glacier logo   Debating Glacial Theory, 1800-1870 – Teaching Notes
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Overview | Learning Objectives | Project Structure | 19th-century Perspectives | Leading Class Debate


The case study follows the development of the glacial theory in the period 1800-1870, with particular emphasis on 1800-1845. Students gain field experience vicariously through Google Earth (see set-up). and read original papers from the period (see Epidoes). Although all this material is online, this is the first website providing comprehensive access. Students may be instructed to write various papers summarizing and interpreting this work, or a class may be organized for a live debate among participants, with students assigned the roles of various historical scientists.

Although the glacial theory is now accepted as the correct interpretation of so much data (not all of which was available in the Nineteenth Century), students should come to appreciate that, at the time in which this study is set, it was not a simple, swift triumph of "right over wrong." They will explore how alternative interpretations developed and were argued, and how differing approaches to study and ways of thinking about Earth processes and history were just as important as the facts themselves in judging the "rights and wrongs" of the glacial case. Students will understand how, at the time: a highly evolved neo-Diluvial flood theory was commonly viewed as a coherent synthesis of a great deal of geologic data and was thus a real scientific alternative to a glacial explanation of certain phenomena; Charles Lyell’s uniformitarian project in geology more or less precluded continental glaciation (ice sheets); and ideas on the nature of climate, as either directional or as steady-state, mitigated against accepting glacial oscillations in the climate system itself.

Learning objectives on nature of science:

  • To understand the interaction of observations and judgments in interpreting "facts" and their meaning, especially over an extended period of time. (To comprehend how alternatives were viewed in historical perspective, and not to prejudge them based on present understanding – to situate oneself within the debate rather than judge it, and thus appreciate the nature of progress realistically.)
  • To understand conceptual change in science. To comprehend the complexity of history and how scientific knowledge may come into focus gradually (as new methods or expanded observations introduce new facts) and gain cogency through persuasion, rather than in a single flash of insight.
  • To understand the development of the glacial theory as a community achievement over a protracted period of time, rather than the achievement of a single "great man," such as Louis Agassiz.

Project Structure The website is organized to accommodate two different pathways of study:

  1. Self-guided research: Students explore material individually and summarize their work in two papers using original (primary) sources. This may be supplemented by class discussion. This is the more comprehensive of the two paths. It is a more traditional, chronological route through the development of ideas.
    Timeline: One class period of orientation to period in question and philosophical issues. Followed by self-guided research leading to papers and presentations (at the instructor’s discretion).


  2. Debate simulation: Students adopt the role of a historical scientist, advocating or criticizing particular features of glacial theory. They become the "expert" on one view and learn the views of others primarily through debate or discussion. There may be prepared (written) position papers, formal (oral) presentations, or just open debate. This option enhances understanding of the role of individual perspectives in science and the complex dynamics of interacting perspectives. It also enhances depth of understanding about scientific reasoning, with the resulting narrowness of scope balanced by the breadth exposed in debate.

    Timeline: One class period of orientation to period in question and philosophical issues; 1/2 class period on preliminary discussion and sharing of ideas; one or more class periods of debate; one class period debriefing, with further discussion and epilog.
    See guidance below on leading debate.

  • In both alternatives, students encounter:

    Overview and Set-Up
    This is a general introduction, with instructions for installing Google Earth and downloading the Tour data file.

    This introduces students to discussion taking place in the early 1800s: observations, problems and basic terminology. This informs students on the nature of recent geologic history — discussion that eventually came to include the possibility of extensive glaciation in, and beyond, the Alps. The background outlines the geological questions that were being asked at this time and the prevailing approaches to their study.

    As stratigraphical knowledge accumulated through the beginning of the Nineteenth Century, the evidence for a recent "upheaval" in Earth history appeared strikingly obvious to early Nineteenth Century geologists in the form of: widespread erratics, "diluvial" or "drift" deposits, and the remains of fauna now extinct in Europe. However, rather than focusing on narrow questions about geological “puzzles,” such as the origin of erratics or the origin of "drift," this case study places such questions in the broader contexts within which they were generally viewed by early Nineteenth Century geologists.

    As an optional supplement, there is also a description of the cultural setting of England in the 1830s, with some comments on women in geology.

    Google Earth Tour
    Some of the material is presented through GoogleEarth. Students view several of the locations studied by naturalists in the early 19th Century and are asked to consider their work in this visual context. At this time geology emphasized local field observation and inductive inference over the global theorizing that had characterized the early history of the discipline (and, indeed, the theory of glaciation was criticized as being based too little on the former and containing too much of the latter).

    Second, students are asked to read original sources from the time period. Access to these sources will be through GoogleBooks. Until recently, personal access to a collection of sources such as these was possible for only a few individuals at two or three institutions in the world. The bibliography provided here is the first, extensive compilation of such sources on this topic.

    A comprehenive list of references is provided in the Bibliography.

    As much as possible, original art work has been used to illustrate the material presented and, in part, this has been made possible through access to original sources. In other instances, when possible, quality photography has been chosen to illustrate the original locales.

    The class activity can be closed with a short epilog of the status of the debate in the 1840s, its resolution in the 1860s, and some interesting discoveries in the 20th century based on themes of the original debate.

  • The debate simulation also includes:

    Debate Profile
    guidance for preparing for debate, including brief comments on the organization of Geological Society meetings and the nature of their debates.

    Role Profiles
    This lists the participants, and links to specific guidance for each role: the general conceptual orientation, the relevant sites on the GoogleEarth Tour and on the list of Episodes, and a hint of the persuasive challenges in the larger group.

19th-Century Perspectives (Instructor's Background)

The teacher may be better prepared to guide and perhaps articulate or shape discussion in a historical perpsective by becoming familiar with the viewpoints through which the "facts" were argued and interpreted in the early and mid-1800s:

  1. Methodological (how to proceed with study; explanations deemed acceptable)
    1. Catastrophist, as championed esp. by
    2. Uniformitarian, as championed esp. by Lyell
    3. Actualistic

  2. Views of Earth history and processes, deemed consistent with the facts in this, and possibly other, cases
    1. Single universal flood (Mosaic Diluvialism)
    2. Multiple regional floods (neo-Diluvialism)
    3. Diluvialism (and general crustal disruption) vs. fluvialism and origin of river valleys
    4. Rapid and intense periods of mountain building vs. gradual mountain building and regional uplift and depression
    5. The nature of the past: geologically different in nature and intensity, separate from the present: Exceptionalism vs. uniformitarianism or vs. actualism
    6. The nature of climate as interpreted from the rock record: directional vs. steady-state, and glacial oscillations

The study places students in a rich environment of ideas at a time when geology was evolving rapidly from the speculative "Earth theory" approaches of the previous century to a disciplined, documentary approach to facts. Debates about theory or the larger interpretation of facts were reserved for discussions after papers had been presented the Geological Society of London, and these discussions were generally not reported upon lest the public think poorly of the state of geologic knowledge. Nevertheless, in Scotland at least, the “glacial theory” caught the public’s imagination in 1840 with Agassiz’s tour ofScotland, which was widely reported on and followed in newspapers.

This was also a time of philosophical reflection on the nature of science. Students are introduced to William Whewell, who was President of the Geological Society of London in 1837 and 1838 (and who may be an optional participant in the debate simulation). Whewell affirmed the Baconian view of science as knowledge founded first upon well-established facts, but which are then brought together by “superinducing” upon them a conception (or theory) which unites them and which provides the “true bond of Unity by which the phenomena are held together” (1840, p. 211):

we bind together facts by superinducing upon them a new conception, this conception, once introduced and applied, is looked upon as inseparably connected with the facts, and necessarily implied in them. Having once had the phenomena bound together in their minds in virtue of the conception, men can no longer easily restore them back to the detached and incoherent condition in which they were before they were thus combined (p.217).
Such a unifying conception is inferred from the data in a number of ways. New hypotheses may be “collected from the facts” and analyzed in the preparation of a fully-formed theory.

According to Whewell, a theory is confirmed over time by prediction, consilience, and coherence – all of which can be applied to the debate here.

  1. Prediction: “The prediction of results, even of the same kind as those which have been observed, in new cases, is a proof of real success in our inductive processes” (1840, p.230).

  2. Consilience (a “jumping together” of facts): “the evidence in favour of our induction is of a much higher and more forcible character when it enables us to explain and determine cases of a kind different from those which were contemplated in the formation of our hypothesis. The instances in which this has occurred, indeed, impress us with a conviction that the truth of our hypothesis is certain. No accident could give rise to such an extraordinary coincidence. No false supposition could, after being adjusted to one class of phenomena, so exactly represent a different class, when the agreement was unforeseen and uncontemplated. That rules springing from remote and unconnected quarters should thus leap to the same point, can only arise from that being the point where truth resides. Accordingly the cases in which inductions from classes of facts altogether different have thus jumped together, belong only to the best established theories which the history of science contains” (1840, p.230).

  3. Coherence: “theories have been built up of parts devised at different times. This being the mode in which theories are often framed, we have to notice a distinction which is found to prevail in the progress of true and of false theories. In the former class all the additional suppositions tend to simplicity and harmony; the new suppositions resolve themselves into the old ones, or at least require only some easy modification of the hypothesis first assumed: the system becomes more coherent as it is further extended. The elements which we require for explaining a new class of facts are already contained in our system. Different members of the theory run together, and we have thus a constant convergence to unity. In false theories, the contrary is the case” (1840, p.233).

In debating the differing views, students might be encouraged to think about the ideas by applying these criteria, which are contemporary with the debate. At the time at which glaciation was being debated, the data appeared to support multiple interpretations, depending upon which data were regarded as belonging together and which methodological system was preferred (e.g. superimposed streams and erratics were bundled together in diluvial interpretations, though not in the glacial interpretation which left the questions of stream valleys unresolved): this made it more than just a debate about glaciation itself.

Students should gain a sense of how judgments were formed on "glacial" matters at this time and, to facilitate this, an instructor may well comment upon the terms fact, theory, and hypothesis, and prediction, consilience, and coherence, as espoused by Whewell.

Leading Class Debate

To revive a sense of history, see the comments on the organization of the GSL meetings and debates.

For reference, you may wish to consult an eyewitness account, with rough transcript, of the original GSL debate in 1840, see S.P. Woodward's account [online] or here.

You may wish to chair the session (or designate a student in the role of facilitator). Your language (addressing students as "Mr. Agassiz", etc.) can help establish the spirit of a historical setting. Students often tend to bypass the problematic conflicts of history and use evidence selectively to argue for a "modern" position. Thus, you may discretely add comments to discussion to help balance the debate — for example, by commenting about excessive reliance on unfruitful theorizing.



Whewell, W. 1840 The philosophy of the inductive sciences founded upon their history, vol.2. London, John W. Parker
      [See in particular Chapter 5, p.212-239]