36 C. R. VAN HISE 



line and semicrystalline rocks of the Blue Ridge in some places 

 are closely folded and have secondary structures, but are in 

 many places not closely corrugated. For instance, the quartz- 

 schists of Tullulah mountains are in very gentle folds. The 

 folding of the pre-Cambrian sediments in western America is 

 also rather simple. The thick Grand Canyon series is but gently 

 undulating. The Uinta sandstone is in a great simple arch. 

 The thick pre-Cambrian series of Montana is gently folded. 

 The pre-Cambrian of the Wasatch and Medicine Bow mountains 

 are somewhat more closely corrugated, but not nearly so closely 

 as many areas of Paleozoics in the New England region. How- 

 ever, there are some districts in which the folding is close and 

 complex. This is the case with the Lower Huronian of the 

 Vermilion and Menominee districts, and to less extent of the 

 Marquette district, all in the Lake Superior region. The folding 

 of the Original Laurentian district is of the most complex kind. 

 However, even in these districts of close folding, it cannot be 

 stated that the shortening is greater than is the case in the 

 closely folded Tertiary rocks of the Alps. 



Thus it appears that somewhat gentle folding is the rule with 

 the pre-Paleozoic sedimentary rocks, as with the Paleozoic and 

 post-Paleozoic, but in occasional districts the deformation, as in 

 the later rocks, is of the most intense character. Therefore, 

 during early geological periods, as during later geological time, 

 orogenic movements have been concentrated along definite 

 zones. Apparently since the beginning of Algonkian time large 

 parts of the continents have escaped violent orogenic movements. 



From the foregoing I do not mean to assert that the pre- 

 Paleozoic sedimentary rocks are upon the average not more 

 closely folded than later rocks. Indeed, the reverse must be 

 the case, for the earlier rocks have partaken in subsequent fold- 

 ings. The point upon which I insist is that there is no such 

 great difference in the amount of deformation as has been 

 thought by many. 



However, it is in the Archean rocks that the apparent plications 

 are most severe, but it is to be remembered that we have here no 



