Across the Gale River stands New Hampshire's only surviving blast furnace, notable for its octagonal shape and remarkable condition. A huge wooden shed once sheltered the furnace and its workers in the space between the river and the upper terrace behind it. Iron ore arrived in two-wheeled oxcarts from mines three miles to the southwest, while charcoal, iron ore, and limestone were fed into the furnace from above. Once lit, the fire burned continuously for four to six months, with water-powered bellows forcing air into the coals; in later years, the hot blast method drew heated air from the top and piped it back down to the fire. As the ore melted, impurities rose as slag and were drawn off, and every 24 hours a clay plug near the bottom was removed so molten iron could run into sand furrows, forming bars called sows and pigs. The glow of the red-hot iron could be seen for miles. Some pig iron was remelted at a refining forge into wrought iron that blacksmiths and foundrymen could reheat, hammer into products, or mold into iron bars, while other pig iron was cast at the furnace into kettles and heating stoves sold in company stores here and in Bath, New Hampshire. Iron pigs and finished products were shipped south on the Connecticut River from Bath.