BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 18, pp. 389-412 October 24, i907 



A THEORY OF CONTINENTAL STRUCTURE APPLIED TO 



NORTH AMERICA* 



BY BAILEY WILLIS 



(Presented in abstract before the Society December 29, 1906) 



CONTENTS 



Page 



Introduction 389 



Hypothesis of continental structure 390 



Positive elements of North America 393 



Negative elements of North America 398 



Theoretical considerations ' 401 



Effects of tangential pressure 403 



Zones of intrusion 408 



Summary 411 



Introduction 



For the purpose of this article the continent of North America may be 

 described as that portion of the lithosphere which lies between the Atlan- 

 tic, Arctic, and Pacific oceans or between their suboceanic masses. Its 

 area is that of the continental platform. Its depth may be taken at ap- 

 proximately 100 miles, the probable average limiting depth of the zone 

 of isostatic adjustment according to Hayford.f 



This continental mass is of large dimensions and exhibits at its sur- 

 face such variety of terranes and such diversity of geologic effects as to 

 indicate beyond any reasonable doubt a heterogeneous constitution. Con- 

 trast the Canadian highlands with the Mississippi embayment, the 

 Atlantic coastal plain with the Pacific Coast ranges, the New England 

 metamorphic province with the Allegheny plateaus, the volcanic belt of 

 the Cordillera with the non-volcanic regions of the East. 



*In reading this article it is desirable to consult the geologic map of North America 

 issued for the Geologic Congress at Mexico, 1906. 



Manuscript received by the Secretary of the Society August 29, 1907. 



Published by permission of the Director of the U. S. Geological Survey. 



to. H. Tittmann and J. F. Hayford : Geodetic operations in the United States, 1903- 

 1906 : A report to the fifteenth general conference of the International Geodetic Asso- 

 ciation. Washington, 1906. 



XXXIV— Bull. Geoi.. Soc. Am., Vol. 18, 1906 (389) 



