New Jersey Limestones. — Westgate. 311 
quently quartz is associated with it and in one slide consider- 
able amounts of biotite. In the hand-specimen it is a uniform, 
light-green, medium -grained rock. 
Quartz-rock also occurs abundantly within the limestone 
area. In the hand-specimen it is simply gray massive quartz. 
Microscopically, it consists wholly of extremely irregular and 
interlocking grains of quartz, usually with a wavy extinction. 
P3'roxene, graphite and magnetite occur in greater or less 
amounts associated with quartz in this rock. The term 
quartzite, which is applied to bedded quartz rock of detrital 
origin, is inapplicable here, for the rock under consideration 
is of an altogether different origin, as will be shown below. 
In typical examples these two rocks are wholly distinct and 
consist of pure aggregates of pyroxene and quartz respect- 
ively. But practically the rocks grade into each other by a 
complete series of intermediate forms. The pyroxene-rock 
generally carries more or less quartz which locally increases 
in amount until it makes half the rock. From this interme- 
diate quartz-pyroxene-rock there are all gradations to a pure 
quartz rock, owing to the gradual relative increase in the 
amount of the quartz over the pyroxene. In considering their 
origin they may be treated together, for they are the two ex- 
tremes of a single continuous series. 
These two rocks are explained as being local phases of the 
limestone due to the local development, on a large scale, of 
the common accessory minerals, pyroxene and quartz. This 
is shown by the following facts: — (1) Near the north end 
of the mountain a dike of diabase cuts across the limestone 
area in an east and west direction. On the south side of the 
dike the rock at the contact is a quartz-rock holding patches 
of greenish pjn-oxene ; further away it is a greenish pyroxene- 
rock without quartz; still further south it is crystalline lime- 
stone. These three varieties grade into each other. The 
relation of the quartz-rock to the diabase dike is accidental, 
for at many other points in the limestone the quartz-rock and 
pyroxene-rook occur at a distance from any eruptive. Other 
examples of the gradual passage from crystalline limestone 
into quartz-rock and pyroxene-rock can be given from the 
same region. (2) The accessory pyroxene of tin- normal 
crystalline limestone is the same in external appearance and 
