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NJ's Piedmont: Formed by volcanoes and erosion
6/15/2017 Volume XLVII, No. 24

New Jersey’s Piedmont – a gently rolling landscape south and east of the Highlands – includes many of this state we’re in’s most populous counties and cities. You may not know it, but there’s a piece of fascinating geologic history right beneath your feet!

Take a journey with Dr. Emile DeVito, New Jersey Conservation Foundation’s staff biologist, into New Jersey’s geologic past, long before humans walked the Earth:

“When the Earth’s landmasses collided around half a billion years ago to form the supercontinent known as Pangaea, giant mountains were created by titanic forces, much like the Himalayas being thrust upward today by the collision of India into Asia!

During the next 250 million years, mountain building forces reversed and high peaks began to erode.

New Jersey’s ancient mountains eventually shrank into mere shadows of their former selves. Only the durable inner core of the ancient Appalachian chain still persists in the northwest Sussex and Warren county landscape. The Taconic Mountains are now noticeable as large hills scattered in New Jersey’s Highlands region.

While these ancient, eroded mountains were part of the original Pangaea continent, the Piedmont region is only half as old.  New Jersey’s Piedmont is located east of the Highlands, fronting on the Hudson River and including much of the Passaic and Raritan River watersheds, Great Swamp, Meadowlands,  and most land northwest of U.S. Highway 1 from Newark to New Brunswick to Trenton.

While the mountains eroded, the land at the edge of the sea was colonized by plants: club mosses the size of redwood trees, ferns, and eventually conifers, but no flowering plants. Animal life colonized land, invertebrates left the sea and insects exploded into the forest habitats.

By the end of the Paleozoic Era about 250 million years ago, the sedimentary and igneous (volcanic) rocks of the New Jersey Piedmont were being formed. By now, certain fish had evolved lungs and left the shackles of their ancient ocean habitats; giant amphibians were living in shallow seas at the edge of the North American continent.

Pangaea was breaking apart. If you had stood at Washington Rock State Park at the edge of the First Watching Mountain at the beginning of the Mesozoic Era, instead of spying on British troop movements in Raritan Bay, you would have seen giant amphibians wallowing where Route 22 now sports Volkswagens. From the Verrazano Bridge, Africa would have been visible on its slow journey eastward as the Newark Rift - precursor to the Atlantic Ocean - opened in front of your eyes!

Author John McPhee described the erosion and slow continental movement best in his popular book, “In Suspect Terrain.”  A movie of New Jersey, where each frame is one hundred thousand years, would make mountains look like waves crashing on a beach, spreading and returning to the sea, as “the flickers and glimpses of a thousand million years.

As Pangaea broke apart, volcanic cones rose throughout the Newark Basin, like Laurel Hill still visible alongside the eastern spur of the New Jersey Turnpike. Violent forces spread lava beneath the surface of New Jersey’s future Piedmont.

The basalt rocks of the Orange, Watchung, Preakness, and Hook mountains, and the diabase of the Sourlands, Cushnetunk (Round Valley) and the magnificent Palisades, are hard rock, derived from lava flows between softer sediments under great pressure.

Everything else eroded away, creating flat plains dissected by meandering rivers like the Raritan and Passaic.

During the Triassic and Jurassic periods of the Mesozoic Era, predatory flesh-eating dinosaurs were slowly giving rise to herbivorous duck-billed hadrosaurs. The first flowering plants, similar to todays’ magnolias and tulip trees, had evolved a partnership with beetles (the first pollinators), and had to reproduce quickly and efficiently, or leave no offspring if found too soon by a plant-munching dinosaur.

Remains of these dinosaurs still exist today in New Jersey, which could be the “Fossil State” if it weren’t already the Garden State! Just east of the Piedmont is the younger and extremely fossil-rich geologic region known as the Inner Coastal Plain. Within the Inner Coastal Plain’s sands and marl sediments, laid down during the close of the Cretaceous Period along an ancient coastline running from Monmouth to Camden and Gloucester counties, one can find dinosaurs, shark teeth and more!

As erosion continued in the northwest New Jersey mountains, silts and muds were carried away by rivers. Sediments were deposited in a shallow sea that ran from Newark to Trenton. Today they can be seen from Donaldson Park as the New Brunswick red cliffs along “the banks of the old Raritan.” Brunswick red shale dominates the Piedmont from Trenton to New Brunswick.

Later, Native Americans flocked to Piedmont rivers, which teemed with wildlife; and European settlers cleared Piedmont forests to grow crops on the fertile floodplains. The Great Falls of the Passaic at Paterson, which powered the silk mills of the 1800s, tumble over a basalt lava ridge and are now an urban national park.

Our Palisades Interstate Park cliffs, where peregrine falcons again nest, remain a scenic wonder, due not only to the foresight and preservation efforts of the Rockefeller family in the early 20th century, but also the recent efforts of activists to ensure that tall corporate towers are not built in the communities adjacent to the park north of the George Washington Bridge,” DeVito concludes.

To find out about the geology and history of New Jersey’s Piedmont in detail, and watch a time-lapse visual of Pangaea breaking apart - go to And be sure to read the classic layperson’s geologic history of eastern North America, “In Suspect Terrain,” by John McPhee.

To learn about New Jersey’s incredible arrays of fossils - fish, amphibians, reptiles, birds and even primitive mammals – visit the New Jersey State Museum in Trenton or go to its website at The museum conducts cutting edge research on our fossil record, and will draw paleontologists from around the world July 10-12 for the 4th International Symposium on Paleohistology.

And more on preserving New Jersey’s land and natural resources, visit the New Jersey Conservation Foundation website at or contact me at



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