680 W. J. MILLER PRE-CAMBRIAN FOLDING IN NORTH AMERICA 



elaborate effort of this kind has very recently been made^ by E. Ruede- 

 mann, whose paper is valuable mainly because of its highly suggestive 

 features. In it he ^Ventures to suggest some possible fundamentals of 

 pre-Cambrian paleogeography/^ It is not too much to say that Ruede- 

 mann has opened up a new and important field of geological inquiry. 



Figure 1. — Map of North America 



Showing, by the short, heavy lines, observed strikes of pre-Cambrian folding and 

 foliation and, by the long, curved, dotted lines, the pre-Cambrian structural trend-lines 

 advocated by Ruedemann. The short, broken lines indicate strikes of pre-Cambrian 

 rocks developed mainly or wholly in post-Cambrian time. 



The present purpose is to confine attention to one very important 

 aspect of the subject, in which the writer has been interested for some 

 years, and this in its application to North America only. This aspect of 

 the subject is the folding and foliation of pre-Cambrian age, with special 



2 R. Ruedemann : N. Y. State Museum Bulletin 240, 1922, pp. 67-152. 



