26 NEW YORK STATE MUSEUM 



This change of elevation is apparently due, not to any change of 

 geologic horizon, but to the westerly trend of the escarpment as- 

 compared with the strike of the sandstone. On the north side of 

 the creek, near the lower railroad track, Piermont, the contact is 

 60 feet above sea level, the change in elevation being due to a 

 fault which crosses the ridge diagonally from northeast to south- 

 west, along the line of the creek, and which has raised the north- 

 ern block relatively to the southern. Good examples of the way 

 the trap is broken by many joints into small wedge-shaped frag- 

 ments are found in a small exposure here, which also shows 

 another phase of trap disintegration, i. e. that of concentric 

 weathering — figure 2. 



From Piermont north to Verdrietege Hook, or Hook mountain,. 

 a distance of 5 miles, the basal contact is not exposed, but it is- 

 possible to determine its position quite accurately. From 

 an elevation of 60 feet at Piermont it ascends to 240 feet, a mile 

 north of Piermont, to about 400 feet south of Nyack, and thence 

 descends to 220 feet in the gap west, of Nyack. This ascent is- 

 accompanied by a departure of the cliff face from the Hudson 

 river, so that at Nyack it is from \ to 1 mile distant. Within this 

 distance the sandstones strike slightly east of north, and the in- 

 creased elevation of the base of the trap in spite of a trend which 

 decreases the altitude of the outcrop can be explained only by 

 supposing it to have ascended to higher geologic horizons. The 

 descent from 400 to 220 feet west of Nyack is due to erosion at the 

 gap and the westward dip of the contact plane. 



Where the trap crosses the road from Kockland lake to Nyack 

 (a, fig. 6) its base is about 320 feet above the sea level, which 

 indicates a slightly lower geologic horizon than farther south. 

 Just north of this point the trap escarpment, which for several 

 miles has not been precipitous, though always a steep slope, 

 turns abruptly eastward almost at right angles with its former 

 course and approaches the river to form the bold and naked cliffs 

 at Verdrietege Hook, so well shown in plate 3. This view well 

 illustrates the mural face of the Palisades where they are boldest. 

 The top of the ridge is tree-clad. The cliff is often 200 or more 



