Millstones and pumice were also exported, but for the former the more gritty lava of Rocca Monfina was later on preferred.
15 ), and millstones, salt (from a marsh at the east end of the harbour), and gypsum are still exported.
Rockland county quarries considerable trap rock, used mostly for road-making and concrete, and Ulster county has for more than a century produced most of the domestic millstones used in the United States.
The surface soil is clay in which are embedded fragments of siliceous sandstone, used for millstones and constructional purposes; the subsoil is limestone.
The mineral products of the district also include lignite, copper, manganese, vitriol, lime, gypsum, volcanic stones (used for millstones) and slates.