I've now given up searching the map! I'm convinced there's neither a Worm's Rock nor a Worm's Well marked on it. Worm's Rock is said to be the place where the Worm would cross the river. I see that Worm Hill is right next to the river - that would be my best guess of where to start looking. I think the only way to find it would be to get out there and walk a few miles of riverbank. With a bit of luck it would be where instinct seems to be telling me it is - next to Worm Hill. As for Worm's Well, my best guess is that its been re-named Lambton Well.