In 1700, all major Western scholars believed that the earth had been created just a few thousand years ago. By 1800, nearly all scientists accepted a great antiquity of unknown duration, and a sequential history expressed in strata of the earth’s crust. These strata, roughly speaking, form a vertical pile, with the oldest layers on the bottom and the youngest on top. By mapping the exposure of these layers on the earth’s surface, this sequential history can be inferred. By 1820, detailed geological maps had been published for parts of England and France, and general patterns had been established for the entirety of both nations. This discovery of “deep time,” and the subsequent resolution of historical sequences by geological mapping, must be ranked among the sweetest triumphs of human understanding.
Few readers will recognize the name of Jean-Etienne Guettard (1715-1786), a leading botanist and geologist of his time, and the initiator of the first “official” attempt to produce geological maps of an entire nation. In 1746, Guettard presented a preliminary “mineralogical map” of France to the Académie Royale des Sciences. In subsequent years, he published similar maps of other regions, including parts of North America. As a result, in 1766, the secretary of state in charge of mining commissioned Guettard to conduct a geological survey and to publish maps for all of France. The projected adas would have included 230 maps, but everyone understood, I suspect, that such a task must be compared with the building of a medieval cathedral, and that no single career or lifetime could complete the job. In 1770, Guettard published the first sixteen maps. The project then became engulfed by political intrigue and finally by a revolution that (to say the least) tended to focus attention elsewhere. Only 45 of the 230 projected maps ever saw the published light of day, and control of the survey had passed to Guettard’s opponents by this time.
Guettard’s productions do not qualify as geological maps in the modern sense, for he made no effort to depict strata, or to interpret them as layers deposited in a temporal sequence—the revolutionary concepts that validated deep time and established the order of history. Rather, as his major cartographic device, Guettard established symbols for distinctive mineral deposits, rock types, and fossils—and then merely placed these symbols at appropriate locations on his map. We cannot even be sure that Guettard understood the principle of superposition—the key concept that time lies revealed in a vertical layering of strata, with younger layers above (superposed upon) older beds. Guettard did develop a concept of “bandes,” or roughly concentric zones of similar rocks, and he probably understood that a vertical sequence of strata might be expressed as such horizontal zones on a standard geographic map. But in any case, he purposely omitted these bandes on his maps, arguing that he wished only to depict facts and to avoid theories.
This focus on each factual tree, combined with his studious avoidance of any theoretical forest of generality or explanation, marked Guettard’s limited philosophy of science, and also (however unfairly) restricted his future reputation, for no one could associate his name with any advance in general understanding. Rhoda Rappoport, a distinguished historian of science from Vassar College and the world’s expert on late-eighteenth-century French geology, writes of Guettard (within a context of general admiration, not denigration): “The talent he most conspicuously lacked was that of generalization, or seeing the implications of his own observations…. Most of his work reveals … that he tried hard to avoid thinking of the earth as having a history.”
But if Guettard lacked this kind of intellectual flair, he certainly showed optimal judgment in choosing a younger partner and collaborator for his geological mapping, for Guettard fully shared this great enterprise with Antoine-Laurent Lavoisier (1743-94), a mere fledgling of promise at the outset of their work in 1766, and the greatest chemist in human history when the guillotine literally cut his career short in 1794.
Guettard and Lavoisier took several field trips together, including a four-month journey in 1767 through eastern France and part of Switzerland. After completing their first sixteen maps in 1770, Lavoisier’s interest shifted away from geology toward the sources of his enduring fame—a change made all the more irrevocable in 1777, when control of the geological survey passed to Antoine Monnet, inspector general of mines, and Lavoisier’s enemy. (Later editions of the maps ignore Lavoisier’s contributions and often don’t even mention his name.)
Nonetheless, Lavoisier’s geological interests persisted, buttressed from time to time by transient hope that he might regain control of the survey. In 1789, with his nation on the verge of revolution, Lavoisier presented his only major geological paper—a stunning and remarkable work that inspired this essay. Amidst his new duties as régisseur des poudres (director of gunpowder), and leading light of the commission that invented the meter as a new standard of measurement—and despite the increasing troubles that would lead to his arrest and execution (for his former role as a farmer-general, or commissioned tax collector)—Lavoisier continued to express his intention to pursue further geological studies and to publish his old results. But the most irrevocable of all changes fractured these plans on May 8,1794, less than three months before the fall of Robespierre and the end of the Terror. The great mathematician Joseph-Louis Lagrange lamented the tragic fate of his dear friend by invoking the primary geological theme of contrasting time scales: “It took them only an instant to cut off his head, but France may not produce another like it in a century.”
All the usual contrasts apply to the team of Guettard and Lavoisier: established conservative and radical beginner; mature professional and youthful enthusiast; meticulous tabulator and brilliant theorist; a counter of trees and an architect of forests. Lavoisier realized that geological maps could depict far more than the mere location of ores and quarries. He sensed the ferment accompanying the birth of a new science, and he understood that the earth had experienced a long history potentially revealed in the rocks of his maps. In 1749, Georges Buffon, the greatest of French naturalists, had begun his monumental treatise (Histoire naturelle, which would eventually run to forty-four volumes) with a long discourse on the history and theory of the earth (see chapter 4).
As he groped for a way to understand this history from the evidence of his field trips, and as he struggled to join the insights published by others with his own original observations, Lavoisier recognized that the principle of superposition could yield the required key: the vertical sequence of layered strata must record both time and the order of history. But vertical sequences differed in all conceivable features from place to place—in thickness, in rock types, in order of the layers. How could one take this confusing welter and infer a coherent history for a large region? Lavoisier appreciated the wisdom of his older colleague enough to know that he must first find a way to record and compile the facts of this variation before he could hope to present any general theory to organize his data.
A geological map by Cuettard and Lavoisier, with Lavoisier’s temporal sequence of strata in the right margin.
Lavoisier therefore suggested that a drawing of the vertical sequence of sediments be included alongside the conventional maps festooned with Guettard’s symbols. But where could the vertical sections be placed? In the margins, of course; for no other space existed in the completed design. Each sheet of Guettard and Lavoisier’s Atlas therefore features a large map in the center with two marginal columns on the side: a tabular key for Guettard’s symbols at the left, and Lavoisier’s vertical sections on the right. If I wished to epitomize the birth of modern geology in a single phrase (admittedly oversimplified, as all such efforts must be), I would honor the passage—both conceptual and geometric—of Lavoisier’s view of history, as revealed in sequences of strata, from a crowded margin to the central stage.
Many fundamental items in our shared conceptual world seem obvious and incontrovertible only because we learned them (so to speak) in our cradle and have never even considered that alternatives might exist. We often regard such notions—including the antiquity of the earth, the
rise of mountains, and the deposition of sediments—as simple facts of observation, so plain to anyone with eyes to see that any other reading could only arise from the province of knaves or fools. But many of these “obvious” foundations arose as difficult and initially paradoxical conclusions born of long struggles to think and see in new ways.
If we can recapture the excitement of such innovation by temporarily suppressing our legitimate current certainties, and reentering the confusing transitional world of our intellectual forebears, then we can understand why all fundamental scientific innovation must marry new ways of thinking with better styles of seeing. Neither abstract theorizing nor meticulous observation can provoke a change of such magnitude all by itself. And when—as in this story of Lavoisier and the birth of geological mapping—we can link one of the greatest conceptual changes in the history of science with one of the most brilliant men who ever graced the profession, then we can only rejoice in the enlarged insight promised by such a rare conjunction.
Most of us, with minimal training, can easily learn to read the geological history of a region by studying the distribution of rock layers on an ordinary geographic map and then coordinating this information with vertical sections (as drawn in Lavoisier’s margins) representing the sequence of strata that would be exposed by digging a deep hole in any one spot. But consider, for a moment, the intellectual stretching thus required, and the difficulty that such an effort would entail if we didn’t already understand that mountains rise and erode, and that seas move in and out, over any given region of our ancient earth.
A map is a two-dimensional representation of a surface; a vertical section is a one-dimensional fisting along a line drawn perpendicular to this surface and into the earth. To understand the history of a region, we must mentally integrate these two schemes into a three-dimensional understanding of time (expressed as vertical sequences of strata) across space (expressed as horizontal exposures of the same strata on the earth’s surface). Such increases in dimensionality rank among the most difficult of intellectual problems—as anyone will grasp by reading the most instructive work of science fiction ever published, E. A. Abbott’s Flatland (originally published in 1884 and still in print), a “romance” (his description) about the difficulties experienced by creatures who five in a two-dimensional world when a sphere enters the plane of their entire existence and forces them to confront the third dimension.
As for the second component of our linkage, I can only offer a personal testimony. My knowledge of chemistry remains rudimentary at best, and I can therefore claim no deep understanding of Lavoisier’s greatest technical achievements. But I have read several of his works and have never failed to experience one of the rarest emotions in my own arsenal: sheer awe accompanied by spinal shivers. A kind of eerie, pellucid clarity pervades Lavoisier’s writing (and simply makes me ashamed of the peregrinations in these essays).
Perhaps, indeed almost certainly, a few other scientists have combined equal brilliance with comparable achievement, but no one can touch Lavoisier in shining a light of logic into the most twisted corners of old conceptual prisons, into the most tangled masses of confusing observations—and extracting new truths expressed as linear arguments accessible to anyone. As an example of the experimental method in science (including the fundamental principle of double-blind testing), no one has ever bettered the document that Lavoisier wrote in 1784 as head of a royal commission (including Benjamin Franklin, then resident in Paris and, ironically, Dr. Guillotin, whose “humane” invention would end Lavoisier’s life) to investigate (and, as results proved, refute) the claims of Dr. Mesmer about the role of animal magnetism in the cure of disease by entrancement (mesmerization).
Lavoisier did not compose his only geological paper until 1789, but Rhoda Rappoport has shown that he based this work upon conclusions reached during his mapping days with Guettard. Lavoisier did not invent the concept of vertical sections; nor did he originate the idea that sequences of strata record the history of regions on an earth of considerable antiquity. Instead, he resolved an issue that may seem small by comparison, but that couldn’t be more fundamental to any hope for a workable science of geology (as opposed to the simpler pleasures of speculating about the history of the earth from an armchair): he showed how the geological history of a region can be read from variation in strata from place to place—or, in other words, how a set of one-dimensional lists of layered strata at single places can be integrated by that greatest of all scientific machines, the human mind, into a three-dimensional understanding of the history of geological changes over an entire region.
(I doubt that Lavoisier’s work had much actual influence, for he published only one paper on this subject and did not live to realize his more extensive projects. Other investigators soon reached similar conclusions, for the nascent science of geology became the hottest intellectual property in late-eighteenth-century science. Lavoisier’s paper has therefore been forgotten, despite several efforts by isolated historians of science through the years, with this essay as the latest attempt, to document the singularity of Lavoisier’s vision and accomplishment.)
From my excellent sample of voluminous correspondence with lay readers during a quarter century of writing these essays, I have grasped the irony of the most fundamental misunderstanding about science among those who love the enterprise. (I am not discussing the different errors made by opponents of science.) Supporters assume that the greatness and importance of a work correlates directly with its stated breadth of achievement: minor papers solve local issues, while great works fathom the general and universal nature of things. But all practicing scientists know in their bones that successful studies require strict limitation: one must specify a particular problem with an accessible solution, and then find a suffciently simple situation where attainable facts might point to a clear conclusion. Potential greatness then arises from cascading implications toward testable generalities. You don’t reach the generality by direct assault without proper tools. One might as well dream about climbing Mount Everest in a T-shirt, wearing tennis shoes, and with a backpack containing only an apple and a bottle of water.
II. CAPTURING THE CENTER
When Lavoisier began his geological work with Guettard in 1766, he accepted a scenario, then conventional, for the history of the earth as revealed by the record of rocks: a simple directional scheme that envisaged a submergence of ancient landmasses (represented today by the crystalline rocks of mountains) under an ocean, with all later sediments formed in a single era of deposition from this stationary sea (on this topic, see Rhoda Rappoport’s important article “Lavoisier’s Theory of the Earth,” British Journal for the History of Science, 1973). Since geologists then lacked techniques for unraveling the contorted masses of older crystalline rocks, they devoted their research to the later stratified deposits, and tried to read history as an uncomplicated tale of linear development. (No fossils had been found in the older crystalline rocks, so early geologists also assumed that the later stratified deposits contained the entire history of life.)
Lavoisier’s key insight led him to reject this linear view (one period of deposition from a stationary sea) and to advocate the opposite idea that sea level had oscillated through time, and that oceans had therefore advanced and retreated through several cycles in any particular region—a notion now so commonplace that any geologist can intone the mantra of earth history: “the seas go in and the seas go out.” Lavoisier reached this radical conclusion by combining the developing ideas of such writers as Buffon and De Maillet with his own observations on cyclical patterns of sedimentation in vertical sections.
Lavoisier christened his 1789 paper with a generous tide characteristic of a time that did not separate literature and science: Observations générales sur les couches modernes horizontales qui ont été déposées par la mer, et sur les consequences qu’on peut tirer de leurs dispositions relativement à l’ancienneté du globe terrestre (General observations on the recent horizontal beds tha
t have been deposited by the sea, and on the consequences that one can infer, from their arrangement, about the antiquity of the earth). Lavoisier’s title may be grand, general, and expansive, but his content remained precise, local, and particular—at first! Lavoisier begins his treatise by distinguishing the properties of sediments deposited in open oceans from those formed along shorelines—a procedure that he then followed to build the data for his central argument that seas advance and retreat in a cyclical pattern over any given region.
After two short introductory paragraphs, Lavoisier plunges right in by expressing puzzlement that two such opposite kinds of rock so often alternate to form multiple cycles in a single vertical section. Criteria of fossils and sediment indicate calm and gende deposition for one kind: “Here one finds masses of shells, mostly thin and fragile, and most showing no sign of wear or abrasion…. All the features [of the rocks] that surround these shells indicate a completely tranquil environment” (my translations from Lavoisier’s 1789 paper). But rocks deposited just above testify to completely different circumstances of formation: “A few feet above the place where I made these observations, I noted an entirely opposite situation. One now sees no trace of living creatures; instead, one finds rounded pebbles whose angles have been abraded by rapid and long-continued tumbling. This is the picture of an agitated sea, breaking against the shore, and violently churning a large quantity of pebbles.” Lavoisier then poses his key question, already made rhetorical by his observations:
The Lying Stones of Marrakech Page 12