The main focus of our class discussions will be the impact of American geology and geologists on the established European geological thinking. A key contribution was that the Appalachian chain (with its well expressed fold and thrust belt) was very different from the Alps, the iconic European mountain range. Coupled with this was the importance of geologists like the Rogers brothers, Hall and Dana. Their works were soon followed by contributions from the geologists associated with the western surveys (Gilbert, Powell and Dutton), and increased professional interactions in the later 19th century (Americans attending international geological congresses, Europeans visiting their American colleagues and field sites). For reference, here is a brief summary (Brief note on the geology of the Appalachians-s4jvxa) that describes the main feature of the Appalachians with diagrams.

Harris notes: Sections 18-20

These notes will introduce the early development of geology in America and its flowering in the later part of the 19th century through the “western surveys”. The impact of American geology and landscapes – and of American geologists – steadily increased during the later 19th century.  We will discuss the first major theoretical contribution to arise from these experiences: the concept of geosynclines.

Greene, chapter 5

This chapter deals with tectonic models that developed in response to American geology. It is hard to overemphasize the role of the Appalachians in this, as reflected in the work of the Rogers brothers who provided the first detailed information on a folded mountain range; and the models of Hall and Dana tried to explain the particular geometry and geography of the the chain.  Greene places these contributions in the context of European tectonic debates. The underlying issues are similar to those in Europe: how to explain the horizontal shortening (contraction versus vertical motions), actualism, etc.

Although the entire chapter is worth reading, we will use’s Dott’s paper to cover some of the material. Please read two sections: (1) p. 122-125 on the contributions of the Rogers brothers – in particular their delineation of “Appalachian” style mountain structure and the explanatory tectonic model; (2) read p. 142-143 after you read the Dott article – it gives a perspective on impact of Dana’s work and how it relates to some of the European ideas.

Dott (1997)

Dott discusses the ideas of Hall and Dana (both early and late versions) – you will need to read the sections on Dana’s early tectonic ideas (p. 285 (bottom)-294), Hall’s geosynclines (p. 294-297), and Dana’s later ideas (p. 298-302). (Feel free to skim the rest!) Dott reviews these theories by going through the publications so you can see how they evolved over time. These sections will provide you a good understanding of the similarities and differences in these theories, and their significance.  I would draw your attention to a significant difference from earlier workers: the idea that the distribution of oceans and continents is a permanent feature.  As you will see in your reading, Dana was the geologist with the “United States Exploring Expedition” of 1938-1842 and gained first-hand experience with this.  In particular, notice that some of his basic ideas on oceans versus continents were already present before he began to work on “geosynclines”.

Kay (1951) – quick (promise)

Kay (1951) illustrates the persistence of Dana’s ideas. This volume was considered the state-of-the-art summary regarding large-scale tectonics in mid-20th century American geology. His elaborate classification uses geosyncline for virtually any thick accumulation with prefixes to accommodate virtually any tectonic setting. Don’t read through the abstract in detail but look over page 107. Keep this in mind when we turn to continental drift and plate tectonics.

Some issues to consider in these readings: 

American Geology

• What was the infrastructure on American geology prior to the founding of the USGS?
• From the information provided about the careers of the major individuals
  • What were the major career pathways?
  • What were the major geological centers?
• What were the goals of the major western surveys? How might they have differed based upon whether you were in Congress versus one of the scientific participants?
• What were the major contributions of the American geology?

Tectonics

• There were four major tectonic models developed in America in the middle half of the 19th century: Rogers brothers, Dana (early version), Hall, and Dana (late version).
• First, the obvious: outline the four theories.
  • How did they work? (Dott has some good diagrams!)
  • Major similarities and differences?
  • How do they reflect the significance of the Appalachians for American geologists?
  • How would you have to modify them to account for the Alps (the mountain ranges that most influenced European geologists)?
  • How did they reflect the experiences of these geologists (you may want to consult my course notes on the early development of American geology).
• How did these fit into the debates between Lyell and the directionalists?
  • What aspects reflect the work of Lyell, Élie de Beaumont and Herschel?
  • What about the components of “uniformity” discussed by Rudwick (1971)?
• Dana’s (1873) geosyncline theory was generally viewed as superior to Hall’s.
  • Why do you think that this was the case?
  • What assumptions about oceans and continents were embedded in his theory?
  • Why was “geosyncline” concept so persistent?

Links to course homepage and course schedule.