62 Geology of Hudson County, New Jersey. 



meadows that have reached the underlying rock, we are en- 

 abled in a general way to sketch the topography of Hudson 

 County as it would appear if the accumulation of superficial ma- 

 terial were removed. A map or model constructed from such 

 data would enable us to determine the depth to which river- 

 channels have been eroded and also aid us in calculating the 

 amount of denudation that the general surface of the county 

 has suiiered. 



From the wells bored in the estuary of Newark Bay, now to a 

 great extent occupied by salt marshes, we find that the rock in 

 some places is more than two hundred feet below the surface -of 

 the marsh. At Hackensack, 18 miles north of the present out- 

 let of the bay, the rock is 104 feet below the surface. 



Although no soundings have been obtained from the southern 

 end of the bay, yet it is fair to assume that here is the greatest 

 depth, probably not less than 300 feet. As the surface of the 

 marsh is 150 or 200 feet below the present level of Bergen Hill, 

 and nearly as much lower than the ridge of Triassic rocks bound- 

 it on the west, the total depth that the valley of the Hackensack 

 has been excavated cannot be less than between 350 and 500 feet. 



To calculate the amount of sandstone and shale that has been 

 removed to form the estuary from Hackensack southward, we 

 have only to compute the contents of a solid 18 miles long, 

 4 miles wide, and 350 to 500 feet thick ; this will give, taking 

 the lowest average of thickness, about 77 cubic miles as the 

 amount of material removed. 



At one point between Jersey City and Lafayette — east of Ber- 

 gen Hill — soundings to the depth of 130 feet failed to reach the 

 bed-rock. The reef of serpentine at Long Dock, Jersey City, 

 is buried to the depth of 179 feet. The following borings, some 

 of them reaching to the bed-rock, are taken from the table at 

 the end of this essay ; excepting those in the Harlem River, they 

 are all on the margins of the old ciiannels and do not show their 

 real depth : — 

 Hudson Eiver, foot of 23d St., 250 ft. from the 



eastern building line of the river street, - 175 ft. to rock. 



Hudson River, foot of Bethune St., line of the 



river street, ------- 196 " rock not reached. 



Hudson River, pier 60 (old No. \ 20 ft. W. of 



bulkhead line, 175 " to bed-rock. 



