GfijJofiy of Rirlinunid ('(nnifii. y. Y\ 165* 



its width, measuring from its assumed furthest eastern extension 

 lo where the sandstone eovers it, averages less than one half 

 mile. ]k)th the eastern and western boundaries of this rock, 

 however, are so obscured by drift that their exact i)ositions can- 

 not be determined, and the outcrop may be Avider or narrower 

 at any point than is indicated on the ma}). 



The only ])laces at_which the diabase is exposed so as to be 

 easily studied, are at and near the so-called ■•granite" quarries 

 at Gi-aniteviJle, and near Port Richmond. The rock is a not a 

 granite, but a coarsely crystalline diabase, mainly composed of 

 augite and a ti-iclinic felds})ar, which is ])robably labradorite. 

 It has been found in welbdiggings within the area indicated on 

 the ma}), iu the* water near the junction of the Fresh Kills and 

 Arthur Kill at Liuoleumville, and outcro})s near Chelsea, on 

 tiie road to S})ringville. It will be noticed that Liuoleumville 

 is just at the northern edge of the submerged Archa?an belt, 

 and near the junction of the Triassic and Cretaceous forma- 

 tions. 'J'he same relative jiosition of the rocks may be seen 

 where this trap-sheet again comes to the surface, as it does about 

 six miles southAvest of the city of New Brunswick, X. J. In 

 fact the trap-dykes seem to siiun the exposed Ai-chteau rocks 

 and cling closely to the Triassic, none being found outside of 

 the red sandstone area. 



The explanation of this curious fact is, as has long since been 

 l)ointed out, that the strata com}:)osing the tilling of the Triassic 

 basin are weaker than a like amount of the metamor}:)hic rocks 

 surrounding it. and hence offer less resistance to the intrusion 

 of tra}3-dykes, which consequently }:)assed through the sediment- 

 ary rock rather than through the harder, stronger gneisses and 

 granites Avhich border it. Xoav, betAveen the Ncav Jersey Trias 

 and that of the Connecticut Valley, Ave haA^e a fold of these 

 metaraor}3hic gneisses and granites, but not a single trap out- 

 burst. This Avoitld seem to indicate that this fold existed be- 

 fore the de}30sition of the sandstone and the subsequent intru- 

 sion of the diabase, only very much higher than it is now : and 

 hence it is improbable that these Triassic rocks ev'er covered the 

 Archfean folded strata, forming a Triassic arch from New Jersey 

 to Connecticut, as has been sn}"i}Josed by some geologists ; for, 

 we should expect, if the Archaean rocks had been folded o/YtT 



