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NEW YORK STATE MUSEUM 



3 An overthrust of the eastern wing over the western, bring- 

 ing the Oambric beds in contact with the Dicellograptus beds in 

 the core of the fold (fig. 4). 



' ^'^^--'A^^^W '^ 



'n.'Q 



rig. 4 Overthrust fault. 



4 Reduction to a plain. The erosion, working proportionally 

 to the elevation of the beds and, later, on the abrasion by the 

 seas of upper Siluric and Devonic time, as evinced by the uncon- 

 formable deposition of the limestones at Becraft mountain 

 (Columbia county), on the " Hudson river '' shales, reduced the 

 surface of the disturbed area to nearly or entirely the condition 

 of a plain, leaving the steeply dipping conformable and inverted 

 series of beds and the overthrust fault as witnesses of the former 

 powerful activity of orogenic forces (fig. 5). 



Fig. 5 Profile through Hudson valley at Watervliet. 



The small anticlines crossing the Vly are the weak western 

 manifestations of the fold-producing forces; for they run parallel 

 to the greater deformations of the crust in the east, while the 

 larger anticlines, pretty examples of which are visible along the 



