Also known as Horse Crag Quarries.
The adit itself was first driven in 1849 by John Barret to connect with the extensive Tilberthwaite Copper mines, and as well as acting for drainage, to allow the passing of ore from higher levels. At the mouth was constructed the Penny Rigg Copper Mill, which was the copper-processing plant for this part of the mine. The adit is over 3,000 ft long, and still drains much of the workings. In 1933 John Willie Shaw noticed that the adit had cut through an area of good slate about 300 ft from the surface. He continued working this until 1938 - by which time he had become too old.
In 1989 - George Tarr applied to operate Horse Crag as an underground closehead. He continued to work Horse crag more or less continually until finally closing in 2001.