Quarrying began in the 18th and 19th centuries on Blackborough Common, working extended along to Ponchydown and perhaps as far south as North Hill. A thriving industry was developed which provided whetstones of a very high quality to a huge market. The stone was soft when first dug and could be shaped, but later it hardened on exposure to air (Edmonds 1975: 70). Unfortunately by 1900 most of the stone was worked out and only three mines remained, and by 1910 the invention of carborundum meant the end of the whetstone industry (Rugg 1999). The mines were driven horizontally into the hill for up to 400 metres and today the remains of the mines can just about be discerned as hollows on the surface (ibid.).