SIXTH REPORT OF THE DIRECTOR I909 I4I 



ON THE SYMMETRIC ARRANGEMENT IN THE ELE- 

 MENTS OF THE PALEOZOIC PLATFORM OF NORTH 

 AMERICA 1 



BY RUDOLF RUEDEMANN 



We wish to present certain facts indicating that the structural 

 development of eastern North America has taken place in such a 

 fashion that a notable symmetric arrangement of its elements has 

 resulted. 



This arrangement becomes especially distinct when the large area 

 of Paleozoic rocks extending from the Canadian protaxis south- 

 ward is considered by itself. This area, which is roughly bounded 

 on the west by a line connecting the head of Lake Superior with 

 the Ozarks and on the east by a line inclosing the Adirondacks 

 and Appalachia, we may for convenience term the Paleozoic 

 platform of North America. It corresponds in its relation to the 

 Canadian shield with that of the " Russian platform " of the 

 European geologists to the Baltic shield. A glance at the geologic 

 map of North America will show that this platform is a direct 

 southward continuation of the Canadian shield or protaxis and 

 bounded by southward converging lines that are direct continuations 

 of the boundaries of that shield 2 [see chart II, where the line 

 M-N indicates the southern boundary of the Canadian shield A], 

 as described by Suess and Willis. In the west the platform, 

 like the Canadian shield, is separated from the Rocky mountain 

 area by the north-south transcontinental depression that extends 

 from the Gulf of Mexico to the mouth of the Mackenzie river and 

 is occupied by Cretaceous and Tertiary rocks. 



Chart II shows that the Canadian shield and its Paleozoic 

 platform together form a- body strikingly similar in its outlines 

 to the whole continent, a fact that can not but suggest that 

 the " Leitlinien " of this large epeirogenic element and the whole 

 continent stand in genetic relationship. 



1 Submitted April 1909. 



' The Mesozoic and Cenozoic embayment of the Mississippi Valley is, 

 in this discussion, left out of consideration, because of younger age;' like- 

 wise the belt of Carbonic rocks to the west and southwest of the Ozarks, 

 that forms the outer slope of the western arm of the platform, roughly 

 corresponding to the area of metamorphic rocks on the opposite slope 

 of the other arm, and properly belonging to the transcontinental 

 depression. 



