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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
thickness。
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 dis