114 NEW YORK STATE MUSEUM 



chians and their northern and southwestern continuation, and another 

 in that of the Rocky mountains, as has been so clearly demonstrated 

 by Walcott (1891, pi. 3; see also Schuchert, 1910, pi. 51); and that 

 b th these depressions exactly follow the trends of the Precam- 

 brian folds in the east and west, the conclusion seems unavoidable 

 that these later fold directions were inherited, at least to a large 

 extent, from Precambrian time. Likewise the generally westward 

 trend of the Arbuckle and Ouachita mountains in Oklahoma, which 

 are considered as indicating the western extension of the Appala- 

 chian system stands in remarkable agreement with the east-west 

 trend of the Precambrian folds of the middle segment of the con- 

 tinent as seen north and south of Lake Superior, and it would seem 

 that even where the later pressure came from a somewhat different 

 direction, the folds would, at least in part, tend to fall into the old 

 direction, which is that of least resistance in that case. This would 

 at least be indicated by the observation of C. W. Honess (1920, 

 p. 121) that in the southern Ouachita mountains a high angle is made 

 by the east or southeast trending axes of many folds with the axis 

 of the principal anticlinorium which trends northeast. 



If the principle of posthumous folds, which to us seems rather 

 one of persistent or inherited folding, with " prenuncial " as well 

 as " posthumous " folding, preceding and following the main orogenic 

 outburst; if this principle has the wide application that it seems to 

 us to possess where Precambrian and Paleozoic folding are compared, 

 then vice versa we may well draw conclusions as to the probable 

 Precambrian fold directions in cases where Paleozoic folding agrees 

 in its direction with that inferred for the Precambrian folding from 

 other inferences, without committing the error of a circulus vitiosus. 

 This may well be the case with the Paleozoic folds trending in 

 northeast and north-south direction, of eastern Brazil and it would 

 fully explain the north-south direction of some of the folds in the 

 western Sahara, if these should be found to contain Paleozoic elements. 

 It should be further noted that the Paleozoic north-south folding 

 of eastern Australia agrees with the north-south Precambrian folding 

 found from western Africa to South Australia. We are inclined 

 to see in these Paleozoic folds' of both eastern Brazil and eastern 

 Australia segments of larger fold systems that in these particular 

 regions have fallen in with previous fold lines. 1 



1 Extremely powerful folding, of course, will follow its own lines as we have 

 seen in India where the Himalayas have overridden the Precambrian folds 

 from the north; or in Europe where the Carpathians and Alps have overwhelmed 

 the Variscan system to a considerable extent. On the other hand, we have 

 seen there may remain Precambrian blocks unaffected by later waves of folding, 

 surrounding them, as in the case of the Bohemian massif and of the block of 

 Montana and Wyoming. 



