42 NEW YORK STATE MUSEUM 



compatible with the assumption that it is connected with the 

 Palisades sheet, as the latter at its apparent termination near Mt 

 Joy has risen far above the base of the formation, and still farther 

 west may have overflowed the floor of the estuary on which the 

 sandstones were deposited. 



Union hill trap. Near Suffern a mass of trap rises above the 

 surrounding glacial deposits forming Union hill. Its greatest 

 length from northeast to southwest is nearly half a mile; its width 

 is about one half that. The rock is not vesicular, not scoriaceous, 

 but of medium texture and suggests an intrusive mass. Its rela- 

 tions to the surrounding sandstones and conglomerates are un- 

 known. The latter are exposed in a ledge below the trap along 

 the southeastern face of the hill. The conglomerate beds dip 

 toward and apparently pass under the trap, but they may abut 

 against it. The latter rises from 120 to 140 feet above the line 

 of contact, which is everywhere concealed beneath drift or talus, 

 and it must therefore have a minimum thickness of this amount. 

 About J of a mile north of this ledge a low boss of trap 50 feet 

 in diameter rises above the terrace of stratified drift along the 

 Mohawk valley. It is not known whether it has any connection 

 with the Union hill mass. 



Dikes 



Dikes are not common within this part of the Newark forma- 

 tion. If the glacial drift were removed, more might be found. 

 Several small ones occur midway between New City and West 

 Nyack. One can be seen in the road directly in front of the 

 house of H. M. Vanderbilt. Two others cross the road a few 

 hundred yards to the east and are marked by low elevations. 

 The most conspicuous dike is apparently from 100 to 130 feet wide 

 and forms a broad swell, about 15 feet high, which can be 

 traced southward from the road for 300 to 400 yards before it 

 dies away beneath the drift. Still farther east, beyond the first 

 bend in the road are two more dikes, making five in all. Owing 

 to the drift, only two can be traced beyond the road, and these are 

 lost as soon as they cease to be conspicuous topographically. 



