318 PROCEEDINGS OF THE ACADEMY OP [1884. 



017 A BEMABEABLE EXP08TJBE OF COLUMNAB TBAP NEAB OBAVGE, 

 NEW JEBSEY. 



BY PROFESSOR ANQELO HEILPRIN. 



The remarkable exposure of trap, near Orange, New Jersey, to 

 which attention has recently been called by the State Geologist, 

 Prof. George H. Cook, is in many respects the finest example of 

 geotechnic architecture to be found in the Eastern United States. 

 Although a true columnar structure is by no means a rarity in this 

 State, indeed, rather the contrary, yet strikingly enough, where 

 any extensive exposure of the trap occurs, there the columnar 

 structure appears to be in most instances either only partially 

 developed, or where developed, only of a very indeterminate 

 character. This is well shown in the case of the Palisades fronting 

 the Hudson River, where, for the greater part of their extent, 

 only an approximation to anything like such structure can be 

 made out. In the case of the locality presently to be described, 

 however, which is situated on the face of the first interior ridge 

 trending parallel with the Palisades, whose age probably differs 

 but little, if at all, from that of the Palisades, we are presented 

 with the reversed condition of things; the columnar structure is 

 here developed, not only on a most imposing scale, but in all the 

 varied conditions under which such structures appear. 



The exposure of O'Rourke's quarry (Plate YIII) is located some 

 one and a half or two miles back of Orange, on the slope of Orange 

 Mountain, and, consequently, in the line of the first trap ridge. 

 It measures 750 feet in length, and 98 feet 2 inches greatest 

 height above the base or working line. The material quarried 

 (worked now for a considerable number of years) is the familiar 

 post-Triassic (?) " trap," or " greenstone," the material of the 

 Palisades quarries, which, until recently, supplied the city of New 

 York with a great part of the Belgian paving blocks. That which 

 immediately arrests the attention of the visitor to the quarry is 

 the magnificent display of the columnar structure, thousands of 

 basaltic columns of the hexagonal and pentagonal pattern appear- 

 ing, if not in the absolute perfection of the similar columns of the 

 Giant's Causeway and Fingal's Cave, in a perfection but very 

 little inferior to these. The base or lower half of the exposure is 



