I’ve heard a lot about the Blowing Stone over the years, saw for the first time today. Wysefool and Rhiannon’s entries under folk-lore are well worth a read, I won’t duplicate them. For a small donation (towards the maintenance of the church in Kingston Lisle) you can pick up a leaflet by L.V. Grinsell (1993) which tells you everything you may need to know about the Blowing Stone. Most of it is included in previous fieldnotes and folklore entries.
Leaflet does say that stone is not officially classed as an ancient monument and is therefore not shown on OS maps in Old English lettering. Grinsell says the interest in the stone is botanical and geological rather than archaeological.
Leaflet is in itself a little gem – worth stopping by to see stone and pick up a leaflet.