DYNAMICAL GEOLOGY. 2QI 



and portions of the continents, as in the collapse and sub- 

 mergence of larger and smaller areas of the land. Athanasius 

 Kircher gave circumstantial descriptions of sunken islands 

 (Atlantis), and of lands raised from the ocean-floor. In the 

 eighteenth century, De Maillet and Buffon ascribed changes 

 of surface conformation to gradual diminution of the ocean 

 volume, while Lazzaro Moro tried to explain the double 

 aspect of emergence of land and ascent of the water-level by 

 means of volcanic catastrophes. The Swiss investigator, J. G. 

 Sulzer, in 1746 suggested the possibility that the position of 

 the earth's centre of gravity was affected by the variable dis- 

 tribution of surface material; and Justi, in 1771, believed in 

 "wanderings " of the Pole. 



In 1702, the Swedish physicist Hjarne had introduced the 

 method of direct observation by having marks hewn on the 

 rocks of the coast, and thus paved the way for the definite 

 knowledge obtained in the case of the Scandinavian move- 

 ments. Scientific opinion then wavered between two chief 

 parties, the one believing with Celsius in the lowering of the 

 ocean-level; and the other and stronger party following Hutton, 

 Playfair, Buch, Lyell, and others in ascribing the relative changes 

 of level to upheaval of the land associated with subterranean 

 volcanicity. Bischof, although he expressed in the chapter 

 on " Heat " his agreement with the Huttonian Theory of 

 Expansion, afterwards attributed secular movements more 

 especially to alternating expansion and diminution of volume 

 produced in deep-seated rocks by chemical transformations. 

 Following this direction of thought, Volger, Mohr, and Vogt 

 thought that the originally sedimentary rocks of Scandinavia 

 had been transformed into crystalline rock, and had under- 

 gone an expansion of volume during the process of crystallisa- 

 tion. 



The French mathematician, Adhemar, was the first scientist 

 who, in seeking an explanation for crust-movement, considered 

 the earth in its cosmogenetic relations. He regarded the 

 influence of the earth's internal heat as quite irrelevant to the 

 climatic conditions at the earth's surface; these he attributed 

 wholly to the action of the sun's heat, and investigated the 

 varying positions of the earth relatively to the sun, with a view 

 to explaining the recurrence of Ice Ages and also the associated 

 periodic rise and retreat of the ocean. Research in this 

 direction thirty years later was greatly advanced by James 



