the origin of species(物种起源)-第68章

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　mainly　areas　of　subsidence；　the　great　archipelagoes　still　areas　of　oscillations　of　level；　and　the　continents　areas　of　elevation。　But　have　we　any　right　to　assume　that　things　have　thus　remained　from　eternity？　Our　continents　seem　to　have　been　formed　by　a　preponderance；　during　many　oscillations　of　level；　of　the　force　of　elevation；　but　may　not　the　areas　of　preponderant　movement　have　changed　in　the　lapse　of　ages？　At　a　period　immeasurably　antecedent　to　the　silurian　epoch；　continents　may　have　existed　where　oceans　are　now　spread　out；　and　clear　and　open　oceans　may　have　existed　where　our　continents　now　stand。　Nor　should　we　be　justified　in　assuming　that　if；　for　instance；　the　bed　of　the　Pacific　Ocean　were　now　converted　into　a　continent；　we　should　there　find　formations　older　than　the　silurian　strata；　supposing　such　to　have　been　formerly　deposited；　for　it　might　well　happen　that　strata　which　had　subsided　some　miles　nearer　to　the　centre　of　the　earth；　and　which　had　been　pressed　on　by　an　enormous　weight　of　superincumbent　water；　might　have　undergone　far　more　metamorphic　action　than　strata　which　have　always　remained　nearer　to　the　surface。　The　immense　areas　in　some　parts　of　the　world；　for　instance　in　South　America；　of　bare　metamorphic　rocks；　which　must　have　been　heated　under　great　pressure；　have　always　seemed　to　me　to　require　some　special　explanation；　and　we　may　perhaps　believe　that　we　see　in　these　large　areas；　the　many　formations　long　anterior　to　the　silurian　epoch　in　a　completely　metamorphosed　condition。　
The　several　difficulties　here　discussed；　namely　our　not　finding　in　the　successive　formations　infinitely　numerous　transitional　links　between　the　many　species　which　now　exist　or　have　existed；　the　sudden　manner　in　which　whole　groups　of　species　appear　in　our　European　formations；　the　almost　entire　absence；　as　at　present　known；　of　fossiliferous　formations　beneath　the　Silurian　strata；　are　all　undoubtedly　of　the　gravest　nature。　We　see　this　in　the　plainest　manner　by　the　fact　that　all　the　most　eminent　palaeontologists；　namely　Cuvier；　Owen；　Agassiz；　Barrande；　Falconer；　E。　Forbes；　&c。；　and　all　our　greatest　geologists；　as　Lyell；　Murchison；　Sedgwick；　&c。；　have　unanimously；　often　vehemently；　maintained　the　immutability　of　species。　But　I　have　reason　to　believe　that　one　great　authority；　Sir　Charles　Lyell；　from　further　reflexion　entertains　grave　doubts　on　this　subject。　I　feel　how　rash　it　is　to　differ　from　these　great　authorities；　to　whom；　with　others；　we　owe　all　our　knowledge。　Those　who　think　the　natural　geological　record　in　any　degree　perfect；　and　who　do　not　attach　much　weight　to　the　facts　and　arguments　of　other　kinds　even　in　this　volume；　will　undoubtedly　at　once　reject　my　theory。　For　my　part；　following　out　Lyell's　metaphor；　I　look　at　the　natural　geological　record；　as　a　history　of　the　world　imperfectly　kept；　and　written　in　a　changing　dialect；　of　this　history　we　possess　the　last　volume　alone；　relating　only　to　two　or　three　countries。　Of　this　volume；　only　here　and　there　a　short　chapter　has　been　preserved；　and　of　each　page；　only　here　and　there　a　few　lines。　Each　word　of　the　slowly…changing　language；　in　which　the　history　is　supposed　to　be　written；　being　more　or　less　different　in　the　interrupted　succession　of　chapters；　may　represent　the　apparently　abruptly　changed　forms　of　life；　entombed　in　our　consecutive；　but　widely　separated　formations。　On　this　view；　the　difficulties　above　discussed　are　greatly　diminished；　or　even　disappear。