THE NEWARK SYSTEM OF NEW JERSEY 555 
three estimates of the thickness of the Lockatong beds in the 
Hunterdon plateau, where the outcrop is so curved, agree closely 
one with another, and also with the various estimates of the 
same beds on Sourland plateau, make it improbable that the 
great thickness of this series is due to faults. So, too, the thick- 
ness of a part of the Brunswick shales involved in a synclinal 
fold can be accurately determined and the possibility of the 
faulting there eliminated. Again a narrow trap dike was traced 
uninterruptedly from the back of Sourland Mountain near Rock- 
town to Copper Hill, a distance of five miles. The dike crosses 
the strike at an angle of 45° and the thickness of the shales 
thus traversed is between 6000 and 7000 feet. There are 
reasons which cannot here be specified for concluding that the 
Sourland trap sheet, and therefore the dike, were intruded into 
the shales during Newark time, and before or contemporaneous 
with the tilting. If these reasons are valid the continuity of the 
dike is proof that the shales traversed by it are not cut by 
faults along the strike. Since such great thicknesses prevail 
in these beds, which are only a part of the whole system, there 
is the more reason for accepting the figures given above. It 
can certainly be claimed for these estimates that they rest upon 
a much larger basis of fact than any previous figures. 
Trap rock.—The trap rocks in the Newark series have been 
described by various writers’ who have shown that both intrusive 
and extrusive sheets occur. In this connection I desire briefly 
to call attention to a few new facts which confirm the conclusions 
of some of the earlier observers. 
Three narrow dikes were found to start from the upper sur- 
face of the Sourland Mountain trap mass, and were traced 
through the overlying shales for several miles. Their existence 
proves conclusively that this sheet is intrusive. It would naturally 
follow that the continuation of Sourland Mountain in Penn- 
sylvania is also intrusive, although Lyman? has published very 
positive views to the contrary. Moreover the fact that the trap 
*Chiefly Cook, RUSSELL, DAvis, DARTON, IDDINGs. 
2 Pennsylvania State Geol. Surv., Final Rept., Vol. III, Pt. II, p. 262. 
