692 "W. J. MILLER PKE-CAMBRIAX FOLDIXG IX NORTH AMERICA 



that there is some evidence that, in western Xew England, structure lines 

 in the pre-Cambrian rocks trend somewhat west of north. If so. such a 

 trend makes a high angle with Euedemann^s lines. 



Appalachian-Piedmont region. — The Appalachian-Piedmont region, 

 from southwestern Xew York to Georgia, contains large bodies of pre- 

 Cambrian rocks; but these have been so highly deformed during Paleo- 

 zoic time, and in part even so closely infolded with metamorphosed 

 Paleozoic strata, that the pre-Cambrian structure lines have been largely 

 obscured, if not in many places wholly obliterated by the Paleozoic 

 deformation. Thus, in the Trenton, Xew Jersey, Quadrangle (Bascom, 

 1909) the pre-Cambrian gneisses are folded along with Paleozoic strata, 

 and strike north 60 to 80 degrees east with them. 



According to Miss Bascom : 



"The prevailing structural features of the Piedmont Plateau are major fold- 

 ing of the Appalachian type, forming anticlinoria and synclinoria which ex- 

 tend for long distances.'" 



In their description of the Washington, D. C. Quadrangle, Williams 

 and Keith state that "typical Appalachian folds are to be seen in the 

 Piedmont region.'' Similar statements are made by Keith in various 

 later folios. 



In the Franklin Furnace, Xew Jersey, folio Spencer says : 



"No estimate can be given of the extent to which the attitude of the ancient 

 rocks was modified by the earth movements which folded and faulted the 

 Paleozoic formations." 



The present general northeast trend of the pre-Cambrian rocks of the 

 Appalachian-Piedmont region cannot, therefore, be assumed to represent 

 pre-Cambrian trend-lines. If, however, the writer, in a recent conversa- 

 tion, properly understood Mr. Keith, who knows the general region so 

 well, there is definite evidence that real pre-Cambrian structure lines are 

 still preserved, and that these run in general more nearly north-south 

 than northeast (see accompanying map). Such being the case, the actual 

 pre-Cambrian structural trend makes a considerable angle with tlie lines 

 shown on Euedemann's map. 



MIXXESOTA, UV.s'COX,S'/V. AXD MTCHIGAX 



Pre-Cambrian structures are well preserved in portions of these States 

 where the great iron ore districts have been carefully studied. Both the 

 Mesabi and Vermilion districts of Minnesota show strikes of about north 

 TO degrees east for many miles, and the newer Cayuna district (southwest 

 of Mesabi) has a structural trend of north 50 degrees east. The struc- 



