Geology of Hudson Coivntii, Kew Jersey. 37 



By fill' the best exposures of tlie tv'jq> are to be seen in the 

 various railroad cuts and tunnels that have been made through 

 Bergeu Hill. 



The eastern face of the trap-sheet is exposed southwest of 

 Lafayette, where the N. J. Central Railroad crosses the Morris 

 Canal ; thence northward, it appears at intervals in the 

 steep hill-side west of Jersey City. The point of rocks called 

 Fairmount, near the eastern end of the Pennsylvania Railroad 

 cut, is an outlying mass of trap, forming an island in the salt 

 marsh ; its isolated position is due to the fact that the trap form- 

 ing it was intruded among the sedimentary beds — which have 

 since been eroded away — at a lower level than the main sheet of 

 trap to the westward with which it is connected ; the trap has 

 been quarried at a number of places near Fairmount, and is well 

 exposed. From this point northward the exposures of trap 

 become more frequent along the eastern slojje of the hill, and 

 at length, at the foot of the hill, directly northwest of Castle 

 Point, the base of the trap-sheet is seen resting on metamor- 

 phosed slates. At the first locality where tlie stratified rocks 

 are exposed beneath the trap, they are mostly slaty in structure, 

 with an inclination of fifteen degrees towards the northwest, 

 and are covered uniformly by the trap. About 150 yards north 

 of the first exjoosure, the metamorphosed slates and quartzites, in 

 beds from a few inches to four feet in thickness, form the lower 

 thirty or forty feet of the clifi, having the usual northwest dip ; 

 ]-esting on the uneven upper surface of these stratified beds, the 

 trap occurs, forming the remaining fifty or sixty feet of the hill. 

 The stratified rocks continue to be exposed more or less per- 

 fectly, until the face of the precipice turns eastward at nearly a 

 right angle, and forms a bold projecting promontory, on which 

 an observing-tower now stands ; at the base of the perpendicular 

 cliffs below the tower, the trap comes down to the level of the 

 marsh, and plainly cuts out the stratified beds which appear on 

 either side of it. Two or three hundred yards southwest of the 

 tower, the stratified slates are exposed in the side of the cliff, 

 some fifty or sixty feet above the marsh, and are inclined at an 

 angle of about 20° towards the southwest, showing that they 

 have been disturbed by the intrusion of the trap, Just around 

 the angle of the cliff, northward of the tower, and along the 



