"Knockers" in Welsh Lead Mines: A Geological Explanation?
In a 1951 article in the Journal of the Ceredigion Antiquarian Society (volume 1 (2), pp 177-180) ‘Some aspects of lead mining in Cardiganshire in the sixteenth and seventeenth centuries,’ W. J. Lewis notes a phenomenon first recorded in W. Hooson’s Miners Dictionary, published in Wrexham in 1747. Miners believed that there was "some being that Inhabits in the concaves and the Hollows of the Earth". These spirits directed certain favored men to the ore by knocking. These "Knockers" could locate rich deposits and guide miners to such veins. This was a widespread belief in Cardiganshire (Ceredigion) and elsewhere in Wales until the nineteenth century.
The travel writer George Borrow toured Wales in 1854 and his book Wild Wales, its people, language and scenery, records a different theory: spirits trying to drive miners mad. Borrow spoke to a lead miner from the Welsh Potosi Mines near Ponterwyd who enjoyed his work except for supernatural interruptions. Wild Wales records one story in which the "spirits of the hill in the mine" made "such noises as frighten the poor fellow who works underground out of his senses." The man had been working alone in a deep shaft when he heard a terrible "rushing noise as if an immense quantity of earth had come tumbling down." His light went out and he became certain that he had been buried alive. After several hours, he decided to check if the shaft was blocked and found it clear. Nothing had fallen, leaving the miner with one last problem: how to get back up the ladder in darkness. These underground spirits had a wicked streak and were easily offended.
The Welsh Knocker is similar to the Tommy-knocker in Cornish tin mines during the eighteenth and nineteenth centuries. Since Cornish and Welsh are close, it is not unreasonable to expect that some of the folklore be shared since it comes from the same Celtic root. In Cardiganshire, many mine captains came from Cornwall and the miners themselves frequently moved in search of work. Tommy-knockers, not to be confused with the Stephen King novel, were small dwarf or goblin like creatures tapping away deep in the rock. Descriptions vary but many were small and thin limbed with large hooked noses.
Cornish legends say that they were the spirits of those involved in the Crucifixion or spirits who could not get into either Heaven or Hell. They warned of cave-ins or could indicate a rich vein but turned nasty if provoked. Whistling, swear words or the sign of the cross offended them and to speak ill of a Tommy-knocker was just asking for trouble! The old custom of leaving part of the midday meal or a piece of tallow in the mine would appease the "Old Men." Like their Welsh counterparts, Cornish Knockers showed themselves to favored miners and lived in the mine after it closed. Stephen King, in the foreword to The Tommy-knockers, quotes the Oxford Unabridged Dictionary, "Tommy-knockers are the ghosts of miners who died of starvation, but still go knocking for food and rescue." This misses the point but makes a better story.
Writing as a geologist with an interest in Welsh lead and copper mines, there are five possible explanations:
1) Collapses or rock falls in earlier parts of the mine that have been abandoned; the sound will carry to the parts still being worked.
2) Differential pressure in the ore body or vein. Metal ores are heavier and denser than the surrounding rock, the resulting pressure relieved by small geological movements. With increasing depth in the Earth’s crust, pressure rises to make deep mines particularly noisy places. Fault planes also causes movement, but where the stresses are too great - the rock will "fail." Collapse earthquakes are small quakes in underground caverns and mines; subsidence in other parts of the mine causes noise further along the seam or ore body.
3) Gases expanding or contracting within the rock. Air pockets, fissures and veins are good sound conductors, noises are often heard some way from its source, particularly if the sound is of a subterranean origin.
4) Underground water in the mine, dripping or forming pools or underground rivers.
5) Echoes of miner’s tools - when hammered mineral veins sound different from surrounding rock due to variations in hardness and density.
In summary, given the working conditions and inevitable echoes of a deep shaft, it is not surprising that any unexplained noise was attributed to a supernatural source. Bronze age miners must have heard similar sounds four thousand years earlier but their legends are not recorded. All trace of them is gone now except for tools and evidence of their activity. The work itself was hard and dangerous with poisonous gases and a constant risk of flooding, rock fall or collapse. The body took in toxic dust with every breath of air or bite of food, slowly accumulating to cause serious health problems. Miners worked under severe stress and so the explanation is as much psychological as geological.
Many people entering long abandoned lead workings have commented on the eerie sound qualities. It should be noted that these were experienced cavers with permission from the landowner and adequate safety equipment; old lead mines are still extremely dangerous places. Readers should leave them alone - just in case Knockers really do exist. After so many years of peace, the Old Men may not welcome trespassers!