REPORT OF THE DIRECTOR I920-2I 113 



universal law that when any zone of the earth's crust is considerably- 

 folded or fractured, subsequent disturbances follow the previous 

 lines, and this simply because these lines appear to be lines of least 

 resistance." Suess (loc. cit., p. 95) emphasizes the wonderful con- 

 stancy of this folding which extends first with a west-northwest 

 and then a west strike through the south of England to Weymouth 

 and the Mendips and states, " The region was folded, as we have 

 seen, at the close of the Carboniferous period, was covered with 

 younger sediments and subsided; then there occurred in the same 

 place a folding of the younger sediments, and this more recent folding 

 coincides in direction with the older folding which preceded it." 

 He proposes to term this phenomenon posthumous folding, adding, 

 "It is very likely that in most other mountain systems repeated 

 movements in the same direction have occurred at very different 

 times ; but seldom do we witness so striking an episode as. is here 

 presented in the subsidence of a great segment of a mountain arc 

 between successive periods of folding; and in this example we find 

 already displayed the extraordinary constancy in the direction of 

 the folding force." 



In applying this important principle in the relations of the 

 Paleozoic mountain systems to the Precambrian fold directions 

 one can not help but be astonished at their general parallelism; 

 and this coincidence of trends can not be attributed to Paleozoic 

 folding that overwhelmed the Precambrian complex since the 

 Paleozoic folding has as a rule affected only the marginal regions, 

 as is most clearly evidenced in the cases of North America, Africa 

 and Australia but also seen in the southeast and southwest portions of 

 the Eurasian basement complex and probably in the eastern margin 

 of South America. 



In the case of the Appalachians it has been persistently claimed 

 by the best authorities on the stratigraphic relations of their com- 

 ponent formations, as notably Ulrich (191 1) and Campbell (1894), 

 that these prove that the folding " has been practically continuous 

 from since early Paleozoic times " (Campbell, loc. cit.). Ulrich, 

 in the diagram of the inland migration of folding in southeastern 

 North America (191 1, fig. 18, p. 440) extends the folding from 

 " earliest Cambrian " to " late Tertiary." * 



If we further consider that we find at the beginning of Cambrian 

 time two geosynclines, one in the place and direction of the Appala- 



1 Also in regard to the Variscan folding of the " Rheinische Schiefergebirge " 

 analogous observations have been made bv W. Bornhardt and especially by Denck- 

 mann (19 12), who have found that the Variscan folding of Carboniferous age 

 was there preceded by Devonian folding, and in the Saar basin followed by 

 Permian folding; the latter folding not being observable in the Rheinische Schie- 

 ergebirge on account of the absence of younger beds (322 A.il:i3, ).-3 



