THE discovery of a series of mysterious rock carvings has sparked a quest by experts to find out exactly what they are.

The designs were found on an sandstone boulder in an isolated area of Northumberland and have left top archaeologists baffled as to what they mean - and who created them.

Rock art experts from Newcastle University were alerted to the site by a local man, who stumbled upon the symbols.

So far, they and investigators from English Heritage and the Royal Commission on Ancient and Historical Monuments of Scotland, have drawn a blank.

Northumberland is widely regarded as possessing the finest collection of prehistoric rock art in England and a group from the university was already carrying out fieldwork in the area looking at prehistoric "cup and ring" rock art.

This pattern of cups and rings of various sizes is the most common kind of ancient art carving found in Britain.

However, the new markings are very different, and include concave spherical shapes about 20cm in diameter, sever-al deep scores, a heart-shaped marking and another that resembles an adult footprint.

Dr Aron Mazel, research associate with the School of Historical Studies at Newcastle University, has been investigating the markings with international rock art authority Stan Beckensall, and, despite having over 60 years of experience between them, have been unable to identify them.

Dr Mazel said: "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.

Stan Beckensall said: "As far as I know, these markings are unique. Nothing like them exists in the British Isles."