the formation of vegetable mould-第43章
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333。
｛36｝ 'Archives de Zoolog。 exper。' tom。 iii。 1874； p。 405。
｛37｝ I state this on the authority of Semper； 'Reisen im Archipel
der Philippinen；' Th。 ii。 1877； p。 30。
｛38｝ Dr。 King gave me some worms collected near Nice； which； as he
believes； had constructed these castings。 They were sent to M。
Perrier； who with great kindness examined and named them for me：
they consisted of Perichaeta affinis； a native of Cochin China and
of the Philippines； P。 Luzonica； a native of Luzon in the
Philippines； and P。 Houlleti； which lives near Calcutta。 M。
Perrier informs me that species of Perichaeta have been naturalized
in the gardens near Montpellier and in Algiers。 Before I had any
reason to suspect that the tower…like castings from Nice had been
formed by worms not endemic in the country； I was greatly surprised
to see how closely they resembled castings sent to me from near
Calcutta； where it is known that species of Perichaeta abound。
｛39｝ 'Zeitschrift fur wissenschaft。 Zoolog。' B。 xxviii。 1877； p。
364。
｛40｝ 'Zeitschrift fur wissenschaft。 Zoolog。' B。 xxviii。 1877； p。
356。
｛41｝ Perrier； 'Archives de Zoolog。 exper。' tom。 3； p。 378； 1874。
｛42｝ This case is given in a postscript to my paper in the
'Transact。 Geolog。 Soc。' （Vol。 v。 p。 505）； and contains a serious
error； as in the account received I mistook the figure 30 for 80。
The tenant； moreover； formerly said that he had marled the field
thirty years before； but was now positive that this was done in
1809； that is twenty…eight years before the first examination of
the field by my friend。 The error； as far as the figure 80 is
concerned； was corrected in an article by me； in the 'Gardeners'
Chronicle；' 1844； p。 218。
｛43｝ These pits or pipes are still in process of formation。
During the last forty years I have seen or heard of five cases； in
which a circular space； several feet in diameter； suddenly fell in；
leaving on the field an open hole with perpendicular sides； some
feet in depth。 This occurred in one of my own fields； whilst it
was being rolled； and the hinder quarters of the shaft horse fell
in； two or three cart…loads of rubbish were required to fill up the
hole。 The subsidence occurred where there was a broad depression；
as if the surface had fallen in at several former periods。 I heard
of a hole which must have been suddenly formed at the bottom of a
small shallow pool； where sheep had been washed during many years；
and into which a man thus occupied fell to his great terror。 The
rain…water over this whole district sinks perpendicularly into the
ground； but the chalk is more porous in certain places than in
others。 Thus the drainage from the overlying clay is directed to
certain points； where a greater amount of calcareous matter is
dissolved than elsewhere。 Even narrow open channels are sometimes
formed in the solid chalk。 As the chalk is slowly dissolved over
the whole country； but more in some parts than in others； the
undissolved residuethat is the overlying mass of red clay with
flints；likewise sinks slowly down； and tends to fill up the pipes
or cavities。 But the upper part of the red clay holds together；
aided probably by the roots of plants； for a longer time than the
lower parts； and thus forms a roof； which sooner or later falls in；
as in the above mentioned five cases。 The downward movement of the
clay may be compared with that of a glacier； but is incomparably
slower； and this movement accounts for a singular fact； namely；
that the much elongated flints which are embedded in the chalk in a
nearly horizontal position； are commonly found standing nearly or
quite upright in the red clay。 This fact is so common that the
workmen assured me that this was their natural position。 I roughly
measured one which stood vertically； and it was of the same length
and of the same relative thickness as one of my arms。 These
elongated flints must get placed in their upright position； on the
same principle that a trunk of a tree left on a glacier assumes a
position parallel to the line of motion。 The flints in the clay
which form almost half its bulk； are very often broken； though not
rolled or abraded； and this may he accounted for by their mutual
pressure； whilst the whole mass is subsiding。 I may add that the
chalk here appears to have been originally covered in parts by a
thin bed of fine sand with some perfectly rounded flint pebbles；
probably of Tertiary age； for such sand often partly fills up the
deeper pits or cavities in the chalk。
｛44｝ S。 W。 Johnson； 'How Crops Feed；' 1870； p。 139。
｛45｝ 'Nature；' November 1877； p。 28。
｛46｝ 'Proc。 Phil。 Soc。' of Manchester； 1877； p。 247。
｛47｝ 'Trans。 of the New Zealand Institute；' vol。 xii。； 1880； p。
152。
｛48｝ Mr。 Lindsay Carnagie； in a letter （June 1838） to Sir C。
Lyell； remarks that Scotch farmers are afraid of putting lime on
ploughed land until just before it is laid down for pasture； from a
belief that it has some tendency to sink。 He adds： 〃Some years
since； in autumn； I laid lime on an oat…stubble and ploughed it
down； thus bringing it into immediate contact with the dead
vegetable matter； and securing its thorough mixture through the
means of all the subsequent operations of fallow。 In consequence
of the above prejudice； I was considered to have committed a great
fault； but the result was eminently successful； and the practice
was partially followed。 By means of Mr。 Darwin's observations； I
think the prejudice will be removed。〃
｛49｝ This conclusion； which； as we shall immediately see； is fully
justified； is of some little importance； as the so…called bench…
stones； which surveyors fix in the ground as a record of their
levels； may in time become false standards。 My son Horace intends
at some future period to ascertain how far this has occurred。
｛50｝ Mr。 R。 Mallet remarks （'Quarterly Journal of Geolog。 Soc。'
vol。 xxxiii。； 1877； p。 745） that 〃the extent to which the ground
beneath the foundations of ponderous architectural structures； such
as cathedral towers； has been known to become compressed； is as
remarkable as it is instructive and curious。 The amount of
depression in some cases may be measured by feet。〃 He instances
the Tower of Pisa； but adds that it was founded on 〃dense clay。〃
｛51｝ 'Zeitschrift fur wissensch。 Zoolog。' Bd。 xxviii。； 1877； p。
360。
｛52｝ See Mr。 Dancer's paper in 'Proc。 Phil。 Soc。 of Manchester；'
1877； p。 248。
｛53｝ 'Lecons de Geologie pratique；' 1845； p。 142。
｛54｝ A short account of this discovery was published in 'The
Times' of January 2； 1878； and a fuller account in 'The Builder；'
January 5； 1878。
｛55｝ Several accounts of these ruins have been published； the best
is by Mr。 James Farrer in 'Proc。 Soc。 of Antiquaries of Scotland；'
vol。 vi。； Part II。； 1867； p。 278。 Also J。 W。 Grover； 'Journal of
the British Arch。 Assoc。' June 1866。 Professor Buckman has
likewise published a pamphlet； 'Notes on the Roman Villa at
Chedworth；' 2nd edit。 1873 Cirencester。
｛56｝ These details are taken from the 'Penny Cyclopaedia；' article
Hampshire。
｛57｝ 〃On the denudation of South Wales；〃 &c。； 'Memoirs of the
Geological Survey of Great Britain；' vol。 1。； p。 297； 1846。
｛58｝ 'Geological Magazine；' October and November； 1867； vol。 iv。
pp。 447 and 483。 Copious references on the subject are given in
this remarkable memoir。
｛59｝ A。 Tylor 〃On changes of the sea…level；〃 &c。； ' Philosophical
Mag。' （Ser。 4th） vol。 v。； 1853； p。 258。 Archibald Geikie；
Transactions Geolog。 Soc。 of Glasgow； vol。 iii。； p。 153 （read
March； 1868）。 Croll 〃On Geological Time；〃 'Philosophical Mag。；'
May； August； and November； 1868。 See also Croll； 'Climate and
Time；' 1875； Chap。 XX。 For some recent information on the amount
of sediment brought down by rivers； see 'Nature；' Sept。 23rd；
1880。 Mr。 T。 Mellard Reade has published some interesting articles
on the astonishing amount of matter brought down in solution by
rivers。 See Address； Geolog。 Soc。； Liverpool； 1876…77。
｛60｝ 〃An account of the fine dust which often falls on Vess
