The Importance of Background Theory, or Why James Hall Left Mountains out of his Theory of Mountain Building

* This is the latest installment of “Problematica.” It is written by Max Dresow…

As far as I know, the English language has no word for an event that’s missing its most important participant. Instead, we have an expression. It dates from 1775, when the lead actor of a traveling theater group absconded with a young lady on the eve of a performance. The incident evidently happened in the summer, but the earliest surviving account comes from The Caledonian Mercury of September 27, 1775. It describes the previous night’s events at the Covent Garden Theatre, in which an actor, Lee Lewis, entertained the audience

with the manner of their performing Hamlet in a company that he belonged to, when the hero who was to play the principal character had absconded with an innkeeper’s daughter; and that when he came forward to give out the play, he added, “the part of Hamlet to be left out, for the night.”

From this comes the expression, “Hamlet without the Prince of Denmark,” or just “Hamlet without the Prince.”

I relate this bit of etymological trivia because geology also has its “Hamlet without the Prince.” It dates from 1866 but is better known from an article published seven years later. Both were written by James Dwight Dana, dean of American geologists and longtime editor of the American Journal of Science, from which position he liked to broadcast his views on a range of topics. And in 1866 his topic was James Hall’s views on mountain building. Hall was a paleontologist who had used a major address to outline a new theory of mountains. That was in 1857, and in the meantime, his view had been endorsed by no less an authority than T. Sterry Hunt of the Canadian geological survey. But Dana was unimpressed. In a biting synopsis, he described Hall’s view as “a theory for the origin of mountains, with the origin of mountains left out.” Which goes to show what some unlucky theater-goers heard in a truncated performance of Hamlet: that brevity truly is the soul of wit.

James Hall, Jr. (1811–1898). Not to be confused with Sir James Hall (1761–1832), friend of James Hutton, who performed experiments on mountain-building using analog models

But why did James Hall leave mountains out of his theory of mountain building? The question has an interesting answer and illustrates the importance of background assumptions in scientific theorizing about the earth. I could just blurt it out, but I doubt it would make sense without context, and anyway, I don’t want to deprive you of the chance to meet James Hall, Jr., who happens to be one of the more complicated figures in the history of paleontology.*

[* Actually, to describe Hall as “complicated” is to put a nice spin on things. Hall was a petty, irascible, and paranoid man, who might have contended for the title of “most unlikable paleontologist” if Henry Fairfield Osborn had never been born. It’s a shame he isn’t more widely known.]

We will return to Hall in a moment. First, I owe you a word on the context of his proposal, and this means heading to the mountains.

* * *

For most of the nineteenth century, the scientific study of mountains was dominated by a single range: the Alps. Stretching some 1,200 kilometers from the azure shores of Nice to the endless grasslands of Hungary, the Alps form a massive scar that runs along the northern border of what is now Italy. Their geological complexity is legend and supplied several of the most difficult problems that exercised nineteenth century geologists (Greene 1982). Especially on the continent, no tectonic theory stood a chance of gaining general acceptance if it did not account for the structure and composition of the Alps. It is for this reason that histories of tectonic theory sometimes read as histories of Alpine geology, with leading roles going to luminaries like Léonce Élie de Beaumont, Eduard Suess, Albert Heim, and Marcel Bertrand.

An der Scheidecke des Martinslochs, Ostseite derselben zuoberst im Flimserthal, Pass nach Elm den 22. Juli 1812, by Hans Conrad Escher, depicting the famous keyhole (Martinsloch) beneath the Glarus thrust fault in the Swiss Alps. Interpretations of the Glarus thrust fault (including its identification as a thrust fault) played a major role in deciphering the structure of the Alps

Yet there was another group of mountains that, while it did not equal the Alps in stature, nonetheless played muse to several important tectonic theories. This was the Appalachians: that ancient chain of forested hills running from Alabama to the Maritimes. American geology cut its teeth on these hills. But this was no mean task, because, as John McPhee observes, the Appalachians are hardly a paradigm of “layer cake legibility” (McPhee 1998, 184). Instead, they form “a compressed, chaotic, ropy enigma four thousand kilometers from end to apparent end, full of overturned strata and recycled rock, of steep faults and horizontal thrust sheets, of folds so tight that what had once stretched twenty miles might now fit into five.” It was this complexity rather than any more superficial excellence that gave the Appalachians their importance for the study of mountain building.

The southern Appalachian Mountains, with characteristic smoky blue shading

Like the Alps, the Appalachians are fold mountains. To picture this, think of what would happen if you pushed a tablecloth across the table from one end while someone held the other end fast. However, unlike the Alps the Appalachians are mountains on the wane, chewed to their roots by millions of years of erosion. Mapping them was one of the first noteworthy achievements of American geology. According to Mott Greene, the mapping of the Appalachians was “the first careful and reasonably complete elucidation of the structure of an entire mountain system of the folded type [anywhere in the world]” (Greene 1982, 123). It was these observations that established the Appalachians as the model for a whole class of folded mountains, and that drew attention to the general “one-sidedness” of mountain chains (as Eduard Suess put it, contrasting structures dominated by inclined and overturned folds with more symmetrical mountains).

Geological Map of the State of Pennsylvania, published in 1858 by Henry Rogers, showing the trend of the Appalachian folds

Credit for deciphering the structure of the Appalachians belongs to a pair of brothers. William Rogers, state geologist of Virginia, studied the range in Virginia and southward. Henry Rogers, state geologist of Pennsylvania, studied it from Pennsylvania to New Jersey. What they found (in the words of a biographical sketch of William) was “that the rocks of this great chain comprised strata ranging in age from the Potsdam [mid-Cambrian] into the Coal Measures [Pennsylvanian].”

The chain comprises five straight, and four curved, belts, which alternate and vary from 100 to 150 miles in length. [The Rogers brothers noted the] persistence of the Appalachians in extent, their marked narrowness, steepness, evenness of crests, and uniform degree of parallelism… They also observed the predominance of southeastern dips, the normal, inverted, and broken flexures, and the passing of the latter into faults. (Roberts 1936, 308)

Or, as Celal Sengor has more recently written: “the [Rogers] brothers showed that the entire Appalachian structure was dominated by inclined to overturned folds with a consistent northwest vergence and by thrust faults dipping to the southeast.”

William Barton Rogers (1804–1882), left, and Henry Darwin Rogers (1808–1866), right. It is interesting to note that William went on to found the Massachusetts Institute of Technology (yes, that one) in 1861. This has recently occasioned some embarrassment as Barton was a slave owner during his time in Virginia, and maintained deep ties to the South after moving to Massachusetts. The MIT website goes so far as to declare Rogers “in many ways, a product of slavery.” “The enslavement of black people [contributed] to his family’s success, [underwrote] his education, advanced his career, and expanded his social connections.”

But this is so much structural description. It does not explain the origin of the sinuous and inverted flexures, the faults, the dips, and the recycled sediments. Nor does it explain the “evenness of crests, and [the] uniform degree of parallelism” that would have impressed itself upon the curiosity of a bird's eye observer. To account for these features, the brothers conjured a wave in the viscous liquid underlying the crust (Rogers and Rogers 1843). Or perhaps it would be better to describe it as a large-scale undulatory movement, which caused the crust to ripple and break in parallel folds. Anyway, it was unlike anything in the record of human experience, which was exactly the point. Whatever caused the Appalachians to rise was a force beyond the ordinary operations of nature, a kind of earthquake on steroids, capable of buckling the crust along a two-thousand mile line. Henry Rogers suggested that the ultimate driver was the expansion of “molten matter and gaseous vapors” in the Earth’s interior (Rogers 1857, 463). This produced “violent pulsations on the surface of the liquid [beneath the crust],” which communicated their motion to the overlying strata, producing flexures.* Faults they ascribed to rifts in the overlying strata caused by the escape of volatile materials. Dikes they ascribed to congealed igneous matter, which filled any fissures that opened during the great spasms.

[* These flexures are at first “temporary”; later they are frozen in place by the injection of molten material from beneath. It is important that the flexes are not frozen in place immediately, since repeated disturbance of the strata is required to produce the inverted flexures characteristic of the chain. Here is Henry Rogers again: “If, during this oscillation, we conceive the whole heaving tract to have been shoved (or floated) bodily forward in the direction of the advancing waves, the union of this tangential with the vertical wave-like movement will explain the peculiar steepening of the front side of each flexure, while a repetition of similar operations would occasion the folding under, or inversion, visible in the more compressed districts” (Rogers 1857, 463–464, emphasis added).]

The Sideling Hill Road Cut in western Maryland (note the car for scale), revealing the innards of a “syncline mountain,” or a region of downfolded strata sandwiched between two “anticlines,” or upfolded structures

It was a rollicking good story, and one offered with all the gravitas of two state geologists speaking from their home turf. But it was not exactly convincing, even to contemporaries. Mott Greene reckons that it was only ever accepted “by a handful of men, and then only for [a] few years” (Greene 1982, 125). The Rogers’ fieldwork and maps, by contrast, “were the foundation of some very fruitful theoretical ideas by other investigators, especially in the undeniable association of thick sequences of sediment with the formation of a mountain system.” First among these was the ornery dynamo of American geology, James Hall, Jr.

* * *

When the Rogers brothers were speculating about subterranean explosions, Hall was state paleontologist of New York. Prior to this he had been the geologist in charge of one quarter of the New York geological survey, with responsibilities for the western part of the state, including Niagara Falls. At first, Hall reported to Ebenezer Emmons, a prominent expert on the very oldest rocks in the country whom Hall would come to detest. (More on this in a moment.) But by 1843 he was fully autonomous and the author of a lavishly illustrated volume, The Geology of New York, Pt. IV: Survey of the Fourth Geological District. The book made his reputation, notwithstanding that he is now better remembered for his eight part, thirteen volume The Palaeontology of New York, which occupied his labors over a nearly fifty year period (1847–1894).

Hall’s map of the middle and western United States from The Geology of New York, Pt. IV. Notice the comparably high level of detail in the region of the Appalachian mountain chain (1843)

Hall’s career was saturated with rivalry, the ugliest example of which spilled into the New York court system and may have precipitated an incident of maritime vandalism. The episode was sparked by a schoolmaster, James Foster, who in 1849 produced a geological cross-section for use in local schools. This would have been “the first private text to publish the momentous results of the New York Survey” and sell them for profit (Schneer 1978, 180). Hall, always concerned about money and eager to reap his own reward, was enraged. Immediately he went on the offensive, enlisting no less a force than Louis Agassiz to discredit Foster. But it wasn’t just Foster in the crosshairs. Hall’s former boss Ebenezer Emmons had served as a consultant on the chart. With Agassiz’s help, Hall set about destroying Emmons’s reputation. Not the most aggressive criticism was voiced in the American Journal of Science:

A large geological chart some six feet or more square, largely lettered and well varnished, has recently been seen by us. It emanates from Albany, N.Y., and appears to have been intended to illustrate geology to the schools of that state. Strange to say, there is not one word of New York geology to be detected in it, and not even a hint with regard to American rocks. With some truth combines much that was formerly supposed to be true, with much that is now known to be false, and is a caricature of geological science though pretending to be made up from the best authorities.

Agassiz was more curt, calling the chart “monstrous,” and declaring that “its mere circulation would be considered abroad as a disgrace to American geologists.” His remarks appeared in the Albany newspapers along with a letter from Hall. Incensed, Foster sued for libel, naming Agassiz and Hall in separate suits. Agassiz was tried first, for damages totaling $20,000, but the case was dismissed after several days of testimony. Before this could happen “the action… resolved itself, from a defense against the charges of an ill-advised schoolmaster, to an open assault on Emmons and his imputed heresies” (Clarke 1912, 211). (The same author describes the cross-examination of Emmons as “annihilating,” something he attributes to extensive coaching of Agassiz’s attorney by Hall.) Hall never appeared before a judge.*

[* I’ve been unable to locate Hall’s letter, but it must’ve been a doozy. He was sued for $40,000, which comes to a million-and-a-half dollars in today's currency.]

“Foster’s Complete Geological Chart: Exhibiting in Their Successive Order of Deposition the Various Rocks that Form the Crust of our Earth, Arranged According to the Best Authorities in Europe and North America.” This is the first version of the chart, published in 1849. An updated version, advertising that it had been corrected by “Professor Ebbons,” was later printed, and may have met a watery demise

The trial was a media sensation, and Emmons paid the heaviest price. Before it began, the New York State legislature voted to cut off all appropriations for the New York Board of Geologists, removing Emmons from his curatorship and expelling Emmons and Hall from the State House (Schneer 1969). (This is the root of the fiction that Emmons was prohibited from practicing geology in New York following the trial.) Smarting, Emmons relocated to North Carolina in 1852. Merely indignant, Hall remained, setting up shop on his own property and paying a series of assistants out of his own pocket.

This much is public record. Now for the gossip. It is widely rumored that Hall was so enraged by the impertinence of Foster’s map that he stole aboard a paddlewheel steamer bound for New York City (Dott 2005). The steamer was carrying the entire printing of Foster’s updated chart, which Hall allegedly tossed into the Hudson— one imagines, with great relish. Such an action would not have been out of character for the famously volatile paleontologist. Hall’s outbursts, often directed at state lawmakers, were the stuff of legend (Yochelson 1998). Likewise his habit of keeping a heavy cane— and even a loaded shotgun— near his desk, which he sometimes brandished in the presence of company. To his credit, Hall seems to have possessed the capacity for forgiveness, and sometimes experienced remorse for his tantrums. Still, he never forgave Emmons, nor did he repay the $4,000 loan the older man reportedly gave him while he was a student at the Rensselaer Institute in Troy.

* * *

Hall unveiled his theory of mountain building at the 1857 meeting of the American Association for the Advancement of Science. The meeting was held in Montreal (for once “American” is not a synonym for “yankee”), and Hall was charged with giving an address as the outgoing president of the society. The address was titled “Geological History of the North American Continent” and touched on a variety of topics, from the scientific status of natural history to the relation of “physical conditions to the vital force and its development” (Hall 1882, 39).* Then, around the middle, it abruptly turned to “mountain and continental phenomena”— that is, to the causes of mountain building.

[* Hall’s address was only published in 1882. The published version seems to be a transcript of the remarks delivered in 1857, however.]

Hall begins with a rundown of the Paleozoic strata of eastern North America. He is especially concerned with the distinctive features of the Hudson River group, which “presents us on the one hand with a series of soft shales becoming coarser and alternating with sandstones above, and on the other with irregular masses of limestone and finally immense masses of coarse sandstones or conglomerates” (Hall 1882, 41). The group attains a thickness of 2,000 feet in Canada, which grows to 6,000 feet (“according to Prof. Rogers”) in Pennsylvania. “In its continuation southward it forms a marked feature in the Appalachian chain gradually dying out as the range declines” (42). This is what we should expect “in any sedimentary group of rocks,” Hall thinks. However, if the group is pursued westward “we find interesting and important changes.”

Tracing it through Canada, west by the islands of Lake Huron and by Green Bay to the Mississippi River and more southerly still by Cincinnati and the mouth of the Ohio, we learn that the coarser sediments gradually disappear, the finer mud alone having been transported, and finally that calcareous matter becomes an important ingredient in the formation and sandstone has become an exception… Here we have an extensive group of strata changing from fine and coarse sedimentary materials and passing through all the intermediate phases until it becomes a shaly limestone. (Hall 1882, 42, emphases mine)

But that’s not all. Not only does the composition of the rocks change as you move westward, so does their thickness. In Wisconsin, the Hudson River group is represented by a measly 100 feet of strata. In Iowa, the number is less than 50 feet. So, on the whole, the formation resembles a wedge that peters out to the west, as finer sediments come to predominate over coarser ones.

A twentieth center representation of the kind of sedimentary accumulation Hall described in his presidential address to the AAAS. Specifically, Hall described what would later be called a “miogeosyncline,” or an accumulation of sedimentation deposited in shallow water in the absence of volcanoes

To explain these features, Hall imagines a time when “the present continent… [was] an open sea” (Hall 1882, 42). The “most rational explanation,” he thinks, “is that a powerful current [brought] these sedimentary materials of sand, clay, and pebbles from the northeast and [distributed] them along the line now marked by the Appalachian chain; or, if you please to assume that there has been a continent to the east of our own which has been subsequently submerged, then the materials have been distributed along its coast.” Key to the view is the idea that “the direction of [the] current has been in the line of the greatest accumulation and coarser materials; and that toward the westward… the current gradually diminished until it essentially ceased and the fine materials were slowly spread over the broad area which they occupy in their diminished thickness.”

Thus from an equable and comparably quiet period when the Potsdam sandstone was spread widely over the bottom of the sea, we [come] to one when powerful currents directed the distribution of the sediments in long lines of deposition, on the seaward side of which we find the gradual thinning out of beds for want of a sufficient transporting agency. (Hall 1882, 43)

This process, Hall thinks, happened over and over again, “from the same source apparently in the northeast, and prolonged in the same direction to the southwest” (52). “You will see, gentleman,” he remarks, “with what an enormous amount of sedimentary deposits I am loading the eastern side of the future incipient continent” (53).

But all this is deposition— what of mountain building? Hall begins his account by raising a skeptical eyebrow at the Rogers’ model. “The system of folding and plication… which has been attributed to later [i.e., post-depositional] violent action,” has in fact “been produced by continued action from a long anterior period” (Hall 1882, 54). Not for Hall these spasms of violent uplift. But even if mountains are not produced by long continued action, Hall suggests, we would still have to “inquire whether [folding and faulting] has anything to do with the production of the mountain chain, or… whether rhetorical eloquence has not made us believe the language without testing the facts.” Hall favors the second option. We should not presuppose that the folds and faults of the Appalachians were produced by a process of uplift, or even (he goes on to say) that upheaval has any role to play in the production of elevation. But then what accounts for the folds and faults of the chain, so suggestive of buckling and violence? And how did a trough of sediment on the seafloor ever become a mountain chain, anyway?

Below: a depiction of Hall’s view of the origin of major structural features of folded mountains, like folds, faults, and trap dykes. Note that the image incorrectly implies that folding produces elevation, when Hall claims just the contrary. Above: a depiction of the warping of the crust by gravitational loading as described by the English astronomer and sometimes-geological theorist John Herschel. (Hall was aware of Herschel’s work (see Hall 1859, especially Note E on pp. 95–96). Indeed, insofar as Hall presents a theory of “elevatory movement” it is just the model of Herschel repurposed)

The first question is the easier to answer. Hall believed, like many of his contemporaries, that the interior of the earth was pliant enough to yield to gravitational loading. This means that as sediment is piled on a particular part of the crust, the crust will begin to describe a downward fold. (Think of setting a bowling ball on a memory-foam mattress.) Now, as the weight of the sediment increases, so will the degree of downward flexure until no more bending is possible. During this process, the upper layers of sediment will become crumpled by compression. At the same time, the lower layers will be fractured by extension (Dott 1979). As Hall put it in a publication of 1859:

By this process of subsidence… the diminished width of surface above, caused by this curving below, will produce wrinkles and folding of the [uppermost] strata. That there may be rents or fractures of the strata beneath is also very probable, and into these may rush the fluid or semi-fluid matter from below, producing trap-dykes. (Hall 1859, 70)

Hall concludes that “the folding of strata [is] a very natural and inevitable consequence of the process of subsidence.” To produce the folds, faults, and dips of the Appalachians, no upheaval is required.

But how is elevation produced in the absence of upheaval? Hall’s answer, destined to confuse generations of geology students, is that “elevation is due to deposition” (Hall 1882, 55). “It is original deposition that not only gives direction to our mountain chains, but [also] determines their elevation.” Folding and crumpling decrease this elevation without effacing it. So, in Mott Greene’s summary, “what elevation there [is] in the Appalachians [is] a function of the thickness of sediment deposited along the line of the current, minus the loss of elevation by contraction and contortion of the strata” (Greene 1982, 128). It is worth underlining that contraction and the contortion do not produce elevation— they limit it. Writes Hall, “If there were no folding or contortion, and if the strata of the Alleghany mountains were as undisturbed as those [to the west],” then the mountains would form “a simple stratified pile of more than twenty thousand feet from the base of the Potsdam to the summit of the Devonian” (Hall 1882, 54).

And consider the plains to the west. Here, a thousand miles from New York, “we have essentially the same set of strata as those forming the Appalachians,” and yet no mountains disturb the monotony of the prairie (56). Why? Because there are “no materials of which to make mountains in the great Mississippi plateau. The general height of the country gives the entire elevation produced by the thickness of the beds, and there can be no more.”

We could have no mountain chains along a great plateau like this, however much the strata may be folded or contorted, unless there should take place a dislocation of the older Laurentian or Huronian rocks from below; and although such a phenomenon would be in accordance with geologic theories [i.e., speculations], respecting the upheaval of mountain chains, yet I suspect that careful search would prove that no such upheaved chain of mountains exists upon the surface of the globe. In fact, that the upheaval of mountain chains, except in the sense that the elevation of the continent is upheaved, has never taken place. (Hall 1882, 56, emphasis added)

With this final remark, the complete picture is at last on the table. Whatever “upheaval” there has been in geological history has been upheaval of the general sort: the raising of entire continental masses, as opposed to the regional uplift of mountain chains. In support of this contention, Hall mentions that the Appalachians are barely higher than the adjacent Catskills, which “have nothing to do with [the Appalachians] so far as being involved in the disturbance of the strata” (56). The Appalachians rose because the entire continent was uniformly uplifted from the East Coast to the Mississippi. And whatever force elevated the continent presumably worked to restore the crust to an equilibrium state determined by gravitational buoyancy, since otherwise a depressed pit of sediments would remain a pit, no matter its general elevation.* (As Hall wrote in 1859, referencing the view of John Herschel, “every continent depressed has the tendency to rise again… It is this ultimate rising of continental masses that I contend for, in opposition to special elevatory movement along the lines of mountain chains” (96).)

[* Like ships with deep hulls, Hall seems to have thought that thicker bits of crust ride higher in the underlying viscous material. So even though a rising tide will lift all ships, it can be expected to lift deeper ones to greater heights. Hall seems to confirm that this is his view in a letter to Joseph Henry (December 26, 1857): “The highest rock of the Green mountains, say 4,000 feet above tide water, is the upper member of the Hudson river group; now the entire thickness of the sediment from the base of the Potsdam to the top of the Hudson river is scarcely less than 10,000 feet. You will see that there is [as] much below the sea level as there is above it, and this I believe to be true in all similar mountain chains.”]

The published transcript of Hall’s address contains no images. However, it seems that Hall shared George Airy’s expectation that tall mountain chains will have deep “roots” (although perhaps not as deep as Airy suspected). Hall also seems to suggest that gravitational factors are involved in producing elevation, such that packages of sediment that began as depressions in the crust find their equilibrium as deep-rooted mountain ranges

Hall did not pretend to know what force worked to uplift entire continents and with them mountain belts. Still, his overall position is clear enough. As he put it in a letter of 1876, “Mountain ranges are not elevated as ranges of mountains, but as part of the continental movement.” Major structural features are determined during deposition, which also determines the overall trend and direction of mountain chains. Nothing else is required to explain the features of folded mountains: just the steady and mechanical action of deposition and uplift. Mountain building is an incremental, almost a passive process. It is the furthest thing in the world from spasms of violence pictured by the Rogers brothers.

So why did Dana call this “A theory for the origin of mountains with the origin of mountains left out”?

* * *

You will have guessed the reason. It is, in Dana's words, that the theory “has its cause for subsidence, but none for the lifting of the thickened sunken crust into mountains” (Dana 1866, 210). Hall declines to speculate about what forces are responsible for general continental uplift. He also fails to explain how general uplift turns a depression into a mountain range, although it seems like he has some kind of gravitational mechanism in mind. Anyway, for those who conceptualize the task of geotheory in dynamical terms— to show how a pile of sediments is lifted into a mountain— the explanation is bound to disappoint.

And even to puzzle. Reactions to Hall’s theory ranged from enthusiasm to befuddlement, with perhaps more of the latter than the former. A famous anecdote has Arnold Guyot leaning over the shoulder of Joseph LeConte during Hall’s address and asking whether LeConte understood what Hall was saying. “Not a word,” LeConte is said to have replied (Dvorak 2021). Dana’s question already hung in the air: How could someone leave mountains out of a theory of mountain building?

James Dwight Dana (1813–1895), the most influential American geologist of his generation

Here at last we come to background theory. To understand Hall, you must understand that he was a uniformitarian: one of relatively few in the American geological community (Bartholomew 1979).* By this I mean that he not only adopted a comparative approach to geological problem solving, but also that he was allergic to the invocation of novel causes, or causes operating at unknown intensities, to explain geological phenomena. The “wave model” for the origin of mountains was not simply wrong, it committed a methodological sin by invoking a totally unknown cause to account for the birth of mountains. More philosophical was to claim that the Appalachians were produced “by continued action from a long anterior period,” all other suggestions being mere rhetorical trickery.

[* Consider Hall’s closing remarks in his AAAS address: “Geology, if we would let alone grand theorizing, is a simple and beautiful study, in which we see everything evolved naturally and harmoniously, without at any time any great and sudden changes. We remark those changes as one who having viewed a city in its progress, should fall asleep for a century and afterward behold the difference. But to one who could have seen stone laid upon stone, and each edifice completed singly, it would have had but the aspect of natural and quiet progress” (Hall 1882, 63).]

In the middle part of the nineteenth century, Lyellian geology was both in the ascendancy and on the ropes. The success of Lyell’s Principles had won its author a place among the inner circle of the geological elite. Henceforth he would be renowned as the person who had “demonstrated, particularly by his exemplary reconstruction of the Tertiary periods, how much [geohistory]… could be explained in causal terms by applying the actualistic method more thoroughly than ever before” (Rudwick 2008, 560). Yet Principles was curiously silent on a problem that would become a leading concern of (especially continental) geologists in the decades following its publication. This was the origin of folded mountains, and in particular, of linear chains. Lyell had impressively little to say about this stuff. The first volume of Principles devoted a scant six pages to the subject (!). There he implied that all elevation is created by “subterranean convulsions” (basically, earthquakes), which nudge up bits crust in modest increments. The only difference between the Alps and the “gently-rising hills” of England is that the former have been nudged up more; but the process is essentially the same wherever marine beds have been turned into dry land. Mountains, then, require no special explanation. Bits of crust are always being raised up and brought low. Mountains are just the bits of crust that have been raised up the highest.

Lyell’s relative lack of interest in mountain building was shared by his influential predecessor, James Hutton. Indeed, as Mott Greene observes, Hutton’s theory of the earth contains no independent account of mountain building as such. “Uplift occur[s], with dislocation, during continental elevation”'; yet “the height of mountains above surrounding country [is] not a phenomenon of structure but of relief. Following the uplift of a continental mass, the secular work of erosion carve[s] out valleys and [wears] the land down” (Greene 1982, 86). So, mountains are the parts of a continental mass that have yet to be brought low by erosion. Anyway, they require no special explanation. In uniformitarian geology, uplift is a primitive phenomenon and mountains are an expected result of uplift, either because some bits of the earth are nudged up more than others (Lyell) or because some parts of the crust escape erosion for longer than others (Hutton).

A Huttonian watercolor of a conical mountain on the Isle of Arran, meant to illustrate a key claim of Hutton’s theory of the earth: that granite is not a primitive rock but sometimes invades sedimentary successions

But not only did uniformitarians fail to take an interest in the dynamic process of mountain building. They also showed a lack of concern with the characteristics of folded mountains: the folds, faults, and trend-lines that preoccupied their continental counterparts. Lyell was especially uninspiring on this score. Apart from an extended criticism of Élie de Beaumont (introduced in the third edition of Principles), Lyell makes little attempt to explain the structure of folded mountains or their distribution in space. Uniformitarian geology was at home in the glens and moorlands of Scotland and on the conical slopes of Mount Etna. It was not well equipped to handle the complexities of the Alps, or even, for that matter, the Appalachians.

Now consider James Hall, working within the Lyellian tradition but faced with the problem of explaining the Appalachians. As a card-carrying uniformitarian, Hall was not concerned to explain continental movement. Uplift was a fact of nature, somehow connected to subterranean activity; but as far as Hall was concerned it was something that could be presupposed, and summoned to produce elevation wherever it was needed. More pressing was the need to explain the major structural features of the Appalachians: those folds, faults, and dykes that had preoccupied the Rogers brothers. Very few resources existed within Lyellian geology to explain such features, and none at all to explain the phenomenon of mountain chains. So Hall produced them. Mountains form chains because sediment is deposited in great linear trenches by powerful ocean currents. These trenches then sag under their own weight, causing the sedimentary layers contained within them to crumple and stretch. When the sediments are returned to sea-level (through ordinary processes of uplift) they already resemble folded mountain sediments. And all this without any paroxysmal upheaval. For a uniformitarian like Hall, the account checked all the boxes.* It just didn’t say exactly how mountains achieved their great elevation; but what uniformitarian ever worried himself with that question anyway?

[* Here is Hall in a letter to George Vose (1864): “If I can sustain the great principle which I advocate, viz.—that mountains are not produced by upheaval but by accumulation and continental elevation I shall feel that I have done something to advance the Science of Geology in true [uniformitarian] principles” (quoted in Merrill 1924, 388, emphasis added).]

So it isn’t true that James Hall left mountains out of his theory of mountain building. He simply failed to describe any special process by which mountains are uplifted, preferring to ascribe this to the familiar phenomenon of (vertical) continental movement. To a Lyellian, this would’ve seemed a reasonable thing to do. Uplift happened— it was a vera causa— even if its own causes were poorly understood. And the highest mountains did seem to be formed of the thickest sedimentary sequences, deposited underwater. To complete the model, Hall simply denied that there was anything special about the process by which these sedimentary sequences were uplifted. (If the causes of uplift were a problem, then they were everyone’s problem, not just Hall’s.) In this way, a background theory that treated uplift as a primitive phenomenon excused Hall— in his opinion— from the need to explain how mountains achieved their great height.

The Appalachian Mountains, again

Dana was right to be critical. For anyone not in thrall to Lyellian dogma, the theory fell silent at a crucial point: the production of elevation. Dana and others wanted to know how sediment trenches on the seafloor became mountains, not just how they became crumpled up. General uplift was at best a partial answer to this question, and in the absence of a more explicit account of how uplift and isostasy interact, it could not explain how trenches of sediment come to dominate landscapes. In later years, Dana would develop his own answer to this question, which would dominate American geology for several decades (Dott 1997). In the process he coined a term that would come to be associated with Hall’s model and his own: “geosynclinal,” soon shortened to “geosyncline.” Its importance can be gleaned from a 1944 presidential address to the Geological Society of America, in which the speaker, Adolph Knopf, praised “the geosynclinal doctrine” as “a great unifying concept, possibly one of the greatest in geologic science” (Knopf 1948, 667).

Alas, the days of the “geosynclinal doctrine” were numbered. Today, it is usually remembered as an almost unfathomable mishmash of ideas, or a “collective hallucination.” Hall’s model, in particular, is singled out as absurd, confused, and basically unintelligible (e.g., Dvorak 2021). But surely this is unfair. Intelligibility is a function of background assumptions, and for those who shared Hall’s assumptions the theory at least made sense. This is not to say it was acceptable, or that it presented no interpretive difficulties. It’s just to say that intelligibility is not an intrinsic property of ideas; audiences matter too (Dear 2006). Whether James Hall really left mountains out of his theory of mountain building is a matter of perspective, and from an important perspective– Hall’s own— he did not.

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