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.
Also see
 
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