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me。 on all of these he would ultimately be proved wrong。
yet it would be nearly impossible to overstate lyell鈥檚 influence。 the principles of geologywent through twelve editions in lyell鈥檚 lifetime and contained notions that shaped geological thinking far into the twentieth century。 darwin took a first edition with him on thebeaglevoyage and wrote afterward that 鈥渢he great merit of the principles was that it altered thewhole tone of one鈥檚 mind； and therefore that； when seeing a thing never seen by lyell； one yetsaw it partially through his eyes。鈥潯n short； he thought him nearly a god； as did many of hisgeneration。 it is a testament to the strength of lyell鈥檚 sway that in the 1980s when geologistshad to abandon just a part of it to acmodate the impact theory of extinctions； it nearlykilled them。 but that is another chapter。
meanwhile； geology had a great deal of sorting out to do； and not all of it went smoothly。
from the outset geologists tried to categorize rocks by the periods in which they were laiddown； but there were often bitter disagreements about where to put the dividing lines鈥攏onemore so than a long…running debate that became known as the great devonian controversy。
the issue arose when the reverend adam sedgwick of cambridge claimed for the cambrianperiod a layer of rock that roderick murchison believed belonged rightly to the silurian。 thedispute raged for years and grew extremely heated。 鈥渄e la beche is a dirty dog；鈥潯urchisonwrote to a friend in a typical outburst。
some sense of the strength of feeling can be gained by glancing through the chapter titlesof martin j。 s。 rudwick鈥檚 excellent and somber account of the issue； the great devoniancontroversy。 these begin innocuously enough with headings such as 鈥渁renas of gentlemanlydebate鈥潯nd 鈥渦nraveling the greywacke；鈥潯ut then proceed on to 鈥渢he greywacke defendedand attacked；鈥潯♀�渞eproofs and recriminations；鈥潯♀�渢he spread of ugly rumors；鈥潯♀�渨eaverrecants his heresy；鈥潯♀�減utting a provincial in his place；鈥潯nd （in case there was any doubtthat this was war） 鈥渕urchison opens the rhineland campaign。鈥潯he fight was finally settledin 1879 with the simple expedient of ing up with a new period； the ordovician； to beinserted between the two。
because the british were the most active in the early years； british names are predominantin the geological lexicon。 devonian is of course from the english county of devon。 cambrianes from the roman name for wales； while ordovician and silurian recall ancient welshtribes； the ordovices and silures。 but with the rise of geological prospecting elsewhere；names began to creep in from all over。jurassic refers to the jura mountains on the border offrance and switzerland。permian recalls the former russian province of perm in the uralmountains。 forcretaceous （from the latin for 鈥渃halk鈥潱e are indebted to a belgian geologistwith the perky name of j。 j。 d鈥檕malius d鈥檋alloy。
originally； geological history was divided into four spans of time： primary； secondary；tertiary； and quaternary。 the system was too neat to last； and soon geologists werecontributing additional divisions while eliminating others。 primary and secondary fell out ofuse altogether； while quaternary was discarded by some but kept by others。 today onlytertiary remains as a mon designation everywhere； even though it no longer represents athird period of anything。
lyell； in his principles； introduced additional units known as epochs or series to cover theperiod since the age of the dinosaurs； among them pleistocene （鈥渕ost recent鈥潱弧liocene（鈥渕ore recent鈥潱弧iocene （鈥渕oderately recent鈥潱弧nd the rather endearingly vague oligocene（鈥渂ut a little recent鈥潱！yell originally intended to employ 鈥湣璼ynchronous鈥潯or his endings；giving us such crunchy designations as meiosynchronous and pleiosynchronous。 thereverend william whewell； an influential man； objected on etymological grounds andsuggested instead an 鈥湣璭ous鈥潯attern； producing meioneous； pleioneous； and so on。 the 鈥湣璫ene鈥潯erminations were thus something of a promise。
nowadays； and speaking very generally； geological time is divided first into four greatchunks known as eras： precambrian； paleozoic （from the greek meaning 鈥渙ld life鈥潱籱esozoic （鈥渕iddle life鈥潱弧nd cenozoic （鈥渞ecent life鈥潱！hese four eras are further dividedinto anywhere from a dozen to twenty subgroups； usually called periods though sometimesknown as systems。 most of these are also reasonably well known： cretaceous； jurassic；triassic； silurian； and so on。
1then e lyell鈥檚 epochs鈥攖he pleistocene； miocene； and so on鈥攚hich apply only to themost recent （but paleontologically busy） sixty…five million years； and finally we have a massof finer subdivisions known as stages or ages。 most of these are named； nearly alwaysawkwardly； after places： illinoian； desmoinesian； croixian； kimmeridgian； and so on in likevein。 altogether； according to john mcphee； these number in the 鈥渢ens of dozens。鈥�
fortunately； unless you take up geology as a career； you are unlikely ever to hear any of themagain。
further confusing the matter is that the stages or ages in north america have differentnames from the stages in europe and often only roughly intersect in time。 thus the northamerican cincinnatian stage mostly corresponds with the ashgillian stage in europe； plus atiny bit of the slightly earlier caradocian stage。
also； all this changes from textbook to textbook and from person to person； so that someauthorities describe seven recent epochs； while others are content with four。 in some books；too； you will find the tertiary and quaternary taken out and replaced by periods of differentlengths called the palaeogene and neogene。 others divide the precambrian into two eras； thevery ancient archean and the more recent proterozoic。 sometimes too you will see the termphanerozoic used to describe the span enpassing the cenozoic； mesozoic； and paleozoiceras。
moreover； all this applies only to units of time 。 rocks are divided into quite separate unitsknown as systems； series； and stages。 a distinction is also made between late and early（referring to time） and upper and lower （referring to layers of rock）。 it can all get terriblyconfusing to nonspecialists； but to a geologist these can be matters of passion。 鈥渋 have seengrown men glow incandescent with rage over this metaphorical millisecond in life鈥檚 history；鈥�
the british paleontologist richard fortey has written with regard to a long…running twentieth…century dispute over where the boundary lies between the cambrian and ordovician。
at least today we can bring some sophisticated dating techniques to the table。 for most ofthe nineteenth century geologists could draw on nothing more than the most hopefulguesswork。 the frustrating position then was that although they could place the various rocksand fossils in order by age； they had no idea how long any of those ages were。 whenbuckland speculated on the antiquity of an ichthyosaurus skeleton he could do no better thansuggest that it had lived somewhere between 鈥渢en thousand； or more than ten thousand timesten thousand鈥潯ears earlier。
although there was no reliable way of dating periods； there was no shortage of peoplewilling to try。 the most well known early attempt was in 1650 when archbishop jamesussher of the church of ireland made a careful study of the bible and other historical sourcesand concluded； in a hefty tome called annals of the old testament ； that the earth had been1there will be no testing here； but if you are ever required to memorize them you might wish to remember johnwilfords helpful advice to think of the eras （precambrian； paleozoic； mesozoic； an（ cenozoic） as seasons in ayear and the periods （permian； triassic jurassic； etc。） as the months。
created at midday on october 23； 4004b。c。 ； an assertion that has amused historians andtextbook writers ever since。
2there is a persistent myth； incidentally鈥攁nd one propounded in many serious books鈥攖hatussher鈥檚 views dominated scientific beliefs well into the nineteenth century； and that it waslyell who put everyone straight。 stephen jay gould； in time鈥檚 arrow； cites as a typicalexample this sentence from a popular book of the 1980s： 鈥渦ntil lyell published his book；most thinking people accepted the idea that the earth was young。鈥潯n fact； no。 as martin j。 s。
rudwick puts it； 鈥渘o geologist of any nationality whose work was taken seriously by othergeologists advocated a timescale confined within the limits of a literalistic exegesis ofgenesis。鈥潯ven the reverend buckland； as pious a soul as the nineteenth century produced；noted that nowhere did the bible suggest that god made heaven and earth on the first day；but merely 鈥渋n the beginning。鈥潯hat beginning； he reasoned； may have lasted 鈥渕illions uponmillions of years。鈥潯veryone agreed that the earth was ancient。 the question was simply howancient。
one of the better early attempts at dating the planet came from the ever…reliable edmondhalley； who in 1715 suggested that if you divided the total amount of salt in the world鈥檚 seasby the amount added each year； you would get the number of years that the oceans had beenin exi