Harris, section 16 

Greene (1982) ch. 3 & 4

Greene provides a good overview of the main developments in tectonics through the mid-19th century. His work predates Laudan’s book – together, these books were major contributors to the reassessment of the history of 19th century geology.  These chapters discuss the major tectonic models (Von Buch, Élie de Beaumont, Lyell, and Herschel/Babbage) and the ongoing theoretical debate about actualism, gradualism and long-term changes. This is a very thoughtful discussion that reveals some of the interplay of observations, theory and personalities.

Since, some of these chapters cover material that we have discussed, I want to provide some notes on the sections that summarize the major tectonics models of the second quarter of the 19th century.

In chapter 3, the main points are the ideas of Von Buch and Élie de Beaumont. Skipping over the summary of Lyell’s Principles, please read Élie de Beaumont’s background (bottom p. 75 – middle p. 78) which gives you a sense of his ability and standing, but you can skim his geological influences (p. 78 – middle p. 83) unless you want to learn more about the French tradition at this time. Next, there is a short, but critical, section on Von Buch’s (p. 83-84) theory that should be read with the brief Laudan selection (below). After this, there is an outline of Élie de Beaumont’s theory as presented in 1831 (p. 84-92) – this should be read with the paper (notes below).

Chapter 4 highlights the other side of the argument, with lots of details on the debates among the various workers (much of which we will skip). First we have the Lyell perspective (p. 93-101) – including his own idea of how mountains form (don’t miss it – is is very brief and at the start of the section). The Herschel/Babbage theory (p. 104-111) is an important contribution which would have a long “afterlife” (along with Élie de Beaumont’s theory) despite being a mixture of logical (loading and lateral flow) and rather strange (isogeotherms). Skipping some of the arguments, you should take a look at Élie de Beaumont’s later version (bottom p. 113-115) to see just how weird it got (the figure helps). Finally, there is an appreciation of Élie de Beaumont’s contributions (middle p. 118-121) that is important because his ideas contributed major components to later 19th century tectonic models, despite the oddity of his later work.

Laudan (1987) p. 187-193

This selection deal with Von Buch’s “Craters of Elevation” model for making mountains. This model was very popular for most of the second quarter of the 19th century – even Élie de Beaumont would incorporate some aspects of it. As you might expect, Lyell rather effectively attacked it in the third volume of the “Principles”. I can understand its appeal as a framework for interpeting volcanic regions (Canary Island, Vesuvius) but I never could quite see how it explains features like the major Alpine chains. Your goal is to understand how Von Buch’s model worked and the range of features it helped explain.

Élie de Beaumont (1831) 

This paper appeared in a British scientific magazine and it is essentially an “abstract” of Élie de Beaumont’s long version (1829) presented for an English-reading audience. We will focus on the opening and closing pages (p. 241-45, 259-264). The opening paragraph refers to the ideas of Cuvier (violent revolutions), Hutton (elevation from below), and Lyell (raising mountains without real revolutions). Élie de Beaumont also asks if the uplifts of mountains were related to “mineralogical and zoological lines of demarcation”. These “lines” are (respectively) angular unconformities (surfaces with abrupt changes in the orientation of strata) and horizons of faunal changes (i.e., Cuvier-style extinction and replacement by a new fauna). In essence, he wants to link together different aspects of geology – the succession of strata and fossils (the target of much of stratigraphic geology since the 1810s) and the formation of mountains (tectonics) – into a coherent causal model. The following introductory pages focus on the nature of unconformities around the flanks of mountains. The idea is that the upheaved beds were elevated and deformed during the uplift of the mountain whereas the overlying flat-lying beds postdate the upheaval. As you read this text, consider (1) What is the evidence for separating strata that predate and postdate the uplift? (2) What is the evidence that the uplift was rapid? (3) How does the unconformity relate to the distribution of fossil species? (4) What is the significance of the direction of a mountain chain? (The orientation of chains would grow in importance to Élie de Beaumont’s later development of his theories.)

The introductory section is followed by a long section (p. 245-259) which summarizes twelve “systems of mountains” recognized by Élie de Beaumont (the number would rise to over one hundred in his later years). Do not try to follow all the details of these twelve systems! Look over system IX as an example (p. 253-254). Notice the kind of information included (location, orientation, rock types, fossil information (minimal at this point), geological age (under various terms such as lias, keuper, oolitic, tertiary). What do you think Élie de Beaumont’s concept of a “system” mean?

After emerging from this mass of detail, he turns to causal geology (bottom p. 259-264). First, Élie de Beaumont infers that mountains with the same orientation (direction) were uplifted at the same time. Second, he argues that such an uplift could have widespread effects on sedimentation and life. Third, he seeks to explain uplifts as the result of long-term cooling of the globe. This idea was well established and had been supported by the work of Cordier and Fourier (as cited in the text). The basic idea is that the Earth is gradually cooling. As the Earth cools, it contracts so that pressure builds up in the crust. The crust buckles when the pressure exceeds the strength of the crust. This is an early version of the “contraction theory” of tectonics and it would persist in some form through the 19th century as an alternative to primarily vertical crustal elevation models.  We will spend more time on this theoretical framework (termed the “Directional Synthesis” by Rudwick) in our next class.

To do:

1. Try to summarize for your self the contrasting tectonic models of Von Buch, Élie de Beaumont, Lyell, and Herschel/Babbage.
   • How did they work?
   • What was the main “drivers” for tectonic deformation?
   • Do they stress vertical or horizontal crustal movements?
   • What were the strengths and weaknesses of each model? 
2. Consider the application of Von Buch’s model. What kind of situations would it help explain? (Think about this in terms of geology in 1820s.) What kind of geological settings would create problems?
3. How did Élie de Beaumont’s general model link the structure of a mountain range, the stratigraphic featues, and Cuvier’s “revolutions”? What was the range of data that he was able to incorporate?
4. Can you itemize some of the features that were included in Élie de Beaumont’s concept of a “system”? Try to list them for Systems IX. How would this compare to Murchinson’s use of the term “system” in the early 1830’s? 
5. The Hershel/Babbage model was distinctly different from the other two – notice that it stresses vertical crustal changes. Why was this model viewed unfavorably by Alpine geologists? What are its implications for the structure of the earth’s interior? Why do you think Lyell liked this model as opposed to those of Von Buch or Élie de Beaumont?
6. To what extent did these models use actualistic versus non-actualistic processes? Gradual or abrupt changes? Postulate a steady-state or directional earth history? 
7. If you were a geologist around 1840-1850, what would you think about all this? Can you see why there were a wide range of ideas and interpretations? Would any of these be convincing enough for you to adopt it fully?

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