BASALTIC ROCKS. 



275 



ring at Pluckemin, and running near the towns of 

 Springfield and Patterson, approaching the primary 

 region near Pompton. 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, slitbite, 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 ful 

 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-Haven. 

 Trap rocks also occur in the State of Maine, 



* Geol. Survey of New-Jersey. 



