Mortar Stones at Black Tor Blowing House
This photograph is dated 21 December 1887. It shows evidence of the tin streaming industry on Dartmoor. The caption refers to Har Tor, which is nowadays marked on OS maps as Hartor Tors (Higher and Lower). The blowing house is on the bank of the River Plym nearby. The stones in the photograph are called mortar stones. These were used for crushing the tin ore in a stamping mill.