The Lying Stones of Marrakech (17 page)

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. C
APTURING
T
HE
C
ENTER

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 that 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:

How can we reconcile such opposite observations? How can such different effects arise from the same cause? How can movements that have abraded quartz, rock crystal, and the hardest stones into rounded pebbles, also have preserved light and fragile shells?

The simple answer to this specific and limited question may then lead to important generalities for the science of geology, and also to criteria for unraveling the particular history of the earth:

At first glance, this contrast of tranquillity and movement, of organization and disorder, of separation and mixture, seemed inexplicable to me; nevertheless, after seeing the same phenomena again and again, at different times and in different places, and by combining these facts and observations, it seemed to me that one could explain these striking observations in a simple and natural manner that could then reveal the principal laws followed by nature in the generation of horizontal strata.

Lavoisier then presents his idealized model of a two-stage cycle as an evident solution to this conundrum:

Two kinds of very distinct beds must exist in the mineral kingdom: one kind formed in the open sea … which I shall call
pelagic
beds, and the other formed at the coast, which I shall call
littoral
beds.

Pelagic beds arise by construction, as “shells and other marine bodies accumulate slowly and peacefully during an immense span of years and centuries.” But littoral beds, by contrast, arise by “destruction and tumult … as parasitic deposits formed at the expense of coastlines.”

In a brilliant ploy of rhetoric and argument, Lavoisier then builds his entire treatise as a set of consequences from this simple model of two types of alternating sediments, representing the cycle of a rising and falling sea. This single key, Lavoisier claims, unlocks the great conceptual problem of moving from one-dimensional observations of vertical sequences in several localities to a three-dimensional reconstruction of history. (I call the solution three-dimensional for a literal reason, emphasized earlier in this essay in my discussion of geological maps: the two horizontal dimensions record geographic variation over the earth's surface, while the vertical dimension marks time in a sequence of strata):

This distinction between two kinds of beds … suddenly dispersed the chaos that I experienced when I first observed terranes made of horizontal beds. This same distinction then led me to a series of consequences that I shall try to convey, in sequence, to the reader.

The remainder of Lavoisier's treatise presents a brilliant fusion of general methodology and specific conclusions, a combination that makes the work such a wonderful exemplar of scientific procedure at its best. The methodological passages emphasize two themes: the nature of proof in natural history, and the proper interaction of theory and observation. Lavoisier roots the first theme in a paradox presented on pages 98—99: the need to simplify at first in order to generalize later. Science demands repetition for proper testing of observations—for how else could we learn that the same circumstances reliably generate the same results? But the conventional geologies of Lavoisier's time stymied such a goal—for one directional period of deposition from a single stationary sea offered no opportunity for testing by repetition. By contrast, Lavoisier's model of alternating pelagic and littoral beds provided a natural experiment in replication at each cycle.

But complex nature defies the needs of laboratory science for simple and well-controlled situations, where events can be replicated under identical
conditions set by few variables. Lavoisier argues that we must therefore try to impose similar constraints upon the outside world by seeking “natural experiments” where simple models of our own construction might work adequately in natural conditions chosen for their unusual clarity and minimal number of controlling factors.