HavingcrossedthePeuquenes，wedescendedintoamountainouscountry，intermediatebetweenthetwomainranges，andthentookupourquartersforthenight。WewerenowintherepublicofMendoza。Theelevationwasprobablynotunder11，000feet，andthevegetationinconsequenceexceedinglyscanty。Therootofasmallscrubbyplantservedasfuel，butitmadeamiserablefire，andthewindwaspiercinglycold。Beingquitetiredwithmydayswork，ImadeupmybedasquicklyasIcould，andwenttosleep。
AboutmidnightIobservedtheskybecamesuddenlyclouded：Iawakenedthearrierotoknowiftherewasanydangerofbadweather；buthesaidthatwithoutthunderandlightningtherewasnoriskofaheavysnow-storm。
Theperilisimminent，andthedifficultyofsubsequentescapegreat，toanyoneovertakenbybadweatherbetweenthetworanges。Acertaincaveofferstheonlyplaceofrefuge：Mr。Caldcleugh，whocrossedonthissamedayofthemonth，wasdetainedthereforsometimebyaheavyfallofsnow。
Casuchas，orhousesofrefuge，havenotbeenbuiltinthispassasinthatofUspallata，and，therefore，duringtheautumn，thePortilloislittlefrequented。ImayhereremarkthatwithinthemainCordillerarainneverfalls，forduringthesummertheskyiscloudless，andinwintersnow-stormsaloneoccur。
Attheplacewherewesleptwaternecessarilyboiled，fromthediminishedpressureoftheatmosphere，atalowertemperaturethanitdoesinalessloftycountry；thecasebeingtheconverseofthatofaPapin’sdigester。
Hencethepotatoes，afterremainingforsomehoursintheboilingwater，werenearlyashardasever。Thepotwasleftonthefireallnight，andnextmorningitwasboiledagain，butyetthepotatoeswerenotcooked。
Ifoundoutthis，byoverhearingmytwocompanionsdiscussingthecause，theyhadcometothesimpleconclusion，“thatthecursedpot[whichwasanewone]didnotchoosetoboilpotatoes。”
March22nd——Aftereatingourpotatolessbreakfast，wetravelledacrosstheintermediatetracttothefootofthePortillorange。Inthemiddleofsummercattlearebroughtupheretograze；buttheyhadnowallbeenremoved：eventhegreaternumberoftheGuanacoshaddecamped，knowingwellthatifovertakenherebyasnow-storm，theywouldbecaughtinatrap。WehadafineviewofamassofmountainscalledTupungato，thewholeclothedwithunbrokensnow，inthemidstofwhichtherewasabluepatch，nodoubtaglacier；——acircumstanceofrareoccurrenceinthesemountains。
Nowcommencedaheavyandlongclimb，similartothatofthePeuquenes。
Boldconicalhillsofredgraniteroseoneachhand；inthevalleystherewereseveralbroadfieldsofperpetualsnow。Thesefrozenmasses，duringtheprocessofthawing，hadinsomepartsbeenconvertedintopinnaclesorcolumns，[4]which，astheywerehighandclosetogether，madeitdifficultforthecargomulestopass。Ononeofthesecolumnsofice，afrozenhorsewasstickingasonapedestal，butwithitshindlegsstraightupintheair。Theanimal，Isuppose，musthavefallenwithitsheaddownwardintoahole，whenthesnowwascontinuous，andafterwardsthesurroundingpartsmusthavebeenremovedbythethaw。
WhennearlyonthecrestofthePortillo，wewereenvelopedinafallingcloudofminutefrozenspicula。Thiswasveryunfortunate，asitcontinuedthewholeday，andquiteinterceptedourview。ThepasstakesitsnameofPortillo，fromanarrowcleftordoorwayonthehighestridge，throughwhichtheroadpasses。Fromthispoint，onaclearday，thosevastplainswhichuninterruptedlyextendtotheAtlanticOceancanbeseen。Wedescendedtotheupperlimitofvegetation，andfoundgoodquartersforthenightundertheshelterofsomelargefragmentsofrock。Wemetheresomepassengers，whomadeanxiousinquiriesaboutthestateoftheroad。Shortlyafteritwasdarkthecloudssuddenlyclearedaway，andtheeffectwasquitemagical。
Thegreatmountains，brightwiththefullmoon，seemedimpendingoverusonallsides，asoveradeepcrevice：onemorning，veryearly，Iwitnessedthesamestrikingeffect。Assoonasthecloudsweredisperseditfrozeseverely；butastherewasnowind，wesleptverycomfortably。
Theincreasedbrilliancyofthemoonandstarsatthiselevation，owingtotheperfecttransparencyoftheatmosphere，wasveryremarkable。Travelershavingobservedthedifficultyofjudgingheightsanddistancesamidstloftymountains，havegenerallyattributedittotheabsenceofobjectsofcomparison。Itappearstome，thatitisfullyasmuchowingtothetransparencyoftheairconfoundingobjectsatdifferentdistances，andlikewisepartlytothenoveltyofanunusualdegreeoffatiguearisingfromalittleexertion，——habitbeingthusopposedtotheevidenceofthesenses。Iamsurethatthisextremeclearnessoftheairgivesapeculiarcharactertothelandscape，allobjectsappearingtobebroughtnearlyintooneplane，asinadrawingorpanorama。Thetransparencyis，Ipresume，owingtotheequableandhighstateofatmosphericdryness。ThisdrynesswasshownbythemannerinwhichwoodworkshrankasIsoonfoundbythetroublemygeologicalhammergaveme；byarticlesoffood，suchasbreadandsugar，becomingextremelyhard；andbythepreservationoftheskinandpartsofthefleshofthebeasts，whichhadperishedontheroad。Tothesamecausewemustattributethesingularfacilitywithwhichelectricityisexcited。Myflannelwaistcoat，whenrubbedinthedark，appearedasifithadbeenwashedwithphosphorus，——everyhaironadog’sbackcrackled；——
eventhelinensheets，andleathernstrapsofthesaddle，whenhandled，emittedsparks。
March23rd——ThedescentontheeasternsideoftheCordilleraismuchshorterorsteeperthanonthePacificside；inotherwords，themountainsrisemoreabruptlyfromtheplainsthanfromthealpinecountryofChile。
Alevelandbrilliantlywhiteseaofcloudswasstretchedoutbeneathourfeet，shuttingouttheviewoftheequallylevelPampas。Wesoonenteredthebandofclouds，anddidnotagainemergefromitthatday。Aboutnoon，findingpasturefortheanimalsandbushesforfirewoodatLosArenales，westoppedforthenight。Thiswasneartheuppermostlimitofbushes，andtheelevation，Isuppose，wasbetweensevenandeightthousandfeet。
IwasmuchstruckwiththemarkeddifferencebetweenthevegetationoftheseeasternvalleysandthoseontheChilianside：yettheclimate，aswellasthekindofsoil，isnearlythesame，andthedifferenceoflongitudeverytrifling。Thesameremarkholdsgoodwiththequadrupeds，andinalesserdegreewiththebirdsandinsects。Imayinstancethemice，ofwhichIobtainedthirteenspeciesontheshoresoftheAtlantic，andfiveonthePacific，andnotoneofthemisidentical。Wemustexceptallthosespecies，whichhabituallyoroccasionallyfrequentelevatedmountains；
andcertainbirds，whichrangeasfarsouthastheStraitofMagellan。
ThisfactisinperfectaccordancewiththegeologicalhistoryoftheAndes；
forthesemountainshaveexistedasagreatbarriersincethepresentracesofanimalshaveappeared；andtherefore，unlesswesupposethesamespeciestohavebeencreatedintwodifferentplaces，weoughtnottoexpectanyclosersimilaritybetweentheorganicbeingsontheoppositesidesoftheAndesthanontheoppositeshoresoftheocean。Inbothcases，wemustleaveoutofthequestionthosekindswhichhavebeenabletocrossthebarrier，whetherofsolidrockorsalt-water。[5]
Agreatnumberoftheplantsandanimalswereabsolutelythesameas，ormostcloselyalliedto，thoseofPatagonia。Weherehavetheagouti，bizcacha，threespeciesofarmadillo，theostrich，certainkindsofpartridgesandotherbirds，noneofwhichareeverseeninChile，butarethecharacteristicanimalsofthedesertplainsofPatagonia。Wehavelikewisemanyofthesametotheeyesofapersonwhoisnotabotanistthornystuntedbushes，witheredgrass，anddwarfplants。Eventheblackslowlycrawlingbeetlesarecloselysimilar，andsome，Ibelieve，onrigorousexamination，absolutelyidentical。Ithadalwaysbeentomeasubjectofregret，thatwewereunavoidablycompelledtogiveuptheascentoftheS。Cruzriverbeforereachingthemountains：Ialwayshadalatenthopeofmeetingwithsomegreatchangeinthefeaturesofthecountry；butInowfeelsure，thatitwouldonlyhavebeenfollowingtheplainsofPatagoniaupamountainousascent。
March24th——EarlyinthemorningIclimbedupamountainononesideofthevalley，andenjoyedafarextendedviewoverthePampas。ThiswasaspectacletowhichIhadalwayslookedforwardwithinterest，butIwasdisappointed：atthefirstglanceitmuchresembledadistantviewoftheocean，butinthenorthernpartsmanyirregularitiesweresoondistinguishable。
Themoststrikingfeatureconsistedintherivers，which，facingtherisingsun，glitteredlikesilverthreads，tilllostintheimmensityofthedistance。
Atmiddaywedescendedthevalley，andreachedahovel，whereanofficerandthreesoldierswerepostedtoexaminepassports。OneofthesemenwasathoroughbredPampasIndian：hewaskeptmuchforthesamepurposeasabloodhound，totrackoutanypersonwhomightpassbysecretly，eitheronfootorhorseback。Someyearsago，apassengerendeavouredtoescapedetection，bymakingalongcircuitoveraneighbouringmountain；butthisIndian，havingbychancecrossedhistrack，followeditforthewholedayoverdryandverystonyhills，tillatlasthecameonhispreyhiddeninagully。Wehereheardthatthesilveryclouds，whichwehadadmiredfromthebrightregionabove，hadpoureddowntorrentsofrain。Thevalleyfromthispointgraduallyopened，andthehillsbecamemerewater-wornhillockscomparedtothegiantsbehind：itthenexpandedintoagentlyslopingplainofshingle，coveredwithlowtreesandbushes。Thistalus，althoughappearingnarrow，mustbenearlytenmileswidebeforeitblendsintotheapparentlydeadlevelPampas。Wepassedtheonlyhouseinthisneighbourhood，theEstanciaofChaquaio：andatsunsetwepulledupinthefirstsnugcorner，andtherebivouacked。
March25th——IwasremindedofthePampasofBuenosAyres，byseeingthediskoftherisingsun，intersectedbyanhorizonlevelasthatoftheocean。Duringthenightaheavydewfell，acircumstancewhichwedidnotexperiencewithintheCordillera。Theroadproceededforsomedistancedueeastacrossalowswamp；thenmeetingthedryplain，itturnedtothenorthtowardsMendoza。Thedistanceistwoverylongdays’journey。Ourfirstday’sjourneywascalledfourteenleaguestoEstacado，andthesecondseventeentoLuxan，nearMendoza。Thewholedistanceisoveraleveldesertplain，withnotmorethantwoorthreehouses。Thesunwasexceedinglypowerful，andtheridedevoidofallinterest。Thereisverylittlewaterinthis“traversia。”andinoursecondday’sjourneywefoundonlyonelittlepool。Littlewaterflowsfromthemountains，anditsoonbecomesabsorbedbythedryandporoussoil；sothat，althoughwetravelledatthedistanceofonlytenorfifteenmilesfromtheouterrangeoftheCordillera，wedidnotcrossasinglestream。Inmanypartsthegroundwasincrustedwithasalineefflorescence；hencewehadthesamesalt-lovingplantswhicharecommonnearBahiaBlanca。ThelandscapehasauniformcharacterfromtheStraitofMagellan，alongthewholeeasterncoastofPatagonia，totheRioColorado；anditappearsthatthesamekindofcountryextendsinlandfromthisriver，inasweepinglineasfarasSanLuisandperhapsevenfurthernorth。TotheeastwardofthiscurvedlineliesthebasinofthecomparativelydampandgreenplainsofBuenosAyres。ThesterileplainsofMendozaandPatagoniaconsistofabedofshingle，wornsmoothandaccumulatedbythewavesoftheseawhilethePampas，coveredbythistles，clover，andgrass，havebeenformedbytheancientestuarymudofthePlata。
Afterourtwodays’tediousjourney，itwasrefreshingtoseeinthedistancetherowsofpoplarsandwillowsgrowingroundthevillageandriverofLuxan。Shortlybeforewearrivedatthisplace，weobservedtothesoutharaggedcloudofdarkreddish-browncolour。Atfirstwethoughtthatitwassmokefromsomegreatfireontheplains；butwesoonfoundthatitwasaswarmoflocusts。Theywereflyingnorthward；andwiththeaidofalightbreeze，theyovertookusatarateoftenorfifteenmilesanhour。Themainbodyfilledtheairfromaheightoftwentyfeet，tothat，asitappeared，oftwoorthreethousandabovetheground；“andthesoundoftheirwingswasasthesoundofchariotsofmanyhorsesrunningtobattle：“orrather，Ishouldsay，likeastrongbreezepassingthroughtheriggingofaship。Thesky，seenthroughtheadvancedguard，appearedlikeamezzotintoengraving，butthemainbodywasimpervioustosight；
theywerenot，however，sothicktogether，butthattheycouldescapeastickwavedbackwardsandforwards。Whentheyalighted，theyweremorenumerousthantheleavesinthefield，andthesurfacebecamereddishinsteadofbeinggreen：theswarmhavingoncealighted，theindividualsflewfromsidetosideinalldirections。Locustsarenotanuncommonpestinthiscountry：alreadyduringtheseason，severalsmallerswarmshadcomeupfromthesouth，where，asapparentlyinallotherpartsoftheworld，theyarebredinthedeserts。Thepoorcottagersinvainattemptedbylightingfires，byshouts，andbywavingbranchestoaverttheattack。Thisspeciesoflocustcloselyresembles，andperhapsisidenticalwith，thefamousGryllusmigratoriusoftheEast。
WecrossedtheLuxan，whichisariverofconsiderablesize，thoughitscoursetowardsthesea-coastisveryimperfectlyknown：itisevendoubtfulwhether，inpassingovertheplains，itisnotevaporatedandlost。WesleptinthevillageofLuxan，whichisasmallplacesurroundedbygardens，andformsthemostsoutherncultivateddistrictintheProvinceofMendoza；itisfiveleaguessouthofthecapital。AtnightIexperiencedanattackforitdeservesnolessanameofthe_Benchuca_，aspeciesofReduvius，thegreatblackbugofthePampas。Itismostdisgustingtofeelsoftwinglessinsects，aboutaninchlong，crawlingoverone’sbody。