darwin and modern science-第115节

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ute；　Dr　G。J。　Hindewho　has　a　wide　experience　in　the　study　of　organisms　by　sectionsand　he　was　aided　at　all　points　by　specialists　in　the　British　Museum　of　Natural　History　and　by　other　naturalists。　　Nor　were　the　chemical　and　other　problems　neglected。

The　verdict　arrived　at；　after　this　most　exhaustive　study　of　a　series　of　cores　obtained　from　depths　twice　as　great　as　that　thought　necessary　by　Darwin；　was　as　follows：〃The　whole　of　the　cores　are　found　to　be　built　up　of　those　organisms　which　are　seen　forming　coral…reefs　near　the　surface　of　the　oceanmany　of　them　evidently　in　situ；　and　not　the　slightest　indication　could　be　detected；　by　chemical　or　microscopic　means；　which　suggested　the　proximity　of　non…calcareous　rocks；　even　in　the　lowest　portions　brought　up。〃

But　this　was　not　all。　　Professor　David　succeeded　in　obtaining　the　aid　of　a　very　skilful　engineer　from　Australia；　while　the　Admiralty　allowed　Commander　F。C。D。　Sturdee　to　take　a　surveying　ship　into　the　lagoon　for　further　investigations。　　By　very　ingenious　methods；　and　with　great　perseverance；　two　borings　were　put　down　in　the　midst　of　the　lagoon　to　the　depth　of　nearly　200　feet。　　The　bottom　of　the　lagoon；　at　the　depth　of　101　1/2　feet　from　sea…　level；　was　found　to　be　covered　with　remains　of　the　calcareous；　green　sea…　weed　Halimeda；　mingled　with　many　foraminifera；　but　at　a　depth　of　163　feet　from　the　surface　of　the　lagoon　the　boring　tools　encountered　great　masses　of　coral；　which　were　proved　from　the　fragments　brought　up　to　belong　to　species　that　live　within　AT　MOST　120　feet　from　the　surface　of　the　ocean；　as　admitted　by　all　zoologists。　　（〃The　Atoll　of　Funafuti；　Report　of　the　Coral　Reef　Committee　of　the　Royal　Society〃；　London；　1904。）

Darwin's　theory；　as　is　well　known；　is　based　on　the　fact　that　the　temperature　of　the　ocean　at　any　considerable　depth　does　not　permit　of　the　existence　and　luxuriant　growth　of　the　organisms　that　form　the　reefs。　　He　himself　estimated　this　limit　of　depth　to　be　from　120　to　130　feet；　Dana；　as　an　extreme；　150　feet；　while　the　recent　very　prolonged　and　successful　investigations　of　Professor　Alexander　Agassiz　in　the　Pacific　and　Indian　Oceans　lead　him　also　to　assign　a　limiting　depth　of　150　feet；　the　EFFECTIVE；　REEF…FORMING　CORALS；　however；　flourishing　at　a　much　smaller　depth。　　Mr　Stanley　Gardiner　gives　for　the　most　important　reef…forming　corals　depths　between　30　and　90　feet；　while　a　few　are　found　as　low　as　120　feet　or　even　180　feet。

It　will　thus　be　seen　that　the　verdict　of　Funafuti　is　clearly　and　unmistakeably　in　favour　of　Darwin's　theory。　　It　is　true　that　some　zoologists　find　a　difficulty　in　realising　a　slow　sinking　of　parts　of　the　ocean　floor；　and　have　suggested　new　and　alternative　explanations：　　but　geologists　generally；　accepting　the　proofs　of　slow　upheaval　in　some　areas　as　shown　by　the　admirable　researches　of　Alexander　Agassizconsider　that　it　is　absolutely　necessary　to　admit　that　this　elevation　is　balanced　by　subsidence　in　other　areas。　　If　atolls　and　barrier…reefs　did　not　exist　we　should　indeed　be　at　a　great　loss　to　frame　a　theory　to　account　for　their　absence。

After　finishing　his　book　on　Coral…reefs；　Darwin　made　his　summer　excursion　to　North　Wales；　and　prepared　his　important　memoir　on　the　glaciers　of　that　district：　　but　by　October　（1842）　we　find　him　fairly　settled　at　work　upon　the　second　volume　of　his　〃Geology　of　the　'Beagle'Geological　Observations　on　the　Volcanic　Islands；　visited　during　the　Voyage　of　H。M。S。　'Beagle'〃。　　The　whole　of　the　year　1843　was　devoted　to　this　work；　but　he　tells　his　friend　Fox　that　he　could　〃manage　only　a　couple　of　hours　per　day；　and　that　not　very　regularly。〃　　（〃L。L。〃　I。　page　321。）　　Darwin's　work　on　the　various　volcanic　islands　examined　by　him　had　given　him　the　most　intense　pleasure；　but　the　work　of　writing　the　book　by　the　aid　of　his　notes　and　specimens　he　found　〃uphill　work；〃　especially　as　he　feared　the　book　would　not　be　read；　〃even　by　geologists。〃　　（Loc。　cit。）

As　a　matter　of　fact　the　work　is　full　of　the　most　interesting　observations　and　valuable　suggestions；　and　the　three　editions　（or　reprints）　which　have　appeared　have　proved　a　most　valuable　addition　to　geological　literature。　　It　is　not　necessary　to　refer　to　the　novel　and　often　very　striking　discoveries　described　in　this　well…known　work。　　The　subsidence　beneath　volcanic　vents；　the　enormous　denudation　of　volcanic　cones　reducing　them　to　〃basal　wrecks；〃　the　effects　of　solfatarric　action　and　the　formation　of　various　minerals　in　the　cavities　of　rocksall　of　these　subjects　find　admirable　illustration　from　his　graphic　descriptions。　　One　of　the　most　important　discussions　in　this　volume　is　that　dealing　with　the　〃lamination〃　of　lavas　as　especially　well　seen　in　the　rocks　of　Ascension。　　Like　Scrope；　Darwin　recognised　the　close　analogy　between　the　structure　of　these　rocks　and　those　of　metamorphic　origina　subject　which　he　followed　out　in　the　volume　〃Geological　Observations　on　South　America〃。

Of　course　in　these　days；　since　the　application　of　the　microscope　to　the　study　of　rocks　in　thin　sections；　Darwin's　nomenclature　and　descriptions　of　the　petrological　characters　of　the　lavas　appear　to　us　somewhat　crude。　　But　it　happened　that　the　〃Challenger〃　visited　most　of　the　volcanic　islands　described　by　Darwin；　and　the　specimens　brought　home　were　examined　by　the　eminent　petrologist　Professor　Renard。　　Renard　was　so　struck　with　the　work　done　by　Darwin；　under　disadvantageous　conditions；　that　he　undertook　a　translation　of　Darwin's　work　into　French；　and　I　cannot　better　indicate　the　manner　in　which　the　book　is　regarded　by　geologists　than　by　quoting　a　passage　from　Renard's　preface。　　Referring　to　his　own　work　in　studying　the　rocks　brought　home　by　the　〃Challenger〃　（Renard's　descriptions　of　these　rocks　are　contained　in　the　〃Challenger　Reports〃。　　Mr　Harker　is　supplementing　these　descriptions　by　a　series　of　petrological　memoirs　on　Darwin's　specimens；　the　first　of　which　appeared　in　the　〃Geological　Magazine〃　for　March；　1907。）；　he　says：

〃Je　dus；　en　me　livrant　a　ces　recherches；　suivre　ligne　par　ligne　les　divers　chapitres　des　〃Observations　geologiques〃　consacrees　aux　iles　de　l'Atlantique；　oblige　que　j'etais　de　comparer　d'une　maniere　suivie　les　resultats　auxquels　j'etais　conduit　avec　ceux　de　Darwin；　qui　servaient　de　controle　a　mes　constatations。　　Je　ne　tardai　pas　a　eprouver　une　vive　admiration　pour　ce　chercheur　qui；　sans　autre　appareil　que　la　loupe；　sans　autre　reaction　que　quelques　essais　pyrognostiques；　plus　rarement　quelques　mesures　au　goniometre；　parvenait　a　discerner　la　nature　des　agregats　mineralogiques　les　plue　complexes　et　les　plus　varies。　　Ce　coup　d'oeil　qui　savait　embrasser　de　si　vastes　horizons；　penetre　ici　profondement　tous　les　details　lithologiques。　　Avec　quelle　surete　et　quelle　exactitude　la　structure　et　la　composition　des　roches　ne　sont'elles　pas　determinees；　l'origne　de　ces　masses　minerales　deduite　et　confirmee　par　l'etude　comparee　des　manifestations　volcaniques　d'autres　regions；　avec　quelle　science　les　relations　entre　les　faits　qu'il　decouvre　et　ceux　signales　ailleurs　par　ses　devanciers　ne　sont'elles　pas　etablies；　et　comme　voici　ebranlees　les　hypotheses　regnantes；　admises　sans　preuves；　celles；　par　exemple；　des　crateres　de　soulevement　et　de　la　differenciation　radicale　des　phenomenes　plutoniques　et　volcaniques！　　Ce　qui　acheve　de　donner　a　ce　livre　un　incomparable　merite；　ce　sont　les　idees　nouvelles　qui　s'y　trouvent　en　germe　et　jetees　la　comme　au　hasard　ainsi　qu'un　superflu　d'abondance　intellectuelle　inepuisable。〃　　（〃Observations　Geologiques　sur　les　Iles　Volcaniques。。。〃；　Paris；　1902；　pages　vi。；　vii。）

While　engaged　in　his　study　of　banded　lavas；　Darwin　was　struck　with　the　analogy　of　their　structure　with　that　of　glacier　ice；　and　a　note　on　the　subject；　in　the　form　of　a　letter　addressed　to　Professor　J。D。　Forbes；　was　published　in　the　〃Proceedings　of　the　Royal　Society　of　Edinburgh〃。　　（Vol。　II。　（1844…5）；　pages　17；　18。）

From　April；　1832；　to　September；　1835；　Darwin　had　been　occupied　in　examining　the　coast　or　making　inland　journeys　in　the　interior　of　the　South　American　continent。　　Thus　while　eighteen　months　were　devoted；　at　the　beginning　and　end　of　the　voyage　to　the　study　of　volcanic　islands　and　coral…reefs；　no　less　than　three　and　a　half　years　were　given　to　South　American　geology。　　The　heavy　task　of　dealing　with　the　notes　and　specimens　accumulated　during　that　long　period　was　left　by　Darwin　to　the　last。　　Finishing　the　〃Volcanic　Islands〃　on　February　14th；　1844；　he；　in　July　of　the　same　year；　commenced　the　preparation　of　two　important　works　which　engaged　him　till　near　the　end　of　the　year　1846。　　The　first　was　his　〃Geological　Observations　on　South　America〃；　the　second　a　recast　of　his　〃Journal〃；　published　under　the　short　title　of　〃A　Naturalist's　Voyage　round　the　World〃。

The　first　of　these　works　contains　an　immense　amount　of　information　collected　by　the　author　under　great　difficulties　and　not　unfrequently　at　considerable　risk　to　life　and　health。　　No　sooner　had　Darwin　landed　in　South　America　than　two　sets　of　phenomena　powerfully　arrested　his　attention。　　The　first　of　these　was　the　occurrence　of　great　masses　of　red　mud　containing　bones　and　shells；　which　afforded　striking　evidence　that　the　whole　continent　had　shared　in　a　series　of　slow　and　gradual　but　often　interrupted　movements。　The　second　related　to　the　great　masses　of　crystal