REPORT OF THE DIRECTOR 1920-21 87 



of Dana of a continental nucleus flanked by two geosynclines. 

 Suess (ibid., p. 290) states that the strike of the Precambrian folds 

 of Laurentia is entirely independent from that of the Appalachians 

 and western Cordilleras. 



We have seen that the folds of the eastern part of the Canadian 

 shield strike northeast or, as Adams and Barlow have stated, 

 approximately parallel to the St Lawrence river. This, however, 

 is also the direction of the Appalachian folds and the evidence is 

 accumulating that these folds were initiated in Precambrian time. 

 Thus Keith (Asheville Folio, 1920) has observed interlocking north- 

 east-southwest bands of different gneisses, showing ancient folding in 

 the southern extension of the Precambrian basement complex 

 in the Appalachian and Piedmont systems. Lebling in his excellent 

 essay " Tektonische Forschungen in den Appalachen " (19 14, 

 p. 511) has, from the studies of Walcott, Grabau and Crosby, pointed 

 out the presence of a longitudinal bar already in the Lower Cambrian 

 of eastern North America, which separates the sea into two faunisti- 

 cally and lithologically different provinces, the western of which con- 

 tains Olenellus thompsoni, the eastern Holmia, Para- 

 do x i d e s and 1 e n u s . Crosby reports that in the Boston basin 

 the grain of the Cambrian sediments decreases in size from north- 

 west to southeast, while on the other side of the bar in New York 

 the opposite takes place. This initial Cambrian bar indicates folding 

 of Precambrian age in the direction and in the place of the Appala- 

 chian geosyncline and in line with the Precambrian folding of eastern 

 Canada. This folding has then continued in that area and direction 

 with interruptions throughout Paleozoic time. 



Berkey has found as well in the Highlands of the Hudson (1907) 

 as on Manhattan island, both the Archean Grenville series (Fordham 

 gneiss, Yonkers gneiss, etc.) and the younger (Proterozoic) series 

 (Manhattan schist, Inwood limestone) which are separated as every- 

 where else by an overlap unconformity. Both are intensely folded 

 and the strike of the axes of the anticlines and synclines is 

 everywhere northeast-southwest. Similar observations have been 

 made farther south in Carolina by Keith. One may well ask him- 

 self whether much of this folding of the Precambrian rocks of 

 the Appalachian region is not also of Precambrian age. We must 

 remember that it agrees in direction with the Precambrian folding 

 of eastern Canada, that such folding existed already on the site 

 of the Appalachians in Precambrian time, as indicated by the above- 

 mentioned observations of Keith, Walcott, Crosby, Berkey and 

 others, and further consider that, as Gilbert already emphasized, 



