South American Geology_第1章_无广告免费看-丁香书院

　　AlthoughinsomerespectsmoretechnicalintheirsubjectsandstylethanDarwin’s“Journal，“thebooksherereprintedwillneverlosetheirvalueandinterestfortheoriginalityoftheobservationstheycontain。Manypartsofthemareadmirablyadaptedforgivinganinsightintoproblemsregardingthestructureandchangesoftheearth’ssurface，andinfacttheyformacharmingintroductiontophysicalgeologyandphysiographyintheirapplicationtospecialdomains。Thebooksthemselvescannotbeobtainedformanytimesthepriceofthepresentvolume，andboththegeneralreader，whodesirestoknowmoreofDarwin’swork，andthestudentofgeology，whonaturallywishestoknowhowamastermindreasonedonmostimportantgeologicalsubjects，willbegladoftheopportunityofpossessingtheminaconvenientandcheapform。
　　Thethreeintroductions，whichmyfriendProfessorJuddhaskindlyfurnished，givecriticalandhistoricalinformationwhichmakesthiseditionofspecialvalue。
　　G。T。B。
　　TABLEOFCONTENTS。
　　CRITICALINTRODUCTION。
　　CHAPTERI——ONTHEELEVATIONOFTHEEASTERNCOASTOFSOUTHAMERICA。
　　UpraisedshellsofLaPlata——BahiaBlanca，Sand-dunesandPumice-pebbles——
　　Step-formedplainsofPatagonia，withupraisedshells——Terrace-boundedvalleyofSantaCruz，formerlyasea-strait——UpraisedshellsofTierradelFuego——Lengthandbreadthoftheelevatedarea——Equabilityofthemovements，asshownbythesimilarheightsoftheplains——Slownessoftheelevatoryprocess——Modeofformationofthestep-formedplains——Summary——
　　GreatshingleformationofPatagonia;itsextent，origin，anddistribution——Formationofsea-cliffs。
　　CHAPTERII——ONTHEELEVATIONOFTHEWESTERNCOASTOFSOUTHAMERICA。
　　ChonosArchipelago——Chiloe，recentandgradualelevationof，traditionsoftheinhabitantsonthissubject——Concepcion，earthquakeandelevationof——
　　VALPARAISO，greatelevationof，upraisedshells，earthormarineorigin，gradualriseofthelandwithinthehistoricalperiod——COQUIMBO，elevationof，inrecenttimes;terracesofmarineorigin，theirinclination，theirescarpmentsnothorizontal——Guasco，gravelterracesof——Copiapo——PERU——
　　UpraisedshellsofCobija，Iquique，andArica——Lima，shell-bedsandsea-
　　beachonSanLorenzo——Humanremains，fossilearthenware，earthquakedebacle，recentsubsidence——Onthedecayofupraisedshells——Generalsummary。
　　CHAPTERIII——ONTHEPLAINSANDVALLEYSOFCHILE：——SALIFEROUSSUPERFICIAL
　　DEPOSITS。
　　Basin-likeplainsofChile;theirdrainage，theirmarineorigin——Marksofsea-actionontheeasternflanksoftheCordillera——Slopingterrace-likefringesofstratifiedshinglewithinthevalleysoftheCordillera;theirmarineorigin——BouldersinthevalleyofCachapual——HorizontalelevationoftheCordillera——Formationofvalleys——Bouldersmovedbyearthquake-
　　waves——Salinesuperficialdeposits——BedofnitrateofsodaatIquique——
　　Salineincrustations——Salt-lakesofLaPlataandPatagonia;purityofthesalt;itsorigin。
　　CHAPTERIV——ONTHEFORMATIONSOFTHEPAMPAS。
　　Mineralogicalconstitution——Microscopicalstructure——BuenosAyres，shellsembeddedintosca-rock——BuenosAyrestotheColorado——S。Ventana——BahiaBlanca;M。Hermoso，bonesandinfusoriaof;P。Alta，shells，bones，andinfusoriaof;co-existenceoftherecentshellsandextinctmammifers——
　　BuenosAyrestoSt。Fe——SkeletonsofMastodon——Infusoria——Inferiormarinetertiarystrata，theirage——Horse’stooth。BANDAORIENTAL——
　　SuperficialPampeanformation——Inferiortertiarystrata，variationof，connectedwithvolcanicaction;MacraucheniaPatachonicaatS。JulianinPatagonia，ageof，subsequenttolivingmolluscaandtotheerraticblockperiod。SUMMARY——AreaofPampeanformation——Theoriesoforigin——Sourceofsediment——Estuaryorigin——Contemporaneouswithexistingmollusca——
　　Relationstounderlyingtertiarystrata。Ancientdepositofestuaryorigin——ElevationandsuccessivedepositionofthePampeanformation——
　　Numberandstateoftheremainsofmammifers;theirhabitation，food，extinction，andrange——Conclusion——SupplementonthethicknessofthePampeanformation——LocalitiesinPampasatwhichmammiferousremainshavebeenfound。
　　CHAPTERV——ONTHEOLDERTERTIARYFORMATIONSOFPATAGONIAANDCHILE。
　　RioNegro——S。Josef——PortDesire，whitepumiceousmudstonewithinfusoria——PortS。Julian——SantaCruz，basalticlavaof——P。Gallegos——
　　EasternTierradelFuego;leavesofextinctbeech-trees——SummaryonthePatagoniantertiaryformations——TertiaryformationsoftheWesternCoast——
　　ChonosandChiloegroups，volcanicrocksof——Concepcion——Navidad——
　　Coquimbo——Summary——Ageofthetertiaryformations——Linesofelevation——
　　Silicifiedwood——ComparativerangesoftheextinctandlivingmolluscaontheWestCoastofS。America——Climateofthetertiaryperiod——OnthecausesoftheabsenceofrecentconchiferousdepositsonthecoastsofSouthAmerica——Onthecontemporaneousdepositionandpreservationofsedimentaryformations。
　　CHAPTERVI——PLUTONICANDMETAMORPHICROCKS：——CLEAVAGEANDFOLIATION。
　　Brazil，Bahia，gneisswithdisjointedmetamorphoseddikes——Strikeoffoliation——RiodeJaneiro，gneiss-granite，embeddedfragmentin，decompositionof——LaPlata，metamorphicandoldvolcanicrocksof——S。
　　Ventana——ClaystoneporphyryformationofPatagonia;singularmetamorphicrocks;pseudo-dikes——FalklandIslands，palaeozoicfossilsof——TierradelFuego，clay-slateformation，cretaceousfossilsof;cleavageandfoliation;
　　formofland——ChonosArchipelago，mica-schists，foliationdisturbedbygraniticaxis;dikes——Chiloe——Concepcion，dikes，successiveformationof——CentralandNorthernChile——Concludingremarksoncleavageandfoliation——Theircloseanalogyandsimilarorigin——Stratificationofmetamorphicschists——Foliationofintrusiverocks——Relationofcleavageandfoliationtothelinesoftensionduringmetamorphosis。
　　CHAPTERVII——CENTRALCHILE：——STRUCTUREOFTHECORDILLERA。
　　CentralChile——BasalformationsoftheCordillera——Originoftheporphyriticclay-stoneconglomerate——Andesite——Volcanicrocks——SectionoftheCordillerabythePeuquenesorPortilloPass——Greatgypseousformation——Peuquenesline;thicknessofstrata，fossilsof——Portilloline——Conglomerate，orthiticgranite，mica-schist，volcanicrocksof——
　　ConcludingremarksonthedenudationandelevationofthePortilloline——
　　SectionbytheCumbre，orUspallataPass——Porphyries——Gypseousstrata——
　　SectionnearthePuentedelInca;fossilsof——Greatsubsidence——Intrusiveporphyries——PlainofUspallata——SectionoftheUspallatachain——
　　Structureandnatureofthestrata——Silicifiedverticaltrees——Greatsubsidence——Graniticrocksofaxis——ConcludingremarksontheUspallatarange;originsubsequenttothatofthemainCordillera;twoperiodsofsubsidence;comparisonwiththePortillochain。
　　CHAPTERVIII——NORTHERNCHILE——CONCLUSION。
　　SectionfromIllapeltoCombarbala;gypseousformationwithsilicifiedwood——Panuncillo——Coquimbo;minesofArqueros;sectionupvalley;
　　fossils——Guasco，fossilsof——Copiapo，sectionupvalley;LasAmolanas，silicifiedwood——Conglomerates，natureofformerland，fossils，thicknessofstrata，greatsubsidence——ValleyofDespoblado，fossils，tufaceousdeposit，complicateddislocationsof——Relationsbetweenancientorificesoferuptionandsubsequentaxesofinjection——Iquique，Peru，fossilsof，salt-deposits——Metalliferousveins——Summaryontheporphyriticconglomerateandgypseousformations——Greatsubsidencewithpartialelevationsduringthecretaceo-ooliticperiod——OntheelevationandstructureoftheCordillera——Recapitulationonthetertiaryseries——
　　Relationbetweenmovementsofsubsidenceandvolcanicaction——Pampeanformation——Recentelevatorymovements——Long-continuedvolcanicactionintheCordillera——Conclusion。
　　INDEX。
　　GEOLOGICALOBSERVATIONSONSOUTHAMERICA
　　BY
　　CHARLESDARWIN。
　　CRITICALINTRODUCTION。
　　Oftheremarkable“trilogy“constitutedbyDarwin’swritingswhichdealwiththegeologyofthe“Beagle，“thememberwhichhasperhapsattractedleastattention，uptothepresenttimeisthatwhichtreatsofthegeologyofSouthAmerica。TheactualwritingofthisbookappearstohaveoccupiedDarwinashorterperiodthaneitheroftheothervolumesoftheseries;hisdiaryrecordsthattheworkwasaccomplishedwithintenmonths，namely，betweenJuly1844andApril1845;butthebookwasnotactuallyissuedtilllateintheyearfollowing，theprefacebearingthedate“September1846。”
　　Altogether，asDarwininformsusinhis“Autobiography，“thegeologicalbooks“consumedfourandahalfyears’steadywork，“mostoftheremainderofthetenyearsthatelapsedbetweenthereturnofthe“Beagle，“andthecompletionofhisgeologicalbooksbeing，itissadtorelate，“lostthroughillness！”
　　Concerningthe“GeologicalObservationsonSouthAmerica，“DarwinwrotetohisfriendLyell，asfollows：——“Myvolumewillbeabout240pages，dreadfullydull，yetmuchcondensed。Ithinkwheneveryouhavetimetolookthroughit，youwillthinkthecollectionoffactsontheelevationofthelandandontheformationofterracesprettygood。”
　　“Muchcondensed“istheverdictthateveryonemustendorse，onrisingfromtheperusalofthisremarkablebook;butbynomeans“dull。”ThethreeandahalfyearsfromApril1832toSeptember1835，werespentbyDarwininSouthAmerica，andweredevotedtocontinuousscientificwork;theproblemshedealtwithwereeitherpurelygeologicalorthosewhichconstitutetheborderlandbetweenthegeologicalandbiologicalsciences。Itisimpossibletoreadthejournalwhichhekeptduringthistimewithoutbeingimpressedbytheconvictionthatitcontainsallthegermsofthoughtwhichafterwardsdevelopedintothe“OriginofSpecies。”ButitisequallyevidentthatafterhisreturntoEngland，biologicalspeculationsgraduallybegantoexerciseamoreexclusiveswayoverDarwin’smind，andtendedtodispossessgeology，whichduringtheactualperiodofthevoyagecertainlyengrossedmostofhistimeandattention。ThewonderfulseriesofobservationsmadeduringthosethreeandahalfyearsinSouthAmericacouldscarcelybedonejusticeto，inthe240pagesdevotedtotheirexposition。ThatheexecutedtheworkofpreparingthebookonSouthAmericainsomewhatthemannerofatask，isshownbymanyreferencesinhisletters。WritingtoSirJosephHookerin1845，hesays，“IhopethisnextsummertofinishmySouthAmericanGeology，thentogetoutalittleZoology，andHURRAHFORMYSPECIESWORK！”
　　Itwouldseemthatthefeelingofdisappointment，whichDarwinsooftenexperiencedincomparingabookwhencompleted，withtheobservationsandspeculationswhichhadinspiredit，wasmorekeenlyfeltinthecaseofhisvolumeonSouthAmericathananyother。Toonefriendhewrites，“Ihaveoflatebeenslavingextrahard，tothegreatdiscomfitureofwretcheddigestiveorgans，atSouthAmerica，andthankallthefates，Ihavedonethree-fourthsofit。WritingplainEnglishgrowswithmemoreandmoredifficult，andneverattainable。Asforyourpretendingthatyouwillreadanythingsodullasmypuregeologicaldescriptions，laynotsuchaflatteringunctiononmysoul，foritisincredible。”Toanotherfriendhewrites，“Youdonotknowwhatyouthreatenwhenyouproposetoreadit——itispurelygeological。Isaidtomybrother，’Youwillofcoursereadit，’
　　andhisanswerwas，’Uponmylife，Iwouldsoonerevenbuyit。’“
　　Inspiteofthesedisparagingremarks，however，wearestronglyinclinedtobelievethatthisbook，despisedbyitsauthor，andneglectedbyhiscontemporaries，willintheendbeadmittedtobeoneofDarwin’schieftitlestofame。Itis，perhaps，anunfortunatecircumstancethatthegreatsuccesswhichheattainedinbiologybythepublicationofthe“OriginofSpecies“has，tosomeextent，overshadowedthefactthatDarwin’sclaimsasageologist，areoftheveryhighestorder。Itisnottoomuchtosaythat，hadDarwinnotbeenageologist，the“OriginofSpecies“couldneverhavebeenwrittenbyhim。Butapartfromthosegeologicalquestions，whichhaveanimportantbearingonbiologicalthoughtandspeculation，suchastheproofsofimperfectioninthegeologicalrecord，therelationsofthelatertertiaryfaunastotherecentonesinthesameareas，andtheapparentinterminglingoftypesbelongingtodistantgeologicalepochs，whenwestudythepalaeontologyofremotedistricts，——thereareotherpurelygeologicalproblems，uponwhichthecontributionsmadebyDarwinareoftheveryhighestvalue。IbelievethattheverdictofthehistoriansofsciencewillbethatifDarwinhadnottakenaforemostplaceamongthebiologistsofthiscentury，hispositionasageologistwouldhavebeenanalmostequallycommandingone。
　　ButinthecaseofDarwin’sprincipalgeologicalwork——thatrelatingtotheoriginofthecrystallineschists，——geologistswerenotatthetimepreparedtoreceivehisrevolutionaryteachings。Theinfluenceofpowerfulauthoritywaslongexercised，indeed，tostiflehisteaching，andonlynow，whenthisunfortunateoppositionhasdisappeared，isthetruenatureandimportanceofDarwin’spurelygeologicalworkbeginningtoberecognised。
　　Thetwofirstchaptersofthe“GeologicalObservationsonSouthAmerica，“
　　dealwiththeproofswhichexistofgreat，butfrequentlyinterrupted，movementsofelevationduringveryrecentgeologicaltimes。Inconnectionwiththissubject，Darwin’sparticularattentionwasdirectedtotherelationsbetweenthegreatearthquakesofSouthAmerica——ofsomeofwhichhehadimpressiveexperience——andthepermanentchangesofelevationwhichweretakingplace。Hewasmuchstruckbytherapiditywithwhichtheevidenceofsuchgreatearthmovementsisfrequentlyobliterated;andespeciallywiththeremarkablewayinwhichtheactionofrain-water，percolatingthroughdepositsontheearth’ssurface，removesalltracesofshellsandothercalcareousorganisms。Itwastheseconsiderationswhichweretheparentsofthegeneralisationthatapalaeontologicalrecordcanonlybepreservedduringthoseperiodsinwhichlong-continuedslowsubsidenceisgoingon。Thisinturn，ledtothestillwiderandmoresuggestiveconclusionthatthegeologicalrecordasawholeis，andnevercanbemorethan，aseriesofmoreorlessisolatedfragments。Therecognitionofthisimportantfactconstitutesthekeystonetoanytheoryofevolutionwhichseekstofindabasisintheactualstudyofthetypesoflifethathaveformerlyinhabitedourglobe。
　　Inhisthirdchapter，Darwingivesanumberofinterestingfacts，collectedduringhisvisitstotheplainsandvalleysofChili，whichbearonthequestionoftheoriginofsaliferousdeposits——theaccumulationofsalt，gypsum，andnitrateofsoda。Thisisaproblemthathasexcitedmuchdiscussionamonggeologists，andwhich，inspiteofmanyvaluableobservations，stillremainstoagreatextentveryobscure。AmongtheimportantconsiderationsinsisteduponbyDarwinisthatrelatingtotheabsenceofmarineshellsinbedsassociatedwithsuchdeposits。Hejustlyarguesthatifthestratawereformedinshallowwaters，andthenexposedbyupheavaltosubaerialaction，allshellsandothercalcareousorganismswouldberemovedbysolution。
　　FollowingLyell’smethod，Darwinproceedsfromthestudyofdepositsnowbeingaccumulatedontheearth’ssurface，tothosewhichhavebeenformedduringthemorerecentperiodsofthegeologicalhistory。
　　HisaccountofthegreatPampeanformation，withitswonderfulmammalianremains——Mastodon，Toxodon，Scelidotherium，Macrauchenia，Megatherium，Megalonyx，Mylodon，andGlyptodon——thisfullofinterest。HisdiscoveryoftheremainsofatrueEquusaffordedaremarkableconfirmationofthefact——
　　alreadymadeoutinNorthAmerica——thatspeciesofhorsehadexistedandbecomeextinctintheNewWorld，beforetheirintroductionbytheSpaniardsinthesixteenthcentury。FullyperceivingtheimportanceofthemicroscopeinstudyingthenatureandoriginofsuchdepositsasthoseofthePampas，DarwinsubmittedmanyofhisspecimensbothtoDr。Carpenterinthiscountry，andtoProfessorEhrenberginBerlin。Manyveryimportantnotesonthemicroscopicorganismscontainedintheformationwillbefoundscatteredthroughthechapter。
　　Darwin’sstudyoftheoldertertiaryformations，withtheirabundantshells，andtheirrelicsofvegetablelifeburiedundergreatsheetsofbasalt，ledhimtoconsidercarefullythequestionofclimateduringtheseearlierperiods。Inoppositiontoprevalentviewsonthissubject，Darwinpointsoutthathisobservationsareopposedtotheconclusionthatahighertemperatureprevaileduniversallyovertheglobeduringearlygeologicalperiods。Hearguesthat“thecauseswhichgavetotheoldertertiaryproductionsofthequitetemperatezonesofEuropeatropicalcharacter，WEREOFALOCALCHARACTERANDDIDNOTAFFECTTHEWHOLEGLOBE。”
　　Inthis，asinmanysimilarinstances，weseethebeneficialinfluenceofextensivetravelinfreeingDarwin’smindfromprevailingprejudices。Itwasthiswideningofexperiencewhichrenderedhimsoespeciallyqualifiedtodealwiththegreatproblemoftheoriginofspecies，andindoingsotoemancipatehimselffromideaswhichwerereceivedwithunquestioningfaithbygeologistswhosestudieshadbeencircumscribedwithinthelimitsofWesternEurope。
　　IntheCordillerasofNorthernandCentralChili，Darwin，whenstudyingstillolderformations，clearlyrecognisedthattheycontainanadmixtureoftheformsoflife，whichinEuropearedistinctiveoftheCretaceousandJurassicperiodsrespectively。Hewasthusledtoconcludethattheclassificationofgeologicalperiods，whichfairlywellexpressesthefactsthathadbeendiscoveredintheareaswherethesciencewasfirststudied，isnolongercapableofbeingappliedwhenwecometothestudyofwidelydistantregions。Thisimportantconclusionleduptothefurthergeneralisationthateachgreatgeologicalperiodhasexhibitedageographicaldistributionoftheformsofanimalandvegetablelife，comparabletothatwhichprevailsintheexistingfaunaandflora。Tothosewhoarefamiliarwiththeextenttowhichthedoctrineofuniversalformationshasaffectedgeologicalthoughtandspeculation，bothlongbeforeandsincethetimethatDarwinwrote，theimportanceofthisnewstandpointtowhichhewasabletoattainwillbesufficientlyapparent。
　　LiketheideaoftheextremeimperfectionoftheGeologicalRecord，thedoctrineofLOCALgeologicalformationsisfoundpermeatingandmouldingallthepalaeontologicalreasoningsofhisgreatwork。
　　InoneofDarwin’sletters，writtenwhilehewasinSouthAmerica，thereisapassagewehavealreadyquoted，inwhichheexpresseshisinabilitytodecidebetweentherivalclaimsuponhisattentionof“theoldcrystallinegroupofrocks，“and“thesofterfossiliferousbeds“respectively。Thesixthchapteroftheworkbeforeus，entitled“PlutonicandMetamorphicRocks——CleavageandFoliation，“containsabriefsummaryofaseriesofobservationsandreasoningsuponthesecrystallinerocks，whichare，webelieve，calculatedtoeffectarevolutioningeologicalscience，and——
　　thoughtheirvalueandimportancehavelongbeenoverlooked——arelikelytoentitleDarwininthefuturetoapositionamonggeologists，scarcely，ifatall，inferiortothatwhichhealreadyoccupiesamongbiologists。
　　Darwin’sstudiesofthegreatrock-massesoftheAndesconvincedhimofthecloserelationsbetweenthegraniticorPlutonicrocks，andthosewhichwereundoubtedlypouredforthaslavas。Uponhisreturn，hesettowork，withtheaidofProfessorMiller，tomakeacarefulstudyofthemineralscomposingthegranitesandthosewhichoccurinthelavas，andhewasabletoshowthatinallessentialrespectstheyareidentical。Hewasfurtherabletoprovethatthereisacompletegradationbetweenthehighlycrystallineorgraniticrock-masses，andthosecontainingmoreorlessglassymatterbetweentheircrystals，whichconstituteordinarylavas。Theimportanceofthisconclusionwillberealisedwhenwerememberthatitwasthenthecommoncreedofgeologists——andstillcontinuestobesoontheContinent——thatallhighlycrystallinerocksareofgreatgeologicalantiquity，andthattheigneousejectionswhichhavetakenplacesincethebeginningofthetertiaryperiodsdifferessentially，intheircomposition，theirstructure，andtheirmodeofoccurrence，fromthosewhichhavemadetheirappearanceatearlierperiodsoftheworld’shistory。
　　VerycompletelyhavetheconclusionsofDarwinuponthesesubjectsbeenjustifiedbyrecentresearches。InEngland，theUnitedStates，andItaly，examplesofthegradualpassageofrocksoftrulygraniticstructureintoordinarylavashavebeendescribed，andtherealityofthetransitionhasbeendemonstratedbythemostcarefulstudieswiththemicroscope。RecentresearchescarriedoninSouthAmericabyProfessorStelzner，havealsoshowntheexistenceofaclassofhighlycrystallinerocks——the“Andengranites“——whichcombineinthemselvesmanyofthecharacteristicswhichwereoncethoughttobedistinctiveoftheso-calledPlutonicandvolcanicrocks。Noonefamiliarwithrecentgeologicalliterature——eveninGermanyandFrance，wheretheoldviewsconcerningthedistinctionofigneousproductsofdifferentageshavebeenmoststoutlymaintained——canfailtorecognisethefactthattheprinciplescontendedforbyDarwinbidfairatnodistantperiodtowinuniversalacceptanceamonggeologistsallovertheglobe。
　　StillmoreimportantaretheconclusionsatwhichDarwinarrivedwithrespecttotheoriginoftheschistsandgneisseswhichcoversolargeanareainSouthAmerica。
　　Carefullynoting，bytheaidofhiscompassandclinometer，ateverypointwhichhevisited，thedirectionandamountofinclinationoftheparalleldivisionsintheserocks，hewasledtoaveryimportantgeneralisation——
　　namely，thatoververywideareasthedirectionstrikeoftheplanesofcleavageinslates，andoffoliationinschistsandgneisses，remainedconstant，thoughtheamountoftheirinclinationdipoftenvariedwithinwidelimits。Furtherthanthisitappearedthattherewasalwaysaclosecorrespondencebetweenthestrikeofthecleavageandfoliationandthedirectionofthegreataxesalongwhichelevationhadtakenplaceinthedistrict。
　　InTierradelFuego，Darwinfoundstrikingevidencethatthecleavageintersectinggreatmassesofslate-rockswasquiteindependentoftheiroriginalstratification，andcouldoften，indeed，beseencuttingacrossitatrightangles。HewasalsoabletoverifySedgwick’sobservationthat，insomeslates，glossysurfacesontheplanesofcleavagearisefromthedevelopmentofnewminerals，chlorite，epidoteormica，andthatinthiswayacompletegraduationfromslatestotrueschistsmaybetraced。
　　Darwinfurthershowedthatinhighlyschistoserocks，thefoliabendaroundandencircleanyforeignbodiesinthemass，andthatinsomecasestheyexhibitthemosttortuousformsandcomplicatedpuckerings。Heclearlysawthatinallcasestheforcesbywhichthesestrikingphenomenamusthavebeenproducedwerepersistentoverwideareas，andwereconnectedwiththegreatmovementsbywhichtherockshadbeenupheavedandfolded。
　　Thatthedistinctfoliaofquartz，feldspar，mica，andothermineralscomposingthemetamorphicschistscouldnothavebeenseparatelydepositedassedimentwasstronglyinsisteduponbyDarwin;andindoingsoheopposedtheviewgenerallyprevalentamonggeologistsatthattime。Hewasthusdriventotheconclusionthatfoliation，likecleavage，isnotanoriginal，butasuperinducedstructureinrock-masses，andthatitistheresultofre-crystallisation，underthecontrollinginfluenceofgreatpressure，ofthematerialsofwhichtherockwascomposed。
　　InstudyingthelavasofAscension，aswehavealreadyseen，Darwinwasledtorecognisethecircumstancethat，whenigneousrocksaresubjectedtogreatdifferentialmovementsduringtheperiodoftheirconsolidation，theyacquireafoliatedstructure，closelyanalogoustothatofthecrystallineschists。Likehispredecessorinthisfieldofinquiry，Mr。PoulettScrope，CharlesDarwinseemstohavebeengreatlyimpressedbythesefacts，andhearguedfromthemthattherocksexhibitingthefoliatedstructuremusthavebeeninastateofplasticity，likethatofacoolingmassoflava。AtthattimethesuggestiveexperimentsofTresca，Daubree，andothers，showingthatsolidmassesundertheinfluenceofenormouspressurebecomeactuallyplastic，hadnotbeenpublished。HadDarwinbeenawareofthesefactshewouldhaveseenthatitwasnotnecessarytoassumeastateofimperfectsolidityinrock-massesinordertoaccountfortheirhavingyieldedtopressureandtension，and，indoingso，acquiringthenewcharacterswhichdistinguishthecrystallineschists。
　　TheviewsputforwardbyDarwinontheoriginofthecrystallineschistsfoundanableadvocateinMr。DanielSharpe，whoin1852and1854publishedtwopapers，dealingwiththegeologyoftheScottishHighlandsandoftheAlpsrespectively，inwhichheshowedthattheprinciplesarrivedatbyDarwinwhenstudyingtheSouthAmericanrocksaffordacompleteexplanationofthestructureofthetwodistrictsinquestion。
　　But，ontheotherhand，theconclusionsofDarwinandSharpeweremetwiththestrongestoppositionbySirRoderickMurchisonandDr。A。Geikie，whoin1861readapaperbeforetheGeologicalSociety“OntheCoincidencebetweenStratificationandFoliationintheCrystallineRocksoftheScottishHighlands，“inwhichtheyinsistedthattheirobservationsinScotlandtendedtoentirelydisprovetheconclusionsofDarwinthatfoliationinrocksisasecondarystructure，andentirelyindependentoftheoriginalstratificationoftherock-masses。
　　Nowitisamostsignificantcircumstancethat，nosoonerdidtheofficersoftheGeologicalSurveycommencethecarefulanddetailedstudyoftheScottishHighlandsthantheyfoundthemselvescompelledtomakeaformalretractionoftheviewswhichhadbeenputforwardbyMurchisonandGeikieinoppositiontotheconclusionsofDarwin。TheofficersoftheGeologicalSurveyhavecompletelyabandonedtheviewthatthefoliationoftheHighlandrockshasbeendeterminedbytheiroriginalstratification，andadmitthatthestructureistheresultoftheprofoundmovementstowhichtherockshavebeensubjected。Thesameconclusionshaverecentlybeensupportedbyobservationsmadeinmanydifferentdistricts——amongwhichwemayespeciallyrefertothoseofDr。H。ReuschinNorway，andthoseofDr。
　　J。LehmanninSaxony。AtthepresenttimetheargumentssoclearlystatedbyDarwinintheworkbeforeus，have，afterenduringoppositionorneglectforawholegeneration，begunto“triumphallalongtheline，“andwemaylookforwardconfidentlytothenearfuture，whenhisclaimtoberegardedasoneofthegreatestofgeologicaldiscoverersshallbefullyvindicated。
　　JOHNW。JUDD。
　　CHAPTERI。ONTHEELEVATIONOFTHEEASTERNCOASTOFSOUTHAMERICA。
　　UpraisedshellsofLaPlata。
　　BahiaBlanca，Sand-dunesandPumice-pebbles。
　　Step-formedplainsofPatagonia，withupraisedShells。
　　Terrace-boundedValleyofSantaCruz，formerlyaSea-strait。
　　UpraisedshellsofTierradelFuego。
　　Lengthandbreadthoftheelevatedarea。
　　Equabilityofthemovements，asshownbythesimilarheightsoftheplains。
　　Slownessoftheelevatoryprocess。
　　Modeofformationofthestep-formedplains。
　　Summary。
　　GreatShingleFormationofPatagonia;itsextent，origin，anddistribution。
　　Formationofsea-cliffs。
　　InthefollowingVolume，whichtreatsofthegeologyofSouthAmerica，andalmostexclusivelyofthepartssouthwardoftheTropicofCapricorn，I
　　havearrangedthechaptersaccordingtotheageofthedeposits，occasionallydepartingfromthisorder，forthesakeofgeographicalsimplicity。
　　Theelevationofthelandwithintherecentperiod，andthemodificationsofitssurfacethroughtheactionoftheseatowhichsubjectsIpaidparticularattentionwillbefirstdiscussed;Iwillthenpassontothetertiarydeposits，andafterwardstotheolderrocks。Onlythosedistrictsandsectionswillbedescribedindetailwhichappeartometodeservesomeparticularattention;andIwill，attheendofeachchapter，giveasummaryoftheresults。Wewillcommencewiththeproofsoftheupheavaloftheeasterncoastofthecontinent，fromtheRioPlatasouthward;and，intheSecondChapter，followupthesamesubjectalongtheshoresofChileandPeru。
　　OnthenorthernbankofthegreatestuaryoftheRioPlata，nearMaldonado，Ifoundattheheadofalake，sometimesbrackishbutgenerallycontainingfreshwater，abedofmuddyclay，sixfeetinthickness，withnumerousshellsofspeciesstillexistinginthePlata，namely，theAzaralabiata，d’Orbigny，fragmentsofMytiluseduliformis，d’Orbigny，PaludestrinaIsabellei，d’Orbigny，andtheSolenCaribaeus，Lam。whichlastwasembeddedverticallyinthepositioninwhichithadlived。Theseshellslieattheheightofonlytwofeetabovethelake，norwouldtheyhavebeenworthmentioning，exceptinconnectionwithanalogousfacts。
　　AtMonteVideo，Inoticednearthetown，andalongthebaseofthemount，bedsofalivingMytilus，raisedsomefeetabovethesurfaceofthePlata：
　　inasimilarbed，ataheightfromthirteentosixteenfeet，M。Isabellecollectedeightspecies，which，accordingtoM。d’Orbigny，nowliveatthemouthoftheestuary。“Voyagedansl’AmeriqueMerid。：Part。Geolog。”page21。AtColoniadelSacramiento，furtherwestward，Iobservedattheheightofaboutfifteenfeetabovetheriver，thereofquitefreshwater，asmallbedofthesameMytilus，whichlivesinbrackishwateratMonteVideo。NearthemouthofUruguay，andforatleastthirty-fivemilesnorthward，thereareatintervalslargesandytracts，extendingseveralmilesfromthebanksoftheriver，butnotraisedmuchaboveitslevel，aboundingwithsmallbivalves，whichoccurinsuchnumbersthatattheAgraciadotheyaresiftedandburntforlime。ThosewhichIexaminedneartheA。S。Juanweremuchworn：theyconsistedofMactraIsabellei，d’Orbigny，mingledwithfewofVenussinuosa，Lam。bothinhabiting，asIaminformedbyM。d’Orbigny，brackishwateratthemouthofthePlata，nearlyorquiteassaltastheopensea。Theloosesand，inwhichtheseshellsarepacked，isheapedintolow，straight，longlinesofdunes，likethoseleftbytheseaattheheadofmanybays。M。d’Orbignyhasdescribedananalogousphenomenononagreaterscale，nearSanPedroontheriverParana，wherehefoundwidelyextendedbedsandhillocksofsand，withvastnumbersoftheAzaralabiata，attheheightofnearly100feetEnglishabovethesurfaceofthatriver。
　　Ibidpage43。TheAzarainhabitsbrackishwater，andisnotknowntobefoundnearertoSanPedrothanBuenosAyres，distantaboveahundredmilesinastraightline。NearerBuenosAyres，ontheroadfromthatplacetoSanIsidro，thereareextensivebeds，asIaminformedbySirWoodbineParish，oftheAzaralabiata，lyingataboutfortyfeetabovetheleveloftheriver，anddistantbetweentwoandthreemilesfromit。“BuenosAyres“
　　etc。bySirWoodbineParishpage168。Theseshellsarealwaysfoundonthehighestbanksinthedistrict：theyareembeddedinastratifiedearthymass，preciselylikethatofthegreatPampeandeposithereaftertobedescribed。Inonecollectionoftheseshells，thereweresomevalvesoftheVenussinuosa，Lam。thesamespeciesfoundwiththeMactraonthebanksoftheUruguay。SouthofBuenosAyres，nearEnsenada，thereareotherbedsoftheAzara，someofwhichseemtohavebeenembeddedinyellowish，calcareous，semi-crystallinematter;andSirW。ParishhasgivenmefromthebanksoftheArroyodelTristan，situatedinthissameneighbourhood，atthedistanceofaboutaleaguefromthePlata，aspecimenofapale-
　　reddish，calcereo-argillaceousstonepreciselylikepartsofthePampeandeposittheimportanceofwhichfactwillbereferredtoinasucceedingchapter，aboundingwithshellsofanAzara，muchworn，butwhichingeneralformandappearancecloselyresemble，andareprobablyidenticalwith，theA。labiata。Besidestheseshells，cellular，highlycrystallinerock，formedofthecastsofsmallbivalves，isfoundnearEnsenada;andlikewisebedsofsea-shells，whichfromtheirappearanceappeartohavelainonthesurface。SirW。Parishhasgivenmesomeoftheseshells，andM。d’Orbignypronouncesthemtobe：——
　　1。Buccinanopsglobulosum，d’Orbigny。
　　2。Olivancillariaauricularia，d’Orbigny。
　　3。Venusflexuosa，Lam。
　　4。Cytheraeaimperfect。
　　5。MactraIsabellei，d’Orbigny。
　　6。Ostreapulchella，d’Orbigny。
　　Besidesthese，SirW。Parishprocured“BuenosAyres“etc。bySirW。Parishpage168。asnamedbyMr。G。B。Sowerbythefollowingshells：——
　　7。Volutacolocynthis。
　　8。Volutaangulata。
　　9。Buccinumnotspec。？。
　　Allthesespecieswith，perhaps，theexceptionofthelastarerecent，andliveontheSouthAmericancoast。Theseshell-bedsextendfromoneleaguetosixleaguesfromthePlata，andmustliemanyfeetaboveitslevel。Iheard，also，ofbedsofshellsontheSomborombon，andontheRioSalado，atwhichlatterplace，asM。d’Orbignyinformsme，theMactraIsabelleiandVenussinuosaarefound。
　　DuringtheelevationoftheProvincesofLaPlata，thewatersoftheancientestuaryhavebutlittleaffectedwiththeexceptionofthesand-
　　hillsonthebanksoftheParanaandUruguaytheoutlineoftheland。M。
　　Parchappe，however，hasdescribedgroupsofsanddunesscatteredoverthewideextentofthePampassouthwardofBuenosAyresD’Orbigny“VoyageGeolog。”page44。，whichM。d’Orbignyattributeswithmuchprobabilitytotheactionofthesea，beforetheplainswereraisedaboveitslevel。
　　BeforeproceedingtothedistrictssouthwardofLaPlata，itmaybeworthwhilejusttostate，thatthereissomeevidencethatthecoastofBrazilhasparticipatedinasmallamountofelevation。Mr。Burchellinformsme，thathecollectedatSantoslatitude24degreesS。oyster-shells，apparentlyrecent，somemilesfromtheshore，andquiteabovethetidalaction。WestwardofRiodeJaneiro，CaptainElliotisassertedseeHarlan“Med。andPhys。Res。”page35andDr。Meigsin“TransactionsoftheAmericanPhilosophicalSociety“，tohavefoundhumanbones，encrustedwithsea-shells，betweenfifteenandtwentyfeetabovethelevelofthesea。
　　BetweenRiodeJaneiroandCapeFrioIcrossedsandytractsaboundingwithsea-shells，atadistanceofaleaguefromthecoast;butwhetherthesetractshavebeenformedbyupheaval，orthroughthemereaccumulationofdriftsand，Iamnotpreparedtoassert。AtBahialatitude13degreesS。，insomepartsnearthecoast，therearetracesofsea-actionattheheightofabouttwentyfeetaboveitspresentlevel;therearealso，inmanyparts，remnantsofbedsofsandstoneandconglomeratewithnumerousrecentshells，raisedalittleabovethesea-level。Imayadd，thatattheheadofBahiaBaythereisaformation，aboutfortyfeetinthickness，containingtertiaryshellsapparentlyoffresh-waterorigin，nowwashedbytheseaandencrustedwithBalini;thisappearstoindicateasmallamountofsubsidencesubsequenttoitsdeposition。AtPernambucolatitude8degreesS。，inthealluvialortertiarycliffs，surroundingthelowlandonwhichthecitystands，Ilookedinvainfororganicremains，orotherevidenceofchangesinlevel。
　　SOUTHWARDOFTHEPLATA。
　　ThecoastasfarasBahiaBlancainlatitude39degreesS。isformedeitherofahorizontalrangeofcliffs，orofimmenseaccumulationsofsand-dunes。WithinBahiaBlanca，asmallpieceoftableland，abouttwentyfeetabovehigh-watermark，calledPuntaAlta，isformedofstrataofcementedgravelandofredearthymud，aboundingwithshellswithotherslyinglooseonthesurface，andthebonesofextinctmammifers。Theseshells，twentyinnumber，togetherwithaBalanusandtwocorals，areallrecentspecies，stillinhabitingtheneighbouringseas。TheywillbeenumeratedintheFourthChapter，whendescribingthePampeanformation;
　　fiveofthemareidenticalwiththeupraisedonesfromnearBuenosAyres。
　　ThenorthernshoreofBahiaBlancais，inmainpart，formedofimmensesand-dunes，restingongravelwithrecentshells，andranginginlinesparalleltotheshore。Theserangesareseparatedfromeachotherbyflatspaces，composedofstiffimpureredclay，inwhich，atthedistanceofabouttwomilesfromthecoast，Ifoundbydiggingafewminutefragmentsofsea-shells。Thesand-dunesextendseveralmilesinland，andstandonaplain，whichslopesuptoaheightofbetweenonehundredandtwohundredfeet。Numerous，small，well-roundedpebblesofpumiceliescatteredbothontheplainandsand-hillocks：atMonteHermoso，ontheflatsummitofacliff，Ifoundmanyofthemataheightof120feetangularmeasurement
　　abovethelevelofthesea。Thesepumicepebbles，nodoubt，wereoriginallybroughtdownfromtheCordillerabytheriverswhichcrossthecontinent，inthesamewayastheriverNegroancientlybroughtdown，andstillbringsdown，pumice，andastheriverChupatbringsdownscoriae：whenoncedeliveredatthemouthofariver，theywouldnaturallyhavetravelledalongthecoasts，andbeencastupduringtheelevationoftheland，atdifferentheights。Theoriginoftheargillaceousflats，whichseparatetheparallelrangesofsand-dunes，seemsduetothetidesherehavingatendencyasIbelievetheyhaveonmostshoal，protectedcoaststothrowupabarparalleltotheshore，andatsomedistancefromit;thisbargraduallybecomeslarger，affordingabasefortheaccumulationofsand-
　　dunes，andtheshallowspacewithinthenbecomessiltedupwithmud。Therepetitionofthisprocess，withoutanyelevationoftheland，wouldformalevelplaintraversedbyparallellinesofsand-hillocks;duringaslowelevationoftheland，thehillockswouldrestonagentlyinclinedsurface，likethatonthenorthernshoreofBahiaBlanca。Ididnotobserveanyshellsinthisneighbourhoodatagreaterheightthantwentyfeet;andthereforetheageofthesea-driftedpebblesofpumice，nowstandingattheheightof120feet，mustremainuncertain。
　　ThemainplainsurroundingBahiaBlancaIestimatedatfromtwohundredtothreehundredfeet;itinsensiblyrisestowardsthedistantSierraVentana。
　　Thereareinthisneighbourhoodsomeotherandlowerplains，buttheydonotabutoneatthefootoftheother，inthemannerhereaftertobedescribed，socharacteristicofPatagonia。Theplainonwhichthesettlementstandsiscrossedbymanylowsand-dunes，aboundingwiththeminuteshellsofthePaludestrinaaustralis，d’Orbigny，whichnowlivesinthebay。Thislowplainisboundedtothesouth，attheCabezadelBuey，bythecliff-formedmarginofawideplainofthePampeanformation，whichI
　　estimatedatsixtyfeetinheight。Onthesummitofthiscliffthereisarangeofhighsand-dunesextendingseveralmilesinaneastandwestline。
　　SouthwardofBahiaBlanca，theriverColoradoflowsbetweentwoplains，apparentlyfromthirtytofortyfeetinheight。Oftheseplains，thesouthernoneslopesuptothefootofthegreatsandstoneplateauoftheRioNegro;andthenorthernoneagainstanescarpmentofthePampeandeposit;sothattheColoradoflowsinavalleyfiftymilesinwidth，betweentheupperescarpments。Istatethis，becauseonthelowplainatthefootofthenorthernescarpment，Icrossedanimmenseaccumulationofhighsand-dunes，estimatedbytheGauchosatnolessthaneightmilesinbreadth。Thesedunesrangewestwardfromthecoast，whichistwentymilesdistant，tofarinland，inlinesparalleltothevalley;theyareseparatedfromeachotherbyargillaceousflats，preciselylikethoseonthenorthernshoreofBahiaBlanca。Atpresentthereisnosourcewhencethisimmenseaccumulationofsandcouldproceed;butif，asIbelieve，theupperescarpmentsonceformedtheshoresofanestuary，inthatcasethesandstoneformationoftheriverNegrowouldhaveaffordedaninexhaustiblesupplyofsand，whichwouldnaturallyhaveaccumulatedonthenorthernshore，asoneverypartofthecoastopentothesouthwindsbetweenBahiaBlancaandBuenosAyres。
　　AtSanBlas40degrees40’S。alittlesouthofthemouthoftheColorado，M。d’OrbignyfoundfourteenspeciesofexistingshellssixofthemidenticalwiththosefromBahiaBlanca，embeddedintheirnaturalpositions。“Voyage“etc。page54。Fromthezoneofdepthwhichtheseshellsareknowntoinhabit，theymusthavebeenupliftedthirty-twofeet。
　　Healsofound，atfromfifteentotwentyfeetabovethisbed，theremainsofanancientbeach。
　　Tenmilessouthward，but120milestothewest，atPortS。Antonio，theOfficersemployedontheSurveyassuredmethattheysawmanyoldsea-
　　shellsstrewedonthesurfaceoftheground，similartothosefoundonotherpartsofthecoastofPatagonia。AtSanJosef，ninetymilessouthinnearlythesamelongitude，Ifound，abovethegravel，whichcapsanoldtertiaryformation，anirregularbedandhillockofsand，severalfeetinthickness，aboundingwithshellsofPatelladeaurita，MytilusMagellanicus，thelatterretainingmuchofitscolour;FususMagellanicusandavarietyofthesame，andalargeBalanusprobablyB。Tulipa，allnowfoundonthiscoast：Iestimatedthisbedatfromeightytoonehundredfeetabovethelevelofthesea。Tothewestwardofthisbay，thereisaplainestimatedatbetweentwohundredandthreehundredfeetinheight：thisplainseems，frommanymeasurements，tobeacontinuationofthesandstoneplatformoftheriverNegro。Thenextplacesouthward，whereIlanded，wasatPortDesire，340milesdistant;butfromtheintermediatedistrictsI
　　received，throughthekindnessoftheOfficersoftheSurvey，especiallyfromLieutenantStokesandMr。King，manyspecimensandsketches，quitesufficienttoshowthegeneraluniformityofthewholelineofcoast。Imayherestate，thatthewholeofPatagoniaconsistsofatertiaryformation，restingonandsometimessurroundinghillsofporphyryandquartz：thesurfaceiswornintomanywidevalleysandintolevelstep-formedplains，risingoneaboveanother，allcappedbyirregularbedsofgravel，chieflycomposedofporphyriticrocks。Thisgravelformationwillbeseparatelydescribedattheendofthechapter。
　　Myobjectingivingthefollowingmeasurementsoftheplains，astakenbytheOfficersoftheSurvey，is，aswillhereafterbeseen，toshowtheremarkableequabilityoftherecentelevatorymovements。RoundthesouthernpartsofNuevoGulf，asfarastheRiverChupatseventymilessouthwardofSanJosef，thereappeartobeseveralplains，ofwhichthebestdefinedarehererepresented。
　　InthefollowingDiagrams：
　　1。BaselineisLevelofsea。
　　2。Scaleis1/20ofinchto100feetvertical。
　　3。Heightisshowninfeetthus：
　　An。M。alwaysstandsforangularortrigonometricalmeasurement。
　　Ba。M。alwaysstandsforbarometricalmeasurement。
　　Est。alwaysstandsforestimationbytheOfficersoftheSurvey。
　　DIAGRAM1。SECTIONOFSTEP-FORMEDPLAINSSOUTHOFNUEVOGULF。
　　>FromEastsealeveltoWesthigh：
　　Terrace1。80Est。
　　Terrace2。200-220An。M。
　　Terrace3。350An。M。
　　TheupperplainisherewelldefinedcalledTableHills;itsedgeformsaclifforlineofescarpmentmanymilesinlength，projectingoveralowerplain。ThelowestplaincorrespondswiththatatSanJosefwiththerecentshellsonitssurface。Betweenthislowestandtheuppermostplain，thereisprobablymorethanonestep-formedterrace：severalmeasurementsshowtheexistenceoftheintermediateoneoftheheightgiveninDiagram1。
　　DIAGRAM2。SECTIONOFPLAINSINTHEBAYOFST。GEORGE。
　　>FromEastsealeveltoWesthigh：
　　Terrace1。250An。M。
　　Terrace2。330An。M。
　　Terrace3。580An。M。
　　Terraces4，5and6notmeasured。
　　Terrace7。1，200Est。
　　NearthenorthheadlandofthegreatBayofSt。George100milessouthoftheChupat，twowell-markedplainsof250and330feetweremeasured：
　　thesearesaidtosweeproundagreatpartoftheBay。Atitssouthheadland，120milesdistantfromthenorthheadland，the250feetplainwasagainmeasured。Inthemiddleofthebay，ahigherplainwasfoundattwoneighbouringplacesTilliRoadsandC。Marquestobe580feetinheight。
　　Abovethisplain，towardstheinterior，Mr。Stokesinformsmethattherewereseveralotherstep-formedplains，thehighestofwhichwasestimatedat1，200feet，andwasseenrangingatapparentlythesameheightfor150
　　milesnorthward。Alltheseplainshavebeenwornintogreatvalleysandmuchdenuded。Thesectionin，Diagram3isillustrativeofthegeneralstructureofthegreatBayofSt。George。AtthesouthheadlandoftheBayofSt。GeorgenearC。ThreePointsthe250plainisveryextensive。
　　DIAGRAM3。SECTIONOFPLAINSATPORTDESIRE。
　　>FromEastsealeveltoWesthigh：
　　Terrace1。100Est。
　　Terrace2。245-255Ba。M。Shellsonsurface。
　　Terrace3。330Ba。M。Shellsonsurface。
　　Terrace4。Notmeasured。
　　AtPortDesirefortymilessouthwardImadeseveralmeasurementswiththebarometerofaplain，whichextendsalongthenorthsideoftheportandalongtheopencoast，andwhichvariesfrom245to255feetinheight：thisplainabutsagainstthefootofahigherplainof330feet，whichextendsalsofarnorthwardalongthecoast，andlikewiseintotheinterior。Inthedistanceahigherinlandplatformwasseen，ofwhichIdonotknowtheheight。Inthreeseparateplaces，Iobservedthecliffofthe245-255feetplain，fringedbyaterraceornarrowplainestimatedataboutonehundredfeetinheight。TheseplainsarerepresentedinthesectionDiagram3。
　　Inmanyplaces，evenatthedistanceofthreeandfourmilesfromthecoast，Ifoundonthegravel-cappedsurfaceofthe245-255feet，andofthe330feetplain，shellsofMytilusMagellanicus，M。edulis，Patelladeaurita，andanotherPatella，toomuchworntobeidentified，butapparentlysimilartoonefoundabundantlyadheringtotheleavesofthekelp。Thesespeciesarethecommonestnowlivingonthiscoast。Theshellsallappearedveryold;theblueofthemusselswasmuchfaded;andonlytracesofcolourcouldbeperceivedinthePatellas，ofwhichtheoutersurfaceswerescalingoff。Theylayscatteredonthesmoothsurfaceofthegravel，butaboundedmostincertainpatches，especiallyattheheadsofthesmallervalleys：theygenerallycontainedsandintheirinsides;andI
　　presumethattheyhavebeenwashedbyalluvialactionoutofthinsandylayers，tracesofwhichmaysometimesbeseencoveringthegravel。Theseveralplainshaveverylevelsurfaces;butallarescoopedoutbynumerousbroad，winding，flat-bottomedvalleys，inwhich，judgingfromthebushes，streamsneverflow。Theseremarksonthestateoftheshells，andonthenatureoftheplains，applytothefollowingcases，soneednotberepeated。
　　DIAGRAM4。SECTIONOFPLAINSATPORTS。JULIAN。
　　>FromEastsealeveltoWesthigh：
　　Terrace1。Shellsonsurface。90Est。
　　Terrace2。430An。M。
　　Terrace3。560An。M。
　　Terrace4。950An。M。
　　SouthwardofPortDesire，theplainshavebeengreatlydenuded，withonlysmallpiecesoftablelandmarkingtheirformerextension。ButoppositeBirdIsland，twoconsiderablestep-formedplainsweremeasured，andfoundrespectivelytobe350and590feetinheight。ThislatterplainextendsalongthecoastclosetoPortSt。Julian110milessouthofPortDesire;
　　seeDiagram4。
　　Thelowestplainwasestimatedatninetyfeet：itisremarkablefromtheusualgravel-bedbeingdeeplywornintohollows，whicharefilledupwith，aswellasthegeneralsurfacecoveredby，sandyandreddishearthymatter：
　　inoneofthehollowsthusfilledup，theskeletonoftheMacraucheniaPatachonica，aswillhereafterbedescribed，wasembedded。Onthesurfaceandintheupperpartsofthisearthymass，therewerenumerousshellsofMytilusMagellanicusandM。edulis，Patelladeaurita，andfragmentsofotherspecies。Thisplainistolerablylevel，butnotextensive;itformsapromontorysevenoreightmileslong，andthreeorfourwide。TheupperplainsinDiagram4weremeasuredbytheOfficersoftheSurvey;theywereallcappedbythickbedsofgravel，andwereallmoreorlessdenuded;the950plainconsistsmerelyofseparate，truncated，gravel-cappedhills，twoofwhich，bymeasurement，werefoundtodifferonlythreefeet。The430
　　feetplainextends，apparentlywithhardlyabreak，tonearthenorthernentranceoftheRioSantaCruzfiftymilestothesouth;butitwastherefoundtobeonly330feetinheight。
　　DIAGRAM5。SECTIONOFPLAINSATTHEMOUTHOFTHERIOSANTACRUZ。
　　>FromEastsealeveltoWesthigh：
　　Terrace1。sloping355Ba。M。Shellsonsurface。463Ba。M。
　　Terrace2。710An。M。
　　Terrace3。840An。M。
　　OnthesouthernsideofthemouthoftheSantaCruzwehaveDiagram5，whichIamabletogivewithmoredetailthanintheforegoingcases。
　　Theplainmarked355feetasascertainedbythebarometerandbyangularmeasurementisacontinuationoftheabove-mentioned330feetplain：itextendsinaN。W。directionalongthesouthernshoresoftheestuary。Itiscappedbygravel，whichinmostpartsiscoveredbyathinbedofsandyearth，andisscoopedoutbymanyflat-bottomedvalleys。Itappearstotheeyequitelevel，butinproceedinginaS。S。W。course，towardsanescarpmentdistantaboutsixmiles，andlikewiserangingacrossthecountryinaN。W。line，itwasfoundtoriseatfirstinsensibly，andthenforthelasthalf-mile，sensibly，closeuptothebaseoftheescarpment：atthispointitwas463feetinheight，showingariseof108feetinthesixmiles。Onthis355-463feetplain，IfoundseveralshellsofMytilusMagellanicusandofaMytilus，whichMr。Sowerbyinformsmeisyetunnamed，thoughwell-knownasrecentonthiscoast;Patelladeaurita;Fusus，I
　　believe，Magellanicus，butthespecimenhasbeenlost;andatthedistanceoffourmilesfromthecoast，attheheightofaboutfourhundredfeet，therewerefragmentsofthesamePatellaandofaVolutaapparentlyV。
　　ancillapartiallyembeddedinthesuperficialsandyearth。Alltheseshellshadthesameancientappearancewiththosefromtheforegoinglocalities。AsthetidesalongthispartofthecoastriseattheSyzygalperiodfortyfeet，andthereforeformawell-markedbeach-line，I
　　particularlylookedoutforridgesincrossingthisplain，which，aswehaveseen，rises108feetinaboutsixmiles，butIcouldnotseeanytracesofsuch。Thenexthighestplainis710feetabovethesea;itisverynarrow，butlevel，andiscappedwithgravel;itabutstothefootofthe840feetplain。Thissummit-plainextendsasfarastheeyecanrange，bothinlandalongthesouthernsideofthevalleyoftheSantaCruz，andsouthwardalongtheAtlantic。
　　THEVALLEYOFTHER。SANTACRUZ。
　　ThisvalleyrunsinaneastandwestdirectiontotheCordillera，adistanceofaboutonehundredandsixtymiles。ItcutsthroughthegreatPatagoniantertiaryformation，including，intheupperhalfofthevalley，immensestreamsofbasalticlava，whichaswellasthesofterbeds，arecappedbygravel;andthisgravel，highuptheriver，isassociatedwithavastboulderformation。Ihavedescribedthisformationinapaperinthe“GeologicalTransactions“volume6page415。Inascendingthevalley，theplainwhichatthemouthonthesouthernsideis355feethigh，isseentotrendtowardsthecorrespondingplainonthenorthernside，sothattheirescarpmentsappearliketheshoresofaformerestuary，largerthantheexistingone：theescarpments，also，ofthe840feetsummit-plainwithacorrespondingnorthernone，whichismetwithsomewayupthevalley，appearliketheshoresofastilllargerestuary。Fartherupthevalley，thesidesareboundedthroughoutitsentirelengthbylevel，gravel-cappedterraces，risingaboveeachotherinsteps。Thewidthbetweentheupperescarpmentsisonanaveragebetweensevenandtenmiles;inonespot，however，wherecuttingthroughthebasalticlava，itwasonlyonemileandahalf。Betweentheescarpmentsofthesecondhighestterracetheaveragewidthisaboutfourorfivemiles。Thebottomofthevalley，atthedistanceof110milesfromitsmouth，beginssensiblytoexpand，andsoonformsaconsiderableplain，440feetabovethelevelofthesea，throughwhichtheriverflowsinagutfromtwentytofortyfeetindepth。Iherefound，atapoint140milesfromtheAtlantic，andseventymilesfromthenearestcreekofthePacific，attheheightof410feet，averyoldandwornshellofPatelladeaurita。Lowerdownthevalley，105milesfromtheAtlanticlongitude71degreesW。，andatanelevationofabout300feet，Ialsofound，inthebedoftheriver，twomuchwornandbrokenshellsoftheVolutaancilla，stillretainingtracesoftheircolours;andoneofthePatelladeaurita。Itappearedthattheseshellshadbeenwashedfromthebanksintotheriver;consideringthedistancefromthesea，thedesertandabsolutelyunfrequentedcharacterofthecountry，andtheveryancientappearanceoftheshellsexactlylikethosefoundontheplainsnearerthecoast，thereis，Ithink，nocausetosuspectthattheycouldhavebeenbroughtherebyIndians。
　　Theplainattheheadofthevalleyistolerablylevel，butwater-worn，andwithmanysand-dunesonitlikethoseonasea-coast。Atthehighestpointtowhichweascended，itwassixteenmileswideinanorthandsouthline;
　　andforty-fivemilesinlengthinaneastandwestline。Itisborderedbytheescarpments，oneabovetheother，oftwoplains，whichdivergeastheyapproachtheCordillera，andconsequentlyresemble，attwolevels，theshoresofgreatbaysfacingthemountains;andthesemountainsarebreachedinfrontofthelowerplainbyaremarkablegap。Thevalley，therefore，oftheSantaCruzconsistsofastraightbroadcut，aboutninetymilesinlength，borderedbygravel-cappedterracesandplains，theescarpmentsofwhichatbothendsdivergeorexpand，oneovertheother，afterthemanneroftheshoresofgreatbays。Bearinginmindthispeculiarformoftheland——thesand-dunesontheplainattheheadofthevalley——thegapintheCordillera，infrontofit——thepresenceintwoplacesofveryancientshellsofexistingspecies——andlastly，thecircumstanceofthe355-453
　　feetplain，withthenumerousmarineremainsonitssurface，sweepingfromtheAtlanticcoast，farupthevalley，Ithinkwemustadmit，thatwithintherecentperiod，thecourseoftheSantaCruzformedasea-straitintersectingthecontinent。Atthisperiod，thesouthernpartofSouthAmericaconsistedofanarchipelagoofislands360milesinanorthandsouthline。Weshallpresentlysee，thattwootherstraitsalso，sinceclosed，thencutthroughTierradelFuego;Imayadd，thatoneofthemmustatthattimehaveexpandedatthefootoftheCordilleraintoagreatbaynowOtwayWaterlikethatwhichformerlycoveredthe440feetplainattheheadoftheSantaCruz。
　　DIAGRAM6。NORTHANDSOUTHSECTIONACROSSTHETERRACESBOUNDINGTHEVALLEY
　　OFTHERIVERSANTACRUZ，HIGHUPITSCOURSE。
　　Theheightofeachterrace，abovetheleveloftheriverfurthesttonearesttotheriverinfeet：
　　A，northandsouth：1，122
　　B，northandsouth：869
　　C，northandsouth：639
　　D，north：notmeasured。D，north？suggestsouth：185
　　E：20
　　BedofRiver。
　　Verticalscale1/20ofinchto100feet;butterraceE，beingonlytwentyfeetabovetheriver，hasnecessarilybeenraised。Thehorizontaldistancesmuchcontracted;thedistancefromtheedgeofANorthtoASouthbeingonanaveragefromseventotenmiles。
　　Ihavesaidthatthevalleyinitswholecourseisborderedbygravel-
　　cappedplains。ThesectionDiagram6，supposedtobedrawninanorthandsouthlineacrossthevalley，canscarcelybeconsideredasmorethanillustrative;forduringourhurriedascentitwasimpossibletomeasurealltheplainsatanyoneplace。AtapointnearlymidwaybetweentheCordilleraandtheAtlantic，IfoundtheplainAnorth1，122feetabovetheriver;allthelowerplainsonthissidewerehereunitedintoonegreatbrokencliff：atapointsixteenmileslowerdownthestream，IfoundbymeasurementandestimationthatBnorthwas869abovetheriver：veryneartowhereAnorthwasmeasured，Cnorthwas639abovethesamelevel：theterraceDnorthwasnowheremeasured：thelowestEnorthwasinmanyplacesabouttwentyfeetabovetheriver。Theseplainsorterraceswerebestdevelopedwherethevalleywaswidest;thewholefive，likegiganticsteps，occurredtogetheronlyatafewpoints。Thelowerterracesarelesscontinuousthanthehigherones，andappeartobeentirelylostintheupperthirdofthevalley。TerraceCsouth，howeverwastracedcontinuouslyforagreatdistance。TheterraceBnorth，atapointfifty-
　　fivemilesfromthemouthoftheriver，wasfourmilesinwidth;higherupthevalleythisterraceoratleastthesecondhighestone，forIcouldnotalwaystraceitcontinuouslywasabouteightmileswide。Thissecondplainwasgenerallywiderthanthelowerones——asindeedfollowsfromthevalleyfromAnorthtoAsouthbeinggenerallynearlydoublethewidthoffromBnorthtoBsouth。Lowdownthevalley，thesummit-plainA
　　southiscontinuouswiththe840feetplainonthecoast，butitissoonlostoruniteswiththeescarpmentofBsouth。ThecorrespondingplainA
　　north，onthenorthsideofthevalley，appearstorangecontinuouslyfromtheCordilleratotheheadofthepresentestuaryoftheSantaCruz，whereittrendsnorthwardtowardsPortSt。Julian。NeartheCordillerathesummit-plainonbothsidesofthevalleyisbetween3，200and3，300feetinheight;at100milesfromtheAtlantic，itis1，416feet，andonthecoast840feet，allabovethesea-beach;sothatinadistanceof100milestheplainrises576feet，andmuchmorerapidlyneartotheCordillera。ThelowerterracesBandCalsoappeartoriseastheyrunupthevalley;thusDnorth，measuredattwopointstwenty-fourmilesapart，wasfoundtohaverisen185feet。FromseveralreasonsIsuspect，thatthisgradualinclinationoftheplainsupthevalley，hasbeenchieflycausedbytheelevationofthecontinentinmass，havingbeenthegreaterthenearertotheCordillera。
　　Alltheterracesarecappedwithwell-roundedgravel，whichrestseitheronthedenudedandsometimesfurrowedsurfaceofthesofttertiarydeposits，oronthebasalticlava。Thedifferenceinheightbetweensomeofthelowerstepsorterracesseemstobeentirelyowingtoadifferenceinthethicknessofthecappinggravel。Furrowsandinequalitiesinthegravel，wheresuchoccur，arefilledupandsmoothedoverwithsandyearth。Thepebbles，especiallyonthehigherplains，areoftenwhitewashed，andevencementedtogetherbyawhitealuminoussubstance，andIoccasionallyfoundthistobethecasewiththegravelontheterraceD。Icouldnotperceiveanytraceofasimilardepositiononthepebblesnowthrownupbytheriver，andthereforeIdonotthinkthatterraceDwasriver-formed。AstheterraceEgenerallystandsabouttwentyfeetabovethebedoftheriver，myfirstimpressionwastodoubtwhethereventhislowestonecouldhavebeensoformed;butitshouldalwaysbeborneinmind，thatthehorizontalupheavalofadistrict，byincreasingthetotaldescentofthestreams，willalwaystendtoincrease，firstnearthesea-coastandthenfurtherandfurtherupthevalley，theircorrodinganddeepeningpowers：sothatanalluvialplain，formedalmostonalevelwithastream，will，afteranelevationofthiskind，intimebecutthrough，andleftstandingataheightneveragaintobereachedbythewater。WithrespecttothethreeupperterracesoftheSantaCruz，Ithinktherecanbenodoubt，thattheyweremodelledbythesea，whenthevalleywasoccupiedbyastrait，inthesamemannerhereaftertobediscussedasthegreaterstep-formed，shell-
　　strewedplainsalongthecoastofPatagonia。
　　ToreturntotheshoresoftheAtlantic：the840feetplain，atthemouthoftheSantaCruz，isseenextendinghorizontallyfartothesouth;andI
　　aminformedbytheOfficersoftheSurvey，thatbendingroundtheheadofCoyInletsixty-fivemilessouthward，ittrendsinland。Outliersofapparentlythesameheightareseenfortymilesfarthersouth，inlandoftheriverGallegos;andaplaincomesdowntoCapeGregorythirty-fivemilessouthward，intheStraitofMagellan，whichwasestimatedatbetweeneighthundredandonethousandfeetinheight，andwhich，risingtowardstheinterior，iscappedbytheboulderformation。SouthoftheStraitofMagellan，therearelargeoutlyingmassesofapparentlythesamegreattableland，extendingatintervalsalongtheeasterncoastofTierradelFuego：attwoplaceshere，110milesapart，thisplainwasfoundtobe950
　　and970feetinheight。

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