have you looked into where the nearest source of fossillised wood has been found to the site?
Is it unique to the area or is there a wide girth of finds?
PeteG
There are no fossil tree sites known in the area. I asked an old lecturer of mine who thought it could be a schist or other metamorphic rock. The problem remains though, that if it's rock worked to a cylindrical shape, why did they do such a crap job? You couldn't accidentally create the irregularities of wood grain.