Shropshire's Geology is very diverse and most geological periods of time, and most rock types, can be found within the county. There is also a large amount of mineral wealth in the county, including lead, barytes, limestone, coal and iron, which helped the area develop the industrial revolution west of Clee Hill and, later, in the Ironbridge Gorge area. Quarrying is still active, with limestone for cement manufacture and concrete aggregate, sandstone, greywacke and dolerite for road aggregate, and sand and gravel for aggregate and drainage filters. Groundwater is an equally important economic resource.