PRINCIPLES OF GEOLOGY -- VOLUME I
CHARLES LYELL'S Principles of Geology is on any reckoning one of the most important books ever published in the earth sciences, and it continues to be significant in modern debates in that field. Furthermore, the concept of "the uniformity of nature" that the Principles embodied and exemplified gave the book a seminal influence on nineteenth-century culture in general, and helped to define what it means to be "scientific."
Among comparable classics, the Principles must be one of the least widely read. There are two simple reasons. The first edition, which is by far the most significant historically, has long been a rarity, and in recent years an increasingly expensive one at that. And the book is very long, and lacks clear internal signposts to the structure of its argument. With this inexpensive reprint edition, the first reason for the neglect of the work will at last disappear; potential readers will no longer need to resort to a rare-book room to read Lyell for themselves. The purpose of this introduction is to alleviate the second problem, by providing an outline of the continuous thread of argument that underlies the 1400-odd pages of the first edition.  This is particularly important, because the existence of such an argument has often been overlooked and the work as a whole misinterpreted as a mere textbook or compilation of contemporary knowledge of the science. Furthermore, attention has often been focused on one part of one of the three volumes, a part which was unquestionably of great importance in Charles Darwin's formulation of his theory of evolution. But this exclusive focus has tended to obscure the significance of Lyell's views on species for his own, more strictly geological purposes.
This introduction, then, offers a guide to the structure of the first edition of the Principles. It does not attempt to make any full assessment of the wider significance of Lyell's work, and is designed simply to make it easier for readers to let Lyell speak for himself. First, however, a brief summary of the origins of the book (for further biographical details see Wilson 1972). 
THE MAKING OF THE PRINCIPLES
Charles Lyell was born in 1797 into a family of Scottish gentry, but his childhood was spent in the south of England. At Oxford, where he was an undergraduate at Exeter College, his conventional studies were enlivened by William Buckland's celebrated extracurricular course on geology; it was this that first aroused Lyell's serious interest in the science. He then moved to London, and qualified as a barrister at Lincoln's Inn. But he practiced that profession only for a short time, before deciding that his talents as a writer might enable him to earn enough (in addition to a modest income from his father) to devote himself full-time to geology. Briefly he held a part-time position at the newly founded King's College in London, and lectured there on geology; but he resigned on finding that the income it produced did not justify the time it took from his geological research and writing (Rudwick 1975a). He became an increasingly prominent member of the scientific intelligentsia in London, making its Geological Society -- the first of its kind in the world -- his main affiliation (Morrell 1976). In 1823 a visit to Paris, which was then the supreme world center of scientific research, brought him into contact with the leading French geologists. This gave his approach to the science a strongly international dimension, and he was the Geological Society's "Foreign Secretary" during the years when the Principles was being written and published.
While Lyell was in Paris, Constant Prevost showed him the already classic Tertiary strata of the Paris basin, and this experience seems to have turned his attention toward these relatively young rocks. It seems also to have suggested to him that, as Prevost contended against the great comparative anatomist Georges Cuvier, such strata could be interpreted wholly in terms of ordinary geological processes like those in the modern world. Accordingly, one of Lyell's earliest scientific papers, read at the Geological Society in 1825, analyzed some geologically recent lake deposits near his Scottish home and compared them explicitly with some of the much older Parisian rocks. In trying in this way to understand and explain the past as far as possible in terms of the present, Lyell was following a method that was already well established among geologists, including, for example, Buckland (Cannon 1976). Where Lyell began to diverge from them was in the strength of his conviction that this was the only proper method for geology to follow; and that its use should determine what should count as scientific. More specifically, Lyell was profoundly influenced by the greatest contemporary philosopher of science (and practicing scientist) John Herschel, who maintained that only verae causae ("true causes") had any business in a scientific explanation (Laudan 1982, 1987; Ruse 1976). Lyell concurred with Herschel in insisting that the only acceptable causal agents were to be those that could be observed producing the kinds of effect that needed explanation. This stress on the efficacy, indeed the sufficiency, of present and observable "causes" was just one of the several distinct meanings of the "uniformity" that Lyell constantly preached in his geology (Rudwick 1971). It is convenient to distinguish it by the modern analytical term actualism (derived from an older use of "actual," which survives in languages other than English, to denote present events and affairs).
Like Prevost in his criticisms of Cuvier's influential views, Lyell also began to diverge from most other geologists in another way. Cuvier, followed by many others, had claimed that the geological evidence was such that it was necessary to infer that sudden events of great violence -- "catastrophes," as they were commonly termed -- had occurred from time to time in the geological past. In a review of the first volume of the Principles, the Cambridge polymath William Whewell later coined the term catastrophism for this view, and that label will serve here for analytical purposes. Lyell, however, rejected this view altogether, and argued forcefully that "modern causes," acting at their present intensities, were entirely adequate to explain the evidence of the past. Whewell's term uniformitarianism, by which he characterized Lyell's position, needs to be treated with caution, however, because it has been used with many and diverse meanings, both at the time and subsequently.
Lyell's earliest geological writings that gave him scope to discuss such theoretical matters were not papers to the Geological Society, but extended essays for the Quarterly Review, the influential Tory periodical read by the British intelligentsia generally. From these essays it is clear that Lyell's early inclination was to combine his actualism and anticatastrophism with a view of the natural world that was held widely among geologists. This was that the earth's history has been broadly developmental or directional, from distant beginnings -- perhaps as an incandescent globe -- toward its present state, with a correspondingly directional or even "progressive" history of life on earth. It is convenient to use the modern analytical term directionalism to denote this overall interpretation of geology (Rudwick 1971). A directionalist view was quite compatible with Lyell's adoption of an actualistic method, and with his denial of catastrophic events in the past, though it certainly did not entail his approach.
In 1827, however, Lyell's views seem to have undergone a radical change in this last respect. He switched abruptly to a view of the overall pattern of earth history that put him virtually in a minority of one among living geologists. He adopted, and began to refine on the basis of the geology of his own day, the cyclic view of earth history that had been proposed forty years earlier by the Scottish natural philosopher James Hutton. Such a view can be referred to by the modern analytical term steady-state (borrowed, of course, from its use by modern cosmologists). At about the same time Lyell began to make notes that are recognizably the germs of what later became the Principles (Wilson 1972, p.169).
It has been plausibly inferred that Lyell's abrupt theoretical change in geology was related intimately to his experience, at just the same time, of reading the theory of transmutation (in modern terms, of organic evolution) by the aging French naturalist and philosopher Lamarck (Bartholomew 1973, 1976; Corsi 1978). Lamarck's work convinced Lyell that the currently fashionable directionalism in geology would lead inexorably to an out-and-out evolutionism in biology, from which the human species -- body, mind, and all -- could not be excluded. That was a path toward materialism that Lyell had no wish to follow; indeed that he fervently wished to avoid. Whatever his reasons-- and this question remains controversial -- there is no doubt that just as Lyell was planning some kind of major work on geology, he adopted one viewpoint that was highly idiosyncratic, and that his contemporaries found highly implausible, along with others that they were far more ready to consider.
Lyell's book was originally designed to be an elementary work on the lines of Jane Marcet's popular Conversations on Chemistry (1806), and he hoped it might sell widely enough to yield him some useful income. But he soon found his work expanding and deepening into a much more serious and substantial scientific treatise.  It should be emphasized, however, that the readers whom Lyell and his publisher hoped the work would attract covered the same wide range as, for example, those of the Quarterly Review. The work was in no way designed just for an audience of "professional scientists" -- that term is in any case anachronistic for the 1830s -- but for the intellectual reading public generally. Lyell's elegant style not only makes the Principles a classic of scientific prose writing; at the time it also made the work widely accessible to a public that found geology an exciting science. 
Lyell's ideas, and his store of empirical evidence to support them, were immensely enriched by a long field trip in 1828-29 through France and Italy, initially in the company of another London geologist, Roderick Murchison.  After his tour of Sicily, which proved to have been the high point of the whole journey, Lyell summarized his fieldwork in a long letter to Murchison. He described the book he was planning in the following terms:
My work is in part written, and all planned. It will not pretend to give even an abstract of all that is known in geology, but it will endeavour to establish the principle[s] of reasoning in the science; and all my geology will come in as illustration of my views of those principles, and as evidence strengthening the system necessarily arising out of the admission of such principles, which, as you know, are neither more nor less than that no causes whatever have from the earliest time to which we can look back, to the present, ever acted, but those now acting; and that they never acted with different degrees of energy from that which they now exert. (Lyell 1881, vol. 1, p. 234)
This brief passage epitomizes the character of the book that began to appear in public little more than a year later.
First, the title of the work was not chosen casually. In the early nineteenth century any scientific work with the word "principles" in its title still evoked the memory of Isaac Newton's Principia; it was not exactly a modest title for a 32-year-old geologist to propose. For Lyell the word carries that full contemporary meaning; it is not (as in many modern works) a synonym of "textbook." The book is not to be 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 fundamental "principle[s] of reasoning" in geology.  Lyell mentions two distinct principles: the geological "causes" or processes observable at the present day are, he asserts, fully 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 clear that the first could be true without entailing the second: it seemed quite conceivable that in the unimaginably long time span of geological history some of the processes known on a small scale within recorded human history might have acted more rarely with paroxysmal or catastrophic intensity.
Third, the two principles are to have a regulative function in the work. It is clear from Lyell's phrasing 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 embodied the more modest claim that it would merely attempt to explain the phenomena of the past "by reference to causes now in operation." This shows that Lyell was well aware that his disagreement with other geologists was not in fact over the desirability of using the present as a key to the past, but over its adequacy. Lyell's belief in his principles, and his conflation of the two, indicate his commitment to an extreme form of actualism. But this position differed only in degree from that of his scientific opponents.
Fourth, Lyell 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 meaning in early nineteenth-century science: Lyell intends to advocate a theory of the broadest possible scope. Although its nature is not made explicit in this letter, the published Principles shows that Lyell's "system" embodies nothing less than the claim that the overall pattern of earth history has been steady-state or cyclic, and not directional at all. What is significant is that Lyell claimed in his letter that this "system" followed "necessarily" from his two principles. That necessity was far from obvious to other geologists.
The first volume of the Principles was published in the summer of 1830 by John Murray, the leading scientific publisher in London. It was to have been a two-volume work, but it expanded in the writing, and (as explained below) Lyell brought out part of the projected second volume in 1832, and the rest in 1833. The volumes are illustrated with a few expensive copper engravings, some of them handcolored to heighten their geological meaning. In addition, the Principles reflects the beginnings of the routine deployment of wood engravings in book publication; these were much cheaper, and had the added advantage of being printed on the same page as the text to which they referred (Rudwick 1976). Perhaps Lyell himself only realized the potential of such illustrations while he was writing the Principles; certainly their frequency in the text increased more than three times between the first volume and the third (the second volume contains none).
The Principles enjoyed an immediate success with the reading public, and new editions followed in quick succession throughout the decade. Lyell's prose style was found attractive; indeed his critics complained that his style betrayed all too much of his lawyer's training. It presented his theoretical case with a consummate use of rhetoric -- in the proper, nonpejorative sense of that word -- that they found it hard to match. Yet in one respect Lyell made his case less easy to follow than it might have been. Like the seamless web of an advocate's persuasive address to a jury, Lyell's case unfolds from chapter to chapter without interruption. His summaries of the contents of successive chapters, set out in the table of contents in each volume, repay detailed study as a guide to his argument; but the chapters themselves lack attractive or succinct titles. Hence the need for a guide to the structure of Lyell's case.
The first volume (1830) opens with an introductory chapter (chap. 1) defining the subject matter of geology. Lyell emphasizes its status as an essentially historical science, and its concern with the causes of the processes underlying earth history. This stress on causal analysis is one of the features which sets the Principles apart from much of the geological work of his contemporaries. However, by deliberately rejecting their strongly anti-theoretical approach, Lyell lays himself open to the charge of leading geology back to the bad old days -- as in Lyell's time they were considered to have been -- of the speculative "theories of the earth" of the previous century and earlier. This presents him with a dilemma, for he must somehow disclaim any affinity with most of the earlier system builders, while leaving himself free to acknowledge the value of one in particular, namely Hutton. To Lyell's contemporaries Hutton seemed as deplorably speculative as any other system builder. Yet Hutton's theory, epitomized by its conclusion that in studying the earth "we find no vestige of a beginning, no prospect of an end," was the one that Lyell proposed to revive and refine. He 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" (p. 4). Thus right at the outset Lyell proclaims his Huttonian intentions quite explicitly.
These remarks lead at once into the first major section of the Principles, a review of the history of geology from antiquity to the early years of the nineteenth century (chaps. II-IV). Much of the detail is borrowed, with scant acknowledgment, from the historical essay in Giovanni Battista Brocchi's already classic monograph (1814) on the Tertiary mollusks of the Sub-Appenine Hills in northern Italy McCartney 1976). The aim of this section, however, is not really to provide historical background but to argue a case as 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 is addressed (Porter 1976). 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 (Lyell 1881, vol. 1, p. 271; Porter 1982). Like many would-be reformers, Lyell rewrites history in order to demonstrate that those whose present views he is attacking are inheritors of a historical tradition that has had a retarding influence on the progress of the science. He contrasts this with the more enlightened tradition in which he finds his own antecedents, though in fact he spreads his praise thinly, and thereby accentuates his own innovative originality.
The tradition he is attacking has, he implies, several related characteristics. It tends to use Scripture to 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 approach that Lyell intends to advocate makes a sharp disjunction between geological research and the interpretation of Scripture; it eschews all cosmogonic ambitions of reaching back to the origin of the earth; it interprets the past history of the earth as a series of events comparable to those still occurring; and it readily accepts a vast time scale for earth history.
Lyell's polemical interpretation of the history of geology naturally entails distortion and oversimplification of the theories of his predecessors (Ospovat 1976). But from his point of view it has the advantage of tarring with the same brush the popular but scientifically worthless speculations of the "Mosaic"  or "Scriptural" geologists of his own time; the far more respectable catastrophism of his former teacher Buckland, with its relatively liberal interpretation of Scripture; and the still more empiricist catastrophism of geologists such as Buckland's Cambridge counterpart, Adam Sedgwick. From its original conception as a popular work, the Principles had retained the function of combating those who were misleading the general public into believing that a literal interpretation of the Creation narrative in Genesis was still tenable. Most other geologists, whether or not they agreed with Lyell on specific issues, would in fact have considered themselves his allies in hoping "to free the science from Moses" (Lyell 1881, vol. 1, p. 268). But Lyell implies that there is an inherent affinity between catastrophist and Mosaic geology, and that this illustrates the grave dangers of slipping in any degree from his own highly restrictive conception of "uniformity."
The importance of Lyell's "history" in the strategy of the whole work becomes clearer in the following chapter (chap. V), which summarizes the lessons to be learned from it. Here he maintains that the slowly increasing reliance on ordinary secondary causes in geology has been similar to the growth of the scientific attitude as a whole; to be Lyellian in geology is, in effect, to be scientific. But he argues that the greatest single factor retarding the progress of geology has been an inadequate conception of the time scale of earth history. Using a favorite tactical device of an analogy with human history (Rudwick 1977), he shows how this inevitably telescopes events together, giving an illusion of swift and extraordinary happenings and astonishing coincidences. It was this, he suggests, that made geologists unwilling to believe in "uniformity" and led them to expect discontinuity between past and present unless the evidence to the contrary was overwhelming. Lyell maintains, however, that the vast time scale which the Huttonian system demanded is now being vindicated by the discovery of more and more strata that need to be intercalated into the succession previously known. Citing his own observations in Sicily, he argues that as a result of this implicit expansion of the time scale it is no longer necessary to postulate causes exceeding in intensity those now in operation; or -- showing a significant elasticity in his conception of uniformity -- those that might conceivably occur in the future. This qualification indicates again that Lyell is not concerned merely to advocate actualism as a method, but to argue for a steady-state or cyclic system in which geological processes are not, as the directionalists suggested, tending toward a state of quiescence.
In placing such emphasis on the sense of the geological time scale, Lyell shows a penetrating awareness of the nature of his task of persuasion. For although his scientific colleagues (unlike the Mosaic pseudogeologists) readily accepted a vast time scale on the intellectual level, Lyell recognized that it was their scientific imagination that needed transforming. Much of the detailed argument of the Principles is therefore designed to draw out the full implications of a belief which they already claimed to hold.
Although a vast time scale is now more generally conceded, Lyell maintains, other habits of mind still continue to retard geology. Of these the most important is a failure to recognize the distorting effect of our viewpoint as subaerial terrestrial beings. This causes us to underestimate the magnitude of submarine and subterranean geological processes. An intelligent aquatic being and a "gnome" confined to subterranean regions would form very different but equally distorted views on geology. Geologists must therefore at least make "an effort both of the reason and the imagination" to allow for the effects of this limitation (p. 81). As with regard to time, here too it is a conversion of the imagination that is needed, if geologists are to gain a true perspective on the problems of earth history. But this argument has a further significance for Lyell. He suggests that it is our naturally biased viewpoint which has led to an overemphasis on the destructive or "wasting" aspects of geological processes and to a corresponding underemphasis on the renovating or formative aspects. By deliberately seeking to correct this natural bias, Lyell can argue that the destructive and formative agencies are in fact in balance. He can thereby maintain that the earth as a whole remains in a steady-state condition. This whole discussion illustrates clearly how Lyell's approach, far from being simply empiricist, embodies a more sophisticated understanding of the role of interpretation in geology than that of many of his contemporaries (Rudwick 1977; Gould 1987, chap. 4).
After some further scathing remarks about those who consider themselves "at liberty to disregard all modern analogy," he leaves what he terms rhetorically the "exploded errors" of the catastrophists, and opens his attack on the "weightier objections" of the directionalists (p. 91). This attack (chaps. 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 steady-state and a directionalist view of earth history. 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 his readers are first prepared to believe that directionalism involves highly uncertain inferences from the available evidence will they give a fair hearing to his alternative interpretation.
Two areas of evidence were widely held to favor a directionalist model of earth history, and Lyell criticizes each in turn. The first is the evidence of directional climatic change in the past history of the earth. In particular, the fossils of the Secondary strata  of Europe were considered to be most closely analogous to the animals and plants now living in tropical regions. This seemed good evidence in support of Leibniz's and Buffon's earlier theory of the gradual cooling of the earth. This had recently been revived in popularity under the scientific authority of Joseph Fourier's work on heat flow and Louis Cordier's calculations from the geothermal gradient; it also seemed to fit well with the "nebular hypothesis" of the origin of the solar system (Rudwick 1971; Lawrence 1977; Brush 1987). lf the earth had had a hot or incandescent origin and had been losing heat continuously by radiation, the climate in any given latitude should show evidence of directional change.
Lyell admitted that his theoretical preconceptions had led him initially to doubt the validity of this evidence, but he claimed that his own experience had forced him to accept it. To the Scottish naturalist John Fleming -- who was perhaps even 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" (Lyell 1881, vol. 1, p. 260). Indeed it was on his own travels that he had found what he believed to be a "crucial experiment" proving the reality of climatic change (chap. 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. Lyell explains, however, that the geologically young strata he had explored in Sicily contain mollusks of extant species which are consistently larger than their living representatives, and he claims this as conclusive evidence that the climate was 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 does not lead Lyell to accept the usual directionalist interpretation of that evidence. A gradually decreasing temperature in Europe during the Tertiary period has somehow to be "reconciled with the existing order of nature," or in other words with the "absolute uniformity" of a steady-state interpretation of earth history (p. 104). This reconciliation is effected by means of what, in a letter to the Sussex geologist Gideon Mantell, he had called "my grand new theory of climate" (Lyell 1881, vol. 1, p. 262). This is a hypothesis of continual climatic 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 (chap. VII). Drawing on published accounts of the physical geography of many different regions, especially on recent explorations of the polar regions, and applying Alexander Humboldt's concept of isothermal lines, he argues that local climate is not a simple function of latitude. It is also 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." Hence, if -- as he would argue later in the work -- there has been a round of ceaseless change in the distribution of land and sea, "there must be a never ending fluctuation in the mean temperature in every zone" (p. 111).
More specifically, Lyell conjectures that major changes in the distribution of continents and oceans could have been such as to generate a global climatic cycle of vast duration. Reviving a notion that goes back to Antiquity, he suggests that the global climate might oscillate between what he terms metaphorically the "winter" and "summer" of the "great year." This highly speculative notion neatly allows him to accept the evidence for a general cooling trend through out the clearly recorded periods of earth history (extending at this time from the Carboniferous to the present), but to interpret it not as a once-for-all directional cooling from a primitively hot globe, but as just one part of an immensely long cycle that could well be reversed and repeated in the future. This leads him to a claim that was as startling to his contemporaries as it may be to modern readers. Given the cyclicity that he postulates, Lyell conjectures that "the huge iguanodon might [in future] reappear in the [English] woods, and the ichthyosaur in the sea, while the pterodactyle might flit again through umbrageous groves of tree ferns" (p. 123). No passage shows more clearly how Lyell intended his system to be not merely steady-state, but -- if the evidence demanded it -- vastly cyclic (Ospovat 1977; Gould 1987). 
This climatic hypothesis is next tested against the actual evidence of past climatic change (chap. VIII). Lyell takes the tropical aspect of the Carboniferous period as an example, and argues, like the Parisian paleobotanist Adolphe Brongniart, that the strata and their fossils indicate a predominately 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 that there is no reason to attribute it to a greater degree of "central heat." Having thus rejected the directionalist interpretation of climatic change, Lyell then attacks the allegedly sudden (that is, catastrophist) nature of the successive changes. He argues that, as in other phenomena, the appearance of sudden change merely reflects the incompleteness of our evidence. If all the successive stages were preserved, the changes would be seen to have been gradual. Lyell concludes that the evidence of climatic change does not support the theory of a directional cooling of the globe; instead it supports his own theory of continual fluctuation around a mean. He suggests that while his theory needs further refinement, it is "more consistent with philosophical caution" to adopt a steady-state explanation as a working hypothesis, rather than a theory of directional change (p. 142). Once again, to be Lyellian is to be scientific.
Having explained away the climatic evidence, Lyell turns to a brief attack on the other main directionalist argument, that of "progress" in organic life (chap. IX). That he deals with this organic aspect only after an extended critique of the inorganic (i.e., climatic) aspect should serve to emphasize that the directionalist system he is attacking was not a purely biological theory: "progressive" biological changes (i.e., the appearance of successively "higher" forms of life) were regarded as having occurred in step with similarly directional changes in the inorganic environment. Once again he correlates the establishment of a steady-state interpretation with the actualistic belief that past events were "governed by the laws now in operation" (p. 144). Since no well-defined faunal succession was known in 1830 for periods before the Carboniferous, Lyell has no great difficulty in arguing here that the apparent progress in the rank of organic life is an illusion, owing simply to the differentially selective preservation of terrestrial and aquatic animals. Thus he argues, for example, that mammalian remains are absent in earlier strata, not because mammals had not yet come into existence, but because most of them are terrestrial and therefore unlikely to be preserved in sediments that are predominately marine in origin.
On the other hand, Lyell does not apply the same reasoning to man himself. Man is the great exception. Lyell accepts at its face value the positive evidence that man appeared on the earth in geologically recent times. But he argues that this is no evidence for "a progressive system" (p. 155). Lyell maintains this inconsistent position because he makes a sharp separation between man's physical and mental characteristics: man's evident superiority is due to his power of reason, particularly his power of improvable reason, which is precisely the feature that distinguishes him clearly from other animals. Hence on the physical level his appearance denotes no special progress in the organic world -- man is just another mammalian species -- while on the "moral" level his appearance is a phenomenon of an entirely different kind (pp. 156, 163). All the same, Lyell has to admit that man's rational powers do in fact 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 that any animal species with new habits might have produced in the past.
Present Inorganic Processes
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 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, operating at 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. This reflects the general recognition, which had emerged from the inconclusive earlier debate between Neptunists and Vulcanists, that both classes of process are in fact important. Unlike Hutton, however, Lyell emphasizes that both aqueous and igneous processes "are instruments of decay as well as reproduction" (p. 167). 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: its action in erosion (chaps. XXII) and in deposition (chaps. XIII-XIV). His consideration of marine currents and tides is similarly divided into a section on their power of erosion (chaps. XV-XVI) followed by one on their power of deposition (chap. XVII).
These chapters need not be analyzed in detail. Like the rest of the Principles they show impressive power in the marshaling of evidence from many published sources, particularly from the massive catalogue (1822-24) of the effects of "modern causes" compiled by the Gotha geologist (and diplomat) Karl von Hoff, as well as from 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 magnitude of 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 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, 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 vulcanism (chaps. 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 Mediterranean world throughout recorded history, in spite of sporadic eruptions. This demonstrates how, even within this geologically short span of time, false conclusions about the past inevitably result from telescoping events that were in fact far apart in date. Lyell also shows how the most recent eruptions have been no different in kind or scale from the most ancient; no dividing line can be drawn there between past and present. This point is stressed particularly in his description of the volcanoes of the Canary Islands, in order to refute the influential "elevation crater" theory of the great Prussian geologist Leopold von Buch; Lyell argues that here too there is no evidence of any former processes different in kind or even in degree from those that have been observed in operation.
The description of earthquakes and their effects (chaps. 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, backward 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 these ruined columns, which halfway up are full of the borings of marine organisms, demonstrate elegantly that the land at this point has undoubtedly suffered both depression and later elevation since classical times. Lyell's choice of a picture of the Temple of Serapis as the frontispiece for the first volume undoubtedly surprised his readers, who expected books on geology to have as their visual summary some landscape or picture of strata, not an antiquarian monument. But in fact Lyell's choice was highly appropriate. The Temple of Serapis epitomizes perfectly his argument that ceaseless nondirectional fluctuations of physical geography have been going on even in historic times, caused not only by superficial aqueous processes but also by deep-seated 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 are exceptionally careful historic records available to support it. He is unable to accept the fact of elevation, despite its impeccable actualism and extreme gradualism, because it cannot be reconciled with his own (more catastrophic!) theory of elevation by earthquakes (pp. 227-32). 
Lyell includes these tectonic phenomena of elevation and depression, along 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, Lyell suggests, is supported by the close spatial connection between volcanic and seismic areas, and it 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 range of hills. It is at this point that Lyell's emphasis on the connection between earthquakes and the elevation or depression of land emerges overtly as an essential part of his strategy. If he can persuade his readers 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 sufficient to explain the elevation of even the greatest mountain ranges, thereby eliminating the need to postulate more intense or sudden earth movements in the past.
Lyell concludes his review of these processes by claiming that "the renovating as well as the destroying causes are unceasingly at work, the repair of the land being as constant as its decay" (p. 473). He senses, however, that there is a possible flaw in this system of perfectly balanced 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 -- unlike earthquakes, which both elevate and depress -- 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 therefore obliged to argue, in an unusually tortuous 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. In a passage that recalls the more explicit providentialism of Hutton, he claims that the humanly 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 terrestrial as well as aquatic species." Above all other processes, it is "essential to the stability of the system" (p. 479).
The argument of the whole volume is summarized by that concluding phrase. Lyell has now interpreted the 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 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.
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 impact 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 the first half of the projected second volume, in order to avoid the delay which the completion of the later sections -- which became the third volume -- would involve (Lyell 1881, vol. 1, p. 355). 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." The argument of the second volume can only be understood fully in the light of the third and final volume.
Lyell opens his argument by claiming that 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 level of species. As with inorganic processes, large-scale features are to be understood in terms of the summation of small-scale events. Therefore, the first topic to be discussed is the objective reality of the species as a basic unit of biological description (chaps. I-IV). It was just this reality that was increasingly in doubt as a result of the growing influence -- especially but not only among French naturalists -- of Lamarck's earlier theory of transmutation (Corsi 1978). Lyell therefore feels bound to discuss Lamarck's theory at length in the Principles. His private reason for opposing transmutation -- his concern that it threatens the "dignity of man" -- is unacknowledged; as always with Lyell, the private realm remains very private indeed (porter 1982). His explicit reason is strictly scientific: he points out that the acceptance of Lamarckian transmutation would have even more profoundly unsettling implications for the work of geologists than it would for biologists. The latter, studying organisms only at one point in geological time, can always proceed for taxonomic purposes as if the species they describe have permanent reality. But if all organic forms are in a state of flux, geologists cannot be certain what they are describing.
Lyell admits that Lamarck's theory has had the attraction of avoiding "the repeated intervention of a First Cause," i.e., an act of creation by divine agency, for every new species (p. 18). But he throws serious doubt on its validity. Lamarck's views on the vast scale of geological time would have been highly attractive to Lyell, but on the question of transmutation it was Lamarck's opponent Cuvier whom Lyell chose 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 by the crucial evidence of the mummified animals found in Egypt. So Lyell, whatever his private reasons for opposing Lamarck, can claim openly that he is bound by his methodology to reject it. He concludes, like Cuvier, that if no transmutation can be seen to have occurred during the largest available time span of recorded human history, there is no warrant for 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," each being adapted permanently to a particular mode of life (p. 65). The units described by the paleontologist in studying the faunas. and floras of ancient strata are therefore not figments of the imagination.
Having established that species are natural units, Lyell turns next to the question of their present geographical distribution and the processes that may account for it (chaps. 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 (Browne 1983). 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 of 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 respect). He emphasizes that even the most improbable or rarely occurring 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 (chaps. VIII-Xl). 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. He deals only briefly with the question of the origin of species, proposing a bare working hypothesis for the circumstances under 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, that species are monogenetic), conditions at that point being suitable for it to exist and 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" (p. 126).
In this discussion Lyell, like his contemporaries, uses the language of "creation" freely and even casually. He later said he had left it to be inferred that he believed in the origin of species by some unknown but natural or "secondary" cause (Lyell 1881, vol. I, p. 467). But he would not have regarded that as incompatible with his highly providentialist sense that new species have always appeared at adaptively appropriate points in space and time. In fact, however, Lyell can afford to express himself vaguely on this vexed question, because the precise mode of origin of species is peripheral to his main geological argument. What matters to him 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.
The origin of species is introduced at this stage, however, only to open 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. 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" (p. 169). 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 competition from other species better adapted to the new conditions, long before it could be transmuted by the imperceptibly slow process that Lamarck had postulated.
If the successive extinction of species is thus "part of the constant and regular course of nature," it is necessary to consider next "whether there are any means provided for the repair of those losses" (p. 179). If Lyell is to show that the organic world, like the inorganic, is part of an overall steady-state system, he 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" (p. 179). He overcomes this difficulty by 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, then, Lyell has to admit that the method of actualism fails and must indeed be inverted. The present must here be interpreted in 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, his argument implies that species production is a relatively sudden event. But this is no more substantial a concession to catastrophism than is his use of sudden earthquakes as the agent of elevation. In both cases large results (the appearance of a new fauna; the elevation of a mountain range) are produced by the summation of piecemeal occurrences of small-scale events, spread over a long period of time.
In spite of this weak evidence on the origin of species, the reader is left in no doubt about Lyell's broader views. 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 longer or shorter period of time, 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. The production and extinction of species are thus processes that are as ceaselessly in operation, and as perpetually in balance, as the inorganic processes of deposition and erosion, elevation and depression. The organic world, like the inorganic, is part of a stable system.
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 (chap. 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, and not, as Sedgwick had recently suggested, by the organic processes of soil formation. Soil is indeed 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.
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 (chaps. 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 that 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 (chaps. XIII-XIV). He throws doubt on the alleged occurrences of fossil man, questioning -- like Cuvier and Buckland before him--the contemporaneity of man and the large extinct mammals (Grayson 1983). But he also criticizes the assumption of Buckland and others that a single catastrophic "diluvial" episode might have been responsible for a variety of alluvial and cave deposits. He next considers the preservation of terrestrial organisms in the much more widespread deposits of lakes and seas (chaps. XV, XVI). Here he emphasizes the "accidental and partial" circumstances which determine whether or not a particular terrestrial species is preserved. He points out that in consequence fossil assemblages of terrestrial organisms can never be reliable indicators of the real specific diversity that existed at earlier periods in earth history. This conclusion is explicitly produced to refute 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 genuinely recent origin of the human species.) Third, Lyell turns to the chances of preservation of aquatic species in lacustrine and marine deposits (chap. XVII). In 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 (chap. XVIII). Lyell interprets the sub-circular form of coral atolls as a reflection of their foundation on the rims of submerged volcanic craters.  He 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. He also argues against the directionalist belief that because limestones are more abundant in later than in earlier strata, there must have been a progressive increase in the abundance of lime-secreting organisms.
The argument of the work is suspended abruptly at this point, owing to Lyell's decision to publish this much before completing the remainder. As a result, the second volume is left incongruously with a frontispiece and a map having no relevance to the contents of the volume as published (p. 304). They were intended to epitomize the argument of what appeared a year later as the third volume.
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, and -- between the lines -- defending the originality of his conclusions. An introductory section (chap. I) then reiterates the main features of his methodology, in answer to the criticisms that had been made since the publication of the first volume. As he wrote privately at the time, "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 contra-distinguished from them, and I must put on all my armour" CLYelll881, vol. 1, p. 376). The Pauline imagery, with its overtones of cosmic conflict, reflects Lyell's view of his work as an almost ideological crusade. He claims that the catastrophist belief in a discordance between present and past processes seriously inhibits discovery: "Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity." With a fine rhetorical twist, 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" (pp. 2-3). These, Lyell asserts, are "two distinct methods of theorizing," and he again uses a 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, the decipherment of the past history of the earth (p. 7).
The first major section (chaps. II-IV) is therefore devoted to what might be termed -- by an extension of Lyell's metaphor -- the syntax of geology; namely, the ways 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 the same age, but represent many different parts of the "Tertiary epoch," and he hints that when the strata in areas of active volcanism and seismicity are taken into account "the line of demarcation between the actual [i.e., present] period and that immediately antecedent, is quite evanescent" (p. 22). This foreshadows his deliberate use of the Tertiary epoch as the chief testing ground for his steady-state system.
The validity of this test, however, depends on establishing that the Tertiary epoch is in fact representative of past geological time. In particular, Lyell has to explain away the apparent contrast between the widespread and rather uniform Secondary strata and the more localized distribution of the Tertiary strata. He interprets this as 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 Tertiary epoch.
He deals next with the apparently abrupt junctions 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 folding map, left incongruously in vol. 2, which shows how large a proportion of Europe was within such areas at one time or another during the Tertiary epoch). 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" on the nature of the fossil record (p. 31). The sequence of strata in 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. As so often, Lyell uses a familiar analogy from contemporary human affairs -- in this case the periodic censuses that had been instituted in Britain at the beginning of the century -- to clarify his geological concepts (Rudwick 1977). 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 complete record "is not the plan of Nature" (p. 34). The geological record is inherently and necessarily fragmentary.
This leads to an analysis of the criteria by which the relative ages of strata, and hence of events in earth history, can 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 marine fossils 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 (chap. 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 extensive. But they are also selected because their species seem to have had much longer durations 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, which will indicate not merely the relative order of strata but also their absolute ages, although only approximately and not in years (Rudwick 1978). The working of this chronometer depends crucially on his belief (set out in the second volume) 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 show a statistical tendency to change continuously and uniformly. Hence it should be possible to estimate quantitatively the 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. Since a few extant species of marine mollusks can be found even in the earliest Tertiary strata, Lyell argues that the average duration of molluscan species is so great that they can be used to construct a chronometer for the whole of the Tertiary epoch.
Lyell does not discuss his method of reconstruction explicitly in terms of a geological chronometer, probably because that metaphor had figured so prominently in the earlier work of catastrophists such as the Swiss natural philosopher Jean-Andre Deluc, with whom Lyell would not have wished to associate himself. In this preliminary section he merely stresses the importance of accurate determinations of the species units of fossil faunas, and explains the value of the expert specific identifications that had been made for him by the Parisian conchologist Gerard Paul Deshayes.  The idea of using these faunal lists for a quantitative measure of the ages of Tertiary strata emerges more clearly in his summary of the divisions he adopts for that epoch: Pliocene, Miocene, and Eocene. These Greek-based names, which had been suggested to him by Whewell, are designed to embody the statistical principle: they refer respectively to the "major," "minor," and "dawn" components of "recent" species in the respective faunas. In fact, Lyell splits the Pliocene in two, and so defines four "periods," based on the percentage of extant species in a total fauna. In order backward 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%). Lyell emphasizes that these periods 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 in time unrepresented by any known strata, and Lyell stresses that formations of intermediate character and age, which will blur the distinctness of his four periods, are therefore likely to be discovered in the future.
Superficially, this roughly quantitative treatment of fossils as indicators of geological age seems little different from the more conventional qualitative use of "characteristic fossils." (The three plates of fossils characteristic of the Pliocene, Miocene, and Eocene are purely illustrative, and were in any case designed by Deshayes, not by Lyell himself.) But as already suggested, there is a profound difference between them. This becomes clear in one brief passage in this section (p. 58). Lyell 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 world. But the assemblage can still be recognized as Eocene in date if it contains a very low percentage of extant species. For the same "machinery" of a uniform rate of organic change will have affected both regions equally, although working on different species; the same 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 -- though certainly not the only 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 steady-state earth history 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.
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 backward 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" (p. 62). Within 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 Tertiary epoch.
The first section, devoted to the Newer Pliocene, is also by far the longest (chaps. 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 Principles because they 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 -- specifically, a "diluvial" episode -- has occurred in the recent past.
Lyell first describes the Newer Pliocene marine strata he had studied in Sicily (chap. VI). He 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 quite recent strata underlie the huge volcanic cone of Etna (chap. VII). He goes on to analyze in detail the structure of Etna itself. Lyell argues that it does not support von Buch's elevation-crater theory of a sudden paroxysmal elevation, but that it has been built up extremely gradually by the successive extrusion of lava flows, just like those that have been observed during historic times (chap. VIII). He then attempts to estimate, very roughly, the age 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" (p. 101).
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 (Rudwick 1969). He prudently avoids hazarding in print any figures for this calibration, for it could be only slightly better than a guess.  But in any case he makes 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 the second volume, which was originally intended to be the final volume of the work (the picture was published incongruously in the truncated second volume).
This does not exhaust the significance of Etna, however. On the 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, the elevation of the Newer Pliocene strata in central 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 (chap. 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 in principle explicable in similar terms. The gradual elevation of the Sicilian 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 supposed contrast 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 crystalline 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 (chap. X), Lyell continues the same argument. He criticizes 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 indicated by his theory of elevation.
Lyell then discusses the nonmarine deposits of Newer Pliocene age (chap. XI). He criticizes particularly the idea of a single "alluvial epoch" (which had been closely associated with the notion of a "diluvial" episode), pointing out that "alluvial" deposits such as coarse gravels have been formed at many periods. The huge "erratic blocks" of the Alps and elsewhere -- rocks often left perched on hilltops tens or hundreds of miles from their sources -- were more difficult for him to explain.  Lyell rejects any suggestion that they might have been transported by a vast tidal wave actuated by the sudden elevation of a mountain range in another part of the globe. He can ascribe those scattered over northern Europe to the actualistic agency of floating marine icebergs; indeed this can be integrated neatly with his climatic theory and his concept of ever-shifting areas of marine deposition. But for the erratics spread over the low ground around the Alps, and even up on to the slopes of the Jura hills beyond the Swiss plain, he has to resort to a rather awkward conjecture: he suggests that they were transported by freshwater icebergs that were suddenly (and catastrophically!) released by the collapse of barriers damming temporary Alpine lakes.
The Older Pliocene period is analyzed more briefly (chaps. XII-XIV). Lyell's description of the celebrated Sub-Apennine strata in Italy, and of the English strata to which he attributes the same age, needs no special comment. To illustrate the volcanic activity of the period, he places here the extinct but well-preserved 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 (chaps. XV, XVI). Lyell describes various marine, freshwater, and volcanic rocks which he attributes to this period. Recalling the arbitrary character of his periods and the implicit temporal gaps between them, he suggests that certain deposits (at Montpellier, in the south of France) may be of an age intermediate between the Miocene and the Older Pliocene: "We are fully prepared for the discovery of such intermediate links" (p. 216).
Lyell's analysis of the Eocene period (chaps. XVII-XX) reverses the usual order of topics by describing the freshwater deposits of central France (chap. XVl1) before discussing the better-known formations -- many of them marine -- in the Paris basin (chap. XVIII). This enables him 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 changes to physical geography and consequently to terrestrial faunas: at this point Lyell was up against one of the strongholds of catastrophism. He therefore argues that the exclusively freshwater deposits to central France show that no marine incursions ever penetrated to that area during Eocene time. He is then able to use Prevost's recent critique of Cuvier's interpretation to 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 of sea level. This reinterpretation, as 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" (p. 248). Moreover, in view of the very high proportion (97%) of extinct species among the marine mollusks to 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 vertebrate faunas than in molluscan faunas. Summarizing this 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" (p. 255).
Under the heading of Eocene volcanic rocks, Lyell next discusses the celebrated volcanic areas of central France (chap. XIX), drawing freely on the great memoir (1827) by the English geologist (and political economist) George Scrope, which Lyell had earlier reviewed and then followed in the field (Rudwick 1974). He stresses particularly the classic evidence that the volcanic eruptions had been of many different dates; but he assigns a very early age, namely Miocene, even to the most recent eruptions. He argues that the extremely fresh appearance of some of the volcanic cones -- as perfectly preserved as the minor cones he had seen on the slopes of Etna, dating from the past few centuries -- 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. This is the more necessary because of Sedgwick's recent support for the neodiluvial catastrophism of the leading Parisian geologist Leonce Elie de Beaumont. By arguing, however implausibly, for the great geological age of even the youngest volcanic cones in central France, Lyell is able to deny once more 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 (as already mentioned) for the frontispiece of the third volume. 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 recorded in terms entirely different in character from the violent diluvial episode postulated by his scientific opponents.
A straightforward description of the Eocene strata in England (chap. XX) leads to a long digression on the mode of elevation and erosion of the Weald area in southern England, which separates the main areas of Eocene strata (chaps. XXI, XXII). The purpose of this digression is again to combat recent catastrophist interpretations of the area, notably by Buckland. Lyell 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 Tertiary strata in adjacent areas (the London and Hampshire basins).
This concludes Lyell's actualistic and steady-state interpretation of Tertiary earth history. His analysis of Secondary strata (chap. XXIII) is very brief. This is certainly not because in 1833 they were less well known than the Tertiary: on the contrary, they were much better known. Nor is it primarily because an equally lengthy treatment of Secondary periods would have required yet another volume. The main reason for his brevity is strategic. Having demonstrated the adequacy of present processes at their present level of intensity for the interpretation for Tertiary time, it is sufficient for the purpose of his overall strategy to treat the Secondary periods summarily, merely "to show that the rules of interpretation adopted by us for the tertiary formations, are equally applicable to the phenomena of the secondary series" (p. 324).
On Deshayes's authority he accepts the magnitude of the faunal discontinuity between the Eocene strata and even the uppermost strata of the underlying Chalk series (those at Maastricht in the Netherlands), 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. He suggests that it might represent a period of time even greater than that which separates the earliest Eocene deposits from the present day. This inference, however startling to modern eyes, shows the consistency with which Lyell is prepared to apply the principle of a uniform rate of change in the organic world, and the geological chronometer founded upon it. On that 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 100% turnover in species, it must represent an even longer period.
For the Secondary strata in general Lyell 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. 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 (for example, the Chalk) should maintain a uniform character over very wide areas, in striking 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 represent conditions or processes different from those of Tertiary time. The stability of the "system" was thus maintained in Secondary earth history as much as in the subsequent Tertiary.
Before proceeding to the Primary rocks, and the conclusion of the Whole work, Lyell digresses to argue against Elie de Beaumont's recent theory of the paroxysmal elevations of mountain ranges (chap. XXIV). 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 any given episode of elevation depends on proving the brevity of the time interval separating the youngest strata affected by the movement 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 [Elie] de Beaumont are correct, his intervals are of indefinite extent" (p. 344).
Having disposed of this most recent -- and most strictly scientific -- challenge to his concept of uniformity, Lyell turns finally to the Primary rocks (chaps. XXV; XXVl), which most of his contemporaries took to be the oldest in the earth's crust. He immediately criticizes the term, claiming that it includes rocks of many different ages, 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" (p. 357). 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 volcanism and elevation. Lyell claims that the so-called Trap rocks, which were generally agreed to be intrusive rocks associated with ancient volcanic activity, are likewise not confined to earlier periods, for they are found among even the Newer Pliocene strata.
The "stratified Primary" 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 be resolved, Lyell argues, only by adopting "the Huttonian hypothesis" of what he terms metamorphism. Schist and gneiss are sediments that have been altered by heat in the proximity of molten granite, in a process analogous to small-scale laboratory experiments and to the larger natural experiments of contact metamorphism near igneous dikes.
Lyell therefore proposes that the stratified Primary rocks should be renamed Metamorphic. For the unstratified Primary 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 terminological proposals are far from trivial. They are introduced to stress Lyell's contention that all the rock types commonly regarded as characteristic of, or even confined to, the earliest periods of earth history can in fact be formed in any period, including the present. The so-called Primary is therefore not primary at all.
This conclusion is illustrated in the table and diagram that immediately follow this final chapter (pp. 386-88). 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. The table, and the diagram that complements it visually, epitomize neatly the steady-state system that emerges from the whole work. All categories of rock, and therefore all causal processes, have existed uniformly in all periods of earth history. Those periods are only carried back as far as the Carboniferous, but in 1833 that was still the earliest period 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 (p. 393)  With the assimilation of the Transition strata into the Secondary period, and the reinterpretation of all the so-called Primary strata as either igneous or metamorphic, the chronicle of earth history is thus left -- as Hutton had famously expressed it -- without vestige of a beginning.
In his "concluding remarks," Lyell acknowledges the Huttonian affinities of his system, but defends himself against the charge of advocating an eternalistic -- and therefore potentially atheistic -- view of the natural world. He protests that this is as unfair to him as it was to Hutton before him. Using the conventional analogy between space in astronomy and time in geology, he stresses that his apparent eternalism merely expresses the intrinsic limits of human knowledge. We must be prepared to find that, as in exploring space, so "in time also, the confines of the universe lie beyond the reach of mortal ken" (p. 393). Echoing Hutton once more, he claims that the stable system of the earth that his interpretation of geology has disclosed 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" (p. 385). Far from being a merely formal or conventional expression of minimal religious sentiment, this is but the culminating example of the deistic and providentialist language with which the Principles is suffused throughout. Lyell was certainly no orthodox Christian; but nor was he the atheistic or antireligious figure that he has sometimes been made out to be in subsequent myth making.
It is appropriate that Lyell's vast extended argument should conclude with an unmistakably Huttonian echo. It was clearly 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 balance and interact to produce a perpetual dynamic stability.
THE LEGACY OF THE PRINCIPLES
In the foregoing analysis of the Principles -- and even more in the text and footnotes of the volumes themselves -- the references to the work of other geologists should make it clear that Lyell's book was not launched into a vacuum of geological theory and practice. It was intended by Lyell, and perceived by others, as a contribution to an already lively debate. By pressing some interpretative principles of the science to their limit, however, and by proposing a radically unorthodox view of the whole shape of earth history, the Principles certainly sharpened that debate and made its terms more explicit.
The process of public dialogue between Lyell and other geologists began with the early reviews of the first volume (1830), and Lyell's response began to become explicit when the third volume was published (1833). By that time the first two volumes were already in a second edition. The next edition of the whole work, which appeared in 1834, was therefore termed the third; the fourth was published in 1835 and the fifth in 1837. The rapid succession bear witness both to the success of the work and to Lyell's rapid uptake of the latest research, by himself and others, in the service of his overall vision of geology. However, the steady-state system that had held the work together found few if any wholehearted adherents. This is reflected in Lyell's decision, in the later 1830s, to separate the work into two distinct parts. Reverting to the popular format that he had initially planned for the Principles, he recast the contents of the original third volume as the Elements of Geology (1838), which summarized the reconstruction of earth history in an introductory fashion. The next (sixth) edition of the Principles (1840) was correspondingly truncated, and confined to setting out Lyell's analysis of "causes now in operation." Both works continued their separate publishing careers, with much updating, to the end of Lyell's life (he died in 1875).
The debate between Lyell and his critics, which was particularly lively in the early years, was never sharply polarized into factions or parties: there was no clear-cut controversy between "catastrophists" and "uniformitarians," if only because those terms meant so many different things to different people. Geologists responded to Lyell's work in many different ways: adopting some points, rejecting others; being persuaded by some of Lyell's arguments and remaining unconvinced by others. In particular, as already mentioned, Lyell's steady-state system never found any significant sup porters (Bartholomew 1976, 1979). In this respect it was unquestionably Lyell's directionalist opponents who were the more successful in swaying geological opinion. It was their developmental vision of earth history that, later in the century, assimilated an evolutionary conception of the history of life -- as Lyell had perceptively anticipated, and feared. 
On the other hand, Lyell's persuasive reinterpretation of geological evidence, in terms of "causes now in operation" operating over humanly unimaginable spans of time, did gradually affect, and indeed transform, the practice of geology during the decade or two that followed the first edition.  The sheer scope of Lyell's vision, and the immense range of the "worked examples" that he offered, were in the end profoundly influential. The heuristic value of seeking whenever possible for actualistic and noncatastrophist explanations has been a fundamental and taken-for-granted principle of the earth sciences ever since. In recent years, however, some geologists have come to recognize once more what Lyell's original critics saw very clearly: namely, that it may at times be both necessary and legitimate to invoke causal processes more intense than those we can observe, or even those of kinds that we have never observed, if the evidence warrants it. But even for neo-catastrophists, as for their nineteenth-century forerunners, the Lyellian approach remains a salutary brake on undisciplined speculation. Charles Lyell, and his Principles, remain forces to be reckoned with.
-- Martin J. S. Rudwick
1. This introduction is adapted, by permission of the History of Science Society, from my article "The Strategy of Lyell's Principles of Geology" (1970); but it has been substantially revised to take account of subsequent research, particularly of the papers given at the Charles Lyell Centenary Symposiun in London in 1975 (published in British Journal of the History of Science, vol. 9, no 2, 1976). This revision was supported by the National Science Foundation under grant no. SE8-88-96206.
2. The first volume (1972) of Wilson's biography is a valuable source of factual information. His broader interpretation of Lyell's significance for the history of science is more fully expressed in a later article (1980). The differences between Wilson's interpretation of the Principles and that put forward in this Introduction are too far-reaching to be discussed here.
3. Anyway his proposed title Conversations on Geology was preempted by an anonymous work (1828) of just the kind he wanted to combat, which gave what would now be termed "equal time" to the scientifically worthless "Scriptural" geologists of the day.
4. Lyell added a glossary of scientific terms to the third volume (Appendices, 61-83) at the request of some of his nongeological readers. It can well serve the same function for modern readers, including those who are geologists, because many of Lyell's technical terms are now obsolete or have changed their meaning.
5. Lyell's extensive field trips on the Continent in 1830, 1831, and 1832 -- the last being combined with his honeymoon!-were also in time to benefit the first edition of the Principles, but did not have such a profound impact on him.
6. The singular in the printed text is either a misreading of the manuscript or an inadvertent slip of Lyell's pen: the plural used in the rest of the sentence makes the sense clear.
7. So called because they claimed the literal scientific accuracy of Genesis, one of the Old Testament books traditionally attributed to Moses himself.
8. "Secondary" was roughly equivalent to the Mesozoic and Upper Paleozoic formations of modern geologists. In terms of the formations in Europe that formed the reference series for all geologists in the 1830s, it extended from the Chalk (in modern terms, Cretaceous) at the top down through the Old Red Sandstone (in modern terms, Devonian) at the bottom.
9. Lyell's contemporaries fully realized the implications of the vast cyclicity he was postulating. This is particularly clear from the famous (and in modern times frequently reproduced) lithograph that Henry De la Beche drew and distributed widely among English geologists, in order to ridicule Lyell's ideas on this point. It showed a "Professor Ichthyosaurus" lecturing- in the post-human-future -- on the subject of a (fossilized) human skull (Rudwick 1975).
10. Lyell referred privately to von Hoff's "German plodding perseverance" and claimed that "he helped me not to my scientific view of causes" (Lyell 1881, vol. 1, 268--69). Though bluntly expressed, the comment was justified, because von Hoff had arranged his data in a purely descriptive manner, rather than in terms of their causal origins (Rudwick 1977).
11. The Temple of Serapis continued to act as frontispiece of the Principles throughout Lyell's life; in later editions it was also embossed in gold, like a secular icon, on the front cover of the book.
12. Lyell changed his mind on this point while visiting the area in 1834 (Lyell 1881, vol. 1,436), and made it the subject of his substantial first paper (1835) to the Royal Society in London.
13. This is the point at which Darwin later out-Lyelled Lyell, with his interpretation of coral reefs and atolls as the signs of successive stages in the submersion of a continent (Stoddart 1976)
14. "Tertiary" survives in the vocabulary of modern geologists as an informal synonym for Cenozoic. In the 18308 it was taken to comprise the relatively recent formations above and therefore younger than the Secondary (except the "Recent" deposits assumed to be coeval with man).
15. Deshayes's tables form the empirical basis of Lyell's analysis, and are printed as a long appendix at the end of the volume (Appendices, 1-45), along with faunal lists of Lyell's own collections of Tertiary assemblages, which Deshayes had identified for him (Appendices, 53-60).
16. In private correspondence, and later in his lectures at King's College, London, he estimated the age of the volcano at about sixty thousand to seventy thousand years, and the underlying "Newer Pliocene" strata at about a hundred thousand years (Rudwick 1975a; Tasch 1977). Though modest by modern standards, such figures were humanly vast enough to be highly impressive in the 18308. Implicitly they extended the total length of recorded earth history into many millions of years, if not into tens or hundreds of millions. As mentioned above, Lyell's contemporaries were not averse to such figures, but he was right to think that they had not yet assimilated all the implications of such a vast time scale.
17. Erratics remained one of the most formidable problems for a Lyellian interpretation until the formulation of the glacial theory in the 1840s and later. This theory postulated a geologically recent "Ice Age," during which erratics could have been transported on glaciers and ice sheets vastly extended beyond their present remnants (Rudwick 1970).
18. The Transition or Grauwacke strata, below and therefore older than the Carboniferous as usually defined, included the oldest formations in which any fossils had been found. In 1835, only two years after this volume of the Principles was published, Murchison proposed the term "Silurian" for the younger and relatively fossiliferous Transition strata (Secord 1986; Rudwick 1985). The widespread recognition of the distinctive Silurian fauna first began to erode the plausibility of Lyell's steady-state interpretation of the fossil record.
19. Lyell himself eventually accepted this, but only belatedly and reluctantly, in the tenth edition of the Principles (1867), published after Darwin's Origin of Species (1859).
20. The nature and timing of Lyell's influence outside the English-speaking world is an important topic on which little historical research has yet been done. The Principles and even the Elements were not translated very promptly into either French or German -- the major scientific languages of the early and late nineteenth century respectively -- but of course the impact of his work could have spread in other ways.
Apart from the Victorian edition of Lyell's correspondence, which has been quoted frequently in the above introduction, the following list is confined to modern (secondary) historical works. These in turn contain full references to the nineteenth-century (primary) sources that have been cited. Lyell's own explicit sources are cited in the footnotes to his three volumes.
Bartholomew, Michael, 1973. Lyell and evolution: an account of Lyell's response to the prospect of an evolutionary ancestry for Man. British Journal for the History Of Science, vol. 6, 261-303.
____, 1976. The non-progression of non-progression: two responses to Lyell's doctrine. Ibid., vol. 9, 166-74.
____, 1979. The singularity of Lyell. History of Science, vol. 17, 276-93.
Brush, Stephen G., 1987. The nebular hypothesis and the evolutionary worldview. Ibid., vol. 25, 245- 78.
Cannon, W. Faye, 1976. Charles Lyell, radical actualism, and theory. British Journal for the History Of Science, vol. 9, 104-20.
Corsi, Pietro, 1978. The importance of French transformist ideas for the second volume of Lyell's Principles of Geology. Ibid., vol. 11, 221-44.
Gould, Steven Jay, 1987. Time's Arrow, Time's Cycle (Cambridge, Mass.: Harvard University Press).
Laudan, Rachel, 1982. The role of methodology in Lyell's science. Studies in the History and Philosophy of Science, vol. 13, 215-49.
____, 1987. From Mineralogy to Geology, The Foundations of a Science, 1650-1830 (Chicago and London: University of Chicago Press).
Lawrence, Philip, 1977. Heaven and earth: the relation of the nebular hypothesis to geology. In Wolfgang Yourgrau and Allen D. Breck (eds.), Cosmology, History and Theology (New York: Plenum), 253-81.
Lyell, Mrs. [Katherine) (ed.), 1881. Life Letters and Journals Of Sir Charles Lyell, Bart. (London: John Murray), 2 vols.
McCartney, Paul J., 1976. Charles Lyell and G. B. Brocchi: a study in comparative historiography. British Journal for the History of Science, vol. 9, 175-89.
Morrell, J. B., 1976. London institutions and Lyell's career: 1820-41. Ibid., 132-46.
Ospovat, Alexander M., 1976. The distortion of Werner in Lyell's Principles of Geology. Ibid., 190-98.
Ospovat, Dov, 1977. Lyell's theory of climate. Journal of the History of Biology, vol. 10, 317-39.
Porter, Roy, 1976. Charles Lyell and the principles of the history of geology. British Journal for the History Of Science, vol. 9, 91-103.
____, 1977. The Making of Geology: Earth Science in Britain, 1660-1815 (Cambridge: Cambridge University Press).
____, 1982. Charles Lyell: the public and private faces of science. Janus, vol. 69, 29-50.
Rudwick, Martin J. S., 1969. Lyell on Etna, and the antiquity of the earth. In Cecil J. Schneer (ed.), 1bward a History of Geology (Cambridge, Mass.: M.I.T. Press), 288-304.
____, 1970a. The strategy of Lyell's Principles Of Geology. Isis, vol. 61, 4-33.
____, 1970b. The glacial theory. History of Science, vol. 8, 136-57.
____, 1971. Uniformity and progression: reflections on the structure of geological theory in the age of Lyell. In Duane H. D. Roller (ed.), Perspectives in the History Of Science and Technology (Norman, Okla.: Oklahoma University Press), 209-27.
____,1974. George Poulett Scrope on the volcanoes of Auvergne: Lyellian time and political economy. British Journal for the History of Science, vol. 7, 205-42.
____, 1975a. Charles Lyell F.R.S. (1797-1875) and his London lectures on geology, 1832-33. Notes and Records Of the Royal Society of London, vol. 29, 231-63.
____, 1975b. Caricature as a source for the history of science: De la Beche's anti-Lyellian sketches of 1831. Isis, vol. 66, 534-60.
____, 1976. The emergence of a visual language for geological science, 1760-1840. History of Science, vol. 14, 149-95.
____, 1977. Historical analogies in the early geological work of Charles Lyell. Janus, vol. 84, 89-107.
____, 1978. Charles Lyell's dream of a statistical palaeontology. Palaeontology, vol. 21, 225-44.
____, 1985. The Great Devonian Controversy: The Shaping of Scientific Knowledge among Gentlemanly Specialists (Chicago and London: University of Chicago Press).
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