147 



already made to the changes induced by the trap of this locality, 

 boih upon the limestone and the red shale. 



The next belt of the igneous rock towards the northeast worthy 

 of especial mention in this place, is that called the Second New- 

 ark Mountain. Where this ridge crosses the Passaic river, form- 

 ing the gorge of the Little Falls, the structure and relations of 

 the rock are finely developed. A little below the Falls, the trap is 

 seen in direct contact with the red sandstone, overlying it in a 

 mass from twenty-five to thirty feet in thickness, and presenting 

 a rather unusual appearance. The lower portion, about fifteen 

 feet in thickness, resting immediately on the stratified rock, is 

 an assemblage of irregular spheroidal ba Is of a somewhat con- 

 centric structure, traversed in all directions by small fissures or 

 joints; externally these are of a rather rusty hue from atmosphe- 

 ric action oxidizing the iron in the rock, but when broken they 

 show a dark, iron-gray colour, with a somewhat metalliferous 

 aspect. The material filling the interstitial portions between the 

 balls, is a dark-coloured, close-grained, very earthy basalt. It 

 sometimes includes crystalline quartz of various colours; among 

 others the amethystine and smoky varieties. 



Above this confused mass of nodular concretions, the rock 

 assumes the true basaltic structure, exhibiting regular columnar 

 prisms, beautifully symmetrical, extending up to the superincum- 

 bent soil. 



At this locality, the trap rock includes crystals of prehnite, 

 stilite, carbonate of lime, and other minerals. 



Somerville Trap Ridge and Biidgewater Copper Mine. — The 

 next point on this first belt of trap at which we meet with any 

 phenomena of a specially instructive nature, is in the neighbour- 

 hood of Somerville, where the ridge has curved round to assume 

 a northwest course. In the various excavations of the old Bridge- 

 water copper mine, we have an opportunity of beholding the 

 action of the trap upon the rock into which it has been intruded. 



At this mine we have ocular evidence that the igneous rock 

 issued through the strata through fissures of contracted width, 

 when compared with the base of the ridge which it constitutes. 



A level extends from a shaft near the southern base of the 

 ridge in a north direction, towards the centre of the, hill, or 



