the formation of vegetable mould-第30章
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buildings were found tolerably perfect； being filled with stones；
broken tiles； rubbish and soil。 The old floors of various rooms
were covered with rubble。 As I was anxious to know how thick the
mantle of mould and rubbish was； which had so long concealed these
ruins； I applied to Dr。 H。 Johnson； who had superintended the
excavations； and he； with the greatest kindness； twice visited the
place to examine it in reference to my questions； and had many
trenches dug in four fields which had hitherto been undisturbed。
The results of his observations are given in the following Table。
He also sent me specimens of the mould； and answered； as far as he
could； all my questions。
MEASUREMENTS BY DR。 H。 JOHNSON OF THE THICKNESS OF THE VEGETABLE
MOULD OVER THE ROMAN RUINS AT WROXETER。
Trenches dug in a field called 〃Old Works。〃
（Thickness of mould in inches shown in parenthesisDP。）
1。 At a depth of 36 inches undisturbed sand was reached （20）
2。 At a depth of 33 inches concrete was reached （21）
3。 At a depth of 9 inches concrete was reached （9）
Trenches dug in a field called 〃Shop Leasows；〃 this is the highest
field within the old walls； and slopes down from a sub…central
point on all sides at about an angle of 2 degrees。
4。 Summit of field； trench 45 inches deep （40）
5。 Close to summit of field； trench 36 inches deep （26）
6。 Close to summit of field； trench 28 inches deep （28）
7。 Near summit of field； trench 36 inches deep （24）
8。 Near summit of field； trench at one end 39 inches deep； the
mould here graduated into the underlying undisturbed sand； and its
thickness （24 inches） is somewhat arbitrary。 At the other end of
the trench； a causeway was encountered at a depth of only 7 inches；
and the mould was here only 7 inches thick （24）
9。 Trench close to the last； 28 inches in depth （24）
10。 Lower part of same field； trench 30 inches deep （15）
11。 Lower part of same field； trench 31 inches deep （17）
12。 Lower part of same field； trench 36 inches deep； at which
depth undisturbed sand was reached （28）
13。 In another part of same field； trench 9。5 inches deep stopped
by concrete （9。5）
14。 In another part of same field； trench 9 inches deep； stopped
by concrete （9）
15。 In another part of the same field； trench 24 inches deep； when
sand was reached （16）
16。 In another part of same field； trench 30 inches deep； when
stones were reached； at one end of the trench mould 12 inches； at
the other end 14 inches thick （13）
Small field between 〃Old Works〃 and 〃Shop Leasows；〃 I believe
nearly as high as the upper part of the latter field。
17。 Trench 26 inches deep （24）
18。 Trench 10 inches deep； and then came upon a causeway （10）
19。 Trench 34 inches deep （30）
20。 Trench 31 inches deep （31）
Field on the western side of the space enclosed within the old
walls。
21。 Trench 28 inches deep； when undisturbed sand was reached （16）
22。 Trench 29 inches deep； when undisturbed sand was reached （15）
23。 Trench 14 inches deep； and then came upon a building （14）
Dr。 Johnson distinguished as mould the earth which differed； more
or less abruptly； in its dark colour and in its texture from the
underlying sand or rubble。 In the specimens sent to me； the mould
resembled that which lies immediately beneath the turf in old
pasture…land； excepting that it often contained small stones； too
large to have passed through the bodies of worms。 But the trenches
above described were dug in fields； none of which were in pasture；
and all had been long cultivated。 Bearing in mind the remarks made
in reference to Silchester on the effects of long…continued
culture； combined with the action of worms in bringing up the finer
particles to the surface； the mould； as so designated by Dr。
Johnson； seems fairly well to deserve its name。 Its thickness；
where there was no causeway； floor or walls beneath； was greater
than has been elsewhere observed； namely； in many places above 2
ft。； and in one spot above 3 ft。 The mould was thickest on and
close to the nearly level summit of the field called 〃Shop
Leasows；〃 and in a small adjoining field； which； as I believe； is
of nearly the same height。 One side of the former field slopes at
an angle of rather above 2 degrees； and I should have expected that
the mould； from being washed down during heavy rain； would have
been thicker in the lower than in the upper part； but this was not
the case in two out of the three trenches here dug。
In many places； where streets ran beneath the surface； or where old
buildings stood； the mould was only 8 inches in thickness； and Dr。
Johnson was surprised that in ploughing the land； the ruins had
never been struck by the plough as far as he had heard。 He thinks
that when the land was first cultivated the old walls were perhaps
intentionally pulled down； and that hollow places were filled up。
This may have been the case； but if after the desertion of the city
the land was left for many centuries uncultivated； worms would have
brought up enough fine earth to have covered the ruins completely；
that is if they had subsided from having been undermined。 The
foundations of some of the walls； for instance those of the portion
still standing about 20 feet above the ground； and those of the
marketplace； lie at the extraordinary depth of 14 feet； but it is
highly improbable that the foundations were generally so deep。 The
mortar employed in the buildings must have been excellent； for it
is still in parts extremely hard。 Wherever walls of any height
have been exposed to view； they are； as Dr。 Johnson believes；
still perpendicular。 The walls with such deep foundations cannot
have been undermined by worms； and therefore cannot have subsided；
as appears to have occurred at Abinger and Silchester。 Hence it is
very difficult to account for their being now completely covered
with earth； but how much of this covering consists of vegetable
mould and how much of rubble I do not know。 The market…place； with
the foundations at a depth of 14 feet； was covered up； as Dr。
Johnson believes； by between 6 and 24 inches of earth。 The tops of
the broken…down walls of a caldarium or bath； 9 feet in depth； were
likewise covered up with nearly 2 feet of earth。 The summit of an
arch； leading into an ash…pit 7 feet in depth； was covered up with
not more than 8 inches of earth。 Whenever a building which has not
subsided is covered with earth； we must suppose； either that the
upper layers of stone have been at some time carried away by man；
or that earth has since been washed down during heavy rain； or
blown down during storms； from the adjoining land； and this would
be especially apt to occur where the land has long been cultivated。
In the above cases the adjoining land is somewhat higher than the
three specified sites； as far as I can judge by maps and from
information given me by Dr。 Johnson。 If； however； a great pile of
broken stones； mortar； plaster； timber and ashes fell over the
remains of any building； their disintegration in the course of
time； and the sifting action of worms； would ultimately conceal the
whole beneath fine earth。
Conclusion。 The cases given in this chapter show that worms have
played a considerable part in the burial and concealment of several
Roman and other old buildings in England； but no doubt the washing
down of soil from the neighbouring higher lands； and the deposition
of dust； have together aided largely in the work of concealment。
Dust would be apt to accumulate wherever old broken…down walls
projected a little above the then existing surface and thus
afforded some shelter。 The floors of the old rooms； halls and
passages have generally sunk； partly from the settling of the
ground； but chiefly from having been undermined by worms； and the
sinking has commonly been greater in the middle than near the
walls。 The walls themselves； whenever their foundations do not lie
at a great depth； have been penetrated and undermined by worms； and
have consequently subsided。 The unequal subsidence thus cau
