structure evolved from a prehistoric form containing the essential core and crucible.' The transition from the mid-fifteenth century European blast furnace to the early nineteenth century charcoal furnace of Pennsylvania was gradual. Technological changes occurred chiefly in the shape and size of the

were not in operation. 1° Puddling furnaces in eastern Pennsylvania tended to use anthracite coal, according to Temin, the proximity of the mines and the earlier development of canal and rail transportation in the East being advantageous. The Safe Harbor Rolling Mill was cited by Temin as using