April26th——Wethisdaymetwithamarkedchangeinthegeologicalstructureoftheplains。FromthefirststartingIhadcarefullyexaminedthegravelintheriver，andforthetwolastdayshadnoticedthepresenceofafewsmallpebblesofaverycellularbasalt。Thesegraduallyincreasedinnumberandinsize，butnonewereaslargeasaman’shead。Thismorning，however，pebblesofthesamerock，butmorecompact，suddenlybecameabundant，andinthecourseofhalfanhourwesaw，atthedistanceoffiveorsixmiles，theangularedgeofagreatbasalticplatform。Whenwearrivedatitsbasewefoundthestreambubblingamongthefallenblocks。Forthenexttwenty-eightmilestheriver-coursewasencumberedwiththesebasalticmasses。Abovethatlimitimmensefragmentsofprimitiverocks，derivedfromitssurroundingboulder-formation，wereequallynumerous。Noneofthefragmentsofanyconsiderablesizehadbeenwashedmorethanthreeorfourmilesdowntheriverbelowtheirparent-source：consideringthesingularrapidityofthegreatbodyofwaterintheSantaCruz，andthatnostillreachesoccurinanypart，thisexampleisamoststrikingone，oftheinefficiencyofriversintransportingevenmoderately-sizedfragments。
Thebasaltisonlylava，whichhasflowedbeneaththesea；buttheeruptionsmusthavebeenonthegrandestscale。Atthepointwherewefirstmetthisformationitwas120feetinthickness；followinguptherivercourse，thesurfaceimperceptiblyroseandthemassbecamethicker，sothatatfortymilesabovethefirststationitwas320feetthick。WhatthethicknessmaybeclosetotheCordillera，Ihavenomeansofknowing，buttheplatformthereattainsaheightofaboutthreethousandfeetabovethelevelofthesea：wemustthereforelooktothemountainsofthatgreatchainforitssource；andworthyofsuchasourcearestreamsthathaveflowedoverthegentlyinclinedbedoftheseatoadistanceofonehundredmiles。
Atthefirstglanceofthebasalticcliffsontheoppositesidesofthevalley，itwasevidentthatthestrataoncewereunited。Whatpower，then，hasremovedalongawholelineofcountry，asolidmassofveryhardrock，whichhadanaveragethicknessofnearlythreehundredfeet，andabreadthvaryingfromratherlessthantwomilestofourmiles？Theriver，thoughithassolittlepowerintransportingeveninconsiderablefragments，yetinthelapseofagesmightproducebyitsgradualerosionaneffectofwhichitisdifficulttojudgetheamount。Butinthiscase，independentlyoftheinsignificanceofsuchanagency，goodreasonscanbeassignedforbelievingthatthisvalleywasformerlyoccupiedbyanarmofthesea。
Itisneedlessinthisworktodetailtheargumentsleadingtothisconclusion，derivedfromtheformandthenatureofthestep-formedterracesonbothsidesofthevalley，fromthemannerinwhichthebottomofthevalleyneartheAndesexpandsintoagreatestuary-likeplainwithsand-hillocksonit，andfromtheoccurrenceofafewsea-shellslyinginthebedoftheriver。IfIhadspaceIcouldprovethatSouthAmericawasformerlyherecutoffbyastrait，joiningtheAtlanticandPacificoceans，likethatofMagellan。Butitmayyetbeasked，howhasthesolidbasaltbeenmoved？Geologistsformerlywouldhavebroughtintoplay，theviolentactionofsomeoverwhelmingdebacle；butinthiscasesuchasuppositionwouldhavebeenquiteinadmissible；because，thesamestep-likeplainswithexistingsea-shellslyingontheirsurface，whichfrontthelonglineofthePatagoniancoast，sweepuponeachsideofthevalleyofSantaCruz。Nopossibleactionofanyfloodcouldthushavemodelledtheland，eitherwithinthevalleyoralongtheopencoast；andbytheformationofsuchstep-likeplainsorterracesthevalleyitselfhadbeenhollowedout。Althoughweknowthattherearetides，whichrunwithintheNarrowsoftheStraitofMagellanattherateofeightknotsanhour，yetwemustconfessthatitmakestheheadalmostgiddytoreflectonthenumberofyears，centuryaftercentury，whichthetides，unaidedbyaheavysurf，musthaverequiredtohavecorrodedsovastanareaandthicknessofsolidbasalticlava。Nevertheless，wemustbelievethatthestrataunderminedbythewatersofthisancientstrait，werebrokenupintohugefragments，andtheselyingscatteredonthebeach，werereducedfirsttosmallerblocks，thentopebblesandlastlytothemostimpalpablemud，whichthetidesdriftedfarintotheEasternorWesternOcean。
Withthechangeinthegeologicalstructureoftheplainsthecharacterofthelandscapelikewisealtered。Whileramblingupsomeofthenarrowandrockydefiles，IcouldalmosthavefanciedmyselftransportedbackagaintothebarrenvalleysoftheislandofSt。Jago。Amongthebasalticcliffs，IfoundsomeplantswhichIhadseennowhereelse，butothersI
recognisedasbeingwanderersfromTierradelFuego。Theseporousrocksserveasareservoirforthescantyrain-water；andconsequentlyonthelinewheretheigneousandsedimentaryformationsunite，somesmallspringsmostrareoccurrencesinPatagoniaburstforth；andtheycouldbedistinguishedatadistancebythecircumscribedpatchesofbrightgreenherbage。
April27th——Thebedoftheriverbecamerathernarrower，andhencethestreammorerapid。Ithereranattherateofsixknotsanhour。Fromthiscause，andfromthemanygreatangularfragments，trackingtheboatsbecamebothdangerousandlaborious。
ThisdayIshotacondor。Itmeasuredfromtiptotipofthewings，eightandahalffeet，andfrombeaktotail，fourfeet。Thisbirdisknowntohaveawidegeographicalrange，beingfoundonthewestcoastofSouthAmerica，fromtheStraitofMagellanalongtheCordilleraasfaraseightdegreesnorthoftheequator。ThesteepcliffnearthemouthoftheRioNegroisitsnorthernlimitonthePatagoniancoast；andtheyhavetherewanderedaboutfourhundredmilesfromthegreatcentrallineoftheirhabitationintheAndes。Furthersouth，amongtheboldprecipicesattheheadofPortDesire，thecondorisnotuncommon；yetonlyafewstragglersoccasionallyvisittheseacoast。AlineofcliffnearthemouthoftheSantaCruzisfrequentedbythesebirds，andabouteightymilesuptheriver，wherethesidesofthevalleyareformedbysteepbasalticprecipices，thecondorreappears。Fromthesefacts，itseemsthatthecondorsrequireperpendicularcliffs。InChile，theyhaunt，duringthegreaterpartoftheyear，thelowercountryneartheshoresofthePacific，andatnightseveralroosttogetherinonetree；butintheearlypartofsummer，theyretiretothemostinaccessiblepartsoftheinnerCordillera，theretobreedinpeace。
Withrespecttotheirpropagation，IwastoldbythecountrypeopleinChile，thatthecondormakesnosortofnest，butinthemonthsofNovemberandDecemberlaystwolargewhiteeggsonashelfofbarerock。Itissaidthattheyoungcondorscannotflyforanentireyear；andlongaftertheyareable，theycontinuetoroostbynight，andhuntbydaywiththeirparents。
Theoldbirdsgenerallyliveinpairs；butamongtheinlandbasalticcliffsoftheSantaCruz，Ifoundaspot，wherescoresmustusuallyhaunt。Oncomingsuddenlytothebrowoftheprecipice，itwasagrandspectacletoseebetweentwentyandthirtyofthesegreatbirdsstartheavilyfromtheirresting-place，andwheelawayinmajesticcircles。Fromthequantityofdungontherocks，theymustlonghavefrequentedthiscliffforroostingandbreeding。Havinggorgedthemselveswithcarrionontheplainsbelow，theyretiretothesefavouriteledgestodigesttheirfood。Fromthesefacts，thecondor，likethegallinazo，musttoacertaindegreebeconsideredasagregariousbird。Inthispartofthecountrytheylivealtogetherontheguanacoswhichhavediedanaturaldeath，orasmorecommonlyhappens，havebeenkilledbythepumas。Ibelieve，fromwhatIsawinPatagonia，thattheydonotonordinaryoccasionsextendtheirdailyexcursionstoanygreatdistancefromtheirregularsleeping-places。
Thecondorsmayoftentimesbeseenatagreatheight，soaringoveracertainspotinthemostgracefulcircles。OnsomeoccasionsIamsurethattheydothisonlyforpleasure，butonothers，theChilenocountrymantellsyouthattheyarewatchingadyinganimal，orthepumadevouringitsprey。Ifthecondorsglidedown，andthensuddenlyallrisetogether，theChilenoknowsthatitisthepumawhich，watchingthecarcass，hassprungouttodriveawaytherobbers。Besidesfeedingoncarrion，thecondorsfrequentlyattackyounggoatsandlambs；andtheshepherd-dogsaretrained，whenevertheypassover，torunout，andlookingupwardstobarkviolently。
TheChilenosdestroyandcatchnumbers。Twomethodsareused；oneistoplaceacarcassonalevelpieceofgroundwithinanenclosureofstickswithanopening，andwhenthecondorsaregorged，togallopuponhorsebacktotheentrance，andthusenclosethem：forwhenthisbirdhasnotspacetorun，itcannotgiveitsbodysufficientmomentumtorisefromtheground。
Thesecondmethodistomarkthetreesinwhich，frequentlytothenumberoffiveorsixtogether，theyroost，andthenatnighttoclimbupandnoosethem。Theyaresuchheavysleepers，asIhavemyselfwitnessed，thatthisisnotadifficulttask。AtValparaiso，Ihaveseenalivingcondorsoldforsixpence，butthecommonpriceiseightortenshillings。OnewhichIsawbroughtin，hadbeentiedwithrope，andwasmuchinjured；
yet，themomentthelinewascutbywhichitsbillwassecured，althoughsurroundedbypeople，itbeganravenouslytotearapieceofcarrion。Inagardenatthesameplace，betweentwentyandthirtywerekeptalive。
Theywerefedonlyonceaweek，buttheyappearedinprettygoodhealth。[2]TheChilenocountrymenassertthatthecondorwilllive，andretainitsvigour，betweenfiveandsixweekswithouteating：
Icannotanswerforthetruthofthis，butitisacruelexperiment，whichverylikelyhasbeentried。
Whenananimaliskilledinthecountry，itiswellknownthatthecondors，likeothercarrion-vultures，soongainintelligenceofit，andcongregateinaninexplicablemanner。Inmostcasesitmustnotbeoverlooked，thatthebirdshavediscoveredtheirprey，andhavepickedtheskeletonclean，beforethefleshisintheleastdegreetainted。RememberingtheexperimentsofM。Audubon，onthelittlesmellingpowersofcarrion-hawks，Itriedintheabove-mentionedgardenthefollowingexperiment：thecondorsweretied，eachbyarope，inalongrowatthebottomofawall；andhavingfoldedupapieceofmeatinwhitepaper，Iwalkedbackwardsandforwards，carryingitinmyhandatthedistanceofaboutthreeyardsfromthem，butnonoticewhateverwastaken。Ithenthrewitontheground，withinoneyardofanoldmalebird；helookedatitforamomentwithattention，butthenregardeditnomore。WithastickIpusheditcloserandcloser，untilatlasthetoucheditwithhisbeak；thepaperwastheninstantlytornoffwithfury，andatthesamemoment，everybirdinthelongrowbeganstrugglingandflappingitswings。Underthesamecircumstances，itwouldhavebeenquiteimpossibletohavedeceivedadog。Theevidenceinfavourofandagainsttheacutesmellingpowersofcarrion-vulturesissingularlybalanced。ProfessorOwenhasdemonstratedthattheolfactorynervesoftheturkey-buzzardCathartesauraarehighlydeveloped，andontheeveningwhenMr。Owen’spaperwasreadattheZoologicalSociety，itwasmentionedbyagentlemanthathehadseenthecarrion-hawksintheWestIndiesontwooccasionscollectontheroofofahouse，whenacorpsehadbecomeoffensivefromnothavingbeenburied，inthiscase，theintelligencecouldhardlyhavebeenacquiredbysight。Ontheotherhand，besidestheexperimentsofAudubonandthatonebymyself，Mr。BachmanhastriedintheUnitedStatesmanyvariedplans，showingthatneithertheturkey-buzzardthespeciesdissectedbyProfessorOwennorthegallinazofindtheirfoodbysmell。Hecoveredportionsofhighly-offensiveoffalwithathincanvascloth，andstrewedpiecesofmeatonit：thesethecarrion-vulturesateup，andthenremainedquietlystanding，withtheirbeakswithintheeighthofaninchoftheputridmass，withoutdiscoveringit。Asmallrentwasmadeinthecanvas，andtheoffalwasimmediatelydiscovered；thecanvaswasreplacedbyafreshpiece，andmeatagainputonit，andwasagaindevouredbythevultureswithouttheirdiscoveringthehiddenmassonwhichtheyweretrampling。Thesefactsareattestedbythesignaturesofsixgentlemen，besidesthatofMr。Bachman。[3]
Oftenwhenlyingdowntorestontheopenplains，onlookingupwards，Ihaveseencarrion-hawkssailingthroughtheairatagreatheight。WherethecountryislevelIdonotbelieveaspaceoftheheavens，ofmorethanfifteendegreesabovethehorizon，iscommonlyviewedwithanyattentionbyapersoneitherwalkingoronhorseback。Ifsuchbethecase，andthevultureisonthewingataheightofbetweenthreeandfourthousandfeet，beforeitcouldcomewithintherangeofvision，itsdistanceinastraightlinefromthebeholder’seye，wouldberathermorethantwoBritishmiles。
Mightitnotthusreadilybeoverlooked？Whenananimaliskilledbythesportsmaninalonelyvalley，mayhenotallthewhilebewatchedfromabovebythesharp-sightedbird？Andwillnotthemannerofitsdescentproclaimthroughoutthedistricttothewholefamilyofcarrion-feeders，thattheirpreyisathand？