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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 caused；
probably explains the great cracks which may be seen in many
ancient walls； as well as their inclination from the perpendicular。
CHAPTER VTHE ACTION OF WORMS IN THE DENUDATION OF THE LAND。
Evidence of the amount of denudation which the land has undergone
Sub…aerial denudationThe deposition of dustVegetable mould； its
dark colour and fine texture largely due to the action of worms
The disintegration of rocks by the humus…acids Similar acids
apparently generated within the bodies of wormsThe action of
these acids facilitated by the continued movement of the particles
of earthA thick bed of mould checks the disintegration of the
underlying soil and rocks。 Particles of stone worn or triturated
in the gizzards of wormsSwallowed stones serve as mill…stones
The levigated state of the castingsFragments of brick in the
castings over ancient buildings well rounded。 The triturating
power of worms not quite insignificant under a geological point of
view。
No one doubts that our world at one time consisted of crystalline
rocks； and that it is to their disintegration through the action of
air； water； changes of temperature； rivers； waves of the sea；
earthquakes and volcanic outbursts； that we owe our sedimentary
formations。 These after being consolidated and sometimes
recrystallized； have often been again disintegrated。 Denudation
means the removal of such disintegrated matter to a lower level。
Of the many striking results due to the modern progress of geology
there are hardly any more striking than those which relate to
denudation。 It was long ago seen that there must have been an
immense amount of denudation； but until the successive formations
were carefully mapped and measured； no one fully realised how great
was the amount。 One of the first and most remarkable memoirs ever
published on this subject was that by Ramsay； ｛57｝ who in 1846
showed that in Wales from 9000 to 11；000 feet in thickness of solid
rock had been stripped off large tracks of country。 Perhaps the
plainest evidence of great denudation is afforded by faults or
cracks； which extend for many miles across certain districts； with
the strata on one side raised even ten thousand feet above the
corresponding strata on the opposite side； and yet there is not a
vestige of this gigantic displacement visible on the surface of the
land。 A huge pile of rock has been planed away on one side and not
a remnant left。
Until the last twenty or thirty years； most geologists thought that
the waves of the sea were the chief agents in the work of
denudation； but we may now feel sure that air and rain； aided by
streams and rivers； are much more powerful agents；that is if we
consider the whole area of the land。 The long lines of escarpment
which stretch across several parts of England were formerly
considered to be undoubtedly ancient coast…lines； but we now know
that they stand up above the general surface merely from resisting
air； rain and frost better than the adjoining formations。 It has
rar