alpine pioneers of geology The western (or Swiss) Alps of Europe hold a special place in the history of geology as well as containing the continent's highest mountains. Their geology consists of gigantic thrust sheets, recumbent overfolds, and slices of basement, deformed and displaced during the collision of the African and European continental plates.
The late eighteenth century saw a large number of Swiss and other students intent upon unravelling the alpine structures, but the dominant figure was Horace-Bénédict de Saussure. His discoveries included much of the Mesozoic and Cenozoic stratigraphy. Then came Arnold Escher of Zürich and Bernhard Studer from Berne who distinguished cover from basement rocks, but who disagreed about the relationships between them. Escher maintained that there were intrusive contacts, while Studer thought that basement and cover had been deformed together. Studer won the day, but Escher gets the credit for recognizing that great overthrusts are present, and that the rocks above the overthrusts have been translated great distances. In the Jura mountains where no basement is seen Jules Thurmann was the first to recognize the box-shaped folds that separate the Mesozoic–Cenozoic rocks from the more-or-less undeformed underlying basement.
By the turn of the century the need was for a structural synthesis to explain the complex distribution of ‘normal’ and ‘inverted’ masses of strata, and of basement and post-orogenic formations. The leader of the new generation of geologists was Albert Heim (1849–1937), a Züricher student of Escher who spent his long life investigating the dynamics of mountain-building and wrote a monumental account of the subject, as well as one on glaciers. He was also concerned with the preparation of the geological map of Switzerland. Early on he had studied the structure of the Glarus Alps, but his interpretation was overtaken by that of Marcel Bertrand, who in 1884 used the same data and initiated the nappe (thrust sheet) theory in the Alps. The Pre-Alps, lying to the north of the great Helvetic Alps, were then seen by H. Schardt (1893) as outliers of a pile of nappes that had originated far to the south. It called for earth movements on a previously unheard-of scale. (At about this time great overthrusts were being postulated to account for the deformation observed in the North-west Highlands of Scotland.) The whole style of alpine folding was hotly debated for many years, with the nappe idea gaining support from Maurice Lugeon, then from Edouard Suess, and in 1903 from Heim himself.
Over the next twenty years or so Lugeon and Heim worked on the structure of the Helvetic nappes, while Rudolph Staub unravelled the complexities of the Graubunden. During this time, too, Emile Argand was at work on the Valais Alps and bringing order to bear upon the synthesis of all the various parts of the alpine structures and upon the different styles of deformation within them. The result of all these investigations was the emergence of the Nappe theory, which Heim described in detail in his
Geologie der Schweiz, and which has been the basis for subsequent refinements, even into the present plate-tectonic age.
D. L. Dineley
Bibliography
Green, M. T. (1982) Geology in the nineteenth century. Cornell University Press, Ithaca and London.
