Portland Grove Whitbed is a type of stone from the Isle of Portland used to construct the "New London Stock Exchange", which is situated in Paternoster Square, in the city of London. The stone contains large, white shell fragments, and large grey shells. Grove Whitbed has a maximum bed height of 2.2 metres and is the most creamy-whiteish of all the Portland stone types.
References
Portland Grove Whitbed Wikipedia(Text) CC BY-SA