the formation of vegetable mould-第17部分
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and from 9 to 10 inches in thickness。 Its lower surface was
somewhat protuberant in the middle； and this part still rested on
broken bricks and mortar； showing the truth of the old workman's
account。 Beneath the brick rubbish the natural sandy soil； full of
fragments of sandstone was found； and this could have yielded very
little； if at all； to the weight of the stone； as might have been
expected if the sub…soil had been clay。 The surface of the field；
for a distance of about 9 inches round the stone； gradually sloped
up to it； and close to the stone stood in most places about 4
inches above the surrounding ground。 The base of the stone was
buried from 1 to 2 inches beneath the general level； and the upper
surface projected about 8 inches above this level； or about 4
inches above the sloping border of turf。 After the removal of the
stone it became evident that one of its pointed ends must at first
have stood clear above the ground by some inches； but its upper
surface was now on a level with the surrounding turf。 When the
stone was removed； an exact cast of its lower side； forming a
shallow crateriform hollow； was left； the inner surface of which
consisted of fine black mould； excepting where the more protuberant
parts rested on the brick…rubbish。 A transverse section of this
stone； together with its bed； drawn from measurements made after it
had been displaced； is here given on a scale of 0。5 inch to a foot
（Fig。 6）。 The turf…covered border which sloped up to the stone；
consisted of fine vegetable mould； in one part 7 inches in
thickness。 This evidently consisted of worm…castings； several of
which had been recently ejected。 The whole stone had sunk in the
thirty…five years； as far as I could judge； about 1。5 inch； and
this must have been due to the brick…rubbish beneath the more
protuberant parts having been undermined by worms。 At this rate
the upper surface of the stone； if it had been left undisturbed；
would have sunk to the general level of the field in 247 years； but
before this could have occurred； some earth would have been washed
down by heavy rain from the castings on the raised border of turf
over the upper surface of the stone。
The second stone was larger that the one just described； viz。； 67
inches in length； 39 in breadth； and 15 in thickness。 The lower
surface was nearly flat； so that the worms must soon have been
compelled to eject their castings beyond its circumference。 The
stone as a whole had sunk about 2 inches into the ground。 At this
rate it would have required 262 years for its upper surface to have
sunk to the general level of the field。 The upwardly sloping；
turf…covered border round the stone was broader than in the last
case； viz。； from 14 to 16 inches； and why this should be so； I
could see no reason。 In most parts this border was not so high as
in the last case； viz。； from 2 to 2。5 inches； but in one place it
was as much as 5。5。 Its average height close to the stone was
probably about 3 inches； and it thinned out to nothing。 If so； a
layer of fine earth； 15 inches in breadth and 1。5 inch in average
thickness； of sufficient length to surround the whole of the much
elongated slab； must have been brought up by the worms in chief
part from beneath the stone in the course of 35 years。 This amount
would be amply sufficient to account for its having sunk about 2
inches into the ground； more especially if we bear in mind that a
good deal of the finest earth would have been washed by heavy rain
from the castings ejected on the sloping border down to the level
of the field。 Some fresh castings were seen close to the stone。
Nevertheless； on digging a large hole to a depth of 18 inches where
the stone had lain； only two worms and a few burrows were seen；
although the soil was damp and seemed favourable for worms。 There
were some large colonies of ants beneath the stone； and possibly
since their establishment the worms had decreased in number。
The third stone was only about half as large as the others； and two
strong boys could together have rolled it over。 I have no doubt
that it had been rolled over at a moderately recent time； for it
now lay at some distance from the two other stones at the bottom of
a little adjoining slope。 It rested also on fine earth； instead of
partly on brick…rubbish。 In agreement with this conclusion； the
raised surrounding border of turf was only 1 inch high in some
parts； and 2 inches in other parts。 There were no colonies of ants
beneath this stone； and on digging a hole where it had lain；
several burrows and worms were found。
At Stonehenge； some of the outer Druidical stones are now
prostrate； having fallen at a remote but unknown period； and these
have become buried to a moderate depth in the ground。 They are
surrounded by sloping borders of turf； on which recent castings
were seen。 Close to one of these fallen stones； which was 17 ft
long； 6 ft。 broad； and 28。5 inches thick； a hole was dug； and here
the vegetable mould was at least 9。5 inches in thickness。 At this
depth a flint was found； and a little higher up on one side of the
hole a fragment of glass。 The base of the stone lay about 9。5
inches beneath the level of the surrounding ground； and its upper
surface 19 inches above the ground。
A hole was also dug close to a second huge stone； which in falling
had broken into two pieces； and this must have happened long ago；
judging from the weathered aspect of the fractured ends。 The base
was buried to a depth of 10 inches； as was ascertained by driving
an iron skewer horizontally into the ground beneath it。 The
vegetable mould forming the turf…covered sloping border round the
stone； on which many castings had recently been ejected； was 10
inches in thickness； and most of this mould must have been brought
up by worms from beneath its base。 At a distance of 8 yards from
the stone； the mould was only 5。5 inches in thickness （with a piece
of tobacco pipe at a depth of 4 inches）； and this rested on broken
flint and chalk which could not have easily yielded to the pressure
or weight of the stone。
A straight rod was fixed horizontally （by the aid of a spirit…
level） across a third fallen stone； which was 7 feet 9 inches long；
and the contour of the projecting parts and of the adjoining
ground； which was not quite level； was thus ascertained； as shown
in the accompanying diagram （Fig。 7） on a scale of 0。5 inch to a
foot。 The turf…covered border sloped up to the stone on one side
to a height of 4 inches； and on the opposite side to only 2。5
inches above the general level。 A hole was dug on the eastern
side； and the base of the stone was here found to lie at a depth of
4 inches beneath the general level of the ground； and of 8 inches
beneath the top of the sloping turf…covered border。
Sufficient evidence has now been given showing that small objects
left on the surface of the land where worms abound soon get buried；
and that large stones sink slowly downwards through the same means。
Every step of the process could be followed； from the accidental
deposition of a single casting on a small object lying loose on the
surface； to its being entangled amidst the matted roots of the
turf； and lastly to its being embedded in the mould at various
depths beneath the surface。 When the same field was re…examined
after the interval of a few years； such objects were found at a
greater depth than before。 The straightness and regularity of the
lines formed by the imbedded objects； and their parallelism with
the surface of the land； are the most striking features of the
case； for this parallelism shows how equably the worms must have
worked； the result being； however； partly the effect of the washing
down of the fresh castings by rain。 The specific gravity of the
objects does not affect their rate of sinking； as could be seen by
porous cinders； burnt marl； chalk and quartz pebbles； having all
sunk to the same depth within the same time。 Considering the
nature of the substratum； which at Leith Hill Place was sandy soil
including many bits of rock； and at Stonehenge； chalk…rubble with
broken flints； considering； also； the presence of the turf…covered
sloping border of mould round the great fragments of stone at both
these places； their sinking does not appear to have been sensibly
aided by their weight； though this was considerable。 ｛50｝
On the number of worms which live within a given space。We will
now show； firstly； what a vast number of worms live unseen by us
beneath our feet； and； secondly； the actual weight of the earth
which they bring up to the surface within a given space and within
a given time。 Hensen； who has published so full and interesting an
account of the habits of worms； ｛51｝ calculates； from the number
which he found in a measured space； that there must exist 133；000
living worms in a hectare of land； or 53；767 in an acre。 This
latter number of worms would weigh 356 pounds； taking Hensen's
standard of the weight of a single worm； namely； three grams。 It
should； however； be noted that this calculation is founded on the
numbers found in a garden； and Hensen believes that worms are here
twice as numerous as in corn…fields。 The above result； astonishing
though it be； seems to me credible； judging from the number of
worms which I have sometimes seen； and from the number daily
destroyed by birds without the species being exterminated。 Some
barrels of bad ale were left on Mr。 Miller's land； ｛52｝ in the hope
of making vinegar； but the vinegar proved bad； and the barrels were
upset。 It should be premised that acetic acid is so deadly a
poison to worms that Perrier found that a glass rod dipped into
this acid and then into a considerable body of water in which worms
were immersed； invariably killed them quickly。 On the morning
after the barrels had been upset； 〃the heaps of worms which lay
dead on the ground were so amazing； that if Mr。 Miller had not seen
them； he could not have thought it possible for such numbers to
have existed in the space。〃 As further
