COKTIISrENTAL PROBLEMS OF GEOLOGY.* 



By G. K. Gilbert. 



Introduction. — For a decade atteutioii has been turned to the con- 

 tinents. Through the distribution of animals and plants Wallace has 

 studied the history of tlie former conn«K'tion and disconnection of land 

 areas. Theories of interchange of land and water have been i)ropounded 

 by Suess and Blytt. By means of geodetic data Helmert lias discussed 

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

 comi^uted tlie strength of terrestrial material necessary to sustain the 

 continental domes. .lames Geikie, treating nominally of coast lines, 

 has considered the shifting relations of land and sea, and a half score 

 of able writers 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 e\idences of change in the geography of the American continent 

 as are contained in the distribution of animals and plants. The inter- 

 continental congresses auxiliary to the World's Fair next summer are 

 to be devoted to the discussion of continental and inter-continental 

 themes ; and a committee, at the head of which stands one of our vice- 

 ])residents, invites the geologists of the world to assemble for the con- 

 sideration of those broader questions of earth structure and earth history 

 which aftect more than one hemisphere. This occasion, too, in which, 

 after three years' sojourn in the land of the raccoon and the opossum, 

 we return to the land of the sable and the beaver, brings forcibly to 

 mind tlie continental extent of our society and its continental liekl. It 

 is not strange, then, that tlie continents have seemed to me a litting 

 tlieme of which to speak to you to-day. Realizing not only the breadth 

 and grandeur, but tlie inherent difficulty of the subject, I do not hoi)e 

 to enlarge the contril)ution the decade has made, nor shall I attempt 

 to summarize it; neither is it my desire to anticipate the discussions 

 of the World's Fair congress. It is my pur])ose rather to state, as 

 clearly as I may, some of the great unsolved problems which the con- 

 ti.nents propound to the coming inter-continental congress of geologists. 



*l'resiileutial address before the (ieological Society of America; delivered Decem- 

 ber 30, 1892. (From the Bulletin Geolocj. Sov. of Jin., vol. i\', pp. 179-190.) 



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