Pleistocene Preserved: The Lost Bone Cave of Port Kennedy

The 1894–96 excavation of the Port Kennedy Bone Cave in Pennsylvania’s Montgomery County.
From the Collection of the Mercer Museum Library, Bucks County Historical Society

On October 29, 1895, more than 90 members attended a meeting at the Academy of Natural Sciences in Philadelphia. Following the routine business of the publication committee’s report and the announcement of one member’s death, Henry Chapman Mercer (1856–1930) rose to speak about the ongoing exploration of a geological feature known as Irwin’s Cave in Montgomery County. The Philadelphia Inquirer covered his presentation the following day with a news/opinion article headlined, “That Big Bone Cave,” its title and tone indicating that most of the newspaper’s readers would already be familiar with Mercer’s project, knowing that the remains of many Ice Age animals had been discovered in Irwin’s Cave as well as the “various theories as to how they came there in such large numbers and at such a depth below the surface.”

As fascinating as the cave’s fossils were, the anonymous reporter hinted that the cave’s contents might answer another question of the day, specifically how long man had lived in the Western Hemisphere. He wrote, “Will something yet be found that will connect the relation of antiquity to the existence of man?”

Irwin’s Cave has come to be known as the Port Kennedy Bone Cave, named after the industrial town and railroad depot that once flourished nearby on the bank of the Schuylkill River. But don’t go looking for that big bone cave today. In fact, you won’t even find Port Kennedy on a modern map. The few structures that remain have since been surrounded by Valley Forge National Historical Park.

A mastodon tooth discovered by a quarry workman led to the exploration of the Port Kennedy Bone Cave in 1871.
Ted Daeschler, Academy of Natural Sciences of Drexel University

When the cave was first discovered in the 1870s, it yielded a treasure trove of Ice Age fossils that contemporary scientists dated to what was then called the Post-Pliocene Period of geological time. Modern scientists have since updated the terminology and classified the fossils as belonging to the late Irvingtonian North American Land Mammal Age of the Mid-Pleistocene Epoch. Either way, the fossils are about 750,000 years old. This find is still considered one of the most important fossil deposits on the continent, offering a glimpse into a time when different species of fauna thrived in a very different climate.

In the 19th century, before there was a park commemorating the 1777–78 winter encampment of George Washington’s Continental Army, there were a number of towns along the Schuylkill River where workers toiled at various industries that exploited the region’s natural resources. Near the village named for local landowner John Kennedy, there were several quarries where workers blasted out valuable limestone.

Workmen had removed nearly all the walls of a cave in one of the quarries and were cutting through its floor when one of them discovered what appeared to be an enormous tooth. The artifact was given to a physician living in nearby Phoenixville, Chester County, who passed it on to Dr. Charles M. Wheatley (1822–82), a paleontologist who also managed several mines in the area.

Wheatley visited the quarry and described his experience in an 1871 article published in the American Journal of Science and Arts. What Wheatley found in Port Kennedy was not really a cave but a vase-shaped sinkhole that had apparently once been open to the surface, forming a natural trap in the landscape for unsuspecting fauna that died there.

The earliest diagram of the Port Kennedy Bone Cave appeared in Charles M. Wheatley’s 1871 article about its discovery.
From American Journal of Science and Arts, Series 3, 1 (April 1871), 237

An 1871 newspaper article originally published in the Philadelphia Public Ledger titled “Ancient Pennsylvania” described the sinkhole as being about 20 feet wide at its top. “At the depth of forty feet,” the article noted, “there is a bed of black clay, eighteen inches thick, filled with leaves, stems, and seed vessels of plants; and scattered through this and in the red clay [beneath it] from six to eight inches in depth, are the fossils referred to.” The article explained that Wheatley was conducting a thorough examination of the remains together with the renowned paleontologist Professor Edward Drinker Cope (1840–97).

Wheatley and Cope confirmed that the tooth had once belonged to an American mastodon. They identified 34 species, including tapirs, sloths, skunks, a saber-toothed cat, some unknown sort of equine animal, and a short-faced bear that looked nothing like those roaming North American forests in the 19th century, as well as plant, insect, reptile and bird fossils.

Edward Drinker Cope classified the fossils from the Port Kennedy Bone Cave.
American Museum of Natural History Library/Image #312408

At the time it was speculated that these unfortunately trapped animals had become covered by plant and rock debris until natural forces had closed the sinkhole. The author of the Public Ledger article wondered whether similar finds might be unearthed in other Pennsylvania limestone quarries and urged quarry owners to bring them “to the notice and examination of men of science,” lest the valuable fossils become “scattered and lost from not attracting any special attention on the part of the workmen.

Despite all the publicity, the bone cave was soon covered over and its location forgotten, probably after John Kennedy died in 1877 and his family went bankrupt. Other entrepreneurs and companies began buying the Port Kennedy limestone quarries including Archibald Irwin and the Ehret Magnesia Manufacturing Co.

In 1893 Irwin’s workers were lowering the floor of one quarry when they blasted into a sort of chasm. They found some fossils but removed them to a refuse heap adjoining the quarry where they remained for about a year. In 1894 a member of the Academy of Natural Sciences of Philadelphia, which was then organizing its museum, discovered a Megalonyx (or ground sloth) tooth among the rubbish. The member shared his find with Dr. Samuel Dixon (1851-1918), then curator and later president of the academy. Dixon visited the quarry, and in one undisturbed area he unearthed the teeth of a tapir and the remains of other mammals. Dixon became convinced that not only had the long-lost bone cave been rediscovered, but it held still more treasures waiting to be unearthed.

Dixon invited Henry Chapman Mercer to join him in the scientific exploration of Irwin’s Cave for the Academy of Natural Sciences. Today Mercer is remembered as a collector of the tools and technology of Colonial America and the Early Republic, now displayed at the Mercer Museum in Doylestown, Bucks County. He also founded the Moravian Pottery and Tile Works whose Arts and Crafts creations can be found in many public buildings including the Pennsylvania State Capitol.

Henry Chapman Mercer, in his early career as an archaeologist, excavated the Port Kennedy Bone Cave,
1894–96.
From the Collection of the Mercer Museum Library, Bucks County Historical Society

Before Mercer embarked on these ventures, however, he had a career in archaeology. When the bone cave was rediscovered, he had been recently appointed curator of American and Prehistoric Archaeology at the University of Pennsylvania Museum. His academic background had been in liberal arts and law, but he established his reputation as an archaeologist with the 1885 publication of a book titled The Lenape Stone, or The Indian and the Mammoth. It described at length his opinion of the controversial discovery of a Native American gorget bearing the crude depiction on one side of what appeared to be Indians hunting a mammoth. The Lenape Stone has since been identified as a forgery, but it still commands a place in Mercer’s museum.

Mercer later described his experience at what he called the “Bone Hole” during three successive autumns in two accounts written for the publications of the Academy of Natural Sciences. In the second he wrote that when Dixon had first asked him to visit the site in 1894, he observed that all the years of blasting out limestone had converted a hillside “into an ampitheatre [sic] several acres in extent, walled with perpendicular escarpments of rock sometimes a hundred feet high.” Standing in the quarry, well below the surface of the ground, Mercer was confronted with what he described as a gallery, its roof long since blasted away. Within there was a vertical bank of “clay, stones and bones,” with the bones sticking out in all directions. There were no complete skeletons but rather the remains of animals small and large jumbled together. There were jawbones without skulls, teeth without jaws, and claws separated from metacarpals.

Mercer and Dixon used whitewash to paint a grid on the wall before carefully removing more than 300 cubic yards of earth containing fossils plus quarry refuse. Then they removed and labeled the actual specimens, noting their original positions. Unfortunately, many of the more brittle bones crumbled into pieces during excavation. Mercer estimated that less than a third of the remains could be saved.

The lengthy and careful excavation was funded by Dixon and Mercer themselves together with contributions from Clarence Bloomfield Moore (1852–1936), who had been president of his family’s paper company before retiring to pursue his interest in archaeology.

Once again Cope, then on the faculty of the University of Pennsylvania, classified the remains. His full report titled “Vertebrate Remains from Port Kennedy Bone Deposit” turned out to be the final effort of his distinguished career. He died in 1897 and the Academy of Natural Sciences published his report posthumously.

Cope concluded that most of the Port Kennedy Bone Cave remains had been those of tapirs.
Ted Daeschler, Academy of Natural Sciences of Drexel University

Cope discovered that most of the remains had been those of tapirs, followed by bears and skunks. Several species of sloths, peccaries and turtles were also represented. He noted that remains of Mastodon americanus, both young and adult individuals, were present. According to Cope the excavations had unearthed the bones of 377 individual animals, representing 66 species, of which 40 were extinct.

No other cave deposit discovered at that time had contained such a large number of species, most of which did not habitually dwell underground in caves, leading Mercer to speculate upon what might have killed all these animals and how they became buried together. Animals were sometimes dragged into caves by predators, but the bone cave remains showed little signs of gnawing and wear. Mercer agreed with earlier scientists that the animals had fallen into a sinkhole while it was open to the surface, but he did not think these were random accidents occurring over a long period of time. Mercer concluded that melting Ice Age glaciers might have caused the Schuylkill River Valley to flood, causing the animals to move, or even stampede, to higher ground where many then fell into the open chasm. There they might have become crushed by the carcasses of other beasts, or they might have drowned when the sinkhole itself filled with water. Perhaps there had been more than one inundation, the water swirling the decaying carcasses into the jumbled condition in which they had been discovered.

Mercer never found what he had really been seeking in the bone cave, namely human remains. He reasoned that had there been humans living in the Schuylkill River Valley at the time, some of them surely would have been chased up the hill by flooding water to perish in the same sinkhole. Mercer wrote in an 1895 report for the Academy of Natural Sciences that if man had been living then in the Western Hemisphere, they should have found “a piece of his skeleton, or a fragment of his handiwork to prove it.”

In Europe manmade tools had been discovered in conjunction with extinct fauna. Mercer had himself visited Paleolithic sites in caves in France and Spain. He had already searched for human artifacts in caves in North America and South America, but never had he come across evidence that North America had been populated before the end of the Ice Age, not counting the dubious Lenape Stone.

The world of the Pleistocene is depicted in The Age of Mammals, a mural by Rudolph F. Zallinger. This part of the mural shows the variety of species that existed during the epoch, including many whose remains were found in the Port Kennedy Bone Cave such as the American mastodon, sloth, saber-toothed cat, and prehistoric wolves and horses.
Copyright ©2018 Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA; peabody.yale.edu. All rights reserved. Photography by Carl Kaufman.

Evidence that man had indeed hunted mammoths in North America would be unearthed during the first half of the 20th century in Clovis, New Mexico. The issue of just how early man arrived in the Western Hemisphere is still puzzling today’s scholars and scientists.

Work ceased at the Port Kennedy Bone Cave when groundwater flooded the site. Ehret Magnesia continued manufacturing insulation products using magnesium carbonate from the local quarries combined with imported asbestos fibers. They deposited their industrial waste back into the quarries. The Port Kennedy Bone Cave was eventually covered over and was lost a second time.

In the 1960s the village of Port Kennedy was largely demolished to make way for U.S. Route 422. The state park at Valley Forge became Valley Forge National Historical Park in 1976. Its boundaries already enclosed some of the old quarries that the state park had purchased over the years, and in 1978 Valley Forge National Historical Park acquired the successor to Ehret Magnesia. In the late 1970s the National Park Service demolished the site’s old manufacturing buildings so that the area could look more like the woods and open fields where the Continental Army had camped.

In 1987 Dr. Edward “Ted” Daeschler began a career at Philadelphia’s Academy of Natural Sciences as a collections manager. The Port Kennedy Bone Cave fossils that had been housed there since their time of excavation stood out to him as a collection in need of some curatorial care. Columbia University Press had recently published a comprehensive review titled Pleistocene Mammals of North America, now considered a classic, and the book made clear to him just how important and unique the Port Kennedy collection was. “There were tapirs and wolverines in the same deposit, the same ecosystem,” he recently commented, mentioning animals whose descendants today inhabit different climates in distant geographical areas. Together with Earle E. Spamer, his colleague at the academy, and David C. Parris of the New Jersey State Museum, Daeschler produced an article for the journal of the Delaware Valley Paleontological Society, published in 1993. The authors stated their intention to “reintroduce this remarkable fossil assemblage to the research community.” They also suggested, “Ideally, the deposit itself should be relocated to establish the feasibility of its re-excavation a century after the last work there.”

This early-20th-century map shows the location of Port Kennedy and its limestone quarries as well as the rail spur that connected them.
King of Prussia Historical Society

Old maps indicated the location of Port Kennedy’s former quarries, including two once located on the property of Archibald Irwin. They showed that the two roads running west from Port Kennedy had remained unchanged and indicated the route of an old railroad spur whose roadbed was still visible in the landscape, features that could help one orient vintage maps to modern topography. Daeschler’s team discovered the field notebook Mercer had kept during his excavations housed at the Bucks County Historical Society. Mercer’s measurements and descriptions allowed them to identify the former location of what was probably the right quarry when two of the authors visited the site in 1990 with Brian Lambert, then natural resources manager at Valley Forge National Historical Park.

Ted Daeschler, now a professor at Drexel University and an associate curator at the Academy of Natural Sciences, remembers the late Brian Lambert for the depth of his knowledge about Valley Forge and his dedication to this historic site. Lambert became the driving force in obtaining a contract and funding for a more in-depth historical search for the exact location of the Port Kennedy Bone Cave in 2003. This time Daeschler worked with Matthew Lamanna of the University of Pennsylvania and Margaret Carfioli of the National Park Service. They studied scientific papers and maps, as well as contemporary images, correspondence and published material. They were able to eliminate all but one of Port Kennedy’s old quarries and confirm the sinkhole’s likely location within it.

Ted Daeschler of Drexel University’s Academy of Natural Sciences and his collaborators located the lost Port Kennedy Bone Cave using documentary evidence, which was later confirmed by noninvasive geophysical investigative techniques.
Frederick Mullison, Academy of Natural Sciences of Drexel University

Their findings from documentary evidence were technologically confirmed in 2004 by a survey crew from the Applied Geoscience Program at the University of Pennsylvania working with a local geophysics company called Enviroscan Inc. The crew used noninvasive geophysical investigative techniques including microgravity and electrical imaging. They located what they described as an underground “anomaly” indicating the presence of a cavity filled with less dense material. It could only be the long-lost sinkhole.

The geophysical survey crew also investigated the urban legend that this old quarry was the final resting place of an old steam locomotive that had been deliberately crashed for an early 20th-century silent movie produced by Siegmund Lubin (1851–1923). A film titled The Valley of Lost Hope contained a scene where a locomotive ran off a cliff to crash spectacularly into a quarry but no one knew exactly where it had been filmed. The 19th-century railroad spur called the Port Kennedy Branch had been constructed to connect the various Port Kennedy quarries and deliver products to the Reading Railroad’s main line at the depot in Port Kennedy. The spur ran directly adjacent to the bone cave quarry. The geophysical survey crew conducted a magnetic survey to determine whether a large iron locomotive might have come to rest somewhere above the sinkhole, but they concluded that wherever Lubin had filmed this scene it had not been the quarry with the Port Kennedy Bone Cave.

During the early 2000s the National Park Service and the Commonwealth of Pennsylvania were also studying this general area of Valley Forge National Historical Park to learn whether the soil still contained traces of asbestos (first detected in 1997) and other contaminants that might pose a risk to the visiting public. Their findings would considerably impact the options for what could be done about the Port Kennedy Bone Cave.

For more than a century, the fossils from the Port Kennedy Bone Cave had remained in the vertebrate paleontology and paleobotany collections at the Academy of Natural Sciences in Philadelphia where they had been examined for various scientific studies by paleontologists from the late 19th century to the present. Daeschler himself wrote a scientific paper titled “Selective Mortality of Mastodons” that became his contribution to a book on paleoecology and paleoenvironments published in 1996. He examined the teeth of mastodons in this collection, noting that it included the remains of many young and juvenile mastodons, more than could probably be accounted for by simply tumbling into a sinkhole the size of the Port Kennedy Bone Cave. He suggested that “Carnivores may have dragged young mastodon remains to hiding places near the sinkhole opening.” These predators might have included some of the carnivores also represented in the Port Kennedy fossil collection, including canids like Armbruster’s wolf (an ancestor to the dire wolf), felids like the saber-toothed tiger, and short-faced bears. His study shows how this fossil collection could be used to illustrate the often-violent life of this period, where a browsing mother herbivore might have been unable to protect her young from a deadly attack. Daeschler’s study also expanded upon the earlier notion that most of the Port Kennedy fossils were the remains of animals simply falling into the sinkhole or being driven there in a flood.

Among the animals identified by Wheatley and Cope during the original exploration of the Port Kennedy Bone Cave was the short-faced bear, an extinct species so named because the deepness of its snout made it appear short compared to the snouts of modern bears.
Ted Daeschler, Academy of Natural Sciences of Drexel University

In the 1990s Daeschler and his colleagues noted that Mercer’s excavation had not mined out the Port Kennedy Bone Cave nor even located the bottom of the sinkhole. They had advocated re-excavation using modern methods. This would not have interfered or detracted from the interpretation of Washington’s winter encampment because the old quarry was not in an area of historical significance or even one that most visitors came across when they walked, biked or drove through Valley Forge National Historical Park.

Following the environmental clean-up of this area during the 2010s, however, the National Park Service discovered still more contamination in the root systems of trees uprooted during a storm. In 2018 the National Park Service began removing trees to cover the ground surface with additional soil and new plantings, which would necessarily bury the Port Kennedy Bone Cave still farther underground. There are no plans at this time to re-excavate the sinkhole, and future efforts, if any, would be conducted by the geology division of the National Park Service, not local staff.

One might say that the Port Kennedy Bone Cave is no longer lost but rather being preserved underground. This find remains important to the history and study of paleontology because, as Ted Daeschler recently observed, unlike many other sites where fossils accumulated over long periods of geological time, the Port Kennedy Bone Cave was filled up like a chimney over a relatively short timeframe, providing a snapshot of a specific period of North America’s very distant past. Or, as Henry Mercer wrote, “As if preserved in a bottle, the remains of so many bears, cats, herbivores, rodents and reptiles of extinct race help to illustrate the conditions of the geological time immediately preceding the present.”

For More Information

The earliest scientific account of the Port Kennedy Bone Cave was “Notice of the Discovery of a Cave in Eastern Pennsylvania Containing Remains of Post-Pliocene Fossils” by Charles M. Wheatley, published in American Journal of Science and Arts, series 3, 1 (April 1871), 235–238. Henry Chapman Mercer’s article “A Preliminary Account of the Re-Exploration in 1894 and 1895 of the ‘Bone Hole,’ Now Known as Irwin’s Cave at Port Kennedy of Montgomery County, Pennsylvania” appeared in the Proceedings of the Academy of Natural Sciences of Philadelphia 47 (1895), 443–446. Mercer’s article titled “The Bone Cave at Port Kennedy, Pennsylvania, and Its Partial Excavation in 1894, 1895 and 1896” and Edward Drinker Cope’s report titled “Vertebrate Remains from Port Kennedy Bone Deposit” were both published in the Journal of the Academy of Natural Sciences of Philadelphia 11 (1897–1901), 193–286.

Edward “Ted” Daeschler’s research appears in “Review and New Data on the Port Kennedy Local Fauna and Flora (Late Irvingtonian), Valley Forge National Historical Park, Montgomery County, Pennsylvania” by Daeschler, Earle E. Spamer, and David C. Parris in The Mosasaur: The Journal of the Delaware Valley Paleontological Society 5 (July 1993), 23-41; and “Selective Mortality of Mastodons (Mammut americanum) from the Port Kennedy Cave (Pleistocene; Irvingtonian) Montgomery County, Pennsylvania” in Palaeoecology and Palaeoenvironments of Late Cenozoic Mammals (University of Toronto Press, 1996).

Lorett Treese is a resident of Chester County and the author of numerous articles and several books on Pennsylvania history, including Valley Forge: Making and Remaking a National Symbol and Railroads of Pennsylvania. Her latest book, A Serpent’s Tale: Discovering America’s Ancient Mound Builders, covers the history of archaeology in America and the nation’s discovery of its ancient history. Her previous article for Pennsylvania Heritage, “Monster Bones: Charles Willson Peale and the Mysterious Nondescript Animal,” appeared in the Spring 2018 issue of the magazine.