QUARRY MATERIALS OF NEW YORK I5I 



PALISADES DIABASE, ROCKLAND COUNTY 



The Palisades of the Hudson are the outcropping edge of an 

 intrusion of diabase or trap, the largest anywhere in the State' and, 

 by reason of its accesible position, the most valuable for the pro- 

 duction of crushed stone. The intrusion altogether is some 60 or 

 70 miles long north and south, and its width within the Rockland 

 county section ranges from one-eighth of a mile to over 2 miles. 



The diabase is in the form of a sheet which has ascended along 

 the inclined beds of Triassic sandstone and shale. The dip of the 

 beds is toward the west and northwest at an angle of from 5 to 

 1 5 . In this direction the diabase soon disappears and becomes 

 buried under an increasing burden of sediments. The thickness of 

 the sheet is several hundred feet at least and in places may be 

 around 1000 feet. Although it follows in general the bedding of the 

 stratified rocks, it is observed in places to cut diagonally across the 

 beds for greater or less distances. 



The trap exposure follows the shore line of the Hudson quite 

 closely from the New Jersey state line to Haverstraw. Here the 

 outcrop swings around to the west away from the river and after 

 continuing in that direction for some 4 miles, thins out or dis- 

 appears beneath the surface. In this part the sheet apparently cuts 

 across the bedded rocks at nearly right angles to their strike. The 

 exposure has been described and mapped very accurately by H. B. 

 Kummel. 1 



The diabase varies more or less in texture from place to place, 

 but has a very uniform composition in which plagioclase, augite and 

 magnetite are predominant and olivine, pyrite, quartz and other 

 minerals are of minor importance. It is grayish to dark green in 

 color, and shows very little alteration. The grain is moderately 

 coarse, except near the upper and lower edges, where it is fine and 

 compact. 



For many years the diabase has been extensively quarried for 

 crushed stone. It has also been worked to a limited extent for pav- 

 ing blocks and for building material, but the difficulty of cutting it 

 has prevented any marked development of these uses. As a road 

 metal it has long been recognized as the standard of quality. The 

 quarries around Haverstraw, Rockland lake and Nyack in recent 

 years have had an output annually of over 1,000,000 cubic yards of 

 crushed stone. 



1 N. Y. State Museum Annual Rep't 52, v. 2, 1900, 



