Rock Cannon - a blast from the past
I’ve walked this footpath countless times and each time seems special. There’s always something new to note or fresh to feel. But today I’ve got a grid reference to pinpoint a blast from the past.
The railway was opened in 1836 and powered by gravity - just release the brakes and freewheel down to the coast with horses to pull the empty wagons 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 by gravity all the way.
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.
The ingredients needed to be well balanced.
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.