Somerset:

The county has a long tradition of supplying freestone and building stone. Quarries at Doulting supplied freestone used in the construction of Wells Cathedral. Bath stone is also widely used. Ralph Allen promoted its use in the early 18th century, as did Hans Price in the 19th century, but it was used long before then. It was mined underground at Combe Down and Bathampton Down Mines, and as a result of cutting the Box Tunnel, at locations in Wiltshire such as Box. Bath stone is still used on a reduced scale today, but more often as a cladding rather than a structural material. Further south, Hamstone is the colloquial name given to stone from Ham Hill, which is also widely used in the construction industry. Blue Lias has been used locally as a building stone and as a raw material for lime mortar and Portland cement. Until the 1960s, Puriton had Blue Lias stone quarries, as did several other Polden villages. Its quarries also supplied a cement factory at Dunball, adjacent to the King's Sedgemoor Drain. Its derelict, early 20th century remains, was removed when the M5 motorway was constructed in the mid-1970s. Since the 1920s, the county has supplied aggregates. Foster Yeoman is Europe's large supplier of limestone aggregates, with quarries at Merehead Quarry. It has a dedicated railway operation, Mendip Rail, which is used to transport aggregates by rail from a group of Mendip quarries.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". In what decade was Mendip Rail built?
unanswerable