REPORT OF THE STATE PALEONTOLOGIST 1902 1225 



of the hill are exposed the Oriskany pebble beds and still lower 

 down, near the foot of the slope, is a small outcrop of Esopus 

 grit with a correspondingly steep dip. Along the foot of the 

 slope is the dried-up bed of a stream, and on the other side of 

 this small valley the Esopus grits lie horizontally, or dipping 

 slightly eastward. 



East and west cross sections of the hill taken at points far- 

 ther north, as at the Old quarry (O), Cloonan's quarry (C), and 

 at the Terry triangulation station, show that the various forma- 

 tions extend with the same simple structural features in more 

 or less regular belts for a considerable distance to the north- 

 ward, the width of the belts of exposure varying locally accord- 

 ing to the topography of the eroded land surface. 



Summary 



The overthrust mass which has been thrown to the west at 

 least 1100 feet forms a veneer to the top of the North hill. The 

 dip of its beds varies from 15° to 25° w. along the eastern edge 

 of the thrust mass, to zero along its central line. On its entire 

 western edge the dip is high, and at one point on the cross 

 road west of Terry station the Oriskany beds dip slightly be- 

 yond the vertical. The high dip of the western edge is probably 

 due to drag and underturning of the free edge of the thrust 

 block. This thrust is probably of the nature of the so called 

 " erosion thrust," 1 where the sliding mass has progressed over 

 a land surface. 



The southern end of the thrust is drawn on the map as cur- 

 ving to the southwest and then to the west-northwest. This 

 is due to the southward slope of the end of the hill by virtue 

 of which the thrust plane intersects the surface of the ground 

 along an approximately east and west line. On the upper, 

 northern, sides of this line the Manlius, Coeymans and New Scot- 

 land limestones overlie the Port Ewen beds beneath and south 

 of the thrust plane; and, at the point B, the second vein of 

 Beeraft, in the overthrust mass, abuts against the Oriskany 

 beds of the under thrust section. 



The present attitude of the thrust plane, dipping 15° toward 

 the west, can not be its original attitude. An orogenic force 

 acting from the eastward might produce a thrust with a plane 



Willis. 1893, p. 223. 



