Inside the bizarre 'binoculars' tunnels cut by Victorian boring machines in North Wales

A Scottish engineer and a wealthy inventor teamed up to build tunnelling machines

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Centuries of slate quarrying left some extraordinary features across the Welsh landscape. Among the strangest of them all are twin tunnels shaped like binoculars that were dug by some of the world's first boring machines.

Their existence in Gwynedd's vast slate mines is a story of Victorian ingenuity and, ultimately, heroic failure. Despite showing promise, the steam-powered tunnelling machines were unable to match the efficiency of low-paid miners equipped only with jumper sticks, hammers and gunpowder.

In the mid 1860s, the machines were trialled at three mines. One was used to cut an opening to the Cookes level at Maenofferen, Blaenau Ffestiniog, where hobnail bootprints can still be seen on slate floors.

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The most celebrated is at the Abercwmeiddaw, near Corris, in southern Gwynedd. Here, bizarre twin tunnels reach around 30 metres into the rock. Cut in 1864, they resemble a giant pair of field glasses.

One recent visitor was Nic Parry from Shrewsbury, who said the experience of exploring the "binoculars tunnel" more than matched their billing. "This was one of those places where you get there and think wow!" she said. "It's as if those patterned lines were drawn on. It was really quite mesmerising!

"When you are stood inside, you tend to wonder about their true history. Nature has started to reclaim them, which I think adds to the beauty of the place."

The first tunnelling machine was designed by Scottish engineer George Hunter, whose father James had developed industrial stone planing machines in Arbroath. Their industrial cutters were widely adopted by the slate industry – though James was to lose a leg in the process.

One was ordered by the Braich Ddu quarry near Trawsfynydd in 1863. Boasting four discs, each 4ft in diameter, it was described as "the largest machine of the kind yet made".

As the so-called "Hunter saw" was manufactured in Arbroath, the only way of getting it to the quarry was by sea, then by boat up the River Dwyryd, followed by a four-mile road journey and, finally, transport along a two-mile length of narrow gauge tramway.

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To oversee its installation, George Hunter and his family left Arbroath for Maentwrog in the Vale of Ffestiniog. Here, he came to the notice of Sir William Fothergill Cooke, joint inventor of the electric telegraph who used his new fortune to buy a house in Aber Iâ, the present-day Portmeirion, near Porthmadog.

As Sir William had invested heavily in Maenofferen quarry, and at Hafod Las quarry, Betws y Coed, he was keen to see if new technology could boost their profits. And as it happened, George had just patented a prototype tunnelling machine which, in trials in Arbroath, had cut a five-inch-deep ring in a stone wall in less than five minutes. Sir William promptly provided the finance for its construction and shipping.

Essentially, the tunneller was a rail-mounted turbine that turned rotating cutters. For the cutting edge, steel bolts were used with sharpened, conical heads. The machine could be adjusted for a cutting diameter of between 5ft 6 and 6ft 6 – around two metres. The cutting head revolved slowly, at one to two revolutions per minute.

Once moved into place, it was clamped in position. Typically, the machine would take about three to five hours to cut a 2ft deep groove into the rock. At this point, the cutting head was withdrawn from the newly-cut groove, and the whole machine was roped back to the tunnel entrance to allow miners through.

They could then start hacking out the core at the head of the tunnel, a process that could take several hours. Only then could the machine be pushed back into the tunnel, clamped back in place and the next core cut.

The first tunnel cut this way was probably at Maenofferen, where a 30ft-long single bore can be seen. But it was a laborious operation. The key weakness was the inability to extract the core without the machine being withdrawn. Over the next few years, modified Cooke & Hunter borers were patented but the central problem remained. Sir William admitted as much: in one patent, he described how the machine was "idle for nine hours out of every 12".

His radical solution was to drive multiple tunnels in parallel. After cutting one bore, the machine would be moved to an adjacent rockface, and a second intersecting bore cut. Once done, it was moved a third adjacent rockface before being returned to the first: the idea being that it could be in constant use.

For this, a cradle was needed to move the machine between each parallel tunnel. The process was tried with some obstinancy at Abercwmeiddaw, creating its telltale binoculars tunnel. At Maenofferen, a bizarre "quadruple bore" tunnel was cut in 1868, forever known as "Cooke's Level".

Unlike the Cooke & Hunter stone cutting and dressing machines, which were adopted widely in the slate mines of northwest Wales, the tunnelling machines failed to justify their investment. Finances were never Sir William's strong point, as JG Isherwood noted in a paper presented to the National Association of Mining History Organisations conference at Bangor University in 2014. He wrote: "Cooke may have had some good ideas, but was perhaps lacking in business acumen.

"In late 1867-early 1868 his enthusiasm led to an investment in the Llanberis Slate Company Ltd which was to cost him dear. The company was already somewhat dubious, and had expended a large amount of shareholder's money to little profit by developing the Gallt-y-Llan slate quarry, near the end of Llyn Peris."

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Despite the enthusiasm generated by the arrival of a boring machine at the quarry, by November 1868 the company had failed and Sir William was left severely depleted. Within a couple of years he would lose what little he had left.

In 1870 he founded another stone-cutting company in London, shortly after withdrawing from leading roles in the Maenofferen and Bettws companies. Despite raising £40,000 in funding, the new company would fold within four years. By 1879 he was dead, leaving an estate worth a mere £17.

George fared a little better, but not without heartache. Of his five children born in Maentwrog, three died, possibly due to typhoid. Shortly after moving to Aberdyfi, as tenants of the Abercwmeiddau quarry, a sixth child was born in 1870.

In a final effort to perfect his tunneller, he filed a patent in 1882 for a machine driven by compressed air. But the world had caught up and overtaken him. In 1880, work began on the first attempt to dig a tunnel under the English Channel. This used a superior rotary boring machine capable of cutting nearly half-a-mile a month.

Despite the two bores reaching 2,110 yards in length, the project became plagued by fears of a subterranean invasion by the French. After a number of injunctions, it was finally abandoned in 1898.

The Cooke & Hunter machines were consigned to become footnotes in the history of tunnelling. In his 2014 paper, Mr Isherwood, a leading authority on their development, wondered what might have been. "Had the tunnellers and over/under cutters been tried in some other material than Welsh slate, and in a more visible locality than a remote corner of Wales, perhaps it would have been their names associated with the first Channel Tunnel attempt, rather than the inventors Brunton, Beaumont and English?"

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