If，however，theconditionoftheworld，whichhasobtainedthroughoutgeologictime，isbutthesequeltoavastseriesofchangeswhichtookplaceinpre-geologictime，thenitseemsnotunlikelythatthedurationofthislatteristothatoftheformerasthevastextentofgeologictimeistothelengthofthebriefepochwecallthehistoricalperiod；andthateventheoldestrocksarerecordsofanepochalmostinfinitelyremotefromthatwhichcouldhavewitnessedthefirstshapingofourglobe。
Itisprobablethatnomoderngeologistwouldhesitatetoadmitthegeneralvalidityofthesereasoningswhenappliedtothephysicsofhissubject，whenceitisthemoreremarkablethatthemomentthequestionchangesfromoneofphysicsandchemistrytooneofnaturalhistory，scientificopinionsandthepopularprejudices，whichreflecttheminadistortedform，undergoasuddenmetamorphosis。Geologistsandpalaeontologistswriteaboutthe\"beginningoflife\"andthe\"first-createdformsoflivingbeings，\"asiftheywerethemostfamiliarthingsintheworld；andevencautiouswritersseemtobeonquitefriendlytermswiththe\"archetype\"wherebytheCreatorwasguided\"amidstthecrashoffallingworlds。\"Justasitusedtobeimaginedthattheancientworldwasphysicallyopposedtothepresent，soitisstillwidelyassumedthatthelivingpopulationofourglobe，whetheranimalorvegetable，intheolderepochs，exhibitedformssostrikinglycontrastedwiththosewhichweseearoundus，thatthereishardlyanythingincommonbetweenthetwo。Itisconstantlytacitlyassumedthatwehavebeforeusalltheformsoflifewhichhaveeverexisted；andthoughtheprogressofknowledge，yearlyandalmostmonthly，drivesthedefendersofthatpositionfromtheirground，theyentrenchthemselvesinthenewlineofdefencesasifnothinghadhappened，andproclaimthatthe\'new\'beginningisthe\'real\'
beginning。
Withoutforaninstantdenyingorendeavouringtosoftendowntheconsiderablepositivedifferences（thenegativeonesaremetbyanotherlineofargument）whichundoubtedlyobtainbetweentheancientandthemodernworldsoflife，webelievetheyhavebeenvastlyoverstatedandexaggerated，andthisbeliefisbaseduponcertainfactswhosevaluedoesnotseemtohavebeenfullyappreciated，thoughtheyhavelongbeenmoreorlesscompletelyknown。
Themultitudinouskindsofanimalsandplants，bothrecentandfossil，are，asiswellknown，arrangedbyzoologistsandbotanists，inaccordancewiththeirnaturalrelations，intogroupswhichreceivethenamesofsub-kingdoms，classes，orders，families，generaandspecies。