the past condition of organic nature-第4章

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soundings　of　the　bottom　of　the　Atlantic；　and　although；　as　we　must　all
regret；　up　to　the　present　time　that　project　has　not　succeeded；　we　have
the　satisfaction　of　knowing　that　it　yielded　some　most　remarkable　results
to　science。　　The　Atlantic　Ocean　had　to　be　sounded　right　across；　to
depths　of　several　miles　in　some　places；　and　the　nature　of　its　bottom
was　carefully　ascertained。　　Well；　now；　a　space　of　about　1；000　miles
wide　from　east　to　west；　and　I　do　not　exactly　know　how　many　from　north　to
south；　but　at　any　rate　600　or　700　miles；　was　carefully　examined；　and　it
was　found　that　over　the　whole　of　that　immense　area　an　excessively　fine
chalky　mud　is　being　deposited；　and　this　deposit　is　entirely　made　up　of
animals　whose　hard　parts　are　deposited　in　this　part　of　the　ocean；　and
are　doubtless　gradually　acquiring　solidity　and　becoming　metamorphosed
into　a　chalky　limestone。　　Thus；　you　see；　it　is　quite　possible　in　this
way　to　preserve　unmistakable　records　of　animal　and　vegetable　life。
Whenever　the　sea…bottom；　by　some　of　those　undulations　of　the　earth's
crust　that　I　have　referred　to；　becomes　upheaved；　and　sections　or
borings　are　made；　or　pits　are　dug；　then　we　become　able　to　examine　the
contents　and　constituents　of　these　ancient　sea…bottoms；　and　find　out
what　manner　of　animals　lived　at　that　period。

Now　it　is　a　very　important　consideration　in　its　bearing　on　the
completeness　of　the　record；　to　inquire　how　far　the　remains　contained　in
these　fossiliferous　limestones　are　able　to　convey　anything　like　an
accurate　or　complete　account　of　the　animals　which　were　in　existence　at
the　time　of　its　formation。　　Upon　that　point　we　can　form　a　very　clear
judgment；　and　one　in　which　there　is　no　possible　room　for　any　mistake。
There　are　of　course　a　great　number　of　animalssuch　as　jelly…fishes；
and　other　animalswithout　any　hard　parts；　of　which　we　cannot
reasonably　expect　to　find　any　traces　whatever：　there　is　nothing　of　them
to　preserve。　　Within　a　very　short　time；　you　will　have　noticed；　after
they　are　removed　from　the　water；　they　dry　up　to　a　mere　nothing；
certainly　they　are　not　of　a　nature　to　leave　any　very　visible　traces　of
their　existence　on　such　bodies　as　chalk　or　mud。　　Then　again；　look　at
land　animals；　it　is；　as　I　have　said；　a　very　uncommon　thing　to　find　a
land　animal　entire　after　death。　　Insects　and　other　carnivorous　animals
very　speedily　pull　them　to　pieces；　putrefaction　takes　place；　and　so；　out
of　the　hundreds　of　thousands　that　are　known　to　die　every　year；　it　is
the　rarest　thing　in　the　world　to　see　one　imbedded　in　such　a　way　that
its　remains　would　be　preserved　for　a　lengthened　period。　　Not　only　is
this　the　case；　but　even　when　animal　remains　have　been　safely　imbedded；
certain　natural　agents　may　wholly　destroy　and　remove　them。

Almost　all　the　hard　parts　of　animalsthe　bones　and　so　onare　composed
chiefly　of　phosphate　of　lime　and　carbonate　of　lime。　　Some　years　ago；　I
had　to　make　an　inquiry　into　the　nature　of　some　very　curious　fossils
sent　to　me　from　the　North　of　Scotland。　　Fossils　are　usually　hard　bony
structures　that　have　become　imbedded　in　the　way　I　have　described；　and
have　gradually　acquired　the　nature　and　solidity　of　the　body　with　which
they　are　associated；　but　in　this　case　I　had　a　series　of　'holes'　in　some
pieces　of　rock；　and　nothing　else。　　Those　holes；　however；　had　a　certain
definite　shape　about　them；　and　when　I　got　a　skilful　workman　to　make
castings　of　the　interior　of　these　holes；　I　found　that　they　were　the
impressions　of　the　joints　of　a　backbone　and　of　the　armour　of　a　great
reptile；　twelve　or　more　feet　long。　　This　great　beast　had　died　and　got
buried　in　the　sand；　the　sand　had　gradually　hardened　over　the　bones；　but
remained　porous。　Water　had　trickled　through　it；　and　that　water　being
probably　charged　with　a　superfluity　of　carbonic　acid；　had　dissolved　all
the　phosphate　and　carbonate　of　lime；　and　the　bones　themselves　had　thus
decayed　and　entirely　disappeared；　but　as　the　sandstone　happened　to　have
consolidated　by　that　time；　the　precise　shape　of　the　bones　was　retained。
If　that　sandstone　had　remained　soft　a　little　longer；　we　should　have
known　nothing　whatsoever　of　the　existence　of　the　reptile　whose　bones　it
had　encased。

How　certain　it　is　that　a　vast　number　of　animals　which　have　existed　at
one　period　on　this　earth　have　entirely　perished；　and　left　no　trace
whatever　of　their　forms；　may　be　proved　to　you　by　other　considerations。
There　are　large　tracts　of　sandstone　in　various　parts　of　the　world；　in
which　nobody　has　yet　found　anything　but　footsteps。　　Not　a　bone　of　any
description；　but　an　enormous　number　of　traces　of　footsteps。　　There　is
no　question　about　them。　　There　is　a　whole　valley　in　Connecticut　covered
with　these　footsteps；　and　not　a　single　fragment　of　the　animals　which
made　them　has　yet　been　found。　　Let　me　mention　another　case　while　upon
that　matter；　which　is　even　more　surprising　than　those　to　which　I　have
yet　referred。　　There　is　a　limestone　formation　near　Oxford；　at　a　place
called　Stonesfield；　which　has　yielded　the　remains　of　certain　very
interesting　mammalian　animals；　and　up　to　this　time；　if　I　recollect
rightly；　there　have　been　found　seven　specimens　of　its　lower　jaws；　and
not　a　bit　of　anything　else；　neither　limb…bones　nor　skull；　or　any　part
whatever；　not　a　fragment　of　the　whole　system！　　Of　course；　it　would　be
preposterous　to　imagine　that　the　beasts　had　nothing　else　but　a　lower
jaw！　　The　probability　is；　as　Dr。　Buckland　showed；　as　the　result　of　his
observations　on　dead　dogs　in　the　river　Thames；　that　the　lower　jaw；　not
being　secured　by　very　firm　ligaments　to　the　bones　of　the　head；　and
being　a　weighty　affair；　would　easily　be　knocked　off；　or　might　drop　away
from　the　body　as　it　floated　in　water　in　a　state　of　decomposition。　The
jaw　would　thus　be　deposited　immediately；　while　the　rest　of　the　body
would　float　and　drift　away　altogether；　ultimately　reaching　the　sea；　and
perhaps　becoming　destroyed。　　The　jaw　becomes　covered　up　and　preserved　in
the　river　silt；　and　thus　it　comes　that　we　have　such　a　curious
circumstance　as　that　of　the　lower　jaws　in　the　Stonesfield　slates。　So
that；　you　see；　faulty　as　these　layers　of　stone　in　the　earth's　crust
are；　defective　as　they　necessarily　are　as　a　record；　the　account　of
contemporaneous　vital　phenomena　presented　by　them　is；　by　the　necessity
of　the　case；　infinitely　more　defective　and　fragmentary。

It　was　necessary　that　I　should　put　all　this　very　strongly　before　you；
because；　otherwise；　you　might　have　been　led　to　think　differently　of　the
completeness　of　our　knowledge　by　the　next　facts　I　shall　state　to　you。

The　researches　of　the　last　three…quarters　of　a　century　have；　in　truth；
revealed　a　wonderful　richness　of　organic　life　in　those　rocks。　Certainly
not　fewer　than　thirty　or　forty　thousand　different　species　of　fossils
have　been　discovered。　　You　have　no　more　ground　for　doubting　that　these
creatures　really　lived　and　died　at　or　near　the　places　in　which　we　find
them　than　you　have　for　like　scepticism　about　a　shell　on　the　sea…shore。
The　evidence　is　as　good　in　the　one　case　as　in　the　other。

Our　next　business　is　to　look　at　the　general　character　of　these　fossil
remains；　and　it　is　a　subject　which　it　will　be　requisite　to　consider
carefully；　and　the　first　point　for　us　is　to　examine　how　much　the
extinct　'Flora'　and　'Fauna'　as　a　'whole'disregarding　altogether　the
'succession'　of　their　constituents；　of　which　I　shall　speak
afterwardsdiffer　from　the　'Flora'　and　'Fauna'　of　the　present
day；how　far　they　differ　in　what　we　'do'　know　about　them；　leaving
altogether　out　of　consideration　speculations　based　upon　what　we　'do
not'　know。

I　strongly　imagine　that　if　it　were　not　for　the　peculiar　appearance　that
fossilised　animals　have；　any　of　you　might　readily　walk　through　a　museum
which　contains　fossil　remains　mixed　up　with　those　of　the　present　forms
of　life；　and　I　doubt　very　much　whether　your　uninstructed　eyes　would
lead　you　to　see　any　vast　or　wonderful　difference　between　the　two。　　If
you　looked　closely；　you　would　notice；　in　the　first　place；　a　great　many
things　very　like　animals　with　which　you　are　acquainted　now：　you　would
see　differences　of　shape　and　proportion；　but　on　the　whole　a　close
similarity。

I　explained　what　I　meant　by　ORDERS　the　other　day；　when　I　described