ThelittleowlAthenecunicularia，whichhasbeensooftenmentioned，ontheplainsofBuenosAyresexclusivelyinhabitstheholesofthebizcacha；
butinBandaOrientalitisitsownworkman。Duringtheopenday，butmoreespeciallyintheevening，thesebirdsmaybeseenineverydirectionstandingfrequentlybypairsonthehillockneartheirburrows。Ifdisturbedtheyeitherenterthehole，or，utteringashrillharshcry，movewitharemarkablyundulatoryflighttoashortdistance，andthenturninground，steadilygazeattheirpursuer。Occasionallyintheeveningtheymaybeheardhooting。
IfoundinthestomachsoftwowhichIopenedtheremainsofmice，andIonedaysawasmallsnakekilledandcarriedaway。Itissaidthatsnakesaretheircommonpreyduringthedaytime。Imayheremention，asshowingonwhatvariouskindsoffoodowlssubsist，thataspecieskilledamongtheisletsoftheChonosArchipelago，haditsstomachfullofgood-sizedcrabs。InIndia[2]thereisafishinggenusofowls，whichlikewisecatchescrabs。
IntheeveningwecrossedtheRioArrecifeonasimpleraftmadeofbarrelslashedtogether，andsleptatthepost-houseontheotherside。
Ithisdaypaidhorse-hireforthirty-oneleagues；andalthoughthesunwasglaringhotIwasbutlittlefatigued。WhenCaptainHeadtalksofridingfiftyleaguesaday，Idonotimaginethedistanceisequalto150Englishmiles。Atallevents，thethirty-oneleagueswasonly76milesinastraightline，andinanopencountryIshouldthinkfouradditionalmilesforturningswouldbeasufficientallowance。
29thand30th——Wecontinuedtorideoverplainsofthesamecharacter。
AtSanNicolasIfirstsawthenobleriveroftheParana。Atthefootofthecliffonwhichthetownstands，somelargevesselswereatanchor。
BeforearrivingatRozario，wecrossedtheSaladillo，astreamoffineclearrunningwater，buttoosalinetodrink。Rozarioisalargetownbuiltonadeadlevelplain，whichformsacliffaboutsixtyfeethighovertheParana。Theriverhereisverybroad，withmanyislands，whicharelowandwooded，asisalsotheoppositeshore。Theviewwouldresemblethatofagreatlake，ifitwerenotforthelinear-shapedislets，whichalonegivetheideaofrunningwater。Thecliffsarethemostpicturesquepart；
sometimestheyareabsolutelyperpendicular，andofaredcolour；atothertimesinlargebrokenmasses，coveredwithcactiandmimosa-trees。Therealgrandeur，however，ofanimmenseriverlikethis，isderivedfromreflectinghowimportantameansofcommunicationandcommerceitformsbetweenonenationandanother；towhatadistanceittravels，andfromhowvastaterritoryitdrainsthegreatbodyoffreshwaterwhichflowspastyourfeet。
FormanyleaguesnorthandsouthofSanNicolasandRozario，thecountryisreallylevel。Scarcelyanythingwhichtravellershavewrittenaboutitsextremeflatness，canbeconsideredasexaggeration。YetIcouldneverfindaspotwhere，byslowlyturninground，objectswerenotseenatgreaterdistancesinsomedirectionsthaninothers；andthismanifestlyprovesinequalityintheplain。Atsea，aperson’seyebeingsixfeetabovethesurfaceofthewater，hishorizonistwomilesandfour-fifthsdistant。
Inlikemanner，themoreleveltheplain，themorenearlydoesthehorizonapproachwithinthesenarrowlimits；andthis，inmyopinion，entirelydestroysthatgrandeurwhichonewouldhaveimaginedthatavastlevelplainwouldhavepossessed。
October1st-WestartedbymoonlightandarrivedattheRioTercerobysunrise。TheriverisalsocalledtheSaladillo，anditdeservesthename，forthewaterisbrackish。Istayedherethegreaterpartoftheday，searchingforfossilbones。BesidesaperfecttoothoftheToxodon，andmanyscatteredbones，Ifoundtwoimmenseskeletonsneareachother，projectinginboldrelieffromtheperpendicularcliffoftheParana。Theywere，however，socompletelydecayed，thatIcouldonlybringawaysmallfragmentsofoneofthegreatmolarteeth；butthesearesufficienttoshowthattheremainsbelongedtoaMastodon，probablytothesamespecieswiththat，whichformerlymusthaveinhabitedtheCordillerainUpperPeruinsuchgreatnumbers。Themenwhotookmeinthecanoe，saidtheyhadlongknownoftheseskeletons，andhadoftenwonderedhowtheyhadgotthere：thenecessityofatheorybeingfelt，theycametotheconclusionthat，likethebizcacha，themastodonwasformerlyaburrowinganimal！
Intheeveningwerodeanotherstage，andcrossedtheMonge，anotherbrackishstream，bearingthedregsofthewashingsofthePampas。
October2nd——WepassedthroughCorunda，which，fromtheluxurianceofitsgardens，wasoneoftheprettiestvillagesIsaw。FromthispointtoSt。Fetheroadisnotverysafe。ThewesternsideoftheParananorthward，ceasestobeinhabited；andhencetheIndianssometimescomedownthusfar，andwaylaytravellers。Thenatureofthecountryalsofavoursthis，forinsteadofagrassyplain，thereisanopenwoodland，composedoflowpricklymimosas。Wepassedsomehousesthathadbeenransackedandsincedeserted；wesawalsoaspectacle，whichmyguidesviewedwithhighsatisfaction；
itwastheskeletonofanIndianwiththedriedskinhangingonthebones，suspendedtothebranchofatree。
InthemorningwearrivedatSt。Fe。IwassurprisedtoobservehowgreatachangeofclimateadifferenceofonlythreedegreesoflatitudebetweenthisplaceandBuenosAyreshadcaused。Thiswasevidentfromthedressandcomplexionofthemen——fromtheincreasedsizeoftheombu-trees——thenumberofnewcactiandotherplants——andespeciallyfromthebirds。InthecourseofanhourIremarkedhalf-a-dozenbirds，whichI
hadneverseenatBuenosAyres。Consideringthatthereisnonaturalboundarybetweenthetwoplaces，andthatthecharacterofthecountryisnearlysimilar，thedifferencewasmuchgreaterthanIshouldhaveexpected。
October3rdand4th——Iwasconfinedforthesetwodaystomybedbyaheadache。Agood-naturedoldwoman，whoattendedme，wishedmetotrymanyoddremedies。Acommonpracticeis，tobindanorange-leaforabitofblackplastertoeachtemple：andastillmoregeneralplanis，tosplitabeanintohalves，moistenthem，andplaceoneoneachtemple，wheretheywilleasilyadhere。Itisnotthoughtproperevertoremovethebeansorplaster，buttoallowthemtodropoff，andsometimes，ifaman，withpatchesonhishead，isasked，whatisthematter？hewillanswer，“Ihadaheadachethedaybeforeyesterday。”Manyoftheremediesusedbythepeopleofthecountryareludicrouslystrange，buttoodisgustingtobementioned。Oneoftheleastnastyistokillandcutopentwopuppiesandbindthemoneachsideofabrokenlimb。Littlehairlessdogsareingreatrequesttosleepatthefeetofinvalids。
St。Feisaquietlittletown，andiskeptcleanandingoodorder。
Thegovernor，Lopez，wasacommonsoldieratthetimeoftherevolution；
buthasnowbeenseventeenyearsinpower。Thisstabilityofgovernmentisowingtohistyrannicalhabits；fortyrannyseemsasyetbetteradaptedtothesecountriesthanrepublicanism。Thegovernor’sfavouriteoccupationishuntingIndians：ashorttimesinceheslaughteredforty-eight，andsoldthechildrenattherateofthreeorfourpoundsapiece。
October5th——WecrossedtheParanatoSt。FeBajada，atownontheoppositeshore。Thepassagetooksomehours，astheriverhereconsistedofalabyrinthofsmallstreams，separatedbylowwoodedislands。IhadaletterofintroductiontoanoldCatalonianSpaniard，whotreatedmewiththemostuncommonhospitality。TheBajadaisthecapitalofEntreRios。In1825thetowncontained6000inhabitants，andtheprovince30，000；
yet，fewastheinhabitantsare，noprovincehassufferedmorefrombloodyanddesperaterevolutions。Theyboasthereofrepresentatives，ministers，astandingarmy，andgovernors：soitisnowonderthattheyhavetheirrevolutions。AtsomefuturedaythismustbeoneoftherichestcountriesofLaPlata。Thesoilisvariedandproductive；anditsalmostinsularformgivesittwograndlinesofcommunicationbytheriversParanaandUruguay。
Iwasdelayedherefivedays，andemployedmyselfinexaminingthegeologyofthesurroundingcountry，whichwasveryinteresting。Wehereseeatthebottomofthecliffs，bedscontainingsharks’teethandsea-shellsofextinctspecies，passingaboveintoaninduratedmarl，andfromthatintotheredclayeyearthofthePampas，withitscalcareousconcretionsandthebonesofterrestrialquadrupeds。Thisverticalsectionclearlytellsusofalargebayofpuresalt-water，graduallyencroachedon，andatlastconvertedintothebedofamuddyestuary，intowhichfloatingcarcasseswereswept。AtPuntaGorda，inBandaOriental，IfoundanalternationofthePampaeanestuarydeposit，withalimestonecontainingsomeofthesameextinctsea-shells；andthisshowseitherachangeintheformercurrents，ormoreprobablyanoscillationoflevelinthebottomoftheancientestuary。
Untillately，myreasonsforconsideringthePampaeanformationtobeanestuarydepositwere，itsgeneralappearance，itspositionatthemouthoftheexistinggreatriverthePlata，andthepresenceofsomanybonesofterrestrialquadrupeds：butnowProfessorEhrenberghashadthekindnesstoexamineformealittleoftheredearth，takenfromlowdowninthedeposit，closetotheskeletonsofthemastodon，andhefindsinitmanyinfusoria，partlysalt-waterandpartlyfresh-waterforms，withthelatterratherpreponderating；andtherefore，asheremarks，thewatermusthavebeenbrackish。M。A。d’OrbignyfoundonthebanksoftheParana，attheheightofahundredfeet，greatbedsofanestuaryshell，nowlivingahundredmileslowerdownnearerthesea；andIfoundsimilarshellsatalessheightonthebanksoftheUruguay；thisshowsthatjustbeforethePampaswasslowlyelevatedintodryland，thewatercoveringitwasbrackish。BelowBuenosAyresthereareupraisedbedsofsea-shellsofexistingspecies，whichalsoprovesthattheperiodofelevationofthePampaswaswithintherecentperiod。
InthePampaeandepositattheBajadaIfoundtheosseousarmourofagiganticarmadillo-likeanimal，theinsideofwhich，whentheearthwasremoved，waslikeagreatcauldron；IfoundalsoteethoftheToxodonandMastodon，andonetoothofaHorse，inthesamestainedanddecayedstate。
Thislattertoothgreatlyinterestedme，[3]andI
tookscrupulouscareinascertainingthatithadbeenembeddedcontemporaneouslywiththeotherremains；forIwasnotthenawarethatamongstthefossilsfromBahiaBlancatherewasahorse’stoothhiddeninthematrix：norwasitthenknownwithcertaintythattheremainsofhorsesarecommoninNorthAmerica。Mr。LyellhaslatelybroughtfromtheUnitedStatesatoothofahorse；anditisaninterestingfact，thatProfessorOwencouldfindinnospecies，eitherfossilorrecent，aslightbutpeculiarcurvaturecharacterizingit，untilhethoughtofcomparingitwithmyspecimenfoundhere：hehasnamedthisAmericanhorseEquuscurvidens。CertainlyitisamarvellousfactinthehistoryoftheMammalia，thatinSouthAmericaanativehorseshouldhavelivedanddisappeared，tobesucceededinafter-
agesbythecountlessherdsdescendedfromthefewintroducedwiththeSpanishcolonists！
TheexistenceinSouthAmericaofafossilhorse，ofthemastodon，possiblyofanelephant，[4]andofahollow-hornedruminant，discoveredbyMM。LundandClauseninthecavesofBrazil，arehighlyinterestingfactswithrespecttothegeographicaldistributionofanimals。Atthepresenttime，ifwedivideAmerica，notbytheIsthmusofPanama，butbythesouthernpartofMexico[5]inlat。20degs。，wherethegreattable-landpresentsanobstacletothemigrationofspecies，byaffectingtheclimate，andbyforming，withtheexceptionofsomevalleysandofafringeoflowlandonthecoast，abroadbarrier；weshallthenhavethetwozoologicalprovincesofNorthandSouthAmericastronglycontrastedwitheachother。Somefewspeciesalonehavepassedthebarrier，andmaybeconsideredaswanderersfromthesouth，suchasthepuma，opossum，kinkajou，andpeccari。SouthAmericaischaracterizedbypossessingmanypeculiargnawers，afamilyofmonkeys，thellama，peccari，tapir，opossums，and，especially，severalgeneraofEdentata，theorderwhichincludesthesloths，ant-eaters，andarmadilloes。NorthAmerica，ontheotherhand，ischaracterizedputtingononesideafewwanderingspeciesbynumerouspeculiargnawers，andbyfourgeneratheox，sheep，goat，andantelopeofhollow-hornedruminants，ofwhichgreatdivisionSouthAmericaisnotknowntopossessasinglespecies。Formerly，butwithintheperiodwhenmostofthenowexistingshellswereliving，NorthAmericapossessed，besideshollow-hornedruminants，theelephant，mastodon，horse，andthreegeneraofEdentata，namely，theMegatherium，Megalonyx，andMylodon。WithinnearlythissameperiodasprovedbytheshellsatBahiaBlancaSouthAmericapossessed，aswehavejustseen，amastodon，horse，hollow-hornedruminant，andthesamethreegeneraaswellasseveralothersoftheEdentata。HenceitisevidentthatNorthandSouthAmerica，inhavingwithinalategeologicalperiodtheseseveralgeneraincommon，weremuchmorecloselyrelatedinthecharacteroftheirterrestrialinhabitantsthantheynoware。ThemoreIreflectonthiscase，themoreinterestingitappears：Iknowofnootherinstancewherewecanalmostmarktheperiodandmannerofthesplittingupofonegreatregionintotwowell-characterizedzoologicalprovinces。
Thegeologist，whoisfullyimpressedwiththevastoscillationsoflevelwhichhaveaffectedtheearth’scrustwithinlateperiods，willnotfeartospeculateontherecentelevationoftheMexicanplatform，or，moreprobably，ontherecentsubmergenceoflandintheWestIndianArchipelago，asthecauseofthepresentzoologicalseparationofNorthandSouthAmerica。
TheSouthAmericancharacteroftheWestIndianmammals[6]seemstoindicatethatthisarchipelagowasformerlyunitedtothesoutherncontinent，andthatithassubsequentlybeenanareaofsubsidence。