Rock Cannons

When it opened in 1836 the Ffestiniog Railway was powered by gravity, pony and water wheel. The brakes were released and gravity took the slate wagons all the way down to Porthmadog and the ponies brought them all the way back to Blaenau. But just beyond the western end of Tanygrisiau reservoir, the wagons went uphill, one at a time, driven by waterwheel.

From the day the railway opened this short uphill section was a bottleneck, and work commenced on the first Moelwyn tunnel, the one that is now flooded by the reservoir. Six years later the tunnel was opened, and thereafter the train truly ran downhill all the way by gravity.

Moelwyn tunnel Rock Cannon
with a piece of paper stuck in each hole

Just a few yards from the old bit of uphill track there is a slab of rock embedded amongst the heather and wild grasses. A bit like any other slab of rock except this one has 17 holes drilled into it. No question of a compressor-driven power tool, but good old hand drilling, five inches into solid granite.

This was not a training ground for apprentice quarrymen, but a rock cannon to be fired on special occasions. The holes were part filled with black powder and covered with stemming (crushed stones) through which a goose quill filled with powder acted as a detonator. Connecting the various holes was a line of goose fat embedded with more black powder. Light the touch fuse, stand well back and enjoy the show.

Too little stemming and the explosions would be damp squibs. Too tightly packed with stemming and the rock would be blasted to smithereens. There were many accidents.

This particular cannon is known to have been fired when the railway was first opened, and again in 1842 when the tunnel was completed. But it is just one of many. Throughout Gwynedd there are more than two hundred and fifty such cannons that have been recorded.

The design of later cannons was refined with channels cut into the rock to link the holes together. Sometimes there are as many as a hundred and sixty holes in a cannon. The timing of each explosion could be controlled or varied by the length of channel between the holes. In this way one of the cannons was designed to beat out 'God Save the Queen'.

The greatest concentrations of cannons occur around quarries, especially those associated with the landed gentry: the reason being that they had a large number of VIP guests to impress, and what better way to do so than with a display of rock cannons.

Cannons would be fired to celebrate weddings, jubilees, declarations of peace, but probably the most extensive displays would be to welcome Royal visits. The Daily Mail’s account of the Prince of Wales’s visit to Blaenau in 1923 gives an idea of how impressive they must have been … each mountain sprang into eruption. The Prince sat in his car and crushed his cap into his hand. And while the roar of the explosions rose above the cheering he banged a fist into the palm of his hand and said, 'I have never seen anything more wonderful – never'.

Ellie filming the Rock Cannon at Porthmadog

Special occasions such as weddings are best held on dry days – especially so if you’re planning to fire cannons. On 6th August 1863 a Blaenau quarry owner F. S. Percival was to marry Miss Jones Parry and …great was the rejoicing in the quarries as the day was a general holiday for them. A large number of rock cannon were prepared to be fired throughout the day of the marriage but that was prevented due to torrential rain. The cannons were fired a month later on the couple’s return from honeymoon.

Wouldn’t it be great if we could get these cannons into action again? But then again I doubt whether we would get past Health and Safety.