the formation of vegetable mould-第16部分
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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 a separate one； and which it was believed had been pasture…land
for more than a century； trenches were dug to see how thick the
vegetable mould was。 By chance the first trench was made at a spot
where at some former period； certainly more than forty years
before； a large hole had been filled up with coarse red clay；
flints； fragments of chalk； and gravel； and here the fine vegetable
mould was only from 4。125 to 4。375 inches in thickness。 In another
and undisturbed place； the mould varied much in thickness； namely；
from 6。5 to 8。5 inches； beneath which a few small fragments of
brick were found in one place。 From these several cases； it would
appear that during the last 29 years mould has been heaped on the
surface at an average annual rate of from 0。2 to 0。22 of an inch。
But in this district when a ploughed field is first laid down in
grass； the mould accumulates at a much slower rate。 The rate；
also； must become very much slower after a bed of mould； several
inches in thickness； has been formed； for the worms then live
chiefly near the surface； and burrow down to a greater depth so as
to bring up fresh earth from below； only during the winter when the
weather is very cold （at which time worms were found in this field
at a depth of 26 inches） and during summer； when the weather is
very dry。
A field； which adjoins the one just described； slopes in one part
rather steeply （viz。； at from 10 degrees to 15 degrees）； this part
was last ploughed in 1841； was then harrowed and left to become
pasture…land。 For several years it was clothed with an extremely
scant vegetation； and was so thickly covered with small and large
flints （some of them half as large as a child's head） that the
field was always called by my sons 〃the stony field。〃 When they
ran down the slope the stones clattered together； I remember
doubting whether I should live to see these larger flints covered
with vegetable mould and turf。 But the smaller stones disappeared
before many years had elapsed； as did every one of the larger ones
after a time； so that after thirty years （1871） a horse could
gallop over the compact turf from one end of the field to the
other； and not strike a single stone with his shoes。 To anyone who
remembered the appearance of the field in 1842； the transformation
was wonderful。 This was certainly the work of the worms； for
though castings were not frequent for several years； yet some were
thrown up month after month； and these gradually increased in
numbers as the pasture improved。 In the year 1871 a trench was dug
on the above slope； and the blades of grass were cut off close to
the roots； so that the thickness of the turf and of the vegetable
mould could be measured accurately。 The turf was rather less than
half an inch； and the mould； which did not contain any stones； 2。5
inches in thickness。 Beneath this lay coarse clayey earth full of
flints； like that in any of the neighbouring ploughed fields。 This
coarse earth easily fell apart from the overlying mould when a spit
was lifted up。 The average rate of accumulation of the mould
during the whole thirty years was only 。083 inch per year （i。e。；
nearly one inch in twelve years）； but the rate must have been much
slower at first； and afterwards considerably quicker。
The transformation in the appearance of this field； which had been
effected beneath my eyes； was afterwards rendered the more
striking； when I examined in Knole Park a dense forest of lofty
beech…trees； beneath which nothing grew。 Here the ground was
thickly strewed with large naked stones； and worm…castings were
almost wholly absent。 Obscure lines and irregularities on the
surface indicated that the land had been cultivated some centuries
ago。 It is probable that a thick wood of young beech…trees sprung
up so quickly； that time enough was not allowed for worms to cover
up the stones with their castings； before the site became unfitted
for their existence。 Anyhow the contrast between the state of the
now miscalled 〃stony field；〃 well stocked with worms； and the
present state of the ground beneath the old beech…trees in Knole
Park； where worms appeared to be absent； was striking。
A narrow path running across part of my lawn was paved in 1843 with
small flagstones； set edgeways； but worms threw up many castings
and weeds grew thickly between them。 During several years the path
was weeded and swept； but ultimately the weeds and worms prevailed；
and the gardener ceased to sweep； merely mowing off the weeds； as
often as the lawn was mowed。 The path soon became almost covered
up； and after several years no trace of it was left。 On removing；
in 1877； the thin overlying layer of turf； the small flag…stones；
all in their proper places； were found covered by an inch of fine
mould。
Two recently published accounts of substances strewed on the
surface of pasture…land； having become buried through the action of
worms； may be here noticed。 The Rev。 H。 C。 Key had a ditch cut in
a field； over which coal…ashes had been spread； as it was believed；
eighteen years before； and on the clean…cut perpendicular sides of
the ditch； at a depth of at least seven inches； there could be
seen； for a length of 60 yards； 〃a distinct； very even； narrow line
of coal…ashes； mixed with small coal； perfectly parallel with the
top…sward。〃 ｛45｝ This parallelism and the length of the section
give interest to the case。 Secondly； Mr。 Dancer states ｛46｝ that
crushed bones had been thickly strewed over a field； and 〃some
years afterwards〃 these were found 〃several inches below the
surface； at a uniform depth。〃
The Rev。 Mr。 Zincke informs me that he has lately had an orchard
dug to the unusual depth of 4 feet。 The upper 18 inches consisted
of dark…coloured vegetable mould； and the next 18 inches of sandy
loam； containing in the lower part many rolled pieces of sandstone；
with some bits of brick and tile； probably of Roman origin； as
remains of this period have been found close by。 The sandy loam
rested on an indurated ferruginous pan of yellow clay； on the
surface of which two perfect celts were found。 If； as seems
probable； the celts were originally left on the surface of the
land； they have since been covered up with earth 3 feet in
thickness； all of which has probably passed through the bodies of
worms； excepting the stones which may have been scattered on the
surface at different times； together with manure or by other means。
It is difficult otherwise to understand the source of the 18 inches
of sandy loam； which differed from the overlying dark vegetable
mould； after both had been burnt； only in being of a brighter red
colour； and in not being quite so fine…grained。 But on this view
we must suppose that the carbon in vegetable mould； when it lies at
some little depth beneath the surface and does not continually
receive decaying vegetable matter from above； loses its dark colour
in the course of centuries； but whether this is probable I do not
know。
Worms appear to act in the same manner in New Zealand as in Europe；
for Professor J。 von Haast has described ｛47｝ a section near the
coast； consisting of mica…schist； 〃covered by 5 or 6 feet of loess；
above which about 12 inches of vegetable soil had accumulated。〃
Between the loess and the mould there was a layer from 3 to 6
inches in thickness； consisting of 〃cores； implements； flakes； and
chips； all manufactured from hard basaltic rock。〃 It is therefore
probable that the aborigines； at some former period； had left these
objects on the surface； and that they had afterwards been slowly
covered up by the castings of worms。
Farmers in England are well aware that objects of all kinds； left
on the surface of pasture…land； after a time disappear； or； as they
say； work themselves downwards。 How powdered lime； cinders； and
heavy stones； can work down； and at the same rate； through the
matted roots of a grass…covered surface； is a question which has
probably never occurred to them。 ｛48｝
The Sinking of great Stones through the Action of Worms。When a
stone of large size and of irregular shape is left on the surface
of the ground； it rests； of course； on the more protuberant parts；
but worms soon fill up with their castings all the hollow spaces on
the lower side； for； as Hensen remarks； they like the shelter of
stones。 As soon as the hollows are filled up； the worms eject the
earth which they have swallowed beyond the circumference of the
stones； and thus the surface of the ground is raised all round the
stone。 As the burrows excavated directly beneath the stone after a
time collapse； the stone sinks a little。 ｛49｝ Hence it is； that
boulders which at some ancient period have rolled down from a rocky
mountain or cliff on to a meadow at its base； are always somewhat
imbedded in the soil； and； when removed； leave an exact impression
of their lower surfaces in the underlying fine mould。 If； however；
a boulder is of such huge dimensions； that the earth beneath is
kept dry； such earth will not be inhabited by worms； and the
boulder will not sink into the ground。
A lime…kiln formerly stood in a grass…field near Leith Hill Place
in Surrey； and was pulled down 35 years before my visit； all the
loose rubbish had been carted away； excepting three large stones of
quartzose sandstone； which it was thought might hereafter be of
some use。 An old workman remembered that they had been left on a
bare surface of broken bricks and mortar； close to the foundations
of the kiln； but the whole surrounding surface is now covered with
turf and mould。 The two largest of these stones had never since
been moved； nor could this easily have been done； as； when I had
them removed； it was the work of two men with levers。 One of these
stones； and not the largest； was 64 inches long； 17 inches broad；
and from 9 to 10 inches in thickness。 Its lower surface was
somewhat protuberant in the middle； and this p
