worms　were　scanty；　and　the　mould　would　then　have　accumulated
  slowly。　　The　average　annual　increase　of　thickness　for　the　whole
  period　is　0。19　of　an　inch。
  Two　other　cases　are　worth　recording。　　In　the　spring　of　1835；　a
  field；　which　had　long　existed　as　poor　pasture　and　was　so　swampy
  that　it　trembled　slightly　when　stamped　on；　was　thickly　covered　with
  red　sand　so　that　the　whole　surface　appeared　at　first　bright　red。
  When　holes　were　dug　in　this　field　after　an　interval　of　about　2。5
  years；　the　sand　formed　a　layer　at　a　depth　of　0。75　in。　beneath　the
  surface。　　In　1842　（i。e。；　7　years　after　the　sand　had　been　laid　on）
  fresh　holes　were　dug；　and　now　the　red　sand　formed　a　distinct　layer；
  2　inches　beneath　the　surface；　or　1。5　inch　beneath　the　turf；　so　that
  on　an　average；　0。21　inch　of　mould　had　been　annually　brought　to　the
  surface。　　Immediately　beneath　the　layer　of　red　sand；　the　original
  substratum　of　black　sandy　peat　extended。
  A　grass　field；　likewise　not　far　from　Maer　Hall；　had　formerly　been
  thickly　covered　with　marl；　and　was　then　left　for　several　years　as
  pasture；　it　was　afterwards　ploughed。　　A　friend　had　three　trenches
  dug　in　this　field　28　years　after　the　application　of　the　marl；　｛42｝
  and　a　layer　of　the　marl　fragments　could　be　traced　at　a　depth；
  carefully　measured；　of　12　inches　in　some　parts；　and　of　14　inches　in
  other　parts。　　This　difference　in　depth　depended　on　the　layer　being
  horizontal；　whilst　the　surface　consisted　of　ridges　and　furrows　from
  the　field　having　been　ploughed。　　The　tenant　assured　me　that　it　had
  never　been　turned　up　to　a　greater　depth　than　from　6　to　8　inches；
  and　as　the　fragments　formed　an　unbroken　horizontal　layer　from　12　to
  14　inches　beneath　the　surface；　these　must　have　been　buried　by　the
  worms　whilst　the　land　was　in　pasture　before　it　was　ploughed；　for
  otherwise　they　would　have　been　indiscriminately　scattered　by　the
  plough　throughout　the　whole　thickness　of　the　soil。　　Four…and…a…half
  years　afterwards　I　had　three　holes　dug　in　this　field；　in　which
  potatoes　had　been　lately　planted；　and　the　layer　of　marl…fragments
  was　now　found　13　inches　beneath　the　bottoms　of　the　furrows；　and
  therefore　probably　15　inches　beneath　the　general　level　of　the
  field。　　It　should；　however；　be　observed　that　the　thickness　of　the
  blackish　sandy　soil；　which　had　been　thrown　up　by　the　worms　above
  the　marl…fragments　in　the　course　of　32。5　years；　would　have　measured
  less　than　15　inches；　if　the　field　had　always　remained　as　pasture；
  for　the　soil　would　in　this　case　have　been　much　more　compact。　　The
  fragments　of　marl　almost　rested　on　an　undisturbed　substratum　of
  white　sand　with　quartz　pebbles；　and　as　this　would　be　little
  attractive　to　worms；　the　mould　would　hereafter　be　very　slowly
  increased　by　their　action。
  We　will　now　give　some　cases　of　the　action　of　worms；　on　land
  differing　widely　from　the　dry　sandy　or　the　swampy　pastures　just
  described。　　The　chalk　formation　extends　all　round　my　house　in　Kent；
  and　its　surface；　from　having　been　exposed　during　an　immense　period
  to　the　dissolving　action　of　rain…water；　is　extremely　irregular；
  being　abruptly　festooned　and　penetrated　by　many　deep　well…like
  cavities。　｛43｝　　During　the　dissolution　of　the　chalk；　the　insoluble
  matter；　including　a　vast　number　of　unrolled　flints　of　all　sizes；
  has　been　left　on　the　surface　and　forms　a　bed　of　stiff　red　clay；
  full　of　flints；　and　generally　from　6　to　14　feet　in　thickness。　　Over
  the　red　clay；　wherever　the　land　has　long　remained　as　pasture；　there
  is　a　layer　a　few　inches　in　thickness；　of　dark…coloured　vegetable
  mould。
  A　quantity　of　broken　chalk　was　spread；　on　December　20；　1842；　over　a
  part　of　a　field　near　my　house；　which　had　existed　as　pasture
  certainly　for　30；　probably　for　twice　or　thrice　as　many　years。　　The
  chalk　was　laid　on　the　land　for　the　sake　of　observing　at　some　future
  period　to　what　depth　it　would　become　buried。　　At　the　end　of
  November；　1871；　that　is　after　an　interval　of　29　years；　a　trench　was
  dug　across　this　part　of　the　field；　and　a　line　of　white　nodules
  could　be　traced　on　both　sides　of　the　trench；　at　a　depth　of　7　inches
  from　the　surface。　　The　mould；　therefore；　（excluding　the　turf）　had
  here　been　thrown　up　at　an　average　rate　of　0。22　inch　per　year。
  Beneath　the　line　of　chalk　nodules　there　was　in　parts　hardly　any
  fine　earth　free　of　flints；　while　in　other　parts　there　was　a　layer；
  2。25　inches　in　thickness。　　In　this　latter　case　the　mould　was
  altogether　9。25　inches　thick；　and　in　one　such　spot　a　nodule　of
  chalk　and　a　smooth　flint　pebble；　both　of　which　must　have　been　left
  at　some　former　time　on　the　surface；　were　found　at　this　depth。　　At
  from　11　to　12　inches　beneath　the　surface；　the　undisturbed　reddish
  clay；　full　of　flints；　extended。　　The　appearance　of　the　above
  nodules　of　chalk　surprised　me；　much　at　first；　as　they　closely
  resembled　water…worn　pebbles；　whereas　the　freshly…broken　fragments
  had　been　angular。　　But　on　examining　the　nodules　with　a　lens；　they
  no　longer　appeared　water…worn；　for　their　surfaces　were　pitted
  through　unequal　corrosion；　and　minute；　sharp　points；　formed　of
  broken　fossil　shells；　projected　from　them。　　It　was　evident　that　the
  corners　of　the　original　fragments　of　chalk　had　been　wholly
  dissolved；　from　presenting　a　large　surface　to　the　carbonic　acid
  dissolved　in　the　rain…water　and　to　that　generated　in　soil
  containing　vegetable　matter；　as　well　as　to　the　humus…acids。　｛44｝
  The　projecting　corners　would　also；　relatively　to　the　other　parts；
  have　been　embraced　by　a　larger　number　of　living　rootlets；　and　these
  have　the　power　of　even　attacking　marble；　as　Sachs　has　shown。　　Thus；
  in　the　course　of　29　years；　buried　angular　fragments　of　chalk　had
  been　converted　into　well…rounded　nodules。
  Another　part　of　this　same　field　was　mossy；　and　as　it　was　thought
  that　sifted　coal…cinders　would　improve　the　pasture；　a　thick　layer
  was　spread　over　this　part　either　in　1842　or　1843；　and　another　layer
  some　years　afterwards。　　In　1871　a　trench　was　here　dug；　and　many
  cinders　lay　in　a　line　at　a　depth　of　7　inches　beneath　the　surface；
  with　another　line　at　a　depth　of　5。5　inches　parallel　to　the　one
  beneath。　　In　another　part　of　this　field；　which　had　formerly　existed
  as　a　separate　one；　and　which　it　was　believed　had　been　pasture…land
  for　more　than　a　century；　trenches　were　dug　to　see　how　thick　the
  vegetable　mould　was。　　By　chance　the　first　trench　was　made　at　a　spot
  where　at　some　former　period；　certainly　more　than　forty　years
  before；　a　large　hole　had　been　filled　up　with　coarse　red　clay；
  flints；　fragments　of　chalk；　and　gravel；　and　here　the　fine　vegetable
  mould　was　only　from　4。125　to　4。375　inches　in　thickness。　　In　another
  and　undisturbed　place；　the　mould　varied　much　in　thickness；　namely；
  from　6。5　to　8。5　inches；　beneath　which　a　few　small　fragments　of
  brick　were　found　in　one　place。　　From　these　several　cases；　it　would
  appear　that　during　the　last　29　years　mould　has　been　heaped　on　the
  surface　at　an　average　annual　rate　of　from　0。2　to　0。22　of　an　inch。
  But　in　this　district　when　a　ploughed　field　is　first　laid　down　in
  grass；　the　mould　accumulates　at　a　much　slower　rate。　　The　rate；
  also；　must　become　very　much　slower　after　a　bed　of　mould；　several
  inches　in　thickness；　has　been　formed；　for　the　worms　then　live
  chiefly　near　the　surface；　and　burrow　down　to　a　greater　depth　so　as
  to　bring　up　fresh　earth　from　below；　only　during　the　winter　when　the
  weather　is　very　cold　（at　which　time　worms　were　found　in　this　field
  at　a　depth　of　26　inches）　and　during　summer；　when　the　weather　is
  very　dry。
  A　field；　which　adjoins　the　one　just　described；　slopes　in　one　part
  rather　steeply　（viz。；　at　from　10　degrees　to　15　degrees）；　this　part
  was　last　ploughed　in　1841；　was　then　harrowed　and　left　to　become
  pasture…land。　　For　several　years　it　was　clothed　with　an　extremely
  scant　vegetation；　and　was　so　thickly　covered　with　small　and　large
  flints　（some　of　them　half　as　large　as　a　child's　head）　that　the
  field　was　always　called　by　my　sons　〃the　stony　field。〃　　When　they
  ran　down　the　slope　the　stones　clattered　together；　I　remember
  doubting　whether　I　should　live　to　see　these　larger　flints　covered
  with　vegetable　mould　and　turf。　　But　the　smaller　stones　disappeared
  before　many　years　had　elapsed；　as　did　every　one　of　the　larger　ones
  after　a　time；　so　that　after　thirty　years　（1871）　a　horse　could
  gallop　over　the　compact　turf　from　one　end　of　the　field　to　the
  other；　and　not　strike　a　single　stone　with　his　shoes。　　To　anyone　who
  remembered　the　appearance　of　the　field　in　1842；　the　transformation
  was　wonderful。　　This　was　certainly　the　work　of　the　worms；　for
  though　castings　were　not　frequent　for　several　years；　yet　some　were
  thrown　up　month　after　month；　and　these　gradually　increased　in
  numbers　as　the　pasture　improved。　　In　the　year　1871　a　trench　was　dug
  on　the　above　slope；　and　the　blades　of　grass　were　cut　off　close　to
  the　roots；　so　that　the　thickness　of　the　turf　and　of　the　vegetable
  mould　could　be　measured　accurately。　　The　turf　was　rather　less　than
  half　an　inch；　and　the　mould；　which　did　not　contain　any　stones；　2。5
  inches　in　thickness。　　Beneath　this　lay　coarse　clayey　earth　full　of
  flints；　like　that　in　any　of　the　neighbouring　ploughed　fields。　　This