the malay archipelago-2-第39部分

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！
————未阅读完？加入书签已便下次继续阅读！


nd　such　as　have　barrier　or　encircling　reefs；　have　suffered　subsidence；　while　our　own　islands；　whose　productions　are　entirely　those　of　the　adjacent　continent；　have　been　separated　from　it。　Now　the　Aru　Islands　are　all　coral　rock；　and　the　adjacent　sea　is　shallow　and　full　of　coral；　it　is　therefore　evident　that　they　have　been　elevated　from　beneath　the　ocean　at　a　not　very　distant　epoch。　But　if　we　suppose　that　elevation　to　be　the　first　and　only　cause　of　their　present　condition；　we　shall　find　ourselves　quite　unable　to　explain　the　curious　river…channels　which　divide　them。　Fissures　during　upheaval　would　not　produce　the　regular　width；　the　regular　depth；　or　the　winding　curves　which　characterise　them；　and　the　action　of　tides　and　currents　during　their　elevation　might　form　straits　of　irregular　width　and　depth；　but　not　the　river…like　channels　which　actually　exist。　If；　again；　we　suppose　the　last　movement　to　have　been　one　of　subsidence；　reducing　the　size　of　the　islands；　these　channels　are　quite　as　inexplicable；　for　subsidence　would　necessarily　lead　to　the　flooding　of　all　low　tracts　on　the　banks　of　the　old　rivers；　and　thus　obliterate　their　courses；　whereas　these　remain　perfect；　and　of　nearly　uniform　width　from　end　to　end。

Now　if　these　channels　have　ever　been　rivers　they　must　have　flowed　from　some　higher　regions；　and　this　must　have　been　to　the　east；　because　on　the　north　and　west　the　sea…bottom　sinks　down　at　a　short　distance　from　the　shore　to　an　unfathomable　depth；　whereas　on　the　east。　a　shallow　sea；　nowhere　exceeding　fifty　fathoms；　extends　quite　across　to　New　Guinea；　a　distance　of　about　a　hundred　and　fifty　miles。　An　elevation　of　only　three　hundred　feet　would　convert　the　whole　of　this　sea　into　moderately　high　land；　and　make　the　Aru　Islands　a　portion　of　New　Guinea；　and　the　rivers　which　have　their　mouths　at　Utanata　and　Wamuka；　might　then　have　flowed　on　across　Aru；　in　the　channels　which　are　now　occupied　by　salt　water。　Then　the　intervening　land　sunk　down；　we　must　suppose　the　land　that　now　constitutes　Aru　to　have　remained　nearly　stationary；　a　not　very　improbable　supposition；　when　we　consider　the　great　extent　of　the　shallow　sea；　and　the　very　small　amount　of　depression　the　land　need　have　undergone　to　produce　it。

But　the　fact　of　the　Aru　Islands　having　once　been　connected　with　New　Guinea　does　not　rest　on　this　evidence　alone。　There　is　such　a　striking　resemblance　between　the　productions　of　the　two　countries　as　only…　exists　between　portions　of　a　common　territory。　I　collected　one　hundred　species　of　land…birds　in　the　Aru　Islands；　and　about　eighty　of　them；　have　been　found　on　the　mainland　of　New　Guinea。　Among　these　are　the　great　wingless　cassowary；　two　species　of　heavy　brush　turkeys；　and　two　of　short　winged　thrushes；　which　could　certainly　not　have　passed　over　the　150　miles　of　open　sea　to　the　coast　of　New　Guinea。　This　barrier　is　equally　effectual　in　the　case　of　many　other　birds　which　live　only　in　the　depths　of　the　forest；　as　the　kinghunters　（Dacelo　gaudichaudi）；　the　fly…catching　wrens　（Todopsis）；　the　great　crown　pigeon　（Goura　coronata）；　and　the　small　wood　doves　（Ptilonopus　perlatus；　P。　aurantiifrons；　and　P。　coronulatus）。　Now；　to　show　the　real　effect　of　such　barrier；　let　us　take　the　island　of　Ceram；　which　is　exactly　the　same　distance　from　New　Guinea；　but　separated　from　it　by　a　deep　sea。　Cut　of　about　seventy　land…birds　inhabiting　Ceram；　only　fifteen　are　found　in　New　Guinea；　and　none　of　these　are　terrestrial　or　forest…haunting　species。　The　cassowary　is　distinct；　the　kingfishers；　parrots；　pigeons；　flycatchers；　honeysuckers；　thrushes；　and　cuckoos；　are　almost　always　quite　distinct　species。　More　than　this；　at　least　twenty　genera；　which　are　common　to　New　Guinea　and　Aru；　do　not　extend　into　Ceram；　indicating　with　a　force　which　every　naturalist　will　appreciate；　that　the　two　latter　countries　have　received　their　faunas　in　a　radically　different　manner。　Again；　a　true　kangaroo　is　found　in　Aru；　and　the　same　species　occurs　in　Mysol；　which　is　equally　Papuan　in　its　productions；　while　either　the　same；　or　one　closely　allied　to　it；　inhabits　New　Guinea；　but　no　such　animal　is　found　in　Ceram；　which　is　only　sixty　miles　from　Mysol。　Another　small　marsupial　animal　（Perameles　doreyanus）　is　common　to　Aru　and　New　Guinea。　The　insects　show　exactly　the　same　results。　The　butterflies　of　Aru　are　all　either　New　Guinea　species；　or　very　slightly　modified　forms；　whereas　those　of　Ceram　are　more　distinct　than　are　the　birds　of　the　two　countries。

It　is　now　generally　admitted　that　we　may　safely　reason　on　such　facts　as　those；　which　supply　a　link　in　the　defective　geological　record。　The　upward　and　downward　movements　which　any　country　has　undergone；　and　the　succession　of　such　movements；　can　be　determined　with　much　accuracy；　but　geology　alone　can　tell　us　nothing　of　lands　which　have　entirely　disappeared　beneath　the　ocean。　Here　physical　geography　and　the　distribution　of　animals　and　plants　are　of　the　greatest　service。　By　ascertaining　the　depth　of　the　seas　separating　one　country　from　another；　we　can　form　some　judgment　of　the　changes　which　are　taking　place。　If　there　are　other　evidences　of　subsidence；　a　shallow　sea　　implies　a　former　connexion　of　the　adjacent　lands；　but　i￡　this　evidence　is　wanting；　or　if　there　is　reason　to　suspect　a　rising　of　the　land；　then　the　shallow　sea　may　be　the　result　of　that　rising；　and　may　indicate　that　the　two　countries　will　be　joined　at　some　future　time；　but　not　that　they　have　previously　been　so。　The　nature　of　the　animals　and　plants　inhabiting　these　countries　will；　however；　almost　always　enable　us　to　determine　this　question。　Mr。　Darwin　has　shown　us　how　we　may　determine　in　almost　every　case；　whether　an　island　has　ever　been　connected　with　a　continent　or　larger　land；　by　the　presence　or　absence　of　terrestrial　Mammalia　and　reptiles。　What　he　terms　〃oceanic　islands　〃possess　neither　of　these　groups　of　animals；　though　they　may　have　a　luxuriant　vegetation；　and　a　fair　number　of　birds；　insects；　and　landshells；　and　we　therefore　conclude　that　they　have　originated　in　mid…ocean；　and　have　never　been　connected　with　the　nearest　masses　of　land。　St。　Helena；　Madeira；　and　New　Zealand　are　examples　of　oceanic　islands。　They　possess　all　other　classes　of　life；　because　these　have　means　of　dispersion　over　wide　spaces　of　sea；　which　terrestrial　mammals　and　birds　have　not；　as　is　fully　explained　in　Sir　Charles　Lyell's　〃Principles　of　Geology；〃　and　Mr。　Darwin's　〃Origin　of　Species。〃　On　the　other　hand；　an　island　may　never　have　been　actually　connected　with　the　adjacent　continents　or　islands；　and　yet　may　possess　representatives　of　all　classes　of　animals；　because　many　terrestrial　mammals　and　some　reptiles　have　the　means　of　passing　over　short　distances　of　sea。　But　in　these　cases　the　number　of　species　that　have　thus　migrated　will　be　very　small；　and　there　will　be　great　deficiencies　even　in　birds　and　flying　insects；　which　we　should　imagine　could　easily　cross　over。　The　island　of　Timor　（as　I　have　already　shown　in　Chapter　XIII）　bears　this　relation　to　Australia；　for　while　it　contains　several　birds　and　insects　of　Australian　forms；　no　Australian　mammal　or　reptile　is　found　in　it；　and　a　great　number　of　the　most　abundant　and　characteristic　forms　of　Australian　birds　and　insects　are　entirely　absent。　Contrast　this　with　the　British　Islands；　in；　which　a　large　proportion　of　the　plants；　insects；　reptiles；　and　Mammalia　of　the　adjacent　parts　of　the　continent　are　fully　represented；　while　there　are　no　remarkable　deficiencies　of　extensive　groups；　such　as　always　occur　when　there　is　reason　to　believe　there　has　been　no　such　connexion。　The　case　of　Sumatra；　Borneo；　and　Java；　and　the　Asiatic　continent　is　equally　clear；　many　large　Mammalia；　terrestrial　birds；　and　reptiles　being　common　to　all；　while　a　large　number　more　are　of　closely　allied　forms。　Now；　geology　has　taught　us　that　this　representation　by　allied　forms　in　the　same　locality　implies　lapse　of　time；　and　we　therefore　infer　that　in　Great　Britain；　where　almost　every　species　is　absolutely　identical　with　those　on　the　Continent；　the　separation　has　been　very　recent；　while　in　Sumatra　and　Java；　where　a　considerable　number　of　the　continental　species　are　represented　by　allied　forms；　the　separation　was　more　remote。

From　these　examples　we　may　see　how　important　a　supplement　to　geological　evidence　is　the　study　of　the　geographical　distribution　of　animals　and　plants；　in　determining　the　former　condition　of　the　earth's　surface；　and　how　impossible　it　is　to　understand　the　former　without　taking　the　latter　into　account。　The　productions　of　the　Aru　Islands　offer　the　strangest　evidence；　that　at　no　very　distant　epoch　they　formed　a　part　of　New　Guinea；　and　the　peculiar　physical　features　which　I　have　described；　indicate　that　they　must　have　stood　at　very　nearly　the　same　level　then　as　they　do　now；　having　been　separated　by　the　subsidence　of　the　great　plain　which　formerly　connected　them　with　it。

Persons　who　have　formed　the　usual　ideas　of　the　vegetation　of　the　tropics　who　picture　to　themselves　the　abundance　and　brilliancy　of　the　flowers；　and　the　magnificent　appearance　of　hundreds　of　forest　trees　covered　with　masses　of　coloured　blossoms；　will　be　surprised　to　hear；　that　though　vegetation　in　Aru　is　highly　luxuriant　and　varied；　and　would　afford　abundance　of　fine　and　curious　plants　to　adorn　our　hothouses；　yet　bright　and　showy　flowers　are；　as　a　general　rule；　altogether　absent；　or　so　very　scarce　as　to　produce　no　effect　whatever　on　the　general　scenery。　To　give　particulars：　I　have　visited　five　distinct　localities　in　the　islands；　I　have　wandered　daily　in　the　forests；　and　have　passed　along　upwards　of　a　hundred　miles　of　coast　and　river　during　a　period　of　six　months；　much　of　it　very　fine　weather；　and　till　just　as　I　was　about　to　leave；　I　never　saw　a　single　plant　of　striking　brilliancy　or　beauty；　hardly　a　shrub　equal　to　a　hawthorn；　or　a　climber　equal　to　a　honeysuckle！　It　cannot　be　said　that　the　flowering　season　had　not　arrived；　for　I　saw　many　herbs；　shrubs；　and　forest　trees　in　flower；　but　all　had　blossoms　of　a　green　or　greenish…white　tint；　not　superior　to　our　lime…trees。　Here　and　there　on　the　river　banks　and　coasts　are　a　few　Convolvulaceae；　not　equal　to　our　garden　Ipomaeas；　and　in　the　deepest　shades　of　the　forest　some　fine　scarlet　and　purple　Zingiberaceae；　but　so　few　and　scattered　as　to　be　nothing　amid　the　mass　of　green　and　flowerless　vegetation。　Yet　the　noble