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。