On the south side of the churchyard lies a rude rough stone, measuring six feet in length, twenty-two inches in breadth at the wide end, and nine inches thick. After rain, water lodges in a weathered basin on its surface, which tradition says was a certain cure for warts.
Originally from 'A History of Barmby Moor' by W D Wood-Rees (1911), and collected in v6 of 'County Folklore'.
I admit it, this is a bit of a speculative one as I can't find a picture anywhere. It might turn out to be obviously, stupidly, too young. But if anyone sees it in the flesh they can report back. (Maybe the more I think about it the more it sounds unconvincing? One of its only mentions elsewhere on the internet also hopes for a prehistoric origin. That's where I get unwarranted encouragement from.)