TheserieswassoperfectthatIcouldnotdoubtthattheselargecrystals，whichhadtheirlongeraxesplacedparalleltoeachother，hadprimarilyoriginatedinthemetamorphosisandaggregationofalternatinglayersoftuff;andhencetheirparallelpositionmustbeattributed(unexpectedthoughtheconclusionmaybe)，nottolawsofchemicalaction，buttotheoriginalplanesofdeposition。Iamtemptedbrieflytodescribethreeothersingularalliedvarietiesofrock;thefirstwithoutexaminationwouldhavepassedforastratifiedporphyriticbreccia，butalltheincludedangularfragmentsconsistedofaborderofpinkishcrystallinefeldspathicmatter，surroundingadarktranslucentsiliceouscentre，inwhichgrainsofquartznotquiteblendedintothepastecouldbedistinguished：thisuniformityinthenatureofthefragmentsshowsthattheyarenotofmechanical，butofconcretionaryorigin，havingresultedperhapsfromtheself-breakingupandaggregationoflayersofinduratedtuffcontainingnumerousgrainsofquartz，——intowhich，indeed，thewholemassinonepartpassed。Thesecondvarietyisareddishnon-porphyriticclaystone，quitefullofsphericalcavities，abouthalfaninchindiameter，eachlinedwithacollapsedcrustformedofcrystalsofquartz。Thethirdvarietyalsoconsistsofapalepurplenon-porphyriticclaystone，almostwhollyformedofconcretionaryballs，obscurelyarrangedinlayers，ofalesscompactandpalercolouredclaystone;eachballbeingononesidepartlyhollowandlinedwithcrystalsofquartz。
PSEUDO-DIKES。
Somemilesuptheharbour，inalineofcliffsformedofslightlymetamorphosedtufaceousandporphyriticclaystonebeds，Iobservedthreeverticaldikes，socloselyresemblingingeneralappearanceordinaryvolcanicdikes，thatIdidnotdoubt，untilcloselyexaminingtheircomposition，thattheyhadbeeninjectedfrombelow。Thefirstisstraight，withparallelsides，andaboutfourfeetwide;itconsistsofwhitish，induratedtufaceousmatter，preciselylikesomeofthebedsintersectedbyit。Theseconddikeismoreremarkable;itisslightlytortuous，abouteighteeninchesthick，andcanbetracedforaconsiderabledistancealongthebeach;itisofapurplish-redorbrowncolour，andisformedchieflyofROUNDEDgrainsofquartz，withbrokencrystalsofearthyfeldspar，scalesofblackmica，andminutefragmentsofclaystoneporphyry，allfirmlyunitedtogetherinahardsparingbase。Thestructureofthisdikeshowsobviouslythatitisofmechanicalandsedimentaryorigin;yetitthinnedoutupwards，anddidnotcutthroughtheuppermoststratainthecliffs。Thisfactatfirstappearstoindicatethatthemattercouldnothavebeenwashedinfromabove(Upfilledfissuresareknowntooccurbothinvolcanicandinordinarysedimentaryformations。AttheGalapagosArchipelago“VolcanicIslands“etc。therearesomestrikingexamplesofpseudo-dikescomposedofhardtuff。);butifwereflectonthesuctionwhichwouldresultfromadeep-seatedfissurebeingformed，wemayadmitthatifthefissurewereinanypartopentothesurface，mudandwatermightwellbedrawnintoitalongitswholecourse。Thethirddikeconsistedofahard，rough，whiterock，almostcomposedofbrokencrystalsofglassyfeldspar，withnumerousscalesofblackmica，cementedinascantybase;therewaslittleintheappearanceofthisrock，toprecludetheideaofitshavingbeenatrueinjectedfeldspathicdike。Themattercomposingthesethreepseudo-dikes，especiallythesecondone，appearstohavesuffered，likethesurroundingstrata，acertaindegreeofmetamorphicaction;andthishasmuchaidedthedeceptiveappearance。AtBahia，inBrazil，wehaveseenthatatrueinjectedhornblendicdike，notonlyhassufferedmetamorphosis，buthasbeendislocatedandevendiffusedinthesurroundinggneiss，undertheformofseparatecrystalsandoffragments。
FALKLANDISLANDS。
Ihavedescribedtheseislandsinapaperpublishedinthethirdvolumeofthe“GeologicalJournal。”Themountain-ridgesconsistofquartz，andthelowercountryofclay-slateandsandstone，thelattercontainingPalaeozoicfossils。ThesefossilshavebeenseparatelydescribedbyMessrs。MorrisandSharpe：someofthemresembleSilurian，andothersDevonianforms。Intheeasternpartofthegrouptheseveralparallelridgesofquartzextendinawestandeastline;butfurtherwestwardthelinebecomesW。N。W。andE。S。E。andevenstillmorenortherly。Thecleavage-planesoftheclay-
slatearehighlyinclined，generallyatanangleofabove50degrees，andoftenvertical;theystrikealmostinvariablyinthesamedirectionwiththequartzranges。Theoutlineoftheindentedshoresofthetwomainislands，andtherelativepositionsofthesmallerislets，accordwiththestrikebothofthemainaxesofelevationandofthecleavageoftheclay-
slate。
TIERRADELFUEGO。
Mynotesonthegeologyofthiscountryarecopious，butastheyareunimportant，andasfossilswerefoundonlyinonedistrict，abriefsketchwillbeheresufficient。TheeastcoastfromtheS。ofMagellan(wheretheboulderformationislargelydeveloped)toSt。Polycarp’sBayisformedofhorizontaltertiarystrata，boundedsomewaytowardstheinteriorbyabroadmountainousbandofclay-slate。Thisgreatclay-slateformationextendsfromSt。LeMairewestwardfor140miles，alongbothsidesoftheBeagleChanneltonearitsbifurcation。Southofthischannel，itformsallNavarinIsland，andtheeasternhalfofHosteIslandandofHardyPeninsula;northoftheBeagleChannelitextendsinanorth-westlineonbothsidesofAdmiraltySoundtoBrunswickPeninsulaintheSt。ofMagellan，andIhavereasontobelieve，stretchesfaruptheeasternsideoftheCordillera。ThewesternandbrokensideofTierradelFuegotowardsthePacificisformedofmetamorphicschists，graniteandvarioustrappeanrocks：thelineofseparationbetweenthecrystallineandclay-slateformationscangenerallybedistinguished，asremarkedbyCaptainKing，bytheparallelismintheclay-slatedistrictsoftheshoresandchannels，ranginginalinebetween[W。20degreesto40degreesN。]and[E。20
degreesto40degreesS。]。(“GeographicalJournal“volume1page155。)
Theclay-slateisgenerallyfissile，sometimessiliceousorferruginous，withveinsofquartzandcalcareousspar;itoftenassumes，especiallyontheloftiermountains，analteredfeldspathiccharacter，passingintofeldspathicporphyry：occasionallyitisassociatedwithbrecciaandgrauwacke。AtGoodSuccessBay，thereisalittleintercalatedblackcrystallinelimestone。AtPortFaminemuchoftheclay-slateiscalcareous，andpasseseitherintoamudstoneorintograuwacke，includingodd-shapedconcretionsofdarkargillaceouslimestone。Herealone，ontheshoreafewmilesnorthofPortFamine，andonthesummitofMountTarn(2，600feethigh)，Ifoundorganicremains;theyconsistof：——
1。Ancylocerassimplex，d’Orbigny“PalFranc“MountTarn。
2。Fusus(inimperfectstate)，d’Orbigny“PalFranc“MountTarn。
3。Natica，d’Orbigny“PalFranc“MountTarn。
4。Pentacrimus，d’Orbigny“PalFranc“MountTarn。
5。Lucinaexcentrica，G。B。Sowerby，PortFamine。
6。Venus(inimperfectstate)，G。B。Sowerby，PortFamine。
7。Turbinolia(？)，G。B。Sowerby，PortFamine。
8。Hamiteselatior，G。B。Sowerby，PortFamine。
M。d’OrbignystatesthatMM。HombronandGrangefoundinthisneighbourhoodanAncyloceras，perhapsA。simplex，anAmmonite，aPlicatulaandModiola。
(“Voyage“PartGeolog。page242。)M。d’Orbignybelievesfromthegeneralcharacterofthesefossils，andfromtheAncylocerasbeingidentical(asfarasitsimperfectconditionallowsofcomparison)withtheA。simplexofEurope，thattheformationbelongstoanearlystageoftheCretaceoussystem。ProfessorE。Forbes，judgingonlyfrommyspecimens，concursintheprobabilityofthisconclusion。TheHamiteselatioroftheabovelist，ofwhichadescriptionhasbeengivenbyMr。Sowerby，andwhichisremarkablefromitslargesize，hasnotbeenseeneitherbyM。d’OrbignyorProfessorE。Forbes，as，sincemyreturntoEngland，thespecimenshavebeenlost。
Thegreatclay-slateformationofTierradelFuegobeingcretaceous，iscertainlyaveryinterestingfact，——whetherweconsidertheappearanceofthecountry，which，withouttheevidenceaffordedbythefossils，wouldformtheanalogyofmostknowndistricts，probablyhavebeenconsideredasbelongingtothePalaeozoicseries，——orwhetherweviewitasshowingthattheageofthisterminalportionofthegreataxisofSouthAmerica，isthesame(aswillhereafterbeseen)withtheCordilleraofChileandPeru。
Theclay-slateinmanypartsofTierradelFuego，isbrokenbydikesandbygreatmassesofgreenstone，oftenhighlyhornblendic(Inagreenstone-dikeintheMagdalenChannel，thefeldsparcleavedwiththeangleofalbite。
Thisdikewascrossed，aswellasthesurroundingslate，byalargeveinofquartz，acircumstanceofunusualoccurrence。)：almostallthesmallisletswithintheclay-slatedistrictsarethuscomposed。Theslatenearthedikesgenerallybecomespaler-coloured，harder，lessfissile，ofafeldspathicnature，andpassesintoaporphyryorgreenstone：inonecase，however，itbecamemorefissile，ofaredcolour，andcontainedminutescalesofmica，whichwereabsentintheunalteredrock。OntheeastsideofPonsonbySoundsomedikescomposedofapalesonorousfeldspathicrock，porphyriticwithalittlefeldspar，wereremarkablefromtheirnumber，——therebeingwithinthespaceofamileatleastonehundred，——fromtheirnearlyequallinginbulktheintermediateslate，——andmoreespeciallyfromtheexcessivefineness(likethefinestinlaidcarpentry)andperfectparallelismoftheirjunctionswiththealmostverticallaminaeofclay-slate。Iwasunabletopersuademyselfthatthesegreatparallelmasseshadbeeninjected，untilI
foundonedikewhichabruptlythinnedouttohalfitsthickness，andhadoneofitswallsjagged，withfragmentsoftheslateembeddedinit。
InSouthernTierradelFuego，theclay-slatetowardsitsS。W。boundary，becomesmuchalteredandfeldspathic。ThusonWollastonIslandslateandgrauwackecanbedistinctlytracedpassingintofeldspathicrocksandgreenstones，includingironpyritesandepidote，butstillretainingtracesofcleavagewiththeusualstrikeanddip。Onesuchmetamorphosedmasswastraversedbylargevein-likemassesofabeautifulmixture(asascertainedbyProfessorMiller)ofgreenepidote，garnets，andwhitecalcareousspar。
Onthenorthernpointofthissameisland，therewerevariousancientsubmarinevolcanicrocks，consistingofamygdaloidswithdarkboleandagate，——ofbasaltwithdecomposedolivine——ofcompactlavawithglassyfeldspar，——andofacoarseconglomerateofredscoriae，partsbeingamygdaloidalwithcarbonateoflime。ThesouthernpartofWollastonIslandandthewholeofHermiteandHornIslands，seemformedofconesofgreenstone;theoutlyingisletsofIlDefensoandD。Raminezaresaidtoconsistofporphyriticlava。(DeterminedbyProfessorJameson。Weddell’s“Voyage“page169。)IncrossingHardyPeninsula，theslatestillretainingtracesofitsusualcleavage，passesintocolumnarfeldspathicrocks，whicharesucceededbyanirregulartractoftrappeanandbasalticrocks，containingglassyfeldsparandmuchironpyrites：thereis，also，someharshredclaystoneporphyry，andanalmosttruetrachyte，withneedlesofhornblende，andinonespotacuriousslatyrockdividedintoquadrangularcolumns，havingabasealmostliketrachyte，withdrusycavitieslinedbycrystals，tooimperfect，accordingtoProfessorMiller，tobemeasured，butresemblingZeagonite。(SeeMr。Brooke’sPaperinthe“LondonPhilosophicalMagazine“volume10。ThismineraloccursinanancientvolcanicrocknearRome。)Inthemidstofthesesingularrocks，nodoubtofancientsubmarinevolcanicorigin，ahighhilloffeldspathicclay-slateprojected，retainingitsusualcleavage。Nearthispoint，therewasasmallhillock，havingtheaspectofgranite，butformedofwhitealbite，brilliantcrystalsofhornblende(bothascertainedbythereflectinggoniometer)andmica;butwithnoquartz。NorecentvolcanicdistricthasbeenobservedinanypartofTierradelFuego。
FivemileswestofthebifurcationoftheBeagleChannel，theslate-
formation，insteadofbecoming，asinthemoresouthernpartsofTierradelFuego，feldspathic，andassociatedwithtrappeanoroldvolcanicrocks，passesbyalternationsintoagreatunderlyingmassoffinegneissandglossyclay-slate，whichatnogreatdistanceissucceededbyagrandformationofmica-slatecontaininggarnets。Thefoliaofthesemetamorphicschistsstrikeparalleltothecleavage-planesoftheclay-slate，whichhaveaveryuniformdirectionoverthewholeofthispartofthecountry：
thefolia，however，areundulatoryandtortuous，whilstthecleavage-
laminaeoftheslatearestraight。Theseschistscomposethechiefmountain-chainofSouthernTierradelFuego，rangingalongthenorthsideofthenorthernarmoftheBeagleChannel，inashortW。N。W。andE。S。E。
line，withtwopoints(MountsSarmientoandDarwin)risingtoheightsof6，800and6，900feet。Onthesouth-westernsideofthisnorthernarmoftheBeagleChannel，theclay-slateisseenwithitsSTRATAdippingfromthegreatchain，sothatthemetamorphicschistshereformaridgeborderedoneachsidebyclay-slate。Furthernorth，however，tothewestofthisgreatrange，thereisnoclay-slate，butonlygneiss，mica，andhornblendicslates，restingongreatbarrenhillsoftruegranite，andformingatractaboutsixtymilesinwidth。Again，westwardoftheserocks，theoutermostislandsareoftrappeanformation，which，frominformationobtainedduringthevoyagesofthe“Adventure“and“Beagle，“seem，togetherwithgranite，chieflytoprevailalongthewesterncoastasfarnorthastheentranceoftheSt。ofMagellan(SeethePaperbyCaptainKinginthe“GeographicalJournal“;alsoaLettertoDr。Fittonin“GeologicalProceedings“volume1
page29;alsosomeobservationsbyCaptainFitzroy“Voyages“volume1page375。IamindebtedalsotoMr。LyellforaseriesofspecimenscollectedbyLieutenantGraves。)：alittlemoreinland，ontheeasternsideofClarenceIslandandS。Desolation，granite，greenstone，mica-slate，andgneissappeartopredominate。Iamtemptedtobelieve，thatwheretheclay-slatehasbeenmetamorphosedatgreatdepthsbeneaththesurface，gneiss，mica-
slate，andotheralliedrockshavebeenformed，butwheretheactionhastakenplacenearerthesurface，feldspathicporphyries，greenstones，etc。haveresulted，oftenaccompaniedbysubmarinevolcaniceruptions。
Onlyoneotherrock，metwithinbotharmsoftheBeagleChannel，deservesanynotice，namelyagranulo-crystallinemixtureofwhitealbite，blackhornblende(ascertainedbymeasurementofthecrystals，andconfirmedbyProfessorMiller)，andmoreorlessofbrownmica，butwithoutanyquartz。
Thisrockoccursinlargemasses，closelyresemblinginexternalformgraniteorsyenite：inthesouthernarmoftheChannel，onesuchmassunderliesthemica-slate，onwhichclay-slatewassuperimposed：thispeculiarplutonicrockwhich，aswehaveseen，occursalsoinHardyPeninsula，isinteresting，fromitsperfectsimilaritywiththat(hereafteroftentobereferredtounderthenameofandesite)formingthegreatinjectedaxesoftheCordilleraofChile。
Thestratificationoftheclay-slateisgenerallyveryobscure，whereasthecleavageisremarkablywelldefined：tobeginwiththeextremeeasternpartsofTierradelFuego;thecleavage-planesneartheSt。ofLeMairestrikeeitherW。andE。orW。S。W。andE。N。E。andarehighlyinclined;theformoftheland，includingStatenIsland，indicatesthattheaxesofelevationhaveruninthissameline，thoughIwasunabletodistinguishtheplanesofstratification。Proceedingwestward，Iaccuratelyexaminedthecleavageoftheclay-slateonthenorthern，eastern，andwesternsides(thirty-fivemilesapart)ofNavarinIsland，andeverywherefoundthelaminaerangingwithextremeregularity，W。N。W。andE。S。E。seldomvaryingmorethanonepointofthecompassfromthisdirection。(Theclay-slateinthisislandwasinmanyplacescrossedbyparallelsmoothjoints。Outoffivecases，theangleofintersectionbetweenthestrikeofthesejointsandthatofthecleavage-laminaewasintwocases45degreesandintwoothers79degrees。)Bothontheeastandwestcoasts，Icrossedatrightanglesthecleavage-planesforaspaceofabouteightmiles，andfoundthemdippingatanangleofbetween45degreesand90degrees，generallytoS。S。W。sometimestoN。N。E。andoftenquitevertically。TheS。S。W。dipwasoccasionallysucceededabruptlybyaN。N。E。dip，andthisbyaverticalcleavage，oragainbytheS。S。W。dip;asinaloftycliffontheeasternendoftheislandthelaminaeofslatewereseentobefoldedintoverylargesteepcurves，rangingintheusualW。N。W。line，Isuspectthatthevaryingandoppositedipsmaypossiblybeaccountedforbythecleavage-
laminae，thoughtotheeyeappearingstraight，beingpartsoflargeabruptcurves，withtheirsummitscutoffandworndown。
InseveralplacesIwasparticularlystruckwiththefact，thatthefinelaminaeoftheclay-slate，wherecuttingstraightthroughthebandsofstratification，andthereforeindisputablytruecleavage-planes，differedslightlyintheirgreyishandgreenishtintsofcolour，incompactness，andinsomeofthelaminaehavingarathermorejasperyappearancethanothers。
Ihavenotseenthisfactrecorded，anditappearstomeimportant，foritshowsthatthesamecausewhichhasproducedthehighlyfissilestructure，hasalteredinaslightdegreethemineralogicalcharacteroftherockinthesameplanes。Thebandsofstratification，justalludedto，canbedistinguishedinmanyplaces，especiallyinNavarinIsland，butonlyontheweatheredsurfacesoftheslate;theyconsistofslightlyundulatoryzonesofdifferentshadesofcolourandofthicknesses，andresemblethemarks(morecloselythananythingelsetowhichIcancomparethem)leftontheinsideofavesselbythedrainingawayofsomedirtyslightlyagitatedliquid：nodifferenceincomposition，correspondingwiththesezones，couldbeseeninfreshlyfracturedsurfaces。InthemorelevelpartsofNavarinIsland，thesebandsofstratificationwerenearlyhorizontal;butontheflanksofthemountainstheywereinclinedfromthem，butinnoinstancethatIsawataveryhighangle。Therecan，Ithink，benodoubtthatthesezones，whichappearonlyontheweatheredsurfaces，arethelastvestigesoftheoriginalplanesofstratification，nowalmostobliteratedbythehighlyfissileandalteredstructurewhichthemasshasassumed。
Theclay-slatecleavesinthesameW。N。W。andE。S。E。direction，asonNavarinIsland，onbothsidesoftheBeagleChannel，ontheeasternsideofHosteIsland，ontheN。E。sideofHardyPeninsula，andonthenorthernpointofWollastonIsland;althoughinthesetwolatterlocalitiesthecleavagehasbeenmuchobscuredbythemetamorphosedandfeldspathicconditionoftheslate。Withintheareaoftheseseveralislands，includingNavarinIsland，thedirectionofthestratificationandofthemountain-
chainsisveryobscure;thoughthemountainsinseveralplacesappearedtorangeinthesameW。N。W。linewiththecleavage：theoutlineofthecoast，however，doesnotcorrespondwiththisline。NearthebifurcationoftheBeagleChannel，wheretheunderlyingmetamorphicschistsarefirstseen，theyarefoliated(withsomeirregularities)，inthissameW。N。W。line，andparallel，asbeforestated，tothemainmountain-axisofthispartofthecountry。Westwardofthismainrange，themetamorphicschistsarefoliated，thoughlessplainly，inthesamedirection，whichislikewisecommontothezoneofolderuptedtrappeanrocks，formingtheoutermostislets。Hencethearea，overwhichthecleavageoftheslateandthefoliationofthemetamorphicschistsextendswithanaverageW。N。W。andE。S。E。strike，isaboutfortymilesinanorthandsouthline，andninetymilesinaneastandwestline。
Furthernorthward，nearPortFamine，thestratificationoftheclay-slateandoftheassociatedrocks，iswelldefined，andtherealonethecleavageandstrata-planesareparallel。AlittlenorthofthisportthereisananticlinalaxisrangingN。W。(oralittlemorewesterly)andS。E。：southoftheport，asfarasAdmiraltySoundandGabrielChannel，theoutlineofthelandclearlyindicatestheexistenceofseverallinesofelevationinthissameN。W。direction，which，Imayadd，issouniforminthewesternhalfoftheSt。ofMagellan，that，asCaptainKinghasremarked，“aparallelrulerplacedonthemapupontheprojectingpointsofthesouthshore，andextendedacrossthestrait，willalsotouchtheheadlandsontheoppositecoast。”(“GeographicalJournal“volume1page170。)Itwouldappear，fromCaptainKing’sobservations，thatoverallthisareathecleavageextendsinthesameline。Deep-waterchannels，however，inallpartsofTierradelFuegohaveburstthroughthetrammelsbothofstratificationandcleavage;
mostofthemmayhavebeenformedduringtheelevationofthelandbylong-
continuederosion，butothers，forinstancetheBeagleChannel，whichstretcheslikeanarrowcanalfor120milesobliquelythroughthemountains，canhardlyhavethusoriginated。
Finally，wehaveseenthatintheextremeeasternpointofTierradelFuego，thecleavageandcoast-linesextendW。andE。andevenW。S。W。andE。N。E。：overalargeareawestward，thecleavage，themainrangeofmountains，andsomesubordinateranges，butnottheoutlinesofthecoast，strikeW。N。W。andE。S。E。：inthecentralandwesternpartsoftheSt。ofMagellan，thestratification，themountain-ranges，theoutlinesofthecoast，andthecleavageallstrikenearlyN。W。andS。E。Northofthestrait，theoutlineofthecoast，andthemountainsonthemainland，runnearlynorthandsouth。Hencewesee，atthissouthernpointofthecontinent，howgraduallytheCordillerabend，fromtheirnorthandsouthcourseofsomanythousandmilesinlength，intoanE。andevenE。N。E。
direction。
WESTCOAST，FROMTHESOUTHERNCHONOSISLANDSTONORTHERNCHILE。
ThefirstplaceatwhichwelandednorthoftheSt。ofMagellanwasnearCapeTresMontes，inlatitude47degreesS。BetweenthispointandtheNorthernChonosIslands，adistanceof200miles，the“Beagle“visitedseveralpoints，andspecimenswerecollectedformefromtheintermediatespacesbyLieutenantStokes。Thepredominantrockismica-slate，withthickfoliaofquartz，veryfrequentlyalternatingwithandpassingintoachloritic，orintoablack，glossy，oftenstriated，slightlyanthraciticschist，whichsoilspaper，andbecomeswhiteunderagreatheat，andthenfuses。Thinlayersoffeldspar，swellingatintervalsintowellcrystallisedkernels，aresometimesincludedintheseblackschists;andI
observedonemassoftheordinaryblackvarietyinsensiblyloseitsfissilestructure，andpassintoasingularmixtureofchlorite，epidote，feldspar，andmica。Greatveinsofquartzarenumerousinthemica-schists;wherevertheseoccurthefoliaaremuchconvoluted。InthesouthernpartofthePeninsulaofTresMontes，acompactalteredfeldspathicrockwithcrystalsoffeldsparandgrainsofquartzisthecommonestvariety;thisrockexhibitsoccasionallytracesofanoriginalbrecciatedstructure，andoftenpresents(likethealteredstateofTierradelFuego)tracesofcleavage-
planes，whichstrikeinthesamedirectionwiththefoliaofmica-schistfurthernorthward。(Thepeculiar，abruptlyconicalformofthehillsinthisneighbourhood，wouldhaveledanyoneatfirsttohavesupposedthattheyhadbeenformedofinjectedorintrusiverocks。AtInchemoIsland，asimilarrockgraduallybecomesgranulo-crystallineandacquiresscalesofmica;andthisvarietyatS。Estevanbecomeshighlylaminated，andthoughstillexhibitingsomeroundedgrainsofquartz，passesintotheblack，glossy，slightlyanthraciticschist，which，aswehaveseen，repeatedlyalternateswithandpassesintothemicaceousandchloriticschists。Hencealltherocksonthislineofcoastbelongtooneseries，andinsensiblyvaryfromanalteredfeldspathicclay-slateintolargelyfoliated，truemica-schist。
Thecleavageofthehomogeneousschists，thefoliationofthosecomposedofmoreorlessdistinctmineralsinlayers，andtheplanesofalternationofthedifferentvarietiesorso-calledstratification，areallparallel，andpreserveoverthis200milesofcoastaremarkabledegreeofuniformityindirection。Atthenorthernendofthegroup，atLow’sHarbour，thewell-
definedfoliaofmica-schisteverywhererangedwithineightdegrees(orlessthanonepointofthecompass)ofN。19degreesW。andS。19degreesE。;andeventhepointofdipvariedverylittle，beingalwaysdirectedtothewestandgenerallyatanangleoffortydegrees;IshouldmentionthatIhadheregoodopportunitiesofobservation，forIfollowedthenakedrockonthebeach，transverselytothestrike，foradistanceoffourmilesandahalf，andallthewayattendedtothedip。Alongtheouterislandsfor100milessouthofLow’sHarbour，LieutenantStokes，duringhisboat-
survey，kindlyobservedformethestrikeofthefoliation，andheassuresmethatitwasinvariablynortherly，andthedipwithonesingleexceptiontothewest。FurthersouthatVallenarBay，thestrikewasalmostuniversallyN。25degreesW。andthedip，generallyatanangleofabout40
degreestoW。25degreesS。butinsomeplacesalmostvertical。Stillfarthersouth，intheneighbourhoodoftheharboursofAnnaPink，S。
EstevanandS。Andres，and(judgingfromadistance)alongthesouthernpartofTresMontes，thefoliationandcleavageextendedinalinebetween[N。11degreesto22degreesW。]and[S。11degreesto22degreesE。];andtheplanesdippedgenerallywesterly，butofteneasterly，atanglesvaryingfromagentleinclinationtovertical。AtA。Pink’sHarbour，wheretheschistsgenerallydippedeasterly，wherevertheanglebecameveryhigh，thestrikechangedfromN。11degreesW。toevenasmuchasN。45degreesW。：
inananalogousmanneratVallenarBay，wherethedipwaswesterly(viz。onanaveragedirectedtoW。25degreesS。)，assoonastheanglebecameveryhigh，theplanesstruckinalinemorethan25degreeswestofnorth。Theaverageresultfromalltheobservationsonthis200milesofcoast，isastrikeofN。19degreesW。andS。19degreesE。：consideringthatineachspecifiedplacemyexaminationextendedoveranareaofseveralmiles，andthatLieutenantStokes’observationsapplytoalengthof100miles，I
thinkthisremarkableuniformityisprettywellestablished。Theprevalence，throughoutthenorthernhalfofthislineofcoast，ofadipinonedirection，thatistothewest，insteadofbeingsometimeswestandsometimeseast，is，judgingfromwhatIhaveelsewhereseen，anunusualcircumstance。InBrazil，LaPlata，theFalklandIslands，andTierradelFuego，thereisgenerallyanobviousrelationbetweentheaxisofelevation，theoutlineofthecoast，andthestrikeofthecleavageorfoliation：intheChonosArchipelago，however，neithertheminordetailsofthecoast-line，northechainoftheCordillera，northesubordinatetransversemountain-axes，accordwiththestrikeofthefoliationandcleavage：theseawardfaceofthenumerousislandscomposingthisArchipelago，andapparentlythelineoftheCordillera，rangeN。11degreesE。whereas，aswehavejustseen，theaveragestrikeofthefoliationisN。19degreesW。
Thereisoneinterestingexceptiontotheuniformityinthestrikeofthefoliation。AtthenorthernpointofTresMontes(latitude45degrees52
minutes)aboldchainofgranite，betweentwoandthreethousandfeetinheight，runsfromthecoastfarintotheinterior，inanE。S。E。line，ormorestrictlyE。28degreesS。andW。28degreesN。(Inthedistance，othermountainscouldbeseenapparentlyrangingN。N。E。andS。S。W。atrightanglestothisone。Imayadd，thatnotfarfromVallenarBaythereisafinerange，apparentlyofgranite，whichhasburstthroughthemica-slateinaN。E。byE。andS。W。byS。line。)Inabay，atthenorthernfootofthisrange，thereareafewisletsofmica-slate，withthefoliainsomepartshorizontal，butmostlyinclinedatanaverageangleof20degreestothenorth。Onthenorthernsteepflankoftherange，thereareafewpatches(somequiteisolated，andnotlargerthanhalfa-crown！)ofthemica-schist，foliatedwiththesamenortherlydip。Onthebroadsummit，asfarasthesoutherncrest，thereismuchmica-slate，insomeplaceseven400feetinthickness，withthefoliaalldippingnorth，atanglesvaryingfrom5degreesto20degrees，butsometimesmountingupto30degrees。Thesouthernflankconsistsofbaregranite。Themica-slateispenetratedbysmallveinsofgranite，branchingfromthemainbody。(Thegranitewithintheseveins，aswellasgenerallyatthejunctionwiththemica-slate，ismorequartzosethanelsewhere。Thegranite，Imayadd，istraversedbydikesrunningforaverygreatlengthinthelineofthemountains;theyarecomposedofasomewhatlaminatedeurite，containingcrystalsoffeldspar，hornblende，andoctagonsofquartz。)LeavingoutofviewtheprevalentstrikeofthefoliainotherpartsofthisArchipelago，itmighthavebeenexpectedthattheywouldhavedippedN。28degreesE。thatisdirectlyfromtheridge，and，consideringitsabruptness，atahighinclination;buttherealdip，aswehavejustseen，bothatthefootandonthenorthernflank，andovertheentiresummit，isatasmallangle，anddirectednearlyduenorth。Fromtheseconsiderationsitoccurredtome，thatperhapsweherehadthenovelandcuriouscaseofalreadyinclinedlaminaeobliquelytiltedatasubsequentperiodbythegraniticaxis。Mr。
Hopkins，sowellknownfromhismathematicalinvestigations，hasmostkindlycalculatedtheproblem：thepropositionsentwas，——Takeadistrictcomposedoflaminae，dippingatanangleof40degreestoW。19degreesS。andletanaxisofelevationtraverseitinanE。28degreesS。line，whatwillthepositionofthelaminaebeonthenorthernflankafteratilt，wewillfirstsuppose，of45degrees？Mr。Hopkinsinformsme，thattheangleofthedipwillbe28degrees31minutes，anditsdirectiontonorth30
degrees33minuteswest。(Onthesouthsideoftheaxis(where，however，I
didnotseeanymica-slate)thedipofthefoliawouldbeatanangleof77
degrees55minutes，directedtowest35degrees33minutessouth。Hencethetwopointsofdipontheoppositesidesoftherange，insteadofbeingasinordinarycasesdirectlyopposedtoeachotheratanangleof180
degrees，wouldherebeonly86degrees50minutesapart。)Byvaryingthesupposedangleofthetilt，ourpreviouslyinclinedfoliacanbethrownintoanyanglebetween26degrees，whichistheleastpossibleangle，and90degrees;butifasmallinclinationbethusgiventothem，theirpointofdipwilldepartfarfromthenorth，andthereforenotaccordwiththeactualpositionofthefoliaofmica-schistonourgraniticrange。Henceitappearsverydifficult，withoutvaryingconsiderablytheelementsoftheproblem，thustoexplaintheanomalousstrikeanddipofthefoliatedmica-
schist，especiallyinthoseparts，namely，atthebaseoftherange，wherethefoliaarealmosthorizontal。Mr。Hopkins，however，adds，thatgreatirregularitiesandlateralthrustsmightbeexpectedineverygreatlineofelevation，andthatthesewouldaccountforconsiderabledeviationsfromthecalculatedresults：consideringthatthegraniticaxis，asshownbytheveins，hasindisputablybeeninjectedaftertheperfectformationofthemica-slate，andconsideringtheuniformityofthestrikeofthefoliathroughouttherestoftheArchipelago，IcannotbutstillthinkthattheiranomalouspositionatthisonepointissomewaydirectlyandmechanicallyrelatedtotheintrusionofthisW。N。W。andE。S。E。mountain-chainofgranite。
DikesarefrequentinthemetamorphicschistsoftheChonosIslands，andseemfeeblytorepresentthatgreatbandoftrappeanandancientvolcanicrocksonthesouth-westerncoastofTierradelFuego。AtS。AndresI
observedinthespaceofhalf-a-mile，sevenbroad，paralleldikes，composedofthreevarietiesoftrap，runninginaN。W。andS。E。line，paralleltotheneighbouringmountain-rangesofalteredclay-slate;buttheymustbeoflongsubsequentorigintothesemountains;fortheyintersectedthevolcanicformationdescribedinthelastchapter。NorthofTresMontes，I
noticedthreedikesdifferingfromeachotherincomposition，oneofthemhavingaeuriticbaseincludinglargeoctagonsofquartz;thesedikes，aswellasseveralofporphyriticgreenstoneatVallenarBay，extendedN。E。
andS。W。nearlyatrightanglestothefoliationoftheschists，butinthelineoftheirjoints。AtLow’sHarbour，however，asetofgreatparalleldikes，oneninetyyardsandanothersixtyyardsinwidth，havebeenguidedbythefoliationofthemica-schist，andhenceareinclinedwestwardatanangleof45degrees：thesedikesareformedofvariousporphyritictraps，someofwhichareremarkablefromcontainingnumerousroundedgrainsofquartz。Aporphyritictrapofthislatterkind，passedinoneofthedikesintoamostcurioushornstone，perfectlywhite，withawaxyfractureandpellucidedges，fusible，andcontainingmanygrainsofquartzandspecksofironpyrites。Intheninety-yarddikeseverallarge，apparentlynowquiteisolated，fragmentsofmica-slatewereembedded：butastheirfoliationwasexactlyparalleltothatofthesurroundingsolidrock，nodoubtthesenewseparatefragmentsoriginallyformedwedge-shapeddependingportionsofacontinuousvaultorcrust，onceextendingoverthedike，butsinceworndownanddenuded。
CHILOE，VALDIVIA，CONCEPCION。
InChiloe，agreatformationofmica-schiststrikinglyresemblesthatoftheChonosIslands。ForaspaceofelevenmilesontheS。E。coast，thefoliawereverydistinct，thoughslightlyconvoluted，andrangedwithinapointofN。N。W。andS。S。E。dippingeitherE。N。E。ormorecommonlyW。S。W。atanaverageangleof22degrees(inonespot，however，at60degrees)，andthereforedecidedlyatalesserinclinationthanamongsttheChonosIslands。Onthewestandnorth-westernshores，thefoliationwasoftenobscure，though，wherebestdefined，itrangedwithinapointofN。byW。
andS。byE。dippingeithereasterlyorwesterly，atvaryingandgenerallyverysmallangles。Hence，fromthesouthernpartofTresMontestothenorthernendofChiloe，adistanceof300miles，wehavecloselyalliedrockswiththeirfoliastrikingonanaverageinthesamedirection，namelybetweenN。11degreesand22degreesW。Again，atValdivia，wemeetwiththesamemica-schist，exhibitingnearlythesamemineralogicalpassagesasintheChonosArchipelago，often，however，becomingmoreferruginous，andcontainingsomuchfeldsparastopassintogneiss。Thefoliaweregenerallywelldefined;butnowhereelseinSouthAmericadidIseethemvaryingsomuchindirection：thisseemedchieflycausedbytheirformingparts，asIcouldsometimesdistinctlytrace，oflargeflatcurves：
nevertheless，bothnearthesettlementandtowardstheinterior，aN。W。andS。E。strikeseemedmorefrequentthananyotherdirection;theangleofthedipwasgenerallysmall。AtConcepcion，ahighlyglossyclay-slatehaditscleavageoftenslightlycurvilinear，andinclined，seldomatahighangle，towardsvariouspointsofthecompass：buthere，asatValdivia，aN。W。andS。E。strikeseemedtobethemostfrequentone。
((FIGURE23。)Iobservedinsomepartsthatthetopsofthelaminaeoftheclay-slate(binFigure23)underthesuperficialdetritusandsoil(a)
werebent，sometimeswithoutbeingbroken，asrepresentedinFigure23，whichiscopiedfromonegivenbySirH。DelaBeche(page42“GeologicalManual“)ofanexactlysimilarphenomenoninDevonshire。Mr。R。A。C。Austen，also，inhisexcellentpaperonS。E。Devon(“GeologicalTransactions“
volume6page437)，hasdescribedthisphenomenon;heattributesittotheactionoffrosts，butatthesametimedoubtswhetherthefrostsofthepresentdaypenetratetoasufficientdepth。Asitisknownthatearthquakesparticularlyaffectthesurfaceoftheground，itoccurredtomethatthisappearancemightperhapsbedue，atleastatConcepcion，totheirfrequentoccurrence;thesuperficiallayersofdetritusbeingeitherjerkedinonedirection，or，wherethesurfacewasinclined，pushedalittledownwardsduringeachstrongvibration。InNorthWalesIhaveseenasomewhatanalogousbutlessregularappearance，thoughonagreaterscale(“LondonPhilosophicalMagazine“volume21page184)，andproducedbyaquitedifferentcause，namely，bythestrandingofgreaticebergs;thislatterappearancehasalsobeenobservedinN。America。)
Incertainspotslargequartzveinswerenumerous，andnearthem，thecleavage，aswasthecasewiththefoliationoftheschistsintheChonosArchipelago，becameextremelytortuous。
AtthenorthernendofQuiriquinaIsland，intheBayofConcepcion，atleasteightrudelyparalleldikes，whichhavebeenguidedtoacertainextentbythecleavageoftheslate，occurwithinthespaceofaquarterofamile。Theyvarymuchincomposition，resemblinginmanyrespectsthedikesatLow’sHarbour：thegreaternumberconsistoffeldspathicporphyries，sometimescontaininggrainsofquartz：one，however，wasblackandbrilliant，likeanaugiticrock，butreallyformedoffeldspar;othersofafeldspathicnaturewereperfectlywhite，witheitheranearthyorcrystallinefracture，andincludinggrainsandregularoctagonsofquartz;
thesewhitevarietiespassedintoordinarygreenstones。Although，bothhereandatLow’sHarbour，thenatureoftherockvariedconsiderablyinthesamedike，yetIcannotbutthinkthatatthesetwoplacesandinotherpartsoftheChonosgroup，wherethedikes，thoughclosetoeachotherandrunningparallel，areofdifferentcomposition，thattheymusthavebeenformedatdifferentperiods。InthecaseofQuiriquinathisisaratherinterestingconclusion，fortheseeightparalleldikescutthroughthemetamorphicschistsinaN。W。andS。E。line，andsincetheirinjectiontheoverlyingcretaceousortertiarystratahavebeentilted(whilststillunderthesea)fromaN。W。byN。andS。E。byS。line;andagain，duringthegreatearthquakeofFebruary1835，thegroundinthisneighbourhoodwasfissuredinN。W。andS。E。lines;andfromthemannerinwhichbuildingswerethrowndown，itwasevidentthatthesurfaceundulatedinthissamedirection。(“GeologicalTransactions“volume6pages602and617。“JournalofResearches“2ndeditionpage307。)
CENTRALANDNORTHERNCHILE。
NorthwardofConcepcion，asfarasCopiapo，theshoresofthePacificconsist，withtheexceptionofsomesmalltertiarybasins，ofgneiss，mica-
schist，alteredclay-slate，granite，greenstoneandsyenite：hencethecoastfromTresMontestoCopiapo，adistanceof1，200miles，andIhavereasontobelieveforamuchgreaterspace，isalmostsimilarlyconstituted。
NearValparaisotheprevailingrockisgneiss，generallyincludingmuchhornblende：concretionaryballsformedoffeldspar，hornblendeandmica，fromtwoorthreefeetindiameter，areinverymanyplacesconformablyenfoldedbythefoliatedgneiss：veinsofquartzandfeldspar，includingblackschorlandwell-crystallisedepidote，arenumerous。Epidotelikewiseoccursinthegneissinthinlayers，paralleltothefoliationofthemass。
Onelargeveinofacoarsegraniticcharacterwasremarkablefrominonepartquitechangingitscharacter，andinsensiblypassingintoablackishporphyry，includingacicularcrystalsofglassyfeldsparandofhornblende：
Ihaveneverseenanyothersuchcase。(Humboldt“PersonalNarrative“
volume4page60，hasdescribedwithmuchsurprise，concretionaryballs，withconcentricdivisions，composedofpartiallyvitreousfeldspar，hornblende，andgarnets，includedwithingreatveinsofgneiss，whichcutacrossthemica-slatenearVenezuela。)
IshallinthefewfollowingremarksontherocksofChilealludeexclusivelytotheirfoliationandcleavage。InthegneissroundValparaisothestrikeofthefoliationisveryvariable，butIthinkaboutN。byW。
andS。byE。isthecommonestdirection;thislikewiseholdsgoodwiththecleavageofthealteredfeldspathicclay-slates，occasionallymetwithonthecoastforninetymilesnorthofValparaiso。Somefeldspathicslate，alternatingwithstrataofclaystoneporphyryintheBellofQuillotaandatJajuel，andtherefore，perhaps，belongingtoalaterperiodthanthemetamorphicschistsonthecoast，cleavedinthissamedirection。IntheEasternCordillera，inthePortilloPass，thereisagrandmassofmica-
slate，foliatedinanorthandsouthline，andwithahighwesterlydip：intheUspallatarange，clay-slateandgrauwackehaveahighlyinclined，nearlynorthandsouthcleavage，thoughinsomepartsthestrikeisirregular：inthemainorCumbrerange，thedirectionofthecleavageinthefeldspathicclay-slateisN。W。andS。E。
BetweenCoquimboandGuascotherearetwoconsiderableformationsofmica-
slate，inoneofwhichtherockpassedsometimesintocommonclay-slateandsometimesintoaglossyblackvariety，verylikethatintheChonosArchipelago。Thefoliaandcleavageoftheserocksrangedbetween[N。andN。W。byN。]and[S。andS。W。byS。]。NearthePortofGuascoseveralvarietiesofalteredclay-slatehaveaquiteirregularcleavage。BetweenGuascoandCopiapo，therearesomesiliceousandtalcaceousslatescleavinginanorthandsouthline，withaneasterlydipofbetween60and70
degrees：highup，also，themainvalleyofCopiapo，thereismica-slatewithahigheasterlydip。InthewholespacebetweenValparaisoandCopiapoaneasterlydipismuchmorecommonthananoppositeorwesterlyone。
CONCLUDINGREMARKSONCLEAVAGEANDFOLIATION。
Inthissouthernpartofthesouthernhemisphere，wehaveseenthatthecleavage-laminaerangeoverwideareaswithremarkableuniformity，cuttingstraightthroughtheplanesofstratification，butyetbeingparallelinstriketothemainaxesofelevation，andgenerallytotheoutlinesofthecoast。(InmypaperontheFalklandIslands“GeologicalJournal“volume3
page267，IhavegivenacuriouscaseontheauthorityofCaptainSulivan，R。N。ofmuchfoldedbedsofclay-slate，insomeofwhichthecleavageisperpendiculartothehorizon，andinothersitisperpendiculartoeachcurvatureorfoldofthebed：thisappearsanewcase。)Thedip，however，isasvariable，bothinangleandindirection(thatis，sometimesbeinginclinedtotheonesideandsometimestothedirectlyoppositeside)，asthestrikeisuniform。InalltheserespectsthereisacloseagreementwiththefactsgivenbyProfessorSedgwickinhiscelebratedmemoirinthe“GeologicalTransactions，“andbySirR。I。Murchisoninhisvariousexcellentdiscussionsonthissubject。TheFalklandIslands，andmoreespeciallyTierradelFuego，offerstrikinginstancesofthelinesofcleavage，theprincipleaxesofelevation，andtheoutlinesofthecoast，graduallychangingtogethertheircourses。ThedirectionwhichprevailsthroughoutTierradelFuegoandtheFalklandIslands，namely，fromwestwithsomenorthingtoeastwithsomesouthing，isalsocommontotheseveralridgesinNorthernPatagoniaandinthewesternpartsofBandaOriental：inthislatterprovince，intheSierraTapalguen，andintheWesternFalklandIsland，theW。byN。orW。N。W。andE。S。E。ridges，arecrossedatrightanglesbyothersrangingN。N。E。andS。S。W。
Thefactofthecleavage-laminaeintheclay-slateofTierradelFuego，whereseencuttingstraightthroughtheplanesofstratification，andwhereconsequentlytherecouldbenodoubtabouttheirnature，differingslightlyincolour，texture，andhardness，appearstomeveryinteresting。Inathickmassoflaminated，feldspathicandalteredclay-slate，interposedbetweentwogreatstrataofporphyriticconglomerateinCentralChile，andwheretherecouldbebutlittledoubtaboutthebedding，Iobservedsimilarslightdifferencesincomposition，andlikewisesomedistinctthinlayersofepidote，paralleltothehighlyinclinedcleavageofthemass。Again，I
incidentallynoticedinNorthWales，whereglaciershadpassedoverthetruncatededgesofthehighlyinclinedlaminaeofclay-slate，thatthesurface，thoughsmooth，waswornintosmallparallelundulations，causedbythecompetentlaminaebeingofslightlydifferentdegreesofhardness。
(“LondonPhilosophicalMagazine“volume21page182。)WithreferencetotheslatesofNorthWales，ProfessorSedgwickdescribestheplanesofcleavage，as“coatedoverwithchloriteandsemi-crystallinematter，whichnotonlymerelydefinetheplanesinquestion，butstrikeinparallelflakesthroughthewholemassoftherock。”(“GeologicalTransactions“volume3page471。)
Insomeofthoseglossyandhardvarietiesofclay-slate，whichmayoftenbeseenpassingintomica-schist，ithasappearedtomethatthecleavage-
planeswereformedofexcessivelythin，generallyslightedconvoluted，folia，composedofmicroscopicallyminutescalesofmica。Fromtheseseveralfacts，andmoreespeciallyfromthecaseoftheclay-slateinTierradelFuego，itmust，Ithink，beconcluded，thatthesamepowerwhichhasimpressedontheslateitsfissilestructureorcleavagehastendedtomodifyitsmineralogicalcharacterinparallelplanes。
Letusnowturntothefoliationofthemetamorphicschists，asubjectwhichhasbeenmuchlessattendedto。Asinthecaseofcleavage-laminae，thefoliapreserveoververylargeareasauniformstrike：thusHumboldtfoundforadistanceof300milesinVenezuela，andindeedoveramuchlargerspace，gneiss，granite，mica，andclay-slate，strikingveryuniformlyN。E。andS。W。anddippingatanangleofbetween60and70
degreestoN。W。(“PersonalNarrative“volume6page59etseq。);itwouldevenappearfromthefactsgiveninthischapter，thatthemetamorphicrocksthroughoutthenorth-easternpartofSouthAmericaaregenerallyfoliatedwithintwopointsofN。E。andS。W。OvertheeasternpartsofBandaOriental，thefoliationstrikeswithahighinclination，veryuniformlyN。N。E。toS。S。W。andoverthewesternparts，inaW。byN。andE。byS。
line。Foraspaceof300milesontheshoresoftheChonosandChiloeIslands，wehaveseenthatthefoliationseldomdeviatesmorethanapointofthecompassfromaN。19degreesW。andS。19degreesE。strike。Asinthecaseofcleavage，theangleofthedipinfoliatedrocksisgenerallyhighbutvariable，andalternatesfromonesideofthelineofstriketotheotherside，sometimesbeingvertical：intheNorthernChonosIslands，however，thefoliaareinclinedalmostalwaystothewest;innearlythesamemanner，thecleavage-laminaeinSouthernTierradelFuegocertainlydipmuchmorefrequentlytoS。S。W。thantotheoppositepoint。InEasternBandaOriental，inpartsofBrazil，andinsomeotherdistricts，thefoliationrunsinthesamedirectionwiththemountain-rangesandadjoiningcoast-lines：amongsttheChonosIslands，however，thiscoincidencefails，andIhavegivenmyreasonsforsuspectingthatonegraniticaxishasburstthroughandtiltedthealreadyinclinedfoliaofmica-schist：inthecaseofcleavage，thecoincidencebetweenitsstrikeandthatofthemainstratificationseemssometimestofail。(CasesaregivenbyMr。Jukesinhis“GeologyofNewfoundland“page130。)Foliationandcleavageresembleeachotherintheplaneswindingroundconcretions，andinbecomingtortuouswhereveinsofquartzabound。(IhaveseeninBrazilandChileconcretionsthusenfoldedbyfoliatedgneiss;andMacculloch“Highlands“
volume1page64，hasdescribedasimilarcase。Foranalogouscasesinclay-slate，seeProfessorHenslow’sMemoirin“CambridgePhilosophicalTransactions“volume1page379，andMacculloch’s“ClassificationofRocks“
page351。Withrespecttobothfoliationandcleavagebecomingtortuouswherequartz-veinsabound，IhaveseeninstancesnearMonteVideo，atConcepcion，andintheChonosIslands。SeealsoMr。Greenough’s“CriticalExamination“page78。)OntheflanksofthemountainsbothinTierradelFuegoandinothercountries，Ihaveobservedthatthecleavage-planesfrequentlydipatahighangleinwards;andthiswaslongagoobservedbyVonBuchtobethecaseinNorway：thisfactisperhapsanalogoustothefolded，fan-likeorradiatingstructureinthemetamorphicschistsoftheAlps，inwhichthefoliainthecentralcrestsareverticalandonthetwoflanksinclinedinwards。(Studerin“EdinburghNewPhilosophicalJournal“
volume23page144。)Wheremassesoffissileandfoliatedrocksalternatetogether，thecleavageandfoliation，inallcaseswhichIhaveseen，areparallel。Whereinonedistricttherocksarefissile，andinanotheradjoiningdistricttheyarefoliated，theplanesofcleavageandfoliationarelikewisegenerallyparallel：thisisthecasewiththefeldspathichomogeneousslatesinthesouthernpartoftheChonosgroup，comparedwiththefinefoliatedmica-schistsofthenorthernpart;soagaintheclay-
slateofthewholeeasternsideofTierradelFuegocleavesinexactlythesamelinewiththefoliatedgneissandmica-slateofthewesterncoast;
otheranalogousinstancesmighthavebeenadduced。(IhavegivenacaseinAustralia。Seemy“VolcanicIslands。”)
Withrespecttotheoriginofthefoliaofquartz，mica，feldspar，andothermineralscomposingthemetamorphicschists，ProfessorSedgwick，Mr。
Lyell，andmostauthorsbelieve，thattheconstituentpartsofeachlayerwereseparatelydepositedassediment，andthenmetamorphosed。Thisview，inthemajorityofcases，Ibelievetobequiteuntenable。Inthosenotuncommoninstances，whereamassofclay-slate，inapproachinggranite，graduallypassesintogneiss，weclearlyseethatfoliaofdistinctmineralscanoriginatethroughthemetamorphosisofahomogeneousfissilerock。(Ihavedescribedin“VolcanicIslands“agoodinstanceofsuchapassageattheCapeofGoodHope。)Thedeposition，itmayberemarked，ofnumberlessalternationsofpurequartz，andoftheelementsofmicaorfeldspardoesnotappearaprobableevent。(Seesomeexcellentremarksonthissubject，inD’Aubuisson’s“TraitedeGeog。”tome1page297。AlsosomeremarksbyMr。Danain“Silliman’sAmericanJournal“volume45page108。)
Inthosedistrictsinwhichthemetamorphicschistsarefoliatedinplanesparalleltothecleavageoftherocksinanadjoiningdistrict，arewetobelievethatthefoliaareduetosedimentarylayers，whilstthecleavage-
laminae，thoughparallel，havenorelationwhatevertosuchplanesofdeposition？Onthisview，howcanwereconcilethevastnessoftheareasoverwhichthestrikeofthefoliationisuniform，withwhatweseeindisturbeddistrictscomposedoftruestrata：andespecially，howcanweunderstandthehighandevenverticaldipthroughoutmanywidedistricts，whicharenotmountainous，andthroughoutsome，asinWesternBandaOriental，whicharenotevenhilly？ArewetoadmitthatinthenorthernpartoftheChonosArchipelago，mica-slatewasfirstaccumulatedinparallelhorizontalfoliatoathicknessofaboutfourgeographicalmiles，andthenupturnedatanangleoffortydegrees;whilst，inthesouthernpartofthissameArchipelago，thecleavage-laminaeofcloselyalliedrocks，whichnonewouldimaginehadeverbeenhorizontal，dipatnearlythesameangle，tonearlythesamepoint？
Seeing，then，thatfoliatedschistsindisputablyaresometimesproducedbythemetamorphosisofhomogeneousfissilerocks;seeingthatfoliationandcleavagearesocloselyanalogousintheseveralabove-enumeratedrespects;
seeingthatsomefissileandalmosthomogeneousrocksshowincipientmineralogicalchangesalongtheplanesoftheircleavage，andthatotherrockswithafissilestructurealternatewith，andpassintovarietieswithafoliatedstructure，Icannotdoubtthatinmostcasesfoliationandcleavagearepartsofthesameprocess：incleavagetherebeingonlyanincipientseparationoftheconstituentminerals;infoliationamuchmorecompleteseparationandcrystallisation。
Thefactoftenreferredtointhischapter，ofthefoliationandtheso-
calledstratainthemetamorphicseries，——thatis，thealternatingmassesofdifferentvarietiesofgneiss，mica-schist，andhornblende-slate，etc——
beingparalleltoeachother，atfirstappearsquiteopposedtotheview，thatthefoliahavenorelationtotheplanesoforiginaldeposition。Wheretheso-calledbedsarenotverythickandofwidelydifferentmineralogicalcompositionfromeachother，Idonotthinkthatthereisanydifficultyinsupposingthattheyhaveoriginatedinananalogousmannerwiththeseparatefolia。Weshouldbearinmindwhatthickstrata，inordinarysedimentarymasses，haveobviouslybeenformedbyaconcretionaryprocess。
InapileofvolcanicrocksontheIslandofAscension，therearestrata，differingquiteasmuchinappearanceastheordinaryvarietiesofthemetamorphicschists，whichundoubtedlyhavebeenproduced，notbysuccessiveflowingsoflava，butbyinternalmolecularchanges。NearMonteVideo，wherethestratification，asitwouldbecalled，ofthemetamorphicseriesis，inmostparts，particularlywelldeveloped，beingasusual，paralleltothefoliation，wehaveseenthatamassofchloriticschist，nettedwithquartz-veins，isentangledingneiss，insuchamannerastoshowthatithadcertainlyoriginatedinsomeprocessofsegregation：
again，inanotherspot，thegneisstendedtopassintohornblendicschistbyalternatingwithlayersofquartz;buttheselayersofquartzalmostcertainlyhadneverbeenseparatelydeposited，fortheywereabsolutelycontinuouswiththenumerousintersectingveinsofquartz。Ihaveneverhadanopportunityoftracingforanydistance，alongthelinebothofstrikeandofdip，theso-calledbedsinthemetamorphicschists，butIstronglysuspectthattheywouldnotbefoundtoextendwiththesamecharacter，veryfarinthelineeitheroftheirdiporstrike。HenceIamledtobelieve，thatmostoftheso-calledbedsareofthenatureofcomplexfolia，andhavenotbeenseparatelydeposited。Ofcourse，thisviewcannotbeextendedtoTHICKmassesincludedinthemetamorphicseries，whichareoftotallydifferentcompositionfromtheadjoiningschists，andwhicharefarextended，asissometimesthecasewithquartzandmarble;thesemustgenerallybeofthenatureoftruestrata。(Macculloch“ClassificationofRocks“page364，statesthatprimarylimestonesareoftenfoundinirregularmassesorgreatnodules，“whichcanscarcelybesaidtopossessastratifiedshape！”)Suchstrata，however，willalmostalwaysstrikeinthesamedirectionwiththefolia，owingtotheaxesofelevationbeinginmostcountriesparalleltothestrikeofthefoliation;buttheywillgenerallydipatadifferentanglefromthatofthefoliation;andtheangleofthefoliationinitselfalmostalwaysvariesmuch：hence，incrossingametamorphosedschistosedistrict，itwouldrequireespecialattentiontodiscriminatebetweentruestrataofdepositionandcomplexfoliatedmasses。
Themerepresenceoftruestratainthemidstofasetofmetamorphicschists，isnoargumentthatthefoliationisofsedimentaryorigin，withoutitbefurthershownineachcase，thatthefolianotonlystrike，butdipthroughoutinparallelplaneswiththoseofthetruestratification。
Asinsomecasesitappearsthatwhereafissilerockhasbeenexposedtopartialmetamorphicaction，forinstancefromtheirruptionofgranite，thefoliationhassupervenedonthealreadyexistingcleavage-planes;soperhapsinsomeinstances，thefoliationofarockmayhavebeendeterminedbytheoriginalplanesofdepositionorofobliquecurrent-laminae：Ihave，however，myself，neverseensuchacase，andImustmaintainthatinmostextensivemetamorphicareas，thefoliationistheextremeresultofthatprocess，ofwhichcleavageisthefirsteffect。Thatfoliationmayarisewithoutanypreviousstructuralarrangementinthemass，wemayinferfrominjected，andthereforeonceliquified，rocks，bothofvolcanicandplutonicorigin，sometimeshavinga“grain“(asexpressedbyProfessorSedgwick)，andsometimesbeingcomposedofdistinctfoliaorlaminaeofdifferentcompositions。Inmyworkon“VolcanicIslands，“Ihavegivenseveralinstancesofthisstructureinvolcanicrocks，anditisnotuncommonlyseeninplutonicmasses——thus，intheCordilleraofChile，therearegiganticmountain-likemassesofredgranite，whichhavebeeninjectedwhilstliquified，andwhich，nevertheless，displayinpartsadecidedlylaminarstructure。(Asremarkedinaformerpartofthischapter，Isuspectthattheboldlyconicalmountainsofgneiss-granite，nearRiodeJaneiro，inwhichtheconstituentmineralsarearrangedinparallelplanes，areofintrusiveorigin。Wemustnot，however，forgetthelessonofcautiontaughtbythecuriousclaystoneporphyriesofPortDesire，inwhichwehaveseenthatthebreakingupandaggregationofathinlystratifiedtufaceousmass，hasyieldedarocksemi-porphyriticwithcrystalsoffeldspar，arrangedintheplanesoforiginaldeposition。)
Finally，wehaveseenthattheplanesofcleavageandoffoliation，thatis，oftheincipientprocessandofthefinalresult，generallystrikeparalleltotheprincipalaxesofelevation，andtotheoutlineoftheland：thestrikeoftheaxesofelevation(thatis，ofthelinesoffissureswiththestrataontheiredgesupturned)，accordingtothereasoningofMr。Hopkins，isdeterminedbytheformoftheareaundergoingchangesoflevel，andtheconsequentdirectionofthelinesoftensionandfissure。Now，inthatremarkablepileofvolcanicrocksatAscension，whichhasseveraltimesbeenalludedto(andinsomeothercases)，Ihaveendeavouredtoshow，thatthelaminationoftheseveralvarieties，andtheiralternations，havebeencausedbythemovingmass，justbeforeitsfinalconsolidation，havingbeensubjected(asinaglacier)toplanesofdifferenttension;thisdifferenceinthetensionaffectingthecrystallineandconcretionaryprocesses。(In“VolcanicIslands。”)OneofthevarietiesofrockthusproducedatAscension，atfirstsight，singularlyresemblesafine-grainedgneiss;itconsistsofquitestraightandparallelzonesofexcessivetenuity，ofmoreorlesscolouredcrystallisedfeldspar，ofdistinctcrystalsofquartz，diopside，andoxideofiron。Theseconsiderations，notwithstandingtheexperimentsmadebyMr。Fox，showingtheinfluenceofelectricalcurrentsinproducingastructurelikethatofcleavage，andnotwithstandingtheapparentlyinexplicablevariation，bothintheinclinationofthecleavage-laminaeandintheirdippingfirsttoonesideandthentotheothersideofthelineofstrike，leadmetosuspectthattheplanesofcleavageandfoliationareintimatelyconnectedwiththeplanesofdifferenttension，towhichtheareawaslongsubjected，AFTERthemainfissuresoraxesofupheavementhadbeenformed，butBEFORE
thefinalconsolidationofthemassandthetotalcessationofallmolecularmovement。
CHAPTERVII。CENTRALCHILE：——STRUCTUREOFTHECORDILLERA。
CentralChile。
BasalformationsoftheCordillera。
Originoftheporphyriticclay-stoneconglomerate。
Andesite。
Volcanicrocks。
SectionoftheCordillerabythePeuquenesarePortilloPass。
Greatgypseousformation。
Peuquenesline;thicknessofstrata，fossilsof。
Portilloline。
Conglomerate，orthiticgranite，mica-schist，volcanicrocksof。
ConcludingremarksonthedenudationandelevationofthePortilloline。
SectionbytheCumbre，orUspallataPass。
Porphyries。
Gypseousstrata。
SectionnearthePuentedelInca;fossilsof。
Greatsubsidence。
Intrusiveporphyries。
PlainofUspallata。
SectionoftheUspallatachain。
Structureandnatureofthestrata。
Silicifiedverticaltrees。
Greatsubsidence。
Graniticrocksofaxis。
ConcludingremarksontheUspallatarange;originsubsequenttothatofthemainCordillera;twoperiodsofsubsidence;comparisonwiththePortillochain。
ThedistrictbetweentheCordilleraandthePacific，onarudeaverage，isfromabouteightytoonehundredmilesinwidth。Itiscrossedbymanychainsofmountains，ofwhichtheprincipalones，inthelatitudeofValparaisoandsouthwardofit，rangenearlynorthandsouth;butinthemorenorthernpartsoftheprovince，theyruninalmosteverypossibledirection。NearthePacific，themountain-rangesaregenerallyformedofsyeniteorgranite，andorofanalliedeuriticporphyry;inthelowcountry，besidesthesegraniticrocksandgreenstone，andmuchgneiss，thereare，especiallynorthwardofValparaiso，someconsiderabledistrictsoftrueclay-slatewithquartzveins，passingintoafeldspathicandporphyriticslate;thereisalsosomegrauwackeandquartzoseandjasperyrocks，thelatteroccasionallyassumingthecharacterofthebasisofclaystoneporphyry：trap-dikesarenumerous。NearertheCordilleratheranges(suchasthoseofS。Fernando，thePrado(Meyen“ReiseumErde“th。
1s。235。)，andAconcagua)areformedpartlyofgraniticrocks，andpartlyofpurpleporphyriticconglomerates，claystoneporphyry，greenstoneporphyry，andotherrocks，suchasweshallimmediatelysee，formthebasalstrataofthemainCordillera。InthemorenorthernpartsofChile，thisporphyriticseriesextendsoverlargetractsofcountryfarfromtheCordillera;andeveninCentralChilesuchoccasionallyoccurinoutlyingpositions。
IwilldescribetheCampanaofQuillota，whichstandsonlyfifteenmilesfromthePacific，asaninstanceofoneoftheseoutlyingmasses。Thishillisconspicuousfromrisingtotheheightof6，400feet：itssummitshowsanucleus，uncoveredforaheightof800feet，offinegreenstone，includingepidoteandoctahedralmagneticironore;itsflanksareformedofgreatstrataofporphyriticclaystoneconglomerateassociatedwithvarioustrueporphyriesandamygdaloids，alternatingwiththickmassesofahighlyfeldspathic，sometimesporphyritic，pale-colouredslatyrock，withitscleavage-laminaedippinginwardsatahighangle。Atthebaseofthehilltherearesyenites，agranularmixtureofquartzandfeldspar，andharshquartzoserocks，allbelongingtothebasalmetamorphicseries。Imayobservethatatthefootofseveralhillsofthisclass，wheretheporphyriesarefirstseen(asnearS。Fernando，thePrado，LasVacas，etc。)，similarharshquartzoserocksandgranularmixturesofquartzandfeldsparoccur，asifthemorefusibleconstituentpartsofthegraniticserieshadbeendrawnofftoformtheoverlyingporphyries。
InCentralChile，theflanksofthemainCordillera，intowhichI
penetratedbyfourdifferentvalleys，generallyconsistofdistinctlystratifiedrocks。Thestrataareinclinedatanglesvaryingfromsometimesevenunderten，totwentydegrees，veryrarelyexceedingfortydegrees：insome，however，ofthequitesmall，exterior，spur-likeridges，theinclinationwasnotunfrequentlygreater。ThedipofthestratainthemainouterlineswasusuallyoutwardsorfromtheCordillera，butinNorthernChilefrequentlyinwards，——thatis，theirbasset-edgesfrontedthePacific。
Dikesoccurinextraordinarynumbers。Inthegreat，central，loftiestridges，thestrata，asweshallpresentlysee，arealmostalwayshighlyinclinedandoftenvertical。BeforegivingadetailedaccountofmytwosectionsacrosstheCordillera，itwill，Ithink，beconvenienttodescribethebasalstrataasseen，oftentoathicknessoffourorfivethousandfeet，ontheflanksoftheouterlines。
BASALSTRATAOFTHECORDILLERA。
Theprevailingrockisapurplishorgreenish，porphyriticclaystoneconglomerate。Theembeddedfragmentsvaryinsizefrommereparticlestoblocksasmuchassixoreightinches(rarelymore)indiameter;inmanyplaces，wherethefragmentswereminute，thesignsofaqueousdepositionwereunequivocallydistinct;wheretheywerelarge，suchevidencecouldrarelybedetected。Thebasisisgenerallyporphyriticwithperfectcrystalsoffeldspar，andresemblesthatofatrueinjectedclaystoneporphyry：often，however，ithasamechanicalorsedimentaryaspect，andsometimes(asatJajuel)isjaspery。Theincludedfragmentsareeitherangular，orpartiallyorquiterounded(SomeoftheroundedfragmentsintheporphyriticconglomerateneartheBathsofCauquenes，weremarkedwithradiiandconcentriczonesofdifferentshadesofcolour：anyonewhodidnotknowthatpebbles，forinstanceflintpebblesfromthechalk，aresometimeszonedconcentricallywiththeirwornandroundedsurfaces，mighthavebeenledtoinfer，thattheseballsofporphyrywerenottruepebbles，buthadoriginatedinconcretionaryaction。);insomepartstherounded，inotherstheangularfragmentsprevail，andusuallybothkindsaremixedtogether：hencethewordBRECCIAoughtstrictlytobeappendedtothetermPORPHYRITICCONGLOMERATE。Thefragmentsconsistofmanyvarietiesofclaystoneporphyry，usuallyofnearlythesamecolourwiththesurroundingbasis，namely，purplish-reddish，brownish，mottledorbrightgreen;
occasionallyfragmentsofalaminated，pale-coloured，feldspathicrock，likealteredclay-slateareincluded;asaresometimesgrainsofquartz，butonlyinoneinstanceinCentralChile(namely，attheminesofJajuel)
afewpebblesofquartz。Inowhereobservedmicainthisformation，andrarelyhornblende;wherethelattermineraldidoccur，Iwasgenerallyindoubtwhetherthemassreallybelongedtothisformation，orwasofintrusiveorigin。Calcareoussparoccasionallyoccursinsmallcavities;
andnestsandlayersofepidotearecommon。Insomefewplacesinthefiner-grainedvarieties(forinstance，atQuillota)，therewereshort，interruptedlayersofearthyfeldspar，whichcouldbetraced，exactlyasatPortDesire，passingintolargecrystalsoffeldspar：Idoubt，however，whetherinthisinstancethelayershadeverbeenseparatelydepositedastufaceoussediment。
Allthevarietiesofporphyriticconglomeratesandbrecciaspassintoeachother，andbyinnumerablegradationsintoporphyriesnolongerretainingtheleasttraceofmechanicalorigin：thetransitionappearstohavebeeneffectedmuchmoreeasilyinthefiner-grained，thaninthecoarser-grainedvarieties。Inoneinstance，nearCauquenes，Inoticedthataporphyriticconglomerateassumedaspheroidalstructure，andtendedtobecomecolumnar。
Besidestheporphyriticconglomeratesandtheperfectlycharacterisedporphyries，ofmetamorphicorigin，thereareotherporphyries，which，thoughdifferingnotatalloronlyslightlyincomposition，certainlyhavehadadifferentorigin：theseconsistofpinkorpurpleclaystoneporphyries，sometimesincludinggrainsofquartz，——ofgreenstoneporphyry，andofotherduskyrocks，allgenerallyporphyriticwithfine，large，tabular，opaquecrystals，oftenplacedcrosswise，offeldsparcleavinglikealbite(judgingfromseveralmeasurements)，andoftenamygdaloidalwithsilex，agate，carbonateoflime，greenandbrownbole。(Thisboleisaverycommonmineralintheamygdaloidalrocks;itisgenerallyofagreenish-
browncolour，witharadiatingstructure;externallyitisblackwithanalmostmetalliclustre，butoftencoatedbyabrightgreenfilm。Itissoftandcanbescratchedbyaquill;undertheblowpipeswellsgreatlyandbecomesscaly，thenfuseseasilyintoablackmagneticbead。Thissubstanceisevidentlysimilartothatwhichoftenoccursinsubmarinevolcanicrocks。Anexaminationofsomeverycuriousspecimensofafineporphyry(fromJajuel)leadsmetosuspectthatsomeoftheseamygdaloidalballs，insteadofhavingbeendepositedinpre-existingair-vesicles，areofconcretionaryorigin;forinthesespecimens，someofthepea-shapedlittlemasses(oftenexternallymarkedwithminutepits)areformedofamixtureofgreenearthwithstonymatter，likethebasisoftheporphyry，includingminuteimperfectcrystalsoffeldspar;andthesepea-shapedlittlemassesarethemselvesamygdaloidalwithminutespheresofthegreenearth，eachenvelopedbyafilmofwhite，apparentlyfeldspathic，earthymatter：sothattheporphyryisdoublyamygdaloidal。Itshouldnot，however，beoverlooked，thatallthestrataherehaveundergonemetamorphicaction，whichmayhavecausedcrystalsoffeldspartoappear，andotherchangestobeeffected，intheoriginallysimpleamygdaloidalballs。Mr。J。D。Dana，inanexcellentpaperonTrap-rocks“EdinburghNewPhilosophicalJournal“
volume41page198，hasarguedwithgreatforce，thatallamygdaloidalmineralshavebeendepositedbyaqueousinfiltration。Imaytakethisopportunityofalludingtoacuriouscase，describedinmyworkon“VolcanicIslands，“ofanamygdaloidwithmanyofitscellsonlyhalffilledupwithamesotypicmineral。M。Rosehasdescribedanamygdaloid，broughtbyDr。Meyen“ReiseumErde“Th。1。s。316，fromChile，asconsistingofcrystallisedquartz，withcrystalsofstilbitewithin，andlinedexternallybygreenearth。)Theseseveralporphyriticandamygdaloidalvarietiesnevershowanysignsofpassingintomassesofsedimentaryorigin：theyoccurbothingreatandsmallintrusivemasses，andlikewiseinstrataalternatingwiththoseoftheporphyriticconglomerate，andwiththeplanesofjunctionoftenquitedistinct，yetnotseldomblendedtogether。Insomeoftheseintrusivemasses，theporphyriesexhibit，moreorlessplainly，abrecciatedstructure，likethatoftenseeninvolcanicmasses。Thesebrecciatedporphyriescouldgenerallybedistinguishedatoncefromthemetamorphosed，porphyriticbreccia-
conglomerates，byallthefragmentsbeingangularandbeingformedofthesamevariety，andbytheabsenceofeverytraceofaqueousdeposition。Oneoftheporphyriesabovespecified，namely，thegreenstoneporphyrywithlargetabularcrystalsofalbite，isparticularlyabundant，andinsomepartsoftheCordillera(asnearSt。Jago)seemedmorecommoneventhanthepurplishporphyriticconglomerate。Numerousdikeslikewiseconsistofthisgreenstoneporphyry;othersareformedofvariousfine-grainedtrappeanrocks;butveryfewofclaystoneporphyry：Isawnotruebasalticdikes。
Inseveralplacesinthelowerpartoftheseries，butnoteverywhere，thickmassesofahighlyfeldspathic，oftenporphyritic，slatyrockoccurinterstratifiedwiththeporphyriticconglomerate;Ibelieveinoneortwocasesblackishlimestonehasbeenfoundinasimilarposition。Thefeldspathicrockisofapalegreyorgreenishcolour;itiseasilyfusible;whereporphyritic，thecrystalsoffeldspararegenerallysmallandvitreous：itisdistinctlylaminated，andsometimesincludesparallellayersofepidote(ThismineralisextremelycommoninalltheformationsofChile;inthegneissnearValparaisoandinthegraniticveinscrossingit，intheinjectedgreenstonecrowningtheC。ofQuillota，insomegraniticporphyries，intheporphyriticconglomerate，andinthefeldspathicclay-slates。);thelaminationappearstobedistinctfromstratification。Occasionallythisrockissomewhatcurious;andatonespot，namely，attheC。ofQuillota，ithadabrecciatedstructure。NeartheminesofJajuel，inathickstratumofthisfeldspathic，porphyriticslate，therewasalayerofhard，blackish，siliceous，infusible，compactclay-slate，suchasIsawnowhereelse;atthesameplaceIwasabletofollowforaconsiderabledistancethejunctionbetweentheslateandtheconformablyunderlyingporphyriticconglomerate，andtheycertainlypassedgraduallyintoeachother。Wherevertheseslatyfeldspathicrocksabound，greenstoneseemscommon;attheC。ofQuillotaabedofwell-crystallisedgreenstonelayconformablyinthemidstofthefeldspathicslate，withtheupperandlowerjunctionspassinginsensiblyintoit。Fromthispoint，andfromthefrequentlyporphyriticconditionoftheslate，Ishouldperhapshaveconsideredthisrockasaneruptedone(likecertainlaminatedfeldspathiclavasinthetrachyticseries)，hadInotseeninTierradelFuegohowreadilytrueclay-slatebecomesfeldspathicandporphyritic，andhadInotseenatJajueltheincludedlayerofblack，siliceousclay-slate，whichnoonecouldhavethoughtofigneousorigin。Thegentlepassageofthefeldspathicslate，atJajuel，intotheporphyriticconglomerate，whichiscertainlyofaqueousorigin，shouldalsobetakeninaccount。
