第1章

EVERYONEknowsthatthatsuperficialfilmoftheearth"ssubstance，hardlytenmilesthick，whichisaccessibletohumaninvestigation，iscomposedforthemostpartofbedsorstrataofstone，theconsolidatedmudsandsandsofformerseasandlakes，whichhavebeendepositedoneupontheother，andhencearetheolderthedeepertheylie。Thesemultitudinousstratapresentsuchresemblancesanddifferencesamongthemselvesthattheyarecapableofclassificationintogroupsorformations，andtheseformationsagainarebrigadedtogetherintostilllargerassemblages，calledbytheoldergeologists，primary，secondary，andtertiary；bythemoderns，palaeozoic，mesozoic，andcainozoic:thebasisoftheformernomenclaturebeingtherelativeageofthegroupsofstrata；thatofthelatter，thekindsoflivingformscontainedinthem。

Thoughbutafilmifcomparedwiththetotaldiameterofourplanet，thetotalseriesofformationsisvastindeedwhenmeasuredbyanyhumanstandard，and，asallactionimpliestime，soarewecompelledtoregardthesemineralmassesasameasureofthetimewhichhaselapsedduringtheiraccumulation。Theamountofthetimewhichtheyrepresentis，ofcourse，intheinverseproportionoftheintensityoftheforceswhichhavebeeninoperation。If，intheancientworld，mudandsandaccumulatedonsea-bottomsattenfoldtheirpresentrate，itisclearthatabedofmudorsandtenfeetthickwouldhavebeenformedtheninthesametimeasastratumofsimilarmaterialsonefootthickwouldbeformednow，and"viceversa"。

Attheoutsetofhisstudies，therefore，thephysicalgeologisthadtochoosebetweentwohypotheses；either，throughouttheageswhicharerepresentedbytheaccumulatedstrata，andwhichwemaycall"geologictime"，theforcesofnaturehaveoperatedwithmuchsameaverageintensityasatpresent，andhencethelapseoftimewhichtheyrepresentmustbesomethingprodigiousandinconceivable，or，intheprimevalepochs，thenaturalpowerswereinfinitelymoreintensethannow，andhencethetimethroughwhichtheyactedtoproducetheeffectsweseewascomparativelyshort。

Theearliergeologistsadoptedthelatterviewalmostwithoneconsent。

Fortheyhadlittleknowledgeofthepresentworkingsofnature，andtheyreadtherecordsofgeologictimeasachildreadsthehistoryofRomeorGreece，andfanciesthatantiquitywasgrand，heroic，andunlikethepresentbecauseitisunlikehislittleexperienceofthepresent。

Evensotheearlierobserversweremovedwithwonderattheseemingcontrastbetweentheancientandthepresentorderofnature。Theelementalforcesseemedtohavebeengranderandmoreenergeticinprimevaltimes。Upheavedandcontorted，riftedandfissured，piercedbydykesofmoltenmatterorwornawayovervastareasbyaqueousaction，theolderrocksappearedtobearwitnesstoastateofthingsfardifferentfromthatexhibitedbythepeacefulepochonwhichthelotofmanhasfallen。

Butbydegreesthoughtfulstudentsofgeologyhavebeenledtoperceivethattheearliesteffortsofnaturehavebeenbynomeansthegrandest。AlpsandAndesarechildrenofyesterdaywhencomparedwithSnowdonandtheCumberlandhills；andtheso-calledglacialepoch——thatinwhichperhapsthemostextensivephysicalchangesofwhichanyrecordremainingoccurred——isthelastandthenewestoftherevolutionsoftheglobe。Andinproportionasphysicalgeography——whichisthegeologyofourownepoch——hasgrownintoascience，andthepresentorderofnaturehasbeenransackedtofindwhat，"hibernice"，wemaycallprecedentsforthephenomenaofthepast，sotheapparentnecessityofsupposingthepasttobewidelydifferentfromthepresenthasdiminished。

Thetransportingpowerofthegreatestdelugewhichcanbeimaginedsinksintoinsignificancebesidethatoftheslowlyfloating，slowlymeltingiceberg，ortheglaciercreepingalongatitssnail"spaceofayardaday。ThestudyofthedeltasoftheNile，theGanges，andtheMississippihastaughtushowslowisthewearingactionofwater，howvastitseffectswhentimeisallowedforitsoperation。ThereefsofthePacific，thedeep-seasoundingsoftheAtlantic，showthatitistotheslow-growingcoralandtotheimperceptibleanimalcule，whichlivesitsbriefspaceandthenaddsitstinyshelltothemuddycairnleftbyitsbrethrenandancestors，thatwemustlookastheagentsintheformationoflimestoneandchalk，andnottohypotheticaloceanssaturatedwithcalcareoussaltsandsuddenlydepositingthem。

Andwhiletheinquirerhasthuslearntthatexistingforces——"givethemtime"——arecompetenttoproduceallthephysicalphenomenawemeetwithintherocks，so，ontheotherside，thestudyofthemarksleftintheancientstratabypastphysicalactionsshowsthattheseweresimilartothosewhichnowobtain。Ancientbeachesaremetwithwhosepebblesarelikethosefoundonmodernshores；thehardenedsea-sandsoftheoldestepochsshowripple-marks，suchasmaynowbefoundoneverysandycoast；nay，more，thepitsleftbyancientrain-dropsprovethatevenintheveryearliestages，the"bowintheclouds"musthaveadornedthepalaeozoicfirmament。SothatifwecouldreversethelegendoftheSevenSleepers，——ifwecouldsleepbackthroughthepast，andawakeamillionagesbeforeourownepoch，inthemidstoftheearliestgeologictimes，——thereisnoreasontobelievethatsea，orsky，ortheaspectofthelandwouldwarnusofthemarvellousretrospection。

Sucharethebeliefswhichmodernphysicalgeologistshold，or，atanyrate，tendtowardsholding。But，insodoing，itisobviousthattheybynomeansprejudgethequestion，astowhatthephysicalconditionoftheglobemayhavebeenbeforeourchaptersofitshistorybegin，inwhatmaybecalled（withthatlicencewhichisimpliedintheoften-usedterm"prehistoricepoch"）"pre-geologictime。"Theviewsindicated，infact，arenotonlyquiteconsistentwiththehypothesis，that，inthestillearlierperiodreferredto，theconditionofourworldwasverydifferent；buttheymaybeheldbysometonecessitatethathypothesis。

Thephysicalphilosopherwhoisaccuratelyacquaintedwiththevelocityofacannon-ball，andtheprecisecharacterofthelinewhichittraversesforayardofitscourse，isnecessitatedbywhatheknowsofthelawsofnaturetoconcludethatitcamefromacertainspot，whenceitwasimpelledbyacertainforce，andthatithasfollowedacertaintrajectory。Inlikemanner，thestudentofphysicalgeology，whofullybelievesintheuniformityofthegeneralconditionoftheearththroughgeologictime，mayfeelcompelledbywhatheknowsofcausation，andbythegeneralanalogyofnature，tosupposethatoursolarsystemwasonceanebulousmass；thatitgraduallycondensed，thatitbrokeupintothatwonderfulgroupofharmoniouslyrollingballswecallplanetsandsatellites，andthattheneachoftheseunderwentitsappointedmetamorphosis，untilatlastourownshareofthecosmicvapourpassedintothatconditioninwhichwefirstmeetwithdefiniterecordsofitsstate，andinwhichithassince，withcomparativelylittlechange，remained。

Thedoctrineofuniformityandthedoctrineofprogressionare，therefore，perfectlyconsistent；perhaps，indeed，theymightbeshowntobenecessarilyconnectedwithoneanother。