before　this　could　have　occurred；　some　earth　would　have　been　washed
  down　by　heavy　rain　from　the　castings　on　the　raised　border　of　turf
  over　the　upper　surface　of　the　stone。
  The　second　stone　was　larger　that　the　one　just　described；　viz。；　67
  inches　in　length；　39　in　breadth；　and　15　in　thickness。　　The　lower
  surface　was　nearly　flat；　so　that　the　worms　must　soon　have　been
  compelled　to　eject　their　castings　beyond　its　circumference。　　The
  stone　as　a　whole　had　sunk　about　2　inches　into　the　ground。　　At　this
  rate　it　would　have　required　262　years　for　its　upper　surface　to　have
  sunk　to　the　general　level　of　the　field。　　The　upwardly　sloping；
  turf…covered　border　round　the　stone　was　broader　than　in　the　last
  case；　viz。；　from　14　to　16　inches；　and　why　this　should　be　so；　I
  could　see　no　reason。　　In　most　parts　this　border　was　not　so　high　as
  in　the　last　case；　viz。；　from　2　to　2。5　inches；　but　in　one　place　it
  was　as　much　as　5。5。　　Its　average　height　close　to　the　stone　was
  probably　about　3　inches；　and　it　thinned　out　to　nothing。　　If　so；　a
  layer　of　fine　earth；　15　inches　in　breadth　and　1。5　inch　in　average
  thickness；　of　sufficient　length　to　surround　the　whole　of　the　much
  elongated　slab；　must　have　been　brought　up　by　the　worms　in　chief
  part　from　beneath　the　stone　in　the　course　of　35　years。　　This　amount
  would　be　amply　sufficient　to　account　for　its　having　sunk　about　2
  inches　into　the　ground；　more　especially　if　we　bear　in　mind　that　a
  good　deal　of　the　finest　earth　would　have　been　washed　by　heavy　rain
  from　the　castings　ejected　on　the　sloping　border　down　to　the　level
  of　the　field。　　Some　fresh　castings　were　seen　close　to　the　stone。
  Nevertheless；　on　digging　a　large　hole　to　a　depth　of　18　inches　where
  the　stone　had　lain；　only　two　worms　and　a　few　burrows　were　seen；
  although　the　soil　was　damp　and　seemed　favourable　for　worms。　　There
  were　some　large　colonies　of　ants　beneath　the　stone；　and　possibly
  since　their　establishment　the　worms　had　decreased　in　number。
  The　third　stone　was　only　about　half　as　large　as　the　others；　and　two
  strong　boys　could　together　have　rolled　it　over。　　I　have　no　doubt
  that　it　had　been　rolled　over　at　a　moderately　recent　time；　for　it
  now　lay　at　some　distance　from　the　two　other　stones　at　the　bottom　of
  a　little　adjoining　slope。　　It　rested　also　on　fine　earth；　instead　of
  partly　on　brick…rubbish。　　In　agreement　with　this　conclusion；　the
  raised　surrounding　border　of　turf　was　only　1　inch　high　in　some
  parts；　and　2　inches　in　other　parts。　　There　were　no　colonies　of　ants
  beneath　this　stone；　and　on　digging　a　hole　where　it　had　lain；
  several　burrows　and　worms　were　found。
  At　Stonehenge；　some　of　the　outer　Druidical　stones　are　now
  prostrate；　having　fallen　at　a　remote　but　unknown　period；　and　these
  have　become　buried　to　a　moderate　depth　in　the　ground。　　They　are
  surrounded　by　sloping　borders　of　turf；　on　which　recent　castings
  were　seen。　　Close　to　one　of　these　fallen　stones；　which　was　17　ft
  long；　6　ft。　broad；　and　28。5　inches　thick；　a　hole　was　dug；　and　here
  the　vegetable　mould　was　at　least　9。5　inches　in　thickness。　　At　this
  depth　a　flint　was　found；　and　a　little　higher　up　on　one　side　of　the
  hole　a　fragment　of　glass。　　The　base　of　the　stone　lay　about　9。5
  inches　beneath　the　level　of　the　surrounding　ground；　and　its　upper
  surface　19　inches　above　the　ground。
  A　hole　was　also　dug　close　to　a　second　huge　stone；　which　in　falling
  had　broken　into　two　pieces；　and　this　must　have　happened　long　ago；
  judging　from　the　weathered　aspect　of　the　fractured　ends。　　The　base
  was　buried　to　a　depth　of　10　inches；　as　was　ascertained　by　driving
  an　iron　skewer　horizontally　into　the　ground　beneath　it。　　The
  vegetable　mould　forming　the　turf…covered　sloping　border　round　the
  stone；　on　which　many　castings　had　recently　been　ejected；　was　10
  inches　in　thickness；　and　most　of　this　mould　must　have　been　brought
  up　by　worms　from　beneath　its　base。　　At　a　distance　of　8　yards　from
  the　stone；　the　mould　was　only　5。5　inches　in　thickness　（with　a　piece
  of　tobacco　pipe　at　a　depth　of　4　inches）；　and　this　rested　on　broken
  flint　and　chalk　which　could　not　have　easily　yielded　to　the　pressure
  or　weight　of　the　stone。
  A　straight　rod　was　fixed　horizontally　（by　the　aid　of　a　spirit…
  level）　across　a　third　fallen　stone；　which　was　7　feet　9　inches　long；
  and　the　contour　of　the　projecting　parts　and　of　the　adjoining
  ground；　which　was　not　quite　level；　was　thus　ascertained；　as　shown
  in　the　accompanying　diagram　（Fig。　7）　on　a　scale　of　0。5　inch　to　a
  foot。　　The　turf…covered　border　sloped　up　to　the　stone　on　one　side
  to　a　height　of　4　inches；　and　on　the　opposite　side　to　only　2。5
  inches　above　the　general　level。　　A　hole　was　dug　on　the　eastern
  side；　and　the　base　of　the　stone　was　here　found　to　lie　at　a　depth　of
  4　inches　beneath　the　general　level　of　the　ground；　and　of　8　inches
  beneath　the　top　of　the　sloping　turf…covered　border。
  Sufficient　evidence　has　now　been　given　showing　that　small　objects
  left　on　the　surface　of　the　land　where　worms　abound　soon　get　buried；
  and　that　large　stones　sink　slowly　downwards　through　the　same　means。
  Every　step　of　the　process　could　be　followed；　from　the　accidental
  deposition　of　a　single　casting　on　a　small　object　lying　loose　on　the
  surface；　to　its　being　entangled　amidst　the　matted　roots　of　the
  turf；　and　lastly　to　its　being　embedded　in　the　mould　at　various
  depths　beneath　the　surface。　　When　the　same　field　was　re…examined
  after　the　interval　of　a　few　years；　such　objects　were　found　at　a
  greater　depth　than　before。　　The　straightness　and　regularity　of　the
  lines　formed　by　the　imbedded　objects；　and　their　parallelism　with
  the　surface　of　the　land；　are　the　most　striking　features　of　the
  case；　for　this　parallelism　shows　how　equably　the　worms　must　have
  worked；　the　result　being；　however；　partly　the　effect　of　the　washing
  down　of　the　fresh　castings　by　rain。　　The　specific　gravity　of　the
  objects　does　not　affect　their　rate　of　sinking；　as　could　be　seen　by
  porous　cinders；　burnt　marl；　chalk　and　quartz　pebbles；　having　all
  sunk　to　the　same　depth　within　the　same　time。　　Considering　the
  nature　of　the　substratum；　which　at　Leith　Hill　Place　was　sandy　soil
  including　many　bits　of　rock；　and　at　Stonehenge；　chalk…rubble　with
  broken　flints；　considering；　also；　the　presence　of　the　turf…covered
  sloping　border　of　mould　round　the　great　fragments　of　stone　at　both
  these　places；　their　sinking　does　not　appear　to　have　been　sensibly
  aided　by　their　weight；　though　this　was　considerable。　｛50｝
  On　the　number　of　worms　which　live　within　a　given　space。We　will
  now　show；　firstly；　what　a　vast　number　of　worms　live　unseen　by　us
  beneath　our　feet；　and；　secondly；　the　actual　weight　of　the　earth
  which　they　bring　up　to　the　surface　within　a　given　space　and　within
  a　given　time。　　Hensen；　who　has　published　so　full　and　interesting　an
  account　of　the　habits　of　worms；　｛51｝　calculates；　from　the　number
  which　he　found　in　a　measured　space；　that　there　must　exist　133；000
  living　worms　in　a　hectare　of　land；　or　53；767　in　an　acre。　　This
  latter　number　of　worms　would　weigh　356　pounds；　taking　Hensen's
  standard　of　the　weight　of　a　single　worm；　namely；　three　grams。　　It
  should；　however；　be　noted　that　this　calculation　is　founded　on　the
  numbers　found　in　a　garden；　and　Hensen　believes　that　worms　are　here
  twice　as　numerous　as　in　corn…fields。　　The　above　result；　astonishing
  though　it　be；　seems　to　me　credible；　judging　from　the　number　of
  worms　which　I　have　sometimes　seen；　and　from　the　number　daily
  destroyed　by　birds　without　the　species　being　exterminated。　　Some
  barrels　of　bad　ale　were　left　on　Mr。　Miller's　land；　｛52｝　in　the　hope
  of　making　vinegar；　but　the　vinegar　proved　bad；　and　the　barrels　were
  upset。　　It　should　be　premised　that　acetic　acid　is　so　deadly　a
  poison　to　worms　that　Perrier　found　that　a　glass　rod　dipped　into
  this　acid　and　then　into　a　considerable　body　of　water　in　which　worms
  were　immersed；　invariably　killed　them　quickly。　　On　the　morning
  after　the　barrels　had　been　upset；　〃the　heaps　of　worms　which　lay
  dead　on　the　ground　were　so　amazing；　that　if　Mr。　Miller　had　not　seen
  them；　he　could　not　have　thought　it　possible　for　such　numbers　to
  have　existed　in　the　space。〃　　As　further　evidence　of　the　large
  number　of　worms　which　live　in　the　ground；　Hensen　states　that　he
  found　in　a　garden　sixty…four　open　burrows　in　a　space　of　14。5　square
  feet；　that　is；　nine　in　2　square　feet。　　But　the　burrows　are
  sometimes　much　more　numerous；　for　when　digging　in　a　grass…field
  near　Maer　Hall；　I　found　a　cake　of　dry　earth；　as　large　as　my　two
  open　hands；　which　was　penetrated　by　seven　burrows；　as　large　as
  goose…quills。
  Weight　of　the　earth　ejected　from　a　single　burrow；　and　from　all　the
  burrows　within　a　given　space。With　respect　to　the　weight　of　the
  earth　daily　ejected　by　worms；　Hensen　found　that　it　amounted；　in　the
  case　of　some　worms　which　he　kept　in　confinement；　and　which　he
  appears　to　have　fed　with　leaves；　to　only　0。5　gram；　or　less　than　8
  grains　per　diem。　　But　a　very　much　larger　amount　must　be　ejected　by
  worms　in　their　natural　state；　at　the　periods　when　they　consume
  earth　as　food　instead　of　leaves；　and　when　they　are　making　deep
  burrows。　　This　is　rendered　almost　certain　by　the　following　weights
  of　the　castings　t