The first
naturalist to examine the Glarus thrust was
Hans Conrad Escher von der Linth (1767–1823). Escher von der Linth discovered that, contradictory to
Steno's law of superposition, older rocks are on top of younger ones in certain
outcrops in Glarus. His son
Arnold Escher von der Linth (1807–1872), the first professor in geology at the
ETH at Zürich, mapped the structure in more detail and concluded that it could be a huge
thrust. At the time, most geologists still accepted the theory of
geosynclines, which states that mountains are formed by vertical movements within the Earth's
crust. Escher von der Linth had therefore difficulty with explaining the size of the thrust fault. In 1848, he invited the British geologist
Roderick Murchison, an international authority, to come and look at the structure. Murchison was familiar with larger thrust faults in Scotland and agreed with Escher's interpretation. However, Escher himself felt insecure about his idea and when he published his observations in 1866 he instead interpreted the Glarus thrust as two large overturned narrow
anticlines. This hypothesis was rather absurd, as he admitted himself in private. Escher's successor as professor at Zürich,
Albert Heim (1849–1937), initially stuck to his predecessor's interpretation of two anticlines. However, some geologists favoured the idea of a thrust. One of them was
Marcel Alexandre Bertrand (1847–1907), who interpreted the structure as a thrust in 1884, after reading Heims observations. Bertrand was familiar with the
Faille du Midi (
Variscan orogeny), a large thrust fault in the
Belgian Ardennes. Meanwhile, British geologists began to recognize the nature of thrust faults in the
Scottish Highlands. In 1883,
Archibald Geikie accepted that the Highlands are a thrust system. Swiss geologists
Hans Schardt and
Maurice Lugeon then discovered in 1893 that in western Switzerland, Jurassic rock layers are on top of younger molasse too, and argued that the structure of the Alps is a large
stack of
nappes, large sheets of rock that had been thrust on top of each other. At the turn of the century, Heim was also convinced of the new theory. He and other Swiss geologists now started mapping the nappes of Switzerland in more detail. From that moment on, geologists began recognizing large thrusts in many mountain chains around the world. However, it was still not understood where the huge
forces that moved the
nappes came from. Only with the arrival of
plate tectonic theory in the 1950s an explanation was found. In plate tectonics, the horizontal movement of
tectonic plates over the Earth's soft
asthenosphere causes horizontal forces within the
crust. Presently, geologists explain the formation of most
mountain chains by the
convergent boundary evolving between
tectonic plates accompanied by a
subduction process in which the heavier plate dives beneath the less dense plate and sinks into the
Earth's mantle. == See also ==