88 NEW YORK STATE MUSEUM 



the Appalachian folding was of deep-seated origin, as revealed by 

 the great erosion, and that such deep-seated folding is more likely 

 to follow predetermined lines such as are given by the Precambrian 

 folds. We are strongly inclined to infer from this evidence that the 

 Appalachian folding is largely of a posthumous character (see p. 

 113) or of folding along older lines. These older lines, however, 

 are those of the eastern margin of Laurentia. 1 



American geologists, including Willis, Clarke, Ulrich, Schuchert and 

 Grabau, have long agreed that the continent formerly extended 

 eastward for a considerable distance (100 miles or more) east of 

 the Appalachians, forming Appalachia. The strike of the Pre- 

 cambrian rocks of the Piedmont plateau leaves little doubt that 

 also this former extension of North America into the ancient 

 Atlantic (" Poseidon " of Schuchert) conformed, in its basement 

 complex with the general structure of Laurentia and was an integral 

 part of it. 



The Rocky mountains with their intense folding, faulting and 

 overthrusting of Mesozoic age seem at" first a hopeless field for a 

 recognition of the Precambrian fold directions. A perusal of the 

 literature, however, brings out the fact that the rocks of the base- 

 ment complex in several areas have clearly retained a direction of 

 folding and foliation that is independent of the Mesozoic and 

 Tertiary folding. 



The general trend of the Rocky mountains is northwest and the 

 boundaries of the Precambrian rocks which form the backbones 

 of the ranges as a rule have the same direction. Thus in Colorado 

 where the waves of the Rocky mountains have been stopped, 

 reflected and bent by the impact with the Colorado massif, they 

 assume a Y-shaped form (see R. T. Chamberlin, 1919, p. 150), two 

 folds merging into one southward; a feature which is faithfully 

 reflected in the Precambrian backbones. Where the first wave has 

 been stopped in the Uinta mountains it has assumed an east-west 

 direction (Suess, v. 3, pt 2, p. 438). Successively the waves have 

 swung around more to the north. It is probable that it is under 

 the influence of such violent bending of the mountain system 

 that the Archean gneisses and schists of the Needle Mountains 

 quadrangle (Whitman Cross et ah, 1905) change their strike as shown 



1 In a recent publication, Berkey and Rice (C. P. Berkey and Marion Rice> 

 Geology of the West Point Quadrangle, N. Y., State Mus. Bui. 225-26, 192 1, 

 p. 51) have claimed a northeast-southwest folding for the Grenville beds of " very 

 ancient Precambrian time," finding their evidence in the marked control over 

 all igneous intrusions resulting in a similar orientation of them and indicating 

 that the Grenville formation which is the oldest in this region must have had 

 this structure before the igneous history began. 



