Geology of Hudson County, New Jersey. 43 



III the cut of the New Jersey Kailroatl through Bergen Hill, 

 near the western end of the cnt, a deep depression occurs in the 

 trap, nearly 900 feet wide ; the place once occupied by shale or 

 sandstone is now filled with drift and gravel, and has been quite 

 extensively excavated for railroad ballast, etc. This area appears 

 to be included betAveen the main trap-sheet and the outcropping 

 edge of a smaller secondary sheet to the Avestward, and extends 

 indefinitely in a north and south direction ; it has been exca- 

 vated to the depth of 30 or 40 feet ; the rock bottom, however, 

 is very much loAver. Other areas analogous to this may be 

 lookfid for along the Avestern slope of Bergen Hill, and should 

 receive close attention from those interested in the drainage of 

 this region. The "big pocket" in the Erie tunnel,* appears 

 to have been a mass of metamorphosed shale included betAveen 

 sheets of trap ; this locality is but a short distance northAvard 

 of the holloAV cut through by the New Jersey Eailroad, Avhich 

 appears to have been eroded from the same series of metamor- 

 phosed shale. This included bed of shale Avas again crossed 

 by the tunnel of the DelaAvare, Lackawanna and Western Eail- 

 road at some distance from the east end of the tunnel ; but the 

 rock also fell in, forming a "jDOcket," as in the Erie tunnel. 



The reservoir built some time since is situated above this 

 broken area. We are thus furnished with three points on the 

 line of this included stratum of shale. 



The trap-sheet that projects eastAvard of the main ridge, and 

 forms Fairmount Point, can be readily traced to its junction 

 with the main trap-sheet at Newark Avenue ; thrust out from 

 the under surface of the main mass, it has followed the bed- 

 ding of the stratified rocks, between Avhich it cooled ; the Jersey 

 City cemetery is situated on this shelf of trap. Passing this 

 ledge a few feet to the eastAvard, soundings sIioav 70 to 80 feet 

 of mud Avithout reaching rock bottom. Other exposures of dikes 

 or outlying masses of trap may be similarly accounted for. 



Wherever the trap is exposed in Hudson County, it appears 

 as a compact dark-bluish rock, impervious to moisture, and usu- 

 ally breaking equally well m all directions. The rock is more 



" Geology of New Jersey," Prof. Cook, !868, p. 216. 



