204 J. V. LEWIS NEWARK TRAP ROCKS OF NEW JERSEY 



are certainly only remnants of the original flows, although still occupying 

 a region some 12 by 40 miles in extent. If extended half as far again, 

 they would spread beyond the most distant remnants at Sand Brook. 

 Considering the thickness of the first and second Watchung extrusives at 

 their southern extremities, it is not unreasonable to assume such an ex- 

 tension' at the time of their origin. 



If thus extended and of earlier origin than the Sand Brook and New 

 Germantown traps, their outcropping edges would now appear in larger 

 curves to the east of these. If, on the other hand, the Sand Brook and 

 New Germantown traps were older than the Watchung sheets, we should 

 expect them to appear in the shales beneath and southwest of the latter, 

 unless they are parts of very limited local flows. This applies with par- 

 ticular force to the New GermantoAvn trap, which is only six miles dis- 

 tant from the Watchung moimtains. There is still another possible con- 

 dition, namely, that neither the small synclinal remnants, on the one 

 hand, nor the Watchung flows, on the other, have ever extended far 

 enough beyond their present boundaries to overlap the regions now occu- 

 pied by the other. In this case their relations can be established only by 

 the stratigraphy, and it is impossible in the homogeneous red shales of 

 this region to attain more than an approximate correlation. Even re- 

 garding the small areas as independent local flows, however, it is more 

 probable, a priori, that the smaller eruptions were contemporaneous with 

 the larger volcanic activity of the adjacent area, especially since the 

 structure shows that they are at least approximately contemporaneous. 



RELATIONS OF THE INTRUSIVE TRAPS 



General characteristics. — The intrusives include the Palisades in the 

 northeast and the entire assemblage of trap outcrops in the southwest 

 except the small extrusive remnants at Sand Brook. Most of these are in 

 the form of sills, or intrusive sheets, with smaller masses appearing as 

 rounded bosses, as the Snake hills and mount Gilboa, or as thin dikes in 

 many localities. 



The Palisades sill. — There has been a wide acceptance among geolo- 

 gists of the "dike-and-sheet" structure of the Palisades trap, as depicted 

 by Darton,* in which the lava is regarded as having been intruded "from 

 a dike which follows at or near the western flank of the outcrop." Dar- 

 ton states that this structure is best exposed in the railroad tunnels 

 across the ridge at Weehawken and near Haverstraw. The "dike-and- 

 sheet" interpretation is thus undoubtedly due to the preponderating in- 

 fluence of these fine exposures where the trap does break upward across 



* Loc. cit., p. 37. 



