knowledge　out　to　its　ultimate　results；　to　have　a　truer；　and
  therefore　a　better；　conception　of　this　wonderful　universe；　and　of
  man's　relation　to　it；　than　the　most　learned　student　who　is　deep…
  read　in　the　records　of　humanity　and　ignorant　of　those　of　Nature。
  The　language　of　the　chalk　is　not　hard　to　learn；　not　nearly　so　hard
  as　Latin；　if　you　only　want　to　get　at　the　broad　features　of　the
  story　it　has　to　tell；　and　I　propose　that　we　now　set　to　work　to
  spell　that　story　out　together。
  We　all　know　that　if　we　〃burn〃　chalk　the　result　is　quicklime。
  Chalk；　in　fact；　is　a　compound　of　carbonic　acid　gas；　and　lime；　and
  when　you　make　it　very　hot　the　carbonic　acid　flies　away　and　the　lime
  is　left。
  By　this　method　of　procedure　we　see　the　lime；　but　we　do　not　see　the
  carbonic　acid。　　If；　on　the　other　hand；　you　were　to　powder　a　little
  chalk　and　drop　it　into　a　good　deal　of　strong　vinegar；　there　would
  be　a　great　bubbling　and　fizzing；　and；　finally；　a　clear　liquid；　in
  which　no　sign　of　chalk　would　appear。　　Here　you　see　the　carbonic
  acid　in　the　bubbles；　the　lime；　dissolved　in　the　vinegar；　vanishes
  from　sight。　　There　are　a　great　many　other　ways　of　showing　that
  chalk　is　essentially　nothing　but　carbonic　acid　and　quicklime。
  Chemists　enunciate　the　result　of　all　the　experiments　which　prove
  this；　by　stating　that　chalk　is　almost　wholly　composed　of　〃carbonate
  of　lime。〃
  It　is　desirable　for　us　to　start　from　the　knowledge　of　this　fact；
  though　it　may　not　seem　to　help　us　very　far　towards　what　we　seek。
  For　carbonate　of　lime　is　a　widely　spread　substance；　and　is　met　with
  under　very　various　conditions。　　All　sorts　of　limestones　are
  composed　of　more　or　less　pure　carbonate　of　lime。　　The　crust　which
  is　often　deposited　by　waters　which　have　drained　through　limestone
  rocks；　in　the　form　of　what　are　called　stalagmites　and　stalactites；
  is　carbonate　of　lime。　　Or；　to　take　a　more　familiar　example；　the　fur
  on　the　inside　of　a　tea…kettle　is　carbonate　of　lime；　and；　for
  anything　chemistry　tells　us　to　the　contrary；　the　chalk　might　be　a
  kind　of　gigantic　fur　upon　the　bottom　of　the　earth…kettle；　which　is
  kept　pretty　hot　below。
  Let　us　try　another　method　of　making　the　chalk　tell　us　its　own
  history。　　To　the　unassisted　eye　chalk　looks　simply　like　a　very
  loose　and　open　kind　of　stone。　　But　it　is　possible　to　grind　a　slice
  of　chalk　down　so　thin　that　you　can　see　through　ituntil　it　is　thin
  enough；　in　fact；　to　be　examined　with　any　magnifying　power　that　may
  be　thought　desirable。　　A　thin　slice　of　the　fur　of　a　kettle　might　be
  made　in　the　same　way。　　If　it　were　examined　microscopically；　it
  would　show　itself　to　be　a　more　or　less　distinctly　laminated　mineral
  substance　and　nothing　more。
  But　the　slice　of　chalk　presents　a　totally　different　appearance　when
  placed　under　the　microscope。　　The　general　mass　of　it　is　made　up　of
  very　minute　granules；　but；　imbedded　in　this　matrix；　are　innumerable
  bodies；　some　smaller　and　some　larger；　but；　on　a　rough　average；　not
  more　than　a　hundredth　of　an　inch　in　diameter；　having　a　well…defined
  shape　and　structure。　　A　cubic　inch　of　some　specimens　of　chalk　may
  contain　hundreds　of　thousands　of　these　bodies；　compacted　together
  with　incalculable　millions　of　the　granules。
  The　examination　of　a　transparent　slice　gives　a　good　notion　of　the
  manner　in　which　the　components　of　the　chalk　are　arranged；　and　of
  their　relative　proportions。　　But；　by　rubbing　up　some　chalk　with　a
  brush　in　water　and　then　pouring　off　the　milky　fluid；　so　as　to
  obtain　sediments　of　different　degrees　of　fineness；　the　granules　and
  the　minute　rounded　bodies　may　be　pretty　well　separated　from　one
  another；　and　submitted　to　microscopic　examination；　either　as　opaque
  or　as　transparent　objects。　　By　combining　the　views　obtained　in
  these　various　methods；　each　of　the　rounded　bodies　may　be　proved　to
  be　a　beautifully　constructed　calcareous　fabric；　made　up　of　a　number
  of　chambers；　communicating　freely　with　one　another。　　The　chambered
  bodies　are　of　various　forms。　　One　of　the　commonest　is　something
  like　a　badly　grown　raspberry；　being　formed　of　a　number　of　nearly
  globular　chambers　of　different　sizes　congregated　together。　　It　is
  called　Globigerina；　and　some　specimens　of　chalk　consist　of　little
  else　than　Globigerina　and　granules。
  Let　us　fix　our　attention　upon　the　Globigerina。　　It　is　the　spoor　of
  the　game　we　are　tracking。　　If　we　can　learn　what　it　is　and　what　are
  the　conditions　of　its　existence；　we　shall　see　our　way　to　the　origin
  and　past　history　of　the　chalk。
  A　suggestion　which　may　naturally　enough　present　itself　is；　that
  these　curious　bodies　are　the　result　of　some　process　of　aggregation
  which　has　taken　place　in　the　carbonate　of　lime；　that；　just　as　in
  winter；　the　rime　on　our　windows　simulates　the　most　delicate　and
  elegantly　arborescent　foliageproving　that　the　mere　mineral　water
  may；　under　certain　conditions；　assume　the　outward　form　of　organic
  bodiesso　this　mineral　substance；　carbonate　of　lime；　hidden　away
  in　the　bowels　of　the　earth；　has　taken　the　shape　of　these　chambered
  bodies。　　I　am　not　raising　a　merely　fanciful　and　unreal　objection。
  Very　learned　men；　in　former　days；　have　even　entertained　the　notion
  that　all　the　formed　things　found　in　rocks　are　of　this　nature；　and
  if　no　such　conception　is　at　present　held　to　be　admissible；　it　is
  because　long　and　varied　experience　has　now　shown　that　mineral
  matter　never　does　assume　the　form　and　structure　we　find　in　fossils。
  If　any　one　were　to　try　to　persuade　you　that　an　oyster…shell　（which
  is　also　chiefly　composed　of　carbonate　of　lime）　had　crystallized　out
  of　sea…water；　I　suppose　you　would　laugh　at　the　absurdity。　　Your
  laughter　would　be　justified　by　the　fact　that　all　experience　tends
  to　show　that　oyster…shells　are　formed　by　the　agency　of　oysters；　and
  in　no　other　way。　　And　if　there　were　no　better　reasons；　we　should　be
  justified；　on　like　grounds；　in　believing　that　Globigerina　is　not
  the　product　of　anything　but　vital　activity。
  Happily；　however；　better　evidence　in　proof　of　the　organic　nature　of
  the　Globigerinae　than　that　of　analogy　is　forthcoming。　　It　so
  happens　that　calcareous　skeletons；　exactly　similar　to　the
  Globigerinae　of　the　chalk；　are　being　formed；　at　the　present　moment；
  by　minute　living　creatures；　which　flourish　in　multitudes；　literally
  more　numerous　than　the　sands　of　the　sea…shore；　over　a　large　extent
  of　that　part　of　the　earth's　surface　which　is　covered　by　the　ocean。
  The　history　of　the　discovery　of　these　living　Globigerinae；　and　of
  the　part　which　they　play　in　rock　building；　is　singular　enough。　　It
  is　a　discovery　which；　like　others　of　no　less　scientific　importance；
  has　arisen；　incidentally；　out　of　work　devoted　to　very　different　and
  exceedingly　practical　interests。
  When　men　first　took　to　the　sea；　they　speedily　learned　to　look　out
  for　shoals　and　rocks；　and　the　more　the　burthen　of　their　ships
  increased；　the　more　imperatively　necessary　it　became　for　sailors　to
  ascertain　with　precision　the　depths　of　the　waters　they　traversed。
  Out　of　this　necessity　grew　the　use　of　the　lead　and　sounding　line；
  and；　ultimately；　marine…surveying；　which　is　the　recording　of　the
  form　of　coasts　and　of　the　depth　of　the　sea；　as　ascertained　by　the
  sounding…lead；　upon　charts。
  At　the　same　time；　it　became　desirable　to　ascertain　and　to　indicate
  the　nature　of　the　sea…bottom；　since　this　circumstance　greatly
  affects　its　goodness　as　holding　ground　for　anchors。　　Some　ingenious
  tar；　whose　name　deserves　a　better　fate　than　the　oblivion　into　which
  it　has　fallen；　attained　this　object　by　〃arming〃　the　bottom　of　the
  lead　with　a　lump　of　grease；　to　which　more　or　less　of　the　sand　or
  mud；　or　broken　shells；　as　the　case　might　be；　adhered；　and　was
  brought　to　the　surface。　　But；　however　well　adapted　such　an
  apparatus　might　be　for　rough　nautical　purposes；　scientific　accuracy
  could　not　be　expected　from　the　armed　lead；　and　to　remedy　its
  defects　（especially　when　applied　to　sounding　in　great　depths）
  Lieut。　Brooke；＇61＇　of　the　American　Navy；　some　years　ago　invented
  a　most　ingenious　machine；　by　which　a　considerable　portion　of　the
  superficial　layer　of　the　sea…bottom　can　be　scooped　out　and　brought
  up　from　any　depth　to　which　the　lead　descends。
  In　1853；　Lieut。　Brooke　obtained　mud　from　the　bottom　of　the　North
  Atlantic；　between　Newfoundland　and　the　Azores；　at　a　depth　of　more
  than　ten　thousand　feet；　or　two　miles；　by　the　help　of　this　sounding
  apparatus。　　The　specimens　were　sent　for　examination　to　Ehrenberg　＇62＇
  of　Berlin；　and　to　Bailey　of　West　Point；＇63＇　and　those　able
  microscopists　found　that　this　deep…sea　mud　was　almost　entirely
  composed　of　the　skeletons　of　living　organismsthe　greater　proportion
  of　these　being　just　like　the　Globigerinae　already　known　to　occur
  in　the　chalk。
  Thus　far；　the　work　had　been　carried　on　simply　in　the　interests　of
  science；　but　Lieut。　Brooke's　method　of　sounding　acquired　a　high
  commercial　value；　when　the　enterprise　of　laying　down　the　telegraph…
  cable　＇64＇　between　this　country　and　the　United　States　was　under