THE NEWARK ROCKS 37 



lava had forced upward the soft mud on the sea bottom, or as if 

 the steam generated by the intense heat had made the wet mud 

 to froth up between the trap clinkers. There can be no doubt 

 as to the extrusive origin of these sheets. 



The crescent-shaped ridges near Morristown, north of White 

 House (near Germantown) and southwest of Flemington (near 

 Sand Brook), are also overflow sheets. 



Intrusive sills. — The Palisades of the Hudson, the Rocky 

 Hill sheet north of Princeton, the Sourland Mountain sheet 

 near Lambertville, and Cushetunk Mountain near White House, 

 are the largest and most prominent of the intrusive sheets. 

 Their position, size, and the shape of their outcrop are indicated 

 on the accompanying maps. In addition to these, which are 

 demonstrably sills or sheets, there are more irregularly shaped 

 masses northwest of Pennington, near Stockton, and at Point 

 Pleasant (west of Stockton), (Fig. 2), the precise relations of 

 which to the inclosing beds are not clearly revealed. They are 

 beyond all doubt intrusive masses, but it is questionable whether 

 they are strictly sheets. In the absence of positive knowledge 

 as to their relations with the sedimentary beds, I prefer to speak 

 of them simply as intrusive masses. 



The evidence of the intrusive origin of all these masses, sills 

 and others, is as follows. Dikes radiate from the upper part 

 of the sills and penetrate the overlying shales for distances 

 up to seven miles, as measured on the surface. The sills 

 are locally unconformable to the inclosing strata, although in 

 general they extend for long distances parallel to their strike. 

 The Sourland Mountain sill makes two sharp bends, by which it 

 changes its horizon several hundred feet. The Rocky Hill sheet 

 crosses the shales obliquely for a total of several thousand feet, 

 and about twenty-five localities are known along the Hudson 

 River where the Palisade sheet can be seen to cut across the 

 shales and sandstones. In New Jersey the Palisade sheet fol- 

 lows closely the strike of the shales, although frequently chang- 

 ing its horizon a few feet. In New York, however, north of 

 Nyack, the trend of the shales would carry it beneath the Hud- 



