28o NEW YORK STATE MUSEUM 



grain structures of granites. As a building stone it finds very little 

 application, probably on account of its somber color. The expense 

 of cutting and dressing trap is also an obstacle to its employment for 

 building or ornamental purposes. 



The trap quarried in New York State is properly a diabase. Its 

 mineral composition varies somewhat in the different occurrences, 

 but the main ingredients are plagioclase feldspar and pyroxene, with 

 more or less of amphibole, olivine, magnetite and sometimes biotite. 

 The texture is characteristic, for the feldspar forms lathshaped 

 crystals which interlace and inclose the p5rroxene and other 

 ingredients in the meshes, and it is this firmly knit fabric which 

 gives the stone the qualities of strength and toughness. 



Occurrence. The largest occurrence of trap in New York is 

 represented by the Palisades of the Hudson and the continuation 

 of the same intrusion which extends southward through New Jersey 

 onto Staten island and is also encountered in the interior of Rock- 

 land county. The Palisades are the exposed edge of a sill or sheet 

 of diabase that is intruded between shales and sandstones of Triassic 

 age. The sheet is several hundred feet thick, in places nearly looo 

 feet, and in general seems to follow the bedding planes of the sedi- 

 mentary strata which dip to the west and northwest at • an angle 

 of from 5° to 15°. The outcrop is narrow, seldom over a mile, and 

 in places is limited to a single steep escarpment. The principal 

 quarries are near Nyack and Haverstraw at the base of the cliffs. 

 Other quarries have been opened near Suffern, Rockland county, 

 on an isolated intrusion, and also near Port Richmond, Staten 

 island, at the southern end of the Palisades sill. 



Trap occurs in numerous places in the Adirondacks, but mostly 

 as narrow dikes. It is especially common in !Essex and Clinton 

 counties, where there are many thousands of dikes that range from 

 a few inches to 20 or 30 feet thick. On the southern border of the 

 region are a few dikes of notable size, such as that in the town of 

 Greenfield, Saratoga county, and at Little Falls in ' the Mohawk 

 valley. A quarry has been opened in the Greenfield occurrence for 

 the supply of crushed stone. 



The quarrying of trap along the face of the Palisades in Rockland 

 county probably will soon be discontinued, as it is designed to 

 purchase the quarry properties for the Palisades Interstate Park. 

 The lands to be included within the park extend from the river 

 line to the top of the Palisades. So far only the quarry of the Man- 

 hattan Trap Rock Co. has been taken over and closed, but nego- 



