The casting house was a wooden shed, which covered the sand moulds where the iron was run. Note the depression in the stone directly above the archway, which probably held the roof of the shed. Long trenches, sloping gradually from the front of the furnace, were made of moulding sand with enough clay to permit their being moulded to the desired shape. When the iron was ready to be drawn, a worker with long handled tongs would grasp the clay plug in the damstone, and with a skilled twist, removed it. The molten metal shot out of the opening, filling the main feeder trench. As this trench filled, guttermen diverted the molten iron into side trenches, forming a series of bars from 4 to 6 feet long and from 60 to 250 pounds each. Bars from the main trench were "sows", while bars from the side trenches were "pigs", hence, the term "pig iron".