I had brought only the first edition (1830–33) of Lyell’s Principles with me to Naples. In this original text, Lyell attributed (tentatively, to be sure) all changes in level to just two discrete and rapid events. He correlated the initial subsidence (to a level where marine clams could bore into the marble pillars) to “earthquakes which preceded the eruption of the Solfatara” (a volcanic field on the outskirts of Pozzuoli) in 1198. “The pumice and other matters ejected from that volcano might have fallen in heavy showers into the sea, and would thus immediately have covered up the lower part of the columns.” Lyell then ascribed the subsequent rise of the pillars to a general swelling and uplift of land that culminated in the formation of Monte Nuovo, a volcanic mound on the outskirts of Pozzuoli, in 1538.
But at the site, I observed, with some surprise, that the evidence for changing levels of land seemed more extended and complex. I noticed the high zone of clam borings on the three columns, but evidence—not mentioned by Lyell—for another discrete episode of marine incursion struck me as even more obvious and prominent, and I wondered why I had never read anything about this event. Not only on the three major columns, but on every part of the complex (see the accompanying figure)—the minor columns at the corners of the quadrangular market area, the series of still smaller columns surrounding a circular area in the middle of the market, and even the brick walls and sides of structures surrounding the quadrangle—I noted a zone, extending two to three feet up from the marble floor of the complex and terminated by a sharp line of demarcation. Within this zone, barnacles and oyster shells remain cemented to the bricks and columns—so the distinct line on top must represent a previous high-water mark. Thus, the still higher zone of clam borings does not mark the only episode of marine incursion. This lower, but more prominent, zone of shells must signify a later depression of land. But when?
Lyell’s original frontispiece (redrafted from an Italian publication of 1820), which includes the bases of the large columns, depicts no evidence for this zone. Did he just fail to see the barnacles and oysters, or did this period of marine flooding occur after 1830? I scoured some antiquarian bookstores in Naples and found several early-nineteenth-century prints of the columns (from travel books about landscapes and antiquities, not from scientific publications). None showed the lower zone of barnacles and oysters. But I did learn something interesting from these prints. None depicted the minor columns now standing both in the circular area at the center, and around the edge of the quadrangle—although these locations appear as flat areas strewn with bric-a-brac in some prints. But a later print of 1848 shows columns in the central circular area. I must therefore assume that the excavators of Pozzuoli reerected the smaller columns of the quadrangle and central circle sometime near the middle of the nineteenth century—while we know that Lyell’s three major columns stood upright from their first discovery in 1749. (A fourth major column still lies in several pieces on the marble floor of the complex.)
All these facts point to a coherent conclusion. The minor columns of the central circle and quadrangle include the lower zone of barnacles and oysters. These small columns were not reerected before the mid-nineteenth century. Lyell’s frontispiece, and other prints from the early nineteenth century, show the three large columns without encrusting barnacles and oysters at the base. Therefore, this later subsidence of land (or rise of sea to a few feet above modern levels) must have culminated sometime after the 1840s—thus adding further evidence for Lyell’s claim of substantial and complex movements of the earth within the geological eye-blink of historic times.
For a few days, I thought that I had made at least a minor discovery at Pozzuoli—until I returned home (and to reality), and consulted some later editions of Lyell’s Principles, a book that became his growing and changing child (and his lifelong source of income), reaching a twelfth edition by the time of his death. In fact, Lyell documented, in two major stages, how increasing knowledge about the pillars of Pozzuoli had enriched his uniformitarian view from his initial hypothesis of two quick and discrete changes toward a scenario of more gradual and more frequent alterations of level.
1. In the early 1830s, Charles Babbage, Lyell’s colleague and one of the most interesting intellectuals of Victorian Britain (more about him later), made an extensive study of the Pozzuoli columns and concluded that both the major fall of land (to the level of the clam borings) and the subsequent rise had occurred in a complex and protracted manner through several substages, and not all at once as Lyell had originally believed. Lyell wrote in the sixth edition of 1840:
Mr. Babbage, after carefully examining several incrustations … as also the distinct marks of ancient lines of water-level, visible below the zone of lithophagous perforations [holes of boring clams, in plain English], has come to the conclusion, and I think, proved, that the subsidence of the building was not sudden, or at one period only, but gradual, and by successive movements. As to the re-elevation of the depressed tract, that may also have occurred at different periods.
2. When Lyell first visited Pozzuoli in 1828, the high-water level virtually matched the marble pavement. (Most early prints, including Lyell’s frontispiece, show minor puddling and flooding of the complex. Later prints, including an 1836 version from Babbage that Lyell adopted as a replacement for his original frontispiece in later editions of Principles, tend to depict deeper water.) In 1838, Lyell read a precise account of this modern episode of renewed subsidence—and he then monitored this most recent change in subsequent editions of Principles. Niccolini, “a learned architect [who] visited the ruins frequently for the sake of making drawings,” found that the complex had sunk about two feet from his first observations in 1807 until 1838, when “fish were caught every day on that part of the pavement where in 1807, there was never a drop of water in calm weather.”
Lyell continued to inquire about this active subsidence—from a British colleague named Smith in 1847, from an Italian named Scacchi in 1852, and from his own observations on a last trip in 1858. Lyell acknowledged several feet of recent sinking and decided to blame the old icon of Vesuvius! The volcano had been active for nearly a hundred years, including some spectacular eruptions during Hamilton’s tenure as British ambassador—after several centuries of quiescence. Lyell assumed that this current subsidence of surrounding land must represent an adjustment to the loss of so much underground material from the volcano’s crater. He wrote: “Vesuvius once more became a most active vent, and has been ever since, and during the same lapse of time the area of the temple, so far as we know anything of its history, has been subsiding.”
In any case, I assume that the prominent layer of encrustation by marine barnacles and oysters, unmentioned by Lyell and undepicted in all my early-nineteenth-century sources—but (to my eyes at least) the most obvious sign of former geological activity at Pozzuoli today, and far more striking, in a purely visual sense, than the higher zone of clam borings—occurred during a more recent episode of higher seas. Again, we can only vindicate Lyell’s conviction about the continuing efficacy of current geological processes.
A conventional essay in the hagiographical mode would end here, with Lyell triumphant even beyond the grave and his own observations. But strict uniformity, like its old alternative of uncompromising catastrophism, cannot capture all the complexity of a rich and flexible world that says yes to at least part of most honorable extremes in human system building.
Uniformity provided an important alternative and corrective to strict catastrophism, but not the complete truth about a complex earth. Much of nature does proceed in Lyell’s slow and nondirectional manner, but genuine global catastrophes have also shaped our planet’s history—an idea once again in vogue, given virtual proof for triggering of the late Cretaceous mass extinction, an event that removed dinosaurs along with some 50 percent of all marine species, by the impact of an extraterrestrial body. Our city of intellectual possibilities includes many mansions, and restriction to one great house will keep us walled off fro
m much of nature’s truth.
As a closing example, therefore, let us return to Lyell’s fascinating colleague, Charles Babbage (1792–1871), Lucasian professor of mathematics at Cambridge, and inventor of early calculating machines that presaged the modern digital computer. The Encyclopaedia Britannica ends an article on this versatile genius by writing: “He assisted in establishing the modern postal system in England and compiled the first reliable actuarial tables. He also invented a type of speedometer and the locomotive cowcatcher.” So why not geology as well!
Babbage presented his studies of Pozzuoli to the Geological Society of London in 1834, but didn’t publish his results until 1847 because, as he stated in a preface written in the third person, “other evocations obliged him to lay it aside”—primarily that cowcatcher, no doubt! Babbage had pursued his studies to affirm Lyell’s key uniformitarian postulate, as clearly indicated in the ample subtitle of his publication: “Observations on the Temple of Serapis at Pozzuoli near Naples, with an attempt to explain the causes of the frequent elevation and depression of large portions of the earth’s surface in remote periods, and to prove that those causes continue in action at the present time.”
By delaying publication until 1847, Babbage needed to add an appendix to describe the recent subsidence also noted by Lyell in later editions of Principles of Geology. Babbage discussed the observations of Niccolini and, especially, of Smith as reported to the Geological Society of London: “Mr. Smith found the floor of the temple dry at high water in 1819, and 18 inches on it at high water in 1845.” But Babbage then integrated these latest data with his previous observations on earlier changes in historical times to reach his general uniformitarian conclusions:
The joint action of certain existing and admitted causes must necessarily produce on the earth’s surface a continual but usually slow change in the relative levels of the land and water. Large tracts of its surface must be slowly subsiding through the ages, whilst other portions must be rising irregularly at various rates.
To generalize this Neapolitan conclusion, Babbage then cited the ongoing work of a young naturalist, based on entirely different phenomena from the other side of the globe: coral atolls of the tropical Pacific Ocean. This young man had not yet become the Charles Darwin whom we revere today. (Publication of The Origin of Species still lay twelve years in the future, and Darwin had revealed his evolutionary suspicions only to a few closest confidants, not including Babbage.) Therefore, Babbage and the scientific community of Britain knew Darwin only as a promising young naturalist who had undertaken a five-year voyage around the world, published a charming book on his adventures and three scientific volumes on the geology of South America and the formation of coral atolls, and now labored in the midst of a comprehensive treatise, which would eventually run to four volumes, on the taxonomy of barnacles.
Darwin’s theory on the origin of coral atolls surely struck his colleagues as the most important and original contribution of his early work. Darwin, labeling his explanation as the “subsidence theory” of coral reefs, explained the circular form of atolls as a consequence of subsidence of the surrounding sea floor. Reefs begin by growing around the periphery of oceanic islands. If the islands then subsided, the corals might continue to grow upward, eventually forming a ring as the central island finally disappeared below the waves.
This brilliant—and largely correct—explanation included two implications particularly favorable to Lyell and his fellow uniformitarians, hence their warm embrace for this younger colleague. First, the subsidence theory provided an excellent illustration for the efficacy and continuity of gradual change—for corals could not maintain their upward growth unless the central islands sank slowly. (Reef corals, filled with symbiotic photosynthetic algae, cannot live below the level of penetration for sunlight into oceanic waters—so any rapid subsidence would extinguish the living reefs.)
Second—and more crucial to the work of Babbage and Lyell at Pozzuoli— the large geographic range of atolls proves that major regions of the earth’s crust must be subsiding, thus also implying that other regions of comparable extent must rise at the same time. Therefore, the fluctuations recorded on Pozzuoli’s pillars need not represent only a local phenomenon, but may also illustrate one of the most fundamental principles of the gradualist, nondirectionalist, and uni-formitarian mechanics of basic planetary behavior. In fact, and above all other implications, Darwin had emphasized his discovery that coral atolls do not form in regions with active volcanoes, while no atolls exist where volcanoes flourish in eruption. This mutual avoidance indicates that large tracts of the earth’s crust, not merely local pinpoints, must be subsiding or rising in concert—with atolls as primary expressions of subsidence, and volcanoes as signs of uplift.
Babbage wrote to praise the young Darwin, but also to assert that he had reached the same uniformitarian conclusions independently, during his own studies of Pozzuoli:
Mr. Darwin, whose voyages and travels extended from 1826 to 1836 [sic; the Beagle voyage lasted from 1831 to 1836], was gradually accumulating and arranging an immense collection of facts relating to the formation of coral and lagoon islands, as well as to the relative changes of level of land and water. In 1838 Mr. Darwin published his views on those subjects, from which, amongst several other very important inferences, it resulted, that he had, from a large induction of facts, arrived at exactly the same conclusion as that which it has been the chief object of this paper to account for, from the action of known and existing causes.
So far, so good—and so fair, and so just. But Babbage then proceeded further—into one of the most ludicrously overextended hypotheses ever advanced in the name of uniformitarian geology. He appended a “supplement” to his 1847 publication on the pillars of Pozzuoli entitled “Conjectures concerning the physical condition of the surface of the moon.” In Babbage’s day, most scientists interpreted lunar craters as volcanic cones—a catastrophic explanation that Babbage wished to challenge. He noted that a region of lunar craters would look very much like a field of earthly coral atolls standing in the bed of a vanished sea:
The perusal of Mr. Darwin’s explanation of the formation of coral reefs and of lagoon island led me to compare these islands with those conical crater-shaped mountains which cover the moon’s surface; and it appears to me that no more suitable place could be found for throwing out the following conjectures, than the close of a paper in which I have endeavoured to show, that known and existing causes lead necessarily to results analogous to those which Mr. Darwin has so well observed and recorded….
If we imagine a sea containing a multitude of such lagoon islands to be laid dry, the appearance it would present to a spectator at the moon would strongly resemble that of a country thickly studded with volcanic mountains, having craters of various sizes. May not therefore much of the apparently volcanic aspect of the moon arise from some cause which has laid dry the bottom of a former ocean on its surface?
Babbage became bolder near the end of his commentary, as he explicitly wondered “if those craters are indeed the remains of coral lagoon islands.” To be fair, Babbage recognized the highly speculative nature of his hypothesis:
The proceeding remarks are proposed entirely as speculations, whose chief use is to show that we are not entirely without principles from which we may reason on the physical structure of the moon, and that the volcanic theory is not the only one by which the phenomena could be explained.
But later discoveries only underscore the irony of what may be the greatest overextension of uniformitarian preferences ever proposed by a major scientist. Babbage suggested that lunar craters might be coral atolls because he wished to confute their catastrophic interpretation as volcanic vents and mountains. Indeed, lunar craters are not volcanoes. They are formed by the even more sudden and catastrophic mechanism of meteoritic impact.
Comprehensive worldviews like uniformitarianism or catastrophism provide both joys and sorrows to their scientific supporters—the great benef
its of a guide to reasoning and observation, a potential beacon through the tangled complexities and fragmentary character of nature’s historical records; but also and ineluctably combined with the inevitable, ever-present danger of false assurances that can blind us to contrary phenomena right before our unseeing eyes. Lyell himself emphasized this crucial point, with his characteristic literary flair, in the closing paragraph to his discussion about the pillars of Pozzuoli— in this case, to combat the prejudice that landmasses must be rock stable, with all changes of level ascribed to movements of the sea:
A false theory it is well known may render us blind to facts, which are opposed to our prepossessions, or may conceal from us their true import when we behold them. But it is time that the geologist should in some degree overcome those first and natural impressions which induced the poets of old to select the rock as the emblem of firmness—the sea as the image of inconstancy.
But we also know that no good deed goes unpunished and that any fine principle can turn around and bite you in the ass. Lyell had invoked this maxim about the power of false theories to emphasize that conventional preferences for catastrophism had been erroneously nurtured by the differential preservation of such evidence in our imperfect geological records. But Georges Cuvier, Lyell’s French colleague, leading catastrophist, and perhaps the only contemporary who could match Lyell’s literary and persuasive flair, had issued the ultimate touché in a central passage of the most celebrated defense for geological catastrophism—his Discours préliminaire of 1812.