THE NEWARK SYSTEM OF NEW JERSEY 549 
west is the Hunterdon escarpment, forming the westward limit 
of the Brunswick shales and marking the line of a great fault, 
by which the rocks of the plateau have been uplifted several 
thousand feet." 
Thirteen to sixteen miles to the north across the low shale 
plain are the gneiss highlands, and eight miles northeastward 
are the curving level crests of the Watchung trap ridges which are 
interbedded with the Brunswick shales, and beyond which the 
shale lowland extends. No high ground meets the eye to the 
east toward New Brunswick thirteen miles away, but to the south 
rises the Rocky Hill trap ridge, at one point deeply cut through 
by the Millstone, and there marking the approximate limit of 
the Brunswick shales. To the southwest there stretches away 
on either side of the narrow plateau on which we stand, a 
strip of rolling lowland, likewise underlain by the Brunswick 
shales. 
These rocks also outcrop above the Lockatong series in the 
northern part of the Hunterdon plateau. They are exposed in 
high bluffs along the Delaware above and below Frenchtown. 
It was found that the shales of this area when traced along their 
strike towards the margin of the formation became rapidly coarser, 
passing along some horizons into massive conglomerates. , It 
will be remembered that similar changes were found to take place 
in the Lockatong and Stockton beds, so that within two or three 
miles of the margin the distinctions between the three subdi- 
visions are largely obliterated. 
Quartzsite conglomerates At a number of points along the 
northwestern boundary of the Newark system there are thick 
accumulations of massive conglomerates, composed chiefly of 
quartzite and hard sandstone. Pebbles of limestone, gneiss and 
shale occur in some layers, but sparingly. All the constituent 
*The height of the plateau above the red shale plain is not due to the fault, 
although the latter lies along the foot of the escarpment. As shown by Professor 
Davis (Proc. Bost. Soc. of Nat. Hist., Vol. XXIV, pp. 365-423) this region was base- 
leveled in Cretaceous times or thereabouts, and the present topography is due to dif- 
ferential degradation of rock masses of unequal hardness, consequent upon an uplift 
which affected the whole region. 
