DYNAMICAL GEOLOGY. 295 



solid crust. Professor Erich von Drygalski, who as an explorer 

 on the Northern Coast and in Polar regions is no less distin- 

 guished as a mathematical physicist than as a geologist and 

 geographer, holds the opinion that phenomena of upheaval and 

 subsidence can be produced by alternating decrease and increase 

 of the temperature at the earth's surface. Professor Bruckner, 

 the chief Swiss authority on fluctuations of level, does not agree 

 with Nordenankar and Suess that the positive movement of 

 Scandinavia may be explained by the gradual depression of 

 the Baltic Sea. On the German coasts of the Baltic, where 

 the variations of the water-level, as in the case of inland seas, 

 depend upon the amount of rainfall and the volume of 

 inflowing river-water, the oscillations leave horizontal lines. 

 But on the Swedish coasts the former coast-lines do not run 

 horizontally, they slope obliquely upward, thus affording 

 evidence, in Bruckner's opinion, that the movement had been 

 an unequal crust-movement. Several geologists who have more 

 recently examined the Swedish coasts, Leonhard Holmstrom 

 (1888), Sieger (1893), and Kayser (1893), arrived at the same 

 result and supported the view of continental oscillations. 



Penck has modified his previous opinion and now accepts 

 independent crust-movement as a concomitant factor in 

 elevating or depressing a coast-line. Bruckner goes farther, he 

 argues that all the present littoral displacements, which are 

 not directly associated with volcanic activity at the surface, 

 are explicable only if we accept crust-movement as an essential 

 condition. 



H. Older Dislocations in the Earth's Crust Tectonic 

 Structure and Origin of the Continents and Mountain- Chains. 

 The terrestrial movements and changes which have been 

 observed within historic times give us but a faint indication 

 of similar phenomena in earlier periods of the earth's history. 

 On studying the dislocations which occurred in past geological 

 epochs, we arrive at a clearer conception of consummated 

 movements and their effects, we perceive how ancient 

 strand displacements have culminated in the complete 

 submersion of islands and continents, or in their emergence, 

 and how mountain-systems have arisen in the neighbourhood 

 of ancient zones of crust-disturbance and weakness. 



With the exception of the observations of Steno, which 

 were far in advance of his time (ante, p. 26), the scientific 



