SYMMETRY ABOUT THE NORTH ATLANTIC 239 



and most of the genera were those of the West European Cretaceous beds, 

 indicating inter-migration along a submerged near-shore shelf.* 

 The general conclusion reached by Suess is as follows : 



"As regards the oft-discussed question of tlie permanence of tlie continents 

 and the oceans, one perceives the following : Individual folded zones become 

 broken and divided into horsts, and younger folds develop- in the horsts. The 

 position of the region of recession and transgression, as well as the arrange- 

 ment of the surface tensions (which find expression in the axes of the folds) 

 within the northern hemisphere, has in its main lines remained the same since 

 Cambrian time — that is, from the existence of the oldest recognized traces of 

 organic life down to the present day. A similar degree of permanence has not 

 characterized the oceans. During this time through depression new oceans 

 have been formed, whose succession in age is stamped in the transgressions. 

 Other oceans have disappeared in part in consequence of the new depressions 

 themselves, and in part through the pushing up of new zones of folding in ac- 

 cordance with the old plan. 



"Thus the margins of the continents and oceans change in spite of the con- 

 tinuity of the plan of the leading lines." 



Modern View of Bradysisms 



Suess has long maintained that secular oscillations are not sufficient 

 to explain the repeated emergences and submergences of the land. The 

 negative movements are, in his view, in part due to the withdrawal of 

 water from the shores to fill the abysses formed by the depression of sec- 

 tions of the sea floor, while the positive movements may be ascribed to the 

 partial filling of the ocean basins by sediments. 



The statement of Milne that the movements of the sea floor in connec- 

 tion with macroseisms are in general downward, while corresponding 

 movements upon continental shores are upward, is supported by 

 the geological evidence obtained through the study of the shorelines of 

 the present day with the use of historical documents. The many works 

 treating of such movements have been collected and critically examined 

 by Issel in an important monograph, f Issel's map of the bradysisms of 

 the entire globe shows that the greater number of the areas of depression 

 now in progress are beneath the sea, while the areas of elevation are upon 

 the land. In those small land areas where depression is going on (for ex- 

 ample, in Italy) there is evidence that this movement was often preceded 

 by an elevation. In Japan especially have these shore elevations been con- 

 firmed, and they appear to have been especially rapid. A questionnaire 

 with this end in view was conducted there a few years since by Professors 



• J. p. Smith : Principles of paleontologic correlation. Journal of Geology, vol. 8, 

 1900, pp. 673-697. 



t Artnro Issel : Le oscillazioni lente del suolo o Bradlslsmi. Saggio di geologia 

 storlca. Atti della R. TJnlversita di Genova, vol. 5, 1885, pp. 417, map. 



