Stories in Slate: Touring an Underground Mine

By Marie Powell (Photos by L. L. Melton)

A tour of an underground mine offered a hands-on science opportunity during a recent trip to the Braich Goch slate mine in North Wales.

We spent more than two hours in the mine tunnels with our expert guide Mark of Corris Mine Explorers. During that time, we explored the abandoned caverns, learned a little mining history, and examined original artifacts used in this once-prosperous slate mine.

The underground tunnels date to 1836, and by 1878 the mine employed about 250 workers producing 7000 tons of slab and roofing slate. In its heyday, families negotiated for mining rights to the chambers, which were known as "bargains," Mark told us. Men and boys aged 10-35 worked the mine in near darkness, hoarding the tallow candles made from sheep fat that provided their only light source. They used clay to carry the candle with them and fix it to the slate walls of the mine as they worked

We had a chance to see several original artifacts used in the mine and left there. These tools date back to the 1860s, Mark said. Using the mallet, a worker would strike the rod three times, then turn and strike three more, for a total of nine strikes. Black powder was packed into the hole. They used copper and brass rods because they don't spark, he added.

Since the mine is full of ledges and drops, and candles were scarce, it was important to have a reliable method of finding their way around the mine in almost total darkness, he said. They used a form of echo-location, orienting themselves to the sounds of dripping water in the cave, or to their own singing.

Most of the time we were able to walk upright, but at times there was barely enough room for a person to crouch. At one point Mark tied us to a rope and let us look out over a drop in the mine to a level below. Staring down at the eerily echoing caverns far below us, we were glad of our headlamps and gear, and hyper-aware of the danger the miners faced every day.

Artifacts lined the mine at strategic locations. Mark pointed out the expected ones, such as a detonation box, explosives, and a "bugle" of black powder. Among the artifacts we saw a 19th Century example of recycling: a jar for W P Hartley's marmalade, probably re-used for drippings from sheep fat, since bread and drippings were a staple of the miner's diet.

These historical artifacts also show the effects of rust, which occurs when water and oxygen goes to work on iron, especially cast iron as would have been the case in the late 1800s.

The walls themselves are a study in stratification, or the layers of rock that form over time. We stopped more than once to examine them.

Mushrooms were visible in several places as well, and Mark pointed out that these fungi can act as agents of erosion on some artifacts, such as this oxidizing nail covered in what looked like red-orange fuzz.

The ochre coloration, generally from iron oxides or limonite, gave the walls of the mine a striking look in places as well.

The geological processes we could clearly see at work in this underground environment made it well worth the trip, and having a knowledgeable guide willing to let us explore at our own pace was invaluable.

Marie Powell is the author of seven books for children, including Dragonflies are Amazing (Scholastic Canada) and a six-book Word Families series (Amicus Publishing). 


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