BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 34, PP.669-678 DECEMBER 30, 1923 



THE LAKE SUPERIOR GEOSYNCLINE ^ 



BY W. 0. HOTCHKISS 



{Presented before the Society of Economic Geologists Dec. 29, 1922) 



CONTENTS 



Page 



Introduction , 669 



Formations included in the syncline 670 



Directions of slopes on which sediments and flows were deposited 670 



Evidences of tilting of the land surfaces 672 



Other facts to be fitted into the story 673 



Hypothesis explaining the foregoing facts 673 



General statement 673 



Size and shape of the bathylith 674 



Rise of the bathylith and its consequences 674 



Introduction 



The rocks surrounding the western half of Lake Superior dip to the 

 southeast in Minnesota and northern Douglas County, Wisconsin, and 

 dip more steeply northwestward in the limb extending southwestward 

 from Keweenaw Point to Minnesota. As the main axis is not far north- 

 west of the outcrop of the south limb, the syncline is not symmetrical. 

 Dips of 25 to 30 degrees are unusually high on the north limb; on the 

 south limb dips vary from 30 to 90 degrees. 



The purpose of this paper is to discuss briefly the major facts as they 

 are now revealed to us in the rocks of this syncline and to construct a 

 hypothesis correlating these major facts in its history. This hypothesis 

 relates the origin of the various formations and their present structure 

 to the intrusion of an enormous bathylith, whose final result is evident 

 to us in the scores of thousands of cubic miles of Keweenawan lavas and 

 intrusives. The gradual foundering of the roof of this bathylith is be- 

 lieved to offer the most plausible explanation of the origin of the present 

 structure. 



^ Manuscript rpceived by the Secretary of the Society April 19, 1923. 



(669) 



