Whenthecondorsarewheelinginaflockroundandroundanyspot，theirflightisbeautiful。Exceptwhenrisingfromtheground，Idonotrecollecteverhavingseenoneofthesebirdsflapitswings。NearLima，Iwatchedseveralfornearlyhalfanhour，withoutoncetakingoffmyeyes：theymovedinlargecurves，sweepingincircles，descendingandascendingwithoutgivingasingleflap。Astheyglidedcloseovermyhead，Iintentlywatchedfromanobliqueposition，theoutlinesoftheseparateandgreatterminalfeathersofeachwing；andtheseseparatefeathers，iftherehadbeentheleastvibratorymovement，wouldhaveappearedasifblendedtogether；buttheywereseendistinctagainstthebluesky。Theheadandneckweremovedfrequently，andapparentlywithforce；andtheextendedwingsseemedtoformthefulcrumonwhichthemovementsoftheneck，body，andtailacted。
Ifthebirdwishedtodescend，thewingswereforamomentcollapsed；andwhenagainexpandedwithanalteredinclination，themomentumgainedbytherapiddescentseemedtourgethebirdupwardswiththeevenandsteadymovementofapaperkite。Inthecaseofanybirdsoaring，itsmotionmustbesufficientlyrapidsothattheactionoftheinclinedsurfaceofitsbodyontheatmospheremaycounterbalanceitsgravity。Theforcetokeepupthemomentumofabodymovinginahorizontalplaneintheairinwhichthereissolittlefrictioncannotbegreat，andthisforceisallthatiswanted。Themovementoftheneckandbodyofthecondor，wemustsuppose，issufficientforthis。Howeverthismaybe，itistrulywonderfulandbeautifultoseesogreatabird，hourafterhour，withoutanyapparentexertion，wheelingandglidingovermountainandriver。
April29th——FromsomehighlandwehailedwithjoythewhitesummitsoftheCordillera，astheywereseenoccasionallypeepingthroughtheirduskyenvelopeofclouds。Duringthefewsucceedingdayswecontinuedtogetonslowly，forwefoundtheriver-courseverytortuous，andstrewedwithimmensefragmentsofvariousancientslatyrocks，andofgranite。
Theplainborderingthevalleyhadhereattainedanelevationofabout1100feetabovetheriver，anditscharacterwasmuchaltered。Thewell-roundedpebblesofporphyryweremingledwithmanyimmenseangularfragmentsofbasaltandofprimaryrocks。ThefirstoftheseerraticboulderswhichInoticed，wassixty-sevenmilesdistantfromthenearestmountain；anotherwhichImeasuredwasfiveyardssquare，andprojectedfivefeetabovethegravel。Itsedgesweresoangular，anditssizesogreat，thatIatfirstmistookitforarock_insitu_，andtookoutmycompasstoobservethedirectionofitscleavage。Theplainherewasnotquitesolevelasthatnearerthecoast，butyetitbetrayednosignsofanygreatviolence。Underthesecircumstancesitis，Ibelieve，quiteimpossibletoexplainthetransportalofthesegiganticmassesofrocksomanymilesfromtheirparent-source，onanytheoryexceptbythatoffloatingicebergs。
Duringthetwolastdayswemetwithsignsofhorses，andwithseveralsmallarticleswhichhadbelongedtotheIndians——suchaspartsofamantleandabunchofostrichfeathers——buttheyappearedtohavebeenlyinglongontheground。BetweentheplacewheretheIndianshadsolatelycrossedtheriverandthisneighbourhood，thoughsomanymilesapart，thecountryappearstobequiteunfrequented。Atfirst，consideringtheabundanceoftheguanacos，Iwassurprisedatthis；butitisexplainedbythestonynatureoftheplains，whichwouldsoondisableanunshodhorsefromtakingpartinthechase。Nevertheless，intwoplacesinthisverycentralregion，Ifoundsmallheapsofstones，whichIdonotthinkcouldhavebeenaccidentallythrowntogether。Theywereplacedonpoints，projectingovertheedgeofthehighestlavacliff，andtheyresembled，butonasmallscale，thosenearPortDesire。