Fine grained stone has been used for grindstones and whetstones. He replaced the waterwheel with water turbines and the grindstones with rolling mills. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone. The mill originally operated an overshot wheel driving three grindstones. Grindstones are a rough stone, usually sandstone, used to sharpen iron. Exports across the Atlantic included linen, woollen goods, coal and grindstones. A vertical shaft beneath the millhouse connects the grindstones with a "tub wheel" turbine. LSA layers included hammer stones and grindstones, along with bone artifacts and mircolithics. Industries included shipbuilding, farming, lumbering and the manufacture of grindstones. They also started using roller mills, as opposed to grindstones. Musket barrels could be used for hardware in fireplaces or for axles in grindstones. After this, Charles Eyland removed the mill machinery, including the two grindstones. He noticed a grouping of exposed rocks, which would make superior grindstones. Other examples are grindstones, discs or car wheels. Each mill in Idar-Oberstein had four or five grindstones.