I've done some research into why this is called the devils pullpit and have come up with two explanations. First is that years and years ago a man fell into it and survived and when asked how did he fall he said he was pulled in by the devil! (something tells me this is made up) and a more believable one is that if you look closely at it you can see the devils face

and i'd better explain that last pic off my little girl jumping is not really off there it's off a bench lol just thought it looked quite convincing