WhenAmerica，andespeciallyNorthAmerica，possesseditselephants，mastodons，horse，andhollow-hornedruminants，itwasmuchmorecloselyrelatedinitszoologicalcharacterstothetemperatepartsofEuropeandAsiathanitnowis。AstheremainsofthesegeneraarefoundonbothsidesofBehring’sStraits[7]andontheplainsofSiberia，weareledtolooktothenorth-westernsideofNorthAmericaastheformerpointofcommunicationbetweentheOldandso-calledNewWorld。Andassomanyspecies，bothlivingandextinct，ofthesesamegenerainhabitandhaveinhabitedtheOldWorld，itseemsmostprobablethattheNorthAmericanelephants，mastodons，horse，andhollow-hornedruminantsmigrated，onlandsincesubmergednearBehring’sStraits，fromSiberiaintoNorthAmerica，andthence，onlandsincesubmergedintheWestIndies，intoSouthAmerica，whereforatimetheymingledwiththeformscharacteristicofthatsoutherncontinent，andhavesincebecomeextinct。
Whiletravellingthroughthecountry，Ireceivedseveralvividdescriptionsoftheeffectsofalategreatdrought；andtheaccountofthismaythrowsomelightonthecaseswherevastnumbersofanimalsofallkindshavebeenembeddedtogether。Theperiodincludedbetweentheyears1827and1830iscalledthe“granseco。”orthegreatdrought。Duringthistimesolittlerainfell，thatthevegetation，eventothethistles，failed；
thebrooksweredriedup，andthewholecountryassumedtheappearanceofadustyhighroad。ThiswasespeciallythecaseinthenorthernpartoftheprovinceofBuenosAyresandthesouthernpartofSt。Fe。Verygreatnumbersofbirds，wildanimals，cattle，andhorsesperishedfromthewantoffoodandwater。Amantoldmethatthedeer[8]usedtocomeintohiscourtyardtothewell，whichhehadbeenobligedtodigtosupplyhisownfamilywithwater；andthatthepartridgeshadhardlystrengthtoflyawaywhenpursued。ThelowestestimationofthelossofcattleintheprovinceofBuenosAyresalone，wastakenatonemillionhead。AproprietoratSanPedrohadpreviouslytotheseyears20，000
cattle；attheendnotoneremained。SanPedroissituatedinthemiddleofthefinestcountry；andevennowaboundsagainwithanimals；yetduringthelatterpartofthe“granseco。”livecattlewerebroughtinvesselsfortheconsumptionoftheinhabitants。Theanimalsroamedfromtheirestancias，and，wanderingfarsouthward，weremingledtogetherinsuchmultitudes，thatagovernmentcommissionwassentfromBuenosAyrestosettlethedisputesoftheowners。SirWoodbineParishinformedmeofanotherandverycurioussourceofdispute；thegroundbeingsolongdry，suchquantitiesofdustwereblownabout，thatinthisopencountrythelandmarksbecameobliterated，andpeoplecouldnottellthelimitsoftheirestates。
Iwasinformedbyaneye-witnessthatthecattleinherdsofthousandsrushedintotheParana，andbeingexhaustedbyhungertheywereunabletocrawlupthemuddybanks，andthusweredrowned。ThearmoftheriverwhichrunsbySanPedrowassofullofputridcarcasses，thatthemasterofavesseltoldmethatthesmellrendereditquiteimpassable。Withoutdoubtseveralhundredthousandanimalsthusperishedintheriver：theirbodieswhenputridwereseenfloatingdownthestream；andmanyinallprobabilityweredepositedintheestuaryofthePlata。Allthesmallriversbecamehighlysaline，andthiscausedthedeathofvastnumbersinparticularspots；forwhenananimaldrinksofsuchwateritdoesnotrecover。Azaradescribes[9]thefuryofthewildhorsesonasimilaroccasion，rushingintothemarshes，thosewhicharrivedfirstbeingoverwhelmedandcrushedbythosewhichfollowed。Headdsthatmorethanoncehehasseenthecarcassesofupwardsofathousandwildhorsesthusdestroyed。