REPORT OF THE DIRECTOR I92O-2I 93 



as well as from western British Columbia (Daly, 191 2, p. 560). 

 The regions where these rocks occur are, however, involved in the 

 intense folding of later age of the Pacific side of North America 

 and there are now but few data 1 available as to their original or 

 Precambrian folding. The same is true of the northern continuation 

 of this plateau and mountain region into Canada 2 and Alaska. 

 Where observations on the trend lines of metamorphic rocks have 

 been made in these regions, they indicate a general direction 

 parallel to the coast line (Blake, 1886, p. 242, etc.) 



Briefly reviewing the principal or directive lines of the Precambrian 

 folding of North America, just described, we find that the north- 

 east of America, including Greenland, exhibits a distinct northeast 

 direction ; that this, in spite of later folding, or rather in part through 

 the latter, is recognizable along the entire east coast of North 

 America. This northeast direction swings in the interior of the 

 continent into an east-west line, and the latter turns into a north- 

 south line as it approaches the Rocky mountain region. The 

 Precambrian folding of North America exhibits thus a grand and 

 simple curvature (see plate 1) which clearly proves this part of the earth- 

 crust to have reacted as one unit against the diastrophic forces active 

 in Precambrian time; or, in other words, a continuation of 

 the Precambrian " nucleus " or protaxis seems to underlie the entire 

 continent as far as Greenland and Mexico, and " Laurentia " 

 originally comprised all this wide territory. The special meaning 

 of the northeast trend in the east, the east- west trend in the middle 

 and the north-south trend in the Rocky mountain region will be 

 discussed in connection with the dominant trends of the other 

 continents. 



b Precambrian Fold System of Eurasia 



It was Richthofen who was first impressed with the wonderful 

 uniformity of the trend lines of the folds of the Precambrian plat- 

 form of northern China (Richthofen 1882). His observations 

 have been verified by Willis (1907) and others, but it was left to 

 Suess to decipher the grand divergency of the trend lines in the 



1 Those available (as Calkins & Jones, 1913, p. 83, for Idaho), indicate a north- 

 west-southeast trend of the folds. 



2 From observations of Daly (1915, p. 531) in British Columbia it follows that 

 in the middle or interior mountain group also, as in the above-cited Rocky 

 mountain area of Montana and Wyoming, a block of Precambrian rocks (Shuswap 

 terrane) has escaped the Cordilleran folding, that has affected the overlying 

 younger formations, excepting in certain narrow zones; but in this terrane, 

 excepting minute crumples, folds are very rare, thereby suggesting, in our view, 

 a much farther extent westward into the Pacific of Archi-America than is at 

 present assumed. 



