'Penrhyn Slate Quarries', c1870. At the end of the 19th century, Penrhyn Quarry near Bethesda in Wales was the world's largest slate quarry. It is significant in the history of the British Labour Movement as the site of two prolonged strikes in 1896 and 1900 by workers demanding better pay and safer conditions. From "Picturesque Europe - The British Isles, Vol. II". [Cassell, Petter & Galpin, London, c1870]