PRESIDENT'S ADDRESS. 53 



dications of them from the study of existing continents, appear to 

 have lacked such relations with each other as to give any satisfac 

 tory history of continuous continental growth. 



The opinion has prevailed among geologists that the North 

 American continent, as a whole, had its origin as a result of the 

 gradual contraction of the mass of the earth, by which certain 

 depressions and elevations were formed upon its crust. . The former, 

 it has been understood, became permanently the ocean beds ; and 

 the latter, gradually rising above the level of the sea, became con 

 tinents, whose outlines were changed, from time to time, by con 

 tinued elevation, alternating with greater or less depressions ; and 

 also by coalescence of previously separated parts, and by accretions 

 upon, and erosion from, their borders. This opinion implies that 

 continental areas were pre-determined, that they have been perma 

 nent in their location, and that no such areas have ever occupied 

 the broad spaces which are now occupied by the great oceans. 



I do not now intend to discuss this theory, but I may say in pass 

 ing, that a number of important facts do not, in my judgment, agree 

 with it, and I regard it as more probable that continental areas 

 have shifted from place to place in past geological time. But with 

 out reference to that theory, certain known ' geological facts seem 

 to show that the present continent arose from the sea in separate por 

 tions, the larger and older being its northeastern portion ; and that 

 the western portions were elevated afterwards, and finally coalesced 

 with the eastern. Furthermore, that the continent reached its 

 present dimensions and shape by more or less extensive accessions 

 upon its borders, especially those of the great gulf and the Pacific 

 ocean. 



While the following remarks will mainly refer to animal forms, 

 certain known facts concerning the vegetable life of the past are so 

 important in this connection that they should be at least briefly 

 mentioned. If we regard the graphite which has been found in the 

 Archaean rocks, and the petroleum of Silurian strata, as having had 

 their origin in land plants, the history of the land vegetation of the 



