 In surrounding valleys stones of cassiterite (SnO2) were washed downstream from outcropping lodes and trapped in the alluvial mud where they could be easily extracted.Later these outcropping tin lodes were worked by 'bounders' and the open workings (coffins) of these early miners are still partially visible at Penstruthal.Early evidence of the antiquity of mining in Gwennap is recorded in the Stannary Roll of 1305–06 which notes that Johannes Margh of Trevarth sent thirty shipments of tin to Truro.