BASALTIC ROCKS. 



275 



cing at Piuckemin, and running near the towns of 

 Springfield and Patterson, approaching the primary 

 region near Pornpton. The rock varies from a fine- 

 grained, compact basaltic trap to coarsely-crystal- 

 lized greenstone, and contains, besides its essential 

 components, hornblende^ feldspar^ and augite, vari- 

 ous mineral ingredients, such as epidote.prehnite, zeo- 

 lite^ stitbite, analcime, and datholite. The trap rocks 

 of New- Jersey evidently repose upon the general 

 sandstone strata of the country, as may be ascer- 

 tained by viewing the eastern base of the Pali- 

 sades skirting the Hudson, or the bed of the Passaic 

 River below the Falls at Patterson, or the Newark 

 Mountains. " From what is now universally ad- 

 mitted," says Professor Rogers,* "concerning the 

 ' igneous origin of trap, it is plain that over this por- 

 tion of territory it has burst up in a molten state 

 through a series of nearly parallel fissures in the 

 strata, and after their consolidation and subsequent 

 disturbance, which caused them to dip towards the 

 northwest, and has overspread their adjacent por- 

 tions without effecting any material change in their 

 stratification, and producing only certain modifica- 

 tions in their mineral contents and structure." In 

 some of the cliffs at Patterson, the greenstone as- 

 sumes a columnar structure ; and between it and the 

 sandstone on which it reposes, we find an interme- 

 diate rock of six or eight feet in thickness, resem- 

 bling toadstone or amygdaloid, holding nodular crys- 

 tals of several minerals, prehnite^ analcime, &c. Be- 

 neath this, a layer of the sandstone of a few inches 

 thickness exhibits a baked appearance, and is fulL 

 of small vesicular cavities, as if produced by the 

 extrication of some gaseous matter or steam. The 

 same appearances are common in the trap rock- 

 near New-Jlaven. 

 Trap rocks also occur in the State of Maine, 



♦ Geol. Survey of New-Jersey. 



