A Natural Resource Management Guide for the County of Morris A ...

The Precambrian Era
The Formation of the Highlands Province
The Precambrian Era extends from the beginning of the earth, more than four billion years ago, to the
beginning of the Paleozoic Era 570 million years ago. The rocks of the mountains in western Morris County,
formed during the middle Proterozoic period (latter part of the Precambrian), are among the most ancient
rocks in North America. They are part of a formation resulting from chemical precipitation of calcareous
sediments, running northeast to Newfoundland and west across the Hudson Bay.
These sediments, and other non-calcareous sediments, compacted into layers of sandstone, shale, and
limestone. As these layers deepened over millions of years, heat and pressure metamorphosed them into
banded gneiss and marble. Meanwhile volcanic activity produced lava flows, creating additional intruding
layers of igneous rock--granites and feldspars. These layered formations are the bedrock of the N.J. Highlands
and have created a landscape characterized by hilly uplands adjacent to steep river cuts.
The Highlands formations transformed dramatically while being deformed, folded, faulted, and thrust up into
mountains. Intense heat and shearing compression further metamorphosed the rock, creating a rich complex
of mineral deposits, some unique to New Jersey. From the Revolutionary War period to the twentieth century,
mineral prospecting and mining, particularly of magnetite iron ore, were basic economic activities in much
of western Morris County and the impetus for settling patterns. Plate 2 depicts abandoned Iron Mines, as
well as active and abandoned sand and gravel operations. Compare their locations with the Bedrock Geology
map in this chapter, and the Landforms map in Chapter 2.
Over time, the Proterozoic bedrock of the Highlands has
been fractured, faulted, and jointed as a result of both
crustal movement and the compression, slippage, and
crushing of grains that comes from bearing the weight of
thousands of feet of rock. Most fractures and faults trend
in a generally northeasterly direction. The nature of these
cracks and faults affect the presence of ground water, its
movement, and the potential for contamination.
The Paleozoic Era
Erosion and More Mountain Building
Near the beginning of the Paleozoic Era, 570 million years
ago, the center of the continental land mass, from the
Highlands to Utah, was covered with the shallow warm
waters of a vast sea. During Proterozoic, Cambrian, and
much of Ordovician time, rivers in the Highlands flowed
southeasterly, washing mountain sediments onto the
continental shelf of the spreading proto-Atlantic Ocean.
Metamorphosed, these sediments would form the
"basement" for the Mesozoic Newark Basin (Piedmont
province).
Figure 1
12
Geologic History of Morris County