I　must　ask　you　to　believe　that　there　is　no　less　conclusive　proof
  that　a　still　more　prolonged　succession　of　similar　changes　occurred；
  before　the　chalk　was　deposited。　　Nor　have　we　any　reason　to　think
  that　the　first　term　in　the　series　of　these　changes　is　known。　　The
  oldest　sea…beds　preserved　to　us　are　sands；　and　mud；　and　pebbles；
  the　wear　and　tear　of　rocks　which　were　formed　in　still　older　oceans。
  But；　great　as　is　the　magnitude　of　these　physical　changes　of　the
  world；　they　have　been　accompanied　by　a　no　less　striking　series　of
  modifications　in　its　living　inhabitants。
  All　the　great　classes　of　animals；　beasts　of　the　field；　fowls　of　the
  air；　creeping　things；　and　things　which　dwell　in　the　waters；
  flourished　upon　the　globe　long　ages　before　the　chalk　was　deposited。
  Very　few；　however；　if　any；　of　these　ancient　forms　of　animal　life
  were　identical　with　those　which　now　live。　　Certainly　not　one　of　the
  higher　animals　was　of　the　same　species　as　any　of　those　now　in
  existence。　　The　beasts　of　the　field；　in　the　days　before　the　chalk；
  were　not　our　beasts　of　the　field；　nor　the　fowls　of　the　air　such　as
  those　which　the　eye　of　men　has　seen　flying；　unless　his　antiquity
  dates　infinitely　further　back　than　we　at　present　surmise。　　If　we
  could　be　carried　back　into　those　times；　we　should　be　as　one
  suddenly　set　down　in　Australia　before　it　was　colonized。　　We　should
  see　mammals；　birds；　reptiles；　fishes；　insects；　snails；　and　the
  like；　clearly　recognisable　as　such；　and　yet　not　one　of　them　would
  be　just　the　same　as　those　with　which　we　are　familiar；　and　many
  would　be　extremely　different。
  From　that　time　to　the　present；　the　population　of　the　world　has
  undergone　slow　and　gradual；　but　incessant　changes。　　There　has　been
  no　grand　catastropheno　destroyer　has　swept　away　the　forms　of　life
  of　one　period；　and　replaced　them　by　a　totally　new　creation；　but　one
  species　has　vanished　and　another　has　taken　its　place；　creatures　of
  one　type　of　structure　have　diminished；　those　of　another　have
  increased；　as　time　has　passed　on。　　And　thus；　while　the　differences
  between　the　living　creatures　of　the　time　before　the　chalk　and　those
  of　the　present　day　appear　startling；　if　placed　side　by　side；　we　are
  led　from　one　to　the　other　by　the　most　gradual　progress；　if　we
  follow　the　course　of　Nature　through　the　whole　series　of　those
  relics　of　her　operations　which　she　has　left　behind。
  And　it　is　by　the　population　of　the　chalk　sea　that　the　ancient　and
  the　modern　inhabitants　of　the　world　are　most　completely　connected。
  The　groups　which　are　dying　out　flourish；　side　by　side；　with　the
  groups　which　are　now　the　dominant　forms　of　life。
  Thus　the　chalk　contains　remains　of　those　strange　flying　and
  swimming　reptiles；　the　pterodactyl；　the　ichthyosaurus；　and　the
  plesiosaurus；　which　are　found　in　no　later　deposits；　but　abounded　in
  preceding　ages。　　The　chambered　shells　called　ammonites　and
  belemnites；　which　are　so　characteristic　of　the　period　preceding　the
  cretaceous；　in　like　manner　die　with　it。
  But；　amongst　these　fading　remainders　of　a　previous　state　of　things；
  are　some　very　modern　forms　of　life；　looking　like　Yankee　pedlars
  among　a　tribe　of　Red　Indians。　　Crocodiles　of　modern　type　appear；
  bony　fishes；　many　of　them　very　similar　to　existing　species　almost
  supplant　the　forms　of　fish　which　predominate　in　more　ancient　seas；
  and　many　kinds　of　living　shellfish　first　become　known　to　us　in　the
  chalk。　　The　vegetation　acquires　a　modern　aspect。　　A　few　living
  animals　are　not　even　distinguishable　as　species；　from　those　which
  existed　at　that　remote　epoch。　　The　Globigerina　of　the　present　day；
  for　example；　is　not　different　specifically　from　that　of　the　chalk；
  and　the　same　may　be　said　of　many　other　Foraminifera。　　I　think　it
  probable　that　critical　and　unprejudiced　examination　will　show　that
  more　than　one　species　of　much　higher　animals　have　had　a　similar
  longevity；　but　the　only　example；　which　I　can　at　present　give
  confidently　is　the　snake's…head　lamp…shell　（Terebratulina　caput
  serpentis）；　which　lives　in　our　English　seas　and　abounded　（as
  Terebratulina　striata　of　authors）　in　the　chalk。
  The　longest　line　of　human　ancestry　must　hide　its　diminished　head
  before　the　pedigree　of　this　insignificant　shell…fish。　　We
  Englishmen　are　proud　to　have　an　ancestor　who　was　present　at　the
  Battle　of　Hastings。　　The　ancestors　of　Terebratulina　caput　serpentis
  may　have　been　present　at　a　battle　of　Ichthyosauria　in　that　part　of
  the　sea　which；　when　the　chalk　was　forming；　flowed　over　the　site　of
  Hastings。　　While　all　around　has　changed；　this　Terebratulina　has
  peacefully　propagated　its　species　from　generation　to　generation；
  and　stands　to　this　day；　as　a　living　testimony　to　the　continuity　of
  the　present　with　the　past　history　of　the　globe。
  Up　to　this　moment　I　have　stated；　so　far　as　I　know；　nothing　but
  well…authenticated　facts；　and　the　immediate　conclusions　which　they
  force　upon　the　mind。
  But　the　mind　is　so　constituted　that　it　does　not　willingly　rest　in
  facts　and　immediate　causes；　but　seeks　always　after　a　knowledge　of
  the　remoter　links　in　the　chain　of　causation。
  Taking　the　many　changes　of　any　given　spot　of　the　earth's　surface；
  from　sea　to　land　and　from　land　to　sea；　as　an　established　fact；　we
  cannot　refrain　from　asking　ourselves　how　these　changes　have
  occurred。　　And　when　we　have　explained　themas　they　must　be
  explainedby　the　alternate　slow　movements　of　elevation　and
  depression　which　have　affected　the　crust　of　the　earth；　we　go　still
  further　back；　and　ask；　Why　these　movements？
  I　am　not　certain　that　any　one　can　give　you　a　satisfactory　answer　to
  that　question。　　Assuredly　I　cannot。　　All　that　can　be　said；　for
  certain；　is；　that　such　movements　are　part　of　the　ordinary　course　of
  nature；　inasmuch　as　they　are　going　on　at　the　present　time。　　Direct
  proof　may　be　given；　that　some　parts　of　the　land　of　the　northern
  hemisphere　are　at　this　moment　insensibly　rising　and　others
  insensibly　sinking；　and　there　is　indirect；　but　perfectly
  satisfactory；　proof；　that　an　enormous　area　now　covered　by　the
  Pacific　has　been　deepened　thousands　of　feet；　since　the　present
  inhabitants　of　that　sea　came　into　existence。
  Thus　there　is　not　a　shadow　of　a　reason　for　believing　that　the
  physical　changes　of　the　globe；　in　past　times　have　been　effected　by
  other　than　natural　causes。
  Is　there　any　more　reason　for　believing　that　the　concomitant
  modifications　in　the　forms　of　the　living　inhabitants　of　the　globe
  have　been　brought　about　in　other　ways？
  Before　attempting　to　answer　this　question；　let　us　try　to　form　a
  distinct　mental　picture　of　what　has　happened；　in　some　special　case。
  The　crocodiles　are　animals　which；　as　a　group；　have　a　very　vast
  antiquity。　　They　abounded　ages　before　the　chalk　was　deposited；　they
  throng　the　rivers　in　warm　climates；　at　the　present　day。　　There　is　a
  difference　in　the　form　of　the　joints　of　the　back…bone；　and　in　some
  minor　particulars；　between　the　crocodiles　of　the　present　epoch　and
  those　which　lived　before　the　chalk；　but　in　the　cretaceous　epoch；　as
  I　have　already　mentioned；　the　crocodiles　had　assumed　the　modern
  type　of　structure。　　Notwithstanding　this；　the　crocodiles　of　the
  chalk　are　not　identically　the　same　as　those　which　lived　in　the
  times　called　〃older　tertiary；〃　which　succeeded　the　cretaceous
  epoch；　and　the　crocodiles　of　the　older　tertiaries　are　not　identical
  with　those　of　the　newer　tertiaries；　nor　are　these　identical　with
  existing　forms。　　I　leave　open　the　question　whether　particular
  species　may　have　lived　on　from　epoch　to　epoch。　　But　each　epoch　has
  had　its　peculiar　crocodiles；　though　all；　since　the　chalk；　have
  belonged　to　the　modern　type；　and　differ　simply　in　their
  proportions；　and　in　such　structural　particulars　as　are　discernible
  only　to　trained　eyes。
  How　is　the　existence　of　this　long　succession　of　different　species
  of　crocodiles　to　be　accounted　for？
  Only　two　suppositions　seem　to　be　open　to　usEither　each　species　of
  crocodile　has　been　specially　created；　or　it　has　arisen　out　of　some
  pre…existing　form　by　the　operation　of　natural　causes。
  Choose　your　hypothesis；　I　have　chosen　mine。　　I　can　find　no　warranty
  for　believing　in　the　distinct　creation　of　a　score　of　successive
  species　of　crocodiles　in　the　course　of　countless　ages　of　time。
  Science　gives　no　countenance　to　such　a　wild　fancy；　nor　can　even　the
  perverse　ingenuity　of　a　commentator　pretend　to　discover　this　sense；
  in　the　simple　words　in　which　the　writer　of　Genesis　records　the
  proceedings　of　the　fifth　and　sixth　days　of　the　Creation。
  On　the　other　hand；　I　see　no　good　reason　for　doubting　the　necessary
  alternative；　that　all　these　varied　species　have　been　evolved　from
  pre…existing　crocodilian　forms；　by　the　operation　of　causes　as
  completely　a　part　of　the　common　order　of　nature；　as　those　which
  have　effected　the　changes　of　the　inorganic　world。
  Few　will　venture　to　affirm　that　the　reasoning　which　applies　to
  crocodiles　loses　its　force　among　other　animals；　or　among　plants。
  If　one　series　of　spe