Although we are accustomed to the idea of extensive ice sheets in the recent past, this was a very difficult concept to accept in the mid-19th century. In some ways, the recent glaciation played a cruel trick on geologists because the resulting widespread erratics posed a difficult problem with no obvious solution in terms of modern processes. Catastrophic (volcanic ejecta, catastrophic floods, great marine inundations) and gradualistic (prolonged marine inundations with iceberg drift) processes were all suggested, and tended to drive the interpretation of landforms in the same direction.

Various workers studied glaciers and their products, but conceptualized them as more local features associated with Alpine valleys. Agassiz changed the debate by becoming a passionate advocate for widespread glaciation, but his ideas were so spectacularly catastrophic that few geologists could comfortably adopt them. The controversy did trigger a major reassessment of landforms that opened up consideration of fluvial and denudation processes as major processes in the development of landforms. It also illustrates how geological interpretations were influenced by the underlying issue of reliability of actualism and gradualism in interpreting earth history.

Harris sect. 17

In reading this summary, you may find some of the Swiss geography a bit hard to picture.  In reading about Charpentier (p. 112), you will want to consult the map on p. 512 of Rudwick (Fig.34.6) – the dark areas at the bottom are present day glacier (in the high Alps); the Jura Mountains are at the top; the Swiss Plain is the lowlands between them (here stippled and termed the “Pays de Vaud”).  The Val de Bagnes – site of the 1818 flood – is the north-south valley in the lower left of the diagram. You will also find some of the maps earlier in the chapter useful.

Rudwick (2008), p. 501-539

This selection reviews the various alternative interpretations for erratics, scratched surfaces, and “drift”, the development of glacial theories as applied around the Alps, and their extension across northern Europe by Agassiz. As you read this, consider just how strange this idea was from both “catastrophic” and “uniformitarian” perspectives. It took thirty years before continental glaciation was accepted in Britain despite the evidence from the Scottish Highlands, and forty years for general acceptance in Germany.

Agassiz (1840)

In this short selection from one of his early works, Agassiz lays out some of the evidence for widespread glaciation, critiques the ideas of his contemporaries (recall the field trip), and (toward the end) discusses the relation of the Ice Age to the (extremely) catastrophic uplift of the Alps.

Finally (and for fun), I must share a note by a (unnamed) participant in the field trip that followed Agassiz’s 1837 address at Neuchâtel. This comes from Imbrie & Imbrie (1979) – sounds like an interesting trip! (I think that the “Englishman” may have been Lyell but have not tried to verify this.)

“In general, I was convinced by my short acquaintance with the leading scientists of the party that a great amount of jealousy and egoism existed between them. Elie de Beaumont was, during the entire trip, as cold as ice. Leopold von Buch was walking straight ahead, eyes on the ground, mumbling against an Englishman who was talking to Elie de Beaumont on the Pyrenees while we were in the Jura, and complaining rather offensively about the stupid remarks made by some amateurs who had joined the group. Agassiz, who was probably still bitter about the sharp criticism made by von Buch of his glacial hypothesis, left the group immediately after departure and was walking a quarter of a league ahead all by himself.”

To dos

The debates over glaciation provide a good window into geology in the middle 19^th century.

• Developing theories
  • What were the alternatives available for interpreting erratics and drift deposits in the mid-1830s?
    • What evidence was used?
    • Why were they reasonable to their advocates?
    • How did they reflect the underlying theoretical stances (c. 1830s)?
  • As noted, various Swiss naturalists developed the idea that the distribution of these features in the vicinity of the Alps could be explained by formerly more extensive alpine glaciers.
    • What was the evidence?
    • What was the reaction of the broader geological community?
• Agassiz’s vision
  • What was Agassiz’s radical transformation of these ideas? What was the basis?
  • What was the venue for Agassiz’s presentation? Who was there? What was their reaction?
  • Clearly the “open question” was the extent of glaciers away from the Alps. What evidence was there for continental glaciations?
  • What were the main problems with his theory?
• The debate about glaciation lasted for several decades (!). Various geologists accepted (and some subsequently abandoned) the idea of widespread glaciation.
  • Agassiz took many of his contemporaries to the field to convince them to accept his ideas. What kind of evidence was used?
  • How was his model modified by Studer? Lyell?
  • Why did British geologists adopt, then somewhat pull back from Agassiz’s ideas?
• Taking a longer view
  • Where did this debate end up? What was the compromise model?
  • How can you place this controversy into the competing geological frameworks of the 1830-40s? (Rather uniquely, it seems that everyone rejected Agassiz’s idea at the 1837 meeting!)
  • Why did it take 30-40 years for a modified version of his theory to be accepted?

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