ORIGINAL ARTICLES. 



Wegener's Displacement Theory. 



By Philip Lake, M.A., F.G.S. 



TN examining ideas so novel as those of Wegener ^ it is not easy 

 -*- to avoid bias. A moving continent is as strange to us as 

 a moving earth was to our ancestors, and we may be as prejudiced 

 as they were. On the other hand, if continents have moved many 

 former difficulties disappear, and we may be tempted to forget the 

 difficulties of the theory itself and the imperfection of the evidence. 

 Those who study the distribution of animals and plants must be 

 especially subject to this temptation, and it will be instructive to note 

 how far they agree in their demands upon the moving continents. 



Wegener himself does not assist his reader to form an impartial 

 judgment. Whatever his own attitude may have been originally, 

 in his book he is not seeking truth ; he is advocating a cause, and is 

 blind to every fact and argument that tells against it. Nevertheless, 

 he is a skilful advocate and presents an interesting case. Perhaps 

 he may claim that if his readers cannot approach the subject 

 without prejudice, he can hardly be expected to perform the 

 functions of a judge. He does not make the attempt. 



It might be useful to trace the gradual change in outlook that has 

 made the motion of a continent conceivable, but it would take too 

 long. Wegener mentions Wettstein, Pickering, F. B. Taylor, and 

 Schwarz as having actually suggested movement, though their 

 ideas are different from his.^ 



In the last part of Das Antlitz der Erde Suess imagines the earth 

 to consist of an outer envelope composed chiefly of the lighter and 

 more acid rocks, an inner envelope of basic rock, and an interior core 

 of still heavier material. He calls the first the Sal, the second the 

 Sima, and the third the Nife. 



Wegener accepts the terminology of Suess, except that he follows 

 Pfeffer in writing Sial instead of Sal. But he thinks that the Sal 

 does not cover the globe completely. It now exists in independent 

 patches, which float in the heavier Sima. Because of their smaller 

 density they rise above the surface of the Sima and constitute the 

 land-masses of the globe, while the Sima itself forms the floor of the 

 oceans. 



In this there is nothing essentially new. It has long been known 

 that plumb-line and pendulum observations point to a deficiency 

 of density beneath the major elevations of the globe and an excess 



^ A. Wegener, Die Entstehung der Kontinente und Ozeane, 2nd ed., 

 Braunschweig, 1920. 



- Wettstein' s notions seem to have been developed in a book pubhshed at 

 Zurich in 1880. The other references are as follows : W. H. Pickering, Journ, 

 of Geol, vol. XV, 1907, p. 23 ; F. B. Taylor, Bull. Geol. Soc. Amer., vol. xxi, 

 1910, p. 179 ; E. H. L. Schwarz, Geog. Journ., vol. xl, 1912, p. 294. 



