REPORT OF THE DIRECTOR I92O-2I 129 



i Long-time, gradual extension of local folding 



The view that the worldwide Precambrian folding could have 

 originated from a long-time, gradual extension of local folding has, 

 to our knowledge, not been advanced or supported by any authors, 1 

 On the contrary such authors as Suess, Uhlich, Andree, Van Hise, 

 Schuchert who have touched the subject of worldwide Precambrian 

 folding have contrasted it with the later localized folding and seen 

 in it the evidence of one or more Precambrian profound and general 

 revolutions that in magnitude far surpassed the later more localized 

 revolutions, a view that also finds general expression in the text- 

 books. Nevertheless, the possibility that this folding involving the 

 whole crust of the earth may be only the expression of an immense 

 length of time and a gradual wandering of the folding process over 

 the whole surface of the earth, is suggested by several facts. 



One of these is the recognition, in recent years, of the immense 

 lapse of time that must be assigned to the Precambrian and that it 

 equals or surpasses all later time of the history of the earth. This 

 long Precambrian earth history finds its expression in the thickness 

 of 32 miles of the combined Archeozoic and Proterozoic rocks as 

 against the 21 miles for all subsequent fossiliferous strata (see 

 Schuchert, 1918, p. 64). There is, hence, a perfect sufficiency of 

 time for a gradual folding of the entire earth crust if other factors 

 should favor such a process. The fact of the gradual wandering 

 of the folding from the older chains into the foreland, after the 

 partial denudation of the older chains, has been described as " zonal 

 wandering of mountain formation" by Stille (1909), and well 

 illustrated by Ulrich (191 1, fig. 16) in his diagram of the origin 

 of the Appalachian system. Suess has pictured in a masterly way 

 the gradual extension of the Altaid folding over Asia from the 

 vertex, and Grabau (19 19) has lately even suggested a migration of 

 geosynclines. 



In the case of the Appalachian system this folding has wandered 

 from the Atlantic coast into the continent. We know now from 

 Adams, Barlow and Coleman!s researches that the folding in the 

 eastern portion of the Canadian shield also came from the Atlantic 

 side (that is, southeast) , and we also have seen before that the folding 



1 It is suggested by Blackwelder (1914, p. 637) for the Archean, when he states: 

 " Whether these facts (greater deformation and metamorphism of Archean than 

 Algonkian) are to be interpreted as indicating a single almost universal orogenic 

 disturbance just before the Algonkian deposits were laid down, or several, if not 

 indeed many, such disturbances affecting successive strips of the continent at 

 different times, is not now determinable. Considering the periodicity and local 

 effects of the foldings in later geologic time, the latter view is perhaps the more 

 favored one." 



