BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 5, pp. 199-202 February i7, 1894 



PLEISTOCENE DISTORTIONS OF THE ATLANTIC SEACOAST 



BY N. S. SHALER 



{Read before the Society December 28, 1893) 

 CONTENTS 



Page 



Evidences of orogenic Action 199 



Extent, Duration and Character of the Movements 200 



Origin of the Movements 201 



No Evidence of massive Elevation . . 202 



Evidences of orogenic Action. 



More than once I have called attention to tlie fact that the Tertiary 

 and Cretaceous beds on the island of Marthas Vineyard, Massachusetts, 

 show throughout an area of about fifty square miles unmistakable evi- 

 dence of mountain-building stresses. The strata, having an aggregate 

 thickness of certainly many hundred, perhaps of some thousand feet, 

 have been thrown into folds of consideral)le amplitude, which are so 

 sharply compressed that the numerous outcrops show dips which aver- 

 age more than 45°. The suggestion that these distortions have been 

 produced by the shearing action of the ice in the last glacial period is 

 completely disproved by the very well developed preglacial topography 

 which this region exhibits — contours of hill and dale which were formed 

 in these soft rocks after they were folded, and on which the drift rests 

 as an incomplete mantle. It is impossible to conceive that the folding 

 of the rocks could have been accomplished without the complete de- 

 struction of the previously existing topography. 



Recently my colleague, ^Ir J. B. Woodworth, has examined the similar 

 distortions of Block island. He informs me that in general character 

 they closely resemble those of Marthas Vineyard. While the horizon 

 of these Block island beds is not as yet clearly determined, the evidence 

 goes to show that they are in part, at least, of Pleistocene age ; they also 

 have preserved their preglacial topography, which is only partly masked 



XXVII — Rur.r,. Ccv.ov. Soc. Am., Vor,. 5, 1893. (.199) 



