at Seathwaite (Lake District) and four in Cornwall, where they are known in Cornwall as merriment holes. There are two basic patterns of construction. The stone may simply have a series of holes drilled at regular intervals. The ignition was carried between adjacent holes by a trail of black powder over the surface of the stone which was held in place by goose grease. A later construction had the holes linked by shallow grooves, often curved to lengthen the interval between bangs. The black powder was then laid in the grooves and covered with powdered stone to keep it in place. The holes are typically an inch in diameter and five inches deep. Modern experiments have shown that a small amount of black powder in the hole with a powder-filled goose feather quill as a fuse, and the whole held in place by powdered slate can produce spectacular sounds and visual effects. References The Rock Cannon of Gwynedd, Griff R. Jones, 2002, External links BBC - Rock cannons - a blast from the past Slatesite - picture of rock cannon with curved connecting grooves Video of a reconstructed rock cannon being fired History of Gwynedd Slate industry in Wales Fireworks