THE NEWARK SYSTEM OF NEW JERSEY 545 
(a) carbonaceous shales, which split readily along the bedding 
planes into thin laminz, but have no true slaty cleavage ; (0) 
hard, massive, black and bluish-purple argillites; (c) dark gray 
and green flagstones; (a) dark red shales approaching a flag- 
stone; (¢) and occasional thin layers of highly calcareous shales. 
There are all gradations between these somewhat distinct 
types, so that the varieties of individual beds are almost 
countless. Some of the argillites are specked with minute crys- 
tals of calcite-and the faces of jdint planes and cavities are fre- 
quently covered with deposits of the same mineral. Minute 
crystals of iron pyrites occur frequently in some layers, but 
apart from them and the calcite, secondary minerals were not 
found, macroscopically, in these beds. 
Both ripple-marks and mud-cracks occur at all horizons in 
the Lockatong beds, showing that shallow water conditions pre- 
vailed throughout the time of their deposition. On the other 
hand, the absence of strong currents or violent shore action is 
indicated by the extreme fineness of the material. 
Owing to the faulting these beds occur in several well-marked 
belts, in each case overlying conformably the Stockton series. 
The first belt reaches the Delaware between Wilburtha and 
Washington’s Crossing, and extends northeastward through 
Ewingville, Lawrenceville, and Princeton, where there are several 
large quarries in the argillite beds. East of the Millstone River 
the limits of this belt cannot be determined accurately owing to 
the veneer of the Jamesburg formation, but from a few scattered 
outcrops and borings, these beds probably cross the Raritan 
River below the mouth of Lawrence Brook. 
The Lockatong beds occur again along the southeastern side 
of the Sourland plateau, resting upon the narrow belt of Stock- 
ton sandstones which forms the escarpment of this upland. From 
the Delaware River to the village of Newmarket the upper lmit 
of the beds lies a little below the trap sheet which forms the 
backbone of the upland. The interval between them is occu- 
pied by the softer red shales of the third series, which are some- 
what metamorphosed near the igneous rock. Northeast of New- 
