Portland Stone is limestone from the Jurassic period quarried on the Isle of Portland, Dorset. It is well known and has been extensively used thoughout the UK, notably in the rebuilding of London after the Great Fire. It's also been exported to various countries, and was used for the United Nations building in New York, for example.
Three main "Portland Beds" are quarried, producing a number of different stones. The Base and Whitbed beds are fine textured and contain few fossil remains, and so are popular for high quality work. The Roach bed is rougher with many fossils.