Traces of a 'Lost' Stonehenge Appear in Rock Quarry

A few tantalizing pieces of evidence hint that there may have been an earlier, lost precursor to Stonehenge somewhere in Wales.

Some of Stonehenge's bluestones were mined from a rocky outcrop called Craig Rhos-y-felin, part of Preseli Hills in Wales. And new research has revealed possible signs of human quarrying at the outcrop that occurred long before and long after, but not at the same time as, the erection of the bluestone megaliths at Stonehenge, according to a new study.

This raises the possibility that one or two of the bluestones from Stonehenge may have first been used in some other, earlier henge in Wales before being removed from that monument and transported to the Salisbury Plain in England. [Stonehenge: 7 Reasons the Mysterious Monument Was Built]

However, the evidence in support of the theory is scant: a few traces of burnt material and one oddly positioned rock. And not everyone is convinced that these clues point to an earlier Stonehenge-like monument.

"While this work adds some detail, it doesn't change the main picture," said Timothy Darvill, an archaeologist at Bournemouth University in England, who has excavated at Stonehenge but was not involved in the current study. "The Preseli Hills are extensive and geologically very complicated, with the result that matching stones to particular outcrops is fraught with difficulties."

In addition, it's possible that much of the archaeological material uncovered is "entirely natural" — not evidence of human work on the landscape, Darvill said.

Preseli Hills rock source

Stonehenge is one of the most mysterious monuments on Earth. The strange rock formation was assembled over a period from about 5,000 years ago to roughly 4,000 years ago. Archaeologists now think the monument's current layout is just one of many it has taken over the years, and that the monument's megaliths were almost constantly being reconfigured on the landscape, said study co-author Rob Ixer, a geologist at University College London and the University of Leicester in England.

The biggest megaliths at Stonehenge, called sarsen stones, are about 30 feet (9 meters) tall and weigh about 25 tons (22.6 metric tons). Those stones come from Marlborough Downs, located about 20 miles (32 kilometers) north of Stonehenge. The monument also makes use of smaller stones, known as bluestones, which weigh up to 4 tons (3.6 metric tons).

Since the 1920s, scientists have known that Stonehenge's mysterious dolerite bluestones came from Preseli Hills, located roughly 155 miles (250 km) away, by land, from Wiltshire, England, where Stonehenge now stands. However, the exact quarrying location in the rocky hills has been a mystery. In recent years, however, geologists have identified several spots in the Preseli Hills where different types of bluestones were mined. [In Photos: A Walk Through Stonehenge]

Hints of human activity

In 2011, Ixer and his colleague Richard Bevins, a geologist at Amgueddfa Cymru, a group of museums in Wales, came across the Preseli Hills site of Craig Rhos-y-felin by accident. As part of his doctoral work 30 years earlier, Blevins had collected, but never analyzed, a rock sample from Craig Rhos-y-felin, which, at the time, was completely concealed behind a wooded area. By chance, Bevins had decided to analyze the piece of rock from Craig Rhos-y Felin, which was made of rhyolite (a volcanic rock), right around the time that Ixer asked him to find a source of the debris from the bluestones. 

Both rocks showed a distinctive swirly "Jovian" pattern. In fact, he found the patterns matched exactly.

Since then, Ixer, Blevins and several other researchers have razed the trees around the outcrop to get a better look at it and conducted extensive archaeological excavations.

The team found no mauls — hammers typically used to chisel rocks during this time period. That's unusual for prehistoric quarry sites.

"The way you recognize prehistoric sites is that you fall over maul after maul," Ixer told Live Science.

Instead, the team hypothesizes that the bluestone rock found at the site could have been sheared off fairly easily by inserting wooden wedges into pre-existing cracks in the rock and then waiting for the rain to swell the rock and create enough pressure to dislodge them.

That theory may also explain why the Stonehenge builders would bother to ferry the rocks such a vast distance when there was no shortage of closer rock sources. (As an alternative theory, some have argued that glaciers carried some of the rocks to the Salisbury Plain.) In the research team's conception, however, people may have taken rocks from there because it was so easy and convenient.

"It's like an IKEA," Ixer said. "You just walk up to it, take what you want and take it away."

The team did find a burnt hazelnut and some charcoal from ancient campsites that date to both the Neolithic and the Bronze Age. The traces of Neolithic human occupation date to 3400 B.C., some 600 years before the first stones were erected at Stonehenge. Meanwhile, the Bronze Age sediments are a mere 4,000 years old (dating to about 2000 B.C.), meaning the quarrying occurred well after the bluestones first came to Stonehenge.

There was also one large, upright slab, called an orthostat, which was angled at a strange position. That rock could not have naturally fallen into that position but was likely placed that way by some of the workers, the researchers wrote in the December issue of the journal Antiquity.

Mismatched dates

Exactly how these rocks fit in with the construction of Stonehenge is extremely murky. One possibility is that the rhyolite bluestone was used in the Stonehenge Cursus or long barrows — a semicircular ceremonial burial trough where people buried their dead — and was eventually repurposed for the great stone monument, Ixer said. The cursus is hundreds of years older than Stonehenge, so its dates match nicely with the oldest Neolithic sediments at Craig Rhos-y-felin, he added.

Another possibility is that there was a proto-Stonehenge monument somewhere in Wales, which was then dismantled and repurposed miles away in what is now England.

However, some Stonehenge researchers maintain that there is no evidence of human quarrying in the area.

"As a geomorphologist who has looked at this site very carefully, I am 100 percent convinced that there is no quarry at Rhos-y-felin," said Brian John, a geomorphologist who blogs about Stonehenge.

And the new results still don't help answer the big questions about the mysterious monument: Who built the structure, and why?

"Stonehenge was a Welsh monument from its very beginning. If we can find the original monument in Wales from which it was built, we will finally be able to solve the mystery of why Stonehenge was built and why some of its stones were brought so far," study co-author Mike Parker Pearson, an archaeologist at University College London, said in a statement.

Follow Tia Ghose on Twitterand Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.