A bronze statue entitled 'The Virgin mother' by artist Damien Hirst is displayed in the courtyard of the Royal Academy of Arts in central London as part of its 238th Summer Exhibition June 7, 2006. [Reuters]

One of Britain's most prestigious art galleries put a block of slate on display, topped by a small piece of wood, in the mistaken belief it was a work of art.

The Royal Academy included the chunk of stone and the small bone-shaped wooden stick in its summer exhibition in London.

But the slate was actually a plinth -- a slab on which a pedestal is placed -- and the stick was designed to prop up a sculpture. The sculpture itself -- of a human head -- was nowhere to be seen.

"I think the things got separated in the selection process and the selectors presented the plinth as a complete sculpture," the work's artist David Hensel told BBC radio.

The academy explained the error by saying the plinth and the head were sent to the exhibitors separately.

"Given their separate submission, the two parts were judged independently," it said in a statement. "The head was rejected. The base was thought to have merit and accepted.

"The head has been safely stored ready to be collected by the artist," it added. "It is accepted that works may not be displayed in the way that the artist might have intended."