Thanks to Neil Baxter for providing details and photo.
A petrified tree is literally a tree that has turned to stone over many years, search on Google for a better explanation, but these things are quite rare!
There is a petrified tree near the canal (Frog Lane end)? Genuine. An older Wiganer told me it has been there since he was a kid, and that it possibly had been thrown over the side of a coal barge - maybe found in pit and used as a tempoary prop.
Location: Get on canal between Bridge at Woodhouse Lane / Seven Stars. Walk along to where the pallet yards were (burnt wire fencing from the fire that happened there last year). Tree is by the said fencing. Looks like a big 'tree shaped rock'.