FAMOUS GEOLOGISTS/Wegener 251 of the Pacific coasts, as contrasted to the wild, irregular ‘ria’ Atlantic coastlines) There were also differences in the volcanic lavas of the two hemispheres, as emphasized by the Vienna petrographer Friedrich Becke (1855–1931) and others The Atlantic lavas contained a greater proportion of sodium, whereas calcium and magnesium prevailed in the Pacific lavas Such differences were intelligible according to the assumptions of continental movements The opening of the Atlantic was matched by the general pressing of the continents against the region of the Pacific Ocean: pressure and compression prevailed at the coasts of the latter whereas tension and splitting occurred at the latter Palaeoclimatology Traces of glaciation during the Permian (ground moraines lying on scratched bedrock) were to be found on the southern continents, e.g., in East India and Australia If the present-day arrangement of the land masses had prevailed at that time, this ‘Permian ice age’ would have required an icecap of seemingly impossible size And the north pole would have been in Mexico, where no trace of glaciation during that period was recorded Following the idea of horizontal displacements, however, all regions subjected to glaciation came together concentric to the southern margin of Africa And one had only to place the south pole in this much reduced glaciated area to give the Permian ice age a much more plausible form Wegener had discussed these palaeoclimatological features since 1912 In 1924, he gave a detailed description of the climatological changes from the Carboniferous through to recent times, following the traces of glaciations, swamps, and deserts, i.e., moraines, coal, salt, and gypsum, throughout Earth’s history (Figure 5) In reconstructing the respective polar shifts, Wegener emphasized that they obviously took place along with the great displacements of the continental blocks In particular, there was temporal coincidence of the best confirmed polar shift, in the Tertiary, and the opening of the Atlantic (Figure 6) Movement of the poles since the Pleistocene might also be related to the final separations of the continents in the north and the south Motive Forces Wegener was very cautious about the forces that might have caused continental displacements First, it was necessary to demonstrate the reality and the manner of the displacements before indulging in the hope of finding their cause Nevertheless, he tentatively suggested two candidates: centrifugal forces caused by the rotation of Earth and tidal-type waves within Earth, generated by the gravitational pull of the sun and the moon In the 1929 revision of Wegener’s theory in Figure Wegener thought continental drift was the key to the climatic changes during Earth’s history This map, published in the 1924 book by Koppen and Wegener, Die Klimate der geologischen Vorzeit, shows traces of glaciation, swamps, and deserts for the Carboniferous E, Traces of glaciation; K, coal; S, salt; G, gypsum; W, desert sandstone Dotted regions indicate arid areas, dashed lines indicate the positions (i.e., the pathways) of the poles, and the bold curved line indicates the respective position of the equator