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at roderick murchison believed belonged rightly to the silurian。 thedispute raged for years and grew extremely heated。 “de la beche is a dirty dog；” murchisonwrote 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’s excellent and somber account of the issue； the great devoniancontroversy。 these begin innocuously enough with headings such as “arenas of gentlemanlydebate” and “unraveling the greywacke；” but then proceed on to “the greywacke defendedand attacked；” “reproofs and recriminations；” “the spread of ugly rumors；” “weaverrecants his heresy；” “putting a provincial in his place；” and （in case there was any doubtthat this was war） “murchison opens the rhineland campaign。” the 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 “chalk”） we are indebted to a belgian geologistwith the perky name of j。 j。 d’omalius d’halloy。
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was discarded by some but kept by others。 today onlytertiary remains as a mon designation everywhere； even though it no longer represents athird period of anything。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 （“most recent”）； pliocene（“more recent”）； miocene （“moderately recent”）； and the rather endearingly vague oligocene（“but a little recent”）。 lyell originally intended to employ “…synchronous” for his endings；giving us such crunchy designations as meiosynchronous and pleiosynchronous。 thereverend william whewell； an influential man； objected on etymological grounds andsuggested instead an “…eous” pattern； producing meioneous； pleioneous； and so on。 the “…cene” terminations 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 “old life”）；mesozoic （“middle life”）； and cenozoic （“recent life”）。 these 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’s epochs—the pleistocene； miocene； and so on—which 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 “tens of dozens。”
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。 “i have seengrown men glow incandescent with rage over this metaphorical millisecond in life’s history；”
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 “ten thousand； or more than ten thousand timesten thousand” years 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 h