Iwillnowgive，first，asketchofthestructureoftherange，asrepresentedinthesection，andwillthendescribeitscompositionandinterestinghistory。Atitswesternfoot，ahillock[N]isseentoriseoutoftheplain，withitsstratadippingat70degreestothewest，frontedbystrata[O]inclinedat45degreestotheeast，thusformingalittlenorthandsouthanticlinalaxis。Someotherlittlehillocksofsimilarcomposition，withtheirstratahighlyinclined，rangeN。E。andS。W。obliquelytothemainUspallataline。Thecauseofthesedislocations，which，thoughonasmallscale，havebeenviolentandcomplicated，isseentolieinhummocksoflilac，purpleandredporphyries，whichhavebeeninjectedinaliquifiedstatethroughandintotheunderlyingclay-slateformation。Severaldykeswereexposedhere，butinnootherpart，thatI
sawofthisrange。Asthestrataconsistofblack，white，greenishandbrown-colouredrocks，andastheintrusiveporphyriesaresobrightlytinted，amostextraordinaryviewwaspresented，likeacolouredgeologicaldrawing。Onthegentlyinclinedmainwesternslope[PP]，abovethelittleanticlinalridgesjustmentioned，thestratadipatanaverageangleof25
degreestothewest;theinclinationinsomeplacesbeingonly19degrees，insomefewothersasmuchas45degrees。Themasseshavingthesedifferentinclinations，areseparatedfromeachotherbyparallelverticalfaults[asrepresentedatPa]，oftengivingrisetoseparate，parallel，uniclinalridges。Thesummitofthemainrangeisbroadandundulatory，withthestratificationundulatoryandirregular：inafewplacesgraniticandporphyriticmasses[Q]protrude，which，fromthesmalleffecttheyhavelocallyproducedinderangingthestrata，probablyformtheupperpointsofaregular，greatunderlyingdome。Thesedenudedgraniticpoints，I
estimatedataboutninethousandfeetinheightabovethesea。Ontheeasternslope，thestrataintheupperpartareregularlyinclinedatabout25degreestotheeast，sothatthesummitofthischain，neglectingsmallirregularities，formsabroadanticlinalaxis。Lowerdown，however，nearLosHornillos[R]，thereisawell-markedsynclinalaxis，beyondwhichthestrataareinclinedatnearlythesameangle，namelyfrom20to30degrees，inwardsorwestward。Owingtotheamountofdenudationwhichthischainhassuffered，theoutlineofthegentlyinclinedeasternflankscarcelyofferstheslightestindicationofthissynclinalaxis。Thestratifiedbeds，whichwehavehithertofollowedacrosstherange，alittlefurtherdownareseentolie，Ibelieveunconformably，onabroadmountainousbandofclay-slateandgrauwacke。Thestrataandlaminaeofthislatterformation，ontheextremeeasternflank，aregenerallynearlyvertical;furtherinwardstheybecomeinclinedfrom45to80degreestothewest：nearVillaVicencio[S]
thereisapparentlyananticlinalaxis，butthestructureofthisouterpartoftheclay-slateformationissoobscure，thatIhavenotmarkedtheplanesofstratificationinthesection。OnthemarginofthePampas，somelow，muchdislocatedspursofthissameformation，projectinanorth-
easterlyline，inthesameobliquemannerasdotheridgesonthewesternfoot，andasissofrequentlythecasewiththoseatthebaseofthemainCordillera。
Iwillnowdescribethenatureofthebeds，beginningatthebaseontheeasternside。First，fortheclay-slateformation：theslateisgenerallyhardandbluish，withthelaminaecoatedbyminutemicaceousscales;italternatesmanytimeswithacoarse-grained，greenishgrauwacke，containingroundedfragmentsofquartzandbitsofslateinaslightlycalcareousbasis。Theslateintheupperpartgenerallybecomespurplish，andthecleavagesoirregularthatthewholeconsistsofmeresplinters。Transverseveinsofquartzarenumerous。AttheCalera，someleaguesdistant，thereisadarkcrystallinelimestone，apparentlyincludedinthisformation。Withtheexceptionofthegrauwackebeingheremoreabundant，andtheclay-slatelessaltered，thisformationcloselyresemblesthatunconformablyunderlyingtheporphyriesatthewesternfootofthissamerange;andlikewisethatalternatingwiththeporphyriticconglomerateinthemainCordillera。Thisformationisaconsiderableone，andextendsseveralleaguessouthwardtonearMendoza：themountainscomposedofitrisetoaheightofabouttwothousandfeetabovetheedgeofthePampas，oraboutseventhousandfeetabovethesea。IinferthisfromtheheightofV。
Vicencio，whichwasascertainedbyMr。Mierstobe5，328feetabovethesea。
Secondly：themostusualbedontheclay-slateisacoarse，white，slightlycalcareousconglomerate，ofnogreatthickness，includingbrokencrystalsoffeldspar，grainsofquartz，andnumerouspebblesofbrecciatedclaystoneporphyry，butwithoutanypebblesoftheunderlyingclay-slate。Inowheresawtheactualjunctionbetweenthisbedandtheclay-slate，thoughIspentawholedayinendeavouringtodiscovertheirrelations。InsomeplacesI
distinctlysawthewhiteconglomerateandoverlyingbedsinclinedatfrom25to30degreestothewest，andatthebottomofthesamemountain，theclay-slateandgrauwackeinclinedtothesamepoint，butatananglefrom70to80degrees：inoneinstance，theclay-slatedippednotonlyatadifferentangle，buttoadifferentpointfromtheoverlyingformation。Inthesecasesthetwoformationscertainlyappearedquiteunconformable：
moreover，Ifoundintheclay-slateonegreat，vertical，dike-likefissure，filledupwithaninduratedwhitishtuff，quitesimilartosomeoftheupperbedspresentlytobedescribed;andthisshowsthattheclay-slatemusthavebeenconsolidatedanddislocatedbeforetheirdeposition。Ontheotherhand，thestratificationoftheslateandgrauwacke，insomecasesgraduallyandentirelydisappearedinapproachingtheoverlyingwhiteconglomerate;inothercasesthestratificationofthetwoformationsbecamestrictlyconformable;andagaininothercases，therewassometolerablywellcharacterisedclay-slatelyingabovetheconglomerate。Thecoarse，mechanicalstructureofmanygrauwackeshasalwaysappearedtomeadifficulty;forthetextureoftheassociatedclay-slateandthenatureoftheembeddedorganicremainswherepresent，indicatethatthewholehasbeenadeep-waterdeposit。Whencehavethesometimesincludedangularfragmentsofclay-slate，andtheroundedmassesofquartzandotherrocks，beenderived？Manydeep-waterlimestones，itiswellknown，havebeenbrecciated，andthenfirmlyrecemented。Themostprobableconclusionappearstobe，thataftertheclay-slateformationhadbeendislocatedandtilted，butwhilstunderthesea，afreshandmorerecentdepositionofclay-slatetookplace，onwhichthewhiteconglomeratewasconformablydeposited，withhereandthereathinintercalatedbedofclay-slate。Onthisviewthewhiteconglomeratesandthepresentlytobedescribedtuffsandlavasarereallyunconformabletothemainpartoftheclay-slate;andthis，aswehaveseen，certainlyisthecasewiththeclay-stonelavasinthevalleyofCanota，atthewesternandoppositebaseoftherange。
Thirdly：onthewhiteconglomerate，strataseveralhundredfeetinthicknessaresuperimposed，varyingmuchinnatureinshortdistances：thecommonestvarietyisawhite，muchinduratedtuff，sometimesslightlycalcareous，withferruginousspotsandwater-lines，oftenpassingintowhitishorpurplishcompact，fine-grainedgritorsandstones;othervarietiesbecomesemi-porcellanic，andtintedfaintgreenorblue;otherspassintoaninduratedshale：mostofthesevarietiesareeasilyfusible。
Fourthly：abed，aboutonehundredfeetthickofacompact，partiallycolumnar，pale-grey，feldspathiclava，stainedwithiron，includingverynumerouscrystalsofopaquefeldspar，andwithsomecrystallisedanddisseminatedcalcareousmatter。Thetufaceousstratumonwhichthisfeldspathiclavarestsismuchhardened，stainedpurple，andhasaspherico-concretionarystructure;itherecontainsagoodmanypebblesofclaystoneporphyry。
Fifthly：thinbeds，400feetinthickness，varyingmuchinnature，consistingofwhiteandferruginoustuffs，insomepartshavingaconcretionarystructure，inotherscontainingroundedgrainsandafewpebblesofquartz;alsopassingintohardgritstonesandintogreenishmudstones：thereis，also，muchofabluish-greyandgreensemi-porcellanicstone。
Sixthly：avolcanicstratum，250feetinthickness，ofsovaryinganaturethatIdonotbelieveascoreofspecimenswouldshowallthevarieties;
muchishighlyamygdaloidal，muchcompact;therearegreenish，blackish，purplish，andgreyvarieties，rarelyincludingcrystalsofgreenaugiteandminuteacicularonesoffeldspar，butoftencrystalsandamygdaloidalmassesofwhite，red，andblackcarbonateoflime。Someoftheblackishvarietiesofthisrockhaveaconchoidalfractureandresemblebasalt;
othershaveanirregularfracture。Someofthegreyandpurplishvarietiesarethicklyspeckledwithgreenearthandwithwhitecrystallinecarbonateoflime;othersarelargelyamygdaloidalwithgreenearthandcalcareousspar。Again，otherearthyvarieties，ofgreenish，purplishandgreytints，containmuchiron，andarealmosthalfcomposedofamygdaloidalballsofdarkbrownbole，ofawhitishinduratedfeldspathicmatter，ofbrightgreenearth，ofagate，andofblackandwhitecrystallisedcarbonateoflime。Allthesevarietiesareeasilyfusible。Viewedfromadistance，thelineofjunctionwiththeunderlyingsemi-porcellanicstratawasdistinct;butwhenexaminedclosely，itwasimpossibletopointoutwithinafootwherethelavaendedandwherethesedimentarymassbegan：therockatthetimeofjunctionwasinmostplaceshard，ofabrightgreencolour，andaboundedwithirregularamygdaloidalmassesofferruginousandpurecalcareousspar，andofagate。
Seventhly：strata，eightyfeetinthickness，ofvariousinduratedtuffs，asbefore;manyofthevarietieshaveafinebasisincludingrathercoarseextraneousparticles;someofthemarecompactandsemi-porcellanic，andincludevegetableimpressions。
Eighthly：abed，aboutfiftyfeetthick，ofgreenish-grey，compact，feldspathiclava，withnumeroussmallcrystalsofopaquefeldspar，blackaugite，andoxideofiron。Thejunctionwiththebedonwhichitrested，wasilldefined;ballsandmassesofthefeldspathicrockbeingenclosedinmuchalteredtuff。
Ninthly：induratedtuffs，asbefore。
Tenthly：aconformablelayer，lessthantwofeetinthickness，ofpitchstone，generallybrecciated，andtraversedbyveinsofagateandofcarbonateoflime：partsarecomposedofapparentlyconcretionaryfragmentsofamoreperfectvariety，arrangedinhorizontallinesinalessperfectlycharacterisedvariety。Ihavemuchdifficultyinbelievingthatthisthinlayerofpitchstoneflowedaslava。
Eleventhly：sedimentaryandtufaceousbedsasbefore，passingintosandstone，includingsomeconglomerate：thepebblesinthelatterareofclaystoneporphyry，wellrounded，andsomeaslargeascricket-balls。
Twelfthly：abedofcompact，sonorous，feldspathiclava，likethatofbedNo。8，dividedbynumerousjointsintolargeangularblocks。
Thirteenthly：sedimentarybedsasbefore。
Fourteenthly：athickbedofgreenishorgreyishblack，compactbasaltfusingintoablackenamel，withsmallcrystals，occasionallydistinguishable，offeldsparandaugite：thejunctionwiththeunderlyingsedimentarybed，differentlyfromthatinmostoftheforegoingstreams，herewasquitedistinct：——thelavaandtufaceousmatterpreservingtheirperfectcharacterswithintwoinchesofeachother。Thisrockcloselyresemblescertainpartsofthatvariedandsingularlava-streamNo。6;itlikewiseresembles，asweshallimmediatelysee，manyofthegreatupperbedsonthewesternflankandonthesummitofthisrange。
Thepileofstrataheredescribedattainsagreatthickness;andabovethelast-mentionedvolcanicstratum，therewereseveralothergreattufaceousbedsalternatingwithsubmarinelavas，whichIhadnottimetoexamine;butacorrespondingseries，severalthousandfeetinthickness，iswellexhibitedonthecrestandwesternflankoftherange。Mostofthelava-
streamsonthewesternsideareofajet-blackcolourandbasalticnature;
theyareeithercompactandfine-grained，includingminutecrystalsofaugiteandfeldspar，ortheyarecoarse-grainedandaboundwithratherlargecoppery-browncrystalsofanaugiticmineral。Veryeasilyfusibleintoajet-blackbead，attractedbythemagnet：thecrystalsaretoomuchtarnishedtobemeasuredbythegoniometer。Anothervarietywasofadull-
redcolour，havingaclaystonebrecciatedbasis，includingspecksofoxideofironandofcalcareousspar，andamygdaloidalwithgreenearth：therewereapparentlyseveralothervarieties。Thesesubmarinelavasoftenexhibitaspheroidal，andsometimesanimperfectcolumnarstructure：theirupperjunctionsaremuchmoreclearlydefinedthantheirlowerjunctions;
butthelatterarenotsomuchblendedintotheunderlyingsedimentarybedsasisthecaseintheeasternflank。Onthecrestandwesternflankoftherange，thestreams，viewedasawhole，aremostlybasaltic;whilstthoseontheeasternside，whichstandlowerintheseries，are，aswehaveseen，mostlyfeldspathic。
Thesedimentarystrataalternatingwiththelavasonthecrestandwesternside，areofanalmostinfinitelyvaryingnature;butalargeproportionofthemcloselyresemblethosealreadydescribedontheeasternflank：therearewhiteandbrown，indurated，easilyfusibletuffs，——somepassingintopaleblueandgreensemi-porcellanicrocks，——othersintobrownishandpurplishsandstonesandgritstones，oftenincludinggrainsofquartz，——
othersintomudstonecontainingbrokencrystalsandparticlesofrock，andoccasionallysinglelargepebbles。Therewasonestratumofabrightred，coarse，volcanicgritstone;anotherofconglomerate;anotherofablack，indurated，carbonaceousshalemarkedwithimperfectvegetableimpressions;
thislatterbed，whichwasthin，restedonasubmarinelava，andfollowedalltheconsiderableinequalitiesofitsuppersurface。Mr。Miersstatesthatcoalhasbeenfoundinthisrange。Lastly，therewasabedlikeNo。
10ontheeasternflankevidentlyofsedimentaryorigin，andremarkablefromcloselyapproachingincharactertoanimperfectpitchstone，andfromincludingextremelythinlayersofperfectpitchstone，aswellasnodulesandirregularfragmentsbutnotresemblingextraneousfragmentsofthissamerockarrangedinhorizontallines：Iconceivethatthisbed，whichisonlyafewfeetinthickness，musthaveassumeditspresentstatethroughmetamorphicandconcretionaryaction。Mostofthesesedimentarystrataaremuchindurated，andnodoubthavebeenpartiallymetamorphosed：manyofthemareextraordinarilyheavyandcompact;othershaveagateandcrystallinecarbonateoflimedisseminatedthroughoutthem。Someofthebedsexhibitasingularconcretionaryarrangement，withthecurvesdeterminedbythelinesoffissure。Therearemanyveinsofagateandcalcareousspar，andinnumerableonesofironandothermetals，whichhaveblackenedandcuriouslyaffectedthestratatoconsiderabledistancesonbothsides。
Manyofthesetufaceousbedsresemble，withtheexceptionofbeingmoreindurated，theupperbedsoftheGreatPatagoniantertiaryformation，especiallythosevariouslycolouredlayershighuptheRiverSantaCruz，andinaremarkabledegreethetufaceousformationatthenorthernendofChiloe。Iwassomuchstruckwiththisresemblance，thatIparticularlylookedoutforsilicifiedwood，andfounditunderthefollowingextraordinarycircumstances。Highuponthiswesternflank，ataheightestimatedat7，000feetabovethesea，inabrokenescarpmentofthinstrata，composedofcompactgreengritstonepassingintoafinemudstone，andalternatingwithlayersofcoarser，brownish，veryheavymudstone，includingbrokencrystalsandparticlesofrockalmostblendedtogether，I
countedthestumpsoffifty-twotrees。Fortheinformationofanyfuturetraveller，Iwilldescribethespotindetail。ProceedingeastwardfromtheAguadelZorro，andafterwardsleavingonthenorthsideoftheroadaranchoattachedtosomeoldgoldmines，youpassthroughagullywithlowbutsteeprocksoneachhand：theroadthenbends，andtheascentbecomessteeper。Afewhundredyardsfartheron，astone’sthrowonthesouthsideoftheroad，thewhitecalcareousstumpsmaybeseen。ThespotisabouthalfamileeastoftheAguadelZorro。Theyprojectedbetweentwoandfivefeetabovetheground，andstoodatexactlyrightanglestothestrata，whichwerehereinclinedatanangleofabout25degreestothewest。Elevenofthesetreesweresilicifiedandwellpreserved;Mr。R。
Brownhasbeensokindastoexaminethewoodwhenslicedandpolished;hesaysitisconiferous，partakingofthecharactersoftheAraucariantribe，withsomecuriouspointsofaffinitywiththeYew。Thebarkroundthetrunksmusthavebeencircularlyfurrowedwithirregularlines，forthemudstoneroundthemisthusplainlymarked。Onecastconsistedofdarkargillaceouslimestone;andfortyofthemofcoarselycrystallisedcarbonateoflime，withcavitieslinedbyquartzcrystals：theselatterwhitecalcareouscolumnsdonotretainanyinternalstructure，buttheirexternalformplainlyshowstheirorigin。Allthestumpshavenearlythesamediameter，varyingfromonefoottoeighteeninches;someofthemstandwithinayardofeachother;theyaregroupedinaclumpwithinaspaceofaboutsixtyyardsacross，withafewscatteredroundatthedistanceof150
yards。Theyallstandataboutthesamelevel。Thelongeststumpstoodsevenfeetoutoftheground：theroots，iftheyarestillpreserved，areburiedandconcealed。Noonelayerofthemudstoneappearedmuchdarkerthantheothers，asifithadformerlyexistedassoil，norcouldthisbeexpected，forthesameagentswhichreplacedwithsilexandlimethewoodofthetrees，wouldnaturallyhaveremovedallvegetablematterfromthesoil。Besidesthefifty-twouprighttrees，therewereafewfragments，likebrokenbranches，horizontallyembedded。Thesurroundingstrataarecrossedbyveinsofcarbonateoflime，agate，andoxideofiron;andapoorgoldveinhasbeenworkednotfarfromthetrees。
Thegreenandbrownmudstonebedsincludingthetrees，areconformablycoveredbymuchindurated，compact，whiteorferruginoustuffs，whichpassupwardsintoafine-grained，purplishsedimentaryrock：thesestrata，which，together，arefromfourtofivehundredfeetinthickness，restonathickbedofsubmarinelava，andareconformablycoveredbyanothergreatmassoffine-grainedbasalt，whichIestimatedat1，000feetinthickness，andwhichprobablyhasbeenformedbymorethanonestream。Thisrockisquiteblack，andfusesintoablackbead，attractedstronglybythemagnet;
itbreakswithaconchoidalfracture;theincludedcrystalsofaugitearedistinguishablebythenakedeye，butarenotperfectenoughtobemeasured：therearemanyminuteacicularcrystalsofglassyfeldspar。
AbovethismassIcouldclearlydistinguishfiveconformablealternations，eachseveralhundredfeetinthickness，ofstratifiedsedimentaryrocksandlavas，suchashavebeenpreviouslydescribed。Certainlytheuprighttreeshavebeenburiedunderseveralthousandfeetinthicknessofmatter，accumulatedunderthesea。Asthetreesobviouslymustoncehavegrownondryland，whatanenormousamountofsubsidenceisthusindicated！
Nevertheless，haditnotbeenforthetreestherewasnoappearancewhichwouldhaveledanyoneeventohaveconjecturedthatthesestratahadsubsided。Astheland，moreover，onwhichthetreesgrew，isformedofsubaqueousdeposits，ofnearlyifnotquiteequalthicknesswiththesuperincumbentstrata，andasthesedepositsareregularlystratifiedandfine-grained，notlikethematterthrownuponasea-beach，apreviousupwardmovement，aidednodoubtbythegreataccumulationoflavasandsediment，isalsoindicated。AtfirstIimagined，thatthestratawiththetreesmighthavebeenaccumulatedinalake：butthisseemshighlyimprobable;for，first，averydeeplakewasnecessarytoreceivethematterbelowthetrees，thenitmusthavebeendrainedfortheirgrowth，andafterwardsre-formedandmadeprofoundlydeep，soastoreceiveasubsequentaccumulationofmatterSEVERALTHOUSANDfeetinthickness。AndallthismusthavetakenplacenecessarilybeforetheformationoftheUspallatarange，andthereforeonthemarginofthewidelevelexpanseofthePampas！HenceIconclude，thatitisinfinitelymoreprobablethatthestratawereaccumulatedunderthesea：thevastamountofdenudation，moreover，whichthisrangehassuffered，asshownbythewidevalleys，bytheexposureoftheverytreesandbyotherappearances，couldhavebeeneffected，Iconceive，onlybythelong-continuedactionofthesea;andthisshowsthattherangewaseitherupheavedfromunderthesea，orsubsequentlyletdownintoit。Fromthenaturalmannerinwhichthestumpsfifty-twoinnumberareGROUPEDINACLUMP，andfromtheirallstandingverticallytothestrata，itissuperfluoustospeculateonthechanceofthetreeshavingbeendriftedfromadjoiningland，anddepositedupright：I
may，however，mentionthatthelateDr。Malcolmsonassuredme，thatheoncemetintheIndianOcean，fiftymilesfromland，severalcocoa-nuttreesfloatingupright，owingtotheirrootsbeingloadedwithearth。
Innearlythemiddleoftherange，therearesomehills[Q]，beforealludedto，formedofakindofgraniteexternallyresemblingandesite，andconsistingofawhite，imperfectlygranular，feldspathicbasis，includingsomeperfectcrystalsapparentlyofalbitebutIwasunabletomeasurethem，muchblackmica，epidoteinveins，andverylittleornoquartz。
Numeroussmallveinsbranchfromthisrockintothesurroundingstrata;anditisasingularfactthattheseveins，thoughcomposedofthesamekindoffeldsparandsmallscalesofmicaasinthesolidrock，aboundwithinnumerableminuteROUNDEDgrainsofquartz：intheveinsordikesalso，branchingfromthegreatgraniticaxisinthepeninsulaofTresMontes，I
observedthatquartzwasmoreabundantinthemthaninthemainrock：I
haveheardofotheranalogouscases：canweaccountforthisfact，bythelong-continuedvicinityofquartzwhencooling，andbyitshavingbeenthusmoreeasilysuckedintofissuresthantheotherconstituentmineralsofgranite？SeeapaperbyM。EliedeBeaumont，“Soc。Philomath。”May1839
“L’Institut。”1839page161。Thestrataencasingtheflanksofthesegraniticorandesitemasses，andformingathickcapononeoftheirsummits，appearoriginallytohavebeenofthesametufaceousnaturewiththebedsalreadydescribed，buttheyarenowchangedintoporcellanic，jaspery，andcrystallinerocks，andintoothersofawhitecolourwithaharshtexture，andhavingasiliceousaspect，thoughreallyofafeldspathicnatureandfusible。Boththegraniticintrusivemassesandtheencasingstrataarepenetratedbyinnumerablemetallicveins，mostlyferruginousandauriferous，butsomecontainingcopper-pyritesandafewsilver：neartheveins，therocksareblackenedasifblastedbygunpowder。
Thestrataareonlyslightlydislocatedcloseroundthesehills，andhence，perhaps，itmaybeinferredthatthegraniticmassesformonlytheprojectingpointsofabroadcontinuousaxis-dome，whichhasgiventotheupperpartsofthisrangeitsanticlinalstructure。
CONCLUDINGREMARKSONTHEUSPALLATARANGE。
Iwillnotattempttoestimatethetotalthicknessofthepileofstrataformingthisrange，butitmustamounttomanythousandfeet。Thesedimentaryandtufaceousbedshavethroughoutageneralsimilarity，thoughwithinfinitevariations。Thesubmarinelavasinthelowerpartoftheseriesaremostlyfeldspathic，whilstintheupperpart，onthesummitandwesternflank，theyaremostlybasaltic。Wearethusremindedoftherelativepositioninmostrecentvolcanicdistrictsofthetrachyticandbasalticlavas，——thelatterfromtheirgreaterweighthavingsunktoalowerlevelintheearth’scrust，andhavingconsequentlybeeneruptedatalaterperiodoverthelighterandupperlavasofthetrachyticseries。Seeonthissubject，“VolcanicIslands“etc。bytheAuthor。Boththebasalticandfeldspathicsubmarinestreamsareverycompact;nonebeingvesicular，andonlyafewamygdaloidal：theeffectswhichsomeofthem，especiallythoselowintheseries，haveproducedonthetufaceousbedsoverwhichtheyhaveflowedishighlycurious。Independentlyofthislocalmetamorphicaction，allthestrataundoubtedlydisplayaninduratedandalteredcharacter;andalltherocksofthisrange——thelavas，thealternatingsediments，theintrusivegraniteandporphyries，andtheunderlyingclay-
slate——areintersectedbymetalliferousveins。Thelava-stratacanoftenbeseenextendingforgreatdistances，conformablywiththeunderandoverlyingbeds;anditwasobviousthattheythickenedtowardsthewest。
Hencethepointsoferuptionmusthavebeensituatedwestwardofthepresentrange，inthedirectionofthemainCordillera：as，however，theflanksoftheCordilleraareentirelycomposedofvariousporphyries，chieflyclaystoneandgreenstone，someintrusive，andothersbelongingtotheporphyriticconglomerateformation，butallquiteunlikethesesubmarinelava-streams，wemustinallprobabilitylooktotheplainofUspallataforthenowdeeplyburiedpointsoferuption。
ComparingoursectionoftheUspallatarangewiththatoftheCumbre，wesee，withtheexceptionoftheunderlyingclay-slate，andperhapsoftheintrusiverocksoftheaxes，astrikingdissimilarityinthestratacomposingthem。Thegreatporphyriticconglomerateformationhasnotextendedasfarasthisrange;norhavewehereanyofthegypseousstrata，themagnesianandotherlimestones，theredsandstones，thesiliceousbedswithpebblesofquartz，andcomparativelylittleoftheconglomerates，allofwhichformsuchvastmassesoverthebasalseriesinthemainCordillera。Ontheotherhand，intheCordillera，wedonotfindthoseendlessvarietiesofinduratedtuffs，withtheirnumerousveinsandconcretionaryarrangement，andthosegritandmudstones，andsingularsemi-porcellanicrocks，soabundantintheUspallatarange。Thesubmarinelavas，also，differconsiderably;thefeldspathicstreamsoftheCordilleracontainmuchmica，whichisabsentinthoseoftheUspallatarange：inthislatterrangewehaveseenonhowgrandascale，basalticlavahasbeenpouredforth，ofwhichthereisnotatraceintheCordillera。Thisdissimilarityisthemorestriking，consideringthatthesetwoparallelchainsareseparatedbyaplainonlybetweentenandfifteenmilesinwidth;andthattheUspallatalavas，aswellasnodoubtthealternatingtufaceousbeds，haveproceededfromthewest，frompointsapparentlybetweenthetworanges。Toimaginethatthesetwopilesofstratawerecontemporaneouslydepositedintwocloselyadjoining，verydeep，submarineareas，separatedfromeachotherbyaloftyridge，whereaplainnowextends，wouldbeagratuitoushypothesis。Andhadtheybeencontemporaneouslydeposited，withoutanysuchdividingridge，surelysomeofthegypseousandothersedimentarymatterformingsuchimmenselythickmassesintheCordillera，wouldhaveextendedthisshortdistanceeastwards;andsurelysomeoftheUspallatatuffsandbasaltsalsoaccumulatedtosogreatathickness，wouldhaveextendedalittlewestward。
HenceIconclude，thatitisfarfromprobablethatthesetwoseriesarenotcontemporaneous;butthatthestrataofoneofthechainsweredeposited，andeventhechainitselfuplifted，beforetheformationoftheother：——whichchain，then，istheoldest？ConsideringthatintheUspallatarangetheloweststrataonthewesternflanklieunconformablyontheclay-
slate，asprobablyisthecasewiththoseontheeasternflank，whereasintheCordilleraalltheoverlyingstratalieconformablyonthisformation：——
consideringthatintheUspallatarangesomeofthebeds，bothlowdownandhighupintheseries，aremarkedwithvegetableimpressions，showingthecontinuedexistenceofneighbouringland;——consideringtheclosegeneralresemblancebetweenthedepositsofthisrangeandthoseoftertiaryorigininseveralpartsofthecontinent;——andlastly，evenconsideringthelesserheightandoutlyingpositionoftheUspallatarange，——Iconcludethatthestratacomposingitareinallprobabilityofsubsequentorigin，andthattheywereaccumulatedataperiodwhenadeepseastuddedwithsubmarinevolcanoeswashedtheeasternbaseofthealreadypartiallyelevatedCordillera。
Thisconclusionisofmuchimportance，forwehaveseenthatintheCordillera，duringthedepositionoftheNeocomianstrata，thebedoftheseamusthavesubsidedmanythousandfeet：wenowlearnthatatalaterperiodanadjoiningareafirstreceivedagreataccumulationofstrata，andwasupheavedintolandonwhichconiferoustreesgrew，andthatthisareathensubsidedseveralthousandfeettoreceivethesuperincumbentsubmarinestrata，afterwardsbeingbrokenup，denuded，andelevatedinmasstoitspresentheight。Iamstrengthenedinthisconclusionoftherehavingbeentwodistinct，greatperiodsofsubsidence，byreflectingonthethickmassofcoarsestratifiedconglomerateinthevalleyofTenuyan，betweenthePeuquenesandPortillolines;fortheaccumulationofthismassseemstome，aspreviouslyremarked，almostnecessarilytohaverequiredaprolongedsubsidence;andthissubsidence，fromthepebblesintheconglomeratehavingbeentoagreatextentderivedfromthegypseousorNeocomianstrataofthePeuquenesline，weknowmusthavebeenquitedistinctfrom，andsubsequentto，thatsinkingmovementwhichprobablyaccompaniedthedepositionofthePeuquenesstrata，andwhichcertainlyaccompaniedthedepositionoftheequivalentbedsnearthePuentedelInca，inthislineofsection。
TheUspallatachaincorrespondsingeographicalposition，thoughonasmallscale，withthePortilloline;anditsclay-slateformationisprobablytheequivalentofthemica-schistofthePortillo，theremetamorphosedbytheoldwhitegranitesandsyenites。ThecolouredbedsundertheconglomerateinthevalleyofTenuyan，ofwhichtracesareseenonthecrestofthePortillo，andeventheconglomerateitself，mayperhapsbesynchronouswiththetufaceousbedsandsubmarinelavasoftheUspallatarange;anopenseaandvolcanicactioninthelattercase，andaconfinedchannelbetweentwoborderingchainsofisletsintheformercase，havingbeensufficienttoaccountforthemineralogicaldissimilarityofthetwoseries。FromthiscorrespondencebetweentheUspallataandPortilloranges，perhapsinageandcertainlyingeographicalposition，oneistemptedtoconsidertheonerangeastheprolongationoftheother;buttheiraxesareformedoftotallydifferentintrusiverocks;andwehavetracedtheapparentcontinuationoftheredgraniteofthePortillointheredporphyriesdivergingintothemainCordillera。WhethertheaxisoftheUspallatarangewasinjectedbefore，orasperhapsismoreprobable，afterthatofthePortilloline，Iwillnotpretendtodecide;butitiswelltorememberthatthehighlyinclinedlava-streamsontheeasternflankofthePortilloline，provethatitsangularupheavementwasnotasingleandsuddenevent;
andthereforethattheanticlinalelevationoftheUspallatarangemayhavebeencontemporaneouswithsomeofthelaterangularmovementsbywhichthegiganticPortillorangegaineditspresentheightabovetheadjoiningplain。
CHAPTERVIII。NORTHERNCHILE。CONCLUSION。
SectionfromIllapeltoCombarbala;gypseousformationwithsilicifiedwood。
Panuncillo。
Coquimbo;minesofArqueros;sectionupvalley;fossils。
Guasco，fossilsof。
Copiapo，sectionupvalley;LasAmolanas，silicifiedwood。
Conglomerates，natureofformerland，fossils，thicknessofstrata，greatsubsidence。
ValleyofDespoblado，fossils，tufaceousdeposit，complicateddislocationsof。
Relationsbetweenancientorificesoferuptionandsubsequentaxesofinjection。
Iquique，Peru，fossilsof，salt-deposits。
Metalliferousveins。
Summaryontheporphyriticconglomerateandgypseousformations。
Greatsubsidencewithpartialelevationsduringthecretaceo-ooliticperiod。
OntheelevationandstructureoftheCordillera。
Recapitulationonthetertiaryseries。
Relationbetweenmovementsofsubsidenceandvolcanicaction。
Pampeanformation。
Recentelevatorymovements。
Long-continuedvolcanicactionintheCordillera。
Conclusion。
VALPARAISOTOCOQUIMBO。
IhavealreadydescribedthegeneralnatureoftherocksinthelowcountrynorthofValparaiso，consistingofgranites，syenites，greenstones，andalteredfeldspathicclay-slate。NearCoquimbothereismuchhornblendicrockandvariousdusky-colouredporphyries。Iwilldescribeonlyonesectioninthisdistrict，namely，fromnearIllapelinaN。E。linetotheminesofLosHornos，andthenceinanorthbyeastdirectiontoCombarbala，atthefootofthemainCordillera。
NearIllapel，afterpassingforsomedistanceovergranite，andesite，andandesiticporphyry，wecometoagreenishstratifiedfeldspathicrock，whichIbelieveisalteredclay-slate，conformablycappedbyporphyriesandporphyriticconglomerateofgreatthickness，dippingatanaverageangleof20degreestoN。E。byN。Theuppermostbedsconsistofconglomeratesandsandstoneonlyalittlemetamorphosed，andconformablycoveredbyagypseousformationofverygreatthickness，butmuchdenuded。Thisgypseousformation，wherefirstmetwith，liesinabroadvalleyorbasin，alittlesouthwardoftheminesofLosHornos：thelowerhalfalonecontainsgypsum，notingreatmassesasintheCordillera，butininnumerablethinlayers，seldommorethananinchortwointhickness。Thegypsumiseitheropaqueortransparent，andisassociatedwithcarbonateoflime。Thelayersalternatewithnumerousvaryingonesofacalcareousclay-shalewithstrongaluminousodour，adheringtothetongue，easilyfusibleintoapalegreenglass，moreorlessindurated，eitherearthyandcream-coloured，orgreenishandhard。Themoreinduratedvarietieshaveacompact，homogeneous，almostcrystallinefracture，andcontaingranulesofcrystallisedoxideofiron。Someofthevarietiesalmostresemblehonestones。Thereisalsoalittleblack，hardlyfusible，siliceo-
calcareousclay-slate，likesomeofthevarietiesalternatingwithgypsumonthePeuquenesrange。
Theupperhalfofthisgypseousformationismainlyformedofthesamecalcareousclay-shalerock，butwithoutanygypsum，andvaryingextremelyinnature：itpassesfromasoft，coarse，earthy，ferruginousstate，includingparticlesofquartz，intocompactclaystoneswithcrystallisedoxideofiron，——intoporcellaniclayers，alternatingwithseamsofcalcareousmatter，——andintogreenporcelain-jasper，excessivelyhard，buteasilyfusible。Strataofthisnaturealternatewithmuchblackandbrownsiliceo-calcareousslate，remarkablefromthewonderfulnumberofhugeembeddedlogsofsilicifiedwood。Thiswood，accordingtoMr。R。Brown，isjudgingfromseveralspecimensallconiferous。Someofthelayersoftheblacksiliceousslatecontainedirregularangularfragmentsofimperfectpitchstone，whichIbelieve，asintheUspallatarange，hasoriginatedinametamorphicprocess。Therewasonebedofamarlytufaceousnature，andoflittlespecificgravity。Veinsofagateandcalcareousspararenumerous。
Thewholeofthisgypseousformation，especiallytheupperhalf，hasbeeninjected，metamorphosed，andlocallycontortedbynumeroushillocksofintrusiveporphyriescrowdedtogetherinanextraordinarymanner。Thesehillocksconsistofpurpleclaystoneandofvariousotherporphyries，andofmuchwhitefeldspathicgreenstonepassingintoandesite;thislattervarietyincludedinonecasecrystalsoforthiticandalbiticfeldspartouchingeachother，andothersofhornblende，chlorite，andepidote。ThestratasurroundingtheseintrusivehillocksattheminesofLosHornos，areintersectedbymanyveinsofcopper-pyrites，associatedwithmuchmicaceousiron-ore，andbysomeofgold：intheneighbourhoodoftheseveinstherocksareblackenedandmuchaltered。Thegypsumneartheintrusivemassesisalwaysopaque。Oneofthesehillocksofporphyrywascappedbysomestratifiedporphyriticconglomerate，whichmusthavebeenbroughtupfrombelow，throughthewholeimmensethicknessoftheoverlyinggypseousformation。ThelowerbedsofthegypseousformationresemblethecorrespondingandprobablycontemporaneousstrataofthemainCordillera;
whilsttheupperbedsinseveralrespectsresemblethoseoftheUspallatachain，andpossiblymaybecontemporaneouswiththem;forIhaveendeavouredtoshowthattheUspallatabedswereaccumulatedsubsequentlytothegypseousorNeocomianformationsoftheCordillera。
Thispileofstratadipsatanangleofabout20degreestoN。E。byN。closeuptothefootoftheCuestadeLosHornos，acrookedrangeofmountainsformedofintrusiverocksofthesamenaturewiththeabovedescribedhillocks。Onlyinoneortwoplaces，onthissouth-easternsideoftherange，Inoticedanarrowfringeoftheuppergypseousstratabrushedupandinclinedsouth-eastwardfromit。Onitsnorth-easternflank，andlikewiseonafewofthesummits，thestratifiedporphyriticconglomerateisinclinedN。E。：sothat，ifwedisregardtheverynarrowanticlinalfringeofgypseousstrataatitsS。E。foot，thisrangeformsaseconduniclinalaxisofelevation。Proceedinginanorth-by-eastdirectiontothevillageofCombarbala，wecometoathirdescarpmentoftheporphyriticconglomerate，dippingeastwards，andformingtheouterrangeofthemainCordillera。Thelowerbedswereheremorejasperythanusual，andtheyincludedsomewhitechertystrataandredsandstones，alternatingwithpurpleclaystoneporphyry。HigherupintheCordillerathereappearedtobealineofandesiticrocks;andbeyondthem，afourthescarpmentoftheporphyriticconglomerate，againdippingeastwardsorinwards。Theoverlyinggypseousstrata，iftheyeverexistedhere，havebeenentirelyremoved。
COPPERMINESOFPANUNCILLO。
>FromCombarbalatoCoquimbo，Itraversedthecountryinazigzagdirection，crossingandrecrossingtheporphyriticconglomerateandfindinginthegraniticdistrictsanunusualnumberofmountain-massescomposedofvariousintrusive，porphyriticrocks，manyofthemandesitic。Onecommonvarietywasgreenish-black，withlargecrystalsofblackishalbite。AtPanuncilloashortN。N。W。andS。S。E。ridge，withanucleusformedofgreenstoneandofaslate-colouredporphyryincludingcrystalsofglassyfeldspar，deservesnotice，fromtheverysingularnatureofthealmostverticalstratacomposingit。Theseconsistchieflyofafinerandcoarsergranularmixture，notverycompact，ofwhitecarbonateoflime，ofprotoxideofironandofyellowishgarnetsascertainedbyProfessorMiller，eachgrainbeinganalmostperfectcrystal。Someofthevarietiesconsistexclusivelyofgranulesofthecalcareousspar;andsomecontaingrainsofcopperore，and，Ibelieve，ofquartz。Thesestrataalternatewithabluish，compact，fusible，feldspathicrock。Muchoftheabovegranularmixturehas，also，apseudo-brecciatedstructure，inwhichfragmentsareobscurelyarrangedinplanesparalleltothoseofthestratification，andareconspicuousontheweatheredsurfaces。Thefragmentsareangularorrounded，smallorlarge，andconsistofbluishorreddishcompactfeldspathicmatter，inwhichafewacicularcrystalsoffeldsparcansometimesbeseen。Thefragmentsoftenblendattheiredgesintothesurroundinggranularmass，andseemduetoakindofconcretionaryaction。
Thesesingularrocksaretraversedbymanycopperveins，andappeartorestconformablyonthegranularmixtureinpartsasfine-grainedasasandstoneofquartz，mica，hornblende，andfeldspar;andthisonfine-
grained，commongneiss;andthisonalaminatedmass，composedofpinkishORTHITICfeldspar，includingafewspecksofhornblende;andlastly，thisongranite，whichtogetherwithandesiticrocks，formthesurroundingdistrict。
COQUIMBO：MININGDISTRICTOFARQUEROS。
AtCoquimbotheporphyriticconglomerateformationapproachesnearertothePacificthaninanyotherpartofChilevisitedbyme，beingseparatedfromthecoastbyatractonlyafewmilesbroadoftheusualplutonicrocks，withtheadditionofaporphyryhavingaredeuriticbase。InproceedingtotheminesofArqueros，thestrataofporphyriticconglomerateareatfirstnearlyhorizontal，anunusualcircumstance，andafterwardstheydipgentlytoS。S。E。Afterhavingascendedtoaconsiderableheight，wecometoanundulatorydistrictinwhichthefamoussilverminesaresituated;myexaminationwaschieflyconfinedtothoseofS。Rosa。Mostoftherocksinthisdistrictarestratified，dippinginvariousdirections，andmanyofthemareofsosingularanature，thatattheriskofbeingtediousImustbrieflydescribethem。Thecommonestvarietyisadull-red，compact，finelybrecciatedstone，containingmuchironandinnumerablewhitecrystallisedparticlesofcarbonateoflime，andminuteextraneousfragments。AnothervarietyisalmostequallycommonnearS。Rosa;ithasabrightgreen，scantybasis，includingdistinctcrystalsandpatchesofwhitecarbonateoflime，andgrainsofred，semi-micaceousoxideofiron;inpartsthebasisbecomesdarkgreen，andassumesanobscurecrystallinearrangement，andoccasionallyinpartsitbecomessoftandslightlytranslucentlikesoapstone。Theseredandgreenrocksareoftenquitedistinct，andoftenpassintoeachother;thepassagebeingsometimesaffectedbyafinebrecciatedstructure，particlesoftheredandgreenmatterbeingmingledtogether。Someofthevarietiesappeargraduallytobecomeporphyriticwithfeldspar;andallofthemareeasilyfusibleintopaleordark-colouredbeads，stronglyattractedbythemagnet。Ishouldperhapshavemistakenseveralofthesestratifiedrocksforsubmarinelavas，likesomeofthosedescribedatthePuentedelInca，hadInotexamined，afewleagueseastwardofthispoint，afineseriesofanalogousbutlessmetamorphosed，sedimentarybedsbelongingtothegypseousformation，andprobablyderivedfromavolcanicsource。
Thisformationisintersectedbynumerousmetalliferousveins，running，thoughirregularly，N。W。andS。E。andgenerallyatrightanglestothemanydikes。Theveinsconsistofnativesilver，ofmuriateofsilver，anamalgamofsilver，cobalt，antimony，andarsenic，generallyembeddedinsulphateofbarytes。SeetheReportonM。Domeyko’saccountofthosemines，inthe“ComptesRendus“tome14page560。IwasassuredbyMr。
Lambert，thatnativecopperwithoutatraceofsilverhasbeenfoundinthesameveinwithnativesilverwithoutatraceofcopper。AttheminesofAristeas，thesilverveinsaresaidtobeunproductiveassoonastheypassintothegreenstrata，whereasatS。Rosa，onlytwoorthreemilesdistant，thereversehappens;andatthetimeofmyvisit，theminerswereworkingthrougharedstratum，inthehopeoftheveinbecomingproductiveintheunderlyinggreensedimentarymass。Ihaveaspecimenofoneofthesegreenrocks，withtheusualgranulesofwhitecalcareoussparandredoxideofiron，aboundingwithdisseminatedparticlesofglitteringnativeandmuriateofsilver，yettakenatthedistanceofoneyardfromanyvein，——acircumstance，asIwasassured，ofveryrareoccurrence。
SECTIONEASTWARD，UPTHEVALLEYOFCOQUIMBO。
Afterpassingforafewmilesoverthecoastgraniticseries，wecometotheporphyriticconglomerate，withitsusualcharacters，andwithsomeofthebedsdistinctlydisplayingtheirmechanicalorigin。Thestrata，wherefirstmetwith，are，asbeforestated，onlyslightlyinclined;butneartheHaciendaofPluclaro，wecometoananticlinalaxis，withthebedsmuchdislocatedandshiftedbyagreatfault，ofwhichnotatraceisexternallyseenintheoutlineofthehill。Ibelievethatthisanticlinalaxiscanbetracednorthwards，intothedistrictofArqueros，whereaconspicuoushillcalledCerroBlanco，formedofaharsh，cream-colouredeuriticrock，includingafewcrystalsofreddishfeldspar，andassociatedwithsomepurplishclaystoneporphyry，seemstofallonalineofelevation。IndescendingfromtheArquerosdistrict，Icrossedonthenorthernborderofthevalley，stratainclinedeastwardfromthePluclaroaxis：ontheporphyriticconglomeratethererestedamass，somehundredfeetthick，ofbrownargillaceouslimestone，inpartscrystalline，andinpartsalmostcomposedofHippuritesChilensis，d’Orbigny;abovethiscameablackcalcareousshale，andonitaredconglomerate。Inthebrownlimestone，withtheHippurites，therewasanimpressionofaPectenandacoral，andgreatnumbersofalargeGryphaea，verylike，and，accordingtoProfessorE。Forbes，probablyidenticalwithG。Orientalis，ForbesMS——acretaceousspeciesprobablyuppergreensandfromVerdachellum，inSouthernIndia。
ThesefossilsseemtooccupynearlythesamepositionwiththoseatthePuentedelInca，——namely，atthetopoftheporphyriticconglomerate，andatthebaseofthegypseousformation。
AlittleabovetheHaciendaofPluclaro，Imadeadetouronthenorthernsideofthevalley，toexaminethesuperincumbentgypseousstrata，whichI
estimatedat6，000feetinthickness。Theuppermostbedsoftheporphyriticconglomerate，onwhichthegypseousstrataconformablyrest，arevariouslycoloured，withoneverysingularandbeautifulstratumcomposedofpurplepebblesofvariouskindsofporphyry，embeddedinwhitecalcareousspar，includingcavitieslinedwithbright-greencrystallisedepidote。Thewholepileofstratabelongingtobothformationsisinclined，apparentlyfromtheabove-mentionedaxisofPluclaro，atanangleofbetween20and30
degreestotheeast。Iwillheregiveasectionoftheprincipalbedsmetwithincrossingtheentirethicknessofthegypseousstrata。
Firstly：abovetheporphyriticconglomerateformation，thereisafine-
grained，red，crystallinesandstone。
Secondly：athickmassofsmooth-grained，calcareo-aluminous，shalyrock，oftenmarkedwithdendriticmanganese，andhaving，wheremostcompact，theexternalappearanceofhonestone。Itiseasilyfusible。Ishallforthefuture，forconvenience’sake，callthisvarietypseudo-honestone。Someofthevarietiesarequiteblackwhenfreshlybroken，butallweatherintoayellowish-ashcoloured，soft，earthysubstance，preciselyasisthecasewiththecompactshalyrocksofthePeuquenesrange。ThisstratumisofthesamegeneralnaturewithmanyofthebedsnearLosHornosintheIllapelsection。Inthissecondbed，orintheunderlyingredsandstoneforthesurfacewaspartiallyconcealedbydetritus，therewasathickmassofgypsum，havingthesamemineralogicalcharacterswiththegreatbedsdescribedinoursectionsacrosstheCordillera。
Thirdly：athickstratumoffine-grained，red，sedimentarymatter，easilyfusibleintoawhiteglass，likethebasisofclaystoneporphyry;butinpartsjaspery，inpartsbrecciated，andincludingcrystallinespecksofcarbonateoflime。Insomeofthejasperylayers，andinsomeoftheblacksiliceousslatybands，therewereirregularseamsofimperfectpitchstone，undoubtedlyofmetamorphicorigin，andotherseamsofbrown，crystallinelimestone。Here，also，weremasses，externallyresemblingill-preservedsilicifiedwood。
Fourthlyandfifthly：calcareouspseudo-honestone;andathickstratumconcealedbydetritus。
Sixthly：athinlystratifiedmassofbrightgreen，compact，smooth-grained，calcareo-argillaceousstone，easilyfusible，andemittingastrongaluminousodour：thewholehasahighlyangulo-concretionarystructure;anditresembles，toacertainextent，someoftheuppertufaceo-infusorialdepositsofthePatagoniantertiaryformation。Itisinitsnaturealliedtoourpseudo-honestone，anditincludeswellcharacterisedlayersofthatvariety;andotherlayersofapalegreen，harder，andbrecciatedvariety;
andothersofredsedimentarymatter，likethatofbedThree。Somepebblesofporphyriesareembeddedintheupperpart。
Seventhly：redsedimentarymatterorsandstonelikethatofbedOne，severalhundredfeetinthickness，andincludingjasperylayers，oftenhavingafinelybrecciatedstructure。
Eighthly：white，muchindurated，almostcrystallinetuff，severalhundredfeetinthickness，includingroundedgrainsofquartzandparticlesofgreenmatterlikethatofbedSix。Partspassintoaverypalegreen，semi-
porcellanicstone。
Ninthly：redorbrowncoarseconglomerate，threeorfourhundredfeetthick，formedchieflyofpebblesofporphyries，withvolcanicparticles，inanarenaceous，non-calcareous，fusiblebasis：theuppertwofeetarearenaceouswithoutanypebbles。
Tenthly：thelastanduppermoststratumhereexhibited，isacompact，slate-colouredporphyry，withnumerouselongatedcrystalsofglassyfeldspar，fromonehundredandfiftytotwohundredfeetinthickness;itliesstrictlyconformablyontheunderlyingconglomerate，andisundoubtedlyasubmarinelava。
Thisgreatpileofstratahasbeenbrokenupinseveralplacesbyintrusivehillocksofpurpleclaystoneporphyry，andbydikesofporphyriticgreenstone：itissaidthatafewpoormetalliferousveinshavebeendiscoveredhere。Fromthefusiblenatureandgeneralappearanceofthefiner-grainedstrata，theyprobablyowetheiroriginlikethealliedbedsoftheUspallatarange，andoftheUpperPatagoniantertiaryformations，togentlevolcaniceruptions，andtotheabrasionofvolcanicrocks。
ComparingthesebedswiththoseintheminingdistrictofArqueros，weseeatbothplacesrockseasilyfusible，ofthesamepeculiarbrightgreenandredcolours，containingcalcareousmatter，oftenhavingafinelybrecciatedstructure，oftenpassingintoeachother，andoftenalternatingtogether：
henceIcannotdoubtthattheonlydifferencebetweenthem，liesintheArquerosbedshavingbeenmoremetamorphosedinconformitywiththeirmoredislocatedandinjectedcondition，andconsequentlyinthecalcareousmatter，oxideofironandgreencolouringmatter，havingbeensegregatedunderamorecrystallineform。
Thestrataareinclined，asbeforestated，from20to30degreeseastward，towardsanirregularnorthandsouthchainofandesiticporphyryandofporphyriticgreenstone，wheretheyareabruptlycutoff。InthevalleyofCoquimbo，neartotheH。ofGualliguaca，similarplutonicrocksaremetwith，apparentlyasouthernprolongationoftheabovechain;andeastwardofitwehaveanescarpmentoftheporphyriticconglomerate，withthestratainclinedatasmallangleeastward，whichmakesthethirdescarpment，includingthatnearestthecoast。Proceedingupthevalleywecometoanothernorthandsouthlineofgranite，andesite，andblackishporphyry，whichseemtolieinanirregulartroughoftheporphyriticconglomerate。Again，onthesouthsideoftheR。Claro，therearesomeirregulargranitichills，whichhavethrownoffthestrataofporphyriticconglomeratetotheN。W。byW。;butthestratificationherehasbeenmuchdisturbed。Ididnotproceedanyfartherupthevalley，andthispointisabouttwo-thirdsofthedistancebetweenthePacificandthemainCordillera。
Iwilldescribeonlyoneothersection，namely，onthenorthsideoftheR。
Claro，whichisinterestingfromcontainingfossils：thestrataaremuchdislocatedbyfaultsanddikes，andareinclinedtothenorth，towardsamountainofandesiteandporphyry，intowhichtheyappeartobecomealmostblended。Asthebedsapproachthismountain，theirinclinationincreasesuptoanangleof70degrees，andintheupperpart，therocksbecomehighlymetamorphosed。Thelowestbedvisibleinthissection，isapurplishhardsandstone。Secondly，abedtwoorthreehundredfeetthick，ofawhitesiliceoussandstone，withacalcareouscement，containingseamsofslatysandstone，andofhardyellowish-browndolomitic？limestone;numerous，well-rounded，littlepebblesofquartzareincludedinthesandstone。
Thirdly，adarkcolouredlimestonewithsomequartzpebbles，fromfiftytosixtyfeetinthickness，containingnumeroussilicifiedshells，presentlytobeenumerated。Fourthly，verycompact，calcareous，jasperysandstone，passingintofifthlyagreatbed，severalhundredfeetthick，ofconglomerate，composedofpebblesofwhite，red，andpurpleporphyries，ofsandstoneandquartz，cementedbycalcareousmatter。Iobservedthatsomeofthefinerpartsofthisconglomerateweremuchinduratedwithinafootofadikeeightfeetinwidth，andwererenderedofapalercolourwiththecalcareousmattersegregatedintowhitecrystallisedparticles;somepartswerestainedgreenfromthecolouringmatterofthedike。Sixthly，athickmass，obscurelystratified，ofaredsedimentarystoneorsandstone，fullofcrystallinecalcareousmatter，imperfectcrystalsofoxideofiron，andIbelieveoffeldspar，andthereforecloselyresemblingsomeofthehighlymetamorphosedbedsatArqueros：thisbedwascappedby，andappearedtopassinitsupperpartinto，rockssimilarlycoloured，containingcalcareousmatter，andaboundingwithminutecrystals，mostlyelongatedandglassy，ofreddishalbite。Seventhly，aconformablestratumoffinereddishporphyrywithlargecrystalsofalbitic？feldspar;probablyasubmarinelava。Eighthly，anotherconformablebedofgreenporphyry，withspecksofgreenearthandcream-colouredcrystalsoffeldspar。Ibelievethatthereareothersuperincumbentcrystallinestrataandsubmarinelavas，butIhadnottimetoexaminethem。
Theupperbedsinthissectionprobablycorrespondwithpartsofthegreatgypseousformation;andthelowerbedsofredsandstoneconglomerateandfossiliferouslimestonenodoubtaretheequivalentsoftheHippuritestratum，seenindescendingfromArquerostoPluclaro，whichthereliesconformablyupontheporphyriticconglomerateformation。Thefossilsfoundinthethirdbed，consistof：——
PectenDufreynoyi，d’Orbigny，“Voyage，PartPal。”
Thisspecies，whichoccurshereinvastnumbers，accordingtoM。D’Orbigny，resemblescertaincretaceousforms。
Ostreahemispherica，d’Orbigny，“Voyage“etc。
Alsoresembles，accordingtothesameauthor，cretaceousforms。
Terebratulaaenigma，d’Orbigny，“Voyage“etc。Pl。22Figures10-12。
Isallied，accordingtoM。d’Orbigny，toT。concinnafromtheForestMarble。Aseriesofthisspecies，collectedinseverallocalitieshereaftertobereferredto，hasbeenlaidbeforeProfessorForbes;andheinformsmethatmanyofthespecimensarealmostundistinguishablefromourooliticT。
tetraedra，andthatthevarietiesamongstthemaresuchasarefoundinthatvariablespecies。Generallyspeaking，theAmericanspecimensofT。
aenigmamaybedistinguishedfromtheBritishT。tetraedra，bythesurfacehavingtheribssharpandwell-definedtothebeak，whilstintheBritishspeciestheybecomeobsoleteandsmootheddown;butthisdifferenceisnotconstant。ProfessorForbesadds，that，possibly，internalcharactersmayexist，whichwoulddistinguishtheAmericanspeciesfromitsEuropeanallies。
Spiriferlinguiferoides，E。Forbes。
ProfessorForbesstatesthatthisspeciesisveryneartoS。linguiferaofPhillipsacarboniferouslimestonefossil，butprobablydistinct。M。
d’OrbignyconsidersitasperhapsindicatingtheJurassicperiod。
Ammonites，imperfectimpressionof。
M。DomeykohassenttoFranceacollectionoffossils，which，Ipresume，fromthedescriptiongiven，musthavecomefromtheneighbourhoodofArqueros;theyconsistof：——
PectenDufreynoyi，d’Orbigny，“Voyage“PartPal。
Ostreahemispherica，d’Orbigny，“Voyage“PartPal。
TurritellaAndii，d’Orbigny，“Voyage“PartPal。PleurotomariaHumboldtiiofVonBuch。
HippuritesChilensis，d’Orbigny，“Voyage“PartPal。
ThespecimensofthisHippurite，aswellasthoseIcollectedinmydescentfromArqueros，areveryimperfect;butinM。d’Orbigny’sopiniontheyresemble，asdoestheTurritellaAndii，cretaceousuppergreensandforms。
NautilusDomeykus，d’Orbigny，“Voyage“PartPal。
Terebratulaaenigma，d’Orbigny，“Voyage“PartPal。
Terebratulaignaciana，d’Orbigny，“Voyage“PartPal。
ThislatterspecieswasfoundbyM。DomeykointhesameblockoflimestonewiththeT。aenigma。AccordingtoM。d’Orbigny，itcomesneartoT。
ornithocephalafromtheLias。AseriesofthisspeciescollectedatGuasco，hasbeenexaminedbyProfessorE。Forbes，andhestatesthatitisdifficulttodistinguishbetweensomeofthespecimensandtheT。hastatafromthemountainlimestone;andthatitisequallydifficulttodrawalinebetweenthemandsomeMarlstoneTerebratulae。Withoutaknowledgeoftheinternalstructure，itisimpossibleatpresenttodecideontheiridentitywithanalogousEuropeanforms。
Theremarksgivenontheseveralforegoingshells，showthat，inM。
d’Orbigny’sopinion，thePecten，Ostrea，Turritella，andHippuriteindicatethecretaceousperiod;andtheGryphaeaappearstoProfessorForbestobeidenticalwithaspecies，associatedinSouthernIndiawithunquestionablycretaceousforms。Ontheotherhand，thetwoTerebratulaeandtheSpiriferpoint，intheopinionbothofM。d’OrbignyandProfessorForbes，totheooliticseries。HenceM。d’Orbigny，nothavinghimselfexaminedthiscountry，hasconcludedthatthereareheretwodistinctformations;buttheSpiriferandT。aenigmawerecertainlyincludedinthesamebedwiththePectenandOstrea，whenceIextractedthem;andthegeologistM。DomeykosenthomethetwoTerebratulaewiththeother-namedshells，fromthesamelocality，withoutspecifyingthattheycamefromdifferentbeds。Again，asweshallpresentlysee，inacollectionofshellsgivenmefromGuasco，thesamespecies，andotherspresentinganalogousdifferences，aremingledtogether，andareinthesamecondition;andlastly，inthreeplacesinthevalleyofCopiapo，Ifoundsomeofthesesamespeciessimilarlygrouped。
Hencetherecannotbeanydoubt，highlycuriousthoughthefactbe，thattheseseveralfossils，namely，theHippurites，Gryphaea，Ostrea，Pecten，Turritella，Nautilus，twoTerebratulae，andSpiriferallbelongtothesameformation，whichwouldappeartoformapassagebetweentheooliticandcretaceoussystemsofEurope。Althoughawarehowunusualthetermmustsound，Ishall，forconvenience’sake，callthisformationcretaceo-
oolitic。ComparingthesectionsinthisvalleyofCoquimbowiththoseintheCordilleradescribedinthelastchapter，andbearinginmindthecharacterofthebedsintheintermediatedistrictofLosHornos，thereiscertainlyaclosegeneralmineralogicalresemblancebetweenthem，bothintheunderlyingporphyriticconglomerate，andintheoverlyinggypseousformation。Consideringthisresemblance，andthatthefossilsfromthePuentedelIncaatthebaseofthegypseousformation，andthroughoutthegreaterpartofitsentirethicknessonthePeuquenesrange，indicatetheNeocomianperiod，——thatis，thedawnofthecretaceoussystem，or，assomehavebelieved，apassagebetweenthislatterandtheooliticseries——I
concludethatprobablythegypseousandassociatedbedsinallthesectionshithertodescribed，belongtothesamegreatformation，whichIhavedenominated——cretaceo-oolitic。Imayadd，beforeleavingCoquimbo，thatM。
GayfoundintheneighbouringCordillera，attheheightof14，000feetabovethesea，afossiliferousformation，includingaTrigoniaandPholadomyaD’Orbigny“Voyage“PartGeolog。page242。;——bothofwhichgeneraoccuratthePuentedelInca。
COQUIMBOTOGUASCO。
Therocksnearthecoast，andsomewayinland，donotdifferfromthosedescribednorthwardsofValparaiso：wehavemuchgreenstone，syenite，feldspathicandjasperyslate，andgrauwackeshavingabasislikethatofclaystone;therearesomelargetractsofgranite，inwhichtheconstituentmineralsaresometimesarrangedinfolia，thuscomposinganimperfectgneiss。Therearetwolargedistrictsofmica-schists，passingintoglossyclay-slate，andresemblingthegreatformationintheChonosArchipelago。
InthevalleyofGuasco，anescarpmentofporphyriticconglomerateisfirstseenhighupthevalley，abouttwoleagueseastwardofthetownofBallenar。IheardofagreatgypseousformationintheCordillera;andacollectionofshellsmadetherewasgivenme。Theseshellsareallinthesamecondition，andappeartohavecomefromthesamebed：theyconsistof：——
TurritellaAndii，d’Orbigny，“Voyage“PartPal。
PectenDufreynoyi，d’Orbigny，“Voyage“PartPal。
Terebatulaignaciana，d’Orbigny，“Voyage“PartPal。
TherelationsofthesespecieshavebeengivenundertheheadofCoquimbo。
Terebratulaaenigma，d’Orbigny，“Voyage“PartPal。
ThisshellM。d’OrbignydoesnotconsideridenticalwithhisT。aenigma，butneartoT。obsoleta。ProfessorForbesthinksthatitiscertainlyavarietyofT。aenigma：weshallmeetwiththisvarietyagainatCopiapo。
SpiriferChilensis，E。Forbes。
ProfessorForbesremarksthatthisfossilresemblesseveralcarboniferouslimestoneSpirifers;andthatitisalsorelatedtosomeliassicspecies，asS。Wolcotii。
Iftheseshellshadbeenexaminedindependentlyoftheothercollections，theywouldprobablyhavebeenconsidered，fromthecharactersofthetwoTerebratulae，andfromtheSpirifer，asoolitic;butconsideringthatthefirstspecies，andaccordingtoProfessorForbes，thefourfirst，areidenticalwiththosefromCoquimbo，thetwoformationsnodoubtarethesame，andmay，asIhavesaid，beprovisionallycalledcretaceo-oolitic。
VALLEYOFCOPIAPO。
ThejourneyfromGuascotoCopiapo，owingtotheutterlydesertnatureofthecountry，wasnecessarilysohurried，thatIdonotconsidermynotesworthgiving。InthevalleyofCopiaposomeofthesectionsareveryinteresting。FromtheseatothetownofCopiapo，adistanceestimatedatthirtymiles，themountainsarecomposedofgreenstone，granite，andesite，andblackishporphyry，togetherwithsomedusky-greenfeldspathicrocks，whichIbelievetobealteredclay-slate：thesemountainsarecrossedbymanybrown-coloureddikes，runningnorthandsouth。Abovethetown，themainvalleyrunsinasouth-eastandevenmoresoutherlycoursetowardstheCordillera，whereitisdividedintothreegreatravines，bythenorthernoneofwhich，calledJolquera，Ipenetratedforashortdistance。Thesection，Section1/3inPlate1，givesaneye-sketchofthestructureandcompositionofthemountainsonbothsidesofthisvalley：astraighteastandwestlinefromthetowntotheCordilleraisperhapsnotmorethanthirtymiles，butalongthevalleythedistanceismuchgreater。Whereverthevalleytrendedverysoutherly，Ihaveendeavouredtocontractthesectionintoitstrueproportion。Thisvalley，Imayadd，risesmuchmoregentlythananyothervalleywhichIsawinChile。
Tocommencewithoursection，forashortdistanceabovethetownwehavehillsofthegraniticseries，togetherwithsomeofthatrock[A]，whichI
suspecttobealteredclay-slate，butwhichProfessorG。Rose，judgingfromspecimenscollectedbyMeyenatP。Negro，statesisserpentinepassingintogreenstone。Wethencomesuddenlytothegreatgypseousformation[B]，withouthavingpassedover，differentlyfrom，inallthesectionshithertodescribed，anyoftheporphyriticconglomerate。Thestrataareatfirsteitherhorizontalorgentlyinclinedwestward;thenhighlyinclinedinvariousdirections，andcontortedbyunderlyingmassesofintrusiverocks;
andlastly，theyhavearegulareastwarddip，andformatolerablywellpronouncednorthandsouthlineofhills。Thisformationconsistsofthinstrata，withinnumerablealternations，ofblack，calcareousslate-rock，ofcalcareo-aluminousstoneslikethoseatCoquimbo，whichIhavecalledpseudo-honestonesofgreenjasperylayers，andofpale-purplish，calcareous，softrotten-stone，includingseamsandveinsofgypsum。Thesestrataareconformablyoverlaidbyagreatthicknessofthinlystratified，compactlimestonewithincludedcrystalsofcarbonateoflime。AtaplacecalledTierraAmarilla，atthefootofamountainthuscomposedthereisabroadvein，orperhapsstratum，ofabeautifulandcuriouscrystallisedmixture，composed，accordingtoProfessorG。Rose，ofsulphateofironundertwoforms，andofthesulphatesofcopperandaluminaMeyen’s“Reise“etc。Th。1，s。394。：thesectionissoobscurethatIcouldnotmakeoutwhetherthisveinorstratumoccurredinthegypseousformation，ormoreprobablyinsomeunderlyingmasses[A]，whichIbelievearealteredclay-slate。
SECONDAXISOFELEVATION。
Afterthegypseousmasses[B]，wecometoalineofhillsofunstratifiedporphyry[C]，whichontheireasternsideblendintostrataofgreatthicknessofporphyriticconglomerate，dippingeastward。Thislatterformation，however，herehasnotbeennearlysomuchmetamorphosedasinmostpartsofCentralChile;itiscomposedofbedsoftruepurpleclaystoneporphyry，repeatedlyalternatingwiththickbedsofpurplish-redconglomeratewiththewell-rounded，largepebblesofvariousporphyries，notblendedtogether。
THIRDAXISOFELEVATION。
NeartheravineofLosHornitos，thereisawell-markedlineofelevation，extendingformanymilesinaN。N。E。andS。S。W。direction，withthestratadippinginmostpartsasinthesecondaxisonlyinonedirection，namely，eastwardatanaverageangleofbetween30and40degrees。Closetothemouthofthevalley，however，thereis，asrepresentedinthesection，asteepandhighmountain[D]，composedofvariousgreenandbrownintrusiveporphyriesenvelopedwithstrata，apparentlybelongingtotheupperpartsoftheporphyriticconglomerate，anddippingbotheastwardandwestward。Iwilldescribethesectionseenontheeasternsideofthismountain[D]，beginningatthebasewiththelowestbedvisibleintheporphyriticconglomerate，andproceedingupwardsthroughthegypseousformation。Bed1consistsofreddishandbrownishporphyryvaryingincharacter，andinmanypartshighlyamygdaloidalwithcarbonateoflime，andwithbrightgreenandbrownbole。Itsuppersurfaceisthroughoutclearlydefined，butthelowersurfaceisinmostpartsindistinct，andtowardsthesummitofthemountain[D]quiteblendedintotheintrusiveporphyries。Bed2，apalelilac，hardbutnotheavystone，slightlylaminated，includingsmallextraneousfragments，andimperfectaswellassomeperfectandglassycrystalsoffeldspar;fromonehundredandfiftytotwohundredfeetinthickness。Whenexaminingitinsitu，Ithoughtitwascertainlyatrueporphyry，butmyspecimensnowleadmetosuspectthatitpossiblymaybeametamorphosedtuff。Fromitscolouritcouldbetracedforalongdistance，overlyinginonepart，quiteconformablytotheporphyryofbed1，andinanothernotdistantpart，averythickmassofconglomerate，composedofpebblesofaporphyrychieflylikethatofbed1：
thisfactshowshowthenatureofthebottomformerlyvariedinshorthorizontaldistances。Bed3，white，muchinduratedtuff，containingminutepebbles，brokencrystals，andscalesofmica，variesmuchinthickness。