184 NEW YORK STATE MUSEUM 



On the borders of the Adirondack region quarries have been 

 opened in the towns of Wilton, Hadley and Greenfield, in Sara- 

 toga county; at Whitehall, in Washington county; at Littlefalls, 

 in Herkimer county; Grindstone Island, Jefferson county; and 

 near Canton in St Lawrence county. The inaccessibility of much 

 of this region and the distance from the large city markets have 

 prevented the opening of more quarries in the gneissic rocks on 

 the borders of the Adirondacks. 



TRAP 



Trap-rock or trap is the common name given to a class of 

 eruptive rocks because of a structural peculiarity, and has no 

 distinctive significance in mineralogical composition. The rocks 

 of the Palisade mountain range and of the Torn mountain, which 

 extends from the New Jersey line, on the west shore of the Hud- 

 son river to Haverstraw, are known as trap-rocks. There is an 

 outcrop on Staten Island, at Graniteville, near Port Richmond, 

 where a large amount of stone has been quarried at the so-called 

 ' granite quarries.' 



The trap-rock of the Palisades range is a crystalline, granular 

 mass of plagioclase feldspar (usually labradorite) augite and 

 magnetite. It is generally finer crystalline than the granite. 

 The colors vary from dark gray through dark green to almost 

 black. 



This trap-rock is hard and tough, but some of it is split readily 

 into blocks for paving. It has been used extensively in New 

 York and adjacent cities for street paving, but since the introduc- 

 tion of granite blocks this use has nearly ceased. On account 

 of its toughness it makes an admirable material for macadamiz- 

 ing roadways. It is so hard that only rock-face blocks are used 

 in constructive work. Several prominent buildings in Jersey 

 City and Hoboken are built of it. There is a large quarry on the 

 river at Rockland lake, near Haverstraw, the output of which 

 is for street work and road material almost exclusively. There 

 are also quarries at Piermont and at Graniteville, Staten Island. 



