likely that the joint problems of the hardness of the granite rock and the preponderance of underground water together with the relatively easy pickings from near the surface made deep mining unviable until the late 18th century. Many small mining enterprises started up on Dartmoor in the late 18th and 19th centuries – 48 mines are known to have produced some tin during this period. Many of these ventures were unsuccessful, despite being given optimistic names like Wheal Fortune, Wheal Lucky and Wheal Prosper (the common prefix Wheal is a Celtic word meaning "mine" or "works"). Some larger mines, however, such as Eylesbarrow and the Vitifer – Birch Tor complex were productive for many years. Almost all of the underground mines re-worked lodes that had already been mined from the surface. Because of the great quantity of underground water, it was necessary to dig horizontal adits into the hillsides to de-water the mines. Dartmoor's topography, cut with deep valleys, helped there and in many cases it was possible to dig to a reasonable depth without the need to pump out water. These adits connected with shafts that were either sunk vertically downwards or followed the line of the steeply dipping lode. Working the lode then took place by stoping from the horizontal levels in the usual manner. When it became necessary to go deeper than the lowest adit, it was essential to pump out the water. Large waterwheels were used for this and where the shaft was higher than a good water supply, the waterwheel was located lower down the hillside and the power transferred up to the shaft by a "flatrod" system. Evidence for these systems survives as double rows of stones with grooves on their tops – these held the pulleys that guided the metal rods. Such stone rows are still visible at Eylesbarrow and at Hexworthy. The discovery of extensive tin deposits in Malaya in the later 19th century had a major impact on the Dartmoor industry, and many miners emigrated. The last tin mine on Dartmoor eventually closed just before the Second World War, although Hemerdon Mine, or Hemerdon Ball, was mined for tungsten and tin on a trial basis in the 1980s, leading to the re-opening this mine with first production in 2015. Processing After collection the tin ore had to be crushed, concentrated and then smelted. Over time a series of ever more sophisticated