NEWARK ROCKS OF ROCKLAND COUNTY, N. Y. 17 



near the top of that group. Those in the quarries and northward 

 along the river for several miles resemble the Brunswick shales. 

 As before noted, the black argillites (Lockatong) do not occur in 

 this area nor the adjoining part of the New Jersey area. 



From Nyack northward to Verdrietege Hook exposures of 

 shale and finegrained sandstone are frequent. At Upper Nyack 

 and in the beds of two small brooks which have cut deep ravines 

 there are good opportunities for study. From Piermont north- 

 ward the trap sheet recedes from the river till at Nyack it reaches 

 a maximum distance of a mile, so that the belt of sandstone and 

 shale east of it is correspondingly wide. But at Verdrietege 

 Hook, two miles north of Nyack, the trap ridge by an abrupt turn 

 reaches the river, and thence north nearly to Haverstraw, a dis- 

 tance of six miles, the sandstone is restricted to a narrow strip 

 locally absent, between the water's edge and the foot of the trap 

 cliffs which rise almost directly from the river. 



In the region west of the Palisades exposures are so widely 

 scattered, owing to the thick accumulations of drift, that anything 

 approaching a complete section is impossible. Locally outcrops 

 are abundant along the tops of the ridges which form such a 

 distinguishing feature of the topography. In other localities they 

 are clustered together along the side slope of the hills, or in some 

 cases along the bottom of the valleys. Very commonly the trans- 

 verse streams, those which have cut their valleys across the ridges 

 or have carved deep ravines in their sides, reveal the bed rock 

 along their channels. But it is quite uncommon to find the longi- 

 tudinal streams flowing on the bare rock. Outcrops are far more 

 abundant along the crests of the ridges than in the bottoms of the 

 valleys, a fact which indicates that the topography of the rock 

 surface beneath the drift is more rugged than that of the present 

 surface. The layer of sand, gravel and stony clay, which unevenly 

 mantles the rocks, is in general thicker in the valleys than on the 

 tops of the ridges, and the topography, rolling as it is at present, 

 is one of less relief than was the surface which preceded the de- 

 position of the glacial drift. 



