the rise and progress of palaeontology-第3部分

快捷操作: 按键盘上方向键 ← 或 → 可快速上下翻页 按键盘上的 Enter 键可回到本书目录页 按键盘上方向键 ↑ 可回到本页顶部! 如果本书没有阅读完，想下次继续接着阅读，可使用上方 "收藏到我的浏览器" 功能 和 "加入书签" 功能！



same。　This　most　important　generalisation　was　rapidly　verified

and　extended　to　all　parts　of　the　world　accessible　to　geologists；

and　now　it　rests　upon　such　an　immense　mass　of　observations　as　to

be　one　of　the　best　established　truths　of　natural　science。　To　the

geologist　the　discovery　was　of　infinite　importance　as　it　enabled

him　to　identify　rocks　of　the　same　relative　age；　however　their

continuity　might　be　interrupted　or　their　composition　altered。

But　to　the　biologist　it　had　a　still　deeper　meaning；　for　it

demonstrated　that；　throughout　the　prodigious　duration　of　time

registered　by　the　fossiliferous　rocks；　the　living　population　of

the　earth　had　undergone　continual　changes；　not　merely　by　the

extinction　of　a　certain　number　of　the　species　which　had　at　first

existed；　but　by　the　continual　generation　of　new　species；　and　the

no　less　constant　extinction　of　old　ones。　



Thus　the　broad　outlines　of　palaeontology；　in　so　far　as　it　is　the

common　property　of　both　the　geologist　and　the　biologist；　were

marked　out　at　the　close　of　the　last　century。　In　tracing　its

subsequent　progress　I　must　confine　myself　to　the　province　of

biology；　and；　indeed；　to　the　influence　of　palaeontology　upon

zoological　morphology。　And　I　accept　this　limitation　the　more

willingly　as　the　no　less　important　topic　of　the　bearing　of

geology　and　of　palaeontology　upon　distribution　has　been

luminously　treated　in　the　address　of　the　President　of　the

Geographical　Section。



The　succession　of　the　species　of　animals　and　plants　in　time

being　established；　the　first　question　which　the　zoologist　or　the

botanist　had　to　ask　himself　was；　What　is　the　relation　of　these

successive　species　one　to　another？　And　it　is　a　curious

circumstance　that　the　most　important　event　in　the　history　of

palaeontology　which　immediately　succeeded　William　Smith's

generalisation　was　a　discovery　which；　could　it　have　been　rightly

appreciated　at　the　time；　would　have　gone　far　towards　suggesting

the　answer；　which　was　in　fact　delayed　for　more　than　half　a

century。　I　refer　to　Cuvier's　investigation　of　the　mammalian

fossils　yielded　by　the　quarries　in　the　older　tertiary　rocks　of

Montmartre；　among　the　chief　results　of　which　was　the　bringing　to

light　of　two　genera　of　extinct　hoofed　quadrupeds；　the

Anoplotherium　and　the　Palaeotherium。　The　rich

materials　at　Cuvier's　disposition　enabled　him　to　obtain　a　full

knowledge　of　the　osteology　and　of　the　dentition　of　these　two

forms；　and　consequently　to　compare　their　structure　critically

with　that　of　existing　hoofed　animals。　The　effect　of　this

comparison　was　to　prove　that　the　Anoplotherium；　though　it

presented　many　points　of　resemblance　with　the　pigs　on　the　one

hand　and　with　the　ruminants　on　the　other；　differed　from　both　to

such　an　extent　that　it　could　find　a　place　in　neither　group。

In　fact；　it　held；　in　some　respects；　an　intermediate　position；

tending　to　bridge　over　the　interval　between　these　two　groups；

which　in　the　existing　fauna　are　so　distinct。　In　the　same　way；

the　Palaeotherium　tended　to　connect　forms　so　different　as

the　tapir；　the　rhinoceros；　and　the　horse。　Subsequent

investigations　have　brought　to　light　a　variety　of　facts　of　the

same　order；　the　most　curious　and　striking　of　which　are　those

which　prove　the　existence；　in　the　mesozoic　epoch；　of　a　series　of

forms　intermediate　between　birds　and　reptilestwo　classes　of

vertebrate　animals　which　at　present　appear　to　be　more　widely

separated　than　any　others。　Yet　the　interval　between　them　is

completely　filled；　in　the　mesozoic　fauna；　by　birds　which　have

reptilian　characters；　on　the　one　side；　and　reptiles　which　have

ornithic　characters；　on　the　other。　So　again；　while　the　group　of

fishes；　termed　ganoids；　is；　at　the　present　time；　so　distinct

from　that　of　the　dipnoi；　or　mudfishes；　that　they　have　been

reckoned　as　distinct　orders；　the　Devonian　strata　present　us　with

forms　of　which　it　is　impossible　to　say　with　certainty　whether

they　are　dipnoi　or　whether　they　are　ganoids。　



Agassiz's　long　and　elaborate　researches　upon　fossil　fishes；

published　between　1833　and　1842；　led　him　to　suggest　the

existence　of　another　kind　of　relation　between　ancient　and　modern

forms　of　life。　He　observed　that　the　oldest　fishes　present

many　characters　which　recall　the　embryonic　conditions　of

existing　fishes；　and　that；　not　only　among　fishes；　but　in　several

groups　of　the　invertebrata　which　have　a　long　palaeontological

history；　the　latest　forms　are　more　modified；　more　specialised；

than　the　earlier。　The　fact　that　the　dentition　of　the　older

tertiary　ungulate　and　carnivorous　mammals　is　always　complete；

noticed　by　Professor　Owen；　illustrated　the　same　generalisation。



Another　no　less　suggestive　observation　was　made　by　Mr。　Darwin；

whose　personal　investigations　during　the　voyage　of　the

Beagle　led　him　to　remark　upon　the　singular　fact；　that　the

fauna；　which　immediately　precedes　that　at　present　existing　in

any　geographical　province　of　distribution；　presents　the　same

peculiarities　as　its　successor。　Thus；　in　South　America　and　in

Australia；　the　later　tertiary　or　quaternary　fossils　show　that

the　fauna　which　immediately　preceded　that　of　the　present　day

was；　in　the　one　case；　as　much　characterised　by　edentates　and；　in

the　other；　by　marsupials　as　it　is　now；　although　the　species　of

the　older　are　largely　different　from　those　of　the　newer　fauna。



However　clearly　these　indications　might　point　in　one　direction；

the　question　of　the　exact　relation　of　the　successive　forms　of

animal　and　vegetable　life　could　be　satisfactorily　settled　only

in　one　way；　namely；　by　comparing；　stage　by　stage；　the　series　of

forms　presented　by　one　and　the　same　type　throughout　a　long

space　of　time。　Within　the　last　few　years　this　has　been　done

fully　in　the　case　of　the　horse；　less　completely　in　the　case　of

the　other　principal　types　of　the　ungulata　and　of　the　carnivora；

and　all　these　investigations　tend　to　one　general　result；　namely；

that；　in　any　given　series；　the　successive　members　of　that　series

present　a　gradually　increasing　specialisation　of　structure。

That　is　to　say；　if　any　such　mammal　at　present　existing　has

specially　modified　and　reduced　limbs　or　dentition　and

complicated　brain；　its　predecessors　in　time　show　less　and　less

modification　and　reduction　in　limbs　and　teeth　and　a　less　highly

developed　brain。　The　labours　of　Gaudry；　Marsh；　and　Cope　furnish

abundant　illustrations　of　this　law　from　the　marvellous　fossil

wealth　of　Pikermi　and　the　vast　uninterrupted　series　of　tertiary

rocks　in　the　territories　of　North　America。



I　will　now　sum　up　the　results　of　this　sketch　of　the　rise　and

progress　of　palaeontology。　The　whole　fabric　of　palaeontology　is

based　upon　two　propositions：　the　first　is；　that　fossils　are　the

remains　of　animals　and　plants；　and　the　second　is；　that　the

stratified　rocks　in　which　they　are　found　are　sedimentary

deposits；　and　each　of　these　propositions　is　founded　upon　the

same　axiom；　that　like　effects　imply　like　causes。　If　there　is　any

cause　competent　to　produce　a　fossil　stem；　or　shell；　or　bone；

except　a　living　being；　then　palaeontology　has　no　foundation；

if　the　stratification　of　the　rocks　is　not　the　effect　of　such

causes　as　at　present　produce　stratification；　we　have　no　means　of

judging　of　the　duration　of　past　time；　or　of　the　order　in　which

the　forms　of　life　have　succeeded　one　another。　But　if　these　two

propositions　are　granted；　there　is　no　escape；　as　it　appears　to

me；　from　three　very　important　conclusions。　The　first　is　that

living　matter　has　existed　upon　the　earth　for　a　vast　length　of

time；　certainly　for　millions　of　years。　The　second　is　that；

during　this　lapse　of　time；　the　forms　of　living　matter　have

undergone　repeated　changes；　the　effect　of　which　has　been　that

the　animal　and　vegetable　population；　at　any　period　of　the

earth's　history；　contains　certain　species　which　did　not　exist　at

some　antecedent　period；　and　others　which　ceased　to　exist　at　some

subsequent　period。　The　third　is　that；　in　the　case　of　many　groups

of　mammals　and　some　of　reptiles；　in　which　one　type　can　be

followed　through　a　considerable　extent　of　geological　time；　the

series　of　different　forms　by　which　the　type　is　represented；　at

successive　intervals　of　this　time；　is　exactly　such　as　it　would

be；　if　they　had　been　produced　by　the　gradual　modification　of　the

earliest　forms　of　the　series。　These　are　facts　of　the　history　of

the　earth　guaranteed　by　as　good　evidence　as　any　facts　in

civil　history。



Hitherto　I　have　kept　carefully　clear　of　all　the　hypotheses　to

which　men　have　at　various　times　endeavoured　to　fit　the　facts　of

palaeontology；　or　by　which　they　have　endeavoured　to　connect

as　many　of　these　facts　as　they　happened　to　be　acquainted　with。

I　do　not　think　it　would　be　a　profitable　employment　of　our　time

to　discuss　conceptions　which　doubtless　have　had　their

justification　and　even　their　use；　but　which　are　now　obviously

incompatible　with　the　well…ascertained　truths　of　palaeontology。

At　present　these　truths　leave　room　for　only　two　hypotheses。

The　first　is　that；　in　the　course　of　the　history　of　the　earth；

innumerable　species　of　animals　and　plants　have　come　into

existence；　independently　of　one　another；　innumerable　times。

This；　of　course；　implies　either　that　spontaneous　generation　on

the　most　astounding　scale；　and　of　animals　such　as　horses　and

elephants；　has　been　going　on；　as　a　natural　process；　through　all

the　time　recorded　by　the　fossiliferous　rocks；　or　it　necessitates

the　belief　in　innumerable　acts　of　creation　repeated　innumerable

times。　The　other　hypothesis　is；　that　the　successive　species　of

animals　and　plants　have　arisen；　the　later　by　the　gradual

modification　of　the　earlier。　This　is　the　hypothesis　of

evolution；　and　the　palaeontological　discoveries　of　the　last

decade　are　so　completely　in　accordance　with　the　requirements　of

this　hypothesis　that；　if　it　had　not　existed；　the　palaeontologist

would　have　had　to　invent　it。



I　have　always　had　a　certain　horror　of　presuming　to　set　a　limi