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CliffsofMoherGeology TherocksthatmakeuptheCliffsofMoherwereformedover300millionyearsagoduring theUpperCarboniferousperiod.BandsofNamuriansandstone,siltstoneandshaleare exposedinaspectacularfashionandhereonecanstudyanexampleofasedimentarybasin normallyonlyvisibleunderthesea. Atthattimealargelandmasswaslocatedtothesouthwestoftheancientmarinebasin. Heavyrainfallonthelandcreatedgreatfloodsthatwashedsandandmudintoancient riversthatflowednortheastwardstothesea.Thesand,siltandmudcarriedbytheselarge riversweredumpedintotheseaatthemouthofgreatdelta(similartothemouthofthe MississippiRiverasweknowittoday).Overthemillionsofyearsthatfollowed,the sedimentswerecompactedintosolidrockandwerepushednorthwardsduetomovements intheearth’splates.Itisthesesedimentaryrocklayersofsandstones,siltstone,mudstone andshalethatmakeuptheCliffsofMohertoday. Therocklayersarerichinfossilformationsandgeologistsconsidertheareaoneofthe world’sforemostnaturallaboratoriesforthestudyofdeltaicdepositionthroughdeepwater systems.EachrocklayerintheCliffsofMoherisarepresentationofaspecificeventinthe lifeoftheancientdeltaasitmigratedintothesea.Individuallayersofrocksvaryfrom centimetrestometresinthicknessbuttogethertheyformanaturalfeaturethatstandsover 200metresabovetheoceanthatthehighestpoint.Justasthepagesofabooktellusapart ofabiggerstory,eachlayerofrocktellssomethingaboutthelocalenvironmentthatexisted over300millionyearsagowhattheserockswereformed. TherearetwotypesoftracefossilsintheCliffsofMoherflagstones.Thesquigglytrails, calledscolicia,arefeedingtrailsleftbysomeunidentifiedmarinecreatureandare commonlyreferredtoasworming.Itcouldhavebeenaworm,asnailoracrustacean.A secondlessobvioustypeoftracefossilisthesmall,circularburrowmark.Theseburrowsare preservedascastsofthefeeding(orescape)burrowleftbyanunidentifiedmarinecreature. Otherflagstonesaremarkedwithfossilizedwaveripplemarks.Justliketheripplemarkswe oftenseeonthebeachorinshallowseawater,theseripplemarksformedinthesandsand siltsontheancientseafloor.Theattractivepatternsleftbythefossilshaveledtoademand forMoherorLiscannorflagstoneandduringthe19thcenturyathrivingquarryingindustry sprungupinthisarea.Thepavingthroughoutthevisitorcentreandonthecliffedge viewingplatforms,wallsandpathwayshasbeendonewithlocalLiscannororMoherslate flags. TodaytheCliffsareundergoingcoastalerosion.Wavesconstantlycrashagainstthefootof thecliffs,andthisincessantwaveactionerodesthecliffbase,causingsectionsoftheupper clifffacetocollapseintotheseaundertheirownweight.Avarietyofcoastallandformscan beseenbothfromthetopofthecliffsandfromoffshore.Seacavesareformedalongthe footofthecliffsandovertimethesedevelopintoSeaStacksandSeaStumps.Wind,rain andiceallcontributetotheerosionofthecliffface. Thegreatseastack(Branaunmore)atthefootoftheCliffsofMoher,belowO’Brien’sTower stands67metreshigh.Thiscolumnofrockwasoncepartofthecliffsbutcoastalerosion slowlyremovedthelayersofrockjoiningittothemainland.Furtherwest,alongthecliffs,a numberofseacaveshaveformedatthefootofthecliffs.Oneofthesefeaturedfamouslyin the2009movie–HarryPotter&theHalfBloodPrince.Alargeseaarchcanalsobeseenat Hag’sHeadbelowtheNapoleonicsignaltowerandmultiplesmallerseaarchescanbeseen fromsealevel. TheCliffsofMoherformpartoftheBurrenandCliffsofMoherGeoparkwhichwasawarded membershipoftheUNESCOsupportedGlobalGeoparksNetworkin2011.
