The History of Science Society
The Strategy of Lyell's Principles of Geology
Author(s): Martin J. S. Rudwick
Source: Isis, Vol. 61, No. 1 (Spring, 1970), pp. 5-33
Published by: The University of Chicago Press on behalf of The History of Science Society
Stable URL: http://www.jstor.org/stable/229146
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The Templeof Serapis at Pozzuoli near Naples gave CharlesLyell a
perfect illustration of his steady-state theor of earth history. After
Roman times the site had evidently sunk below sea level, where the
columnshad been boredby marineorganisms,but it had been
re-elevatednearlyto the originallevel duringan earthquakein 1538.
(Thefrontispiece ofLyell's Principles of Geology, Vol. _, London:
Murray, 1830.)
Thte
of
rategy
Principles
of
Lyels
Geology
By Martin J. S. Rudwick*
I
CHARLES LYELL HAS SUFFERED the posthumous fate of being interpretedon
almost any terms but his own. To some historians he has been little more than a
Baptist to Darwin's Messiah, preparing the way to evolution by natural selection in
spite of his own strange reluctance to accept the good news. To others he has been
primarily a secularist prophet, proclaiming for one area of natural phenomena a new
freedom from the cramping influence of religiously motivated explanation. Yet in his
own eyes he was first and foremost a geologist, concerned above all to develop a
method that would be adequate for this historical science and to use that method in the
service of a distinctive vision of earth history. Any interpretation of Lyell which overlooks the nature of his primary interest in science or relegates it to a minor position is
surely bound to be defective.
This applies with particular force to the analysis of Lyell's greatest work, the Principles of Geology.' Only if we first seek to understand this work on its own terms, as
geology, shall we be in a position to evaluate the relation of its argument to other areas
of science and to even wider attitudes and beliefs. For example, Lyell was certainly
enough of a natural philosopher not to confine himself narrowly to geological evidence, and he was able to master many aspects of contemporary biological thinking
and even to contribute significantly to its development. It is undeniable, moreover,
that the later influence of his biological thought was of the highest historical importance. But the question that needs to be asked is whether he himself regarded his biological work as a digression from his geology or as an essential part of his geological
argument. Those who have seen Lyell primarily as a forerunner of Darwin have concentrated attention on only a few chapters in the shortest (the second) of the three
volumes of the Principles, and it is at least arguable that in isolating those chapters
from their context their meaning has also been distorted. Similarly, Lyell's emphasis
on the slow and gradual action of existing causes is always duly stressed, but often
* CambridgeUniversity.I am gratefulto members of the History of Science Seminarat Cambridge, and especiallyto Dr. R. M. Young, for
valuable comments on a draft of this article. A
condensed version is published as an introduction to the reprint edition of Charles Lyell's
attempt to explain the former changes of the
earth's surface by references to causes now in
operation(London:Murray,Vol. I, 1830;Vol. II,
1832; Vol. III, 1833).This will be cited hereafter
as PG. In this article the first edition of each
volume will be used, since it is here that Lyell's
position is influencedleast by the reservations
and modifications that later criticism obliged
him to make.
Principles of Geology (New York: Johnson Re-
print, 1970).
1 Charles Lyell, Principles of Geology, being an
5
6
MARTIN J. S. RUDWICK
with the implicitassumptionthat only such causescould be "natural"or "scientific"
and so escapefromtheologicalovertones.Lyellwas indeedconcernedto arguefor the
adequacyof existingnaturalprocessesin geologicalexplanation;but here again the
questionthatneedsto be askedis whetherhe regardedexplanationin thesetermsas an
end in itselfor merelyas a tool to be used in the establishmentof a morefundamental
geological-and perhapsalso theological-position.
It is certainlyprematureto attempta full analysisof Lyell'sintellectualdevelopment2or any broad evaluationof his place in nineteenth-century
science; this will
require,amongmanyotherthings,a far deeperand moresympatheticunderstanding
of his opponentsthan has hithertobeen presented.This articlesimply attemptsto
analyzethe structureof the firsteditionof thePrinciplesin orderto discoverwhetherit
can providea more comprehensivekey to the nature of Lyell'sview of geological
science.It maythenbe possibleboth to evaluatethe criticismsmadeagainstit3andto
trace the significanceof the modificationsthat Lyell introducedin successivelater
editions.This task presupposes,of course,that Lyell'sworkhas a definablestructure,
and that the orderof topicsdiscussedis not arbitraryor even merelya matterof concommented,Lyellusesthe "languageof
venientexposition.But as his contemporaries
an advocate"4throughoutthe Principles, and this reflectsnot merelyhis legal training but also the fundamentallypersuasiveintentionof the work.Indeed,it is the contentionof this articlethat the structureof the Principles is so carefullydesigned,both
in outlineand in detail,in the serviceof a sustainedpersuasiveargumentthat it fully
deservesthe term"strategy."
2 For briefdiscussionssee LeonardG. Wilson,
"The IntellectualBackgroundin CharlesLyell's
Principles of Geology, 1830-1833," in C. J.
Schneer,ed., Towarda Historyof Geology(Cambridge, Mass.: M.I.T. Press, 1969),pp. 426-443;
"The Originsof CharlesLyell's Uniformitarianism," Geological Society of America, Special
Paper,1967,89:35-62; and "TheDevelopmentof
the Concept of Uniformitarianismin the Mind
of Charles Lyell," Actes de Xe Congres internationaled'Histoire des Sciences, Ithaca (Paris:
Hermann,1964),Vol. II, pp. 993-996.
Geology: A Letter from W. D. Conybeare to
CharlesLyell, 1841,"Proceedingsof theAmerican
PhilosophicalSociety, 1967, 101:272-287. [W. H.
Fitton], "Elementsof Geology, by CharlesLyell,
Esq., F.R.S., ...," EdinburghReview, 1839, 69:
406-466. Adam Sedgwick, "Address to the
Geological Society, Delivered on the Evening of
the Anniversary,Feb. 18, 1831,"Proceedingsof
the GeologicalSocietyofLondon,1831,1:281-316.
[GeorgePoulett Scrope],"Principlesof Geology
3 A few of the more importantearly criticisms
by Englishscientistsare as follows: W. D. Conybeare, "On Mr. Lyell's 'Principlesof Geology,"'
PhilosophicalMagazine and Annals, 1830, N.S.
8:215-219; continued as "An Examination of
those Phaenomenaof Geology, which seem to
bear most directlyon theoreticalSpeculations,"
Phil. Mag., 1830-1831, 8:359-362, 401-406; 9:
19-23, 111-117, 188-197, 258-270; also his
"Report on the Progress, Actual State, and
Ulterior Prospects of Geological Science,"
Report of the British Associationfor the Advancementof Science, Ist & 2nd Meetings 18311832, 1833, 365-414. Conybearelaterrestatedhis
argumentsmore informallyin a letter to Lyell:
M. J. S. Rudwick,"A Critiqueof Uniformitarian
well], "Principles of Geology ... by Charles
Lyell ... Vol. I.. .," BritishCritic,1831,9:180206; "Principles of Geology ... Vol. II ...,"
... Vol. I ...
.,"
Quarterly Review, 1830, 43:41 1-
469; "Principlesof Geology ... 3d Edition.. .,"
Quart. Rev., 1835, 53:406-448. [William Whe-
Quart.Rev., 1832,47:103-132; see also Whewell,
The History of the InductiveSciences (London,
1837),Bk. XVIII, Ch. 8.
4 Sedgwick, "Address to the Geological
Society ...
1831," loc. cit. Fitton, though much
morefavorablyinclinedtowardLyell'sargument,
made the same commenton the early editions of
the Principles:"The book at first appearedto us
to be the productionof an advocate, deeply impressed with the dignity and truth of his cause.
The tone was rather that of eloquent pleading
than of strictphilosophicalenquiry. . ." (Fitton,
"Elementsof Geology,"p. 410).
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
7
This thesis can be supported in the first instance by considering Lyell's own description of the Principles at an early but crucial stage in the construction of the work.
Immediately after his expedition to Sicily in the winter of 1828-1829 (which, he said,
had produced geological results exceeding his warmest expectations) he described his
forthcoming work to Roderick Murchison in the following terms:
My work is in part written,and all planned.It will not pretendto give even an abstract
of all thatis knownin geology,but it will endeavourto establishtheprincipleof reasoning
in the science; and all my geology will come in as illustrationof my views of those
principles, and as evidence strengtheningthe system necessarilyarising out of the
admissionof such principles,which, as you know, are neithermore nor less than that
no causeswhateverhave fromthe earliesttime to whichwe can look back, to the present,
ever acted, but those now acting; and that they never acted with differentdegreesof
energyfromthatwhichtheynow exert.5
Within this brief passage are several points of the highest importance for any understanding of the Principles.
First, the word "principles" was not chosen idly for the title of the work: it carries
its full meaning and is not (as in many modern works) a synonym of "textbook." The
book is not a summary, still less a compilation, of contemporary geological knowledge.
Second, the detailed geology is to be selected for its value in illustrating the use,of a
fundamental "principle of reasoning" in geology. It is significant that although Lyell
first uses the word "principle" in the singular, he immediately goes on to define two
logically distinct principles: the geological "causes" or processes observable in the
present day are, he asserts, accurately representative of those that have acted in the
past, not only in kind but also in degree. Throughout his work Lyell consistently conflates these two assertions, although to his contemporaries it was perfectly clear that
the first could be true without entailing the second: human history might record
small-scale examples of most kinds of processes without eliminating the possibility
that in the far longer time span of geological history some of these processes might
have acted occasionally with paroxysmal or catastrophic intensity.
Third, the two principles are to have a regulative function in the work. It is clear
from Lyell's phraseology that they are going to determine what is and what is not
admissible in the construction of his geological hypotheses. When the work was
published, however, its subtitle only acknowledged a more modest function for the
principles: the work would merely attempt to explain the phenomena of the past "by
reference to causes now in operation." This indicates that Lyell was aware that his
disagreementwith other geologists was not over the desirability of using the present as
a key to the past, but over its adequacy.6 An explicit methodology of actualism had
5 K. M. Lyell, ed., Life, Letters and Journals of
Sir Charles Lyell, Bart. (London: Murray, 1881),
Divine Miracle (Leiden:Brill, 1959; 2nd impression under the title The Principle of Uni-
Vol. I, p. 234. This will hereafterbe abbreviated formity, 1963).Theword"actualism"will be used
in this article for the methodof interpretingthe
past in terms of present processes, while the
6 See W. F. Cannon, "The Uniformitarian- word "uniformitarianism"
will be reservedfor the
CatastrophistDebate," Isis, 1960,51:38-55. For theory that past processes have never exceeded
an analysis of the concept of uniformity in those of the present in intensity and that the
geology, see R. Hooykaas, Natural Law and earthas a whole has had a steady-statehistory.
toLLJ.
8
MARTIN J. S. RUDWICK
become commonplace in geology many years before; what was disputed was the
extent to which present causes were an adequate key to the interpretation of all the
varied phenomena of the past. Lyell's belief in his principles, and his conflation of the
two, indicate his commitment to an extreme form of actualism, but this position does
not differ qualitativelyfrom that of his scientific opponents.
Fourth, Lyell however not only conflates uniformity of kind and uniformity of
degree, but also asserts that such uniformity "necessarily" entails a definite "system."
The detailed geology in the Principles is to be used not merely to illustrate and justify
an extreme form of actualistic method, but also to substantiate a major theoretical
framework. The word "system" should be given the full weight of its contemporary
meaning in geology; Lyell intends to provide an explanatory framework of the broadest possible scope. The nature and content of his system is not explained in this letter,
but the assertion that it necessarily follows from his two principles is sufficient to
suggest its character. If processes observable at present are representative,in degree as
well as in kind, of all those that have acted in the past, there cannot have been any
overall directional trend in the history of the earth, which must therefore be in a
"steady-state" condition.7 The strategy of the Principles confirms this early indication
that the most fundamental object of the work was to establish, by means of the two
principles, a nondirectional steady-state theory of the earth, in opposition to theories
involving directional changes either in the earth itself or in the forms of life on earth.
Lyell's contemporaries rightly saw the Principles primarily as the work of a system
builder, for they recognized that his uniformitarianinterpretation of earth history
aimed at being an explanation as comprehensive as the directionalist synthesis it was
designed to supplant.8
III
The first volume (1830) opens with an introductory chapter (Ch. I) defining the
subject matter of geology, emphasizing its status as an essentially historical science,
and stressing its concern with the causation of the processes underlying earth history.
The stress on causal analysis is one of the features which sets the Principles apart from
much of the other geological work of the period, which was more purely descriptive.
By deliberately breaking with this strongly anti-theoretical tradition, however, Lyell
lays himself open to the charge of leading geology back to the old contentious days of
speculative "theories of the earth." This presents him with a serious dilemma, for he
must somehow disclaim any affinity with most of the earlier system builders while
leaving himself free to acknowledge the influence of one in particular, namely James
Huftton. Hutton's system, epitomized by its conclusion "we find no vestige of a be7There is an obvious logical flaw in this Time (London:Hutchinson, 1965).
reasoning,since it would be possibleto construct
8
a system combining extreme actualism with an
See the coniments of, e.g., Sedgwick, Conyoveralldirectionaltrend, but in the presentcon- beare, and Whewell (op. cit., n. 3). I have outtext the important point is that Lyell believed lined a comparison of the directionalist and unithat a steady-statesystem was "necessarily"en- formitarian systems in "Uniformity and Protailed by his principles. My use of the term gression: Reflections on the Structure of Geo"'steady-state"
is of course borrowedfrom mod- logical Theory in the Age of Lyell," to be pubern cosmology; the analogy with the Lyellian lished in the proceedings of the Symposium on
debate has been noted by, among others, S. the History of Science and Technology, held at
Toulmin and J. Goodfield, The Discovery of the University of Oklahoma, April 1969.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
9
ginning,-no prospect of an end," was almost the only one of its period to advocate a
steady-state rather than a directional model of earth history;9 yet to many of Lyell's
contemporaries Hutton seemed as deplorably speculative as any other system builder.
Lyell therefore tries to forestall the criticism that his own system too is merely speculative, by emphasizing that geology must not be confused with "Cosmogony." In other
words, geology must exclude speculations about the origin of the earth and confine
itself to an analysis of the subsequent changes that the earth has undergone; Hutton,
Lyell maintains, was the first to realize this, and his view "will ultimately prevail."
Thus, right at the outset Lyell states his Huttonian viewpoint openly, and it was as a
revival of Huttonian geology that his work was correctly interpreted by many of his
critics.10Lyell was able to restrict the subject matter of geology in this way only because he was arguing, like Hutton, for a steady-state and not a directional model of
earth history, and because he therefore shared Hutton's view that no evidence of the
"primitive"state of the earth could have survived.
These remarks of Lyell's lead at once into the first major section of the work, a
review of the history of geology from antiquity to the early years of the nineteenth
century (Chs. II-IV). The aim of this section is not to provide historical background
but to argue a case as forcefully and persuasively as possible. This so-called history
of geology is a highly polemical tract for the times; to treat it as straight history
would be to ignore the contemporary situation to which the book was addressed. Indeed, Lyell admitted privately that the historical form was merely a discreet disguise
and that he would have liked to extend the account to include living authors in order to
make the attack more pointed still.I' Like many would-be reformers, Lyell tries to rewrite history to prove his own antecedents and to demonstrate that his own approach
is not an innovation but a return to the true path that geology should follow. Conversely, he argues that those whose present position he is attacking are also inheritors
of an earlier tradition, but one that has had a retardinginfluence on the progress of the
science.
The tradition he is attacking has, he implies, several related characteristics.It tends
to use Scriptureto support or contribute evidence for geological theories; it tries to use
the phenomena of geology to infer the origin of the earth; it views the history of the
earth as a series of highly dramatic or extraordinary events; and it is reluctant to
accept an indefinitely long time scale. By contrast, the tradition that Lyell sets before
9 James Hutton, Theory of the Earth with
Proofs and Illustrations, 2 vols. (Edinburgh,
and the Concept of a Dynamic Earth," in
1795), Vol. I, p. 200. Hutton's thought seems to
have reached Lyell almost entirely through the
significantlymodified exposition in John Play-
122-141.
'0 PG, Vol. I, p. 4. It was not only Lyell's opponents, such as Conybeare, Sedgwick, and
Whewell, who interpretedthe Principlesin this
way: Fitton used half his essay review of Lyell's
work to urge the fuller recognition of Hutton's
priority as founder of the "true theory of the
Earth"(Fitton, "Elementsof Geology,"p. 466).
11LLJ, Vol. I, p. 271. The polemicalcharacter
of Lyell's"history"has beenemphasizedrecently
by Walter F. Cannon, "Charles Lyell Is PermittedTo Speak for Himself," in TheCambridge
fair's Illustrations of the Huttonian Theory
(Edinburgh,1802): cf. LLJ, Vol. II, pp. 47-48.
The cyclic natureof Hutton'stheorywas pointed
out by S. I. Tomkeieff,"James Hutton and the
Philosophy of Geology," Transactions of the
Edinburgh Geological Society, 1949, 14:253-276;
reprinted in Proceedings of the Royal Society of
Edinburgh, 1950, Sec. B, 63:387-400. R. H.
Schneer, ed., Toward a History of Geology, pp.
Dott, Jr., has emphasizedmore recentlythe predominanceof the conceptof steady-statedynamic Network in Victorian History (London: Routequilibriumin Hutton's work: "James Hutton ledge andKeganPaul, in press).
10
MARTIN J. S. RUDWICK
his readersas worthyof emulation12makesa sharpdisjunctionbetweengeologicalresearchand the interpretationof Scripture;it eschewsall cosmogonicambitionsof
reachingbackto the originof the earth;it interpretsthe past historyof the earthas a
seriesof eventscomparableto those still occurring;and it readilyacceptsa vast time
scalefor earthhistory.
Lyell'shighly"Whiggish"interpretationof the historyof geologynaturallyentails
of thetheoriesof his predecessors.Butfromthe point
distortionandoversimplification
of viewof his polemicsit has the advantageof tarringwiththe samebrushthe popular
but scientificallyworthlessspeculationsof the "Mosaic"or "Scriptural"
geologistsof
his own time;13the far morerespectablecatastrophismof his formerteacherWilliam
Buckland,with its relativelyliberalinterpretationof Scripture,14and the still more
empiricistcatastrophismof geologistssuch as Adam Sedgwick.15The Principles had
originallybeen conceivedas popular"Conversationson Geology,"16 and in spite of
the transformationof the work into a seriousscientifictreatise,it had retainedits
originaldidacticfunctionof combattingthose who weremisleadingthe generalpublic
into believingthat a literalinterpretationof the Mosaic narrativewas still tenable.
Most othergeologistswouldhave consideredthemselveshis allies in hoping "to free
the sciencefromMoses,"whetheror not they agreedwith him in scientificopinions,17
but`in Lyell'seyes many-even among his scientificcolleagues-were on the same
slipperyslope as the Mosaic geologists.Bucklandin particularseemedto him to betray an inherentaffinitybetweencatastrophistand Mosaic geology and to illustrate
the grave dangersof slippingin any degreefrom a strict relianceon "uniformity."
Althoughthis was in fact unfairto most of those who held a directionalistviewpoint,
it was neverthelessLyell'sopinion,and
as someof themlaterprotestedemphatically,18
it explainshis farfromobjectiveviewof his predecessors.
The importanceof Lyell's "history"in the strategyof the whole work becomes
clearerin the followingchapter(Ch. V), which summarizesthe lessonsto be learned
London, 1828), who devoted much attention to
the theoriesof the "Mosaic geologist" Granville
Penn.
17LLJ, Vol. I, p. 268. E.g., Lyell had written
earlier that Andrew Ure's New System of Geology (London, 1829) "is to prove the Hebrew
cosmogony, and that we ought all to be burnt at
Smithfield" (LLJ, Vol. I, p. 238). But those
sharing Lyell's imaginary martyrdom would
have been almostthe whole scientificcommunity,
not just the very few geologistswho acceptedhis
with Religion Explained . .. (Oxford, 1820); and
in his majorscientificwork, ReliquiaeDiluvianae; concept of unifoimity. When Ujre's book apor Observationson the Organic Remains Con- peared,it receivedits most severecriticismfrom
tained in Caves, fissures, and Diluvial Gravel, Sedgwick ("An Address ... 1830," loc. cit.) with
and on OtherGeologicalPhenomenaAttestingthe all the scientific authority of his position as
Action of an UniversalDeluge (London:Murray, Woodwardian Professor of Geology at Cambridgeand Presidentof the GeologicalSociety of
1823).
London, although in geological matters Sedg15 E.g., in "An Address deliveredat the AnniversaryMeeting of the Geological Society of wick as a directionalistfound himselfopposed to
London, on the 19th February, 1830," Proc. Lyell'suniformitarianism.
18 For a typical example of such a protest,
Geol.Soc. Lond.,1830,1:187-212.
16LLJ,Vol. I, p. 177. Ironicallythis attractive expressedwith unusual freshnessbecause it was
title, modelled on Mrs. Marcet's popular Con- not intended for publication, see Conybeare's
versationson Chemistry,was appropriatedby an letterto Lyell (see Rudwick,"A Critiqueof Unianonymous writer (Conversationson Geology, formitarianGeology").
12 Especially Italian writers, whose views he
culled mainly from the historicalintroductionto
Giovanni Battista Brocchi, Conchiologiafossile
subappenninacon osservationigeologiche sugli
Apenninie sul suolo adiacente, 2 tomi (Milan,
1814).
13 Cf. Milton Millhauser, "The Scriptural
Geologists,"Osiris, 1954,11:65-86.
-14Especially in his inaugural lecture, Vindiciae Geologicae;or the Connexionof Geology
THE STRATEGYOF LYELL'SPRINCIPLES OF GEOLOGY
11
from it. Here he maintainsthat the slowlyincreasingrelianceon ordinarysecondary
causesin geologyis similarto the growthof the scientificattitudeas a whole; to be
But he arguesthat the greatestsingle
Lyellianin geologyis, in effect,to be scientific.19
factor retardingthe progressof geology has been an inadequateconceptionof the
time scale of earthhistory.Using a favoritetacticaldevice of an analogyto human
history,he showshow this inevitablytelescopesevents,givingthe illusionof swiftand
extraordinary
happeningsand astonishingcoincidences.It was this, he suggests,that
made geologistsunwillingto believein uniformity,and led them to expectdiscontinuity betweenpast and presentunlessthe evidenceto the contrarywas overwhelming.
But the vasttimescalewhichthe Huttoniansystemdemandedis now beingvindicated,
he maintains,by the discoveryof moreand morestratawhichneedto be intercalated
into the successionpreviouslyknown.Citinghis own observationsin Sicily,he argues
that as a resultof this expansionof the time scaleit is no longernecessaryto postulate
causesexceedingin intensitythose now in operationor-showing a significantelasticity in his conceptionof uniformity-thosethatmightconceivablyoccurin the future.
This qualificationaboutthe futureemphasizesagainthatLyellis not concernedmerely
to advocateactualismas a method,but to arguefor a steady-statesystemin which
geologicalprocessesarenot, as the directionalistssuggested,tendingtowarda stateof
quiescence.
In placingsuch emphasison the sense of the geologicaltime scale, Lyell shows a
penetratingawarenessof the natureof his task of persuasion.For althoughhis scientific colleagues(unlikemanyof the Mosaicpseudo-geologists)readilyaccepteda vast
time scaleon the intellectuallevel, Lyell seems to have recognizedthat it was their
scientificimagination
that neededtransforming.Muchof the detailedargumentof the
Principlesis thereforedesignedto drawout the full implicationsof a beliefwhichthey
alreadyprofessed.
Althougha vast time scaleis now more generallyconceded,Lyellmaintains,other
habitsof mindstillcontinueto retardgeology.Of thesethe mostimportantis a failure
to recognizethe distortingeffectof our viewpointas subaerialterrestrialbeings.This
causes us to underestimatethe magnitudeof submarineand subterraneangeological
processes.An intelligentaquaticbeing or a gnomeconfinedto subterraneanregions
would form very different,but equallydistorted,views on geology. Geologistsmust
thereforeat leastmake"aneffortboth of the reasonandthe imagination"to allowfor
the effectsof this limitation.20 As withregardto time,heretoo it is a conversionof the
imaginationthat is neededif geologistsareto gain a trueperspectiveon the problems
of earth history.But this argumenthas a furthersignificancefor Lyell. He suggests
that it is our naturallybiasedviewpointwhichhas led to an overemphasison destructive or "wasting"aspects of geological processesand to a correspondingunderemphasison the renovatingor formativeaspects.By deliberatelyseekingto correctthis
naturalbias, Lyellcan arguethat a balanceexistsbetweenthe destructiveand formativeagencies,andhe cantherebymaintainthattheearthas a wholeremainsin a steadystatecondition.
After some furtherscathingremarksabout those who consider themselves"at
libertyto disregardall modernanalogy,"he leaves what he hopefullycalls the "ex19Cf. Cannon, "CharlesLyell Is PermittedTo
Speakfor Himself."
20PG, Vol. I, p. 81.
12
MARTIN J. S. RUDWICK
ploded errors" of the catastrophists and opens his attack on the "weightier objections" of the directionalists.2' This attack (Chs. VI-IX) would have been placed more
logically in a later part of the work, where the actual evidence of the rocks could have
been tested against both a uniformitarian and a directionalist view of earth history.22
But Lyell seems to have felt that the scientific authority and popularity of the directionalist view were so great that confidence in it had to be undermined at the outset: only
if the reader is first prepared to believe that directionalism involves highly uncertain
inferences from the available evidence will he be able to give a fair hearing to the
alternative of uniformitarianism.
Two areas of evidence were widely held to favor a directionalist model of earth
history, and Lyell criticized each in turn. The first was the evidence of directional
climatic change in the past history of the earth. In particular, the fossils of the Secondary strata of Europe found their closest living analogues in the animals and plants
now living in tropical regions. This seemed good evidence in support of Leibniz's and
Buffon's earlier theory of gradual refrigeration, which had recently been revived in
popularity under the scientific authority of Fourier's work on heat flow and Louis
Cordier's calculations from the geothermal gradient.23 If the earth had had a hot or
incandescent origin and had been losing heat continuously by radiation, it was to be
expected that the climate in any given latitude would show evidence of directional
change.
Lyell admitted that his uniformitarian preconceptions had led him initially to
doubt the validity of this evidence, but his own experience had forced him to accept it.
To John Fleming-perhaps the only naturalist of the time who was more ardently
uniformitarian than Lyell himself-he wrote: "As a staunch advocate of absolute uniformity in the order of Nature, I have tried in all my travels to persuade myself that the
evidence was inconclusive, but in vain."24Indeed it was in his own travels that he had
found what he believed to be an experimentum crucis proving the reality of climatic
change (Ch. VI). It was always possible to argue, as Fleming did, that the tropical
appearance of the more ancient faunas and floras was illusory: they were merely
analogous to present tropical organisms, and since they did not belong to living species,
it was impossible to prove that their ecological preferences had really been tropical.
But the geologically young strata which Lyell had explored in Sicily contained mollusks of extant species which were consistently larger than their living representatives,
and he felt that this was conclusive evidence that the climate had been somewhat
warmer in the Mediterranean in geologically recent times. By analogy, therefore, the
evidence of older periods should also be accepted as valid.
But this did not lead him to accept the full directionalist interpretation of the evidence. A gradually decreasing temperature in Europe during the Tertiary period had
21Ibid., p. 91. Catastrophistsand directionalists were of course overlappingcategories, but
Lyell was rightto distinguishtheirpositions.
22 This point was made at the time by Lyell's
friend George Poulett Scrope (see n. 3). Scrope
was an ardent actualist but no uniformitarian;
see his Considerations on Volcanos, . .. leading to
the Establishment of a New Theory of the Earth
turesdu globeterrestreet desespacesplanetaires,"
Mdmoires de l'Acadeimie Royale des Sciences de
l'Institut de France, 1827, 7:569-604. L. Cordier,
"Essai sur la temperaturede l'interieur de la
terre," Me'm.Acad. Roy. Sci., 1827, 7:473-555.
24 LLJ, Vol. I, p, 260. Cf. John Fleming, "On
the value of the evidencefrom the animal kingdom, tending to prove that the Arctic regions
formerly enjoyed a milder climate than at pre-
(London, 1825).
sent," Edinburgh New Philosophical Journal,
23 J. B. J. Fourier, "M6moiresur les tempera1829,6:277-288.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOG Y
13
somehow to be "reconciled with the existing order of nature,"25or in other words with
the "absolute uniformity" of a steady-state interpretation of earth history. This reconciliation is effected by means of what, in a letter to Gideon Mantell, he called "my
grand new theory of climate."26This is an hypothesis of continual fluctuation around a
mean, which can account for any degree of local climatic change "easily and naturally,"
without recourse to any sudden or directional changes on a global scale (Ch. VII).
Drawing on published accounts of the physical geography of many different regions,
especially on recent explorations of the polar regions, and applying Humboldt's concept of isothermal lines,27he argues that local climate is greatly influenced by the distribution of land and sea, the direction of winds and currents, and other similar factors: "latitude is one only of many powerful causes, which determine the climate of
particular regions of the globe."28Hence, if there has been a round of ceaseless change
in the distribution of land and sea (as he would argue in the rest of the work), "there
must be a never ending fluctuation in the mean temperature of every zone."29 (It is
ironic that this argument leads Lyell into an inversion of his actualistic principle when
he warns the geologist "not hastily to assume that the temperature of the earth in the
present era is a type of that which most usually obtains" ;30 a similar refusal to use the
present as an inflexible criterion for the interpretation of the past was a leading feature
of the thought of many of Lyell's opponents.31)
This climatic hypothesis is next tested against the actual evidence of past climatic
change (Ch. VIII). Lyell takes the tropical aspect of the Carboniferous period as an
example, and argues, like Adolphe Brongniart,32that the strata and their fossils indicate a predominantly marine environment with scattered islands. But unlike Brongniart he uses this reconstruction to show that on his theory a climate warmer than that
now found in Europe would follow naturally, and there is no reason to attribute it to a
greater degree of "central heat." Having thus eliminated the directional character of
climatic change, Lyell then attacks the allegedly sudden (that is, catastrophist) nature
of the successive changes. As in other phenomena, he argues, the appearance of sudden
change merely reflects the incompleteness of our evidence, and if all the successive
stages were preserved, the change would be seen to have been gradual. Lyell concludes that the reality of climatic change does not support the theory of a directional
cooling of the globe, but instead supports his own theory of continual fluctuation
around a mean. He suggests that while further research should be directed to this
theory, it is "more consistent with philosophical caution" to adopt a steady-state
25PG, Vol. I, P. 104.
...
without help from a comet, or any
astronomicalchange,or any cooling down of the
originalred-hot nucleus, or any change of inclination of axis or central heat, or volcanic hot
vapours and waters and other nostrums,but all
easily and naturally,I will give you a receiptfor
growing tree-fernsat the pole, or if it suits me,
pines at the equator; walruses under the line,
and crocodilesin the arcticcircle"(LLJ, Vol. I, p.
262).
27 Alexandre de Humboldt, "Des lignes isothermeset de la distributionde la chaleursur la
28PG,Vol. I, p. 111;cf. LLJ,Vol.1, p. 270.
29 PG, Vol. I, p. 115.
30 Ibid.,p. 105.
31 E. g., Sedgwick("Addressto the Geological
Society ... 1831"): "Whatis this but to limit the
richesof the kingdomsof natureby the povertyof
our own knowledge?" See also Whewell's His-
globe," Memoires de Physique et de Chzimiede la
Soctifed'Arcueil, 1817, 3:462-602.
Naturelles, 1828, 15:225-258 (trans. in Edinb.
26"
tory of the Inductive Sciences.
32
Adolphe Brongniart,"Considerationsgenerales sur la naturede la vegetationqui couvrait
la surface de la terre aux diverses epoques de
formations de son ecorce," Annales des Sciences
New Phil. J., 1829, 6:349-371).
14
MARTIN J. S. RUDWICK
explanation as a working hypothesis, ratherthan a theory of directional change.33
Having explained away the climatic evidence for directionalism, Lyell turns to a
brief attack on the other main directionalist argument, that of "progress" in organic
life (Ch. IX). His extended critique of the climatic, that is inorganic, aspect of a developmental model of earth history, before discussing the organic aspect, should
serve to emphasize that directionalism was not a purely biological theory: it was a
coherent synthesis of geology and biology in which "progressive" biological changes
(that is, the appearance of successively "higher" forms of life) were regarded as having
occurred-by whatever means-in step with similarly directional changes in the inorganic environment.34Once again he confuses the establishment of a uniformitarian
interpretation with the actualistic belief that past events were "governed by the laws
now in operation."35Since no well-defined faunal succession was known in 1830 for
periods before the Carboniferous, Lyell has no great difficultyin arguing here that the
apparent progress in the rank of organic life is an illusion, due simply to the differentially selective preservation of terrestrial and aquatic animals. Thus he argues for
example that mammalian remains are absent in the earlier strata, not because mammals had not then come into existence, but because most of them are terrestrial and
therefore unlikely to be preserved in sediments that are predominantly marine in
origin.
On the other hand, Lyell does not apply the same reasoning to man himself; here he
accepts at its face value the positive evidence that man appeared on the earth in geologically recent times. But he argues that man's recent appearance is no evidence for
"a progressive system."36Lyell is only able to maintain this inconsistent position because he makes a sharp separation between man's physical and mental characteristics: man's evident superiority is attributed only to his power of reason, which is
precisely the feature that distinguishes him clearly from other animals. Hence on the
physical level his appearance denotes no progress in the organic world, while on the
"moral" level his appearance is a phenomenon of an entirely different kind.3 All the
same, Lyell has to admit that man's rational powers now enable him to exercise an
important influence on his physical environment. This might have been held to invalidate the actualistic use of the present as a reliable key to the more ancient, prehuman periods of earth history. To forestall this criticism, Lyell is therefore obliged to
argue that the physical effects which man has produced on the earth's surface are limited
and localized in character and strictly analogous to those which any animal species
with new habits might have produced in the past.
Iv
This concludes Lyell's preliminary lines of attack-on Mosaic geology and on the
catastrophism and directionalism of his scientific opponents-and it clears the ground
33 PG, Vol. I, p. 142. This assumptionof the
superior scientific status of uniformitarianism,
which is repeated frequently in the Principles,
was an aspect of Lyell's work that his opponents
(e.g., Conybeare and Whewell), in their equal
concern to be "scientific," found especially
galling. But it was a natural consequence of
Lyell's belief that his system followed necessarilyfrom what he regardedas the fundamental
"principleof reasoning"in geology.
34 For an influentialand highly respectedexposition of the directionalistsynthesis,produced
probably in response to Lyell's Principles, see
H. T. De La Beche, Researches in Theoretical
Geology(London,1834).
35PG, Vol. I, p. 144.
36
Ibid.,p. 155.
37 Ibid.,pp. 156, 163.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
15
for the presentation of his own system. The rest of the first volume and the whole of
the second are devoted to a description and analysis of geological processes now in
operation. This is designed primarily to demonstrate that these processes, operatingat
their present intensity, are completely adequate to explain all the phenomena of the
past. Three categories of processes are considered in turn: the inorganic, the organic,
and those involving an interaction between the two.
Inorganic processes are divided for convenience into the aqueous and the igneous,
following the arrangementof Karl von Hoff's massivecompilation of moderngeological
changes, on which Lyell draws heavily.38 The division also reflects the general recognition of the importance of both aqueous and igneous processes, a recognition which had
grown out of the compromise between the neptunist and vulcanist positions of the turn
of the century. Unlike Hutton, however, Lyell emphasizes that both aqueous and
igneous processes "are instruments of decay as well as of reproduction";39 or, in other
words, each contributes to both sides of the balance of forces that maintains the earth
in a steady-state condition. This belief is reflected in Lyell's classification of aqueous
processes. He considers first the action of running water, but divides this into two
parts: the action of running water in erosion (Chs. X-XII) and in deposition (Chs.
XIII-XIV). His consideration of marine currents and tides is similarly divided into a
section on their power of erosion (Chs. XV-XVI) followed by one on their power of
deposition (Ch. XVII).
These chapters need not be analyzed in detail. Like the rest of the Principles they
show impressive power in the marshalling of evidence from many sources, including
prominently Lyell's own observations in France and Italy. They are also interspersed
with many barbed comments on the illogicality of "some theorists" in assuming that it
is necessary to postulate past processes more drastic than those that are still in operation. Throughout the argument the emphasis is on the magnitudeof the effects which
these present processes can achieve, even at their present level of intensity and even
within the geologically short period of recorded human history. The implication is
clear: given the immensity of the geological time scale and the fragmentary nature of
our evidence of past periods, these same processes at their present intensity are quite
adequate to explain everything that geology describes. This emphasis on the magnitude of present processes shows that Lyell has no special commitment to the slowness
or gradualness of geological change (that is, to gradualism)for its own sake. On the
contrary, the more catastrophist he can be-within the strict limits allowed by his
version of actualistic method-the more easily he can persuade his readers to accept a
steady-state system in which the past has been no more catastrophic-but also no less
-than the present.
Lyell's survey of igneous processes follows similar lines. It too is divided into two
main parts, dealing with volcanic and seismic phenomena. As in previous sections he is
concerned above all to emphasize the magnitude of these effects, quite explicitly in
order to undermine the credibility of the directionalist belief that they are now far
less intense than they were in the geological past. On his usual policy of "proceeding
from the known to the unknown" he gives special prominence in the section on
38
K. E. A. von Hoff, Geschichteder durch
Cberlieferung nachgewiesenen natiirlichen Verdnderungen der Erdoberflche (Gotha, Vol. I,
1822; Vol. II, 1824). (The third volume was pub-
lished in 1834, after the Principles.)Lyell's estimate of his debt to von Hoff (LLJ, Vol. 1, pp.
268-269)is somewhatungenerous.
39PG, Vol. I, p. 167.
16
MARTIN J. S. RUDWICK
vulcanism (Chs. XVIII-XXII) to the exceptionally well recorded volcanic history of
Vesuvius and Etna, both of which he had studied at first hand in 1828. If there were no
human records to date the various eruptions, Lyell argues, it would be easy to conclude that they all occurred during a single disastrously catastrophic episode. Yet in
fact these very regions had been some of the most attractive habitable areas in the
Mediterraneanworld throughout recorded history, in spite of sporadic eruptions. This
demonstrates then, even within this geologically short span of time, the false conclusions about the past which inevitably result from telescoping events. Lyell also
shows how the most recent eruptions have been no differentin kind or in scale from the
most ancient; no dividing line can be drawn there between present and past. This point
is stressed particularly in his description of the volcanoes of the Canary Islands, in
order to refute the catastrophism of Leopold von Buch's influential "elevation crater"
theory,40and he argues that here too there is no evidence of any former process different in kind or even in degree from those that have been observed in operation.
The description of earthquakes and their effects (Chs. XXIII-XXVI) likewise gives
greatest prominence to the most authentically documented cases, such as the great
Calabrian earthquake of 1783. Lyell is chiefly concerned here to show the magnitude
of the permanent physical effects of earthquakes, especially in altering the level of
large tracts of land. But these physical effects of earthquakes (as opposed to their
destructive effects on human life) have been recorded most fully in the more recent
periods of history; and Lyell therefore arranges his catalogue of earthquakes in reverse chronological order, backwards from the most recent. In particular, he gives a
detailed analysis of the controversial phenomena of the so-called Temple of Serapis at
Pozzuoli near Naples. He argues that recent archeological work demonstrates that the
land at this point has undoubtedly suffered both depression and later elevation since
classical times. It is no accident that Lyell chose a picture of the the Temple of Serapis
to be the frontispiece for the first volume, for it epitomizes perfectly his argument that
ceaseless nondirectionalfluctuations of physical geography have been going on even in
historic times, caused not only by superficial aqueous processes but also by deepseated igneous processes.
Yet it is significant that when Lyell is faced with an example of modern elevation
that has not been accompanied by earthquakes, he refuses to accept its reality at all.
He ridicules von Buch's "extraordinary notion" that the land around the Baltic is
"slowly and insensibly rising," although there were exceptionally careful historic
records available to support it. He is unable to accept the fact of the elevation, despite
its impeccable actualism and extreme gradualism, because it cannot be reconciled with
his own (more catastrophic!) theory of elevation by earthquakes.41
40
Leopold von Buch, "Ueber die Zusammen- tain Parts of Sweden," Philosophical Transacsetzung der basaltischenInseln und iuberErhe- tions of the Royal Society of London, 1835, 1-38.
Once convinced that elevation could occur
bungs-Cratere," Abhandlungen der physikalischen
Klasse der Kon iglich Akademie der Wissen without earthquakes,he turned this example to
good advantage as further evidence for the
schaften, Berlin, 1820, 1818-1819:51-68. See also
his great monograph Physikalische Beschreibung gradual nature of mountain elevation. (In
modern geology the rise is attributed to slow
der Canarischen Inseln (Berlin, 1825).
41PG, Vol. I, pp. 227-232. Lyell changed his isostaticrecoveryfrom the weight of the Pleistomind on this point while visiting the area in cene ice sheet over Scandinavia.)For the history
1834(LLJ, Vol. I, p. 436); see his paper "On the of the problem,see E. Wegmann,"evolution des
Proofs of a GradualRising of the Land in Cer- idees sur le de placement des lignes de rivage.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
17
Lyell includes these tectonic phenomena of elevation and depression with the volcanic under the general heading of igneous processes, because he follows the Huttonian
view that there is a close causal relation between them: earthquakes and volcanic
eruptions are essentially alternative manifestations of the same processes of magmatic
intrusion and expansion occurring at great depths. This, he suggests, is supported by
the close spatial connection between volcanic and seismic areas and accounts for the
fact that earthquakes,like volcanoes, commonly affect the same region again and again.
Hence the time required for successive lava flows to build up a large volcanic cone
could also be time enough for successive earthquakes to convert an area of sea into a
mountain range.
It is at this point that Lyell's emphasis on the connection betweeri earthquakes and
the elevation or depression of land emerges overtly as an essential part of his strategy in
advocating a uniformitarian system. If he can persuade the reader that even the earthquakes of historic times have effected permanent changes in the level of the land, he can
argue that similar earthquakes throughout geological time are sufficientto explain the
elevation of even the greatest mountain ranges, thereby eliminating the need to postulate more intense or sudden earth movements in the past. But more than that, he can
avoid the cyclic overtones of Hutton's system, whereby the slow destruction of one
continent by erosion would be followed by the elevation of another new continent from
the floor of the ocean. He can replace this cyclic mechanism with one that is even
more strictly steady-state in character: "The renovating as well as the destroying
causes are unceasingly at work, the repair of the land being as constant as its decay."42
There is a perfect balance at all times between the constructive and the destructive
geological agencies.
But Lyell feels there is a possible flaw in this system of balancing forces. He argues
that if seismic movements of elevation and depression were exactly matched, the net
effect of all igneous processes would be unbalanced, because volcanic processes tend
only to increase the inequalities, building up volcanic cones and lava flows on the surface. In order to maintain the stability and balance of the system he is thereforeobliged
to argue, in an exceptionally involved piece of reasoning, that the total amount of
seismic subsidence must exceed the total amount of elevation. It is on this highly
speculative note that he concludes his interpretation of inorganic geological processes,
observing, in a passage that recalls the more explicit providentialism of Hutton, that
the apparently destructive agency of earthquakes is necessary for the maintenance of
a balance between land and sea and hence for "the subserviency of our planet to the
support of terrestrialas well as aquatic species." Above all other processes it is "essential to the stability of the system."43
The argument of the whole volume is summarized by that concluding phrase. Lyell
has now interpretedthe whole range of inorganic geological processes in such a way as
to demonstrate that the physical features of the earth are in a state of perpetual flux.
But this principle of change consists of endless fluctuation around a stable mean, not
Origines en Fennoscandie," Mejmoires de la
Societe Vaudoise des Sciences Naturelles, 1967,
14: 129-190; and "Changing Ideas about Moving
Shorelines," in Sclneer, ed., Toward a History of
Geology, pp. 386-414.
42
PG, Vol. 1, p. 473. Hutton had in fact guarded
himself against being interpretedas postulating
any crudely cyclic process (Theory of the Earth,
Vol. I, pp. 198-199), but this brief qualification
could easilybe overlookedby the reader.
43
PG, Vol. I, p. 479.
18
MARTIN J. S. RUDWICK
of overall directional alteration. Erosion is balanced by deposition, seismic subsidence by seismic elevation and vulcanism; the details of geography change continually, and with them the pattern of local climate; but the overall nature of the globe
remains constant.
V
As foreshadowed in the concluding remarks of the first volume, the second (1832)
continues the argument on the same lines but deals with organic processes. Because of
its subsequent effect on Charles Darwin, the first part of this volume, which deals with
the nature and history of organic species, is probably the most widely known section of
the Principles. Yet in Lyell's own scheme it is not a purely biological digression or
parenthesis; it is an essential part of his geological argument. Lyell had originally intended to publish the whole work in two volumes, and it was only at a late stage that
he decided to publish separately about one-half of the projected second volume, in
order to avoid the delay which the completion of the final sections would involve.44
He therefore stated clearly in the preface of this truncated second volume that its
contents would "be found absolutely essential to the understanding of the theories
hereafter to be proposed."45The argument of the second volume can only be understood fully in the light of the third and final volume.
All questions about the history of life-its progressive development or uniform
maintenance as part of a stable system-must be related ultimately to the question of
changes at the specific level. Therefore the first topic to be discussed is the objective
reality of the species as a basic unit of biological description (Chs. I-IV). It was just
this reality which had recently been placed in doubt by Geoffroy St. Hilaire's revival of
Lamarck's transmutation theory.46Lyell feels bound to discuss Lamarck's theory at
length in the Principles, maintaining that its acceptance would have even more profoundly unsettling implications for the work of geologists than for biologists. The
latter, studying organisms only at one moment of geological time, can always proceed as if the species they describe have permanent reality, but geologists cannot be
certain what they are describing if all organic forms are in a state of constant flux.
While admitting that Lamarck's theory has had the attraction of avoiding "the
repeated intervention of a First Cause" for every new species,47Lyell throws serious
doubt on its validity. Lamarck's views on the scale of geological time would have been
highly attractive to Lyell, but on the question of transmutation it was Lamarck's
opponent Georges Cuvier whom Lyell was obliged to follow. Cuvier's immense scientific authority had lent prestige to catastrophist theories in geology, but he had argued
for sudden revolutions precisely because he believed that present "causes" were inadequate to explain the phenomena of geology. Similarly he had argued against transmutation on the grounds that it was unsupported by actualistic evidence, in particular
44LLJ, Vol. I, p. 355. For this reason, references in Lyell's correspondenceto the "second"
volume need to be interpretedwith care: often
they referto the materialpublishedin Vol. III.
45 PG, Vol. II, preface.
46 Lyell had read Lamarck'sPhilosophiezoologique(Paris,1809)in 1827(LLJ,Vol. I, p. 168),
possibly as a result of reading the highly commendatory reference to it in Geoffroy's "Re-
cherchessur l'organizationdes gavials; . . . et sur
cette question, si les gavials ... descendent,par
voie non interrompuede generation,des gavials
antediluviens ... ," Meimoires du MusJum
d'Histoire Naturelle, 1825, 12 :97-155 (seep. 151).
Lamarck'sbook was reissuedin 1830, probably
in response to Geoffroy's championing his
cause.
47 PG, Vol. II, p. 18.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
19
by the critical evidence of the mummified animals found in Egypt.48 So Lyell, like
Cuvier, is bound by his methodology to conclude that if no transmutation can be seen
to have occurred during the largest available span of recorded human history, there is
no warrantfor assuming that the still longer periods of geological time would have had
any greater effect. To argue otherwise would be to invert the principle of actualism
that he had employed so effectively in his analysis of inorganic processes. Of course,
Lyell accepts the variability of species, but-like Cuvier again-he argues that there
are definite limits to the degree to which individuals can vary from their parent type,
whether under human domestication, hybridization, or ecological changes in the wild.
There is no evidence for the "indefinite capacity of varying from the original type"
which would be required for transmutation. Lyell concludes that "species have a real
existence in nature,"49each being adapted permanently to a particular mode of life.
The units described by the paleontologist in studying the faunas and floras of ancient
strata are therefore not figments of the imagination.
Having established the reality of species units, Lyell turns next to the question of
their present geographical distribution and the processes that may account for it
(Chs. V-VII). Like the previous topic, this is introduced explicitly for its geological importance. Although adaptation is universal, it cannot by itself explain the facts of biogeography: similar ecological habitats are occupied by different organisms in different
faunal and floral provinces. In order to understand the reasons for the existence of such
provinces it is first necessary to consider the means available to species to alter their
geographical ranges in the course of time. Some such changes are possible even without any alterations in physical geography. All species have various means of dispersal
by which they may spread to new areas, and Lyell reviews the means available to different groups of organisms (including man, who forms no exception in this), while he
emphasizes that even improbable means may become important in the long span of
geological time.
But the principle of change introduced by this discussion now raises the wider
problem of changes in the specific composition of faunas and floras, or in other words
the processes that may be responsible for the introduction and elimination of species
(Chs. VJII-XI). Lyell's description of the means of geographical dispersal of species
leads to the question of the spatio-temporal points of origin from which species may
have been dispersed. At this stage he deals with the question of the origin of species
only briefly, proposing a bare working hypothesis for the circumstancesunder which
new species may be introduced, without discussing the means. His hypothesis is simply
that each species has come into existence at a single point in space and time (that is,
species are monogenetic), conditions at that point being suitable for it to exist and
48 [B.-G.-E. de Lacepede] "Rapport des Professeurs du Mus6umn, Sur les Collections d'histoire naturelle rapportees d'Egypte, par E.
Geoffroy," Mem. Mus. Hist. Nat., 1802, 1:234241. Georges Cuvier, Recherches sur les ossemens
fossiles de quadrupedes, o~i l'on retablit les
characteres de plusieurs espcces d'animaux que
les re'volutionsdu globe paroissent avoir detruites
(Paris, 1812), Discours prilirninaire. Cuvier reiterated the same argument in later versions of
the Discours, e.g., in the most recent edition that
would have been available to Lyell at this time:
Discours sur les revolutions du globe et sur les
changernents qu'elles ont produits dans le regne
animnal(6me ed., Paris, 1830), pp. 121 ff. See also
William Coleman, Georges Cuvier Zoologist. A
Study in the History of Evolution Theory (Cambridge, Mass. :Harvard Univ. Press, 1964).
49 PG, Vol. II, p. 65. For a more detailed
analysis of this section of the Principles, see
William Coleman, "Lyell and the 'Reality' of
Species, 1830-1833," Isis, 1962, 53:325-338.
20
MARTIN J. S. RUDWICK
survive for some period of time. Lyell suggests that the observed patterns of distribution of species are consistent with the assumption that species have in the course of
time spread from such unique points of origin. He implies that these points are distributed "uniformly" in space and time, arguing that faunas and floras of high endemicity do not support the idea of special localized "centres or foci of creation" at
which "the creative energy has been in greater action than in others."50In this discussion Lyell uses the language of "creation" freely, though he later said he had left it
to be inferred that he believed in the origin of species by some unknown but secondary
cause.51 It is possible for him to express himself vaguely on this point without intellectual dishonesty, because the precise mode of origin of species is peripheral to his
main geological argument. What matters at this stage is simply to establish that new
species appear on the scene one by one-by whatever means-suitably adapted to the
ecology of the habitat in which they are to live. By implication this process not only
occurs at points uniformly distributed in space and time, but also without any inherent directional tendency: new species are not of higher rank than earlier ones. Any
process that involved adaptive improvement, however slight or gradual, would have
undermined Lyell's fundamental opposition to all directionalist interpretations of the
history of life.
But the origin of species is introduced at this stage only as a preliminary to a discussion of the processes which regulate the continued existence and survival of species
after their original appearance. Lyell describes the ecological checks and balances
between different organisms, which tend to maintain the stability of organic communities. But this stability is perpetually threatened from two directions. The chance
dispersal of a single species to a new area, even without any change in physical geography, can have drastic effects on the communities into which it is introduced, for
example if it is a predator against which the established species have no defense. But in
addition, the ceaseless changes in physical geography (analyzed in the first volume)
must always tend to increase the probability of such radical ecological effects, often
eliminating the physical or biotic environment on which particular species depend for
their survival. Moreover, even relatively minor and gradual physical changes may
occasionally have sudden and drastic effects, for example with the final submergence of
a narrow isthmus or the flooding of a continental area depressed below sea level. (This
is another point at which Lyell is able to provide for relatively catastrophic effects
within an actualistic framework.) He therefore concludes that an incessantly fluctuating physical geography implies an equally incessant process of extinction: "amidst the
vicissitudes of the earth's surface, species cannot be immortal, but must perish one
after the other, like the individuals which compose them."52 Even Lamarck's theory
offers no escape from this conclusion, he maintains, because in changing physical circumstances a previously well adapted species would be eliminated by other species
better adapted to the new conditions, long before it was able to be transmuted by the
imperceptiblyslow process that Lamarck had postulated.
If the successive extinction of species is thus "part of the constant and regular course
50PG, Vol. II, p. 126.
51LLJ, Vol. I, p. 467; cf. Walter F. Cannon,
"The Impact of Uniformitarianism. Two Letters
from John Herschel to Charles Lyell, 1836-1837,"
Proc. Am. Phil. Soc., 1961, 105:301-314. Lyell's
earlyviewson the origin of speciespose historical
problemswhichcannot yet be regardedas settled
and which cannot be discussedwithin the scope
of the presentarticle.
52PG, Vol. II, p. 169.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOG Y
21
of nature," it is necessary to consider next "whether there are aniymeans provided for
the repair of these losses."53If he is to show that the organic world, like the inorganic,
is part of an overall steady-state system, Lyell must at least establish the possibility
that the production of new species is as constant and regular a process as their extinction. Yet he is on difficult ground at this point, because he cannot produce any positive
evidence for species production as a "cause now in operation," and he is forced to
explain why "so astonishing a phenomenon can escape the attention of naturalists."54
He overcomes this difficultyby assuming that species production, like extinction, is an
event that is distributed uniformly in space and time; hence he argues that it would be
extremely unlikely that any single instance would have been accessible to scientific
observation within the span of modern human history. At this point, therefore, Lyell
has to admit that the method of actualism fails and must indeed be inverted: the present must here be interpretedin the light of the past; that is, by the geological evidence
that new species have been introduced-by whatever means-in replacement of those
that have become extinct. Whatever mechanism (if any) he had in mind, he implies
that species production is a relatively sudden event. But this is no more substantial a
concession to catastrophism than his use of sudden earthquakes as the agent of elevation. The important point is that in both cases large results (the appearance of a new
fauna, the elevation of a mountain range) are produced by the summation of piecemeal occurrencesof smaller-scaleevents, spread over a long period of time.
In spite of the weak evidence on the origin of species, the reader is left in little doubt
about Lyell's own belief. The organic world, like the inorganic on which it depends, is
subject to perpetual flux, yet without any directional change in its overall character.
Species, the adaptively stable units of the organic world, come somehow into existence
at ecologically appropriate but broadly distributed points in space and time; they survive for a period in dynamic ecological equilibrium with other organisms, spreading
more or less widely; but sooner or later they are eliminated by the pressures of the
ever-changing physical and biotic environment. Species production and extinction are
thus as ceaselesslyin operation, and as perpetuallyin balance, as the inorganic processes
of deposition and erosion, elevation and depression; the organic world, like the inorganic, is part of a stable system.
VI
Having concluded his analysis of organic processes "now in operation," Lyell
devotes the rest of the second volume to a discussion of the ways in which the organic
world affects the inorganic. The first section (Ch. XII) is in the nature of a parenthesis,
being a further attack on certain directionalist interpretations. In particular, Lyell is
concerned here to reiterate that the continual destruction of land areas by erosion is
balanced by the igneous processes of elevation and vulcanism, not, as Sedgwick had
recently suggested,55by the organic processes of soil formation. Soil is to some extent
a "conservative" agent, reducing the rate at which erosion would otherwise operate;
but Lyell emphasizes that it is in no sense an "equipoise" to erosion. It is to igneous
forces that Sedgwick should look for assurance that erosion is indeed counteracted, so
that habitable dry land is-providentially-a permanent feature of the globe.
53
Ibid., p. 179.
54 Ibid.
55 See n. 3. The suggestionwas not originalto
Sedgwickand has a long previoushistory.
22
MARTIN J. S. RUDWICK
Lyell's main discussion of the effects of organisms on the inorganic world is in
reality an analysis of the circumstances under which organisms are likely to be preserved as fossils (Chs. XIII-XVII). The importance of this section does not emerge
clearly until the third and final volume. Like the rest of his analysis of causes now in
operation, it is an essential part of Lyell's program for the reconstruction of the past
history of the earth. The evidence of the fossil record cannot be used as a reliable guide
to the history of the organic world without a correct understanding of the complex
relation between living organic communities and the fragmentary record which they
may leave in the fossil state. Lyell treats this topic systematically, considering first the
preservation of terrestrial organisms in terrestrial deposits such as peat, alluvium,
volcanic tuffs, and cave deposits (Chs. XIII, XIV). Here he throws doubt on the
alleged occurrences of fossil man, questioning-like Buckland-the contemporaneity
of man and the large extinct mammals; but he also criticizes the assumption of Buckland and others that a single paroxysmal "diluvial" episode might have been responsible for a variety of alluvial and cave deposits. He next considers the preservation of
terrestrialorganisms in the much more widespread deposits of lakes and seas (Chs. XV,
XVI). Here he emphasizes the "accidental and partial" circumstanceswhich determine
whether or not a particular terrestrialspecies is preserved, and he points out that fossil
assemblages of terrestrial organisms are therefore an unreliable indication of the real
specific diversity of earlier periods in earth history. This conclusion is explicitly produced to counter the directionalist inference that organic communities were less diverse
in earlier periods. (Lyell argues that man, on the other hand, is in principle extremely
likely to be preserved in the fossil record by reason of his widespread movements and
activities on land and at sea; the absence of any actual traces of man, except in extremely recent deposits, is therefore evidence for the low antiquity of the human
species.) Third, Lyell turns to the chances of preservation of aquatic species in lacustrine and marine deposits (Ch. XVII). By contrast to the previous sections, the emphasis here is on the high chances of preservation of those organisms-especially marine
mollusks-that have hard skeletal parts. The implication, to be drawn out fully in the
third volume, is that the fossil assemblages of these organisms provide the most representative sample of the organic world of former periods.
The second volume ends with a brief discussion of coral reefs and limestones (Ch.
XVIII). Lyell interprets the subcircular form of coral atolls as a reflection of their
foundation on the rims of submergedvolcanic craters; anidhe uses their distribution as
an argument in favor of his earlier speculation that seismic subsidence exceeds elevation in total amount, thereby ensuring the dynamic stability of the physical geography
of the globe.56 He also argues against the directionalist belief that because limestones
are more abundant in later than in earlier strata, there mnusthave been a progressive
increase in the abundance of lime-secretingorganisms.
The argument of the work is suspended abruptly at this point because of Lyell's
decision to publish this much before completing the remainder.As a result, the second
56 This is of course the line of argument that
Darwin later developed, and improved upon, in
his work on coral reefs. Darwin not only interpreted their varied forms as stages in a single
gradualistic process, but also used their distribution as evidence for a uniformitarian theory of
the simultaneous elevation and depression of
adjacent tracts of ocean floor: "On certain areas
of elevation and subsidence in the Pacific and Indian Oceans, as deduced from the study of coral
formations," Proc. Geol. Soc. Lond., 1837, 2:552554; Darwin, The Structure anid Distribution of
Coral Reefs (London, 1842).
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
23
volume is left incongruously with a frontispiece and a map having no relevance to the
contents of the volume as published.57They were intended to epitomize the argument
of what appeared eventually as the third volume.
VII
The third volume (1833) opens with a long autobiographical preface, explaining the
history of the work and the reasons for the delay in its completion. An introductory
section (Ch. I) then reiterates the main features of its methodology, in answer to the
criticisms that had been made since the publication of the first volume.58Lyell emphasizes the anti-heuristic effect of the catastrophist belief in a discordance between present and past processes: "Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity." He contrasts this with his own "earnest
and patient endeavour to reconcile the former indications of change with the evidence
of gradual mutations now in progress."59These, Lyell asserts, are "two distinct
methods of theorizing," and he again uses an historical retrospect to defend his own
method by pointing to the results it has achieved. In conclusion Lyell emphasizes that
the "preliminary treatises" contained in the first two volumes have been an essential
groundwork for this third volume, which is the culmination of the whole work. A study
of present processes is "the alphabet and grammar of geology"; only by first learning
this language thoroughly is it possible to proceed to the real business of geology, that is
to the deciphermentof the past history of the earth.60
The first major section (Chs. II-IV) is therefore devoted to what might be termedby an extension of Lyell's metaphor-the syntax of geology, namely the principles of
reconstructing the sequence of geological events. After an elementary summary of the
main categories of rocks, Lyell concentrates attention on the Tertiary strata. He emphasizes that the Tertiary strata in different areas are not all of the same age, but represent many different parts of the "Tertiaryepoch," and he hints that when the strata in
areas of active vulcanism and seismicity are taken into account "the line of demarcation between the actual period and that immediately antecedent, is quite evanescent."'"
This foreshadows his deliberate use of the Tertiary epoch as the chief testing ground
for his uniformitariansystem.
The validity of this test, however, depends on establishing that the Tertiary epoch
is in fact representativeof past geological time. In particular, Lyell has to explain away
the apparent contrast between the widespreadand ratheruniform Secondary strata and
the more localized distribution of the Tertiary strata in Europe. He interprets this as
PG, Vol. II, p. 304.
"In it [i.e., Ch. I] I am grappling not with
the ordinary arm of flesh, but with principalities
and powers, with Sedgwick, Whewell, and others,
for my rules of philosophising, as contradistinguished from them, and I must put on all
my armour" (LLJ, Vol. I, p. 376). This Pauline
imagery, with all its overtones of cosmic conflict, is far more than a commonplace metaphor
of a Bible-reading generation: it is a revealing
indication of Lyell's view of his own place in
what he felt to be an ideological crusade.
59PG, Vol. III, pp. 2-3. His opponents not
unnaturally objected to this polemical descrip57
58
tion of theirmethod and criticizedthe aprioristic
implications of Lyell's own use of "reconciliation."
60 Ibid., p. 7; cf. his remarkto Fleming in 1829
that the book he was writingwas to be "a general
workon theyoungerepochsof the earth'shistory"
(LLJ, Vol. I, p. 254). Lyell frequentlyuses the
metaphorof decipherment:e.g., his referenceto
Champollion'swork on the hieroglyphicproblem, likening the fossil mollusks to the "demotic" languageof nature(ibid.,p. 251).
61
PG, Vol. III, p. 22. The referenceis chieflyto
the Sicilian"NewerPliocene"strata.
24
MARTIN J. S. RUDWICK
due to the contrast between a predominantly marine geography (in the part of the
globe that now forms Europe) in the Secondary epoch, and a predominantly continental geography, with more localized areas of marine deposition, in the same area during
the Tertiaryepoch.
He deals next with the apparently abruptjunctions that are often observed between
successive groups of strata. These are not, he argues, the signs of occasional sudden
changes in either the inorganic or the organic world; they are the natural result of perpetually shifting areas of deposition (hence the significance of the map, left incongruously in Vol. II, which shows how large a proportion of Europe was within such areas
at one time or another during the Tertiaryepoch). Recalling his earlier conclusion that
the processes of species production and extinction are continually in operation everywhere, he illustrates the effect of "the working of this machinery"62on the nature of
the fossil record. The sequence of stratain any given region is bound to show apparently
sudden breaks, simply because the area of deposition has from time to time shifted elsewhere and then returned later, by which time the overall specific composition of the
fauna and flora will have changed considerably. In other words, he concludes, the apparently sudden and simultaneous production of many new species or extinction of
many others is an illusion due to the fragmentary record of the strata: "the whole
economy of the existing causes" indicates clearly that the preservation of any more
The geological record is inherently and
complete record "is not the plan of Nature."S63
necessarily fragmentary.
This leads to an analysis of the criteriaby which the relative ages of strata, and hence
of events in earth history, may be established. Lyell first mentions the fundamental
but not always applicable criterion of the superposition of strata. He then denies that
lithological character can be used, except with the greatest caution, because in principle the circumstances determining the nature of the sediment can never be universal,
and in practice it is a matter of observation that distinctive rock types are frequently
repeated in a sequence of strata. The character of the fossils is a more reliable criterion
of contemporaneity, though it too must be used with caution. Recalling his earlier
analysis of faunal and floral provinces and of the chances of preservation, he concludes
that marinefossils are the most reliable, not only on account of their higher chance of
fossilization but also because their provinces are generally wider than those of terrestrial species.
These general principles are then applied in a preliminary fashion to the special
problems of the Tertiary strata (Ch. V). For this most recent epoch of earth history,
Lyell selects the marine mollusks as the most appropriate indicators of geological age.
This is partly because (as already mentioned) their shells are easily entombed and well
preserved and partly because their faunal provinces are wide in extent; but they are
also selected because their species seem to have had much longer duration on average
than those of, for example, the Mammalia.
This last reason is of great importance in Lyell's argument, for it hints at the radically
original nature of his idea of geochronology. He is not concerned merely to identify
strata by a few specially characteristic fossils, as most of his contemporaries were
doing; he is attempting instead to set up a roughly quantitative geological chronometer,
62 Ibid., p. 31. Lyell's use of this metaphor is
perhaps further evidencethat he did indeed envisage a naturalistic "mechanism"for species
production.
63
Ibid.,p. 34.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
25
which will indicate not merely the relative order of strata but also their absolute dates
(though not in years). The working of this chronometer depends crucially on his belief
that over the vast periods of geological time there is an essentially uniform rate of
change in the organic world. Species originate and become extinct at various times and
in various places, and they survive for longer or shorter periods; but given the ceaseless
fluctuations of physical geography, on which the origin, continuation, and extinction
of every species ultimately depend, the overall specific composition of the fauna and
flora will tend to change continuously and uniformly. Hence it should be possible to
estimate quantitativelythe relative ages of any two deposits by comparing the proportion of extant to extinct species in each. The greater the proportion of extinct species,
the greater the age of the fauna represented.64Since a few extant species of marine
mollusks can be found even in the earliest Tertiary strata, Lyell argues that in this
group the average duration of species is so great that they can be used to construct a
chronometer for the whole of the Tertiaryepoch.
Lyell never discusses his method of reconstruction explicitly in terms of a geological
chronometer, probably because that metaphor had figuredso prominently in the earlier
work of catastrophists such as Jean-Andre De Luc, with whom he would not wish to
appear to associate himself.65In this preliminary section Lyell merely stresses the importance of accurate determinations of the species units of fossil faunas and explains
the value of the expert specific identifications by Paul Deshayes, whose tables form the
empirical basis of Lyell's analysis.66But the idea of using these for a quantitative
measure of the ages of Tertiary strata emerges more clearly in his summary of the
divisions he adopts for that epoch. Lyell defines four "periods," based on the percentage of extant species in a total fauna: in order backwards from the Recent period (the
period of man's existence), they are the Newer Pliocene (90-95 %), Older Pliocene
(c. 35-50 %), Miocene (c. 18%), and Eocene (c. 3 %). He emphasizes that these are
merely arbitrary divisions, adopted for convenience of description; their separation
does not imply sudden changes in faunal character between them. Indeed, the discontinuities between the percentages defining the periods are indications of the huge
gaps of time unrepresentedby any known strata, and Lyell stresses that strata of intermediate character and age, which will blur the distinctness of his four periods, are
therefore very likely to be discovered in the future.
Superficially,this rough quantitative treatment of fossils as indicators of geological
age seems little differentfrom the more conventional qualitative use of "characteristic
fossils." But as already suggested, there is a profound difference between them. This
64
Lyell does not discuss this in explicitly
statistical terms, still less in terms of modern
survivorshipcurves; but clearly he recognized
that the relationship would not be a simple
linearone.
65 De Luc had used the rates of present geological processesas "chronometers"to date the
paroxysmalemergenceof the presentcontinents
fromthe floor of the ocean.A morerecent,and to
Lyellmorepalatable,applicationof the sameidea
was Scrope'ssuggestionthat the successivelava
flows in Auvergne,with their differentdegreesof
elevation above the presentcoursesof the rivers,
"exhibita natural scale for measuringthe duration of the process" (of valley erosion)-a
natural chronometer for the successive eruptions, based on the assumptionof a uniformrate
of erosion: G. P. Scrope, Memoir on the Geology
of Central France, Including the Volcanic Formations of Auvergne, the Velay and the Vivarrais, 2
vols. (London, 1827); see p. 162 of text. Lyell's
composition of a review of Scrope's work
(Quart. Rev., 1827, 36:437-483), and his own
study of the area in 1828, seem to have been
majoreventsin his intellectualdevelopment.
66 PG, Vol. III, App. I, pp. 1-46.
26
MARTIN J. S. RUDWICK
becomes clear in one brief passage in this section.67Lyell here maintains that the recognition of certain strata as, say, Eocene in date does not depend on the recognition of
any characteristic Eocene fossils at all. The particular species present may be totally
different from those of any previously known Eocene deposit, because the newly
described strata may have been formed in a quite different faunal province in another
part of the globe. But the assemblage can still be recognized as Eocene in date
if it is found that there is a very low percentage of extant species in its molluscan
assemblage. For the same "machinery" of a uniform rate of organic change will have
affected both regions equally, although working on different species; the same geological chronometer can therefore be applied universally.
Lyell's use of a faunal chronometer for the reconstruction of earth history can now
be seen as a crucial reason for his insistence on the stability of species. Unless these
faunal units remain morphologically stable and therefore taxonomically recognizable
throughout the period of their existence, Lyell's quantitative assessment of the lapse of
geological time would be invalid. To accept any process of gradual and continuous
transmutation would be to undermine the method on which his demonstration of uniformitarian earth history crucially depends.
Having analyzed the principles on which the geological past is to be interpreted "by
reference to causes now in operation," Lyell is at last in a position to apply these
principles to the positive evidence of the past. As already mentioned, he concentrates
attention on the Tertiary epoch primarily because it is nearest to the present. If he can
demonstrate the adequacy of present processes for the explanation of this portion of
geological time and show that a steady-state system is applicable here, his readers will
be more inclined to believe that the same principles may be valid for even earlier
epochs too.
VIII
The main part of the third volume is therefore devoted to a detailed analysis of the
Tertiary epoch. Lyell takes each of his four periods in turn, but he treats them in order
backwards from the most recent, explicitly for the methodological reason that "this
retrospective order of inquiry is the only one which can conduct us gradually from the
known to the unknown."68Within each of his periods Lyell discusses the marine formations of that date, the freshwater deposits, and the contemporaneous igneous
activity. This is not merely for the sake of orderly exposition: it is designed to demonstrate the uniform existence of the same processes and the same environments throughout the Tertiaryepoch.
The first section, devoted to the Newer Pliocene, is also the longest (Chs. VI-XI).
This reflects the greater attention that Lyell himself had given to these geologically
young rocks, but he had become interested in them precisely because of their special
theoretical significance.They are given great prominence in the Principlesbecause they
A "retrospective"order of stratigraphicaldesCf. Sedgwick'sremark in 1830, before the cription had in fact been used, though without
publication of the Principles(though doubtless such an explicitly methodological intention, in
with some knowledgeof Lyell's intentions),that one of the classic geologicalworks of the 1820's:
by detailed studies of Tertiary geology "alone W. D. Conybeareand W. Phillips,Outlinesof the
can we expect to comprehendthe more intricate Geology of England and Wales, with an introducphaenomenaof still older periods, and to con- tory compendium of the general principles of that
nect them with the great physicallaws by which science, and comparative views of the structure of
67
68
Ibid., Vol. III, p. 58.
all matter is governed" ("An Address . .. 1830").
foreign countries (London, 1822).
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
27
play a crucial role in breaking down the conceptual gap between past and present,
smoothing the transition, and showing that no sudden change of geological or organic
processes (a diluvial episode) occurred in the recent past.
Lyell first describes the Newer Pliocene marine strata he had studied in Sicily (Ch.
VI). lie stresses three points about them: the insignificant proportion of extinct
molluscan species which they contain, the evidence that they accumulated very slowly
and therefore represent an extremely long period of time, and their remarkable degree
of elevation above sea level in central Sicily. He then suggests that similar, geologically
recent strata underlie the huge volcanic cone of Etna (Ch. VII), and he goes on to
analyze the structure of Etna itself. Lyell argues that it does not support von Buch's
elevation-cratertheory of a sudden paroxysmal elevation, but that it has been built up
extremely gradually by the same processes that were observed in historic times (Ch.
VIII). He then attempts to estimate, very roughly, the rate of growth of the volcano,
and he concludes that it "must have required an immense series of ages anterior to our
historic periods, for its growth; yet the whole must be regarded as the product of a
modern portion of the newer Pliocene epoch."69
This lengthy analysis of Etna is thus an important part of Lyell's whole argument.
His geological chronometer based on fossil mollusks gives him a means of dating the
Tertiary epoch semi-quantitatively, but it is Etna which enables him to hint at a
calibration of this chronometer in terms of the years of human history.70He prudently avoids hazarding any strict estimate for this calibration, but he makes it clear
that the time scale of Tertiary history is almost unimaginably vast in comparison with
that of human history. Such a vivid illustration of the magnitude of geological time is
a valuable aid in his task of persuading his readers to accept the scientific implications
of such a time scale. This in part explains his choice of a picture of Etna for the frontispiece of what was originally intended to be the second and final volume of the work.
This does not exhaust the significance of Etna, however, for on the "neo-Huttonian"
theory explained in the first volume the eruptive action of a volcano is only the surface
manifestation of the deep-seated processes which are also responsible for the elevation
of land. Therefore Lyell argues that the elevation of the Newer Pliocene strata in
Sicily could have taken place very gradually over a long period of time by a series of
intermittent earthquakes, just as the growth of Etna was proceeding during the same
period by a series of intermittent eruptions (Ch. IX). This argument is important, because (as already mentioned) it will enable him to maintain that any greater degree of
elevation, even of the highest mountain ranges, is explicable in similar terms. The
gradual elevation of the strata is also supported by the form of the valleys and ancient
sea cliffs cut into them, and indirectly by the nature of the fauna and flora now inhabiting the region.
The sulpposedcontrast between present and past is also attacked at other points on
the basis of these Sicilian strata. Lyell infers that their elevation is due to the subterranean injection of vast masses of molten material which on cooling form the crystal69 PG, Vol. III, p. 101. Lyell is not consistent
in his use of "period,""epoch,"and "era."Here
he refersto "the new Pliocene epoch," and elsewhereto "successiveTertiaryeras"(ibid.,p. 59).
The usage adoptedin the presentpaperis that of
Lyell's initial exposition(ibid.,pp. 52-56), where
the "NewerPliocene period"is describedas one
of the "subdivisionsof the Tertiaryepoch."
70 This section of the Principles is analyzed in
greaterdetail in MartinJ. S. Rudwick,"Lyell on
Etna, andthe Antiquityof the Earth,"in Schneer,
ed., Toward a History of Geology, pp. 288-304.
28
MARTIN J. S. RUDWICK
line igneous rocks that are commonly seen in the eroded cores of older mountain
ranges. Thus he can argue (like Hutton) that the formation of granite and similar
rocks is not solely a feature of more primitive periods of earth history, but is a process
still in operation.
Turning from Sicily to the volcanic areas of Italy (Ch. X), Lyell continues the same
argument, criticizing those who contrast the insignificant scale of modern changes with
the vast scale of ancient geological effects, pointing out that they fail to take account of
the magnitude of the time scale during which the latter effects have been produced. A
brief survey of Newer Pliocene marine strata in other parts of the world leads Lyell to
comment that these strata are generally visible above sea level only in areas subject to
earthquakes, as expected on his theory of elevation.
Lyell then discusses the nonmarine deposits of Newer Pliocene age (Ch. XI). He
criticizes particularly the idea of a single "alluvial epoch" (which had been closely
associated with the theory of a diluvial episode), pointing out that alluvial deposits
have been formed at many periods. The huge erratic blocks of the Alps and elsewhere
were more difficult for him to explain (as indeed they continued to be until the advent
of the glacial theory).7' Lyell rejectsany suggestion that erratics might have been transported by a vast tidal wave actuated by the sudden elevation of a mountain range in
another part of the globe.72But while he can ascribe the Northern erratics to the more
actualistic agency of floating marine icebergs, he is obliged to postulate that those in
the Alps have been transported by icebergs suddenly released by the collapse of barriers damming temporary lakes.
The Older Pliocene period is analyzed more briefly (Chs. XII-XIV). Lyell's description of the celebrated Subapennine strata, and of the English strata to which he attributes the same date, needs no special comment. To illustrate the volcanic activity of
the period, he places here the extinct but well-preserved volcanic cones of Catalonia
and the Eifel, which he had visited in 1830 and 1831. He uses a picture of some of the
Catalonian cones as the frontispiece of the third volume, but the reason for this choice
emerges more clearly in his later discussion of the similar cones in Central France.
The Miocene period is also treated briefly (Chs. XV, XVI). Lyell describes various
marine, freshwater, and volcanic rocks which he attributes to this period. Recalling
the arbitrarycharacter of his periods and the implicit temporal gaps between them, he
suggests that certain deposits at Montpellier may be of an intermediate age (Miocene/
Pliocene): "we are fully preparedfor the discovery of such intermediatelinks."73
Lyell's analysis of the Eocene period (Chs. XVII-XX) reverses the usual order of
topics by describing the freshwater deposits of Central France (Ch. XVII) before discussing the formations of the Paris area (Ch. XVIII). By this reversal he is able to introduce an interpretation of the latter which avoids any need for postulating catastrophic events. For these Parisian deposits, with their abrupt alternations of freshwater and marine strata, had been central to Cuvier's theory of sudden continent-wide
71 These difficultiesare discussedmore fully in
M. J. S. Rudwick, "The Glacial Theory,"
History of Science, 1970, 8 (in press).
soudainsqui ont produitles lignesde demarcation
qu'on observe entre certains etages consecutifs
des terrainsde sediment,"Ann. Sci. Nat., 1829-
72 Cf.
lie de Beaumont, "Recherches sur 1830, 18:5-25, 284-416; 19:5-99, 177-240. A
quelque-unesdes revolutions de la surface du long abstractwas translatedin Phil. Mag., 1831,
globe, presentantdiff6rentsexemples de coinci- N.S., 10:241-264.
dence entre le redressementdes couches de certains systemesde montagnes,et les changements
73 PG, Vol. III, p. 216.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOGY
29
changes in physical geographyand consequently in terrestrialfaunas,74and therefore at
this point Lyell was up against one of the strongholds of catastrophism. But the exclusively freshwater deposits in Central France show that no marine incursions ever
penetrated to that area during Eocene time, and Lyell is able to use Constant Prevost's
recent critique of Cuvier's interpretation75to show how the freshwater and marine
strata around Paris could have accumulated simultaneously in different parts of the
area, as in a modern gulf or estuary, without sudden changes in sea level. This reinterpretation, he points out, makes it "more easy to explain the manner of their
origin and to reconcile their relations to the agency of known causes."76Moreover, in
view of the very high proportion (97 %) of extinct species among the marine mollusks
in these strata, Lyell argues that it is hardly surprising that all the vertebrate fossils,
without exception, are also extinct. Notwithstanding Cuvier's opinion, no general
revolutions need be invoked to account for this: it merely reflects a much higher rate of
change in vertebratefaunas compared with molluscan. Summarizingthis section, Lyell
stresses the normality of the world revealed by his interpretation of the Eocene deposits. They bear witness to a period as tranquil as the present; contrary to what the
directionalists tended to suggest, "we are naturally led to conclude, that the earth was
at that time in a perfectly settled state, and already fitted for the habitation of man."77
Under the heading of Eocene volcanic rocks, Lyell next discusses the celebrated
volcanic areas of Central France (Ch. XIX), drawing freely on Scrope's great memoir.78
He stresses particularly the classic evidence that the volcanic eruptions had been of
many different dates; but he attributes a relatively early date-Miocene-even to the
most recent eruptions, arguing that the very fresh appearance of some of the volcanic
cones is no indication of their real age. His reason for this very surprising conclusion
soon emerges: he is concerned to attack the belief that these volcanic rocks can be
sharply divided into antediluvial and postdiluvial categories.79This is the more necessary because of Sedgwick's recent support for the neodiluvial catastrophism of
Leonce 1hie de Beaumont.80By arguing for the great geological age of even the youngest volcanic cones in Central France, Lyell is denying that there is any evidence for a
geologically recent diluvial episode; for any such event would certainly have eroded or
swept away such cones of loose unconsolidated material. This explains the significance
of the similar cones in Catalonia, an illustration of which Lyell chose for the frontispiece of this volume, as has been mentioned. To combat the possible revival of
Mosaic geology on a more scientific basis, Lyell cites Fleming in support of the view
that the scriptural Flood was in any case entirely different in character from the violent diluvial episode postulated by his scientific opponents.81
II
See n. 48.
Constant Prevost, "Les Continentsactuels,
ont-ils e, a plusieursreprises,submergespar la
75
mer?" Memoires de la Socijtj d'Histoire Naturelle de Paris, 1828, 4:249-346.
76 PG, Vol. III, p. 248.
77 Ibid., p. 255.
78 See n. 65.
79 E. g.,
C. Daubeny, "On the Volcanoesof the
Auvergne," Edinb. New Phil. J., 1820-1821, 3:
359-367; 4:89-97, 300-315; "On the Diluvial
Theory, and on the Origin of the Valleys of
Auvergne," Edinb. New Phil. J., 1831, 10:201-
229. (The most recent volcanoes are now dated
as late Pleistocene, i.e., Recent or Newer
Pliocene in Lyell's terms, and their eruptions
would have been contemporarywith Paleolithic
man.)
80 See nn. 3 and 72.
81PG, Vol. III, pp. 271-272; John Fleming,
"TheGeologicalDeluge, as interpretedby Baron
Cuvier and Professor Buckland, inconsistent
with the testimonyof Moses andthe Phaenomena
of Nature,"Edinb.Phil.J., 1826, 14:205-239. See
also Leroy E. Page, "Divulialismand Its Critics
in Great Britain in the Early Nineteenth Century," in Schneer, ed., Toward a History of
Geology, pp. 257-271.
30
MARTIN J. S. RUDWICK
A straightforwarddescription of the Eocene strata in England (Ch. XX) leads to a
long digression on the mode of elevation and erosion of the English Weald, which
separates the main areas of Eocene strata (Chs. XXI, XXII). The purpose of this
digression is again to combat various catastrophist interpretations of the area.82Lyell
argues that there was no sudden episode of elevation of the strata or of diluvial erosion of the valleys: the anticlinal elevation of the Weald was very gradual, the Chalk
and earlier rocks were eroded from the center chiefly by gradual marine erosion, and
the material so produced contributed to the equally gradual and simultaneous accumulation of the Tertiarystrata in the adjacent areas.
Ix
This concludes Lyell's actualistic and uniformitarian interpretation of Tertiary
earth history. His analysis of Secondary strata (Ch. XXIII) is very brief. This is certainly not because they were less well known than the Tertiary in 1833-on the contrary, they were much better known-nor is it primarily because an equally lengthy
treatment of the Secondary periods would have required yet another volume. The
main reason for his brevity is methodological. Having demonstrated the adequacy of
present processes at their present level of intensity for the interpretation of Tertiary
time, it is sufficientfor the purpose of his overall strategyto treat the Secondary periods
summarily, merely "to show that the rules of interpretation adopted by us for the
tertiaryformations, are equally applicable to the phenomena of the secondary series."83
On Deshayes' authority he accepts the magnitude of the faunal discontinuity between the Eocene strata and even the uppermost (Maestricht) strata of the underlying
Chalk series, there being no molluscan species in common. He attributes this, however,
not to any sudden episode of mass extinction and subsequent faunal replacement, but
to a huge gap in the fossil record, suggesting that it might represent a period of time
even greater than that which separates the earliest Eocene deposits from the present
day! This shows clearly the consistency with which he was prepared to apply the
principle of a uniform rate of change in the organic world and the geological chronometer founded upon it. On his chronometer the period from Eocene to the present has
been long enough to produce a 97 % turnover in the molluscan fauna; therefore, since
the Chalk/Eocene discontinuity is marked by a 1000% turnover in species, it must
representan even longer period.
For the Secondary strata in general he stresses again the reasons for their apparent
contrast to the Tertiary. The geography of the Secondary epoch in the area that now
forms Europe was predominantly marine; and since large areas of that ancient sea
floor have by now been lifted above sea level, it is only natural, he argues, that some
Secondary formations should maintain a uniform character over very wide areas in
contrast to the patchy distribution of the Tertiary deposits. Similarly, the longer time
that has elapsed since their deposition is also sufficient to account for their generally
greater degree of consolidation and tectonic disturbance. None of these features,
Lyell implies, can be taken to representconditions or processes differentfrom those of
Tertiarytime; for Secondary time the stability of the system is maintained also.
82 EspeciallyBuckland'spaper"Onthe Formation of the Valley of Kingsclere and of other
Valleysby the Elevationof the Stratathat enclose
them; and on the Evidencesof the originalCon-
tinuity of the Basins of London and Hampshire,"
Trans. Geol. Soc. Lond., 1829, Ser. 2, 2 (Pt. 3):
119-130.
83 PG, Vol. III,p. 324.
THE STRATEGY OF LYELL'S PRINCIPLES OF GEOLOG Y
31
Before proceeding to the Primary rocks, and the conclusion of the whole work,
Lyell digresses to argue against llie de Beaumont's recent theory of the paroxysmal
elevation of mountain ranges (Ch. XXIV).84 Here again Lyell asserts that the key to a
correct interpretation of the phenomena is a proper appreciation of the magnitude of
geological time and the fragmentary nature of the succession of strata. For the suddenness attributed to the episodes of elevation depends on proving the brevity of the
time interval separating the youngest strata affected by the movements from the oldest
strata unaffected. On Lyell's view of the fragmentary nature of the record, such
intervals cannot be shown to have been short at all: "even if all the facts appealed to
by de Beaumont are correct, his intervals are of indefinite extent."85
Having disposed of this most recent-and most strictly scientific-challenge to his
concept of uniformity, Lyell turns finally to the Primary rocks (Chs. XXV, XXVI).
He immediately criticizes this term for covering rocks of many differentages, not all of
them older than the Secondary strata. "Unstratified primary" rocks, such as granite,
deserve the Huttonian name Plutonic to denote their deep-seated igneous origin. Like
Hutton, Lyell maintains that granite is not "the oldest of rocks," predating the appearance of life on earth; on the contrary, "it is now ascertained that this rock has
been produced again and again, at successive eras";86 it is often seen penetrating
Secondary strata, and it may be assumed to be forming even at the present time
beneath the main centers of vulcanism and elevation. The so-called Trap rocks, of
volcanic origin, are likewise not confined to earlier periods, for they are found
among even the Newer Pliocene strata.
The "stratifiedPrimary"rocks such as schist and gneiss are somewhat more difficult
for Lyell to explain. In some respects they look like ordinary sediments, yet they often
seem to merge into granite. This apparent contradiction can only be resolved, Lyell
argues, by adopting "the Huttonian hypothesis" of metamorphism:schist and gneiss
are sediments which have been altered by heat in the proximity of molten granite,
analogous to laboratory experiments and to the larger natural experiments of contact
metamorphism near igneous dikes.
Lyell therefore proposes that the stratifiedPrimary rocks should be renamed Metamorphic. For the unstratifiedPrimary the name Plutonic is already available. For the
two categories together, that is for all Primary rocks, Lyell proposes the term Hypogene, or "nether-formed." These changes are far more than merely terminological.
They are introduced to stress Lyell's contention that all the rock types commonly regarded as characteristicof, or even confined to, the earliest periods of earth history can
in fact be formed in any period, including the present. The Primary is not primary at
all.
This conclusion is illustrated in the table immediately following this final chapter.87
Under each period of geological time Lyell lists examples not only of alluvial, marine,
and freshwater deposits, and volcanic rocks, but also of visible or inferred hypogene
rocks, both plutonic and metamorphic. This table epitomizes perfectly the uniformiSee n. 72.
PG, Vol. ILL,p. 344; cf. his remarkto Scrope,
"It is by fossil zoology alone that all dates of the
relative upheaving of mountain chains must be
decided, or guessed at" (LLJ, Vol. I, p. 272).
86 PG, Vol. III,p. 357.
84
85
87 Ibid.,pp. 386-387. For an earliertable of the
same kind, showingthe sedimentaryand igneous
rocksof eachperiodin parallelcolumns, see Ami
Boue, "SynopticalTableof the Formationsof the
Crust of the Earth and of the Chief Subordinate
Masses," Edinb. Phil. J., 1825, 13:130-145.
32
MARTIN J. S. RUDWICK
tarian system which emerges from the whole work: all categories of rock, and therefore all causal processes, have existed uniformly in all periods. The geological periods
are carriedback as far as the Carboniferous, which in 1833 was still the earliest with a
clearly defined stratal succession. Significantly, however, Lyell extends the "Carboniferous Group" downward to include even the poorly known "Grauwacke and transition limestone," the oldest strata he recognized.88With the assimilation of the Transition strata into the Secondary period, and the neo-Huttonian interpretation of all the
so-called Primary strata as merely metamorphic, the chronicle of earth history is thus
left without vestige of a beginning.
Lyell's "concluding remarks"are therefore devoted to defending himself against the
charge of advocating an eternalistic system. He complains that this is as unfair to him
as it was to Hutton before him. Using a favorite analogy between space in astronomy
and time in geology, he stresses that his eternalism is epistemological, not ontological.
We must be preparedto find that, as in exploring space, so "in time also, the confines
of the universe lie beyond the reach of mortal ken."89The stable system of the earth,
revealed by geology, shows its designfulness precisely by virtue of its stability; to
assume that we shall ever find evidence of its beginning or its end would be "inconsistent with a just estimate of the relations which subsist between the finite powers of
man and the attributes of an Infinite and Eternal Being."90
x
It is entirely appropriate that Lyell's vast extended argument should conclude with
that Huttonian echo. Lyell may have seen the Huttonian system largely through the
refracting medium of Playfair's exposition; but it is clear that it was Hutton's vision
that inspired him to construct an even grander system on the firmer foundations of
the geology of his own time-a system of almost infinite complexity, but one in which
both inorganic and organic processes balanced and interacted to produce a perpetual
dynamic stability.
If this interpretation of the Principles is valid, we should see Lyell's steady-state or
uniformitarian system as his fundamental scientific commitment. This is not to deny
that there were many other concerns that impinged upon his work. The Principles
certainly demonstrates his concern for the separation of geological research from the
interpretation of Scripture; his interest in finding naturalistic explanations for
even the most puzzling geological phenomena; his emphasis on the adequacy
of observable geological processes in the interpretation of those phenomena; and, not
least, his acute perception of the immensity of geological time and of the fragmentary
nature of the geological record. Yet all these areas of emphasis are used in the strategy
of the Principles, not as arguments of interest in themselves, but as tactical devices to
be deployed in the service of a uniformitariansystem of earth history.
It is surely in Lyell's commitment to this system that we should look for a key to his
reluctance to accept a progressionist view of the history of life or, ultimately, a transmutationist view of the mechanism of that progression. For it is ironic that the
88 PG, Vol. III, p. 393. The Transition strata
tion of the historyof life.
included those that Murchison shortly after89 Ibid.,p. 384; cf. alsoLLJ,Vol. 1, pp. 269-270,
ward termed Silurian, the distinctive fauna of 382.
which was largely responsible for undermining
90PG, Vol. III, p. 385.
the credibilityof Lyell's steady-stateinterpreta-
THE STRATEGY OF LYELL'SPRINCIPLESOF GEOLOGY
33
uniformitythat later generations of geologists and biologists came to accept from Lyell
was that of his actualistic methodology; they came to reject the uniformity of his
steady-state system in favor of a developmental model much closer to that of his
directionalist opponents.
This, however, still leaves us with the most fundamental question of all: what was
the source of the strength and tenacity of Lyell's commitment to a steady-state system?
Did he value it chiefly for its avoidance of the problem of the ultimate origin of the
earth and the related problem of creation? Or should we take seriously his recurrent
analogy between time and space and conclude that he saw uniformitarianismprimarily
as a theory which, by the grandeur of the views it disclosed, would raise geology to the
heights of prestige enjoyed by the science of astronomy? Yet even if that were true,
was this analogy itself to be valued on grounds of scientific prestige alone-or because
it added the dimension of geological time to the sublime vision of a universe of perfect
and wise design, a universe fully under the dominion of providential natural laws, and
therefore, as Hutton had believed, one which needed no irruptions of divine power to
throw doubt upon its perfection?