FAMOUS GEOLOGISTS/Suess 237 years, he extended his field studies to the Carpathians, the Sudetes, and the Apennines In applying the comparative method, which he had already used in his palaeontological work, he found that all these mountain ranges (including the Alps) had certain structures in common As a result, in 1875, he published his first major book, The Origin of the Alps, a comprehensive discussion of the origin and the structure of mountain chains, anticipating most of his later ideas on tectonics Suess’s actual entry to these ideas involved studies on earthquakes, following a visit to Calabria in 1871, where Suess witnessed the devastation of the great earthquake of 1870 This gave rise to the idea of a systematic compilation of historical accounts of earth tremors in lower Austria, i.e., in a region far away from any volcanic activity Suess found that these Austrian earthquakes were distributed along specific lines that cut across quite different rock formations Thus, in 1873, he published two major articles on earthquakes in lower Austria and in southern Italy, concluding that earthquakes are restricted to specific structures within Earth’s crust and are thus due to the same forces as those that gave rise to the formation of mountains (Figure 3) The revolutionary concept that Suess now set forth in The Origin of the Alps abandoned the idea of similarity of the structure of mountain chains, which had dominated geology for nearly a century Contrary to the theory of mountain formation by vertical upheavals due to eruptive rocks, favoured by Leopold von Buch (1774–1853) and Leonce E´ lie de Beaumont (1798–1874), Suess set forth his view of horizontal movements as the essential cause of the formation of folded mountain chains, entertaining the idea of unilateral horizontal overthrustings by tangential pressures, in the case of the Alps, directed from south to north And Suess stated a fundamental difference between the mountain chains and their older, rigid ‘forelands’ (Vorlaă nder), which act, so to speak, as earth dams against the mobile chains As a further characteristic feature of developing mountain chains, he put forward the idea of ‘hinterlands’, i.e., their usually curved and relatively depressed ‘inner’ sides (Figure 4) These inner sides were the location of volcanism and earthquakes, due to the tensions caused by the movement of the newly forming mountains towards the forelands Already during his visit Figure Sketch of the main lines of strike for the folds of the Carpathians and the Balkans, from the first volume (1885) of Suess’ Das Antlitz der Erde The Carpathian Mountains, in particu lar, initiated Suess’ thoughts about groups of curved lines, and tangential and unilateral movements, as opposed to the prevail ing assumption of a symmetrical structure of folded mountain chains The actual structure of the mountain chains (i.e., the disposition of the folds) depended on the form of the foreland and the resistance of its materials to the volcanic areas of southern Italy in 1871, Suess had thought of volcanoes and earthquakes as being associated with regions of rupture within Earth’s crust Thus, earthquakes and volcanism were closely related to the process of mountain formation Suess explicitly stated that volcanoes and intrusions were just the side effects of mountain formation A Contracting Earth In The Origin of the Alps, Suess also first introduced his ideas on the forces that could have brought about mountain ranges and their accompanying phenomena: namely, the contraction or shrinking of the earth due to its continuous cooling In the 1840s, the American geologist James Dwight Dana (1813– 1895) had proposed the idea of unequal radial contraction of the earth due to cooling, linking this to the origin of earthquakes In the early 1870s, Dana and other geologists extended the contraction hypothesis as the basic assumption of the formation of mountains Thus, Suess was neither the creator nor the chief advocate of the contraction hypothesis However, it was Suess who – referring to Dana, to Robert Mallet’s (1810–81) ideas on ‘volcanic energy’, and to Charles Darwin’s (1809–82) theory of the origin of earthquakes due to the formation of fissures – most clearly used the contraction hypothesis for more than Figure A map from Suess 1873 book Die Erdbeben Nieder Oă sterreichs, showing the distribution of earthquakes in lower Austria According to the position of the strongest effect of the respective earthquakes (years given near the names of the villages), Suess constructed three ‘earthquake lines’ (Erdbebenlinien) The Thermen Linie (A B) was named according to the thermal and sulphur springs along this line (for instance, at Brunn, Voslau, and Meidling) The Kamp Linie (C D) and the Murz Linie (E F) were both named according to rivers of the area