To reach the specifics of Pozzuoli on a literary journey, we must follow the path of Lyell’s general theory. Lyell, a barrister by original profession, sought to reform the science of geology on both substantive and methodological grounds. He based his system—one might say his brief—on two fundamental propositions. First, the doctrine of gradualism: modern causes, operating entirely within the range of rates now observable, can explain the full spectrum of geological history. Apparently grandiose or catastrophic events truly arise by a summation of small changes through the immensity of geological time—the deep canyon carved grain by grain, the high mountain raised in numerous increments of earthquake and eruption over millions of years.
Second, the claim for a nondirectional or steady-state earth. Standard geological causes (erosion, deposition, uplift, and so on) show no trend either to increase or decrease in general intensity through time. Moreover, even the physical state of the earth (relative temperatures, positions of climatic belts, percentages of land and sea) tends to remain roughly the same, or to cycle around and around, through time. Change never slows or ceases; mountains rise and erode; seas move in and out. But the average state of the earth experiences no systematic trend in any sustained direction. Lyell even believed at first, though he changed his mind by the 1850s, when he finally concluded that mammals would not be found in the oldest strata, that the average complexity of life had remained constant. Old species die, and new species originate (by creation or by some unknown natural mechanism). But clams remain clams, and mammals mammals, from the earliest history of life until now.
When a scientist proposes such a comprehensive system, we often gain our best insights into the sources and rationale for his reforms by explicating the alternative worldview of his opponents. New theories rarely enter a previous conceptual void; rather, they arise as putative improvements or replacements for previous conventionalities. In this case, Lyell’s perceived adversaries advocated an approach to geology often labeled either as catastrophism or directionalism (in opposition to Lyell’s two chief tenets of gradualistic change on an earth in steady state).
Catastrophists argued that most geological change occurred in rare episodes of truly global paroxysm, marked by the “usual suspects” of volcanism, mountain building, earthquakes, flooding, and the like. Most catastrophists also held that the frequency and intensity of such episodes had decreased markedly through time, thus contrasting a feisty young earth with a much calmer planet in its current maturity.
For most catastrophists, these two essential postulates flowed logically from a single theory about the earth’s history—the origin of the planet as a molten fireball spun off from the sun (according to the hypothesis, then favored, of Kant and Laplace), followed by progressive cooling. As this cooling proceeded, the outer crust solidified while the molten interior contracted continuously. The resulting instability—caused, almost literally, by an enlarging gap between the solidified crust and the contracting molten interior—eventually induced a sudden global readjustment, as the crust fractured and collapsed upon the contracted molten core. Thus, directionalism based on continuous cooling linked the catastrophism of occasional readjustment by crustal collapse with the hypothesis of a pervasive “arrow of time” leading from a fiery beginning, replete with more frequent and more intense paroxysms, to our current era of relative calm and rarer disruption.
Incidentally, this account of catastrophism as a genuine and interesting scientific alternative to Lyellian uniformity disproves the conventional canard, originally floated as a rhetorical device by Lyell and his partisans, but then incorporated uncritically as the conventional wisdom of the profession. In this Manichaean account, catastrophism represented the last stronghold for enemies of modern science: theologically tainted dogmatists who wanted to preserve both the literal time scale of Genesis and the miraculous hand of God as a prime mover by invoking a doctrine of global paroxysm to compress the grand panoply of geological change into a mere few thousand years. In fact, by the 1830s, all scientists, catastrophists and uniformitarians alike, had accepted the immensity of geological time as a central and proven fact of their emerging profession (see chapter 5). Catastrophists upheld a different theory of change on an equally ancient earth—and their views cannot be judged less “scientific,” or more theologically influenced, than anything touted by Lyell and his school.
The personal, social, and scientific reasons behind Lyell’s chosen commitments represent a complex and fascinating subject well beyond the scope of this essay. But we may at least note the overt strategy, chosen by this master of persuasive rhetoric, this barrister manqué, to promulgate his uniformitarian doctrine as the centerpiece of his textbook, Principles of Geology. In part, he chose the substantive route of arguing that the world, as revealed by geological evidence, just happens to operate by gradual and nondirectional change. But Lyell awarded primacy of place to a methodological claim: only such a uniformitarian approach, he urged, could free the emerging science of geology from previous fetters and fanciful, largely armchair, speculation.
If global paroxysms forge most of history, Lyell argued, then how can we ever develop a workable science of geology—for we have not witnessed such events in the admittedly limited duration of human history, and we can therefore identify no observational basis for empirical study. And if a tumultuous past operated so differently from a calmer present, then how can we use modern processes—the only mechanisms subject to direct observation and experiment, after all—to resolve the past? But on an earth in steady state, built entirely by modern causes acting at current intensities, the present becomes, in an old pedagogical cliché, “the key to the past,” and the earth’s entire history opens to scientific study. Thus, in a famous statement of advocacy, Lyell condemned catastrophism as a doctrine of despair, while labeling his uniformitarian reform as the path to scientific salvation:
Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity, than this assumption of the discordance between the former and the existing causes of change. It produced a state of mind unfavourable in the highest conceivable degree to the candid reception of the evidence of those minute, but incessant mutations, which every part of the earth’s surface is undergoing…. The student, instead of being encouraged with the hope of interpreting the enigmas presented to him in the earth’s structure,—instead of being prompted to undertake laborious inquiries into … causes now in operation, was taught to despond from the first. Geology, it was affirmed, could never rise to the rank of an exact science,—the greater number of phenomena must for ever remain inexplicable….
In our attempt to unravel these difficult questions, we shall adopt a different course, restricting ourselves to the known or possible operations of existing causes…. We shall adhere to this plan … because … history informs us that this method has always put geologists on the road that leads to truth,—suggesting views which, although imperfect at first, have been found capable of improvement, until at last adopted by universal consent. (From the introductory chapter to the third and final volume of Lyell’s Principles, 1833)
Major intellectual struggles cannot be won by success in easy and rudimentary skirmishes. Adversaries must also be outflanked on their home ground, where superior knowledge and forces should have rendered them invincible. A new theory must meet and encompass the hardest and most apparently contradictory cases head-on. Lyell understood this principle and recognized that he would have to bring the Vesuvius of Pliny and Kircher, of Pompeii and Emma Hamilton’s fire, into his uniformitarian camp—not as a prisoner, but as a proud example. No other place or subject receives even half so much attention throughout the three volumes of Principles of Geology.
Lyell centered his uniformitarian case for Naples and Vesuvius upon two procedural themes that embodied all his logical and literary brilliance as geology’s greatest master of argument. He first invoked the cardinal geological principle of appropriate scale by pointing out that a
Vesuvian eruption, while ultimately catastrophic for the baker or blacksmith of Pompeii, not only causes no planetary disruption at its own moment of maximal intensity, but then falls even further into insignificance when several hundred years of subsequent quiescence erase its memory from the populace and erode its products from the landscape.
Why, then, should such a local catastrophe serve as an unquestioned model for extrapolation to sudden global doom? Perhaps we should draw an opposite lesson from the same event: local means local—and just as the canyon deepens grain by grain, so does the mountain chain rise gradually, eruption by eruption over extended time. At most, Vesuvius teaches us that increments of gradualism may be large at human scale—the lava field versus the eroded sand grain— but still small by global standards. In 1830, Lyell summarized a long chapter, “History of the volcanic eruptions in the district around Naples,” by writing:
The vast scale and violence of the volcanic operations in Campania, in the olden time, has been a theme of declamation…. Instead of inferring, from analogy that … each cone rose in succession,—and that many years and often centuries of repose intervened between each eruption—geologists seem to have conjectured that the whole group sprung up from the ground at once, like the soldiers of Cadmus when he sowed the dragon’s teeth.
Moreover, Lyell continued in closing the first volume of his tenth edition (1867), even by purely local standards, natural catastrophes usually impose only a fleeting influence upon history. Most inhabitants view Campania as a land of salubrious tranquillity. As for Vesuvius itself, even the worst natural convulsion cannot match the destructive power of human violence and venality. In a striking literary passage, Lyell reminds us that Vesuvius posed maximal danger to the Roman empire when Spartacus housed the troops of his slave revolt in the volcano’s quiescent crater in 73 B.C., not when lavas and poisonous gases poured out in A.D. 79:
Yet what was the real condition of Campania during those years of dire convulsion? “A climate,” says Forsyth, “where heaven’s breath smells sweet and wooingly—a vigorous and luxuriant nature unparalleled in its productions—a coast which was once the fairy-land of poets, and the favourite retreat of great men.” … The inhabitants, indeed, have enjoyed no immunity from the calamities which are the lot of mankind; but the principal evils which they have suffered must be attributed to moral, not to physical, causes—to disastrous events over which man might have exercised a control, rather than to inevitable catastrophes which result from subterranean agency. When Spartacus encamped his army of ten thousand gladiators in the old extinct crater of Vesuvius, the volcano was more justly a subject of terror to Campania than it has ever been since the rekindling of its fires.
For his second theme, Lyell emphasized the importance of interpreting evidence critically, but not necessarily literally. The geological record, like most archives of human history, features more gaps than documents. (In a famous metaphor, later borrowed by Darwin for a crucial argument in The Origin of Species, Lyell compared the geological record to a book with very few pages preserved, of these pages few lines, of the lines few words, and of the words few letters.) Moreover, the sources of imperfection often operate in a treacherous way because information does not disappear at random, but rather in a strongly biased fashion—thus tempting us to regard some causes as dominant merely because the evidence of their action tends to be preserved, while signs of truly more important factors may differentially disappear from the record.
Lyell recognized that catastrophes usually leave their signatures, for extensive outpourings of lava, or widespread fracturing of strata by earthquakes, resist erasure from the geological record. But the publishers of time often print equally important evidence for gradual change—the few inches of sediment that may accumulate during millions of years in clear calm seas, or the steady erosion of a riverbed grain by grain—upon missing pages of the geological book. This bias not only overemphasizes the role of catastrophes in general, but may also plant the false impression that intensity of geological change has diminished through time—for if the past favors the preservation of catastrophes, while the present yields more balanced data for all modes of change, then a literal and uncritical reading of geological evidence may inspire erroneous inferences about a more tumultuous past.
Lyell summarized this crucial argument about biases of preservation in a brilliant metaphor for Mount Vesuvius. “Suppose,” he writes, “we had discovered two buried cities at the foot of Vesuvius, immediately superimposed upon each other, with a great mass of tuff and lava intervening, just as Portici and Resina, if now covered with ashes, would overlie Herculaneum.” (When Lyell visited the area in 1828, excavations at Herculaneum had proceeded further than those at Pompeii—hence Lyell’s primary citation of a town that now ranks second to Pompeii for memorializing the destructive powers of Vesuvian eruptions.) If we read such a sequence literally, we would have to infer a history built by sudden and catastrophic changes. The remains of an Italian city, littered with modern debris of beer cans and bicycles, would overlie the strata of a Roman town replete with fragments of amphoras and chariots—with only a layer of volcanic rocks between. We would then conclude that a violent catastrophe had triggered a sudden mutation from Latin to Italian, and from chariot wheels to automobile tires (for we would note the genuine relationships while missing all the intermediary stages)—simply because the evidence for nearly two thousand years of gradual transitions failed to enter a historical record strongly biased toward the preservation of catastrophic events.
The frontispiece to Lyell’s Principles of Geology, showing the three pillars of Pozzuoli, with evidence for a substantial rise and fall of sea level in historic times.
A successful campaign for substantial intellectual reform also requires a new and positive symbol or icon, not just a set of arguments (as presented so far) to refute previous interpretations. Vesuvius in flames, the icon of Pliny or Kircher, must be given a counterweight—some Neapolitan image, also a consequence of Vesuvian volcanism, to illustrate the efficacy of modern causes and the extensive results produced by accumulating a series of small and gradual changes through substantial time. Lyell therefore chose the Roman pillars of Pozzuoli— an image that he used as the frontispiece for all editions of Principles of Geology (also as an embossed golden figure on the front cover of later editions). By assuming this status as an introductory image in the most famous geological book ever written, the pillars of Pozzuoli became icon numero uno for the earth sciences. I cannot remember ever encountering a modern textbook that does not discuss Lyell’s interpretation of these three columns, invariably accompanied by a reproduction of Lyell’s original figure, or by an author’s snapshot from his own pilgrimage.
II. RAISING (AND LOWERING) THE COLUMNS OF POZZUOLI
In exchanging the pillars of Pozzuoli for the fires of Vesuvius as a Neapolitan symbol for the essence of geological change, Lyell made a brilliant choice and a legitimate interpretation. The three tall columns—originally interpreted as remains of a temple to Serapis (an Egyptian deity much favored by the Romans as well) but now recognized as the entranceway to a marketplace—had been buried in later sediment and excavated in 1750. The marble columns, some forty feet tall, are “smooth and uninjured to the height of about twelve feet above their pedestals.” Lyell then made his key observation, clearly illustrated in his frontispiece: “Above this is a zone, about nine feet in height, where the marble has been pierced by a species of marine perforating bivalve—Lithodomus.”
From this simple configuration, a wealth of consequences follow—all congenial to Lyell’s uniformitarian view, and all produced by the same geological agents that shaped the previously reigning icon of Vesuvius in flames. The columns, obviously, were built above sea level in the first or second century A.D. But the entire structure then became partially filled by volcanic debris, and subsequently covered by sea water to a height of twenty feet above the bases of the columns. The nine feet of marine clam holes (the same animals th
at, as misnamed “shipworms,” burrow into piers, moorings, and hulls of vessels throughout the world) prove that the columns then stood entirely underwater to this level—for these clams cannot live above the low-tide line, and the Mediterranean Sea experiences little measurable tide in any case. The nine feet of clam borings, underlain by twelve feet of uninjured column, implies that an infill of volcanic sediments had protected the lower parts of the columns—for these clams live only in clear water.
But the bases of the columns now stand at sea level—so this twenty-foot immersion must have been reversed by a subsequent raising of land nearly to the level of original construction. Thus, in a geological moment of fewer than two thousand years, the “temple of Serapis” experienced at least two major movements of the surrounding countryside (without ever toppling the columns)—more than twenty feet down, followed by a rise of comparable magnitude. If such geological activity can mark so short a time, how could anyone deny the efficacy of modern causes to render the full panoply of geological history in the hundreds of millions of years actually available? And how could anyone argue that the earth has now become quiescent, after a more fiery youth, if the mere geological moment of historical time can witness so much mobility? Thus, Lyell presented the three pillars of Pozzuoli as a triumphant icon for both key postulates of his uniformitarian system—the efficacy of modern causes, and the relative constancy of their magnitude through time.
The notion of a geologist touring Naples, but omitting nearby Pozzuoli, makes about as much sense as a tale of a pilgrim to Mecca who visited the casbah but skipped the Kaaba. Now I admire Lyell enormously as a great thinker and writer, but I have never been a partisan of his uniformitarian views. (My very first scientific paper, published in 1965, identified a logical confusion among Lyell’s various definitions of uniformity.) But my own observations of the pillars of Pozzuoli seemed only to strengthen and extend his conclusions on the extent and gradual character of geological change during historical times.
The Lying Stones of Marrakech Page 19