the formation of vegetable mould-第24章
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
10 years。
The accumulation during 21。5 years on a swampy field near Maer
Hall； amounted to nearly 1。9 inch in 10 years。
The accumulation during 7 years on a very swampy field near Maer
Hall amounted to 2。1 inches in 10 years。
The accumulation during 29 years； on good； argillaceous pasture…
land over the Chalk at Down； amounted to 2。2 inches in 10 years。
The accumulation during 30 years on the side of a valley over the
Chalk at Down； the soil being argillaceous； very poor； and only
just converted into pasture （so that it was for some years
unfavourable for worms）； amounted to 0。83 inch in 10 years。
In these cases （excepting the last） it may be seen that the amount
of earth brought to the surface during 10 years is somewhat greater
than that calculated from the castings which were actually weighed。
This excess may be partly accounted for by the loss which the
weighed castings had previously undergone through being washed by
rain； by the adhesion of particles to the blades of the surrounding
grass； and by their crumbling when dry。 Nor must we overlook other
agencies which in all ordinary cases add to the amount of mould；
and which would not be included in the castings that were
collected； namely； the fine earth brought up to the surface by
burrowing larvae and insects； especially by ants。 The earth
brought up by moles generally has a somewhat different appearance
from vegetable mould； but after a time would not be distinguishable
from it。 In dry countries； moreover； the wind plays an important
part in carrying dust from one place to another； and even in
England it must add to the mould on fields near great roads。 But
in our country these latter several agencies appear to be of quite
subordinate importance in comparison with the action of worms。
We have no means of judging how great a weight of earth a single
full…sized worm ejects during a year。 Hensen estimates that 53；767
worms exist in an acre of land； but this is founded on the number
found in gardens； and he believes that only about half as many live
in corn…fields。 How many live in old pasture land is unknown； but
if we assume that half the above number； or 26；886 worms live on
such land； then taking from the previous summary 15 tons as the
weight of the castings annually thrown up on an acre of land； each
worm must annually eject 20 ounces。 A full…sized casting at the
mouth of a single burrow often exceeds； as we have seen； an ounce
in weight； and it is probable that worms eject more than 20 full…
sized castings during a year。 If they eject annually more than 20
ounces； we may infer that the worms which live in an acre of
pasture land must be less than 26；886 in number。
Worms live chiefly in the superficial mould； which is usually from
4 or 5 to 10 and even 12 inches in thickness； and it is this mould
which passes over and over again through their bodies and is
brought to the surface。 But worms occasionally burrow into the
subsoil to a much greater depth； and on such occasions they bring
up earth from this greater depth； and this process has gone on for
countless ages。 Therefore the superficial layer of mould would
ultimately attain； though at a slower and slower rate； a thickness
equal to the depth to which worms ever burrow； were there not other
opposing agencies at work which carry away to a lower level some of
the finest earth which is continually being brought to the surface
by worms。 How great a thickness vegetable mould ever attains； I
have not had good opportunities for observing； but in the next
chapter； when we consider the burial of ancient buildings； some
facts will be given on this head。 In the two last chapters we
shall see that the soil is actually increased； though only to a
small degree； through the agency of worms； but their chief work is
to sift the finer from the coarser particles； to mingle the whole
with vegetable debris； and to saturate it with their intestinal
secretions。
Finally； no one who considers the facts given in this chapteron
the burying of small objects and on the sinking of great stones
left on the surfaceon the vast number of worms which live within
a moderate extent of ground on the weight of the castings ejected
from the mouth of the same burrowon the weight of all the
castings ejected within a known time on a measured spacewill
hereafter； as I believe； doubt that worms play an important part in
nature。
CHAPTER IVTHE PART WHICH WORMS HAVE PLAYED IN THE BURIAL OF
ANCIENT BUILDINGS。
The accumulation of rubbish on the sites of great cities
independent of the action of wormsThe burial of a Roman villa at
AbingerThe floors and walls penetrated by wormsSubsidence of a
modern pavementThe buried pavement at Beaulieu AbbeyRoman
villas at Chedworth and BradingThe remains of the Roman town at
SilchesterThe nature of the debris by which the remains are
coveredThe penetration of the tesselated floors and walls by
wormsSubsidence of the floorsThickness of the mouldThe old
Roman city of WroxeterThickness of the mouldDepth of the
foundations of some of the BuildingsConclusion。
Archaeologists are probably not aware how much they owe to worms
for the preservation of many ancient objects。 Coins； gold
ornaments； stone implements； &c。； if dropped on the surface of the
ground； will infallibly be buried by the castings of worms in a few
years； and will thus be safely preserved； until the land at some
future time is turned up。 For instance； many years ago a grass…
field was ploughed on the northern side of the Severn； not far from
Shrewsbury； and a surprising number of iron arrow…heads were found
at the bottom of the furrows； which； as Mr。 Blakeway； a local
antiquary； believed； were relics of the battle of Shrewsbury in the
year 1403； and no doubt had been originally left strewed on the
battle…field。 In the present chapter I shall show that not only
implements； &c。； are thus preserved； but that the floors and the
remains of many ancient buildings in England have been buried so
effectually； in large part through the action of worms； that they
have been discovered in recent times solely through various
accidents。 The enormous beds of rubbish； several yards in
thickness； which underlie many cities； such as Rome； Paris； and
London； the lower ones being of great antiquity； are not here
referred to； as they have not been in any way acted on by worms。
When we consider how much matter is daily brought into a great city
for building； fuel； clothing and food； and that in old times when
the roads were bad and the work of the scavenger was neglected； a
comparatively small amount was carried away； we may agree with Elie
de Beaumont； who； in discussing this subject； says； 〃pour une
voiture de materiaux qui en sort； on y en fait entrer cent。〃 ｛53｝
Nor should we overlook the effects of fires； the demolition of old
buildings； and the removal of rubbish to the nearest vacant space；
Abinger； Surrey。Late in the autumn of 1876； the ground in an old
farm…yard at this place was dug to a depth of 2 to 2。5 feet； and
the workmen found various ancient remains。 This led Mr。 T。 H。
Farrer of Abinger Hall to have an adjoining ploughed field
searched。 On a trench being dug； a layer of concrete； still partly
covered with tesserae （small red tiles）； and surrounded on two
sides by broken…down walls； was soon discovered。 It is believed；
｛54｝ that this room formed part of the atrium or reception…room of
a Roman villa。 The walls of two or three other small rooms were
afterwards discovered。 Many fragments of pottery； other objects；
and coins of several Roman emperors； dating from 133 to 361； and
perhaps to 375 A。D。； were likewise found。 Also a half…penny of
George I。； 1715。 The presence of this latter coin seems an
anomaly； but no doubt it was dropped on the ground during the last
century； and since then there has been ample time for its burial
under a considerable depth of the castings of worms。 From the
different dates of the Roman coins we may infer that the building
was long inhabited。 It was probably
