the formation of vegetable mould-第15部分
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the holes。 The soil beneath the layer of lime was either gravelly
or of a coarse sandy nature； and differed considerably in
appearance from the overlying dark…coloured fine mould。 Coal…
cinders had been spread over a part of this same field either in
the year 1833 or 1834； and when the above holes were dug； that is
after an interval of 3 or 4 years； the cinders formed a line of
black spots round the holes； at a depth of 1 inch beneath the
surface； parallel to and above the white layer of lime。 Over
another part of this field cinders had been strewed； only about
half…a…year before； and these either still lay on the surface or
were entangled among the roots of the grasses； and I here saw the
commencement of the burying process； for worm…castings had been
heaped on several of the smaller fragments。 After an interval of
4。75 years this field was re…examined； and now the two layers of
lime and cinders were found almost everywhere at a greater depth
than before by nearly 1 inch； we will say by 0。75 of an inch。
Therefore mould to an average thickness of 0。22 of an inch had been
annually brought up by the worms； and had been spread over the
surface of this field。
Coal…cinders had been strewed over another field； at a date which
could not be positively ascertained； so thickly that they formed
（October； 1837） a layer； 1 inch in thickness at a depth of about 3
inches from the surface。 The layer was so continuous that the
over…lying dark vegetable mould was connected with the sub…soil of
red clay only by the roots of the grasses； and when these were
broken； the mould and the red clay fell apart。 In a third field；
on which coal…cinders and burnt marl had been strewed several times
at unknown dates； holes were dug in 1842； and a layer of cinders
could be traced at a depth of 3。5 inches； beneath which at a depth
of 9。5 inches from the surface there was a line of cinders together
with burnt marl。 On the sides of one hole there were two layers of
cinders； at 2 and 3。5 inches beneath the surface； and below them at
a depth in parts of 9。5； and in other parts of 10。5 inches there
were fragments of burnt marl。 In a fourth field two layers of
lime； one above the other； could be distinctly traced； and beneath
them a layer of cinders and burnt marl at a depth of from 10 to 12
inches below the surface。
A piece of waste； swampy land was enclosed； drained； ploughed；
harrowed and thickly covered in the year 1822 with burnt marl and
cinders。 It was sowed with grass seeds； and now supports a
tolerably good but coarse pasture。 Holes were dug in this field in
1837； or 15 years after its reclamation； and we see in the
accompanying diagram （Fig。 5）； reduced to half of the natural
scale； that the turf was 1 inch thick； beneath which there was a
layer of vegetable mould 2。5 inches thick。 This layer did not
contain fragments of any kind； but beneath it there was a layer of
mould； 1。5 inch in thickness； full of fragments of burnt marl；
conspicuous from their red colour； one of which near the bottom was
an inch in length； and other fragments of coal…cinders together
with a few white quartz pebbles。 Beneath this layer and at a depth
of 4。5 inches from the surface； the original black； peaty； sandy
soil with a few quartz pebbles was encountered。 Here therefore the
fragments of burnt marl and cinders had been covered in the course
of 15 years by a layer of fine vegetable mould； only 2。5 inches in
thickness； excluding the turf。 Six and a half years subsequently
this field was re…examined； and the fragments were now found at
from 4 to 5 inches beneath the surface。 So that in this interval
of 6。5 years； about 1。5 inch of mould had been added to the
superficial layer。 I am surprised that a greater quantity had not
been brought up during the whole 21。5 years； for in the closely
underlying black； peaty soil there were many worms。 It is；
however； probable that formerly； whilst the land remained poor；
worms were scanty； and the mould would then have accumulated
slowly。 The average annual increase of thickness for the whole
period is 0。19 of an inch。
Two other cases are worth recording。 In the spring of 1835； a
field； which had long existed as poor pasture and was so swampy
that it trembled slightly when stamped on； was thickly covered with
red sand so that the whole surface appeared at first bright red。
When holes were dug in this field after an interval of about 2。5
years； the sand formed a layer at a depth of 0。75 in。 beneath the
surface。 In 1842 （i。e。； 7 years after the sand had been laid on）
fresh holes were dug； and now the red sand formed a distinct layer；
2 inches beneath the surface； or 1。5 inch beneath the turf； so that
on an average； 0。21 inch of mould had been annually brought to the
surface。 Immediately beneath the layer of red sand； the original
substratum of black sandy peat extended。
A grass field； likewise not far from Maer Hall； had formerly been
thickly covered with marl； and was then left for several years as
pasture； it was afterwards ploughed。 A friend had three trenches
dug in this field 28 years after the application of the marl； ｛42｝
and a layer of the marl fragments could be traced at a depth；
carefully measured； of 12 inches in some parts； and of 14 inches in
other parts。 This difference in depth depended on the layer being
horizontal； whilst the surface consisted of ridges and furrows from
the field having been ploughed。 The tenant assured me that it had
never been turned up to a greater depth than from 6 to 8 inches；
and as the fragments formed an unbroken horizontal layer from 12 to
14 inches beneath the surface； these must have been buried by the
worms whilst the land was in pasture before it was ploughed； for
otherwise they would have been indiscriminately scattered by the
plough throughout the whole thickness of the soil。 Four…and…a…half
years afterwards I had three holes dug in this field； in which
potatoes had been lately planted； and the layer of marl…fragments
was now found 13 inches beneath the bottoms of the furrows； and
therefore probably 15 inches beneath the general level of the
field。 It should； however； be observed that the thickness of the
blackish sandy soil； which had been thrown up by the worms above
the marl…fragments in the course of 32。5 years； would have measured
less than 15 inches； if the field had always remained as pasture；
for the soil would in this case have been much more compact。 The
fragments of marl almost rested on an undisturbed substratum of
white sand with quartz pebbles； and as this would be little
attractive to worms； the mould would hereafter be very slowly
increased by their action。
We will now give some cases of the action of worms； on land
differing widely from the dry sandy or the swampy pastures just
described。 The chalk formation extends all round my house in Kent；
and its surface； from having been exposed during an immense period
to the dissolving action of rain…water； is extremely irregular；
being abruptly festooned and penetrated by many deep well…like
cavities。 ｛43｝ During the dissolution of the chalk； the insoluble
matter； including a vast number of unrolled flints of all sizes；
has been left on the surface and forms a bed of stiff red clay；
full of flints； and generally from 6 to 14 feet in thickness。 Over
the red clay； wherever the land has long remained as pasture； there
is a layer a few inches in thickness； of dark…coloured vegetable
mould。
A quantity of broken chalk was spread； on December 20； 1842； over a
part of a field near my house； which had existed as pasture
certainly for 30； probably for twice or thrice as many years。 The
chalk was laid on the land for the sake of observing at some future
period to what depth it would become buried。 At the end of
November； 1871； that is after an interval of 29 years； a trench was
dug across this part of the field； and a line of white nodules
could be traced on both sides of the trench； at a depth of 7 inches
from the surface。 The mould； therefore； （excluding the turf） had
here been thrown up at an average rate of 0。22 inch per year。
Beneath the line of chalk nodules there was in parts hardly any
fine earth free of flints； while in other parts there was a layer；
2。25 inches in thickness。 In this latter case the mould was
altogether 9。25 inches thick； and in one such spot a nodule of
chalk and a smooth flint pebble； both of which must have been left
at some former time on the surface； were found at this depth。 At
from 11 to 12 inches beneath the surface； the undisturbed reddish
clay； full of flints； extended。 The appearance of the above
nodules of chalk surprised me； much at first； as they closely
resembled water…worn pebbles； whereas the freshly…broken fragments
had been angular。 But on examining the nodules with a lens； they
no longer appeared water…worn； for their surfaces were pitted
through unequal corrosion； and minute； sharp points； formed of
broken fossil shells； projected from them。 It was evident that the
corners of the original fragments of chalk had been wholly
dissolved； from presenting a large surface to the carbonic acid
dissolved in the rain…water and to that generated in soil
containing vegetable matter； as well as to the humus…acids。 ｛44｝
The projecting corners would also； relatively to the other parts；
have been embraced by a larger number of living rootlets； and these
have the power of even attacking marble； as Sachs has shown。 Thus；
in the course of 29 years； buried angular fragments of chalk had
been converted into well…rounded nodules。
Another part of this same field was mossy； and as it was thought
that sifted coal…cinders would improve the pasture； a thick layer
was spread over this part either in 1842 or 1843； and another layer
some years afterwards。 In 1871 a trench was here dug； and many
cinders lay in a line at a depth of 7 inches beneath the surface；
with another line at a depth of 5。5 inches parallel to the one
beneath。 In another part of this field； which had formerly existed
as
