GEOLOGICAL SECTION OF NEW JERSEY’ 
HENRY B. KUMMEL 
Trenton, N. J. 
PRE-CAMBRIAN ROCKS 
The pre-Cambrian rocks of New Jersey comprise certain white 
crystalline limestones with closely associated quartzites and conglom- 
erates and a great complex of granitoid gneisses, pegmatites, and 
magnetites which, because of their resistance to erosion, underlie 
the Highlands of the state. 
Franklin limestone.—The Franklin limestone in its more common 
phases is a white, highly crystalline, coarsely granular limestone 
or marble, ranging in composition from a nearly pure carbonate of 
lime to a dolomite. Some of it is rather siliceous and in a few places 
thin beds of sandstone have been noted. At Franklin Furnace and 
Sterling Hill it contains large beds of zinc ore and magnetite veins 
are also present in a few places. Graphite is widely disseminated 
in the limestone, and with mica, pyroxene, and chondrodite fre- 
quently gives the rock a gneissic structure. 
The Franklin limestone is unconformably overlain by basal mem- 
bers of the Cambrian system. It contains intercalated masses of 
gneiss, and is injected by numerous bodies of pegmatite, neither 
of which rocks are associated with the Cambrian formation. On 
the other hand, the Hardyston quartzite, the lowest member of the 
Cambrian, locally contains fragments derived from these pegmatites, 
and even fragments of the coarse-grained limestone itself. ‘That 
the Franklin limestone was metamorphosed to its present condition 
long before the deposition of the lowermost Cambrian sediments has 
been abundantly demonstrated. 
The gneisses—The gneisses appear in many varieties and of 
different sorts so intricately mingled that detailed representation of 
« In the preparation of this paper, I have drawn freely from the published reports 
of my associates on the Geological Survey of New Jersey and of those workers on the 
U. S. Geological Survey who have dealt with the problems of this area. To Dr. A. C. 
Spencer, in particular, am I indebted for data on the pre-Cambrian rocks. 
So 
