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American Geomorphology at the Dawn of the 20thCenturyAntony R. Orme aa University of California, Los AngelesPublished online: 15 May 2013.
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Physical Geography, 2004, 25, 5, pp. 361–381.Copyright © 2004 by V. H. Winston & Son, Inc. All rights reserved.
AMERICAN GEOMORPHOLOGY AT THE DAWN OF THE 20TH CENTURY
Antony R. OrmeDepartment of Geography
University of CaliforniaLos Angeles, California 90095-1524
Abstract: A geomorphologist, William Morris Davis, founded the Association of American Geographers in 1904. Today, a century later, it is timely to reflect on the nature of geomorphology so long ago, on paths taken and paths ignored. By 1904, the heroic age of American geomorphology, of the western explorations, had passed. Powell was dead, Dutton was retired and ill, and Gilbert seemed destined at the time for lonely retirement. In their stead, Davis strode the field like a colossus. His cycle of erosion, nurtured for 20 years, fit well into the evolutionary dogma of the age. With its emphasis on time, the perceived relevance of structure and process atrophied. While Earth’s main relief features were still attributed mainly to a cooling and contracting planet, Dutton’s isostasy and Taylor’s mobilism received short shrift. In any case, depending on who one believed, Earth was only 20 to 400 million years old. Furthermore despite advances in mechanics and applied sciences, geomorphic processes were largely ignored. This was soon to change— from an expanding time scale based on radioactive decay, a reinvigorated Gilbert’s field studies and flume experiments, Udden’s work on wind, and advances in geodesy, geo-physics, hydrology, and scientific methodology. That these advances lingered so long in the wings was more a reflection of the restrictive Davisian stage than of the many paths potentially open to geomorphology as the 20th century dawned. [Key words: geomorphol-ogy, Earth-science theory, history of science.]
INTRODUCTION
A geomorphologist, William Morris Davis, was instrumental in founding the Association of American Geographers in 1904, thereby providing another forum for the dissemination of his particular approach to geomorphology based primarily on the cycle of erosion. Despite, or perhaps because of, the major advances in the field triggered by the western explorations between 1865 and 1890, Davis’s cyclic approach to landforms, nurtured for 20 years, had become the dominant paradigm in American geomorphology by the dawn of the 20th century (Davis, 1899). Other approaches were ignored or postponed, in part because the Earth sciences as a whole were still wrestling with the age of Earth and the causes of mountain build-ing, in part because advances in cognate sciences ranging from thermodynamics to hydrology had yet to be applied significantly to the study of geomorphic processes.
The Davisian system spread across much of the world, generated many disciples, and persisted into the mid-20th century before advances in the understanding of Earth time and crustal mobility, augmented by more profound studies of process, caused it to be superseded. Yet this need not have been. By 1900, prior debates about Earth time were about to be revolutionized, continental mobility was being
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discussed by geodesists and geophysicists, the implications of climate change were being evaluated, and Gilbert, Udden, and others were paving the way for a better understanding of process.
This paper examines some of the predominant themes in the Earth and related sciences at the dawn of the 20th century, shows how the emerging field of geomor-phology was channeled into the Davisian system at the expense of other avenues of enquiry, and discusses how some of the advances in science that were to influence later ideas were already in place by 1900. The discussion focuses on selected sci-entific themes around that time, namely the age of Earth, cyclicity, mountain build-ing, crustal mobility, and fluvial and aeolian processes. In short, this paper focuses on concepts of time, so essential to the Davisian cycle of erosion; on elements of structure, which the Davisian system assumed as given; and on selected processes, which the Davisian system largely ignored. It concludes with an assessment of the emergence of a distinctively American school of geomorphology by 1900.
CONCEPTS OF TIME
Concepts of time are critical to that branch of the Earth sciences that examines the development of landforms. Defending the Huttonian vision of slow changes in Earth’s surface features in the context of Newtonian calculus, John Playfair (1802, p. 117) stated that “Time performs the office of integrating the infinitesimal parts of which this progression is made up.” The relevance of time to this essay is illustrated from two themes that engaged scientists at the dawn of the 20th century, namely the age of Earth and the cyclic concept.
The Age of Earth
The age of Earth may be of little direct significance to geomorphology because most modern landforms have been shaped by processes during the relatively recent geologic past. Nevertheless, this age has indirect significance because it provides the time limits within which these processes operate. If Earth time is limited, it is necessary to invoke rapid processes, even catastrophes, to explain its surface fea-tures. As Earth time is expanded, there is more opportunity for processes to function at normally observable rates and for change to be accommodated. This was of course the dilemma that faced scholars during earlier centuries when restrictive biblical timescales necessitated catastrophic explanations of rocks and landforms. This dilemma was rudely awakened by James Hutton’s enquiry into the origins of Earth, of which he found “no vestige of a beginning—no prospect of an end” (Hutton, 1788, p. 304).
In 1650, Archbishop James Ussher invoked the year 4004 BC for the Earth’s ori-gin and 2348 BC for Noah’s Flood (Ussher, 1650). By the early 19th century, this biblical timescale was in retreat before the onslaught of the actualists or uniformi-tarians, stimulated by Hutton and Playfair but championed by Charles Lyell (1797–1875), whose work in turn influenced Charles Darwin (1809–1882) to invoke 300 million years for the post-Cretaceous denudation of England’s Wealden dome (Darwin, 1859). Even so, catastrophist views long lingered in the United States.
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Most influential American scientists of the period, such as Amos Eaton (1776–1842) and Benjamin Silliman (1780–1864), were catastrophists, with but a small minority, notably Francis Gilmer (1790–1826), espousing uniformitarian views emerging from Europe (Merrill, 1924). Indeed, for many years after its inception (as Silliman's Journal) in 1818, the American Journal of Science fostered catastrophist beliefs. Writing in that journal in 1821, J. W. Wilson stated “Is it not the best theory of the Earth, that the Creator, in the beginning, or at least at the general deluge, formed it with all its present grand characteristic features?” (Wilson, 1821, p. 253).
Between 1830 and 1860, however, catastrophism within the United States yielded to uniformitarianism, a response in part to Charles Lyell’s visits during the 1840s. Lyell’s view of limitless time was in turn challenged by two groups of scien-tists who brought newer approaches to the subject. One group, those concerned with the physics of the solar system and of Earth as a cooling planet, an idea pro-posed by Descartes in the 17th century, sought to derive an age for Earth from inferred rates of cooling. Variations of this theme followed the lead of William Thomson (later Lord Kelvin) in Britain who at one time or another believed Earth to be between 20 and 400 million years old. In the United States, Alexander Winchell (1824–1887) of Michigan reduced Earth’s age to 3 million years (Winchell, 1870), while Clarence King (1842–1901), the first director of the United States Geological Survey (USGS), suggested an age of not more than 24 million years (King, 1893). The other group comprised geologists who derived an age for Earth from rates of sedimentation and mechanical and chemical denudation suggested by the strati-graphic record. Notable among these was Clyde Walcott, then at the USGS, who deduced an age of 55 million years (Walcott, 1890).
Thus, at the dawn of the 20th century, and based on several theoretical assump-tions, Earth’s age was thought to be somewhere between 20 and 400 million years old. Whereas a limited age posed problems, a greater age was not an insuperable constraint for geomorphologists concerned with the fashioning of present land-forms—provided that these were shaped on a relatively immobile continental plat-form uninterrupted by major structural disruptions of Earth’s crust.
As the new century opened, however, Earth’s age was about to be greatly extended by reference to the radioactive decay of its rocks and minerals. Radioac-tivity, discovered by Becquerel in 1896 and advanced by the Curies, was soon applied to rocks by Rutherford, Soddy, Strutt, and Boltwood. Then, based on the uranium-lead method, Arthur Holmes (1890–1965) measured some Precambrian rocks from the United States as 1310–1435 million years old (Holmes, 1911, 1913), while Joseph Barrell (1869–1919) advocated an age of between 550 and 700 mil-lion years for the base of the Cambrian (Barrell, 1917). Advances in radiometric dat-ing have since dated the Earth’s origins to around 4600 million years.
The extent to which William Morris Davis was influenced by these developments is unclear. It seems likely that, provided there was sufficient time for a cycle of ero-sion to generate a peneplain, the longer Earth’s timescale, the more cycles that could be accommodated and the more peneplains that could be consumed by later processes. How much time was actually needed for an erosion cycle to achieve peneplanation was unclear but contemporary scholars invoked periods ranging from 5 million to 30 million years.
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Cyclic Concepts
When early 20th century geomorphologists focused attention on the Davisian cycle of erosion, cyclic concepts were by no means new. More than a century ear-lier, Hutton (1788) had proposed a cyclic pattern for Earth events, while even enlightened catastrophists such as Cuvier (1769–1832) invoked several catastro-phes to explain the extinctions of life forms evident from the rock record (Cuvier, 1812). In like vein, Timothy Conrad (1803–1877) later invoked a sequence of cre-ations to explain the extinctions seen in the fossil record of Cenozoic deposits beneath the Atlantic coastal plain (Conrad, 1839). These several creations were separated by climate changes which, reflecting the growing interest in glacial the-ory (Agassiz, 1840), he attributed to episodic refrigeration. In Europe, meanwhile, notions of cyclic changes in Earth–Sun relations (e.g., Adhémar, 1842) were leading scientists to build a case for cyclic climate change (e.g., Croll, 1864). By this time, American stratigraphers were identifying rhythms and cycles in the rock record (Newberry, 1873).
In 1847, the distinguished American scientist, James Dwight Dana (1813–1895) of Yale, proposed that the epochs reflected in the geologic record were due to the alternation of prolonged periods of quiet with pulses of more or less rapid change, the latter attributable to Earth’s contraction (Dana, 1847). Joseph Le Conte (1823–1902), the polymath who became professor of geology, zoology, and botany at the University of California in 1869, also favored long periods of crustal quiescence fol-lowed by brief periods of rapid movement and mountain building. Thus:
Geological history, like all other history, has its periods of comparative quiet, during which the forces of change are gathering strength; and periods of revolution, during which the accumulated forces manifest themselves in conspicuous changes in physical geography and climate, and therefore in rapid movements in the march of evolution of organic forms. (Le Conte, 1877, p. 100)
Davis’s cycle of erosion, first proposed in 1884, was thus a derivative of hypoth-eses promoted earlier. In particular, the advocacy of Dana and Le Conte for periods of lengthy quiescence separated by brief pulses of rapid change was clearly reflected in Davis’s concept of prolonged peneplanation separated by brief oroge-nies which reset the erosion clock and initiated new cycles of erosion. The Davisian system also reflected the evolutionary dogma of the later 19th century in which pro-gressive orderly change through time was interrupted and then restarted by cyclic changes in natural systems (Chorley et al., 1973). In this, Davis was supported by the belief in geologic rhythms, or “correlated pulsations” inferred by Thomas Chamberlin (1843–1928), a leading theorist and glacial geologist of the time (Chamberlin, 1898). In like fashion, the anthropomorphic concepts of youth, matu-rity and old age with which Davis garnished his cycle had already had frequent air-ing among evolutionists.
What was surprising about the Davisian system was its persistence in an age when the instability of Earth’s crust and mounting evidence for climate change were
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being widely discussed across the sciences. Diastrophism could be invoked to trig-ger a new cycle of erosion and to tilt former peneplains (Davis, 1904), but persistent crustal instability was incompatible with the prolonged denudation required for peneplanation, and therefore was best ignored. These arguments came full circle when geologists later invoked the Davisian model to show that Earth’s crust had indeed experienced prolonged structural quiescence between brief orogenies, the very belief inherited from Dana and Le Conte that had led Davis to design his model in the first place.
As for climate, Grove Karl Gilbert (1843–1918) had invoked climate change aris-ing from Earth’s orbital perturbations, specifically the precession of the equinoxes, to explain rhythmic bedding found in late Cretaceous marine sediments in Colorado (Gilbert, 1895c). But Davis was not likely to disrupt his fine model for orbital perturbations which, at the time, few understood and even fewer believed. As Davis and his followers showed, climate change could be incorporated into the Davisian cycle through related changes in base level that triggered rejuvenation and new cycles of erosion, but the reasons for climate change were rarely explored.
UNDERSTANDING STRUCTURE
Structural issues played a major role in the development of Earth sciences during the 19th century but were accorded short shrift, other than as passive background, by most American geomorphologists during the earlier 20th century. This con-trasted with the emerging German school of geomorphologists, led by Albrecht Penck (1858–1945) and his son, Walther Penck (1888–1923), with their strong foundations in structural geology (e.g., Penck, 1894; Penck, 1924; Chorley, 1963). That American geomorphologists viewed structure as background, rather than as an interactive force, may be attributed to the emergence of the Davisian cycle which, ideally, assumed initial rapid uplift followed by prolonged structural quiescence during which the erosion cycle played out. Davis (1905) himself cautioned about complications resulting from structural forces, but many of his disciples were less cautious. Structure was further downgraded when Davis and his followers trans-ferred their allegiance to geography and the latter sought to distinguish itself from geology. This move reduced the input of structural geologists to geomorphology as practiced by geographers. Yet toward the close of the 19th century, important debates were taking place regarding mountain building and the broader mobility of Earth’s crust.
Orogeny
The limitations of early 19th century science militated against any clear under-standing of mountain building but, if a consensus could be gleaned from the litera-ture of the time, a majority explained mountains as a response to unfathomable paroxysmal subterranean forces, including great earthquakes, while a minority still looked to divine intervention.
Toward the middle of the 19th century, however, mountain building began to be explained by forces generated during the assumed cooling and contraction of a
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formerly molten Earth. This was not a uniquely American idea, for many European geologists, notably Elie de Beaumont (1798–1874) and Henry de la Beche (1796–1855), favored similar notions (Greene, 1982). Nevertheless, evidence from North American continental margins offered seemingly strong support for the hypothesis, notably from the complex fold systems of the Appalachian Mountains so admirably mapped by the Rogers brothers in the 1830s and 1840s (Rogers and Rogers, 1843).
The contraction hypothesis, oft-defined by Dana between 1846 and 1873, stated that slow cooling of Earth’s interior led to contraction of the crust, forming basins into which oceans retreated and from which continental swells became separated by marginal, elongate geosynclines (Dana, 1847). Lateral stresses generated between the subsiding basins and rising swells then compressed sediments accu-mulating in the geosynclines, culminating in mountainous fold belts. By feedback, including what later became known as isostasy, onshore denudation and offshore sedimentation accentuated both continental uplift and oceanic subsidence. Anom-alies within fold belts were explained through variations in the stress fields and rocks involved. In a similar vein, Le Conte (1872) viewed Earth as a series of con-centric shells wherein the thin, more rapidly cooling outer crust would shrink and fracture from massive horizontal pressures set up as the underlying rocks cooled and contracted more slowly. These pressures were released in the direction of least resistance, namely upwards. He suggested that “mountain ranges are formed by a crushing or mashing together horizontally of the whole crust and a thickening or swelling upward of the squeezed mass” (Le Conte, 1876, p. 297). He deduced that compression and uplift had reduced the sediments forming California’s Coast Ranges from about 25 km to 10 km in width.
The distinguished paleontologist James Hall (1811–1898) used similar evidence to support an alternative model. Like Dana and Le Conte, Hall (1859, 1882) viewed the great thickness of folded Paleozoic strata in the Appalachians as evidence of massive shallow water sedimentation in a marginal geosyncline. Sedimentation provoked continuing basin subsidence and compression that deformed the rocks and generated metamorphism, but led to no significant increase in elevation. Unlike Dana and Le Conte, he opposed contraction as a mechanism and invoked later epeirogenic uplift to explain the elevation of the Appalachian fold belt.
The contraction hypothesis of mountain building was the dominant paradigm from the 1840s to the 1870s and, despite growing awareness of its absurdities, sur-vived into the early 20th century, essentially because alternative hypotheses also posed problems (e.g., Willis, 1893). That North America possessed cordilleras that paralleled both the Atlantic and Pacific coasts supported the concept of marginal deformation which, with the prevailing belief in fixed continents, persisted until alternative concepts were promulgated in response to better understanding of crustal mechanics and the plate-tectonic revolution later in the century. Paradoxi-cally, most geomorphologists around 1900 accepted episodic mountain building confined to deforming continental margins while also identifying extensive pene-plains, and therefore prolonged stability, for those same margins. Absurdity was most evident in the massively deformed Pacific mountain system where, for exam-ple, Fairbanks (1904) identified a Pliocene peneplain among the summit elevations
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of the Santa Lucia Mountains and a Pleistocene peneplain in the Salinas River valley.
Epeirogeny and Isostasy
During the later 19th century, the mountain-building problem became closely involved with questions regarding epeirogeny and isostasy. Epeirogeny, the gentle flexuring of Earth’s crust, was invoked to explain the widespread warping of sedi-mentary rocks beyond the main orogenic belts, essentially as an extension of the more intense lateral forces responsible for mountain building (Merrill, 1924).
Around this time, the concept of isostasy was invoked to explain both epeirog-eny and orogeny. The term isostasy was coined in 1882 by the American army officer and scientist, Clarence Dutton (1841–1912), in a review of Fisher’s The Physics of the Earth's Crust (1881), and was elaborated in an address to the Philo-sophical Society of Washington in 1889 (Dutton, 1882a, 1889). But the concept and its geophysical basis were by no means new. In 1837, for example, John Her-schel (1792–1871) had suggested that gravity anomalies observed by surveyors in mountainous regions were related to sediment loading at ocean margins that caused sea-floor subsidence and consequent uplift of continental margins. Survey anomalies measured in India in the 1840s then led to the conflicting hypotheses offered by Pratt (1855) and Airy (1855) regarding the nature and behavior of Earth’s crustal rocks. In his 1881 book, Osmond Fisher (1817–1914), a leading British opponent of the contraction hypothesis, suggested that Earth’s rigid crust rode in approximate hydrostatic equilibrium on a plastic or liquid substratum. Such flota-tion allowed the crust to shift laterally, which in turn produced narrow fold belts and crustal thickening. Fisher’s ideas found favor with Dutton who, from a theoret-ical perspective, had earlier stated that the mechanical force arising from contrac-tion by cooling was many times less than the quantity required for mountain building (Dutton, 1876). Based on his observed “great denudation” of the Colorado Plateau (Dutton, 1882b), Dutton now invoked isostasy (Fisher’s “hydrostatic equi-librium”) as the mechanism responsible for both mountain building and continuing degradation. In a seminal observation, he stated that “wherever broad mountain platforms occur and have been subjected to great erosion the loss of altitude by degradation is made good by the rise of the platform” (Dutton, 1889, p. 204).
Dutton’s observations on isostasy have profound implications for Earth’s surface form but during his time they were largely ignored by geomorphologists. There are three main reasons for this. First, shortly after his 1889 address, Dutton’s 15-year involvement with the western surveys came to an end and, although maintaining scientific interests, he made minimal contributions to critical debates between 1890 and his death in 1912 (Orme, 2005). Second, with the paucity of crustal data then available, neither Dutton nor Fisher, nor indeed other scientists of the time, clearly understood isostasy. Third, whereas the concept was soon embraced by geo-physicists and geodesists (e.g., Hayford, 1909), most contemporary geologists were reluctant to enthuse over isostatic models based on mathematical assumptions of crustal behavior that could not be proven at the time. There were exceptions. For example, deformed Pleistocene shorelines around Lake Bonneville had led Gilbert
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368 ANTONY R. ORME
(1890) to recognize the nature of crustal loading and unloading by lake waters. In strange contrast, however, Gilbert (1895a) believed that the Rocky Mountains could be supported by the strength of Earth’s crust. Thus, while welcoming the gravity measurements obtained by the U.S. Coast and Geodetic Survey (Gilbert, 1895b), Gilbert appears to have remained confused about the broader implications of isos-tasy. Indeed, for several decades, there was a disconnect between the work of geod-esists and field geologists regarding the significance of gravity anomalies (Mabey, 1980). Even after Andrew Lawson (1861–1952) of the University of California, Berkeley, published on The geological implications of the doctrine of isostasy in 1924, few entered the lists to challenge the prevailing Davisian system of landform development.
Thus, at the dawn of the 20th century, isostasy as a global process-response mechanism was ignored by most geomorphologists. Whereas some form of local, even regional, isostatic adjustment to loading and unloading by glacier ice or sedi-ment could be invoked from survey data, widespread adjustments to the denuda-tion of orogenic belts and epeirogenic swells were inconceivable. If accepted by those wedded to the Davisian system, they would upset the orderly progress leading to peneplanation, indeed tarnish the entire model. A notable exception was Reginald Daly (1871–1957), Davis’s successor at Harvard in 1912, who explained the accordant summits of alpine ranges not as remnants of former peneplains but as subtle interactions between erosion and isostasy (Daly, 1905). But Daly was then but a small voice in a vast conformist arena.
Continental Mobility
Notions of continental mobility long preceded Wegener’s concept of continental drift of 1912 and the later plate-tectonic revolution. Similarities between Carbonif-erous plant fossils in Europe and North America, for example, led Snider (1858) to suggest that these continents had once been joined. Most such ideas were soon dis-missed in the scientific circles of the late 19th century, dominated as they were by a belief in crustal stability and only vague ideas about subcrustal forces. Despite dif-fering views on the causes of orogeny, such worthies as Dana, Dutton, and Chamberlin believed in the permanence of continents, while allowing that their margins could be deformed and augmented by subsidence and mountain building and the whole mass subject to isostatic adjustment.
Nevertheless, certain features of the geological record continued to puzzle sci-entists. The Rogers brothers in the 1840s had suggested that the Appalachian fold belt had been fed by sediments from an older continent to the southeast (Rogers and Rogers, 1843). Indeed, arising from the mountain-building controversy, many sci-entists around the dawn of the 20th century had come to believe in the existence of former continents, or at least land bridges, over the sites of present ocean basins while denying that the present continents had themselves moved significantly (e.g., Williams, 1897; Schuchert, 1910).
The issue of continental mobility also became embroiled in notions regarding Moon’s relationship with Earth. Fisher (1881), among others, suggested that the Pacific Ocean basin had formed as a crustal scar following Moon’s departure from
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Earth. William Pickering (1907) believed that Moon’s departure occurred when the subcrust was still molten and that, drawn by Moon’s gravity, the rifting and westward movement of the Americas away from the more easterly continents occurred on a bed of magma.
Meanwhile, Frank Taylor (1860–1938) suggested that Earth had captured, rather than lost, Moon in geologic time and that an increase in Earth’s rotational speed had driven the continents toward the equator (Taylor, 1898). Revisiting the theme in 1908, Taylor suggested that a change in the oblateness of Earth’s spheroid of rota-tion as a result of the Moon’s capture in the Cretaceous had caused landmasses focused on the poles to begin creeping toward the equator. Disenchanted with the contraction hypothesis, he suggested that divergent continental creep away from the poles was responsible for the world’s Cenozoic mountain belts (Taylor, 1910). He also thought that the Mid-Atlantic Ridge was likely the residual of a rift system away from which the adjacent continents had moved. For a mechanism, he was inclined to reject internal causes and invoke tidal forces. As his detractors pointed out, however, if tidal forces could move continents and raise mountains, the friction involved would almost certainly brake Earth’s rotation, perhaps to a standstill. Fur-ther, if Moon’s capture in the Cretaceous was invoked to explain Cenozoic moun-tain chains, what explanation was available for earlier orogenies?
While the above proposals were generally considered outrageous, a few years later Alfred Wegener (1880–1930) aired a more coherent hypothesis on continental displacement which was to have far-reaching, if not immediate, impact on ques-tions of crustal mobility (Wegener, 1912). His ideas were expanded into a book on Die Entstehung der Kontinente und Ozeane (Wegener, 1915), the third edition of which was translated into English in 1924. This translation reached a much wider audience and led the American Association of Petroleum Geologists to convene a symposium in 1926 at which, despite the presence of Wegener and Taylor, the con-cept of continental drift was largely dismissed, even ridiculed (van Waterschoot van der Gracht, 1928). Like Taylor, Wegener’s concept focused on tidal forcing and the flight of continents from the poles (Pohlflucht), and it likewise foundered on the question of an acceptable mechanism. As Chester Longwell of Yale emphasized, “this rebellion against the established order . . . must have a sounder basis than imaginative appeal” (Longwell, in van Waterschoot van der Gracht, 1928, p. 145).
With few exceptions, the United States scientific community remained a bastion of opposition to continental mobility until developments in paleomagnetism and marine geology initiated the plate tectonic revolution in the 1950s. Certainly, at the dawn of the 20th century, geomorphology was not yet prepared for these concepts. Indeed, although it may now seem otherwise, Davis (1889) was really reflecting contemporary stabilism when he postulated that the original (Permian) drainage of the Appalachians may have flowed from the coast toward the northwest, from a continent that subsequently subsided and vanished. While later offering an alterna-tive model, his student, Douglas Johnson (1878–1944), claimed Davis’s scheme as “one of the most brilliant examples of close deductive reasoning to be found in physiographic literature” (Johnson, 1931, p. 56). However, as with isostasy, had continental mobility been accepted at the time, such fine reasoning would have been challenged sooner rather than later.
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370 ANTONY R. ORME
UNDERSTANDING PROCESS
During its long innings, the Davisian model came to be recognized for its weak-ness in understanding process. Thus, in a retrospective symposium on the relative merits of the Davisian and Penckian systems, staged by the Association of American Geographers in 1940, John Leighly of the University of California, Berkeley, could write:
Davis’s great mistake was the assumption that we knew the processes involved in the development of land forms. We don’t; and until we do we shall be ignorant of the general course of their development. In his eagerness to set up a general system, Davis jumped over the preliminary, necessarily painfully slow study of processes, and so left his system with an inadequate foundation. (Leighly, 1940, p. 225)
This critique has merit because, while Davis and his followers designed models for various environments based on differences between processes, they rarely analyzed those processes in detail. Nevertheless, to support the critique, it is necessary to understand what information was or was not available to geomorphologists at the time, focusing here on fluvial and aeolian processes.
Fluvial Processes
Unquestionably, an understanding of the fluvial system underpinned the Davisian model in which an initially mountainous landscape was reduced through time to a peneplain. The stages of youth, maturity and old age that demonstrated a river’s behavior over time were described qualitatively in terms of the landscape’s assumed response rather than in verifiable terms regarding fluvial processes, stream flows, and channel efficiency. Information then available on river behavior was largely ignored.
I have written elsewhere about the twin foundations of geomorphology between 1650 and 1850 (Orme, 1989). In essence, one foundation lay in the historical approach to Earth science that led through the writings of Hutton and Lyell to Darwinian evolutionary concepts. To many geomorphologists, especially those in the anglophone tradition, this was the only true foundation, with evolving land-forms viewed as extensions of the geological record. Such was the impact of evolu-tionary thinking on late 19th and early 20th century science (Stoddart, 1966). The other foundation lay in the application of classical mechanics to problems faced by practicing engineers that led to the better understanding of geomorphic processes. This foundation, built by civil and military engineers in continental Europe, was long ignored by most American geomorphologists owing in part to challenges of language and mathematics, but largely to the supremacy of the historical or evolu-tionary approach to understanding landforms (Orme, 2002).
In late 19th century America, these foundations were clearly moving along diver-gent paths. The historical approach came to be reflected in the Davisian model that stressed progressive and irreversible change through time, while the mechanistic
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approach was applied by engineers to scientific challenges facing the developing nation, notably in the realms of water supply, canal and river navigation, and flood protection. This divergence, this separation of a theoretical model from practical work in river behavior, need not have occurred. Work by European hydraulic engi-neers over the previous hundred years strongly influenced the Mississippi River sur-vey directed by Andrew Humphreys (1810–1883) and Henry Abbot (1831–1927). Their thorough report not only introduced European hydrodynamic work to America but also yielded a wealth of quantitative data on a vast river system (Humphreys and Abbot, 1861). From the 1870s, at sites from New England to California, aided by developments in gauging technology, various agencies had begun obtaining contin-uous records of stream velocity and discharge, so important to issues of water supply and irrigation potential. The USGS established its first regular gauging station, at Embudo on the Rio Grande in New Mexico, in 1889.
Quantitative understanding of fluvial processes was to be of major significance to the subsequent growth of geomorphology, but not during the supremacy of the Davisian model. European concepts of régime (Surell, 1841) and pente d’équilibre(Dausse, 1857) clearly influenced Gilbert’s thinking on river behavior, from his early work in the Henry Mountains (Gilbert, 1877) to his later experimental studies, but his equilibrium concept was not appreciated at the time. Thus, as the 20th cen-tury dawned and the timebound Davisian model became dominant, British engi-neers in India were quantifying channel form and refining equilbrium concepts into the timeless regime theory (Kennedy, 1895), while Gilbert was about to begin his field and flume studies on the transportation of debris by streams (Gilbert, 1914). Such work was largely ignored by Davis and his disciples who seemingly drew their inspiration from evolutionary biology rather than from experimental studies in ther-modynamics and hydrodynamics. Although geographer John Leighly (1934) and geologist William Rubey (1938) later kept alive something of Gilbert’s legacy, it was not until the 1950s that new ideas, notably those emerging from the USGS, led to geomorphology being refashioned around an understanding of fluvial processes so carefully developed over the preceding 300 years (e.g., Leopold et al., 1964).
Aeolian Processes
In 1905, Davis applied his cyclic concept to arid regions. Adapting Passarge’s work in the Kalahari Desert, published in 1904, to his own model, Davis (1905) sought to show how arid landscapes passed through stages of youth, maturity, and old age by inferences about fluvial erosion and vague allusions to wind action. He was doubtless influenced by his field experiences in the American West where, owing to the presence of moisture-capturing mountains, stream flows and flash floods play major roles in shaping the desert environment. While he admitted “reaching too far into the field of untestable speculation” (Davis, 1905, p. 394), he also ignored studies that might have given his paper more authority. His followers perpetuated the problem, notably Charles Keyes (1912) who described a scheme whereby deserts could be leveled by progressive deflation, which he termed eolation.
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As with fluvial processes, prior work on aeolian processes was largely ignored if it failed to support or clarify the Davisian model. However, as early as the 1850s, William Phipps Blake (1826–1906) had described both deflation and ventifaction in the western deserts (Blake, 1855, 1858), returning later to the theme to explain desert pavement (Blake, 1904). While at Augustana College in Illinois, Johan August Udden (1859–1932) conducted seminal work on aeolian processes, notably on wind-blown sand (Udden, 1894), on wind directions derived from sand ripples, on dust storms of the Great Plains during the 1890s, and on the aeolian origin of loess (Udden, 1897). He devised simple yet ingenious methods of sampling blow-ing sand and defined grain-size parameters for a grade scale which, as later modi-fied by Wentworth, is still used (Udden, 1898, 1914). Wisely, he cautioned that parameters such as mean grain size, sorting, and skewness, though useful descrip-tors, were not necessarily diagnostic of aeolian environments.
The pioneer studies of Blake, Udden, and others were not incorporated into the Davisian model. Davis’s last paper, prepared in 1933 but published posthumously in 1938, did indeed focus on desert processes, specifically sheetfloods and stream-floods. Yet, having never seen a sheetflood in action, Davis relied heavily on W. J. McGee’s much earlier measurements of sheetflood erosion in the Sonoran Desert (McGee, 1897).
Other Processes
The above examples shed light on the geomorphic processes that were being studied at the time the Davisian model was being developed. Similar examples could be extracted for processes associated with Pleistocene glaciers, notably from the work of Chamberlin and Leverett in the Midwest, for shore processes from contemporary coastal engineers, and for weathering studies being made by soil sci-entists. An exception would lie with periglacial processes, the study of which was in its infancy around 1900. In that year, Matthes (1900) coined the term nivation, but the term periglacial was not introduced, by Lozinski, until 1909 (Lozinski, 1912). Nevertheless, in a remarkable postscript to the Davisian system, Louis Peltier (1950) could still propose that entire landscapes could be planed off by frost action and related processes (cryoplanation) during a periglacial cycle!
AN AMERICAN GEOMORPHOLOGY IN THE EARLY 20TH CENTURY
At the dawn of the 19th century, geomorphology as a discrete science did not exist, the term had not been coined, and scholars expressed their interest in land-forms under many disparate rubrics. There was certainly no distinctive American school of thought on such matters, and such influences as occurred were essentially European, mostly British. Furthermore, the North American continent had so far yielded little scientific information upon which to develop testable hypotheses. Although this was to change, the earlier decades of the century saw field observa-tion and description prevail over synthesis and explanation.
By the dawn of the 20th century, there had emerged a distinctive American school of geomorphology, the term geomorphology had been introduced to
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America by McGee in 1888, European influence was much diluted, and American ideas were traveling overseas. We may reasonably ponder when and why a distinc-tive American school of geomorphology emerged. The simple answer is that this development was the natural outgrowth of an expanding nation that had achieved much over the previous hundred years, and that a portion of these achievements focused on the natural sciences. A more profound answer is inevitably more com-plex.
During the earlier 19th century, American scientists looked mainly to Europe for their inspiration, to European books, to visits by Europeans, and increasingly to European immigrants. Catastrophism, diluvialism, uniformitarianism and the like were readily adopted by American scholars according to their ilk. British texts and journals were much in demand. Thus did Robert Bakewell’s Introduction to Geol-ogy (1813), and Lyell’s Principles of Geology (1830–1833) do much to spur debate through their several editions. Visitors to America, from Volney in the 1790s to Lyell in the 1840s, and immigrants like Agassiz who arrived in 1846 and was appointed to Harvard in 1847, also did much to fashion scientific thinking. This is not to say that American Earth scientists were bereft of ideas—there were simply not very many of them, nor were there many institutions to encourage intellectual debate. Simply, when opportunity arose, American scientists tended to ascribe to prevailing European notions. Thus Silliman augmented the first American edition of Bakewell’s Introduction to Geology in 1829 with 126 pages of his own lecture notes from Yale that revealed an ambivalent diluvialism in keeping with Bakewell’s text.
By 1850, however, a discernible American flavor had begun to emerge in discus-sions of surface features and processes. This was in part a reflection of facts accu-mulated and hypotheses engendered by the various public state surveys that had progressed in fits and starts over the previous two decades (Merrill, 1924). In addi-tion, American scientists were now venturing abroad in their own right, notably Dana who accompanied The Great United States Exploring Expedition (the Wilkes Expedition) to the Pacific Ocean between 1838 and 1843. Based on his own field observations rather than the writings of others, the reports from this expedition show that Dana (1849) was among the first American scientists to develop a keen understanding of geomorphic processes in general, and of fluvial processes in par-ticular.
During the 1850s, various railroad and military surveys began to develop a better understanding of the American West. John Strong Newberry (1822–1892) and Ferdinand Vandeveer Hayden (1829–1887) reported features and processes on scales that were then unknown to scientists elsewhere. These observations paved the way, after the Civil War interlude, for the more thorough western explorations, and notably the works of Powell, Gilbert, Dutton, and McGee, that were to move America to the forefront of contemporary Earth science (Chorley et al., 1964). Suf-fice it to note here that western exploration had been absorbed into the USGS in 1879 and was essentially over by 1890. At the dawn of the 20th century, many of the leading figures who had given initial definition to a distinctively American style of geomorphology were passing from the scene. Dana had died in 1895, Le Conte and Powell in 1902. Dutton, who had ceased working part-time for the USGS in 1890, retired from the army in 1901. Gilbert, widowed in 1899, seemed at the time
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destined for lonely retirement (Pyne, 1980), and McGee had moved to other inter-ests.
As the cast of characters changed, so the stage became dominated by the Davisian system, with but a few contrary outliers, notably Rollin Salisbury (1858–1922) at Chicago. It was against this background that the Association of American Geographers was formed. In an address to Section E of the American Association for the Advancement of Science in St. Louis in December 1903, Davis lamented the low standing of geography within a section that nominally included both geography and geology (Martin, 2003). In a meeting after this address, 13 attendees supported Davis’s proposal for “an American Geographers’ Club or Association, in which membership shall be limited to mature geographical experts” (letter from Davis to Ellsworth Huntington in 1904, quoted in Chorley et al., 1973, p. 418).
Davis’s 13 supporters at the St. Louis meeting in 1903 were dominantly natural scientists with varied interests in surface features. They included Charles Dryer, Nevin Fenneman, Frederick Gulliver, Christopher Hall, Mark Jefferson, Curtis Marbut, W. J. McGee, Rollin Salisbury, George Shattuck, and Ralph Tarr, all geo-morphologists or geologists of one persuasion or another. Additionally, Cyrus Adams was interested in biogeography and cartography, and H. C. Cowles described himself as a physiographic ecologist (Fig. 1). Subsequent organizational meetings also included Henry Gannett, Chief Geographer of the USGS, and geolo-gists Grove Karl Gilbert of the USGS, Angelo Heilprin from the Sheffield Scientific School at Yale, and William Libby. These were, as Davis wished, “mature geograph-ical experts.” The youngest were in their mid-30s, Davis was 54, Gannett was 58, and Gilbert was 61.
The 26 founding members of the Association of American Geographers at its inaugural meeting in Philadelphia in December 2004 were likewise dominated by natural scientists. They elected Davis as president, Gilbert and Heilprin as vice-presidents, and Albert Brigham, professor of geology at Colgate University, as sec-retary/treasurer. Ralph Tarr, professor of dynamic geology and physical geography at Cornell University, Cyrus Adams of the Cincinnati Society of Natural History, and Henry Cowles, botany instructor at the University of Chicago, were elected coun-cilors. Of the 21 papers presented at the inaugural meeting, some orally, some by title, all but one could be broadly classified as physical geography.
It comes as little surprise, therefore, that the Association of American Geogra-phers was initially dominated by geomorphology in general, and by Davisian geo-morphology in particular. Although by 1909 Brigham could report to Fenneman that there were fewer “pure physiography” papers being presented, the association provided a pulpit for the Davisian scheme in all its persuasive forms. Geomorphol-ogy did, of course, continue to be represented in other associations and journals, and Davis himself continued to publish in geology magazines, but geographical geomorphology was distinctly Davisian. Studies that had relevance to geomorphol-ogy in the broader context, such as those dealing with crustal instability or geomor-phic processes, were seemingly discouraged or ignored within the new association, although they continued to appear elsewhere. Therein lay the strengths and weak-ness of the field at the time.
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CONCLUSION
The dawn of the 20th century saw geomorphology in America, and to varying degrees elsewhere, ensconced in the Davisian system, with its cycle of erosion viewing landforms in terms of their youth, maturity and old age. The predominance of Davisian geomorphologists among the founding members of the Association of American Geographers did much to ensure the persistence of their particular idiom for several more decades, at least among geographers.
This need not have been. Had these geomorphologists been more enlightened, or less conformist to the Davisian model, many of the ideas that were then being debated among scientists elsewhere could have been incorporated into schemes that, even by contemporary standards, would have been more realistic. This is par-ticularly pertinent with respect to concepts of crustal mobility that were being
Fig. 1. Natural scientists involved in founding the Association of American Geographers, 1903–1904. Source: Based on Martin, 2003; AAG archives; and contemporary biographies.
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openly debated among geodesists and geophysicists at the time, and of river behav-ior and regime theory that were being considered by hydrologists and engineers in many parts of the world, including the United States. As it was, Davis conceived a model that leaned heavily on evolutionary thinking and on the evidence for denu-dation described by Powell, Dutton, and Gilbert during the 1870s and 1880s. But Davis selected just what he needed to support his model, and ignored the more pro-found observations of Dutton on isostasy and of Gilbert on epeirogeny and process. Only when Davis and his immediate disciples departed the scene, was the stage gradually opened for alternative thinking. Even then, despite the work of geogra-phers such as Leighly, it was not until the 1950s that Gilbert’s notions regarding flu-vial processes and equilibrium theory reemerged along a broad front.
The Davisian system began withering when its prophet departed the scene. It finally crumbled during the 1950s and 1960s—as the plate-tectonic revolution dis-mantled assumptions of prolonged crustal stability; as the renewed focus on geo-morphic processes exposed the insecure foundations of the Davisian system; and as quantitative methods began testing qualitative concepts. Nevertheless, despite a subsequent spate of process studies, it was not until the 1990s that the renewed search for a universal model in geomorphology began to integrate continental-scale denudation with three-dimensional crustal mobility (e.g., Molnar and England, 1990), although debate on this theme long preceded formulation of the Davisian system.
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