NEWARK ROCKS OF ROCKLAND COUNTY, N. Y. 25 



This assumed relationship is indicated by the diagrammatic cross- 

 section shown in figure 1. 



Fig. 1 Diagrammatic cross-section of the Palisades trap ridge, showing its probable relations to 

 the sandstones. The thickness and position of the feeding dike are largely hypothetical. 



From Rockland lake northward the trap ridge curves gradually 

 to the left so that it crosses the strike of the sandstones at a 

 continually greater angle. West of High Tor, near Haverstraw, 

 its trend is at right angles to the sandstones which outcrop close 

 to the southern margin. This change of trend is due primarily 

 to a change in the trend of the feeding dike, which here bends 

 westward. At the same time, however, the base of the sheet 

 ascends from lower to higher horizons in the sandstones. The 

 ascent is sometimes made by abrupt steps and in other cases by a 

 gradual oblique trend. These changes are best shown between 

 Rockland lake and Haverstraw, and instances of both will be 

 cited below. West of Little Tor, near the end of the hook, the 

 trap apparently loses much of its sheet-like character, while at 

 the same time the dike characteristics are more marked. It does 

 not, however, become a simple dike, since at various places there 

 is slight evidence to show that the lava spread between the beds 

 laterally from the fissure up which it ascended. Details of the 

 structural relationship are noted below. 



Local details of the structural relations. The basal contact is 

 the one most frequently exposed. At Sneden's landing it has 

 an elevation of about 120 feet above the river, and ledges of arkose 

 sandstone and varicolored shales are exposed beneath the trap, 

 but the actual contact is not revealed. Northward the base of 

 the trap gradually descends in elevation till just south of Over- 

 peck creek, Piermont, it passes beneath the level of the river. 



