200 N. S. SHALER — PLEISTOCENE DISTORTIONS. 



by the drift, showing that here also the hypothesis of glacial shoving 

 cannot be reasonably advanced to account for the distortion of the strata. 

 Accepting these indications as evidence of orogenic action at a compara- 

 tively recent time, the question is as to their relation to the other move- 

 ments along the Atlantic coastline. 



Extent, Duration and Character of the Movements. 



It seems in the first place evident that the Atlantic coast from South 

 Carolina northward to the Saint Lawrence has been the seat of recurring 

 mountain-building action since the Triassic time. These movements, 

 in so far as we can clearly determine them, have not operated in the 

 country south and west of this district. The distortions which flexed 

 the Triassic or Rhetic deposits appear to have occurred in the Jurassic 

 time, or at least before the deposition of the Cretaceous. The last named 

 period seems to have passed, as did the division of the Tertiary, without 

 the action of the mountain-building forces being manifested. At the end 

 of this period, but long enough before the glacial epoch to permit the 

 development of a complete topography, with wide valleys and low, arched 

 hills, came the folding and faulting which has dislocated the beds in 

 southeastern Massachusetts. 



It seems tolerably clear that this New England disturbance was not 

 local, though its particular manifestations are peculiar. The action of 

 the same forces, though operating in a somewhat dissimilar manner, is 

 traceable southward along the coast, as has been shown by the studies of 

 McGee and others, on the faulting which is there developed. The contin- 

 uation of these breaks to the northward in foldings rather than in faultings 

 finds its parallel in what we observe in the movements which occurred 

 in the interval between the deposition of the Carboniferous and the 

 period of the Trias. In the eastern Tennessee district we find the dis- 

 placements effected, in the main, by faulting; in southwestern Virginia 

 the folds become more common, and thence northwardly they increase 

 in relative importance until the dislocations disappear in a series of 

 small but characteristic anticlines ill the region near Catskill, New York. 



These dislocations along the Atlantic coast seem to indicate, especially 

 when taken with those which distorted the Triassic beds, that this shore 

 was the seat of mountain-building work long after it apparently had 

 ^ceased in the more interior portion of the Appalachian system. So far 

 as they go, they afford additional evidence that a coastline is nominally 

 the seat of orogenic work. 



The Marthas Vineyard foldings appear to be the most recent of any 

 well developed anticlines in the eastern portion of the United States. 



