Miners breaking up rock by setting a fire on it. When the rock cooled it would crack and shatter which made it easy to work with picks. Greater break up could be achieved by pouring cold water over the hot rock. This process was used in Saxony, Hungary and the Harz mines before the introduction of blasting powder. From Underground Life: or, Mines and Miners by Louis Simonin (London, 1869). Wood engraving.