688 W. J, MILLER PRE-CAMBRL\N FOLDING IN NORTH AMERICA 



dential address at the 1922 meeting of the Geological Societ}^ of America, 

 the great scenes of diastrophism during the Paleozoic were in the eastern 

 part of the continent, while in later geologic time the scenes shifted to 

 the western part. Xor can it be maintained that these foldings devel- 

 oped progressively in any direction or directions, or, in other words, that 

 successive strips of the continent were affected, as suggested for the pre- 

 Cambrian by Ruedemann, because^ for example, the great Rocky Moun- 

 tain disturbance, far within the continent, took place well after the Sierra 

 jSTevada folding along the margin of the continent. Furthermore, in 

 post-Cambrian time much of North America has been unaffected by any 

 notable folding. This is an important fact in view of Ruedemann's ad- 

 vocacy of universal pre-Cambrian folding. In brief, North America in 

 post-Cambrian time has been only very locally affected by notable fold- 

 ings, mostly widely separated in space and time. Surely, then, the conti- 

 nent has not, in post-Cambrian time, responded to universal, long-time 

 folding as a unit ! In the absence of anything like definite facts to the 

 contrary, is it not reasonable to believe that similar conditions obtained 

 during the vast lapse of pre-Cambrian time ? 



Third. In regard to Ruedemann's conclusion that North America re- 

 sponded uniformly to the diastrophic forces of folding, evidence will now 

 be presented at some length to show that sucli was not the case. 



Observed Strikes of pre-Cambrian Folding and Foliation 



general statemext 



The map accompanying this paper shows two features — the general 

 trend-lines of pre-Cambrian folding and foliation as observed by Ruede- 

 mann and many of the more important actually observed strikes of pre- 

 Cambrian folds and foliation. Several hundred pieces of literature deal- 

 ing with regions in which pre-Cambrian rocks occur were examined in 

 order to secure the data for the strikes recorded on this map. In many 

 publications the necessary structural data are ^vholly lacking. Further 

 search would hi'mg to light a considerable number of other observations, 

 but these would mainly only fill in detail without essentially altering the 

 situation as represented on the map. . Folding and foliation of pre-Cam- 

 brian rocks almost certainly produced after pre-Cambrian time are not 

 recorded, except in a few cases by short broken lines, as in the Appa- 

 la^ihian region and a few other places. In a few of the recorded cases 

 post-Cambrian diastrophism may have been an important factor, but at 

 most in onlv a few. 



