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NEW YORK STATE MUSEUM 



or whether the trap rests on successive beds of sandstone in a 

 series of steps which ascend westward. 



The upper contact. Much less is known of the upper contact of 

 the trap and shale. For most of the distance the trap disappears- 

 beneath the glacial drift, and its actual contact with the shale 

 is not visible. From the state line to Sparkill its position can 

 not be accurately located, owing to the thick drift deposits. At 

 Sparkhill there is an abrupt offset of J mile corresponding to the 

 offset of the basal contact, caused by the fault along the line of 

 Overpeck creek. 



From Sparkill northward to West Nyack the upper contact 

 apparently crosses the strike of the shales somewhat obliquely. 

 East of Orangeburg and 2 miles north of Sparkill the westward 

 slope of the trap ridge is marked by cliffs, a fact which suggests- 

 that here the feeding dike rises above the surface. The same 

 feature was noted 2 miles farther north near the Clarkstown- 

 Orangeburg township line. 



Fig. 5 Dike in the sandstone beneath the Palisades, south of Long Clove. 



The actual contact of trap and sandstone is shown a quarter 

 of a mile south of the Nyack-Clarksville road, along the road to 

 Sparkill (b, fig. 6). It is not conformable to the sedimentary 

 series, and fragments of highly indurated shale and sandstone,. 

 6 to 15 inches in diameter, are included in the upper part of the 

 trap. The latter is fine grained but not vesicular nor amyg- 

 daloidal. 



