They mingle the whole intimately together, like a gardener who
prepares fine soil for his choicest plants. In this state it is
well fitted to retain moisture and to absorb all soluble
substances, as well as for the process of nitrification. The bones
of dead animals, the harder parts of insects, the shells of land-
molluscs, leaves, twigs, &c., are before long all buried beneath
the accumulated castings of worms, and are thus brought in a more
or less decayed state within reach of the roots of plants. Worms
likewise drag an infinite number of dead leaves and other parts of
plants into their burrows, partly for the sake of plugging them up
and partly as food.

The leaves which are dragged into the burrows as food, after being
torn into the finest shreds, partially digested, and saturated with
the intestinal and urinary secretions, are commingled with much
earth. This earth forms the dark coloured, rich humus which almost
everywhere covers the surface of the land with a fairly well-
defined layer or mantle. Hensen {83} placed two worms in a vessel
18 inches in diameter, which was filled with sand, on which fallen
leaves were strewed; and these were soon dragged into their burrows
to a depth of 3 inches. After about 6 weeks an almost uniform
layer of sand, a centimeter (0.4 inch) in thickness, was converted
into humus by having passed through the alimentary canals of these
two worms. It is believed by some persons that worm-burrows, which
often penetrate the ground almost perpendicularly to a depth of 5
or 6 feet, materially aid in its drainage; notwithstanding that the
viscid castings piled over the mouths of the burrows prevent or
check the rain-water directly entering them. They allow the air to
penetrate deeply into the ground. They also greatly facilitate the
downward passage of roots of moderate size; and these will be
nourished by the humus with which the burrows are lined. Many
seeds owe their germination to having been covered by castings; and
others buried to a considerable depth beneath accumulated castings
lie dormant, until at some future time they are accidentally
uncovered and germinate.

Worms are poorly provided with sense-organs, for they cannot be
said to see, although they can just distinguish between light and
darkness; they are completely deaf, and have only a feeble power of
smell; the sense of touch alone is well developed. They can
therefore learn but little about the outside world, and it is
surprising that they should exhibit some skill in lining their
burrows with their castings and with leaves, and in the case of
some species in piling up their castings into tower-like
constructions. But it is far more surprising that they should
apparently exhibit some degrees of intelligence instead of a mere
blind instinctive impulse, in their manner of plugging up the
mouths of their burrows. They act in nearly the same manner as
would a man, who had to close a cylindrical tube with different
kinds of leaves, petioles, triangles of paper, &c., for they
commonly seize such objects by their pointed ends. But with thin
objects a certain number are drawn in by their broader ends. They
do not act in the same unvarying manner in all cases, as do most of
the lower animals; for instance, they do not drag in leaves by
their foot-stalks, unless the basal part of the blade is as narrow
as the apex, or narrower than it.

When we behold a wide, turf-covered expanse, we should remember
that its smoothness, on which so much of its beauty depends, is
mainly due to all the inequalities having been slowly levelled by
worms. It is a marvellous reflection that the whole of the
superficial mould over any such expanse has passed, and will again
pass, every few years through the bodies of worms. The plough is
one of the most ancient and most valuable of man's inventions; but
long before he existed the land was in fact regularly ploughed, and
still continues to be thus ploughed by earth-worms. It may be
doubted whether there are many other animals which have played so
important a part in the history of the world, as have these lowly
organized creatures. Some other animals, however, still more lowly
organized, namely corals, have done far more conspicuous work in
having constructed innumerable reefs and islands in the great
oceans; but these are almost confined to the tropical zones.


{1} 'Lecons de Geologie Pratique,' tom. i. 1845, p. 140.

{2} 'Transactions Geolog. Soc.' vol. v. p. 505. Read November 1,

{3} 'Histoire des progres de la Geologie,' tom. i. 1847, p. 224.

{4} 'Zeitschrift fur wissenschaft. Zoologie,' B. xxviii. 1877, p.

{5} 'Gardeners' Chronicle,' April 17, 1869, p. 418.

{6} Mr. Darwin's attention was called by Professor Hensen to P. E.
Muller's work on Humus in 'Tidsskrift for Skovbrug,' Band iii. Heft
1 and 2, Copenhagen, 1878. He had, however, no opportunity of
consulting Muller's work. Dr. Muller published a second paper in
1884 in the same periodical--a Danish journal of forestry. His
results have also been published in German, in a volume entitled
'Studien uber die naturlichen Humusformen, unter deren Einwirkung
auf Vegetation und Boden,' 8vo., Berlin, 1887.

{7} 'Bidrag till Skandinaviens Oligochaetfauna,' 1871.

{8} 'Die bis jetzt bekannten Arten aus der Familie der
Regenwurmer,' 1845.

{9} There is even some reason to believe that pressure is actually
favourable to the growth of grasses, for Professor Buckman, who
made many observations on their growth in the experimental gardens
of the Royal Agricultural College, remarks ('Gardeners' Chronicle,'
1854, p. 619): "Another circumstance in the cultivation of grasses
in the separate form or small patches, is the impossibility of
rolling or treading them firmly, without which no pasture can
continue good."

{10} I shall have occasion often to refer to M. Perrier's
admirable memoir, 'Organisation des Lombriciens terrestres' in
'Archives de Zoolog. exper.' tom. iii. 1874, p. 372. C. F. Morren
('De Lumbrici terrestris Hist. Nat.' 1829, p. 14) found that worms
endured immersion for fifteen to twenty days in summer, but that in
winter they died when thus treated.

{11} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., 1829, p. 67.

{12} 'De Lumbrici terrestris Hist. Nat.' &c., p. 14.

{13} Histolog. Untersuchungen uber die Regenwurmer. 'Zeitschrift
fur wissenschaft. Zoologie,' B. xix., 1869, p. 611.

{14} For instance, Mr. Bridgman and Mr. Newman ('The Zoologist,'
vol. vii. 1849, p. 2576), and some friends who observed worms for

{15} 'Familie der Regenwurmer,' 1845, p. 18.

{16} 'The Zoologist,' vol. vii. 1849, p. 2576.

{17} 'Familie der Regenwurmer,' p. 13. Dr. Sturtevant states in
the 'New York Weekly Tribune' (May 19, 1880) that he kept three
worms in a pot, which was allowed to become extremely dry; and
these worms were found "all entwined together, forming a round mass
and in good condition."

{18} 'De Lumbrici terrestris Hist. Nat.' p. 19.

{19} 'Archives de Zoologie experimentale,' tom. vii. 1878, p. 394.
When I wrote the above passage, I was not aware that Krukenberg
('Untersuchungen a. d. physiol. Inst. d. Univ. Heidelberg,' Bd.
ii. p. 37, 1877) had previously investigated the digestive juice of
Lumbricus. He states that it contains a peptic, and diastatic, as
well as a tryptic ferment.

{20} On the action of the pancreatic ferment, see 'A Text-Book of
Physiology,' by Michael Foster, 2nd edit. pp. 198-203. 1878.

{21} Schmulewitsch, 'Action des Sucs digestifs sur la Cellulose.'
Bull. de l'Acad. Imp. de St. Petersbourg, tom. xxv. p. 549. 1879.

{22} Claparede doubts whether saliva is secreted by worms: see
'Zeitschrift fur wissenschaft. Zoologie,' B. xix. 1869, p. 601.

{23} Perrier, 'Archives de Zoolog. exper.' July, 1874, pp. 416,

{24} 'Zeitschrift fur wissenschaft. Zoologie,' B. xix, 1869, pp.

{25} De Vries, 'Landwirth. Jahrbucher,' 1881, p. 77.

{26} M. Foster, 'A Text-Book of Physiology,' 2nd edit. 1878, p.

{27} M. Foster, ut sup. p. 200.

{28} Claparede remarks ('Zeitschrift fur wisseuschaft. Zoolog.'
B. 19, 1869, p. 602) that the pharynx appears from its structure to
be adapted for suction.

{29} An account of her observations is given in the 'Gardeners'
Chronicle,' March 28th, 1868, p. 324.

{30} London's 'Gard. Mag.' xvii. p. 216, as quoted in the
'Catalogue of the British Museum Worms,' 1865, p. 327.

{31} 'Familie der Regenwurmer,' p. 19.

{32} In these narrow triangles the apical angle is 9 degrees 34
seconds, and the basal angles 85 degrees 13 seconds. In the
broader triangles the apical angle is 19 degrees 10 seconds and the
basal angles 80 degrees 25 seconds.

{33} See his interesting work, 'Souvenirs entomologiques,' 1879,
pp. 168-177.

{34} Mobius, 'Die Bewegungen der Thiere,' &c., 1873, p. 111.

{35} 'Annals and Mag. of N. History,' series ii. vol. ix. 1852, p.

{36} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 405.

{37} I state this on the authority of Semper, 'Reisen im Archipel
der Philippinen,' Th. ii. 1877, p. 30.

{38} Dr. King gave me some worms collected near Nice, which, as he
believes, had constructed these castings. They were sent to M.
Perrier, who with great kindness examined and named them for me:
they consisted of Perichaeta affinis, a native of Cochin China and
of the Philippines; P. Luzonica, a native of Luzon in the
Philippines; and P. Houlleti, which lives near Calcutta. M.
Perrier informs me that species of Perichaeta have been naturalized
in the gardens near Montpellier and in Algiers. Before I had any
reason to suspect that the tower-like castings from Nice had been
formed by worms not endemic in the country, I was greatly surprised
to see how closely they resembled castings sent to me from near
Calcutta, where it is known that species of Perichaeta abound.

{39} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.

{40} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.

{41} Perrier, 'Archives de Zoolog. exper.' tom. 3, p. 378, 1874.

{42} This case is given in a postscript to my paper in the
'Transact. Geolog. Soc.' (Vol. v. p. 505), and contains a serious
error, as in the account received I mistook the figure 30 for 80.
The tenant, moreover, formerly said that he had marled the field
thirty years before, but was now positive that this was done in
1809, that is twenty-eight years before the first examination of
the field by my friend. The error, as far as the figure 80 is
concerned, was corrected in an article by me, in the 'Gardeners'
Chronicle,' 1844, p. 218.

{43} These pits or pipes are still in process of formation.
During the last forty years I have seen or heard of five cases, in
which a circular space, several feet in diameter, suddenly fell in,
leaving on the field an open hole with perpendicular sides, some
feet in depth. This occurred in one of my own fields, whilst it
was being rolled, and the hinder quarters of the shaft horse fell
in; two or three cart-loads of rubbish were required to fill up the
hole. The subsidence occurred where there was a broad depression,
as if the surface had fallen in at several former periods. I heard
of a hole which must have been suddenly formed at the bottom of a
small shallow pool, where sheep had been washed during many years,
and into which a man thus occupied fell to his great terror. The
rain-water over this whole district sinks perpendicularly into the
ground, but the chalk is more porous in certain places than in
others. Thus the drainage from the overlying clay is directed to
certain points, where a greater amount of calcareous matter is
dissolved than elsewhere. Even narrow open channels are sometimes
formed in the solid chalk. As the chalk is slowly dissolved over
the whole country, but more in some parts than in others, the
undissolved residue--that is the overlying mass of red clay with
flints,--likewise sinks slowly down, and tends to fill up the pipes
or cavities. But the upper part of the red clay holds together,
aided probably by the roots of plants, for a longer time than the
lower parts, and thus forms a roof, which sooner or later falls in,
as in the above mentioned five cases. The downward movement of the
clay may be compared with that of a glacier, but is incomparably
slower; and this movement accounts for a singular fact, namely,
that the much elongated flints which are embedded in the chalk in a
nearly horizontal position, are commonly found standing nearly or
quite upright in the red clay. This fact is so common that the
workmen assured me that this was their natural position. I roughly
measured one which stood vertically, and it was of the same length
and of the same relative thickness as one of my arms. These
elongated flints must get placed in their upright position, on the
same principle that a trunk of a tree left on a glacier assumes a
position parallel to the line of motion. The flints in the clay
which form almost half its bulk, are very often broken, though not
rolled or abraded; and this may he accounted for by their mutual
pressure, whilst the whole mass is subsiding. I may add that the
chalk here appears to have been originally covered in parts by a
thin bed of fine sand with some perfectly rounded flint pebbles,
probably of Tertiary age; for such sand often partly fills up the
deeper pits or cavities in the chalk.

{44} S. W. Johnson, 'How Crops Feed,' 1870, p. 139.

{45} 'Nature,' November 1877, p. 28.

{46} 'Proc. Phil. Soc.' of Manchester, 1877, p. 247.

{47} 'Trans. of the New Zealand Institute,' vol. xii., 1880, p.

{48} Mr. Lindsay Carnagie, in a letter (June 1838) to Sir C.
Lyell, remarks that Scotch farmers are afraid of putting lime on
ploughed land until just before it is laid down for pasture, from a
belief that it has some tendency to sink. He adds: "Some years
since, in autumn, I laid lime on an oat-stubble and ploughed it
down; thus bringing it into immediate contact with the dead
vegetable matter, and securing its thorough mixture through the
means of all the subsequent operations of fallow. In consequence
of the above prejudice, I was considered to have committed a great
fault; but the result was eminently successful, and the practice
was partially followed. By means of Mr. Darwin's observations, I
think the prejudice will be removed."

{49} This conclusion, which, as we shall immediately see, is fully
justified, is of some little importance, as the so-called bench-
stones, which surveyors fix in the ground as a record of their
levels, may in time become false standards. My son Horace intends
at some future period to ascertain how far this has occurred.

{50} Mr. R. Mallet remarks ('Quarterly Journal of Geolog. Soc.'
vol. xxxiii., 1877, p. 745) that "the extent to which the ground
beneath the foundations of ponderous architectural structures, such
as cathedral towers, has been known to become compressed, is as
remarkable as it is instructive and curious. The amount of
depression in some cases may be measured by feet." He instances
the Tower of Pisa, but adds that it was founded on "dense clay."

{51} 'Zeitschrift fur wissensch. Zoolog.' Bd. xxviii., 1877, p.

{52} See Mr. Dancer's paper in 'Proc. Phil. Soc. of Manchester,'
1877, p. 248.

{53} 'Lecons de Geologie pratique,' 1845, p. 142.

{54} A short account of this discovery was published in 'The
Times' of January 2, 1878; and a fuller account in 'The Builder,'
January 5, 1878.

{55} Several accounts of these ruins have been published; the best
is by Mr. James Farrer in 'Proc. Soc. of Antiquaries of Scotland,'
vol. vi., Part II., 1867, p. 278. Also J. W. Grover, 'Journal of
the British Arch. Assoc.' June 1866. Professor Buckman has
likewise published a pamphlet, 'Notes on the Roman Villa at
Chedworth,' 2nd edit. 1873 Cirencester.

{56} These details are taken from the 'Penny Cyclopaedia,' article

{57} "On the denudation of South Wales," &c., 'Memoirs of the
Geological Survey of Great Britain,' vol. 1., p. 297, 1846.

{58} 'Geological Magazine,' October and November, 1867, vol. iv.
pp. 447 and 483. Copious references on the subject are given in
this remarkable memoir.

{59} A. Tylor "On changes of the sea-level," &c., ' Philosophical
Mag.' (Ser. 4th) vol. v., 1853, p. 258. Archibald Geikie,
Transactions Geolog. Soc. of Glasgow, vol. iii., p. 153 (read
March, 1868). Croll "On Geological Time," 'Philosophical Mag.,'
May, August, and November, 1868. See also Croll, 'Climate and
Time,' 1875, Chap. XX. For some recent information on the amount
of sediment brought down by rivers, see 'Nature,' Sept. 23rd,
1880. Mr. T. Mellard Reade has published some interesting articles
on the astonishing amount of matter brought down in solution by
rivers. See Address, Geolog. Soc., Liverpool, 1876-77.

{60} "An account of the fine dust which often falls on Vessels in
the Atlantic Ocean," Proc. Geolog. Soc. of London, June 4th, 1845.

{61} For La Plata, see my 'Journal of Researches,' during the
voyage of the Beagle, 1845, p. 133. Elie de Beaumont has given
('Lecons de Geolog. pratique,' tom. I. 1845, p. 183) an excellent
account of the enormous quantity of dust which is transported in
some countries. I cannot but think that Mr. Proctor has somewhat
exaggerated ('Pleasant Ways in Science,' 1879, p. 379) the agency
of dust in a humid country like Great Britain. James Geikie has
given ('Prehistoric Europe,' 1880, p. 165) a full abstract of
Richthofen's views, which, however, he disputes.

{62} These statements are taken from Hensen in 'Zeitschrift fur
wissenschaft. Zoologie.' Bd. xxviii., 1877, p. 360. Those with
respect to peat are taken from Mr. A. A. Julien in 'Proc. American
Assoc. Science,' 1879, p. 354.

{63} I have given some facts on the climate necessary or
favourable for the formation of peat, in my 'Journal of
Researches,' 1845, p. 287.

{64} A. A. Julien "On the Geological action of the Humus-acids,"
'Proc. American Assoc. Science,' vol. xxviii., 1879, p. 311. Also
on "Chemical erosion on Mountain Summits;" 'New York Academy of
Sciences,' Oct. 14, 1878, as quoted in the 'American Naturalist.'
See also, on this subject, S. W. Johnson, 'How Crops Feed,' 1870,
p. 138.

{65} See, for references on this subject, S. W. Johnson, 'How
Crops Feed,' 1870, p. 326.

{66} This statement is taken from Mr. Julien, 'Proc. American
Assoc. Science,' vol. xxviii., 1879, p. 330.

{67} The preservative power of a layer of mould and turf is often
shown by the perfect state of the glacial scratches on rocks when
first uncovered. Mr. J. Geikie maintains, in his last very
interesting work ('Prehistoric Europe,' 1881), that the more
perfect scratches are probably due to the last access of cold and
increase of ice, during the long-continued, intermittent glacial

{68} Many geologists have felt much surprise at the complete
disappearance of flints over wide and nearly level areas, from
which the chalk has been removed by subaerial denudation. But the
surface of every flint is coated by an opaque modified layer, which
will just yield to a steel point, whilst the freshly fractured,
translucent surface will not thus yield. The removal by
atmospheric agencies of the outer modified surfaces of freely
exposed flints, though no doubt excessively slow, together with the
modification travelling inwards, will, as may be suspected,
ultimately lead to their complete disintegration, notwithstanding
that they appear to be so extremely durable.

{69} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 409.

{70} 'Nouvelles Archives du Museum,' tom. viii. 1872, pp. 95,

{71} Morren, in speaking of the earth in the alimentary canals of
worms, says, "praesepe cum lapillis commixtam vidi:" 'De Lumbrici
terrestris Hist. Nat.' &c., 1829, p. 16.

{72} Perrier, 'Archives de Zoolog. exper.' tom. iii. 1874, p. 419.

{73} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., p. 16.

{74} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 418.

{75} This conclusion reminds me of the vast amount of extremely
fine chalky mud which is found within the lagoons of many atolls,
where the sea is tranquil and waves cannot triturate the blocks of
coral. This mud must, as I believe ('The Structure and
Distribution of Coral-Reefs,' 2nd edit. 1874, p. 19), be attributed
to the innumerable annelids and other animals which burrow into the
dead coral, and to the fishes, Holothurians, &c., which browse on
the living corals.

{76} Anniversary Address: 'The Quarterly Journal of the
Geological Soc.' May 1880, p. 59.

{77} Mr. James Wallace has pointed out that it is necessary to
take into consideration the possibility of burrows being made at
right angles to the surface instead of vertically down, in which
case the lateral displacement of the soil would be increased.

{78} 'Elements of Geology,' 1865, p. 20.

{79} 'Lecons de Geologie pratique, 1845; cinquieme Lecon. All
Elie de Beaumont's arguments are admirably controverted by Prof. A.
Geikie in his essay in Transact. Geolog. Soc. of Glasgow, vol. iii.
p. 153, 1868.

{80} 'Illustrations of the Huttonian Theory of the Earth,' p. 107.

{81} Mr. E. Tylor in his Presidential address ('Journal of the
Anthropological Institute,' May 1880, p. 451) remarks: "It appears
from several papers of the Berlin Society as to the German 'high-
fields' or 'heathen-fields' (Hochacker, and Heidenacker) that they
correspond much in their situation on hills and wastes with the
'elf-furrows' of Scotland, which popular mythology accounts for by
the story of the fields having been put under a Papal interdict, so
that people took to cultivating the hills. There seems reason to
suppose that, like the tilled plots in the Swedish forest which
tradition ascribes to the old 'hackers,' the German heathen-fields
represent tillage by an ancient and barbaric population."

{82} White of Selborne has some good remarks on the service
performed by worms in loosening, &c., the soil. Edit, by L.
Jenyns, 1843, p. 281.

{83} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.

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