Post Eagle Newspaper


May 18, 2024

45°F, few clouds
New Jersey

Time Now


New Jersey’s ‘Marl’ Pits
Yield Dinosaur Discoveries

Ever wonder how New Jersey towns like Marlton and Marlboro got their names? Look no further than “marl,” a soil also known as greensand.

Marl deposits date to the time when the southeastern half of this state we’re in was the sea floor, and greensand was deposited in coastal bays and freshwater river mouths. The marl contains fossils of ancient shelled invertebrates and freshwater and marine forms of every vertebrate group – fish, amphibians, reptiles, birds, and even primitive mammals!

Colonial-era farmers discovered that marl – which contains clay and calcium carbonate – made great fertilizer. Many marl pits were dug in the narrow geographic band now known as the Inner Coastal Plain. Greensand was sold to farmers all over New Jersey and beyond.

Marl pits contained more than fertilizer. In about 1838, a farmer in Haddonfield, Camden County, spotted gigantic bones in a sand pit on his property. Two decades later, fossil hobbyist William Parker Foulke heard about the bones while vacationing nearby.

Foulke called in his friend, paleontologist Joseph Leidy, and hired a crew of diggers. They excavated the bones of an animal larger than an elephant, with structural features of both a lizard and a bird.

The fossilized bones were the world’s first nearly complete dinosaur skeleton. The dinosaur died along the shallow coastline during the Cretaceous period 65 to 145 million years ago and sank to the bottom, where its skeleton fossilized in the greensand.

The creature was named Hadrosaurus foulkii after Foulk and Haddonfield, and was the first mounted dinosaur ever to be displayed to the public when it was put on exhibit at the Academy of Natural Sciences in Philadelphia in 1868.

Nearly 160 years after the dinosaur discovery made Haddonfield the birthplace of American paleontology, the Garden State is still rich in fossils.

“New Jersey is a great place to be if you’re a paleontologist,” says David Parris, paleontologist and head curator of natural history at the New Jersey State Museum in Trenton.

The state’s most productive fossil region is the Inner Coastal Plain, which runs from Raritan Bay to the upper reaches of the Delaware Bay in Salem County. During the Cretaceous period – when New Jersey was located much closer to the equator, the Earth was warmer and sea levels higher – the Atlantic coastline was located there.

Thanks to their ancient history, the sediments of the Inner Coastal Plain contain fossils of both sea creatures like mosasaurs and giant crocodiles, and land creatures that lived in swamps on the edge of the continent, like the hadrosaurus.

Two Inner Coastal Plain sites where land has been permanently preserved are especially good for finding fossils.

The first is within Monmouth County’s Historic Walnford Park, preserved with the help of New Jersey Conservation Foundation in the 1970s. The dig site, called Ellisdale, is yielding thousands of fossils of all sizes, from large to microscopic, all being studied at the New Jersey State Museum.

The second is the former Inversand Quarry in Mantua Township, Gloucester County, where mosasaurs – ancient sea lizards resembling Komodo dragons – were excavated. Thanks to donors, Rowan University purchased the quarry in 2016. It is now called the Jean and Ric Edelman Fossil Park and is available to Rowan students as well as schools and individuals attending “Community Dig” days.

The former quarry must be continually pumped to keep out water, but the marl there is so soft that paleontologists can dig with a garden trowel rather than having to chip through rock.

Due to suburban development, the site where “Haddy” the hadrosaurus was discovered is no longer a viable dig site. In fact, its exact location was lost until 1984 when a local Boy Scout named Chris Brees used old maps and Joseph Leidy’s descriptions to rediscover it. Thanks to Brees’ Eagle Scout project, the site is marked with a plaque commemorating its amazing history.

If you want to learn more about New Jersey’s Inner Coastal Plain and the fossils discovered there, take time to visit the New Jersey State Museum. Among the exhibits are a full-size hadrosaurus, made from casts of the original bones excavated in Haddonfield in 1858, and a giant crocodile from Burlington County just found in the last couple of years!

You can even watch as scientists carefully remove this fossil crocodile from the rock in which it is embedded.  The original Haddonfield dinosaur is kept at the Academy of Natural Sciences and is too fragile to be displayed. Find out more about the NJ State museum exhibit at

For a great online dinosaur exhibit, go to the Academy of Natural Sciences website at

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


The State We’re In
by Michele S. Byers
Executive Director
New Jersey Conservation Foundation