the past condition of organic nature-第4节

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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　the
animal　kingdom　as　being　divided　in　sub…kingdoms；　classes　and　orders。　If
you　divide　the　animal　kingdom　into　orders；　you　will　find　that　there　are
about　one　hundred　and　twenty。　　The　number　may　vary　on　one　side　or　the
other；　but　this　is　a　fair　estimate。　　That　is　the　sum　total　of　the　orders
of　all　the　animals　which　we　know　now；　and　which　have　been　known　in　past
times；　and　left　remains　behind。

Now；　how　many　of　those　are　absolutely　extinct？　　That　is　to　say；　how　many
of　these　orders　of　animals　have　lived　at　a　former　period　of　the　world's
history；　but　have　at　present　no　representatives？　　That　is　the　sense　in
which　I　meant　to　use　the　word　〃extinct。〃　　I　mean　that　those　animals　did
live　on　this　earth　at　one　time；　but　have　left　no　one　of　their　kind　with
us　at　the　present　moment。　　So　that　estimating　the　number　of　extinct
animals　is　a　sort　of　way　of　comparing　the　past　creation　as　a　whole　with
the　present　as　a　whole。　　Among　the　mammalia　and　birds　there　are　none
extinct；　but　when　we　come　to　the　reptiles　there　is　a　most　wonderful
thing：　out　of　the　eight　orders；　or　thereabouts；　which　you　can　make　among
reptiles；　one…half　are　extinct。　　These　diagrams　of　the　plesiosaurus；
the　ichthyosaurus；　the　pterodactyle；　give　you　a　notion　of　some　of　these
extinct　reptiles。　　And　here　is　a　cast　of　the　pterodactyle　and　bones　of
the　ichthyosaurus　and　the　plesiosaurus；　just　as　fresh　as　if　it　had　been
recently　dug　up　in　a　churchyard。　Thus；　in　the　reptile　class；　there　are
no　less　than　half　of　the　orders　which　are　absolutely　extinct。　　If　we
turn　to　the　'Amphibia'；　there　was　one　extinct　order；　the
Labyrinthodonts；　typified　by　the　large　salamander…like　beast　shown　in
this　diagram。

No　order　of　fishes　is　known　to　be　extinct。　　Every　fish　that　we　find　in
the　stratato　which　I　have　been　referringcan　be　identified　and
placed　in　one　of　the　orders　which　exist　at　the　present　day。　　There　is
not　known　to　be　a　single　ordinal　form　of　insect　extinct。　　There　are
only　two　orders　extinct　among　the　'Crustacea'。　　There　is　not　known　to
be　an　extinct　order　of　these　creatures；　the　parasitic　and　other　worms；
but　there　are　two；　not　to　say　three；　absolutely　extinct　orders　of　this
class；　the　'Echinodermata'；　out　of　all　the　orders　of　the　'Coelenterata'
and　'Protozoa'　only　one；　the　Rugose　Corals。

So　that；　you　see；　out　of　somewhere　about　120　orders　of　animals；　taking
them　altogether；　you　will　not；　at　the　outside　estimate；　find　above　ten
or　a　dozen　extinct。　　Summing　up　all　the　orders　of　animals　which　have
left　remains　behind　them；　you　will　not　find　above　ten　or　a　dozen　which
cannot　be　arranged　with　those　of　the　present　day；　that　is　to　say；　that
the　difference　does　not　amount　to　much　more　than　ten　per　cent。：　and　the
proportion　of　extinct　orders　of　plants　is　still　smaller。　　I　think　that
that　is　a　very　astounding；　a　most　astonishing　fact；　seeing　the　enormous
epochs　of　time　which　have　elapsed　during　the　constitution　of　the　surface
of　the　earth　as　it　at　present　exists；　it　is；　indeed；　a　most　astounding
thing　that　the　proportion　of　extinct　ordinal　types　should　be　so
exceedingly　small。

But　now；　there　is　another　point　of　view　in　which　we　must　look　at　this
past　creation。　　Suppose　that　we　were　to　sink　a　vertical　pit　through　the
floor　beneath　us；　and　that　I　could　succeed　in　making　a　section　right
through　in　the　direction　of　New　Zealand；　I　should　find　in　each　of　the
different　beds　through　which　I　passed　the　remains　of　animals　which　I
should　find　in　that　stratum　and　not　in　the　others。　　First；　I　should
come　upon　beds　of　gravel　or　drift　containing　the　bones　of　large
animals；　such　as　the　elephant；　rhinoceros；　and　cave　tiger。　　Rather
curious　things　to　fall　across　in　Piccadilly！　　If　I　should　dig　lower
still；　I　should　come　upon　a　bed　of　what　we　call　the　London　clay；　and　in
this；　as　you　will　see　in　our　galleries　upstairs；　are　found　remains　of
strange　cattle；　remains　of　turtles；　palms；　and　large　tropical　fruits；
with　shell…fish　such　as　you　see　the　like　of　now　only　in　tropical
regions。　　If　I　went　below　that；　I　should　come　upon　the　c