|This idea of a 'druidic oracle' stone and much more besides can be found at http://www.nidderdale.org/Antiquarian/Brimham%20Rooke/Illustrations.htm
Mr Rooke holds the usual opinion of the Britons as being ignorant, I'm afraid.
Some Account of the Brimham Rocks in Yorkshire
In a Letter to the Rev. Mr. Norris, Secretary
By Hayman Rooke Esq.
Read at the Society of Antiquaries, May 25th 1786.
I think [this] may be called an oracular stone, though it goes by the name of the Great Cannon. It rests upon a bed of rock, where a road plainly appears to have been made leading to the hole (a), which at the entrance is three feet wide, six feet deep, and about three feet six inches high. Within this aperture on the right hand is a round hole, marked (b), two feet diameter, perforated quite through the rock, sixteen feet, and running from south to north. In the above mentioned aperture, a man might lie concealed, and predict future events to those that come to consult the oracle, and is heard distinctly on the north side of the rock, where the hole is not visible. This might make the credulous Britons think the predictions proceeded solely from the rock deity. The voice on the outside is as distinctly conveyed to the person in the aperture, as was several times tried.
Posted by Rhiannon
16th March 2005ce