A reef under a hill: Just one of the delights of Coral Caverns
Deborah Painter (USA)
Why is there a reef in a cavern under a hill in south-central Pennsylvania in the USA?
My good friends Richard Hedges and David Hawk and I wanted to know the answer. We had seen various websites which describe an amazing commercial cave with one wall composed of fossil corals, stromatoporoids, brachiopods and crinoids. The three of us were already planning a weekend trip to Pittsburgh, Pennsylvania, to go to a conference, and Coral Caverns seemed a perfect stop on the way home. It was just off the Pennsylvania Turnpike and so seemed ideal.
We looked online and obtained directions to the little hamlet of Manns Choice (Fig. 1). We tried calling (814) 977-9570 beforehand to find out if we needed reservations but all we got was a friendly voice on an answering machine. The cavern, we had read, was located at 123 Cavern Street, and was open on weekends only in May, June, September and October, and seven days a week during the months of July and August by appointment.
A prominent sign on the Pennsylvania Turnpike points out which exit to take to Manns Choice. No signs for Coral Caverns or the nearby Shawnee State Park were posted. However, the beautiful old stone Jean Bonnet Tavern, a landmark, was quite near the Turnpike (Fig. 2).
We followed the instructions to take the Pennsylvania Turnpike to exit 11, Bedford. But the exit does not take one directly to Manns Choice, even though the hamlet, and Route 31, can be clearly seen from the multilane highway. Instead, the rural route took us south to Bedford, a very pretty town. Here, we turned right at the first light (Pitt Street, Route 30) and then continued west to the Jean Bonnet Tavern. Then, we bore left onto Route 31 West. We went along Route 31 two kilometres and then saw the signs for Manns Choice. Once we turned right onto Main, we passed an ice cream parlour. Very close to this was a sharp turn to the south (left) and a small street named Cavern Street with a red polished granite marker reading “Coral Caverns”.
Okay, we were definitely close now …
We turned left onto Cavern, which only has one turn from Main. From there, we saw a steep drive up a narrow gravel path to the top of a hill. This looked like the perfect site for a mystery, so we took this road to a plateau atop the hill. Here, we saw a parking area and a rustic cabin with what looked like a man standing rigidly on the front porch (Fig. 3). Drawing nearer, we saw that what we thought was a man was a life size mannequin of a miner, whose concrete overalls were smeared with yellowish paint to look like he had just emerged covered with yellow clay.
We were worried that we had arrived too late and that the cavern had just closed for the day. A very young looking mom and her little boy walked over to our car. Mrs van Deventer and her cheerful and equally young looking hubby Bill then greeted us. “Are we too late?” We asked him. “No, we have time. Come on.” And Mr van Deventer then gave us a tour of the van Deventer’s own personal cavern.
“If you arrive in the spring, fall and winter the cave is only open on weekends, when I or my wife will give a tour. During the summer, college students assist.”
The safe entrance was easy to access (Fig. 4).
Several shafts opened up on the floor of the cave very near our walking path and barriers had been erected to prevent accidental falls (Fig. 5).
A recessed room contains a ‘cave chimney’ and a very narrow cement staircase (Fig. 6).
It was here that in 1928, three Boy Scouts used ropes to lower themselves into the cave. They reported to the quarry company a wall comprised of a huge fossil coral reef, fossil trilobites, black volcanic rock, helictites (gravity defying cave formations; Fig.7), large calcite crystals, cave popcorn (fossil brachiopods) and a multitude of ‘cave straws’.
Since this natural entrance is so steep and difficult to access, Native Americans did not use this cave for shelter from the elements. No artefacts or evidence exist, nor is there evidence for fire usage.
Wonderland Coral Caverns opened for business in 1932 using the narrow, extremely steep and slippery stairwell of cement. Fortunately, we twenty-first century visitors do not have to enter via that staircase. One has to have nothing but admiration for visitors from the 1930s through the middle 1980s.
Fortunately, no accidents ever resulted, and the cave was closed to the public in 1985 to avoid pushing the owner’s luck any further. Bill van Deventer purchased the property and constructed a new and safe entrance in 1999. The stairwell still stands. It is a reminder of an era when tourists were expected to be willing to take a chance if they wanted to enter the cave.
The stairwell now vanishes into the gloom in a romantically mysterious way. Speaking of romance, the owner of the cave during the 1980s was Steven Hall. He chose his own cave to get married in back in 1984. He and his bride took their vows in the Cathedral Room with the wedding party in attendance. Their wedding photos are still on display in the gift shop.
Unusual features in the cave include the presence of tiny two- or three-inch-long and nearly perfect clear calcite crystals. They are the result of past flooding in the cave. In the cave is a Little Town of Bethlehem that looked like its namesake. However, the Tibetan Temple looked more like a very small squashed ice cream cone. I liked the ‘whirlpool’ effect scoured into the side of the cave by groundwater rushing through when the cave was wetter (Fig. 8).
Some of the attractive cave decorations include multicoloured ribbons, formed when calcite laden water ran along cracks and seams in the ceiling before the water evaporated. Over time, this created a ribbon effect. The ‘cave ribbons’, running along the ceiling, really do resemble cream and light brown striped ribbons, or bacon strips, if you will. These, combined with the cave popcorn and the soda straws, made us hungry. Initiation for the new guides is to make them drink soda through a cave formation called a ‘soda straw’.
But the reef… that was what excited me most. There it was, looking like an almost vertical wall of brown (Fig. 9).
We could see the individual brachiopods and stromatoporoids (Fig. 10).
Due to the contact with iron, some of the reef had dark brown/red hues. The stromatoporoids were in life a variety of sponge, now rare, that have a very hard external structure. In fact, zoologists once wrongly classified stromatoporoids as corals. This coral reef is a dramatic demonstration of the fact that millions of years ago, the rocks forming the Alleghenies were at the bottom of a shallow sea.
This was the Devonian Helderberg formation, which is over 370 million years old. The Devonian was not the first time that central Pennsylvania has been a shallow sea and coastal plain; that had happened once before, millions of years previously, during the Cambrian Period. Nor will it be the last, in all likelihood, that this area will be underwater.
Many stages of earth dynamics had to take place in the process that took a reef and turned it into the wall of a cave. At some point, it was covered in sediment. Then, the tectonic forces of a continental collision pushed up the shallow sea bottom limestones and formed the Acadia Mountains during the later Devonian, 270 million years BP. The Acadia range extended south to Virginia.
As time passed and the Permian period saw the closing of the proto-Atlantic Ocean, the appearance of this land that would one day be called Pennsylvania began to take on more of its modern appearance. It became an Eastern Seaboard coastline and mountainous area. More erosion and then uplift occurred. The most recent mountain building episode was the one that formed the modern Allegheny Mountains.
Next, ground water created the cave and its formations. We could literally see the results of that immense force that formed the Alleghenies: it is vividly shown in the nearly 90 degree inclined strata. This great nine meter tall slab really gave us a sense of the immense passage of time that had elapsed between the existence of the reef under the surface of that sunlit sea and the present time, when all that was left of the coral reef was gray, brown and white rock.
A 2009 paper by Misty L. Wertz and Tamra A. Schiappa clarified the differences between the reef community at Coral Caverns and the reef community outside the caverns (Fig. 11). Those within the cavern itself are predominantly of the stromatoporoid genus Clathrodictyon. These are radial in morphology and can be distinguished from bryozoans or corals by looking under a magnifying glass for the individual tubes. Brachiopods include species within the genera Anastrophia and Macropleura.
Outside the cave, Wertz and Schiappa identified a transition to the Devonian New Creek and Corriganville Formations, also siliciclastics and carbonates. The real corals in the vicinity of Coral Caverns occur in these formations. Horn corals were horn shaped individual coral animals that grew to large sizes, sometimes 13cm in length. None are within the commercial cave’s slab of fossil reef animals.
The Coral Caverns site is from an early time of the Devonian. About 321km due east of Manns Choice by way of the Pennsylvania Turnpike, and off Interstate 476 near Quakertown, is Red Hill, a world class late Devonian fossil site under private management. That one represents a freshwater lake environment teeming with fish from the lineage that gave rise to amphibians.
The entire cave tour lasts about 40 minutes and the cost (at the time of our visit) was $19 – US currency only, the owner does not work with credit cards. After the tour, we lingered in the small gift shop. The main features here are the generally accurate and beautiful dioramas (Figs. 12 and 13), and mining instruments (Fig. 14). David had to purchase some genuine tiny Pennsylvania fossil corals and small calcite crystals direct from the Cavern. That was a treat.
References
Cheney ,Jim. November 15,2023. Exploring the Little-Known Coral Caverns in Bedford County,PA: Exploring the Little-Known Coral Caverns in Bedford County, PA – Uncovering PA
Show Caves of the United States of America, Coral Caverns page. http://www.showcaves.com.
Stome, Ralph W. 1932. Pennsylvania Caves. Pennsylvania Geological Survey Fourth Series, Bulletin G 3, p. 13-18. Survey.
Wertz, Misty L., and Tamra A. Sciappa. 2009. The Geological Society of America: Abstract: PALEOENVIRONMENTAL RECONSTRUCTION OF CORAL CAVERNS, BEDFORD COUNTY, PENNSYLVANIA (North-Central Section – 43rd Annual Meeting (2-3 April 2009))