WOOLER, England, Oct. 9 (UPI) -- There's a mystery afoot in northern England: rock carvings that no one can quite decipher.
The carvings -- in an isolated sandstone boulder near Wooler in North Northumberland near the Scottish border -- include a group of concave spherical shapes of around 20 centimeters in diameter. Another of the symbols looks like an adult footprint. There also are several deep scores and a heart-shaped marking.
The markings were found by a farmhand who showed them to experts from the University of Newcastle upon Tyne. They, in turn, consulted with bodies such as English Heritage and the Royal Commission on Ancient and Historical Monuments of Scotland.
The experts have discarded theories the markings were created by the sharpening of metal tools or that someone made them recently.
"We have absolutely no idea what they are, as they are nothing like anything we or anybody else we have talked to have seen before," said Dr. Aron Mazel, research associate with the School of Historical Studies. "They are not the cup and ring marks which we have been studying as part of the Northumberland prehistoric rock art project -- they appear to be more recent than that."
Mazel noted people have occupied the Northumberland area since the start of the Mesolithic period around 10,000 years ago.
Northumberland is widely regarded as possessing the finest collection of prehistoric rock art in England. Most of the carvings are in the cup and ring style and can be found on rocks throughout the county.