206 BULLETIN OF THE NEW YORK STATE MUSEUM 



points. And the supply of stone Is Inexhaustible. On the 

 Hudson river between Peekskill and Fishkill there is a fine 

 section exposed of these rocks. The Ramapo river valley, 

 traversed by the N. Y., L. E. & W. railway, the Harlem and 

 the New York City and Northern, extend into and cross 

 the belt and afford transportation to New York city. 



On the borders of the Adirondack region quarries have 

 been opened in the towns of Wilton, Hadley and Greenfield 

 in Saratoga county; at Whitehall, in Washington county; 

 at Little Falls, In Herkimer 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 

 rock borders of the Adirondacks. 



Trap-Rocks 



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 Torne 

 mountain, which extends from the New Jersey line, on the 

 west shore of the Hudson river to Haverstraw, are known 

 as trap-rocks. There is an outcrop on Staten Island, near 

 the north shore, 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 a plagioclose feldspar (labradorite usually) 

 augite and magnetite. It is generally finer-crystalline than 

 the granite. The colors vary from dark gray through dark 

 green and 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 introduction of granite blocks this use has nearly ceased. 

 On account of its toughness it makes an admirable material 

 for macadamizing roadways. It is so hard that only rock-face 

 blocks are used in constructive work. Several prominent 



