BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 4, pp. 179-190 February 27, 1893 



CONTINENTAL PROBLEMS 



Annual Address by the President, G. K. Gilbert 



(Read before the Society December 30, 1892) 



CONTENTS 



Page 



Introduction 179 



Differentiation of continental and oceanic Plateaus 180 



Rigidity versus Isostasy 182 



Nature of density Differences 183 



What caused the continental Plateau? 183 



Why do continental Areas rise and fall? 186 



Are Continents permanent? 187 



Do Continents grow ? 187 



Summary 190 



Introduction. — For a decade attention has been turned to the continents. 

 Through the distribution of animals and plants Wallace has studied the 

 history of the former connection and disconnection of land areas. Theo- 

 ries of interchange of land and water have been propounded by Suess 

 and Blytt. By means of geodetic data Helmert has discussed the broad 

 relations of the geoid to the theoretic spheroid. Darwin has computed 

 the strength of terrestrial material necessary to sustain the continental 

 domes. James Geikie, treating nominally of coast lines, has considered 

 the shifting relations of land and sea, and a half score of able writera 

 have debated the question of continental permanence. The American 

 Society of Naturalists, now holding its annual meeting at Princeton, N. J., 

 devoted yesterday's session to the consideration of such evidences of 

 change in the geography of the American continent as are contained in 

 the distribution of animals and plants. The intercontinental congresses 

 auxiliary to the World's Fair next summer are to be devoted to the dis- 

 cussion of continental and intercontinental themes ; and a committee, at 

 the head of which stands one of our vice-presidents, invites the geologists 

 of the world to assemble for the consideration of those broader questions 

 of earth structure and earth history which affect more than one hemi- 



XXVII— Bull. Gkol. Soc. Am., Vol. 4, 1892. (179) 



